plastic injection molding machine

Factors affecting the quality of injection molding

1. Injection pressure: the reason for the need for injection pressure is to offset the resistance in the process of melt flow, or the resistance in the flow process to eliminate the pressure of the injection machine, the two are just the opposite, in order to ensure the smooth progress of the filling environment;

2. Injection time: reasonable injection time is conducive to the ideal filling of the melt, and the ear is very important to improve the surface quality of the product and reduce the dimensional tolerance;

3. Injection temperature: the injection temperature must be controlled within the range of M, the temperature is too low, the plasticization of molten materials is not good, which affects the quality of forming parts and increases the difficulty of processing; If the temperature is too high, the raw material is easy to decompose;

Two, the shortcomings of injection molding process

1, product molding must use injection molding and blow molding two sets of mold and a valve hollow core mold, and the injection mold should be able to withstand high pressure, molding equipment cost is high;

2. The temperature of the injection blank is high, and it needs a long cooling and shaping time after blowing in the injection mold, which prolongs the whole molding cycle of the product and affects the production efficiency.

3. The internal stress of the injection molding blank is large, and it is easy to be subjected to uneven cooling during the transformation of the mold. Stress cracking is easy to occur when producing products with complex shapes and large sizes.

4. The operation skills of the operators are higher

First, the advantages of injection molding process

plastic injection molding machine

1. Injection mold can be used to accurately control the wall thickness distribution of the billet, so that the wall thickness of the container is more uniform, avoiding the thinning phenomenon that is prone to occur in the corner of general blow molding products. The weight of the product can be controlled at +0.1g, the accuracy of the thread can be controlled within the range of 100μM, the mouth size is accurate, and the fine neck product molding precision is high.

2, the obtained products do not need to be processed for E times, no joints, saving the dressing time of the products;

3. The blank made by injection can all enter the blow molding mold, and there is no waste in the process, reducing the waste of forming materials;

4, can get smooth surface products, no scratches, surface text and pattern clear;

5, small batch production can be carried out economically;

6. Wide range of application for plastic varieties;

7, high degree of automation, multi-mode production, high production efficiency.

Before starting, the injection molding machine and auxiliary machine must be inspected to ensure that the equipment is in normal condition (according to the requirements of L1 equipment operation records). If any problems are found, the maintenance personnel should be notified in time.

2.Power supply for injection molding machine

 

Turn on the power supply of the injection molding machine, the mold temperature of the mechanical and electrical source, the general mold temperature is set to 80℃, the drying mechanical and electrical source (raw materials need to be dried at 80℃ for 4 hours), the cold water mechanical and electrical source, the exhaust fan and other power supply, turn on the injection molding machine oil pump motor screw and begin to heat up.

3.Grease is applied to the guide post

Wipe the oil stains on the parting surface, guide post, guide sleeve, slider, cavity and oblique guide post of the die with oiling paper. Apply grease to the surface of guide post, guide sleeve, slider and oblique guide post to prevent the die from wear during long working time.

4.Confirm mold condition

Confirm the mold condition, check whether there is damage, whether the oil circuit is smooth, whether the pipe connection is connected in place, whether there is oil leakage phenomenon.

5.Automatic cleaning key

When the temperature meets the requirements, discharge the material, open the baffle of the feeding port, press the automatic cleaning key of the operation panel of the injection molding machine, and clean the material for 2-3 times. After the completion of the cleaning, clean the remaining material of the nozzle and the mold suction nozzle.

plastic injection molding machine

In 1980, France produced the world’s largest screw injection molding machine, with an injection capacity of 170kg. From the 1980s to recent years, the development of injection molding machine is mainly concentrated in several aspects: namely, the application of precision automatic control system and various auxiliary equipment in automatic molding; Precision machinery and high performance hydraulic system; Various special injection molding machine development and computer aided design of complex shape parts plastic flow analysis to determine the best injection conditions; Application of various energy saving technologies in injection molding machine.

Working principle of injection molding machine

Injection molding machine referred to as injection molding machine, injection molding is the use of plastic thermophysical properties, the material from the hopper into the barrel, the barrel outside by heating ring heating, so that the material melt, in the barrel is equipped with external power motor drive rotation of the screw, the material in the double action of the screw shear gradually plasticized, melting and homogenizing, when the screw rotation, Material in the groove friction force and shear force under the action of the molten material pushed to the head of the screw, at the same time, the screw in the material reaction backward, so that the head of the screw to form a storage space, complete the plasticization process, and then the screw in the injection cylinder piston reasoning under the action of high speed, high pressure, the storage room of the molten material through the nozzle into the mold cavity, After the molten material in the cavity is kept under pressure, cooled and solidified, the mold is opened under the action of the mold closing mechanism, and the finished product is ejected from the mold and dropped through the ejecting device.

Composition structure of injection molding machine

Injection molding machine according to the injection molding process requirements is a mechanical and electrical integration of a strong machine, mainly composed of injection parts, closing parts, frame, hydraulic system, heating system, control system, feeding device and so on.

plastic injection molding machine

At present, the common injection molding device has single cylinder type and double cylinder type.

Plasticized parts have two kinds: plunger type and screw type. In the process of continuous rotation of the screw, the plastic realizes the change of physical state, and is finally injected into the mold cavity in a molten state. Therefore, the plasticized component is the core component to achieve uniform plasticizing and quantitative injection.

To provide customers with plastic products development, mold design, product manufacturing and injection molding, its products are widely used in every field of life today, such as household appliances, instruments, wires and cables, building equipment, communications electronics, automotive industry, aerospace, daily hardware and so on.

The overall production process of plastic products is: raw material selection – raw material coloring and matching – design casting mold – machine decomposition injection molding – printing – assembly detection of finished products – packaging factory.

Plastic products are made by injection molding or blow molding, so every time you design a sample, you have to open a new mold, and the mold is generally tens of thousands to hundreds of thousands of dollars, so in addition to the raw material price of plastic products, the cost of the mold is also very large. There may be many parts to make a finished product, and each part needs a separate mold. For example, the trash can is divided into: the barrel body — the lid, the liner, the handle several parts.

Generally speaking, the plastic factory refers to the processing of plastic products with plastic raw materials, semi-finished products and finished products, such as MP3 shell, telephone shell, mobile phone shell, computer monitor shell and other plastic accessories. And finished products such as plastic cups, plastic washbasins, plastic buckets, and other daily necessities. Its essence is called plastic processing plant.

Why we need to set mold protection to prevent damage? Beside the injection molding machine itself, the second most expensive piece of equipment we use on a daily basis is the mold. If the molds are damaged, you are not only responsible for the cost of maintenance, but also for downtime and labor costs.If done correctly, the mold can rest on something as thin as a business card. Here are three key components for setting up mold protection on injection molding machines:

1. Starting position of mold protection

When do you reach the point in the mold where you might break when the mold is closed? In the figure above, this point is when the mold touches the guide pin. This is where we want to start mold protection; close the die until there is a small gap between the protrusion of the half die and the other half and there is a risk of damage. Then look at the mold location on the controller to see where you want mold protection to start.

2. Position of die protection end

You need to stop protecting the mold if the mold fully closed. This is called the clamping position or die contact position on the machine. Clamp the die in manual die setting mode until there is no gap between the half dies. For the figure above, the mold position is 0.05 inches. So,we must set the jig position on the machine slightly higher than the actual position to protect it.

3. Speed and pressure of mold preservation

And we need to set suitable speed and pressure for the machine,which is allowed to reach during die protection. In general, we are concerned to slow down the holding of the die during this period and set the pressure low enough so that if something gets in the way of the half die, the die will stop the jig motion and emit a jig alarm.

Don’t forget closing pressure is the most important aspect of die protection Settings!

Following these simple steps, you will help protect valuable mold asset.

Contact: kiles020801@gmail.com

Thanks!

1. The forming parts refer to the parts related to the forming cavity of the moving and fixing parts.
2. The pouring system is to melt the plastic
3. Guide part in the injection mold, the guide part is used to guide the dynamic and fixed mold of the mold, so that the mold can be accurately matched when the mold is closed.
4. Push out mechanism refers to the device that pushes out the plastic parts from the mold after parting.
5. In order to meet the requirements of injection process on mold temperature, the temperature regulating system is needed to adjust the temperature of the mold. General thermoplastic injection mold is mainly designed mold cooling system.
6 exhaust system is in order to form the plastic itself volatile gas out of the mold, often in the parting surface open exhaust groove. For small plastic parts of the mold, can directly use parting surface or push rod and mold clearance exhaust.
7. Supporting parts are parts used to install and hold or support the forming parts and the aforementioned parts of the mechanism.
8. Lateral parting and core pulling mechanism is when some plastic parts have lateral concave and convex shape of the hole or boss, must first put the side concave and convex shape of the flap module or the side of the core from the plastic parts off or out.
The passage through which the basic structure of the plastic injection mold passes from the injector nozzle into the mold cavity, as shown in Figure 1-1, includes the main flow channel, diverter channel, gate and cold hole.

(1) Forming part. That is, the cavity part of plastic products formed directly after mold assembly, including punch, concave die, core, rod or insert.

(2) Mold guide part. It is a part set up to align the center shaft correctly when moving and fixing the die, including the guide post, the pilot hole cover, or the inclined conical piece.

(3) Product launching part. The molding injection product is pushed out from the molding cavity, including the ejector rod, the fixing plate, the pushing plate, the pad, etc.

(4) core extraction part. When injection molding plastic products with pits or side holes are demoulded, core mechanism components for pits and side holes forming, such as inclined guide posts, sliding blocks, bending, etc., should be extracted first.

(5) Specific heating and cooling parts of the mold. It refers to the control system suitable for the temperature of injection molding process of plastic products, such as resistance heating plate, rod and electrical control element; Circulating cooling water pipes are used for cooling parts.

 

(6) The specific supporting part of the mold. Refers to dynamic, fixed die plate, positioning ring, lifting ring, various fastening screws and other auxiliary parts, to ensure that the mold can work correctly.

(7) Pouring melt channel. It refers to the channel that can introduce the melt injected by the nozzle into the mold cavity, which can be usually divided into the main channel, the shunt channel, the bushing (gate) and the cold groove.

(8) Exhaust hole. It refers to the air discharge part in the mold cavity. General small products do not need special exhaust holes, the air in the cavity can be discharged from the gap of the accessories; For molds of large injection products, vent holes must be set up.

Raw material increase

Labor costs have skyrocketed

Difficulty in recruiting staff

Large turnover of personnel

Product price decline

The problem of increasingly fierce competition in the industry.

I

njection molding industry has entered the era of transformation, small profit and reshuffle, injection molding workshop management needs to establish a “scientific, perfect, systematic, standardized” operation management system, so that “everything is managed, everyone is in charge” of the working atmosphere of the department, for the injection molding workshop each post work efficiency improvement, manpower reduction has the following measures and suggestions:

First, the upper and lower mold workers to improve work efficiency, reduce manpower measures

1. Do a good job in the production planning arrangement to reduce the number of machine replacement due to improper scheduling.

2. Reasonably set the number of thimble and ejection length to reduce the frequency of broken pins in production.

3. To strengthen the process of production mold cleaning, lubrication, the bartender  work, reduce the mold failure rate.

4. Strictly control the phenomenon of die pressing in the process of injection molding and reduce the number of die falling maintenance.

5. Use appropriate tools to take the adhesive parts of the mold, prevent the mold from being injured by careless operation, and reduce the number of mold maintenance.

6. Make the upper and lower mold tool car and the hanging ring waiting equipment positioning storage area, reduce the time to find the upper mold tools.

7. Promote the “fast mold up method” to refine every action of the upper and lower molds and convert internal time into external time.

8. Reduce the clamping force and open locking speed to reduce mold deformation and impact.

9. The mold channel entrance is designed as a sinking hole, and quick joint is used to reduce the time of disassembling and assembling the water nozzle.

2. Measures to improve work efficiency and reduce manpower for mold testers

By improving the level of mold designers, improving the working quality and efficiency of mold testers, and reducing the workload of mold testers, the purpose of reducing mold testers is achieved:

1. Engaged in mold design with mold flow analysis software, optimized mold structure, improved mold runner, gate, cooling, exhaust, demoulding and other effects.

2. Reduce the increase of mold modification, mold repair and mold test caused by mold structure problems

3. Conduct injection molding technology training for mold designers, and give full consideration to material properties, injection molding process requirements and injection molding quality requirements when designing molds

4. Provide injection molding training to mold testers, improve their ability to find, analyze and deal with problems, improve the quality and efficiency of mold testing, and reduce the number of mold testing.

5. Specify the number of new mold test (no more than 3 times)

6. Do a good job of preparation before mold test, choose the appropriate injection molding machine, scientific mold test to shorten the time of mold test, reduce the test modulus.

7. Formulate the process of mold trial, standardize the requirements of mold trial, clarify the purpose of mold trial, increase the responsibility of all departments, and reduce the number of invalid mold trial from the management.

8. Select experienced, professional and responsible personnel for mold trial, shorten the time of mold trial and increase the number of mold sets.

Measures to improve work efficiency and reduce manpower for the personnel of the aircraft transfer

1. Implement automatic and unmanned injection molding to reduce the adjustment caused by the instability of manual boot.

2. Control the ambient temperature of the workshop to achieve the purpose of stable mold temperature, material temperature and injection molding process conditions. (ring)

3. Formulate standard process conditions, arrange production machines reasonably, and ensure the repetition of process conditions. (law)

4. Strengthen the injection process management, prohibit the injection process operators, mold workers, feeding. Staff and other non-technical personnel adjust the machine to prevent process fluctuations and changes in the quality of rubber parts. (people)

5. To do a good job of guaranteed  injection molding machine, to ensure that the repeat precision of injection molding machine and the stability and reliability of the process conditions. (machine)

6. Filter the cooling water to prevent the mold temperature change caused by the rusting of the water channel system resulting in abnormal quality. (machine)

7. Strictly control the quality of raw materials, water inlet materials and pumping granular materials. Water inlet materials need to be recycled after dust screening to prevent the adjustment caused by raw material problems. (material)

8. The preventive maintenance, the use of injection mold,  work, reduce the die failure and rotary die after the fixed mold, machine work. Use special paper to clean the oil on the mold before the mold testing machine, reduce the time of mold testing and save materials.

9. Conduct comprehensive and systematic training of injection molding technical personnel, master the knowledge of material, machine, mold, process and defect analysis, improve their ability to analyze and deal with problems, improve their injection molding technical level and control ability of injection molding process, reduce blind machine adjustment, and take the road of scientific injection molding.

10. For special moulds (such as multi-neutron moulds), precautions should be marked on the moulds to make problems obvious and prevent personnel from making mistakes.

11. The pipe should be cleaned before the shutdown and then cooled, to prevent the material from burning the screw can not be cleaned, use the screw cleaning agent to save the time of cleaning the pipe.

Iv. Measures for ingredients to improve work efficiency and reduce manpower

1. The batching room needs to increase the number of mixer (mixer), the color and the type of plastic material ingredients, equipped with enough and appropriate tools to clean the mixer, improve the efficiency of cleaning the mixer, shorten or reduce the time and workload of cleaning the mixer.

2. If the mixer is more, a variety of materials can be mixed at the same time to reduce the number of ingredients.

3. Change the traditional way of batching by shift, implement single batching, make raw material rack, complete the materials required by the order in one time, reduce the time and workload of cleaning mixer.

4. Do a good job in the ingredients plan and make the ingredients board to prevent the phenomenon of wrong materials and multiple materials. Materials before and after ingredients should be clearly marked to reduce the amount of ingredients by reducing the occurrence of problems.

5. Conduct training for batching staff to improve their working ability, quality and efficiency, so as to achieve the purpose of reducing staff.

6. Use color master, color master proportional valve, edge crusher and central feeding system to cancel the batching link and reduce batching staff.

7. The number of batching staff in one class can be reduced by changing the concept of batching, improving the efficiency of batching, doing well the label of batching and implementing single shift batching.

Five. Feeding staff to improve work efficiency, reduce manpower measures

1. Make suitable feeding ladder to facilitate feeding and improve feeding efficiency.

2. Place the materials to be filled in the designated area according to the machine, and the materials of each machine shall be clearly marked. So as not to add the wrong ingredients.

3. Use edge automatic suction machine instead of manual feeding.

4. Adopt central feeding system and color master proportional valve to realize automatic feeding.

5. Improve the filling bucket and reduce the feeding frequency to reduce the feeding personnel.

Vi. Measures to improve work efficiency and reduce manpower for crushing staff

1. The crusher shall be added to the crusher room, and the crusher shall be divided according to the type and color of raw materials to reduce the workload of cleaning the crusher.

2. Make the rubber box bracket, reduce the time for the crusher to take the water outlet and reduce the labor intensity.

3. Use the automatic transmission belt crusher to reduce the workload of the crusher (one person can use two of the same crusher).

4. Isolate the area where the crusher is placed to avoid cross contamination. Strictly control the purity of the nozzle material, reduce the time for the crusher to clean the foreign matter in the nozzle material.

5. By improving mold quality, injection molding technology and management level, controlling defective products and water inlet material quantity, reducing the workload of crusher.

6. The mold adopts hot runner system to reduce the water inlet material and the amount of broken material.

7. The edge crusher is used to realize automatic and unmanned crushing.

8. When the crusher is out of service, cover with dust cover to reduce the workload of cleaning the crusher.

9. Train shatterers to improve their work quality, efficiency and responsibility, so as to reduce the number of shatterers.

7. Measures for injection molding machine operators to improve work efficiency and reduce manpower

1. Use manipulator and conveyor belt instead of hand to take out products and water orifice, realize automatic and unmanned operation production, reduce manual boot.

2. Must be prepared to injection mold cleaning, lubrication,  protection, prevent the thimble, slider, guide pin, guide sleeve, wear and tear, caused flash products. Do a good job of cleaning the rubber chips, rubber silk, oil and dust on the molding surface to reduce the rough edges around the products caused by the damage and pressing of the parting surface. Bartender  (mould)

3. Adopt in-mold shear gate technology or change the direct feeding mode to point gate to reduce the time of cutting water gate. (Mold design)

4. Improve the steel of the mold, improve the rigidity and hardness of the mold, and the mold should add the brace head, reduce the raw edge of the product caused by the mold compression deformation. Wear resistant steel is used for mold gate position, slider and moving parts and special treatment is carried out to reduce the burring caused by excessive wear of these parts. (Material of mold)

5. Do a good job of mold testing, thoroughly improve mold problems, improve mold quality, set technological conditions scientifically, and prevent products and water mouth from sticking mold phenomenon.

6. Optimize the layout of the machine in the injection molding workshop, so that one operator can simultaneously see the processing of two or more injection molding machine products. Improve the working efficiency of operators, to achieve workshop automation, unmanned operation production.

7. Do a good job in injection molding machine maintenance insurance  prevent machine hinge, elder brother Lin Zhu wear, clamping precision injection molded parts caused by poor raw edges. (Maintenance of machine)

8. Reduce mold locking force to prevent mold deformation caused by excessive mold locking force and rough edges. Scientific setting of opening and closing mold parameters, reduce the speed of opening and closing mold, reasonable setting of low pressure protection parameters, to prevent the rough edge caused by mold collision. (Setting of process)

9. Use appropriate tools for gate and raw edge processing, improve processing tools and techniques, improve processing efficiency and quality, and reduce machining manpower.

10. Make clear the processing parts, processing standards, processing requirements and processing methods of products, reduce unnecessary processing actions and shorten post-processing time. For the internal plastic parts, do not affect the function, size and assembly effect of the raw edge does not need to be processed, reduce the processing amount. And adhere to the principle of not allowing the production of flying edge mold.

11. Improve the salary of operators (slightly higher than the salary standard of peers), reduce the loss of operators, stabilize the staff team, the use of skilled workers boot (a skilled worker can be up to 2 skilled workers), is also one of the methods to reduce the airport manpower to improve the working efficiency of operators.

12. Strengthen job training for operators, improve their work quality, work efficiency and work responsibility, and mobilize the enthusiasm of employees.

Eight. IPQC measures to improve work efficiency and reduce manpower

1. Clear product quality standards (size, appearance, material, assembly, color…) And focus on the abnormal points of customer complaints and returns, and do a good job of the “first inspection record form” of products. Only after the first inspection is confirmed OK, can it be put into mass production.

2. Change the concept of “post-inspection”, strengthen the process control, for plastic parts prone to change parts (thimble, parting surface, pinhole…) And the time when quality is easy to change (meal time, shift time…) Focus on monitoring, try to stabilize the quality of injection parts, in order to reduce or eliminate IPQC personnel.

3. Establish the idea that “the quality of plastic products is from injection molding, not from seeing”, that is to say, “quality products are designed, manufactured, managed and controlled, rather than tested out”.

4. Implement scientific injection molding, gradually realize automatic and unmanned production mode, prevent quality fluctuations and adverse defects in the process of injection molding, so as to achieve the quality state of product quality without IPQC.

Ix. Measures for mold repair personnel to improve work efficiency and reduce manpower

1. To strengthen the use and maintenance of injection mold, the bartender  work, reduce the die failure rate, reduce the modulus. Strengthen the mold rust prevention work, reduce the occurrence of mold rust phenomenon.

2. Use appropriate mold steel (corrosion resistance, wear resistance, pressure resistance), and ensure that the mold has enough steel and hardness, prolong the service life of the mold.

3. The moving parts of the mold (vulnerable workpiece) are made into inserts, wear-resistant steel is used and quenched to facilitate quick maintenance and increase service life.

4. Reasonable setting of thimble times and thimble stroke (on the basis of the smooth release of the product, more than one top). And to do a good job of cleaning, lubricating, protecting  thimble, thimble way to avoid empty change traditional thimble mode, prevent burning needle, needle breakage phenomenon.

5. Enhance the protection consciousness of the mold, prohibit the phenomenon of “die pressing”, and reasonably set low-voltage protection parameters, and install “mold monitoring and protection device” if necessary for special molds.

6. The mold nozzle adopts the wire-drawing structure to prevent foreign bodies such as wire drawing and mold surface viscose chips and dust during the injection production process, which should be cleaned in time to avoid damaging the mold.

7. Install the thimble spring on all molds. If there is fracture, it should be replaced immediately to avoid the phenomenon of needle burning and broken caused by the imbalance of ejection.

8. There should be a certain amount of spare parts of the mould that are prone to loss and multiple failure parts, so that when the above parts of the mould fail, they can be replaced in time, so as to shorten the time of mould repair and reduce the manpower of mould repair.

9. Reduce the clamping force of injection molding machine (each machine should be controlled below 100) and the speed of unended closing mold to prevent mold deformation and collision.

10. Measures to improve work efficiency and reduce manpower for machine repair personnel

1. Change the idea for the maintenance of equipment is broke by the ex post maintenance into prevention concept. (preventive  bao and predictive  difference).

2. Make the injection molding machine use, maintenance, security  rules, and arrange the specialist injection molding machine and peripheral equipment

Mobile phone shell is usually made of PC(polycarbonate) or PC+ABS material molding, due to the relatively poor liquidity of PC, so the process is usually filled with high mold temperature, high material temperature; The gate used is usually the point gate, and graded injection molding should be used when filling, to find the gate position and the V-P(injection – pressure maintaining) switching position, which will be of great help to solve the gate mark and underinjection fly-side and other anomalies.

The following is the main molding conditions of mobile phone products, introducing the melt temperature, mold temperature, injection speed, back pressure and other molding parameters setting points for attention.

Melting temperature and mold temperature

The optimal setting of molding temperature is related to many factors, such as injection molding machine size, screw configuration, mold and molding product design and molding cycle time. In general, to allow gradual melting of the plastic, lower temperatures are set at the back of the tube/feed area and higher temperatures at the front of the tube. However, if the screw is not designed properly or the L/D value is too small, the reverse temperature setting can also be used.

In terms of mold temperature, high temperature molds provide a better surface appearance, less residual stress, and are easier to fill for thinner or longer forms. And low die temperature can shorten the forming cycle.

Rotation speed of screw

40 to 70rpm is recommended, but it depends on the design of the machine and screw.

In order to fill the mold as quickly as possible, the injection pressure should be as high as possible, usually about 850 to 1,400kg/cm2 and up to 2,400kg/cm2.

Back pressure

Generally, the lower the better, but for uniform feed, it is recommended to use 3 to 14kg/cm2. Injection molding speed, rate of fire and gate design has a great relationship, the use of direct gate or edge gate, in order to prevent sunbeam phenomenon and wave flow mark phenomenon, the application of slower rate of fire. In addition, if the thickness of the finished product is more than 5MM, slow shooting helps to avoid bubbles or dents. Generally speaking, the principle of rate of fire is fast for thin and slow for thick.

Elimination of common defects

a. Air mark: reduce the flow rate of the melt overgate and increase the mold temperature.

b. Undernote: Improve injection pressure, speed, material temperature, mold temperature, improve the amount of glue.

c. Flying edge: reduce the plastic filling pressure, control the V-P switching point to prevent over-filling, improve the clamping force, and check the mold fit.

d. Deformation: Control mold temperature to prevent uneven shrinkage deformation caused by mold temperature difference, through pressure maintenance adjustment.

e. Weld mark: improve mold temperature, material temperature, control the flow of each section to prevent trapped gas, improve the flow front temperature, increase exhaust.

Secondary processing   

The post-processing of mobile phone shell usually includes spraying, color spraying, printing, sandwich printing, electroplating, vacuum evaporation, hot pressing nut, annealing, ultrasonic welding and so on.

By spraying, electroplating and other post-processing methods, the appearance of plastics can be improved, and the friction resistance of plastic surface can be improved. Hot pressing ultrasonic welding and other post-processing methods can add some inserts for easy assembly; Annealing treatment can eliminate the internal stress of products and improve the performance of products.

The number 1 represents PET, or polyethylene terephthalate

Mineral water bottles, carbonated drink bottles are made of this material. Dong Jinshi pointed out that hot water can not be recycled in beverage bottles. This material is heat-resistant to 70℃, which is only suitable for warm or frozen drinks. When loaded with high temperature liquid or heated, it is easy to deform and dissolve harmful substances to human body. Scientists found that after 10 months of use, the plastic could release carcinogens and become toxic to humans. So when you’re done, throw it away. Don’t use it as a water cup, or use it as a storage container for anything else. (The girl in the United Arab Emirates got cancer because she used the same mineral water bottle for 16 months, resulting in the release of carcinogen DEHP.)

The number 2 stands for HDPE, high density polyethylene

Plastic containers for cleaning supplies and bath products. At present, plastic bags used in supermarkets and shopping malls are mostly made of this material, which can withstand 110℃ high temperature. Plastic bags marked with food can be used to contain food. Plastic containers containing cleaning supplies and bath products can be reused after careful cleaning, but these containers are usually not easy to clean, residual original cleaning supplies, become a hotbed of bacteria, cleaning is not thorough, it is best not to recycle.

The number 3 represents PVC, or polyvinyl chloride

Common raincoat, building materials, plastic film, plastic box, etc. Good plasticity, cheap price. But can only withstand 81℃ high temperature. According to reports, this material of plastic products are easy to produce toxic and harmful substances from two aspects, one is the production process is not fully polymerized single molecule vinyl chloride, the second is harmful in plasticizer. These two substances in the encounter of high temperature and grease is easy to precipitate, poison with food into the human body, easy to cause cancer. Currently, containers of this material are used less often to package food. If in use, do not allow it to get hot.

The number 4 stands for LDPE, low density polyethylene

Plastic wrap, plastic film and so on are this material. Heat resistance is not strong, usually, qualified PE wrap in the temperature of more than 110℃ will appear hot melt phenomenon, will leave some plastic preparations that the human body can not decompose. In addition, wrap the food in plastic wrap and heat it. The fat in the food is easy to dissolve the harmful substances in the plastic wrap. Therefore, the food into the microwave oven, the first to remove the wrapping film.

The number 6 stands for PS, polystyrene

This is the material used to make instant noodles in bowls and foam fast food boxes. Heat-resistant and cold-resistant, but not in the microwave to avoid the release of chemicals due to excessive temperature. And can not be used to contain strong acids (such as orange juice), strong alkalinity.

PVC products with a plastic injection molding

PC is a material that is widely used, especially in the manufacture of baby bottles, space cups and so on. In recent years, baby bottles have become controversial because they contain BPA. Experts point out that, in theory, as long as in the process of making PC, bisphenol A 100% converted into plastic structure, it means that the product is completely free of bisphenol A, let alone release. However, if A small amount of BPA is not converted into the plastic structure of PC, it may be released into food or drink. The higher the temperature of the residual bisphenol A in PC, the more and faster the release rate. Therefore, hot water should not be served in PC water bottles. If the container has any fall or damage, it is recommended to stop using, because plastic products if there is a fine surface pit, easy to hide bacteria. Avoid repeated use of aging plastic appliances.

Suction machine will be mixed material into the injection molding machine barrel, heated in the barrel to melt and plasticize state, injected into the mold cavity, cooling in the cavity, demoulding, and then through the ring cutting pad, to complete the injection molding production, this is the injection molding cover production process. So cooling shaping becomes an important part of the molding time of injection products. The cooling water channel is an important part of the mold. Cap quality, speed, mostly depends on cooling water.

In the traditional mold, the cooling waterway is generally processed by CNC, and the cooling waterway can only be processed by the way of drilling through the milling machine to produce the internal waterway network, and through the internal water stop and external plug way to adjust the waterway flow. This leads to the layout of the waterway has great limitations, the waterway can only be cylindrical straight holes, unable to turn around in the mold cavity. When the mold products with complex shapes are encountered, the traditional waterway can not be completely close to the surface of the injection parts, the cooling efficiency is low and the cooling is uneven, resulting in a long injection cycle and large product deformation.

Figure 1:3D model of a traditional waterway
In the beginning of the production of drinks and other plastic caps and claw caps, the traditional waterway is still competent, but with the product packaging more complex, the shape of the cap is more and more unique, uneven shape, resulting in the cooling effect of the traditional waterway is limited.

A New journey: Opportunities for 3D printing to gain innovation
However, with the development of 3D printing technology, especially metal 3D printing (SLM, selective laser melting) technology has been quite mature, and SLM technology has been widely used in aerospace and medical manufacturing industry. In the aerospace sector, GE has verified 35 percent of 3D-printed parts with the verification aircraft, and the C919 has used 3D printed parts on a large scale.

And the bottle cap mold technology, also because of 3D printing ushered in a new life. 3D printing technology, also known as additive manufacturing, is a technology that manufactures solid parts by adding materials layer by layer. Compared with traditional material removal and cutting processing technology, additive manufacturing is a manufacturing method “from scratch”.

For cosmetic bottle caps, this layer by layer 3D printing technology can create an all-powerful cooling water – depending on the shape of the water, it can change according to the shape of the product, anywhere in the mold cavity, there will be no cooling blind spots inside the mold. (as shown below)

Figure 2:3D model and side section of the shaped waterway
Using this water channel, it can make the bottle cap can speed up the cooling speed, shorten the molding cycle of the product, in addition, the cooling balance, reduce product defects, improve product yield.

But can this technological innovation really bring such an advantage to the enterprise? Many people are taking a wait-and-see attitude. In the situation that the author understands, since 2015 through this technology to do mold enterprises spring up one after another, but the quality is uneven, difficult to identify, but whether the enterprise can go to the last or the key to test – technology!

During the three years from 2018 to 2020, there was an enterprise that accumulated a lot and rose against the tide. With their far-sighted strategic vision,

In 2007, Shanghai Yishu Laser Technology Co., Ltd. was established. Through the development and application of 3D printing technology, it is committed to the research and development of injection mold cutting-edge technology, taking the lead in the research of this technology.

Aiming at the two kinds of water channels for the current cosmetics bottle cap mold: traditional water way and following water way, the fast mold flow analyst used Autodesk Moldflow software to analyze the data of the cosmetic bottle cap in the two kinds of water way: insert temperature, cooling time, mold temperature state, etc. To find out if the following waterways really do have a magic effect.

Injection system function: injection system is one of the most important parts of injection molding machine, generally have plunger type, screw type, screw preplastic plunger injection type 3 main forms. At present the most widely used screw type. Its function is that, in a cycle of the plastic injection machine, a certain amount of plastic can be heated in a specified time after plasticizing, under a certain pressure and speed, the molten plastic is injected into the mold cavity through the screw. After injection, the molten material injected into the mold cavity is kept in shape.

Composition of the injection system: The injection system is composed of a plasticizing device and a power transmission device.

The plasticizing device of screw injection molding machine is mainly composed of feeding device, barrel, screw and nozzle. The power transmission device includes the injection cylinder, the injection seat moving cylinder and the screw drive device (the glue motor).

(2) Mold closing system

The function of the mold closing system: the function of the mold closing system is to ensure the mold closing, opening and ejecting products. At the same time, after the mold is closed, enough clamping force is provided to the mold to resist the pressure of the mold cavity caused by the molten plastic entering the mold cavity, so as to prevent the mold from opening and causing the bad situation of the product.

• Plastic Products Mould Making Machine

The composition of the die closing system: The die closing system is mainly composed of the die closing device, the die adjusting machine, the ejector mechanism, the front and rear fixed template, the moving template, the die closing cylinder and the safety protection mechanism.

(3) Hydraulic system

The role of hydraulic transmission system is to realize the injection molding machine according to the various actions required by the process to provide power, and to meet the requirements of the injection molding machine parts required pressure, speed, temperature, etc. It is mainly composed of hydraulic components and hydraulic auxiliary components, wherein oil pump and motor are the power source of injection molding machine. Various valves control oil pressure and flow to meet the requirements of injection molding process.

(4) Electrical control system

Electrical control system and hydraulic system reasonable coordination, can achieve the injection machine process requirements (pressure, temperature, speed, time) and various procedures. Mainly by electrical appliances, electronic components, meters, heaters, sensors and other components. Generally there are four control methods, manual, semi-automatic, automatic, adjustment.

(5) Heating/cooling system

The heating system is used to heat the cylinder and the injection nozzle. The cylinder of the injection molding machine generally uses the electric heating ring as the heating device, which is installed on the outside of the cylinder and tested by thermocouple. Heat conduction through the cylinder wall provides heat source for plasticizing materials. The cooling system is mainly used to cool the oil temperature, the oil temperature is too high will cause a variety of failures, so the oil temperature must be controlled. The other place that needs to be cooled is near the feeding port of the feeding pipe to prevent the raw materials from melting, resulting in the normal feeding of raw materials.

(6) lubrication system

Lubrication system is the injection molding machine dynamic template, mold regulating device, connecting rod hinge and other parts of the relative motion to provide lubrication circuit, in order to reduce energy consumption and improve the life of parts, lubrication can be regular manual lubrication, can also be automatic electric lubrication;

• Plastic Products Mould Making Machine

(7) Safety protection and monitoring system

The safety device of injection molding machine is mainly used to protect the safety of people and machines. It is mainly composed of safety door, hydraulic valve, limit switch, photoelectric detection element, etc., to realize electrical – mechanical – hydraulic interlock protection.

The monitoring system mainly monitors the oil temperature, material temperature, system overload, as well as the process and equipment failure of the injection molding machine, and gives instructions or alarms if abnormal conditions are found

The composition of injection molding machine

In terms of composition, the injection molding machine can be divided into feeding section, plasticizing section (also called compression section) and melting section (also called metering section or homogenizing section). According to the different lengths of each section, we can divide the screw into gradual type, mutant type and universal type, whose characteristics and application scope are shown in the following table.

In addition to the injection system, injection molding machine also has a closing system, hydraulic system, electrical control system, lubrication system, heating and cooling system, safety monitoring system.

1. The following product defects may occur in plastic injection molding products affected by moisture content:

1). Product dents and bubbles – caused by hygroscopic materials that are not well dried, and residual monomers and other compounds in the materials. To determine the cause of the pores, just observe whether the bubbles of the plastic product appear instantaneously when the mold is opened or after cooling. If it occurs instantaneously when the mold is opened, it is mostly a material problem. If it occurs after cooling, it is a problem with the mold or injection molding conditions.

Dent phenomenon caused by excessive moisture content

Dent phenomenon caused by excessive moisture content

2). Product weld line (stitching line) – product seam is usually caused by low temperature and low pressure at the seam

Seams caused by excessive moisture content

3). The product is brittle – due to the degradation of the material during the injection molding process or other reasons.

4). Material discoloration – due to scorching or degradation and other reasons.

5). Product silver wire and stripe

2. Injection molding defects caused by high water content in the plastic

The meaning of moisture management

1). Determination of moisture content of plastic raw materials

Moisture is an important indicator that affects the physical properties of plastic particles. Therefore, the monitoring of moisture content in the production process of raw materials for plastic particles is essential. For the buyer, the detection of the moisture content of the raw materials can enable both parties to better agree on product quality and specifications and avoid commercial disputes. At the same time, it also provides a scientific basis for the drying conditions of raw materials.

2). Determine the efficiency of the dryer, optimize the drying procedure, and improve the production efficiency.

Most engineering plastics and plastic alloy pellets contain different degrees of moisture, and the moisture is distributed on the particle surface and inside the particle. In addition, plastic particles usually have a certain degree of hygroscopicity. The air humidity in the production workshop, the packaging process, the transportation process, the storage environment and other external environmental conditions will have a certain impact on the moisture content in the material. Therefore, the raw materials must be dried with drying equipment before the molding of plastic products. The control of drying time is very important for the subsequent product forming process and product quality.

If the drying time is too short, the moisture in the plastic particles cannot be completely discharged, which will affect the internal quality and appearance quality of the plastic products, and cause processing difficulties. The inherent quality of plastic products is manifested in that the performance indicators are significantly reduced, the internal stress is increased, it is easy to crack, and the polymer is hydrolyzed and degraded; decrease, etc.
If the drying time is too long, the physical and chemical properties of the plastic particles themselves may be damaged, such as: degradation or volatilization of low-molecular-weight additives, decreased thermal stability, decreased toughness, and increased brittleness.

3. For the following common engineering plastics, the impact of excessive water content in the plastic injection moulding is as follows

1). PA Resin Moisture Content

As we all know, nylon is an engineering plastic that absorbs water easily, especially the water absorption rate of unmodified PA6 and PA66 is as high as 1.5%-1.9%. Nylon packaging bags are mostly multi-layer aluminum foil bags, which can be used directly. If the raw materials are exposed to the air for more than one hour, they must be dried.

If nylon with excessive water content is processed, the probability of burrs and jets will increase, and the tensile strength and impact strength of the product will also decrease.

2). PET, PBT Resin Moisture Content

The water absorption rate of PET and PBT is not very high, but it is extremely sensitive to the moisture content. Once the moisture content exceeds the allowable range, only insignificant jets appear on the surface of the product, while the tensile strength and impact strength are greatly reduced. Therefore, PET and PBT must be dried before processing.

3). POM Resin Moisture Content

The water absorption rate of POM is very low, and the water content has little effect on the mechanical properties of the product. However, it is still necessary to pay attention to the fact that the water accumulated on the surface of POM is likely to form a jet flow during processing, resulting in surface defects.

4. How to measure moisture content in plastics

At present, the most accurate test method for testing water content in the world is Karl Fischer test method. It has been adopted by many international standards, such as ISO, ASTM, DIN, BS, and JIS. Common test standards ISO 15512, ISO 15512, SH/T 1770.

Karl Fischer moisture analyzer for plastics

The principle of the Karl Fischer test is very simple, that is, the weight change is measured by the reaction of SO2, iodine and water in the chemical reagent. It can objectively reflect the total water content in the sample.

How to check moisture content in plastics:

※Insoluble in organic solvents or slow dissolution, the cassette furnace method is recommended. Since some substances are easily oxidized at 100-300 ℃, it is recommended to use dry nitrogen as the carrier gas. After nitrogen can be dried through molecular sieves, the moisture residue can be as low as <10ugH2O/L.

※The low moisture content of plastic is easy to absorb moisture, so it should be analyzed immediately after opening. The bonding force between plastic and moisture is very strong, and the water content is low. Coulomb method is recommended. The heating temperature is 100-300 degrees, and the temperature gradient can be used. Set 40-60ml/min on the cassette furnace, and the analysis time is 5-20min.

5. Plastic drying method

After measuring the moisture content, it is necessary to carry out corresponding drying measures. The dryer uses the motor to suck the cold air into the air duct — the heating wire — the hot air — blowing it into the barrel to achieve the purpose of drying, just like a hair dryer.

It is recommended to take the following preventive measures to improve the moisture content of raw materials when injection molding engineering plastics:

1). Store the material head and recycled material in a closed container

2). Unused containers or tapes should be sealed

3). Put a lid on the hopper

SPECIAL PROMOTION

Feel free to contact us if any questions

Welding marks in injection moulding can be distinguished from cracks as long as ink is applied to the product; with this phenomenon, flashing is also likely to occur at the welding marks. This is an indication that the stress of the material has reached a higher level at the weld line. Because of this, dents rarely occur at the weld marks. If you want to avoid weld lines, you can only change the position of the gate so that the weld lines are inconspicuous or pleasing to the eye.

Below are some ways for how to solve plastic products weld line in injection molding:

1. Improper gate design

1). If the melt speed of each gate entering the cavity is inconsistent, it is easy to cause weld lines at the intersection. In this regard, the gate form with less shunt should be used, and the gate position should be selected reasonably. If possible, try to choose a little glue .

2). If the number of gates is different, or the cross-sectional area of ​​the gate is too small, so that the melt is divided into multiple strands after entering the cavity, and the flow rate is not the same, it is easy to produce weld lines. In this regard, the number of gates should be reduced as much as possible. Increase the gate cross-sectional area.

2. Improperly designed cold wells

If the cold slug well in the mold is not large enough or the position is incorrect, the cold slug will enter the cavity and produce weld lines. In this regard, the size and position of the cold slug well should be reconsidered.

3. The cross-sectional area of ​​the main channel or the branch channel is too small

The cross-sectional area of ​​the inlet part of the main runner or the branch runner of the gating system is too small, which leads to an increase in the flow resistance of the melt and causes poor welding. In this regard, the cross-sectional area of ​​the main runner and the branch runner should be enlarged.

4. Improperly designed cooling system

If the cooling system of the mold is poorly designed, the melt is cooled too quickly and unevenly in the cavity, resulting in weld lines when the melt is converging. In this regard, the design of the cooling system should be re-examined.

5. Insufficient plasticizing ability of injection molding machine

If the plasticizing ability of the plastics injection molding machine is insufficient, the plastic cannot be fully plasticized, resulting in weld lines when filling the mold. In this regard, the plasticizing ability of the plastic injection moulding machine should be checked.

6. Nozzle hole diameter is too small

If the diameter of the nozzle hole is too small, the filling speed will be slow, and the weld line will be easily produced. For this, a nozzle with a larger diameter should be used.

7. Too little lubricant in the raw material

If the lubricant is too small, the fluidity of the melt is poor, and it is easy to produce weld lines. In this regard, the additive of the lubricant should be appropriately increased.

8. Too much moisture or volatile matter in the raw material

If there is too much moisture or volatile matter in the raw material, a large amount of gas will be generated after heating, so that the exhaust gas is not enough to cause welding lines. In this regard, the raw material should be fully dried, or the raw material containing too much volatile component should be used less.

9. Injection pressure and injection speed too low

The injection pressure and injection speed are too low, and the temperature of the melt in the cavity is different. This kind of melt is easy to produce weld lines when the flow is divided and merged. For this, the injection pressure and injection speed should be appropriately increased.

10. Melt temperature is too low

If the melt temperature is too low, the low temperature melt is prone to produce weld lines when the melt is divided and merged. For this, the melt temperature should be appropriately increased.

11. The wall thickness of the plastic part is too thin

When the wall thickness of the plastic part is too thin, the melt solidifies very fast, resulting in the formation of weld lines. In this regard, care should be taken not to be too thin when designing the wall thickness of the plastic part.

12. Too many inserts on plastic parts

If there are too many inserts on the plastic part, when the melt flows through these inserts, its flow rate, streamline and temperature will change. When the melt rejoins, it is easy to produce weld lines. For this, the number of inserts should be minimized.

13. The wall thickness of the plastic parts is too different

If the difference in wall thickness of the plastic parts is too large, the melt will mostly meet at the thin wall when filling the mold, and weld lines are likely to be formed here.

SPECIAL PROMOTION

Feel free to contact us if any questions

ring of the material.

How is the weld lines in injection molding happened:

When the molten plastic encounters inserts, holes, areas where the flow rate is discontinuous, or areas where the filling flow is interrupted in the cavity, the fusion of multiple strands of melt occurs when gate injection molding occurs, the material cannot be completely fused and then weld line in injeciton moulding is happened.

Main causes of knit lines in injection molding:

1. The plastic melt that passes through the gate at high speed directly enters the cavity, then contacts the surface of the cavity to solidify, and then is pushed by the subsequent plastic melt, leaving traces of meandering.

2. When the mold adopts the multi-gate pouring scheme, the plastic melt flow fronts converge with each other; the melt flow fronts will also be divided into two in the hole position and the obstacle area; the uneven wall thickness will also lead to weld lines in plastic molding.

3. The side gate is used. When the plastic passes through the gate, there is no stagnation area or when the stagnation area is insufficient, it is easy to cause spray marks injection moulding.

How to avoid weld lines in injection molding:

1). Plastic injecion molding equipment

Improper settings of plastic injection molder is the most reasons when flow mark in injection molding happened. Poor plasticization and uneven melt temperature can prolong the molding cycle and make plasticization more complete. If necessary, replace the machine with a large plasticizing capacity.

2). The plastic injection Mold

(1) The mold temperature is too low, and the mold temperature should be appropriately increased or the local temperature at the weld seam should be increased purposefully.

(2) The flow channel is small, too narrow or too shallow, and the cold material well is small. The size of the runner should be increased to improve the efficiency of the runner, and at the same time increase the volume of the cold well.

(3) Expand or reduce the gate section and change the gate position. Gate opening should try to avoid melt flow around inserts and holes. The gate where injection filling occurs should be corrected, migrated or buffered by a stopper. Try not to use or use less and more gates.

(4) Poor exhaust or no exhaust holes. The exhaust channel should be opened, expanded or dredged, including the use of inserts and thimble gaps to exhaust.

3). Plastic Injection Molding Process

(1) Increase the injection pressure and prolong the injection time.

(2) Adjust the injection speed: high speed allows the melt to reach the confluence without cooling down, and low speed allows time for the air in the cavity to be discharged.

(3) Adjust the temperature of the barrel and nozzle: the viscosity of the plastic is small at high temperature, the flow state is smooth, and the weld line becomes thinner; the temperature is low, the decomposition of gaseous substances is reduced.

(4) The release agent should be used as little as possible, especially the silicon-containing release agent, otherwise the material flow will not be fused.

(5) Reduce the clamping force to facilitate exhaust.

(6) Increase the screw speed to reduce the viscosity of the plastic; increase the back pressure to increase the density of the plastic.

4). Plastic Raw materials

(1) The raw materials should be dry and the liquid additives in the formula should be minimized.

(2) Appropriately add lubricants and stabilizers to plastics with poor fluidity or high heat sensitivity, and use plastics with good fluidity or high heat resistance if necessary.

5). Plastic Product Design

(1) The wall thickness is small, and the parts should be thickened to avoid premature curing.

(2) The position of the insert is improper and should be adjusted.

6). Improper Use of Mold Releasing Agent

Too much release agent dosage or incorrect selection will cause weld marks on the surface of plastic parts. In injection molding, generally only a small amount of release agent is evenly applied to parts that are not easy to release from the mold, such as threads. In principle, the amount of release agent should be minimized.

The selection of various release agents must be determined according to the molding conditions, the shape of the plastic parts and the variety of raw materials. For example, pure zinc stearate can be used in all kinds of plastics except polyamide and clear plastic, but can be used in polyamide and clear plastic when mixed with oil. Another example is the silicone oil toluene solution that can be used for various plastics, and can be used for a long time after brushing, but it needs to be heated and dried after brushing, and the usage is more complicated.

6). Other Reasons

When the moisture or volatile content of the raw materials used is too high, the oil stains in the mold are cleaned, the cold material in the mold cavity or the fiber filler in the melt is poorly distributed, the design of the mold cooling system is unreasonable, and the melt solidifies too fast, The temperature of the insert is too low, the nozzle hole is too small, the plasticizing capacity of the injection molding machine is not enough, and the pressure loss in the barrel of the injection molding machine is too large, which will lead to different degrees of poor welding. In this regard, in the process of operation, according to different situations, the raw materials should be pre-dried, the mold should be cleaned regularly, the cooling water channel setting of the mold should be changed, the flow of cooling water should be controlled, the temperature of the insert should be increased, and the nozzle with a larger aperture should be used instead. Larger specifications of injection molding machines and other measures to solve.

Feel free to contact us if any questions

1. Various two-shot injection molding technologies

During the overmolding process, the cover material is injected over, under, around, or into the substrate to form a complete part. This process can be done by multiple injection molding or insert injection molding. A commonly used covering material is elastic resin.

Multi-injection: Multi-injection is a good method of medical device processing if the construction of the covering material allows it. This technique requires specially designed injection molding machines equipped with multiple barrels in order to inject different resins into one injection mold. Barrels should be placed side-by-side or in an L-shape, with one or more injection points to inject resin into the mold.

When using the same injection point, known as co-molding, the resulting composite part is a core resin material covered by an outer layer. When multiple injection points are used, called double shot injection molding, one material is molded on top of another, creating a multi-layered structure.

But multiple injection molding is not suitable for all products. When over-molding, the slider must be moved or the core must be moved to another cavity, and another method is to feed the core by another shot barrel of the multi-shot injection molding machine.

Insert injection molding: To produce products such as fully covered injection handles, insert injection molding is required. To achieve full coverage, the substrate must be removed from the original cavity and placed into another core and cavity for injection of the covering material.

During this process, another mold should be running at the same time on the same or another different size injection molding machine (depending on the injection part size). Typically the substrate is much larger than the cover material and may require preheating to bring the surface temperature close to the melting point of the cover material for optimum bond strength.

2. Double shot injection moulding

Double shot injection moulding is know as overmolding because the two materials end up fully combined, rather than just creating a layered structure, and can be used for individual parts or component materials. Regardless of the application, it is critical to ensure the desired mechanical or chemical bond strength between the substrate and cover material.

3. Cautions for multi-material injection molding

In general, to enhance adhesion, the cover material resin should have the same melting temperature as the base material. If the melting temperature of the cover material is too low, the surface of the substrate cannot be melted and the bond between the two is not strong enough. However, if the melting temperature is too high, the base material will soften and deform. In severe cases, the covering material will penetrate the base material, resulting in the failure of parts processing. Therefore, matching materials are selected to ensure good bonding.

In general, matching materials should have similar chemical properties or contain matching composite components. When the substrate and cover material do not match, there is usually only a mechanical interlock, not a chemical bond.

There are also some issues to be aware of in multi-material injection molding, the most common of which include: insufficient chemical or mechanical bond strength between polymers, incomplete material filling of single or multiple parts, and flash flashing of single or multiple material parts.

The injection molding machine must maintain injection consistency. In addition, the ratio of the shot volume of the injection molding machine barrel to the size of the injection molded part is also an important factor affecting the injection quality. This ratio is critical for all injection molding operations and is especially important in overmolding.

The anti-return device can separate the covering material like a sluice. It is easier to operate the anti-return device when the secondary injection material is metal. If the metal base material and relatively elastic plastic are used, the operation of the anti-return device is more difficult.

You May Like Below Molding Machines

Get Assistance About Multi Materials Injection Molding Solutions

The basic classification of mold based on construction shown on picture below

1. Standard Injection Molds
The standard plastic injection mold is the most simple design, basically the standard molds is same as two plate molds construction, they divided in two side : cavity side and core side, cavity side is the side that construct to flowing plastic material from nozzle to cavity parts, basically they consist of sprue, runner.

Standard Injection Molds

core side construct to make shape for core, demolding system and ejection system, at this side we design ejection system.
standard mold have one parting line, and have one opening direction. this type of mold use in all kinds of plastic parts that doesn’t have undercut, inner and outer screw.
Light brown color little and straight in ejection system is shown ejector pin.

2. Slide Injection Mold
development from this mold type is the used slider parts in various molds types, basic slide mold is transfer horizontal movement of mold to vertical movement, this types of molds is used to make parts with undercut, you should see more at the post when we need slider for learn more.

Slide Injection Mold

3. Three plate molds
basically three plate molds has two parting line, and floating plate, floating plate support by support pin, Since the mold has two parting planes, the runner system can be located on one side of floating plate or make special plate that attach in floating plate, we called runner plate, see post about runner plate. Three plate molds are used because of their flexibility in gating location. this types of molds is flexible even use in multiple cavity.

Three Plate Mold Construction

note : floating plate also called cavity plate or plate number 3, to know more the different between two plate mold and three plate mold see the posting about Basic and Types Molds Construction

4. Split Cavity Mold
basically the split cavity is same as 2 plate standard mold, but the cavity have split block to make undercut product or external threads.

Slide Injection Mold Tooling

this type of mold use when the slider is not enough to make the undercut or the threads. the disadvantages of this mold is when use for little parts, the construction will difficult.

5. Mold With Screw Device

this mold special to make thread forming, the core can be rotate when demolding process, both internal or external threads can be forming by this type mold.

Platic Mold with Screw Ejection System

from those picture we can see that they have gear device, the gear will rotate when form thread.

6. Stripper Ejector Mold
this type of mold have special purpose to make a cup shape without undercut, stripper ejector will make ejection more easy, same movement and power at the product and without a lot of marks in product

Plastic Stripper Ejector Mold

Molds with complex and difficult design can be integrated or combined one to the others mold type.

SPECIAL PROMOTION

Runner System Construction in injection mold

Plastic Sprue
sprue will contact first time with melt plastic, at the injection process, sprue always contact with nozzle from plastic injection molding machine, so consider when design the sprue consider the ball radius of nozzle, make sure it isn’t make undercut on sprue.The dimensions of the sprue depend primarily on the dimensions of the molded part in particular the wall thickness, too little sprue will make sprue cold faster and make insufficient flow.

Main Runner in injection mold

First time when design runner system, determine number of cavities, shape and gate types, then arrange the cavity layout,at the multi cavity of mold balancing of runner is important, balancing ensures virtually equal flow of plastic trough each gate.
To achieve balancing runner layout must be though,

Sub Runner in injection mold
this part will continues flow from main runner until the gate, the dimension of sub runner and how much sub runner system will be, is very depending on how much cavity of the mold, and how the layout, what the layout use herring bone, H type, or star type. at the picture above use H type runner layout.

Cold Slug in injection mold
when runner layout bent, clod slug may be required to continue plastic flow of better quality to the cavities.The cold slug well helps the flow of material through the runner system by stopping colder, higher viscosity material moving at the forefront of the molten mass entering into the cavity.The length of the well is usually equal to or greater about 1,5-2 time than the runner diameter.

Runner gate in injection mold
Basic purpose of the gate is to limit the flow of the melted plastic, but it must allow that melted plastic flow and fill the cavity easily.
considering the fluidity of the material, gate should be made near the center of gravity of molding or the line to make flow uniform and melted material even, then make the gate thick but still considering melted plastic material, becouse thin part will cooled easily and faster.
the gate type is very various depend on part shape, mold layout, mold system, etc, here some explanation about design those gate type:
1. Direct gate
2. Side, edge gate
3. Tab gate
4. film gate
5. fan gate
6. Disc gate

Plastic runner geometry in injection mold
they are various geometry that we can use in runner, such us
1. full round
2. half round
3. trapezoid
use full round and trapezoid shape is recommended in various mold. Half round runners are not recommended because of their low volume to surface ratio

Plstic runner dimensions in injection mold
The diameter of a runner depends on its length in addition to the part volume, part flow length, injection machine capacity, and gate size, Generally runner must never be smaller than the largest wall thickness of the product, it’s usually make from 3 mm until 15 mm

The runner should be large enough to minimize pressure loss, yet small enough to maintain satisfactory cycle time, Large runners are not economical because of the amount of energy that goes into forming, and then regrinding the material that solidifies within them.

Plastic runner layout in injection mold
In general they are three type of runner layout
1. “H” bridge (branching) runner system
2. Standard (herringbone) runner system (conventional runner)
3. Radial (star) runner system
look at picture below shown standard runner and H bridge type runner.

Balancing the runner system ensures that all mold cavities fill at the same rate and pressure, if the product have not similar product geometry, it is recommended to use mold analysis software like mold flow or C-Mold.

Feel free to contact us for any questions about plastic mold runner system and plastic sprue in Plastic Injection Molding.

SPECIAL PROMOTION