Injection molding process
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.
