Double colors automotive product injection molding

Material and process characteristics of car lights

Car lights generally consist of a base and a lamp shell. The material of the base is usually a thermosetting material - BMC (bulk molding compound). The lamp shell can be made of PMMA, PP, ABS and other materials, usually two or three colors. In terms of the two-color car lamp production process, special attention should be paid to the injection part of the two-color injection molding machine. The center distance of the two screws should correspond to the center distance of the two-color mold. In addition, there are the following important points that need to be paid more attention to:

1. Factors influencing the stable molding of car lights

(1) Control unit response: too long switching point, noise interference, unstable command output, unstable temperature;

(2) Noise from the hydraulic system: pressure instability, valve positioning quality, hysteresis, and oil pipe damping changes;

(3) Differences in mechanical systems: oil seal internal leakage, damping, friction differences, screw check valve positioning, and anti-return effect;

(4) Uneven plasticization: differences in plasticization properties;

(5) Mold temperature control.

2. Frequently asked questions about the design of special plastic tube sets for car lights and taillights

(1) The screw is idling and no material is fed;

(2) The screw requires too much torque to rotate;

(3) The plastic is not completely melted;

(4) Screw metering is unstable;

(5) Uneven plastic mixing;

(6) Low-temperature molded plastics are prone to temperature rise;

(7) There are bubbles in the molded product;

(8) The inside of the molded product is easy to turn black and turn yellow;

(9) The screw is prone to corrosion, wear and tear, and has a short service life.

3. Main design points of screw tube group

The plastic plasticizing screw and tube group is the heart component of the injection molding machine. It is responsible for the transportation, melting, mixing, metering and other functions of plastic raw materials. Therefore, the plastic plasticizing screw is closely related to the quality of the molded product.

The main purpose of improving the plasticizing screw is to:

(1) Improve shear mixing effect;

(2) Mix evenly;

(3) Improve plasticizing ability;

(4) Ensure the uniformity of melt temperature.

4. Key points in the design of special screws for tail lights

(1)L/D ratio: 21~23;

(2) The surface roughness must be extremely smooth to avoid material accumulation;

(3) Increase the corrosion resistance of electroplating layer thickness;

(4) Compression ratio: 2.3, feeding section: about 50%, compression section: about 30%, metering section: about 20%.

5. Countermeasures against bad car lights

(1) Scorching - reduce the injection pressure, slow down the injection in multiple stages, and evacuate the mold;

(2) Silver streak—thoroughly dry the plastic pellets, increase the back pressure, lower the melt temperature, and reduce the firing rate;

(3) Bubbles - increase back pressure, lower melt temperature, use dehumidification dryer, increase gate or runner size;

(4) Bonding line—increase melt temperature, increase filling speed, increase exhaust gas and mold temperature;

(5) Burrs—increase the clamping force, reduce the filling pressure, and reduce the melt temperature;

(6) Shrinkage - Uniform thickness design, increase the holding pressure and time, and replace the check valve.