You must be clear about two-color injection molding technology for car lights!

Time:2023-11-07 11:39:32 / Popularity: / Source:

Two-shot injection molding is currently one of the more popular advanced injection molding methods, which provides meaningful saving potential and new design possibilities for product manufacturing. This article mainly discusses development status and trends of two-color injection molding, with particular emphasis on application of automotive lights.
two-color injection molding technology for car lights 

1 Definition of two-color injection molding

Multi-color and multi-material injection molding process refers to combining several kinds of plastics into multifunctional parts in a manufacturing process or a production unit. This technology uses a variety of materials for injection molding, combines characteristics of different materials in molding process for assembly or other suitable bonding methods to improve functionality and aesthetics of product, provide meaningful saving potential and new design possibilities for product manufacturing.

2 Necessary conditions for multi-color injection molding

Matching materials for multi-color injection molding must meet two basic compatibility conditions, namely, adhesion compatibility and processing compatibility.
Multi-color injection molding also puts forward new requirements for injection equipment. As far as injection unit is concerned, parallel co-directional, parallel opposite, horizontal and vertical L-shaped, and Y-shaped co-directional single-cylinder injection structures can be used. As far as mixed nozzles are concerned, special nozzles such as patterns, waves, flow marks, gradients, and interlayers can be selected. As far as clamping die is concerned, standard type, vertical turntable type, horizontal turntable type, shaft type, manipulator rotation type and other mechanisms can be selected.
One of key factors of multi-color injection molding is variability of computer control program. Because even same type of multi-color products, if different mold designs are used, different electronic control programs must be used.

3 Multi-color molding technology for car lights

With development of national economy, automobile industry has become a pillar industry of country. Rapid development of current automotive industry has put forward higher and higher requirements for automotive lighting.
two-color injection molding technology for car lights 
Quality of automobile lighting is very important to driving safety. Therefore, laws and regulations of various countries in the world have strict requirements on automobile lighting. Design of lamp must not only meet safety requirements of regulations, but also meet some other requirements. For example, appearance must be integrated with appearance of the entire car, beautiful and practical, in line with requirements of aerodynamics, so that driver and passengers feel comfortable and convenient. Therefore, design technology of car lights is also changing with development of automobile industry.

4 Material and process characteristics of car lights

A car lamp is generally composed of a base and a lamp shell. Material of base is usually a thermosetting material-BMC (bulk molding compound). Lamp shell can be processed from materials such as PMMA, PP, ABS, etc., usually in two or three colors. In production process of two-color car lights, special attention should be paid to injection part of two-color injection molding machine. Center distance of two screws corresponds to center distance of two-color mold. In addition, following important points need to be paid attention to:

1. Influencing elements of stable forming of car lights

(1) Control unit response: too long switching point, noise interference, unstable command output, unstable temperature;
(2) Noise of hydraulic system: unstable pressure, valve positioning quality, hysteresis, and changes in tubing damping;
(3) Differences in mechanical systems: oil seal leakage, damping, friction differences, screw check valve positioning, and check effect;
(4) Uneven plasticization: differences in plasticization quality;
(5) Mold temperature control.

2. Frequently Asked Questions in Design of Plastic Tube Groups for Car Lights and Tail Lights

(1) Screw does not feed when idling;
(2) Torque required by screw is too large to rotate;
(3) Plastic has not completely melted;
(4) Screw measurement is unstable;
(5) Uneven plastic mixing;
(6) Low-temperature molding plastics are easy to rise in temperature;
(7) There are bubbles in molded product;
(8) It is easy to spit black and turn yellow in molded product;
(9) Screw is easy to corrode, wear, and has a short service life.

3. Main design focus of screw barrel group

Plastic plasticizing screw barrel group is heart component of injection molding machine. It is responsible for transportation, melting, mixing, metering and other functions of plastic raw materials. Therefore, plastic plasticizing screw is closely related to quality of molded product.
Main purpose of improving plasticizing screw is to:
(1) Improve effect of shearing and mixing;
(2) Uniform mixing;
(3) Improve plasticizing ability;
(4) Ensure uniformity of melt temperature.

4. Design key points of special screws for taillights

(1) L/D ratio: 21~23;
(2) Surface roughness must be extremely smooth to avoid material accumulation;
(3) Increase corrosion resistance of plating layer thickness;
(4) Compression ratio: 2.3, feed section: about 50%, compression section: about 30%, metering section: about 20%.

5. Countermeasures for poor light emission

(1) Scorching-reduce injection pressure, multi-stage deceleration injection, and mold vacuum;
(2) Silver pattern—dry plastic pellets thoroughly, increase back pressure, lower melt temperature, and reduce rate of fire;
(3) Bubbles-increase back pressure, lower melt temperature, use a dehumidifying dryer, and increase gate or runner size;
(4) Bonding line-increase melt temperature, increase filling speed, increase exhaust and mold temperature;
(5) Burrs-increase clamping force, reduce filling pressure, and lower melt temperature;
(6) Shrinkage-uniform thickness design, increase pressure and time of holding pressure, and replace check valve.

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