Two-color injection molding is one of the most popular advanced molding methods currently, offering significant cost-saving potential and new design possibilities for product manufacturing. This article focuses on the current development and trends of two-color injection molding, with a special emphasis on its application in automotive headlights. Readers interested in this technology are welcome to share this article.
Definition of Two-Color Injection Molding
Multi-color and multi-material injection molding is the process of combining several plastics into multifunctional components within a single manufacturing step or production unit. This technique involves using multiple materials for injection molding and combining the characteristics of different materials during the molding process through assembly or other suitable bonding methods. This aims to improve product functionality and aesthetics, bringing significant cost-saving potential and new design possibilities to product manufacturing.
Essential Conditions for Multi-Color Injection Molding
The paired materials in multi-color injection molding must meet two basic compatibility conditions: adhesive compatibility and processing compatibility.
Multi-color injection molding also introduces new requirements for injection molding equipment. In terms of injection units, configurations can include parallel, co-directional, parallel, counter-directional, transverse, and L-shaped and Y-shaped co-directional single-cylinder structures. For mixing nozzles, options include special nozzles for patterns, waves, flow marks, gradients, and laminations. Regarding clamping mechanisms, choices include standard, vertical turntable, horizontal turntable, rotating shaft, and robotically rotated types.
One of the key factors in multi-color injection molding is the variability of computer control programs. Even identical types of multi-color products may require different electronic control programs if different mold designs are used.
Multi-Color Molding Technology for Headlights
With the development of the national economy, the automotive industry has become a cornerstone industry of the country. The rapid development of the automotive industry has led to increasingly higher requirements for automotive lighting.
The quality of automotive lighting manufacturing is crucial for driving safety, leading to strict regulations on automotive lighting in countries around the world. The design of lighting fixtures must not only comply with regulatory safety requirements but also meet other criteria, such as integrating aesthetically with the overall vehicle design, being practical, and meeting aerodynamic needs to provide comfort and convenience for drivers and passengers. Thus, the design technology of vehicle lights is constantly evolving in the automotive industry.
Materials and Process Characteristics of Vehicle Lights
Vehicle lights typically consist of a base and a shell, with the base usually made of thermosetting material—BMC (Bulk Molding Compound), and the shell processed from materials such as PMMA, PP, ABS, usually in two or three colors. In the production of two-color vehicle lights, special attention must be paid to the injection part of the two-color injection molding machine, especially the center distance between the two screws corresponding to the center distance in the two-color mold. Additionally, several important aspects should be considered:
Influencing Factors for Stable Molding of Vehicle Lights
- Control unit response: prolonged switching points, noise interference, unstable command output, unstable temperature.
- Noise in the hydraulic system: unstable pressure, valve positioning quality, hysteresis, changes in oil tube damping.
- Differences in the mechanical system: internal leakage of oil seals, damping, friction differences, screw check valve positioning and effectiveness.
- Uneven plasticization: differences in plasticizing quality.
- Mold temperature control.
Common Issues in Tail Light-Specific Plastic Tube Group Design
- Screw idling without feeding.
- Excessive torque required for screw rotation.
- Incomplete melting of plastics.
- Unstable screw metering.
- Uneven mixing of plastics.
- Low-temperature molding plastics prone to temperature rise.
- Presence of bubbles in molded products.
- Molded products prone to turning black or yellow.
- Screw prone to corrosion and wear, short service life.
Main Design Focus of Screw Tube Group
- The plasticizing screw tube group, as the heart component of the injection molding machine, is responsible for the transport, melting, mixing, and metering of plastic materials, thus directly affecting the quality of the molded product.
The main objectives of improving the plasticizing screw include:
- Enhancing shear mixing effect.
- Ensuring uniform mixing.
- Increasing plasticizing capacity.
- Ensuring uniform melt temperature.
- Design Focus for Tail Light-Specific Screws
- L/D ratio: 21~23.
- Extremely smooth surface roughness to avoid material accumulation.
- Increased electroplating layer thickness for corrosion resistance.
- Compression ratio: 2.3, with about 50% feeding section, 30% compression section, and 20% metering section.
- Countermeasures for Defective Injection in Vehicle Lights
- For burn marks—reduce injection pressure, use multi-stage deceleration injection, and vacuum the mold.
- For silver streaks—thoroughly dry the plastic pellets, increase back pressure, lower melt temperature, reduce injection speed.
- For bubbles—increase back pressure, lower melt temperature, use a dehumidifying dryer, enlarge the gate or runner size.
- For weld lines—raise melt temperature, increase filling speed, improve venting and mold temperature.
- For flash—increase clamping force, reduce filling pressure, lower melt temperature.
- For shrinkage—use uniform thickness design, increase holding pressure and time, replace the non-return valve.
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