Design Points for Injection Molds of Automotive Interior Parts
The design points for injection molds for automotive interior parts encompass various aspects, from mold structure and material selection to process parameters.
Mold Structure Design:
1. Parting Line Design: The parting line is an important component of the mold, and its design directly affects product demolding and appearance quality.
Relief: To reduce mold assembly workload and save manufacturing time, areas outside the sealing surface need relief. Generally, the relief depth for fixed and moving mold halves is about 0.5-1mm. However, when there are hot runner channels and gates on the parting line, a certain sealing distance must be maintained before applying relief.
R-Corner Parting Line: Machining into a smooth transition difference facilitates machining and mold fitting.
2. Ejection Mechanism:
Draft Angle: A proper draft angle can prevent product scratching and ejection marks (such as whitening, deformation, and breakage). When designing deep-cavity structures, the outer surface draft angle should be greater than the inner surface draft angle to ensure that the mold core does not shift during injection molding. This results in uniform product wall thickness and ensures the material strength of the product opening. Generally, it should be at least 5 degrees, especially for textured parts.
Core Pulling Slider Mechanism: When the plastic part cannot be smoothly demolded in the mold opening direction, a core pulling slider mechanism should be added. If there are no special requirements, try to avoid core-pulling structures and consider changing the hole axis and rib direction to the mold opening direction, using methods such as core-pin penetration of the cavity and core.
3. Lifter Mechanism: The angle of the lifter should not exceed 15°, should be greater than 12° in principle, and all should be equipped with guide pins for reinforcement. The lifter angle should be 2° to 3° greater than the lifter pin angle. When setting the guide pin, it is necessary to check the lifter ejection state to ensure that the lifter base does not interfere with the guide pin, providing a distance of more than 5mm. The commonly used materials for lifters are NAK80 or 2738, they should not be the same material as the mold core.
Cooling System: Fully consider cooling; water channels should be arranged as much as possible, and the diameter should be large to improve production efficiency and ensure product quality.
4. Gating System:
Gate Location: The gate location should avoid leaving marks on the product appearance surface, especially for parts with high appearance requirements, such as door panels.
Runner Design: A reasonable runner design can ensure that the molten plastic evenly fills the cavity, avoiding defects such as material shortage and weld lines.
Venting System: Effective venting can avoid air entrapment and improve product quality.
Mold Material Selection:
Mold Base Material: P20 is commonly used to reduce material costs.
Lifter Material: NAK80 or 2738 is commonly used.
Mold Core Material: Select appropriate mold steel based on product requirements and production volume.
Process Parameters:
Injection Molding Parameters: Adjustments need to be made according to the specific material and product, such as melt temperature, injection pressure, holding pressure time, and cooling time.
Other Considerations:
Appearance Requirements: Automotive interior parts usually have high external requirements, especially the A-surface (appearance surface), which must not have defects such as spots, gate marks, sink marks, weld lines, and flash. For textured parts, the draft angle design should be reasonable.
Assembly Relationship: Consider the fitting clearance with other parts, such as the fitting clearance between the door panel and the instrument panel, A-pillar trim panel, B-pillar trim panel, and sill, which is generally 5-8mm, to avoid assembly interference.
Mold Machining: Mold design must consider manufacturability. The designed mold should be machinable, mainly considering ease of machining, convenient machining, saving machining time, and improving machining efficiency.
