China Automotive Interior Part Injection Mold Development Key Points and Common Defect Prevention

Automotive interior parts include instrument panels, door trims, center consoles and pillar trims. These products determine the visual and tactile quality of the cabin. Most interior parts have large size, complex curved shape, 皮纹 or matte texture, with strict limit on color difference, warpage, dimension and texture reproduction. Different from ordinary structural part molds, interior mold development needs to coordinate large-size deformation control, surface quality, weather resistance and production cycle, combining molding process to reduce defects for stable mass delivery.

1. Product Structure Review at Early Stage

Check wall thickness uniformity in 3D data review. Adjacent wall thickness difference should be controlled properly, as sudden thickness change easily causes sink mark and internal stress. Demolding draft angle is evaluated for buckles, boss columns and reinforcing ribs on products. The draft angle of appearance surface increases with texture depth to prevent drag mark and whitening. Matching tolerance, lap structure and stop position are confirmed for multi-part splicing interior assemblies. Embedded insert structure is evaluated for locating limit to avoid offset and flash during injection.

2. Mold Steel Grade and Surface Treatment Selection

Polishing-friendly, corrosion-resistant and texture-stable mold steel such as S136, 2316 and NAK80 are selected for A-class appearance surface. Heat treatment ensures uniform hardness and less deformation in subsequent machining. Surface treatment is arranged according to appearance demand: mirror polishing for high-gloss parts, chemical etching for matte textured parts. Chrome plating or PVD coating can be adopted for mass-production molds to improve wear resistance and reduce scratch and maintenance frequency. Etching processing is finished after surface inspection to avoid mottled texture.

3. Gating and Runner System Design

Long flow path of large interior parts easily causes weld line, short shot and uneven stress. Submarine gate, horn gate or hot runner side gating are used for A-class surface, with gate mark hidden in invisible area. Multi-gate layout is optimized with mold flow analysis to adjust melt balance, and weld lines are guided to non-appearance rib positions. Synchronization of valve pins in hot runner is calibrated to guarantee consistent feeding speed and reduce batch color difference.

4. Cooling and Venting System Design

Uniform cooling reduces warpage, sink mark and internal stress. Cooling channels follow product contour, with extra cooling inserts at deep ribs and boss columns. Independent mold temperature control stabilizes temperature gradient and cooling rate difference. Trapped gas is the main inducement of weld line, burning mark and bubble. Vents are opened at melt convergence, rib depth and buckle slots. Removable vent inserts are convenient for regular carbon cleaning. Large interior molds can add vacuum exhaust structure.

5. Ejection, Guide and Positioning Design

Uneven ejection force leads to ejection whitening, dent and deformation. Ejector pins, ejector blocks and top plates are combined for ejection. Ejection points are arranged on reinforcing ribs and non-appearance zones. Ejector plates are equipped with guide posts and limit reset structure for smooth movement. Angle, stroke and clearance of lifters are calculated in advance to avoid jamming and product drag. Multiple positioning stops are used on parting surface to prevent misalignment and flash after long-term production.

6. Prevention and Control of Common Defects

Sink marks are solved by optimizing rib-wall ratio, strengthening local cooling and adjusting packing curve. Weld line quality is improved by adjusting gate position, optimizing exhaust and raising mold temperature appropriately. Warpage is controlled by pre-deformation compensation according to mold flow simulation result. Texture drag mark is eliminated by sufficient draft angle and fillet at texture root. Flash is managed by parting surface fitting, balanced clamping force and vent depth control. Silver streak and yellowing are controlled by hot runner temperature, raw material drying and exhaust optimization.

7. Trial Molding Verification and Mass Acceptance Standard

Check appearance, dimension, assembly, deformation and texture effect in trial molding, and record defect change under different mold temperature, material temperature and packing parameters. Verify mold movement and hot runner thermal expansion state in continuous multi-batch trial. Make modification priority list, focusing on A-class surface defects first. Mold maintenance specification is delivered together with molds, clarifying vent cleaning, surface protection and lubrication of moving parts. Risk of appearance, assembly and deformation should be handled in advance in the whole development cycle to cut mold modification cost.