Glue inlet for electroplated parts should be edge-injected based on product structure, and material should not affect assembly or appearance. All types of latent glue infusion should be avoided to prevent powder generation during automatic cut-off and pouring, which can affect surface quality of electroplated product. Previous designs often used edge-injection, with beveled tops or sliders. Demolding angle of beveled tops or sliders should be sufficiently large to prevent powder generation during demolding.

 

Number of glue inlets should be selected based on product shape and injection volume. When multiple gates are used for slender parts, a sequential valve hot runner system should be used to control and eliminate weld lines. This molded product is slender, and glue inlet is single-point. Main issues were: difficulty maintaining pressure, shrinkage, and substandard appearance. Solution: Replace with a two-point sequential valve hot runner.
Problem Description
This mold uses a single-point, large-gate hot runner, but insufficient attention was paid to shrinkage at both ends of part. This problem severely impacted product at both ends, compromising product quality.

 

Problem: Excessive injection pressure caused shrinkage at both ends of part, which could not be eliminated.
Measure: Replace hot runner with a three-point sequential valve hot runner system.

When selecting shrinkage rate for decorative molding products, special consideration should be given to impact of injection molding process on product dimensions. Generally, injection molding pressures for decorative molding products are very high. To minimize surface shrinkage, based on past experience, shrinkage range provided by material supplier should be selected, but lower value should be selected. For products with very high length requirements, design should include a reduced glue margin at both ends to facilitate length adjustment after mold trials.

 

Electroplating process places high demands on appearance of plastic parts. Various injection molding defects such as shrinkage, bubbles, flash, and parting lines must be avoided. To ensure surface finish, injection molding typically utilizes high speed and high pressure, placing high demands on mold strength. Sufficient impact resistance should be considered during mold design.
Case 1
Touran GP2 bumper project: Mold number: M100046. Scuff strip is approximately 1000mm long and 3mm thick. Considering long length of electroplated part, injection molding process requires high holding pressure. Therefore, mold strength design was prioritized, ensuring it met requirements.

 

This mold uses a beveled ejector and a slider core pull. Bottom surface of product has numerous parting lines, and beveled ejector can create unevenness during ejection, which is exacerbated after electroplating. Therefore, when processing similar buckle positions under a surface, using an lifter core pulling method is not recommended. Parting lines can cause buildup after electroplating process, affecting surface smoothness. If conditions permit, using large or concealed slides is recommended to minimize parting line.
Problem Description
For New Lavida project, trim products often have numerous buckle positions. During mold design, a core-pulling solution with a small slider per buckle position is typically used. Because slider is a moving component, parting lines become increasingly pronounced, and numerous. Furthermore, plating can cause buildup, affecting smoothness of product surface.

 

This mold uses flat ejector pins for ejection, positioned below exterior A surface. During mold trials, it was discovered that increasing injection pressure resulted in a slight whitening of surface of test product. The higher injection pressure, the more pronounced whitening. Cause Analysis: Injection pressure pushes flat ejector pins downward, causing slight deformation of ejector plate. After injection, when pressure is released, ejector plate rebounds, causing flat ejector pins to whiten product. Corrective Action: Flat ejector pins were converted into inserts, and flat ejectors were added around perimeter of product.
Problem Description: For AP11 project, model number M090286, product uses a flat ejector and a straight ejector. Straight ejector has ejector pin marks on product. The higher injection pressure, the more obvious marks become.

 

Grilles and trims are often elongated, making deformation a significant concern. Layout of cooling water circuits is crucial. When arranging circuits, consider aligning them horizontally with product, with segmented inlet and outlet circuits to facilitate mold temperature adjustment, thus control product deformation.
Problem Description: Model Z project, M100411, mold flow analysis revealed significant product warping. When designing water channel, we considered adopting a segmented design, aligning it longitudinally with product. By adjusting water temperature, we were able to control product deformation, achieving significant results.

 

Subsequent processes for decorative strip products often involve electroplating and painting, requiring high surface finishes. Therefore, mold core material should possess a high polish. Previously, upper molds were typically made of NAK80, a material with a high polish and a hardness of around HRC40. Lower molds were typically made of P20 or 2738, with a hardness of HRC28-33. Sliders were typically made of H13, with a hardness of HRC48-52. A problem: Upper mold core is easily dented by slider, resulting in product flash and requiring surface reduction. Thorough consideration and research were made in subsequent material selection. In principle, upper mold core is made of 2343 ESR, with a hardness of HRC48-52; slider is 718HH, with a hardness of HRC35-38 or NAK80; lower mold core is made of P20 or 2738 to avoid these issues.

 

 Trim products are often long strips, often subject to significant warping and deformation at their ends. To ensure that product meets vehicle assembly requirements after injection molding and electroplating, deformation can be addressed during early stages of product design based on mold flow analysis results and references to similar products. This reduces number of mold modifications and shortens product development cycle.
Problem Description: Before mold opening, mold flow analysis revealed a 4.7mm upward warpage at both ends of product.
Solution: A 2.5mm downward warpage was applied to both ends of product.