Two-color injection molding uses a two-color injection molding machine and a two-color mold to mold products in two or more colors. Products molded using this process exhibit distinct colors. This allows for color matching to achieve desired appearance. This process creates aesthetically pleasing products that resist fading. It is widely used in automotive, home appliance, and communications products.
Currently, two-color injection molding machines in China primarily consist of two side-by-side injection tables and a rotating platen, making the entire machine at least twice as large as a typical injection molding machine. Due to large size of automotive exterior fenders, injection molding is difficult, requiring a 1,600-ton injection molding machine. Currently, there are no two-color injection molding machines of this size on domestic market. Therefore, our product achieves second color of glue by employing a unique mechanism that breaks through conventional glue feeding methods.
Following is design approach and structure of a two-color mold for an automotive exterior fender:

 

Product Material: PP/PE; Partial Two-Color Material: EPDM; Product Size: 578mm * 365mm * 816mm; Average Glue Thickness: 1.7mm; Total Product Weight: Approximately 1000g; Mold Cavity: 1+1.
Product's exterior is large, with inner surface serving as exterior. Average glue thickness is only 1.7mm, and wall thickness is uneven, ranging from 1.5mm in the center to 2mm at the ends. This makes molding this product very challenging. One end of product has two-color glue at the bottom, and an undercut on the top requires a lateral core pull mechanism. Multiple irregularly shaped holes around perimeter of product in the front mold also require a lateral core pull mechanism. Product analysis revealed that gating system for this mold required addressing high injection pressure, making injection molding difficult, as well as addressing injection molding method and sequence control for two different materials.

To address difficulty of molding thin-walled products, a single part is designed with three sequential needle valve hot nozzles for glue injection.

 

To address two-color injection molding process and sequence control, gating system with two-color glue at the bottom of one end of part was moved from a single-point hot runner to a cold runner on non-operator side of mold. This resulted in two gating systems at 90-degree angles. Injection molding machine manufacturer added a 160-ton injection molding platform to non-operator side of 1600-ton injection molding machine, resolving glue injection problem.

 

Proper exhaust can increase injection speed and ensure optimal filling and holding pressure, ultimately producing a high-quality product. Because fender's surface is relatively smooth and lacks ribs, exhaust is designed only around mold parting surface.

 

Control cavity seal at EPDM glue point when injecting PP/PE materials. This is achieved through hydraulic cylinder-controlled positioning.
When injecting EPDM material in mold closed state, slide moves shovel back 3.5mm through oil cylinder. Thickness of EPDM glue is exactly 3.5mm (blue part).

 

Front side of two-color glue top has an undercut, requiring a lateral core-pulling mechanism. Undercut is 34.5mm. To prevent interference between rear mold slide and the other slide, front mold is designed with an inclined spring.

 

Product has multiple irregular holes around its perimeter. During design process, holes were designed to allow for interlocking between front and rear molds, simplifying design as much as possible. However, since this was not possible, a hydraulic cylinder and microswitch were used to control core-pulling mechanism.

 

Because product is 816mm tall, thickness of front and rear mold materials is greater than 700mm. Considering cost, processing technology, and manufacturing cycle, front mold plate is split into two pieces, with rear mold center raised to accommodate mold material. Stoppers are positioned around parting surface of A and B plates. Stoppers are also designed between two A plates of front mold and between rear mold core and B plates to ensure mold precision and strength.

 

A good cooling system is the most direct way to shorten mold's injection molding cycle. Because 70% of the entire injection molding cycle is spent on cooling, a well-designed cooling system is crucial for molds, especially large ones.

 

A good ejector system not only ensures smooth product removal but also ensures product quality. Deformation, whitening, and cracking during ejection process should be avoided. Due to soft material of fender and thin adhesive thickness of product, ejector system should be designed to minimize deformation.

 

A qualified mold must not only produce qualified products, have a reliable internal structure, ensure safe production, and be cost-effective, but also ensure that mold's external water, oil, electrical systems are well designed to ensure easy and reliable installation during production.
In short, while ensuring production of high-quality, qualified products, mold structure should be simplified as much as possible to reduce manufacturing costs.
Four sets of top oil circuit templates of rear mold are integrated with one set of total inlet and outlet to connect with injection molding machine, two sets of side oil circuit mold plates are integrated with one set of total inlet and outlet