Project Background
This project involves the creation of two-color plastic end caps for BMW’s new energy vehicle series. This project uses a 1000-ton two-color injection molding machine, which makes the mold considered large and complex.
The product to be designed is an integrated piece that combines structural and aesthetic elements. This means the piece in question is visually appealing and functional. This means there are very high expectations for the molding process where the fillers are precisely separated.
Mold Structure and Operating Logic
The BMW end cap mold adopts a two-color injection molding technique.
Each operation cycle within the molding process must ensure the opening and closing sequence of the mold is executed in a precisely timed manner with the ejection sequence of the front mold:
During the opening of the mold, while the parting surface opens and ejects, the front mold must also concurrently open and eject to ensure there is smooth demolding and the ejection is without deformation.
During the closing of the mold, the parting surface must be advanced, then reset, and the front mold closed. This sequence ensures the two-color mold core is properly aligned for the injection cycle.
This complex synchronous design ensures that the two-color end cap is free from misalignment and overflow during molding. It results in a precise and aesthetically pleasing two-color bonding line.
Materials and Process Design
First Injection: We use PC (Polycarbonate) material to form a rigid substrate for the end caps, providing high strength and dimensional stability.
Second Injection: We use TPE (Thermoplastic Elastomer) material for overlay, achieving a soft touch, anti-slip properties, and a sealing function.
To ensure a perfect bond between the two materials, GBM optimized the injection temperature, pressure, cooling system, and mold cavity venting multiple times.
Simultaneously, the mold employs a high-precision guiding and positioning structure to effectively prevent misalignment or overflow issues in the two colors.
Machining and Inspection
The mold weighs approximately 12 tons and is made of 1.2344/H13 high-strength mold steel.
Machining accuracy reaches ±0.005mm.
A rotary two-shot mold structure is used, ensuring smooth and reliable operation.
Through two-color bond strength testing and surface appearance inspection, the bond line is smooth and flawless.
Project Outcomes
- Compatible Machine: 1000-ton two-color injection molding machine
- Mold Manufacturing Cycle: 60 days
- First Trial Success Rate: 100%
- Mold Life: >1,000,000 cycles
- Customer Feedback: The BMW project team highly recognized GBM’s two-color mold design capabilities and machining precision. The product is now in stable mass production.
