Application Case Analysis of Prototype Molds in Mobile Phone Middle Frame R&D-News

In the process of smartphones upgrading towards thinner, lighter, and highly integrated designs, the mobile phone middle frame, as a core structural component supporting the screen and carrying internal parts, its precision, strength, and lightweight performance directly determine the product experience. Prototype molds (verification molds), with core advantages of low cost, fast cycle, and iterability, have become a key tool for verifying design feasibility and optimizing process parameters during the middle frame R&D phase. Taking an ultra-thin glass fiber-reinforced middle frame R&D project of a leading mobile phone manufacturer as a case, this article analyzes the practical path and application value of prototype molds in the development of complex structural components.

Project Background: Core Pain Points in Ultra-Thin Middle Frame R&D

This project aimed to develop an ultra-thin middle frame suitable for 5G mobile phones, with a target wall thickness of only 0.35mm, 28% thinner than traditional products. Meanwhile, it needed to meet the performance requirements of flexural strength ≥65MPa and no deformation in drop tests. The initial design adopted PC/ABS alloy material, but faced three core pain points: uneven melt flow caused by ultra-thin wall thickness, which easily led to weld lines and short shots; the material contained glass fiber components, causing severe wear to the mold; the structure included 32 precision buckles and interface holes, and the assembly gap needed to be controlled within ±0.03mm. If mass production molds were directly opened, mold modification costs would exceed 300,000 RMB once design defects occurred, and the R&D cycle would be extended by more than 2 months. The project team ultimately chose prototype molds for preliminary verification.

Process Selection: Design of Composite Prototype Mold Scheme

In response to the requirements, the mold manufacturer formulated a composite prototype mold scheme of "CNC master mold + silicone mold replication + 3D printed conformal cooling channel". First, five-axis CNC machining was used to make a high-precision master mold, with 45# steel as the base material. Key cavities were processed by wire electrical discharge machining (WEDM), and deep grooves and acute-angle structures were processed by electrical discharge machining (EDM). The dimensional tolerance was controlled within ±0.02mm, and the surface roughness was polished to Ra≤0.01μm, perfectly reproducing the buckle curvature and hole layout in the design drawings. To reduce mold wear caused by glass fiber, the master mold cavity was treated with XR-DLC coating to form a 3μm-thick diamond-like carbon film, increasing the hardness to 3200HV and reducing the friction coefficient to 0.05.

In the silicone mold replication stage, 3 sets of silicone molds were made based on the master mold, each capable of producing 20 trial parts. Batch trial production of 60 middle frame prototypes was completed in only 12 days, shortening the cycle by 60% compared with traditional mass production molds. During trial production, Moldflow analysis revealed 0.12mm warpage deformation at the corners of the middle frame due to uneven cooling, and weld lines concentrated in key appearance areas. The technical team immediately optimized the prototype mold structure, embedding 3D printed conformal cooling channels in the mold inserts to make the channels closely fit the cavity contour. This shortened the cooling time by 35%, controlled the temperature difference within ±2℃, and opened 0.02mm-wide exhaust grooves in the weld line areas, using porous breathable steel to improve exhaust efficiency.

Parameter Iteration: Prototype Molds Empowering Material and Process Adaptation

The iterative optimization of materials and process parameters was also efficiently verified by prototype molds. The pass rate of initial PC/ABS alloy trial parts in drop tests was only 62%. The team quickly verified the glass fiber-reinforced POM material (grade FG2025K) through prototype molds, increasing the flexural modulus of the middle frame to 8GPa and the drop test pass rate to 91%. Meanwhile, injection molding parameters were adjusted with the help of prototype molds, adopting a high-speed and high-pressure molding scheme with an injection speed of 800mm/s and an injection pressure of 200MPa. Combined with a stepped holding pressure curve, the filling time was shortened to 0.8s, effectively eliminating short shots and improving weld line strength by 40%.

Core Value: Cost Reduction, Risk Control, and R&D Efficiency Improvement

The application of prototype molds significantly reduced R&D risks and costs. Through full-size inspection and performance testing of 60 prototypes, the project team identified 3 buckle assembly interference issues and 2 hole deviation defects in advance, and adjusted the mold cavity structure accordingly, with a total design change response time of only 9 hours. Compared with the scheme of directly opening mass production molds, the total investment in the prototype mold stage was less than 30,000 RMB, only 1/10 of the mass production mold cost, and the defect rate of subsequent mass production was controlled within 8% from the expected 38%. The final finalized middle frame prototype, tested by a coordinate measuring machine, had a flatness error of ≤±0.03mm, fully meeting the design requirements and providing accurate data support for the design of mass production molds.

This case fully reflects the core value of prototype molds in mobile phone middle frame R&D: they are not only "low-cost trial-and-error tools" but also "verification carriers" for process optimization. Compared with the traditional R&D model, prototype molds have achieved three major breakthroughs: first, shortening the middle frame R&D cycle from 3 months to 45 days to meet the time-sensitive requirements of model iteration; second, providing practical basis for material selection and process setting through rapid verification of multiple materials and parameters; third, avoiding structural and assembly defects in advance, greatly reducing mold modification costs in the mass production stage.

Industry Trend: Digital Upgrade Direction of Prototype Molds

With the upgrading of 5G technology and lightweight demands, the requirements for mold precision and material adaptability of mobile phone middle frames continue to increase. Prototype molds are evolving towards digitalization and intelligence. By integrating AI parameter recommendation systems and digital twin technology, real-time monitoring and parameter optimization of the molding process can be achieved. In the future, prototype molds will further become a "standard tool" for R&D of core mobile phone components, promoting faster breakthroughs in the industry in fields such as ultra-thin structures and new material applications, and providing solid support for the innovation and iteration of smart phones.