The Injection Molding Process of Glass for Mobile Phones

Do you know the injection molding process of glass for the mobile phone and its key points? Lens Technology is one of the main glass screen supplier for famous mobile phones such as Apple Inc, Samsung, Xiaomi, Huawei, etc., which ranks only second to Bourne Optics. Therefore, Qunfei Zhou is also known as the queen of mobile phone glass.
 
There are three layers for the mobile phone screens. 
The bottom is the backlight; the middle is the touch panel, and the first layer is the mobile phone glass. This layer of glass used to be made by injection molding and sheet slicing. Nowadays, the amount of inorganic glass is used much, but injection molding products are still very popular. The main reason is that injection molding can produce products with curvature and inclinations. This is unmatched by other processes. Molding is the unique advantage of the injection molding process.
 

1. Glass materials for mobile phones

The material of mobile phone plastic glass currently are mainly PMMA. It has light transmittance greater than 91%, good surface hardness, and can reach more than 3H after hardening treatment. Currently, the main materials used are LG's IH830, Mitsubishi's VRI-40 and French ATO's MI-7. The hardness and light transmittance of PC is not as good as PMMA, so it is rarely used.
 
2. Molds for mobile phone glass
No defects are allowed in the mold cavity of injection molding mobile phone glass. Therefore, we must first ensure that the steel has good mirror polishing performance. The most commonly used is ASSAB's S136 (similar to 1420) that has undergone ESR (electroslag remelting). For products with particularly high requirements, you can also choose ASSAB's OPTIMAX. The steel material is generally vacuum heat treated, so that the metallographic structure is uniform, the grain is refined, the heat treatment deformation is small and the surface oxidation is slight.
 
3. Design of mobile phone glass
Gate design for molds: fan gates should be used. Considering the favorable filling angle, the width is also designed to be as wide as possible. Generally speaking, in terms of thickness, if the side of the pouring is connected to the exterior surface, the gate must be set at both directions of fixed and moving molds and should be more than 0.15mm away from the product appearance surface. Special attention should be paid to the fact that the PMMA lens is very brittle. When the product is ejected, if it sticks to the mold and the ejection is not smooth, small cracks may appear and the product will be scrapped. For this reason, it is best to design the draft angle on the side of the gate.
 
Lens ejection from the mold: Generally, the ejector pin is designed on the runner, and the lens is directly taken out by the nozzle during injection molding production. However, sometimes the strength is not enough, and the sprue will be broken; the product cannot be ejected; cracks or crashes will occur. At this time, it is necessary to set an overflow groove at the diagonal corner of the gate, and design a push rod under the overflow groove. The overflow groove can not only pull the product to stay at the back mold when the mold is opened, but also the push rod can be used when ejecting.
 

4. Injection molding machines for mobile phone glass

The injection molding machine for mobile phone glass requires precise travel accuracy, good repeatability and good environmental protection without generating pollutants. Now the mainstream models are arburg, sumitomo, NissEI, FANUC and other brands of motors, which are accurate, pollution-free and have low noise. Their average tonnages are between 80 and 120 tons.
 
5. Injection molding process and defect detection
The injection molding process mainly adopts medium and high speeds, and the holding time is medium and short. It requires no internal stress, scratches, cracks, flow lines, impurities, water splashes, etc.
 
6. Environment
Lens processing has strict environmental requirements, and it requires a dust free room with special treatment. The grade of a dust free room should reach grade 10,000 so as to ensure the qualified rate of production. This is the biggest investment and prerequisite for lens injection molding.
 
Conclusion
In the field of injection molding, the molding of mobile phone glass is not very high-end, but the required resources and technical details in all aspects, quality, efficiency and cost control of glass injection molding are directly related to the quality, efficiency and cost of screen production of mobile phones. A slight move in one part may affect the situation as a whole, so we should be serious about every aspect.