The rear cover of tablet computers belongs to high-precision appearance injection molded parts, requiring high surface gloss, no sink marks or weld lines, strict dimensional tolerance and high flatness control. Most of them adopt thin-wall and large-area structures, which impose extremely high requirements on mold steel selection, processing technology, heat treatment and assembly manufacturing. Reasonable material selection and standardized manufacturing are the key to ensuring mass production yield and appearance quality.
1. Principles of Material Selection for Tablet Rear Cover MoldsThe material selection of tablet rear cover molds must first meet the core requirements of mirror polishing, corrosion resistance, high hardness, wear resistance and deformation resistance. Meanwhile, it should take into account the rigid bearing capacity of large-area cavities, fatigue resistance for long-term mass production, and the convenience of later texture finishing and polishing maintenance. Material selection shall be comprehensively determined according to plastic material type, production quantity and surface process grade. High-gloss finish and fine textured appearance parts give priority to corrosion-resistant mirror mold steel, while ordinary matte structural parts can adopt pre-hardened plastic mold steel. For large-area thin-wall cavities, it is necessary to consider the uniformity of steel structure to avoid cavity collapse and deformation under high injection pressure.
2. Common Mold Steel Selection and Application ScenariosPre-hardened P20 mold steel features good overall machinability without overall quenching, and can be directly polished and assembled after processing. It is suitable for small and medium batch production of tablet rear cover molds with ordinary matte surface. Its hardness is controlled at 48 to 52 HRC after heat treatment, with excellent cutting performance and short processing cycle at a moderate cost. It is also commonly used for structural inserts and slider auxiliary parts. NAK80 mold steel delivers outstanding polishing performance with uniform structure and low impurity content, achieving a high mirror effect. It is applicable to the cavity and core of high-gloss spray-free tablet rear covers. Supplied in pre-hardened state without quenching deformation, it maintains good dimensional stability and is ideal for mass production of precision thin-wall appearance parts.
S136 stainless mold steel possesses excellent rust and corrosion resistance with high mirror polishing grade, compatible with ABS, PC, PC plus glass fiber and other plastic raw materials. It is especially suitable for injection molding of modified materials that easily produce corrosive gas, avoiding rusting, yellowing and surface fogging during long-term production. It is the first choice for high-end tablet rear cover molds with high-gloss mirror and fine etching texture. Its hardness can reach 50 to 54 HRC after heat treatment, with prominent wear resistance and cracking resistance. For ultra-high production demand molds requiring long-term deformation resistance, H13 hot work mold steel is adopted. After quenching and tempering, it features higher hardness, toughness and thermal fatigue resistance, capable of withstanding repeated impact of high-speed and high-pressure injection molding, suitable for molding glass fiber reinforced materials and mass production over one million shots.
3. Selection of Structural Parts and Auxiliary MaterialsGuide pins, guide bushes, positioning pins, ejector pins and other standard parts are made of high-hardness bearing steel or alloy tool steel to ensure high matching precision and wear resistance, stable mold opening and closing without shaking, and maintain long-term mold clamping accuracy. Sliders, angle lifters and other moving forming parts adopt the same or similar material grade as the cavity to prevent pulling damage caused by moving wear and ensure consistent polishing of forming surfaces. Standard mold bases are made of high-quality structural steel plates with sufficient rigidity and bending resistance, adapting to the mold clamping force demand of large-area tablet rear cover molds and avoiding template deformation affecting product flatness.
4. Manufacturing Process Flow of Tablet Rear Cover MoldsIn the early stage of mold manufacturing, carry out 3D structural parting, cavity layout, gating system and cooling system layout, set shrinkage rate according to product shrinkage, determine parting surface, undercut slider and insert assembly structure scheme, and complete drawing splitting and processing process arrangement. Then proceed with roughing, using CNC milling machine for roughing of mold inserts and templates, reserving reasonable finishing allowance to release internal stress of steel and reduce deformation during subsequent processing and application.
After roughing, conduct heat treatment such as quenching and tempering according to steel type to evenly improve hardness and toughness, refine metallographic structure, and ensure dimensional stability of molds in later use.
After heat treatment, perform finishing and precision grinding through precision milling, surface grinding, jig grinding and other processes to guarantee dimensional accuracy and geometric tolerance of cavity curved surfaces, parting surfaces and matching surfaces, meeting assembly gap and flatness requirements of tablet rear covers.
After finishing, conduct mirror polishing or texture etching. High-gloss surfaces are polished step by step with abrasive paper to mirror grade, while textured parts are discharged and etched according to design requirements with uniform and delicate texture without color difference. Finally, complete mold assembly, parting surface fitting, water channel pressure test and mold trial debugging, adjust ejection clearance and slider fitting clearance, optimize gating and cooling structure after trial molding, and deliver for mass production after confirming product appearance, size and warpage meet standards.
5. Key Control Points in ManufacturingFor processing of large-area tablet rear cover mold inserts, layered cutting and low-speed feeding are adopted to reduce deformation caused by cutting stress. Control heating and cooling rate during heat treatment to avoid cracking and uneven hardness. Polishing shall follow the order from coarse to fine, prohibiting forced polishing leading to local corner collapse and curved surface deformation. High-gloss polishing shall be carried out in dust-free environment to prevent scratches. Ensure uniform aperture and symmetrical layout of cooling water channels, conduct pressure leakage test after processing to avoid mold steel rusting caused by water leakage. Strictly control parting surface fitting accuracy and coaxiality of guide pins and guide bushes during assembly to ensure smooth mold opening and closing, no flash and no deformation in long-term production.
