Mica sheet punching die design
Mica sheet punching die design is a specialized technology for punching mica sheets (a high-temperature resistant insulating material with a thickness of 0.1-1mm). Suitable for punching components such as insulating gaskets and spacers in motors and electrical appliances, it can punch complex contours with a dimensional accuracy of ±0.05mm and a cut roughness of Ra 1.6μm or less. Mica sheets are brittle and easily break (Mohs hardness 2.5-3), so the key to die design is to reduce punching force and control punching speed to avoid defects such as chipping and cracking during punching. Initially, the punching clearance should be determined based on the thickness of the mica sheet. For a 0.1mm thick mica sheet, the clearance should be 0.01-0.02mm, and for a 1mm thick sheet, the clearance should be 0.05-0.1mm to ensure a smooth cut.
The mold structure consists of a high-precision punch, a die, an elastic pressure plate and a fine guide mechanism. The punch is made of tungsten steel (WC-Co 94%), with a hardness of HRA90-92. The length of the working part is 5-8 times the thickness of the mica sheet (2.5-4mm for 0.5mm thick), and the cutting edge is precisely processed by EDM (radius <0.01mm) to avoid stress concentration and cracking of the mica sheet. The die is made of the same material, and the clearance with the punch is uniform (±0.002mm) through slow wire EDM. The slope of the die edge is 0.5°-1° to reduce the blanking resistance. The elastic pressure plate is made of polyurethane rubber (hardness 60-70ShoreA), and the pressing force is 15%-20% of the blanking force (about 1-2kN for 0.1mm thick mica sheet). The mica sheet is completely pressed before blanking to prevent slippage.
The guiding and positioning system needs to achieve micron-level accuracy, using ball guide pins and guide sleeves (diameter 10-20mm) with a clearance of 0.001-0.003mm to ensure that the coaxiality error of the punch and die is less than 0.005mm. Positioning uses a combination of precision stop pins and guide plates. The stop pin position accuracy is ±0.01mm, and the guide plate spacing is 0.05-0.1mm larger than the width of the mica sheet to ensure smooth feeding without jamming. For rolled mica sheets, a servo feeder (feeding accuracy ±0.01mm) and a tension control device (tension 5-20N) are equipped to prevent the mica sheets from stretching and deforming.
Blanking process parameters must be strictly matched to the characteristics of the mica sheet. The blanking speed should be controlled at 10-30 strokes/minute, far lower than that of metal, to avoid excessive impact and resulting breakage. The blanking force is calculated using the formula F=KLTσb (K is a safety factor of 1.5-2, L is the blanking circumference, T is the thickness, and σb is the tensile strength). The blanking force for a 0.5mm thick mica sheet is approximately 5-10kN. This requires a small precision press (10-20kN tonnage) equipped with a buffer device to reduce peak blanking force by 30%. A specialized silicone-based lubricant (viscosity 5-10 cSt) is used for lubrication, forming an extremely thin oil film (1-2μm thick) on the die surface, reducing the friction coefficient to below 0.05 and preventing the mica sheet from sticking to the die.
Special care should be taken in debugging and maintenance. When testing the mold, first use waste mica sheets for trial punching and check the edge quality of the blanked parts. If the edge collapses, reduce the blanking gap (±0.005mm each time) or reduce the blanking speed; if the size is out of tolerance, adjust the positioning device (±0.01mm). After every 500 times of work, use compressed air to clean the mica debris on the surface of the mold, check whether there are tiny cracks on the punch edge (observe with a 10x magnifying glass), and replace it immediately if cracks appear (tungsten steel punches cannot be repaired). When storing, the mold needs to be placed in a dry and clean environment, and soft paper should be placed between the punch and the die to prevent the blades from damaging each other. Check the storage status of the mica sheets regularly (monthly) to avoid moisture and deterioration that affect the blanking quality.
