Die sharpening is primarily necessary because when the cutting edge of a punch die wears down to a certain extent, its originally sharp edge becomes dull, leading to a decrease in the size and precision of the stamped parts, along with the appearance of larger burrs. However, in many cases, a skilled and knowledgeable technician can restore the sharpness of the cutting edge and improve the surface quality of the processed workpiece by sharpening the die. Generally speaking, if the die is sharpened at the appropriate time, its service life can be extended by more than 100%, and the precision of the punch press can be maintained for a long time, preventing burrs and flash.
Since die sharpening is so valuable, how do you determine when a CNC punching die needs sharpening?
In most cases, the number of punching passes can be used to determine the extent of the problem. After a certain number of passes, noticeable burrs often appear, such as rounded corners on the upper die cutting edge and loss of shine. However, each case requires specific analysis. Ultimately, the operator is the most familiar with the equipment's operation, and daily maintenance is performed by the operator. Therefore, operators should conduct regular machine inspections, performing a minor inspection every three days and a major inspection every five days.
The inspection of CNC punching die grinding mainly considers these three aspects.
1. Check the radius of the cutting edge. If the radius is greater than R0.15mm, it is recommended to sharpen it; if it is greater than R0.25mm, it must be sharpened.
2. Check the punching quality for large burrs or loss of original luster. If any of these issues arise, sharpening is necessary.
3. If there is excessive collapse around the punch hole, the stamping process generates more noise than usual, or the processing is significantly more difficult than usual, it is also necessary to sharpen the blade.
In short, one cannot simply look at the number of stampings; one must consider the actual situation. So, how should one perform die sharpening?
Generally, sintered alumina grinding wheels with a hardness of D~J and an abrasive size of 46~60 are used. It is best to choose grinding wheels suitable for high-speed steel grinding. When sharpening, the punch is vertically clamped in the V-groove or fixture of the magnetic chuck of the surface grinder. The grinding amount per pass is 0.03~0.05mm. Repeat grinding until the punch is sharp. The maximum grinding amount is generally 0.1~0.3mm. When the grinding force is large or the die is close to the grinding wheel, adding coolant can prevent the die from overheating and cracking or annealing. A high-quality multi-purpose coolant should be selected according to the manufacturer's requirements. The downward feed of the grinding wheel is 0.03~0.08mm, the transverse feed is 0.13~0.25mm, and the transverse feed rate is 2.5~3.8m/min.
In addition, after sharpening, demagnetize in time, use an oilstone to polish the cutting edge, remove burrs, and grind out a rounded corner with a radius of 0.03~0.05mm to prevent the cutting edge from cracking and rusting. Finally, the height of the mold should be adjusted to be the same as before sharpening.
Friendly reminder: Improper sharpening will accelerate the damage to the cutting edge of the mold and reduce its service life. Therefore, you must find a knowledgeable and experienced technician to operate it and choose a professional and suitable sharpening machine.
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