Use and maintenance of CNC punch press molds

At present, in the field of sheet metal stamping processing, CNC turret punch presses are widely used for their fast stamping speed, high processing accuracy, strong mold versatility, and flexible and diverse products. The molds used by CNC turret punch presses have high precision and quality requirements and fast stamping speed. After users purchase a certain quality of mold, the level of its use and maintenance directly affects the processing quality of the workpiece and the service life of the mold. The mold is also an important part of controlling the operating cost of the equipment. Therefore, learning and mastering some knowledge in this area and applying it to practice will also play an important role in improving efficiency and reducing costs.

The following article discusses the use and maintenance of CNC turret punch press molds. Some technical points that should be followed in the use and maintenance of CNC turret punch press molds, and corresponding solutions to practical problems are proposed, which may have a good guiding role for users. Ensure the best mold gap.

The mold gap refers to the sum of the gaps on both sides when the punch enters the lower die. It is related to the plate thickness, material and stamping process. Choosing a suitable die gap can ensure good punching quality, reduce burrs and collapse, keep the plate flat, effectively prevent material carrying and extend the life of the die.

By checking the condition of the stamping waste, it can be determined whether the die gap is appropriate. If the gap is too large, the waste will have a rough and undulating fracture surface and a smaller bright surface. The larger the gap, the larger the angle formed by the fracture surface and the bright surface, and curling and fracture will be formed during punching, and even a thin edge protrusion will appear. On the contrary, if the gap is too small, the waste will have a small angle fracture surface and a larger bright surface.

When performing local stamping such as grooving, step punching, and shearing, the lateral force will deflect the punch and cause the single-sided gap to be too small. Sometimes the blade edge offset is too large to scratch the lower die, causing rapid wear of the upper and lower dies.

When the die is stamped with the optimal gap, the fracture surface and the bright surface of the waste have the same angle and overlap with each other, which can minimize the blanking force and the burrs of the punching are also very small.

2. Timely sharpening can effectively extend the service life of the mold.

If the workpiece has too large burrs or produces abnormal noise during stamping, it may be that the mold is blunted. Check the punch and the die. When the edge wears and produces an arc with a radius of about 0.1Omm, it is time to sharpen it.

Practice shows that regular micro-grinding instead of waiting until it is necessary to sharpen it will not only maintain good workpiece quality and reduce blanking force, but also extend the life of the mold by more than double.

In addition to knowing when to sharpen the mold, it is particularly important to master the correct sharpening method. The mold sharpening procedures are as follows:

1) When sharpening, hold the punch vertically in the V-groove or fixture of the magnetic chuck of the surface grinder. The grinding amount each time is 0.0:3~0.05mm. Repeat the grinding until the punch is sharp. The maximum grinding amount is generally 0.1, 0.3mm.

2) Use sintered alumina grinding wheel with hardness D'J and abrasive grain size of 46-60. It is best to choose a grinding wheel suitable for high-speed steel grinding.

3) When the grinding force is large or the mold is close to the grinding wheel, adding coolant can prevent the mold from overheating and cracking or annealing. High-quality multi-purpose coolant should be selected according to the manufacturer's requirements.

4) The downward feed of the grinding wheel is 0.03 and 0.08mm, the lateral feed is 0.13-0.25mm, and the lateral feed rate is 2.5 and 3.8m/min.

5) After sharpening, use oilstone to grind the edge, remove burrs, and grind out a radius of 0.0:3 and 0.Ot5mm to prevent the edge from cracking.

6) Demagnetize the punch and spray lubricating oil to prevent rust.

3. Methods to eliminate and reduce sticking

Due to the force and heat during flushing, the fine particles of the sheet will be bonded to the surface of the punch, resulting in poor punching quality. To remove the sticking material, you can use a fine oilstone to polish it. The polishing direction should be the same as the direction of the punch movement. This will avoid the generation of further sticking. Do not use coarse gauze to polish it, so as to avoid the punch surface becoming rougher and more prone to sticking.

Reasonable mold gap and good stamping process will reduce the generation of sticking. To prevent overheating, lubrication is generally used. If the waste material rebounds, the following methods can be taken: and necessary sheet lubrication will reduce the sticking material, which will reduce friction. If lubrication is not possible or there is a problem, use multiple punches of the same size to punch in turn, so that it can have a longer cooling time before being reused.

Stop using the overheated mold. Use programmable control to change the mold, interrupt its long-term repeated work, or reduce its stamping frequency.

4. Measures to prevent sheet deformation when punching many holes

If many holes are punched on a plate, the plate cannot remain flat due to the accumulation of punching stress. Each time a hole is punched, the material around the hole will deform downward, causing tensile stress on the upper surface of the plate and compressive stress on the lower surface. For a small number of punching holes, the effect is not obvious, but when the number of punching holes increases, tensile and compressive stresses accumulate somewhere until the material deforms.

One way to eliminate this type of deformation is to punch every other hole first, and then return to punch the remaining holes. Although this will also generate stress, it relieves the stress accumulation when punching sequentially in the same direction, and also makes the stresses of the front and rear groups of holes offset each other, thereby preventing the deformation of the sheet.

5. Try to avoid punching too narrow strips

When the die is used to punch a sheet with a width less than the thickness of the sheet, the lateral force will cause the punch to bend and deform, making the gap on one side too small or the wear more severe. In severe cases, the lower die will be scratched, causing damage to both the upper and lower dies.

It is recommended not to step punch narrow strips with a width less than 2.5 times the thickness of the sheet. When shearing too narrow strips, the sheet tends to bend into the opening of the lower die instead of being completely cut off, and may even wedge into the side of the die. If the above situation cannot be avoided, it is recommended to use a fully guided die with a stripper plate to support the punch.

6. Surface hardening of punches and its scope of application

Although heat treatment and surface coating can improve the surface characteristics of punches, they are not general methods to solve stamping problems and extend the life of molds. Generally speaking, coating increases the surface hardness of the punch and improves the lubricity of the side, but when punching large tonnage and hard materials, these advantages disappear after about 1,000 punches.

6. Surface hardened punches can be used for the following situations:

Punching soft or sticky materials (such as aluminum);

Punching thin abrasive materials (such as glass epoxy sheets);

Punching thin hard materials (such as stainless steel):

Frequent step punching;

Abnormal lubrication conditions.

Surface hardening usually adopts titanium plating, nitriding and other methods. The surface hardening layer is a molecular structure with a thickness of 12, 60U m. It is part of the punch matrix, not just a coating.

Surface hardened molds can be sharpened in the usual way. Surface hardening will reduce the wear of the mold when punching stainless steel plates, but it cannot extend its service life. Proper lubrication, timely sharpening and operation according to regulations are effective methods.

Seven. Inspection when the punch die is not well centered

If the CNC punch die is not well centered, causing rapid die passivation and poor workpiece processing quality, the following points can be inspected: Check the level of the machine tool and readjust it if necessary; Check and lubricate the die holes and guide keys on the turntable, and repair them in time if they are damaged; Clean the lower die seat of the turntable to ensure accurate installation of the lower die, and check the wear of its keys or keyways, and replace them if necessary; Use a special core rod to calibrate the die position, and adjust it in time if there is any deviation.

The above content is for normal situations. In view of the different specific types and specifications of punches and dies, users must also understand and summarize experience in combination with reality to give full play to the best performance of the die.