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CNC turret punch presses are more and more widely used in the metal processing industry, and mold is one of its most important components. What do you know about the turret punch die? I hope that today’s article can help everyone to better understand the turret punch die!

Turret Punch Mold Structure

The mold is also called CNC turret punching die, digital punching die, and CNC punching die. It usually consists of three parts: upper mold, lower mold, and mold base. It is further subdivided into 8 small parts: 1. Upper mold; 2. Return plate; 3. Lower mold; 4. Spring; 5. Tool station; 6. Upper mold seat; 7. Lower mold seat; 8. Mold seat.

Turret Punch Mold Type

There are various types of turret punching dies. Here are just a few commonly used special dies:

• Perforated mold

Perforated mold, which is also called perforated mold, means that a pair of molds can punch multiple holes at the same time. For punching plates, the efficiency can be improved several times. When making a perforated mold, it should be ensured that the minimum distance between the hole and the hole, and the minimum distance between the hole and the edge of the plate should not be less than twice the thickness of the plate. If the distance is too small, it will cause distortion and deformation of the plate and affect the processing effect. The connection between them is also easy to break.

• Shutter and bridge mold

Shutter molds and bridge molds belong to the punching and stretch forming molds, which are commonly used molds for cabinets.

• Counterbore mold

Counterbore molds are extrusion molding molds, which are mainly used to press small round holes on the flat surface and are simple and beautiful in processing.

Turret Punch Mold Grading

The general thick turret punch die is generally classified according to the aperture size that the die can process to facilitate the selection of the die. It is usually divided into five gears: A, B, C, D, and E.

A(1/2”) station: processing range Ø1.6～Ø12.7mm

B(1-1/2”) station: processing range Ø12.7～Ø31.7mm

C(2”) Station: Processing range Ø31.7～Ø50.8mm

D(3-1/2”) station: processing range Ø50.8～Ø88.9mm

E(4-1/2”) station: processing range Ø88.9～Ø114.3mm

Maintenance of Turret Punching Die

Just as the maintenance of the machine can ensure that the machine is in the best condition for a long time, maintain the best performance, and prolong the service life, our turret punch die also needs maintenance. The following are seven maintenance recommendations:

• Guarantee the best mold gap

Die gap refers to the sum of the gaps on both sides of the punch entering the lower die. It is related to plate thickness, material, and stamping process.

Choosing a suitable mold gap can ensure good punching quality, reduce burrs and collapse, keep the sheet flat, effectively prevent stripping, and extend the life of the mold.

By checking the stamping waste, you can determine whether the mold gap is appropriate. If the gap is too large, the waste will have rough undulating fracture surfaces and smaller shiny surfaces. The greater the gap, the greater the angle formed by the fracture surface and the bright surface, curling, and fracture will occur during punching, and even a thin edge protrusion will appear. On the contrary, if the gap is too small, the scrap will have a small angle fracture surface and a larger bright surface.

When performing partial punchings such as grooving, nibbling, and shearing, the lateral force will deflect the punch and cause the unilateral gap to be too small. Sometimes the edge offset may scratch the lower die and cause rapid wear of the upper and lower dies.

When the die is punched with the best clearance, the broken surface and the bright surface of the waste have the same angle and overlap each other, so that the punching force can be minimized and the punching burr is also small.

• Timely sharpening can effectively extend the service life of the mold

If the workpiece has excessive burrs or abnormal noise during punching, the mold may be passivated. Check the punch and the lower die. When the edge wear produces an arc with a radius of about 0.10mm, it must be sharpened.

The practice has shown that frequent small amounts of sharpening, rather than waiting for sharpening when necessary, will not only maintain good workpiece quality, reduce the punching force, but also more than double the life of the mold.

In addition to knowing when the mold is sharpened, it is especially important to master the correct sharpening method. The mold sharpening rules are as follows:

1. Use sintered alumina grinding wheel, hardness D~J, abrasive grain size 46~60, it is best to choose a grinding wheel suitable for high-speed steel grinding. 2. When sharpening, clamp the punch vertically in the V-groove or clamp of the magnetic chuck of the surface grinder, and the grinding amount is 0.03~0.05mm each time, and the grinding is repeated until the punch is sharp and the maximum grinding amount is Generally 0.1~0.3mm.

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 0.03~0.08mm, the lateral feed is 0.13~0.25mm, and the lateral feed speed is 2.5~3.8m/mi

5. After sharpening, polish the cutting edge with oilstone to remove the burrs, and grind out a rounded corner with a radius of 0.03~0.05mm, which can prevent the cutting edge from cracking.

6. The punch is demagnetized and sprayed with lubricating oil to prevent rust.

• Methods to eliminate and reduce sticky materials

Due to the pressure and heat during punching, the small particles of the sheet material will be bonded to the surface of the punch, resulting in poor punching quality. To remove the sticky material, it can be polished with a fine oilstone, and the direction of the polishing should be the same as the direction of the punch movement so that further sticky materials will be avoided after the light is finished. Don’t use roving cloth for sanding, so as to avoid the punch surface is rougher and sticky material is more likely to appear. Reasonable die clearance, a good stamping process, and necessary sheet material lubrication will reduce the occurrence of sticky materials. To prevent overheating, lubrication is generally used, which will reduce friction. If lubrication is not possible or scrap rebound occurs, the following methods can be adopted:

Using multiple punches of the same size alternately for punching can make it have a longer cooling time before being reused. Stop using the overheated mold. Through programming to control mold change, interrupt its long-term repetitive work, or reduce its stamping frequency.

• Measures to prevent sheet deformation when punching a lot of holes

If many holes are punched on a plate, the plate cannot be kept flat due to the accumulated punching stress. Each time a hole is punched, the material around the hole deforms downwards, causing tensile stress on the upper surface of the sheet and compressive stress on the lower surface. For a small amount of punching, the effect is not obvious, but when the number of punching increases, tensile and compressive stresses accumulate somewhere until the material is deformed.

One way to eliminate this kind 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 during sequential punching in the same direction, and also makes the stresses of the two sets of holes offset each other, thereby preventing the deformation of the sheet.

• Try to avoid punching narrow strips

When the die is used to punch a sheet with a width less than the thickness of the sheet, the punch will bend and deform due to lateral force, which will make the gap on one side too small or aggravate the abrasion. In severe cases, it will scratch the lower die and cause the upper and lower dies. Damaged at the same time.

It is not recommended to nibble narrow sheets with a width less than 2.5 times the thickness of the sheet. When cutting a narrow strip, the sheet tends to bend into the opening of the lower die instead of being completely cut off, or even wedged into the side of the die. If the above situation cannot be avoided, it is recommended to use a fully guided die with a return plate that supports the punch.

• The surface hardening of the punch and its scope of application

Although heat treatment and surface coating can improve the surface characteristics of the punch, it is not a general method to solve the stamping problem and extend the life of the die. Generally speaking, the coating improves the surface hardness of the punch and improves the lubricity of the side surface. However, when punching large tonnage and hard materials, these advantages disappear after about 1000 punches.

For the following situations, surface hardened punches can be used

1. Punching soft or viscous materials (such as aluminum);
2. Thinning abrasive materials (such as glass epoxy sheet); thinning hard materials (such as stainless steel); frequent nibbling;
3. Abnormal lubrication: surface hardening usually uses methods such as titanium plating and nitriding. The surface hardening layer is a molecular structure with a thickness of 12 to 60 μm. It is a part of the punch matrix, not just a coating.

The surface-hardened mold can be sharpened in the usual way. Surface hardening will reduce the wear of the die when punching stainless steel plates, but it will not extend its service life. However, proper lubrication, timely sharpening, and operation according to regulations are effective methods.

• Overhaul when the punch die position is not neutral

If the center of the punch die position is not good, which causes rapid passivation of the die and poor processing quality of the workpiece, you can repair it from the following points:

1. Check the level of the machine tool and readjust if necessary;
2. Check and lubricate the die holes and guide keys on the turntable, and repair them in time if they are damaged;
3. Clean the lower die seat of the turntable so that the lower die can be installed accurately, and check the wear of its key or keyway, and replace it if necessary;
4. Use a special mandrel to calibrate the mold station, and adjust in time if there is a deviation.

The above content is for the general situation. In view of the different specifications of the specific types of punches and molds, users should also understand and summarize experience based on the actual situation, and give play to the best performance of the mold.