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The use and maintenance of CNC turret punch mould


First, to ensure the best mold clearance

The die gap is the sum of the gaps between the two sides of the punch into the lower die. It is related to plate thickness, material and stamping process. Selecting the right mold gap can ensure good punching quality, reduce burrs and collapse, keep sheet leveling smooth, effectively prevent tape, and prolong mold life.

By checking the situation of stamping waste, it can be determined whether the mold gap is appropriate. If the gap is too large, the waste will have a rough undulating fracture surface and a smaller shiny surface. The larger the gap, the greater the angle formed by the fracture surface and the bright surface. When the hole is punched, curling and breaking occur, and even a thin edge protrusion appears. Conversely, if the gap is too small, scrap will appear with a small angle fracture surface and a larger shiny surface.

When performing local punching such as slotting, nibbling, shearing, etc., the lateral force will cause the punch to deflect and cause the unilateral clearance to be too small. Sometimes the edge deviation will scratch the lower die, causing rapid wear of the upper and lower molds.

When the die is punched with the best clearance, the fracture surface and the glossy surface of the scrap have the same angle and coincide with each other, so that the blanking force can be minimized and the punching burrs are also small.

Second, timely grinding can effectively extend the life of the mold

If the workpiece has excessive burrs or unusual noise during stamping, the mold may be passivated. Check the punch and the lower die. When the blade edges are worn to produce a circular arc with a radius of about 0.10 mm, it must be sharpened.

Practice has shown that frequent sharp grinding rather than waiting until the non-abrasive grinding can not only maintain a good workpiece quality, reduce the blanking force, but also can extend the life of the mold more than doubled.

In addition to knowing when the mold is sharpened, it is especially important to have a proper sharpening method. The mold grinding procedure is as follows:

1) The use of sintered alumina Grinding Wheel, hardness D ~ J, abrasive grain size 46 ~ 60, the best choice for high-speed steel grinding wheel.

2) When sharpening, the punch is clamped vertically in the V-groove or fixture of the magnetic chuck of the surface grinding machine, and the grinding amount is 0.03-0.05mm each time. The grinding is repeated until the punch is sharp and the maximum grinding amount is obtained. It is generally 0.1~0.3mm.

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

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

5) After sharpening, use the stone to grind the edge, remove the burr, and grind a radius of 0.03~0.05mm to prevent the edge from cracking.

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

Third, eliminate and reduce the method of sticking materials

Due to the pressure and heat during stamping, fine particles of the sheet material are bonded to the surface of the punch, resulting in poor punching quality. Detachable material can be ground with fine whetstone, and the direction of sanding should be the same as the direction of movement of the punch, so that light will prevent further sticking. Do not grind with roving cloth, etc., so that the surface of the punch is rougher and sticking material is more likely to occur. A reasonable die clearance, a good stamping process, and the necessary sheet lubrication will reduce the stickiness. To prevent overheating, lubrication is generally used, which reduces friction. If it cannot be lubricated or there is a rebound of waste, the following methods can be used:

Alternately using multiple punches of the same size alternately punches, allowing them to have a longer cooling time before being reused. Use the overheated mold for rest. Programmatically change molds to interrupt their long repetitive work or reduce their punching frequency.

Fourth, to punch a lot of holes to prevent sheet metal deformation measures

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

One way to eliminate this distortion is to punch first every other hole and then return to punching the remaining holes. In this way, although stress is also produced, it relieves the stress accumulation in the sequential punching in the same direction, and also causes the stress in the front and rear two sets of holes to cancel each other, thereby preventing the sheet material from being deformed.

Fifth, try to avoid punching too narrow strips

When the die is used for punching blanks with a width less than the thickness of the plate, the punch is bent due to the lateral force, so that the gap on one side is too small or the wear is increased. In severe cases, the lower die is scratched and the upper and lower molds are scratched. At the same time damaged.

It is not recommended to nib out narrow strips 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 die opening instead of being completely cut off, or even wedge into the side of the die. If it is impossible to avoid the above situation, it is recommended to use a fully guided die with a backing plate counteracting the punch.

Six, punch surface hardening and its scope of application

Although heat treatment and surface coatings improve punch surface characteristics, they are not a general solution to stamping problems and extended tool life. In general, the coating improves the surface hardness of the punch and improves the lubricity of the side, but these advantages vanish after about 1000 stampings at high tonnage, hard material stamping.

Seven, surface hardened punch can be used for the following situations:

Soft or sticky material (such as aluminum);

Thin abrasive materials (such as glass epoxy); thin hard materials (such as stainless steel);

Irregular lubrication condition.

Surface hardening is usually performed by methods such as titanium plating and nitriding. The surface hardened layer is a molecular structure with a thickness of 12 to 60 μm. It is a part of the punch base, and not just a coating.

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

Eight, the punch die position is not good when the maintenance of neutral

If the centering of the die position of the press is not good, resulting in rapid passivation of the die, and the workpiece processing quality is poor, the following points may be overhauled:

Check the level of the machine and readjust it if necessary;

Check and lubricate the die holes and guide keys on the turntable and repair them in case of damage.

Clean the lower mold base of the turntable so that the lower mold can be accurately installed, and check the wear of the key or keyway and replace it if necessary;

Use a special mandrel to calibrate the mold station and adjust in time if there is any deviation.

The above content is for the general situation, in view of the different types of punch and die specific specifications, the user must combine the actual to understand and sum up experience to play out the best performance of the mold.

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