Solutions To 15 Common Stamping Die Problems

1. Pay attention to the punch before use

① Clean the punch with a clean cloth.
②Check whether there are scratches or dents on the surface. If so, use oilstone to remove.
③ Apply oil in time to prevent rust.
④When installing the punch, be careful not to have any tilt. Use a soft material tool such as a nylon hammer to tap it lightly. Tighten the bolt only after the punch is correctly positioned.

2. Installation and debugging of die

The installation and adjustment of the die must be particularly careful. Because punching dies, especially large and medium-sized dies, are not only costly, but also difficult to move with heavy weight and trace amounts, so personal safety should always be given top priority. For the die of the infinite position device, a pad of wood should be added between the upper and lower dies. After the punch workbench is cleaned, the mold to be tested in the clamping state is placed on the appropriate position on the table.

Press the slider stroke selected according to the process documents and the design requirements of the die, adjust to the bottom dead center and 10-15mm greater than the closed height of the die before the die is moved onto the stage, adjust the slider connecting rod, move the die, and ensure that the die handle is aligned. The quasi-mold shank hole and reach the appropriate mold height. Generally, the blanking die first fixes the lower die (not tightened) and then fixes the upper die (tighten). T-bolts of the pressure plate should be tightened with a suitable torque wrench (lower die) to ensure that the same bolts have consistent and ideal pre-clamping force.

It can effectively prevent the pre-tightening force caused by physical strength, gender, and feel errors caused by manual tightening of the thread from being too large or too small, and the same thread pre-tightening force is unequal, which will cause the upper and lower molds to shift during the stamping process, the gap changes, and the cutting edge A failure such as the port has occurred.

Fully lubricate the mold and prepare the normal production materials before the mold test. Start the punching mold 3 to 5 times in an empty stroke to confirm that the mold is operating normally, and then try punching again. Adjust and control the depth of the punch into the die, check and verify the performance and operational flexibility of mechanisms and devices such as die guiding, feeding, pushing and unloading, side pressure and elastic pressure, and then make appropriate adjustments to achieve the best technical state. For large, medium and small dies, 3, 5, and 10 pieces were tested for the initial inspection of production suspension, and 10, 15, and 30 pieces were re-inspected after being qualified. After marking inspection, punching surface and burr inspection, all dimensions and shape and position accuracy meet the requirements of the drawings, before they can be delivered to production.
3. Stamping burrs

①The mold gap is too large or uneven, readjust the mold gap.
②The mold material and heat treatment are improper, resulting in the concave mold inverted cone or the cutting edge is not sharp, the material should be selected reasonably, the material of the mold working part should be made of cemented carbide, and the heat treatment method is reasonable.
③ Stamping wear, grinding punch or insert.
④The punch enters the concave mold too deep, adjust the depth of the punch into the concave mold.
⑤ The guiding structure is not precise or the operation is improper. Check the guiding accuracy of the guide post and the punching press in the mold and standardize the press operation.

4. Jump scrap

Large mold gap, short punch, material influence (hardness, brittleness), adhesion caused by too high stamping speed, too viscous stamping oil or too fast oil droplets, stamping vibration, swarf divergence, vacuum adsorption and mold core Insufficient demagnetization can cause waste debris to be brought to the mold surface.

① The sharpness of the cutting edge. The larger the rounded corner of the cutting edge, the more likely it is to cause the scrap to rebound. For thinner stainless steel, the inclined cutting edge can be used.
②For relatively regular waste materials, increase the complexity of the waste materials or add polyurethane ejector pins on the punch to prevent the waste materials from jumping, and increase scratches on the edge of the die.
③Whether the mold gap is reasonable. Unreasonable mold gaps can easily cause scrap to rebound. For small diameter holes, the gap is reduced by 10%, and the gap is enlarged if the diameter is greater than 50.00 mm.
④ Increase the depth of the mold. When each station die is stamped, the requirement of the modulus is certain, and the modulus is small, which is easy to cause the scrap to rebound.
⑤ Whether there is oil stain on the surface of the processed material.
⑥ Adjust the stamping speed and stamping oil concentration.
⑦Using vacuum adsorption.
⑧ Demagnetize the punches, inserts and materials.
5. Crushing, scratching

① There are oil stains and waste debris on the material belt or mold, which can cause crushing. It is necessary to wipe the oil stains and remove the waste debris.
②The mold surface is not smooth, so the surface finish of the mold should be improved.
③The surface hardness of the parts is not enough, and the surface needs chrome plating, carburizing, boronizing and other treatments.
④Material strain and unstable, reduce lubrication, increase pressure stress, adjust spring force.
⑤Process the mold that skips waste.
⑥ When the product is scratched to the mold positioning or other places during operation, it is necessary to modify or lower the mold positioning, and educate the operator to handle it gently.

6. The outer surface of the workpiece is scratched after bending

①The surface of the raw material is not smooth, clean and plain material.
②There is waste in the molded blocks, and the waste between the blocks is removed. .
③The forming block is not smooth, electroplating and polishing the forming block to improve the smoothness of the convex and concave mold.
④The bending radius R of the punch is too small, increase the bending radius of the punch
⑤The mold bending clearance is too small, adjust the bending and matching clearance of the upper and lower molds.
⑥The concave mold forming block is equipped with rollers for forming.

7. Leak punching

The situation of missing punching is generally caused by the fact that the punch is not found broken, the punch is missed after the mold is repaired, and the punch is sinking. After the mold is repaired, the first piece must be confirmed, and the sample should be compared with the sample to check whether there is any missing. If the head sinks, the hardness of the upper die backing plate should be improved.
8. Abnormal stripping

①The stripper plate and the punch are too tightly matched, the stripper plate is inclined, the height of the equal height screw is not uniform, or the other stripper device is improper, the stripper should be trimmed, and the stripper screw adopts a combination of sleeve and hexagon socket screws. .
②The mold gap is too small, and the punch needs a large demolding force when it is separated from the material, causing the punch to be bitten by the material, and the lower mold gap needs to be increased.
③The concave mold has an inverted cone to trim the concave mold.
④ The blanking hole of the concave die is not aligned with the leaking hole of the lower mold seat, and the leaking hole is trimmed.
⑤Check the condition of processed materials. The material is dirty and adheres to the mold, so that the punch is bitten by the material and cannot be processed. After punching the warped material, the punch will be clamped. If the warped material is found, it needs to be flattened before processing.
⑥ The cutting edge of the punch and lower die should be sharpened in time. A sharp-edged die can produce a beautiful cut surface. If the cutting edge is blunt, additional punching pressure is required. Moreover, the rough section of the workpiece produces great resistance, causing the punch to be bitten by the material.
⑦Appropriate use of oblique edge punches.
⑧ Minimize wear, improve lubrication conditions, and lubricate plates and punches.
⑨Insufficient spring or rubber elasticity or fatigue loss, replace the spring in time.
⑩The gap between the guide post and the guide sleeve is too large, repair or replace the guide post and guide sleeve.
Accumulation of parallelism error, re-grind and assemble.
The hole on the push piece block is not vertical, so that the small punch is offset. Repair or replace the push piece block.
The punch or guide post is not installed vertically, re-assemble to ensure verticality.

9. The bending edge is not straight and the size is unstable

①Increase the crimping or pre-bending process
②Insufficient material pressing force, increase pressing force
③The round corners of convex and concave molds wear asymmetrically or the bending force is uneven. Adjust the gap between the convex and concave molds to make them uniform and polish the rounded corners of the convex and concave molds.
④The height dimension cannot be less than the minimum limit dimension
10. Thinning of extrusion material on curved surface

①. Die fillet is too small, increase the fillet radius of the die
②. The gap between the convex and concave molds is too small, correct the gap between the convex and concave molds

11. The bottom of the concave part is not flat

①The material itself is not flat, and the material needs to be leveled
②The contact area between the top plate and the material is small or the ejecting force is not enough, the ejecting device needs to be adjusted to increase the ejecting force
③There is no ejector device in the die, and the ejector device should be added or corrected
④Add shaping process

12. Stainless steel flanging deformation

Apply a high-quality forming lubricant to the material before the flanging, which can better separate the material from the mold and move smoothly on the surface of the lower mold during forming. This gives the material a better opportunity to distribute the stress generated when it is bent and stretched, and prevents the deformation on the edge of the formed flanging hole and the wear of the bottom of the flanging hole.
13. Material distortion

A large number of holes are punched in the material, resulting in poor flatness of the material, which may be caused by the accumulation of stamping stress. When a hole is punched, the material around the hole is stretched downwards, which increases the tensile stress on the upper surface of the plate, and the downward punching movement also causes the compressive stress on the lower surface of the plate to increase. For punching a small number of holes, the result is not obvious, but as the number of punched holes increases, the tensile and compressive stresses also double until the material is deformed.

One of the ways to eliminate this deformation is to punch every other hole, and then return to punch the remaining holes. Although this produces the same stress on the plate, it disintegrates the accumulation of tensile stress/compressive stress due to continuous punching one after another in the same direction. This also allows the first batch of holes to share the partial deformation effect of the second batch of holes.

①Replace the worn-out die guide components and punches in time.
②Check whether the mold gap is unreasonable (too small), and increase the lower mold gap.
③ Minimize wear, improve lubrication conditions, and lubricate plates and punches. The amount of oil and the number of oil injections depend on the conditions of the processing material. For rust-free materials such as cold-rolled steel plates and corrosion-resistant steel plates, the mold must be filled with oil. The oil filling points are the guide sleeve, the oil injection port, and the lower mold. Use light engine oil for oil. For materials with rust, the rust powder will be sucked between the punch and the guide sleeve during processing, resulting in dirt, which prevents the punch from sliding freely in the guide sleeve. In this case, if oil is applied, the rust will be more likely to be stained. Therefore, when flushing this material, the oil should be wiped clean instead, decomposed once a month, use gasoline (diesel) oil to remove the dirt on the punch and lower mold, and then wipe clean before reassembly. This will ensure that the mold has good lubricating properties.
④Improper sharpening method will cause the annealing of the mold and increase the wear. You should use a soft abrasive wheel, use a small amount of knife, a sufficient amount of coolant, and often clean the wheel.
15. Prevent punching noise

Punch is the most critical necessary equipment for the sheet metal processing industry. The punching press will produce mechanical transmission noise, punching noise and aerodynamic noise when it is working. The maximum value of this noise can reach 125dB(A), which greatly exceeds the noise index requirements of 85dB(A) and below specified by the national standard. And the surrounding environment (such as offices, residential areas, meeting rooms, etc.) cause extremely serious injuries and pollution. Effective management of this noise has become an urgent problem to be solved. In particular, the implementation of my country’s first “Noise Law” and the increasing scale of environmental protection industrialization have accelerated the urgency of noise control.

Starting from the noise source of the press and the mold structure, the following points must be paid attention to to reduce the noise:
①Pay attention to mold maintenance and cleaning, and keep the cutting edge sharp.
②The shape, quantity, material and cutting line of the die edge are long. The contact surface of the die edge and the part should not be too large. The punch is used for oblique edge step blanking, so that the die has different cutting depths at different positions, and the whole process realizes real Cut off instead of squeezing off synchronously.
③The cutting edge of the mold must be perpendicular to the mounting surface, and the clearance between the cutting edges of the convex and concave molds should be reasonable. When unloading is difficult, the gap between the lower mold and the discharge force can be increased, and a soft surface unloading plate should be used.
④The matching accuracy between the working templates, processing some exhaust grooves.
⑤ The stop baffle is changed to small pieces, and the stripper plate and lower template are changed to inserts to reduce the attack area.
⑥The source of the ejector top of the stripper plate is changed to a T-shaped ejector rod, the spring is installed on the upper mold seat, and the contour sleeve is matched with the ejector rod to ensure that the stripper plate still has a certain amount of free movement when the mold is opened.
⑦Keep the lubrication well, the mold has no interference and is smooth.
⑧The surface of the upper and lower mold seats is cushioned with aluminum plates for impact.
⑨After the mold is debugged, install a sound insulation cover or sponge board sound insulation treatment on the punch.
⑩Improve the accuracy of the punch press and reduce the structure noise. Install a cushioning and noise-reducing oil cylinder on the worktable. The gear adopts helical gears for enhanced lubrication and a gear cover is installed. A silencer is installed in the pneumatic system.
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