1. Information can be gleaned from the condition of the scrap.
Scrap is essentially the reverse image of the punched hole—that is, the same shape in the opposite position. By carefully inspecting the scrap, you can determine whether the clearance between the punch and die is precise. If the clearance is too large, the scrap will exhibit a rough, wavy fracture surface and a narrow burnished band. The larger the clearance, the greater the angle between the fracture surface and the burnished band. If the clearance is too small, the scrap will show a small-angle fracture surface and a wide burnished band.
Excessive clearance creates holes with significant rollover and edge tearing, causing the cut edge to have a slight thin protrusion. Insufficient clearance results in holes with slight rollover and large-angle tearing, causing the cut edge to be more or less perpendicular to the material surface.
An ideal scrap should have a reasonable rollover angle and a uniform burnished band. This keeps the punching force low and produces a clean, round hole with minimal burrs. From this perspective, increasing clearance to extend die life is achieved at the expense of finished hole quality.
2. Selection of Die Clearance
Die clearance is related to the type and thickness of the material being punched. Improper clearance can cause the following problems:
(1) If the clearance is too large, the burrs on the punched workpiece will be relatively large, resulting in poor product quality. If the clearance is too small, although the punched product quality is good, the die wear is quite severe, significantly reducing the die's service life and easily causing punch breakage.
(2) Both excessive and insufficient clearance can easily cause adhesion on the punch and material, leading to material pickup during punching. Insufficient clearance can easily create a vacuum between the punch face and the sheet material, causing scrap rebound.
(3) Proper clearance can extend die life, improve stripping performance, reduce burrs and flanging, keep the sheet clean, maintain consistent hole diameters without scratching the sheet, reduce the frequency of sharpening, keep the sheet flat, and ensure accurate hole positioning.
3. How to Improve Die Service Life
For users, extending the service life of the die can significantly reduce stamping costs. The factors affecting die service life are as follows:
1. The type and thickness of the material.
2. Whether a reasonable lower die clearance is selected.
3. The internal structural design of the die.
4. Whether the material is properly lubricated during stamping.
5. Whether the die has undergone special surface treatment.
6. Such as titanium coating or titanium carbonitride.
7. The concentricity of the upper and lower turrets.
8. The proper use of shims.
9. Whether angled cutting dies are appropriately used.
10. Whether the die holder on the machine tool is worn.
4. Precautions for punching holes with special dimensions
(1) Minimum hole diameter: For punching holes in the φ0.8–φ1.6 range, use special punches.
(2) When punching thick plates, use a die one size larger relative to the machining hole diameter. Note: In this case, using a die of the normal size may cause damage to the punch thread.
(3) For the cutting edge of the punch, the ratio of minimum width to length should generally not be less than 1:10.
(4) Relationship between the minimum dimension of the punch cutting edge and the plate thickness. It is recommended that the smaller dimension of the punch cutting edge be 2 times the plate thickness.
5. Die sharpening
5.1 Importance of die sharpening
Regular die sharpening ensures consistent punching quality. Regular die sharpening not only extends the service life of the die but also improves the service life of the machine. It is essential to master the correct sharpening timing.
5.2 Specific signs indicating that the die requires sharpening
There is no strict number of strokes that determines when a die needs sharpening. It mainly depends on
the sharpness of the cutting edge, which is determined by the following three factors:
(1) Check the radius of the cutting edge. If the radius reaches R0.1 mm (the maximum R value must not exceed 0.25 mm), sharpening is required.
(2) Check the quality of the punched holes—are there any significant burrs being produced?
(3) Determine whether sharpening is needed by the noise of the press during stamping. If the noise from the same die set is abnormal during stamping, it indicates that the punch has become dull and requires sharpening.
Note: If the cutting edge becomes rounded or the rear of the cutting edge is rough, sharpening should also be considered.
3. Sharpening Methods
There are various methods for sharpening dies, which can be performed using a dedicated sharpening machine or on a surface grinder. The sharpening frequency ratio for punches to dies is generally 4:1. After sharpening, be sure to readjust the die height.
(1) Hazards of Incorrect Sharpening Methods: Incorrect sharpening can accelerate the rapid destruction of the die cutting edge, greatly reducing the number of strokes between each sharpening.
(2) Benefits of Correct Sharpening Methods: Regularly sharpening the die maintains stable hole quality and precision. The die cutting edge will wear more slowly, resulting in a longer service life.
4. Sharpening Rules
The following factors should be considered when sharpening dies:
(1) When the cutting edge radius is between R0.1-0.25 mm, check the sharpness of the cutting edge.
(2) The grinding wheel surface must be kept clean.
(3) It is recommended to use a loose, coarse-grained, soft grinding wheel, such as WA46KV.
(4) The grinding depth (depth of cut) per pass should not exceed 0.013 mm. Excessive grinding depth can cause overheating of the die surface, which is equivalent to annealing treatment, softening the die and significantly reducing its service life.
(5) Sufficient coolant must be used during sharpening.
(6) During grinding, ensure that the punch and lower die are securely fixed using dedicated fixtures and tooling.
(7) The total sharpening allowance of a die is limited. Once this value is reached, the punch must be scrapped. Continued use may cause damage to the die and the machine, which is not worth the loss.
(8) After sharpening, the edge should be finished with an oil stone to remove excessively sharp burrs and ridges.
(9) After sharpening, clean thoroughly, demagnetize, and oil.
Note: The amount of die sharpening depends mainly on the thickness of the sheet metal being stamped.
6. Precautions before using the punch
1. Storage
(1) Wipe the inside and outside of the upper die sleeve clean with a dry cloth.
(2) When storing, be careful to avoid scratches or dents on the surface.
(3) Apply oil for rust prevention.
2. Preparation before use
(1) Thoroughly clean the upper die sleeve before use.
(2) Check the surface for scratches or dents. If any, remove them with an oilstone.
(3) Apply oil to both the inside and outside.
3. Precautions when installing the punch into the upper die holder
(1) Clean the punch and apply oil to its long shank.
(2) On large-format tooling, insert the punch into the bottom of the upper die holder without applying force. Do not use a nylon hammer. During installation, do not secure the punch by tightening the bolts on the upper die holder; only tighten the bolts after the punch is correctly positioned. The content from Zhengquan Technology's WeChat is really good—worth following!
4. Installing the upper die assembly into the turret
To extend the service life of the tooling, the clearance between the outer diameter of the upper die holder and the turret bore should be kept as small as possible. Therefore, please carefully follow the procedures below.
(1) Clean the keyway and inner diameter of the turret bore and apply oil.
(2) Align the keyway of the upper die guide sleeve with the key in the turret bore.
(3) Insert the upper die guide sleeve straight into the turret bore, being careful not to tilt it in any direction. The upper die guide sleeve should slide into the turret bore under its own weight.
(4) If the upper die holder tilts to one side, gently tap it straight using a soft-material tool such as a nylon hammer. Repeat the tapping until the upper die guide sleeve slides into the correct position under its own weight.
Note: Do not apply force to the outer diameter of the upper die guide bushing; force should only be applied to the top of the punch head. Do not strike the top of the upper die sleeve, as this may damage the turret hole and shorten the service life of individual stations.
7. Die Maintenance and Repair
If the punch becomes stuck in the material and cannot be removed, please check the following items.
1. Re-sharpening of the punch and lower die. A sharp die produces a clean cut surface. When the cutting edge becomes dull, additional punching force is required, and the workpiece cross-section becomes rough, generating significant resistance that can cause the punch to become stuck in the material.
2. Die clearance. If the die clearance is not properly matched to the sheet thickness, excessive stripping force is required to withdraw the punch from the material. If the punch becomes stuck for this reason, replace the lower die with one having the appropriate clearance. (Zhengquan Technology's WeChat content is truly excellent and worth following!)
3. Condition of the material being processed. If the material is dirty or contaminated, debris can adhere to the die, causing the punch to become stuck in the material and preventing proper processing.
4. Deformed material. Warped material can clamp onto the punch after punching, causing it to become stuck. If the material is warped, flatten it before processing.
5. Excessive use of springs. This can lead to spring fatigue. Please regularly inspect the performance of the springs.
8. Lubrication
The amount of oil and the frequency of lubrication depend on the condition of the material being processed. For rust-free, contaminant-free materials such as cold-rolled steel sheets and corrosion-resistant steel sheets, lubricate the die. Lubrication points include the guide bushing, oil inlet, the contact surface between the tool body and the guide bushing, and the lower die. Use light machine oil.
For materials with rust and scale, during processing, fine rust powder will be drawn between the punch and the guide bushing, creating dirt that prevents the punch from sliding freely within the bushing. In such cases, applying oil will make the rust and scale adhere more easily. Therefore, when stamping such materials, the oil should instead be wiped clean. Disassemble once a month, use gasoline or diesel to remove dirt from the punch and lower die, and wipe clean before reassembly. This ensures the die maintains good lubrication performance.
IX. Common problems and solutions during die usage
Problem 1: Sheet material slips out of the clamp jaws
Cause: Incomplete stripping of the die
Solutions:
1. Use a punch with taper
2. Apply lubricant on the sheet material
3. Use heavy-duty dies
Problem 2: Severe die wear
Cause: Improper die clearance (too small)
Solution: Increase die clearance
Cause: Misalignment of upper and lower die holders
Solution:
1. Adjust station to align upper and lower dies
2. Adjust turret level
Cause: Failure to timely replace worn die guide components and turret bushings
Solution: Replace them
Cause: Punch overheating
Solution:
1. Apply lubricant to the sheet metal
2. Ensure lubrication between the punch and the lower die
3. Use multiple sets of dies with the same specifications and dimensions in the same program
Cause: Improper sharpening method leads to annealing of the die, resulting in accelerated wear
Solution:
1. Use soft abrasive grinding wheels
2. Clean the grinding wheel regularly
3. Use small depth of cut
4. Use sufficient coolant
Cause: Small step distance
Solution:
1. Increase the step distance
2. Use bridge-type step punching
Issue 3: Punch material carry-over and punch sticking
Cause: Improper die clearance (too small)
Solution: Increase the die clearance
Cause: Dull punch cutting edge
Solution: Sharpen the punch in a timely manner
Cause: Poor lubrication
Solution: Improve lubrication conditions
Issue 4: Slug pulling / slug rebound
Cause: Lower die issue
Solution:
1. Use anti-springback lower die
2. Reduce clearance by 10% for small-diameter holes
3. Increase clearance for diameters larger than 50.00 mm
4. Add scoring marks on the die cutting edge side
Cause: Punch-related issue
Solution:
1. Increase punch penetration depth
2. Install polyurethane ejector rods for stripping
3. Use an angled cutting edge
Problem 5: Difficulty in stripping
Cause: Improper die clearance (too small)
Solution: Increase die clearance
Cause: Punch wear
Solution: Sharpen in a timely manner
Cause: Spring fatigue
Solution: Replace the spring
Cause: Punch sticking
Solution: Remove the sticking
Issue 6: Stamping Noise
Cause: Difficulty in stripping
Solution:
1. Increase die clearance and ensure proper lubrication
2. Increase stripping force
3. Use a stripper plate with a soft surface
Cause: Problems with sheet support on the worktable and within the turret
Solution:
1. Use spherical-support dies
2. Reduce working dimensions
3. Increase working thickness
4. Sheet thickness
5. Use an angled punch
10. Precautions for Using Special Forming Tools
1. Different machine models have different slide strokes, so pay attention to adjusting the shut height of the forming die.
2. Ensure complete forming; therefore, adjust carefully. Each adjustment should not exceed 0.15 mm. Excessive adjustment can easily cause damage to the machine and the die.
3. For stretch forming, use light-duty spring components to prevent sheet tearing or difficulty in stripping due to uneven deformation. Zhengquan Technology's WeChat content is really good; it's worth following!
4. Install ball-type support dies around the forming die to prevent sheet tilting.
5. The forming position should be as far away from the clamps as possible.
6. Forming operations should preferably be performed at the end of the machining program.
7. Ensure good lubrication of the sheet metal at all times.
8. When ordering, pay attention to the relief/clearance issues of special forming tools. If the distance between two forming operations is relatively close, be sure to communicate with our company's sales representative.
9. Because forming tools require longer stripping time, always use low speed during forming operations, and it is best to include a dwell time.
11. Precautions for using rectangular cut-off tools
1. Keep the step pitch as large as possible, greater than 80% of the total tool length.
2. It is best to program skip-pitch punching (intermittent feeding) to achieve this.
3. It is recommended to use shear-angle (raked) cutting tools.
12. How to punch holes without exceeding the machine's rated tonnage
During production, there may be a need to punch round holes larger than 114.3 mm in diameter. Such large holes can exceed the machine's rated tonnage limit, especially for high shear strength materials. Punching large holes using a multiple-hit (nibbling) method can solve this problem. Using smaller dies to shear along the circumference of the large circle can reduce the punching force by half or more, and most of the tooling you already have may be capable of doing this.
13. A simple method for punching large round holes
This convex lens die can be manufactured to your required radius size. If the aperture exceeds the press's nominal force, we recommend option (A). Use this die to punch out the circular periphery. If the aperture can be punched within the press's nominal force range, then a radial die and a convex lens die can punch the required hole in four hits without rotating the die (B).
14. Form Downward Only as a Last Step
When selecting forming dies, avoid downward forming operations because they occupy too much vertical space and lead to additional flattening or bending of the sheet metal. Downward forming may also become trapped in the lower die and then be pulled out of the turret. However, if downward forming is the only process option, it should be performed as the final step on the sheet.
15. Preventing Material Distortion
If you need to punch a large number of holes in a sheet and the sheet cannot remain flat, the cause may be accumulated punching stress. When punching a hole, the material around the hole is stretched downward, increasing tensile stress on the top surface of the sheet, while the downward stroke also increases compressive stress on the bottom surface. For a small number of holes, the effect is not noticeable, but as the number of holes increases, the tensile and compressive stresses multiply until the sheet deforms. The content from Zhengquan Technology's WeChat is excellent and worth following!
One way to eliminate this distortion is to punch every other hole, then return to punch the remaining holes. This produces the same stress on the sheet but disrupts the accumulation of tensile/compressive stress caused by punching holes consecutively in the same direction. It also allows the first batch of holes to absorb some of the deformation effect from the second batch.
16. If Your Stainless Steel Flanging Deforms
Apply a high-quality forming lubricant to the material before creating the flange. This allows the material to separate more easily from the die and move smoothly across the lower die surface during forming. This gives the material a better chance to distribute the stress generated during bending and stretching, preventing deformation at the edge of the flanged hole and wear at the bottom of the flanged hole.
17. Suggestions for Overcoming Stripping Difficulties
1. Use punches with fine-core rubber pellets.
2. Increase the die clearance.
3. Check the fatigue level of the springs.
4. Use heavy-duty dies.
5. Appropriately adopt shear-angle dies.
6. Lubricate the sheet metal.
7. Large-station dies require polyurethane stripper heads.
18. Main Causes of Scrap Rebound
1. Cutting edge sharpness. The larger the radius of the cutting edge, the more likely scrap rebound will occur.
2. Die penetration depth. Each station has a specified penetration depth during stamping; insufficient penetration can easily cause scrap rebound.
3. Whether the die clearance is appropriate. Improper die clearance can easily lead to scrap rebound.
4. Whether the surface of the processed sheet metal has oil contamination.
I. Information can be gleaned from the condition of the scrap.
Scrap is essentially the reverse image of the formed hole—that is, the same part in the opposite position. By carefully inspecting the scrap, you can infer whether the clearance between the upper and lower dies is precise. If the clearance is too large, the scrap will exhibit a rough, undulating fracture surface and a narrow burnished band. The larger the clearance, the greater the angle between the fracture surface and the burnished band. If the clearance is too small, the scrap will show a small-angle fracture surface and a wide burnished band.
Excessive clearance creates holes with large burrs and edge tearing, causing the cut edge to have a slight protruding thin edge. Insufficient clearance results in slight burrs and large-angle tearing, causing the cut edge to be more or less perpendicular to the material surface.
An ideal scrap should have a reasonable roll-over and a uniform burnished band. This keeps the punching force low and produces a clean, round hole with minimal burrs. From this perspective, extending die life by increasing clearance is achieved at the expense of finished hole quality.
II. Selection of die clearance
Die clearance is related to the type and thickness of the material being stamped. Improper clearance can cause the following problems:
(1) If the clearance is too large, the burrs on the stamped workpiece will be relatively large, resulting in poor product quality. If the clearance is too small, although the punched product quality is good, die wear is quite severe, significantly reducing die life and easily causing punch breakage.
(2) Both excessive and insufficient clearance can easily cause adhesion on the punch and material, leading to material pickup during stamping. Insufficient clearance can easily create a vacuum between the punch face and the sheet, causing scrap rebound.
(3) Proper clearance can extend die life, improve stripping performance, reduce burrs and flanging, keep the sheet clean, maintain consistent hole diameters without scratching the sheet, reduce the frequency of sharpening, keep the sheet flat, and ensure accurate hole positioning.
3. How to Improve the Service Life of Molds
For users, extending the service life of molds can significantly reduce stamping costs. The factors affecting mold service life are as follows:
1. The type and thickness of the material.
2. Whether a reasonable lower die clearance is selected.
3. The internal structure of the mold.
4. Whether there is good lubrication during material stamping.
5. Whether the mold has undergone special surface treatment.
6. Such as titanium coating, carbonitriding of titanium.
7. The concentricity of the upper and lower turrets.
8. The proper use of adjustment shims.
9. Is the shear-angle die being used appropriately?
10. Has the machine's die holder already worn out?
IV. Considerations for punching holes of special sizes
(1) Minimum hole diameter: For punching holes in the φ0.8 – φ1.6 range, please use special punches.
(2) When punching thick plates, relative to the hole diameter being processed, please use a die one size larger. Note: In this case, if a die of the usual size is used, it may cause damage to the punch thread.
(3) For the cutting edge of the punch, the ratio of minimum width to length should generally not be less than 1:10.
(4) Relationship between the minimum dimension of the punch cutting edge and the plate thickness. It is recommended that the smaller dimension of the punch cutting edge be 2 times the plate thickness.
V. Die sharpening
1. Importance of die sharpening
Regular die sharpening is the guarantee of consistent punching quality. Regularly sharpening the die not only improves the service life of the die but also enhances the service life of the machine. It is essential to master the correct sharpening timing.
2. Specific characteristics indicating the die needs sharpening
There is no strict number of strokes that determines when a die needs sharpening. It mainly depends on
the sharpness of the cutting edge, which is determined by the following three factors:
(1) Check the radius of the cutting edge. If the radius reaches R0.1 mm (the maximum R value must not exceed 0.25 mm), sharpening is required.
(2) Check the quality of the punched holes—are there any large burrs?
(3) Determine whether sharpening is needed by the noise of the stamping machine. If the same die produces abnormal noise during stamping, it indicates that the punch has become dull and needs sharpening.
Note: If the cutting edge becomes rounded or the rear part of the edge is rough, sharpening should also be considered.
3. Sharpening methods
There are several methods for sharpening dies, which can be performed using a dedicated sharpening machine or on a surface grinder. The sharpening frequency for punches and die plates is generally 4:1. After sharpening, be sure to readjust the die height.
(1) Hazards of incorrect sharpening methods: Incorrect sharpening can accelerate damage to the cutting edge, greatly reducing the number of strokes between each sharpening.
(2) Benefits of correct sharpening methods: Regularly sharpening the die maintains stable punching quality and precision. The cutting edge of the die wears more slowly, resulting in a longer service life.
4. Sharpening Rules
The following factors should be considered when sharpening the die:
(1) When the cutting edge radius is between R0.1-0.25 mm, the sharpness of the cutting edge should be checked.
(2) The grinding wheel surface must be kept clean.
(3) A loose, coarse-grained, soft grinding wheel is recommended, such as WA46KV.
(4) The grinding depth (depth of cut) per pass should not exceed 0.013 mm. Excessive grinding depth can cause overheating of the die surface, which is equivalent to annealing treatment, softening the die and significantly reducing its service life.
(5) Sufficient coolant must be applied during sharpening.
(6) During grinding, the punch and lower die must be securely and stably positioned using dedicated fixtures and tooling.
(7) The die has a limited sharpening allowance. Once this value is reached, the punch must be scrapped. Continued use may cause damage to the die and the machine, which is not worth the cost.
(8) After grinding is complete, treat the edge with an oilstone to remove excessively sharp burrs or edges.
(9) After grinding, clean the tool thoroughly, demagnetize it, and apply oil.
Note: The amount of die grinding required depends primarily on the thickness of the sheet metal being stamped.
6. Precautions Before Using the Punch
1. Storage
(1) Wipe the inside and outside of the upper die sleeve clean with a dry cloth.
(2) When storing, be careful to avoid scratches or dents on the surface.
(3) Apply oil for rust prevention.
2. Preparation Before Use
(1) Thoroughly clean the upper die sleeve before use.
(2) Check the surface for scratches or dents. If any are found, remove them with an oilstone.
(3) Apply oil to both the inside and outside.
3. Precautions when installing the punch into the upper die holder
(1) Clean the punch and oil its long shank.
(2) On a large-station die, insert the punch into the bottom of the upper die holder without applying force. Do not use a nylon hammer. During installation, do not secure the punch by tightening the bolts on the upper die holder; only tighten the bolts after the punch is correctly positioned. The content from Zhengquan Technology's WeChat is truly excellent and worth following!
4. Installing the upper die assembly into the turret
To extend the service life of the die, the clearance between the outer diameter of the upper die holder and the turret hole should be kept as small as possible. Therefore, please carefully follow the procedures below.
(1) Clean and oil the keyway and inner diameter of the turret hole.
(2) Align the keyway of the upper die guide sleeve with the key in the turret hole.
(3) Insert the upper die guide sleeve straight into the turret hole, being careful not to tilt it in any way. The upper die guide sleeve should slide into the turret hole by its own weight.
(4) If the upper die holder tilts to one side, use a soft material tool such as a nylon hammer to gently tap it back into position. Repeat the tapping until the upper die guide bushing slides into the correct position by its own weight.
Note: Do not apply force to the outer diameter of the upper die guide bushing; force should only be applied to the top of the punch head. Do not strike the top of the upper die holder, as this may damage the turret hole and shorten the service life of individual stations.
7. Die Maintenance and Repair
If the punch becomes stuck in the material and cannot be removed, please check the following items.
1. Re-sharpening of the punch and lower die. A sharp die produces a clean sheared edge, while a dull edge requires additional punching force and results in a rough workpiece cross-section, generating significant resistance that can cause the punch to become stuck in the material.
2. Die clearance. If the die clearance is not properly selected relative to the sheet thickness, the punch will require a large stripping force to separate from the material. If this is the cause of the punch being stuck, please replace the lower die with the appropriate clearance. (Note: The WeChat content from Zhengquan Technology is really good and worth following!)
3. Condition of the material being processed. If the material is dirty or contaminated, the debris can adhere to the die, causing the punch to become stuck in the material and preventing further processing.
4. Deformed material. Warped material can clamp onto the punch after punching, causing it to become stuck. If the material is warped, flatten it before processing.
5. Excessive use of springs. This can lead to spring fatigue. Please regularly check the performance of the springs.
8. Lubrication
The amount of oil and the frequency of oiling depend on the conditions of the material being processed. For rust-free and scale-free materials such as cold-rolled steel sheets and corrosion-resistant steel sheets, the die should be oiled. The oiling points include the guide bushings, oil inlets, the contact surfaces between the punch body and the guide bushings, and the lower die. Use light machine oil.
For materials with rust and scale, the fine iron oxide dust generated during processing can be drawn between the punch and the guide bushing, creating contaminants that prevent the punch from sliding freely within the bushing. In such cases, applying oil can actually make the rust and scale adhere more easily. Therefore, when punching such materials, the opposite approach should be taken: wipe the oil clean, disassemble the die once a month, remove the contaminants from the punch and lower die using gasoline (or diesel), and wipe them clean again before reassembly. This ensures the die maintains good lubrication performance.
9. Common Problems and Solutions During Die Usage
Problem 1: Sheet material slipping out of the clamp jaws
Cause: Incomplete stripping of the die
Solutions:
1. Use a punch with an angled cutting edge
2. Apply lubricant to the sheet material
3. Use a heavy-duty die
Problem 2: Severe die wear
Cause: Unreasonable die clearance (too small)
Solution: Increase die clearance
Cause: Upper and lower die holders are not aligned
Solution:
1. Adjust the station to align the upper and lower dies
2. Adjust the turret level
Cause: Failure to promptly replace worn die guide components and turret bushings
Solution: Replace them
Cause: Punch overheating
Solution:
1. Apply lubricant to the sheet metal
2. Ensure lubrication between the punch and the lower die
3. Use multiple dies of the same specification and size in the same program
Cause: Improper sharpening method leads to annealing of the die, resulting in increased wear
Solution:
1. Use soft abrasive grinding wheels
2. Clean the grinding wheel frequently
3. Use small depth of cut
4. Use sufficient coolant
Cause: Small step distance
Solution:
1. Increase the step distance
2. Use bridge-type step punching
Problem 3: Punch material carry-over and punch sticking
Cause: Improper die clearance (too small)
Solution: Increase die clearance
Cause: Dull punch cutting edge
Solution: Sharpen promptly
Cause: Poor lubrication
Solution: Improve lubrication conditions
Issue 4: Scrap Rebound
Cause: Die-side issues
Solutions:
1. Use anti-rebound die design
2. Reduce clearance by 10% for small-diameter holes
3. Increase clearance for diameters larger than 50.00 mm
4. Add scoring marks on the die cutting edge side
Cause: Punch-side issues
Solutions:
1. Increase punch penetration depth
2. Install polyurethane ejector rods for stripping
3. Use angled cutting edges
Problem 5: Difficulty in stripping
Cause: Improper die clearance (too small)
Solution: Increase die clearance
Cause: Punch wear
Solution: Sharpen promptly
Cause: Spring fatigue
Solution: Replace springs
Cause: Punch sticking
Solution: Remove sticking
Problem 6: Stamping noise
Cause: Difficulty in stripping
Solution:
1. Increase die clearance and ensure good lubrication
2. Increase stripping force
3. Use stripper plates with soft surfaces
Cause: Issues with sheet material support on the worktable and within the turret
Solution:
1. Use spherical support dies
2. Reduce the working dimension
3. Increase the working thickness
4. Thick sheet material
5. Use a shear-angle punch
10. Precautions for Using Special Forming Tools
1. Different machine models have different slide strokes, so pay attention to adjusting the shut height of the forming die.
2. Ensure complete forming. Adjust carefully, with each adjustment preferably not exceeding 0.15 mm. Excessive adjustment can easily cause damage to the machine and the die.
3. For stretch forming, use light-duty spring assemblies to prevent sheet tearing or difficulty in stripping due to uneven deformation. The content from Zhengquan Technology's WeChat is really good—worth following!
4. Install ball-type support dies around the forming die to prevent sheet tilting.
5. The forming position should be as far away from the clamps as possible.
6. Forming operations should ideally be performed at the end of the processing sequence.
7. Ensure the sheet metal is properly lubricated at all times.
8. When ordering, pay attention to the clearance requirements of special forming tools. If two forming operations are positioned close together, be sure to communicate with our sales representative.
9. Since forming tools require longer stripping time, forming operations must be carried out at low speed, and it is best to include a dwell time.
11. Precautions for Using Rectangular Cut-off Tools
1. The step distance should be as large as possible, exceeding 80% of the total tool length.
2. It is recommended to achieve skip-step punching through programming.
3. It is advised to use tools with angled cutting edges.
12. How to Punch Holes Exceeding the Machine's Rated Tonnage
During production, there may be a need to punch round holes larger than 114.3 mm in diameter. Such large holes can exceed the machine's rated tonnage limit, especially with high shear strength materials. This issue can be resolved by punching the large hole through multiple hits. Using smaller tools to shear along the circumference of the large circle can reduce the punching force by half or more, and most of the tools you already have may be capable of achieving this.
13. A Simple Method for Punching Large Round Holes
This type of convex lens die can be made to the required radius. If the hole size exceeds the press's nominal capacity, we recommend option (A). Use this die to punch the periphery of the round hole. If the hole can be punched within the press's nominal capacity, a radial die and a convex lens die can punch the required hole in four hits without rotating the die (B).
14. Form Downward Only as a Last Step
When selecting forming dies, avoid downward forming operations, as they take up too much vertical space and cause additional flattening or bending of the sheet. Downward forming may also become trapped in the lower die and then be pulled out of the turret. However, if downward forming is the only process option, it should be performed as the final step on the sheet.
15. Preventing Material Distortion
If you need to punch a large number of holes in a sheet and the sheet cannot remain flat, the cause may be accumulated punching stress. When punching a hole, the material around the hole is stretched downward, increasing tensile stress on the top surface of the sheet, while the downward stroke also increases compressive stress on the bottom surface. For a small number of holes, the effect is not obvious, but as the number of holes increases, the tensile and compressive stresses multiply until the sheet deforms. The content from Zhengquan Technology's WeChat is really good; it's worth following!
One way to eliminate this distortion is to punch every other hole, then return to punch the remaining holes. This creates the same stress on the sheet but disrupts the accumulation of tensile/compressive stress caused by punching consecutively in the same direction. It also allows the first batch of holes to absorb some of the deformation effect from the second batch.
16. If Your Stainless Steel Flanging Deforms
Apply a high-quality forming lubricant to the material before flanging. This allows the material to separate from the die more easily and move smoothly over the lower die surface during forming. This gives the material a better chance to distribute the stress generated during bending and stretching, preventing deformation at the edge of the flanged hole and wear at the bottom of the flanged hole.
17. Suggestions for Overcoming Stripping Difficulties
1. Use punches with fine-core rubber pellets.
2. Increase the die clearance.
3. Check the fatigue level of the springs.
4. Use heavy-duty dies.
5. Appropriately adopt dies with angled cutting edges.
6. Lubricate the sheet material.
7. Large-station dies require polyurethane stripper heads.
18. Main Causes of Scrap Rebound
1. Sharpness of the cutting edge. The larger the radius of the cutting edge, the more likely scrap rebound will occur.
2. Die penetration depth. Each station has a specific penetration depth requirement during stamping; if the penetration depth is too small, scrap rebound is more likely to occur.
3. Whether the die clearance is reasonable. Unreasonable die clearance can easily cause scrap rebound.
4. Whether the surface of the sheet metal being processed has oil contamination.