It is rare to have such a complete stamping die information, valuable experience!

Time：2023-07-31 08:29:55 / Popularity： / Source：

1. Information seen from waste situation

Scrap is essentially inverse image of formed hole. That is, same parts in opposite positions. By checking scrap, you can tell if upper and lower die clearances are correct. If gap is too large, scrap will have a rough, undulating fracture surface and a narrow bright band area. The larger gap, the larger angle formed by fracture surface and bright band region. If gap is too small, scrap will exhibit a slightly angled fracture surface and a broad bright band area.

Excessive gaps create holes with larger curls and edge tears, causing section to protrude slightly with a thin edge. A gap that is too small creates a slight hem and a high angle tear in band, resulting in a section that is more or less perpendicular to surface of material.
An ideal scrap should have a reasonable slump angle and a uniform bright band. This keeps punching force to a minimum and creates a clean round hole with minimal burrs. From this point of view, extending life of mold by increasing gap is at the expense of quality of finished hole.

2. Selection of mold gap

Clearance of die is related to type and thickness of material being stamped. Unreasonable clearance can cause following problems:
(1) If gap is too large, burrs of stamped workpiece will be relatively large, and stamping quality will be poor. If gap is too small, although quality of punching is better, wear of mold will be serious, which will greatly reduce service life of mold and easily cause breakage of punch.
(2) If gap is too large or too small, it is easy to cause adhesion on punch material, which will cause material to be carried during stamping. If gap is too small, it is easy to form a vacuum between bottom surface of punch and sheet and cause waste to rebound.
(3) Reasonable clearance can prolong life of mold, unloading effect is good, burr and flanging are reduced, plate is kept clean, hole diameter is consistent, plate will not be scratched, number of sharpening is reduced, plate is kept straight, and punching positioning is accurate.
Please refer to table below to select mold clearance (data in the table are percentages)

Clearance selection (total clearance)
Material	Minimum(%)	Most(%)	Maximum(%)
Copper	8	12	16
Brass	6	11	16
Low-carbon steel	10	15	20
Aluminum (soft)	5	10	15
Stainless steel	15	20	25
%*material thickness = mold gap

3. How to improve service life of mold

For users, improving service life of mold can greatly reduce stamping cost. Factors that affect service life of mold are as follows:
1. Type and thickness of material;
2. Whether to choose a reasonable die clearance;
3. Structural form of mold;
4. Whether there is good lubrication when material is stamped;
5. Whether mold has undergone special surface treatment;
6. Such as titanium plating, titanium carbon nitride;
7. Alignment of upper and lower turrets;
8. Reasonable use of adjusting gaskets;
9. Is it appropriate to use oblique edge molds;
10. Whether mold base of machine tool has been worn out;

4. Problems that should be paid attention to when stamping special size holes

(1) Minimum aperture
Please use a special punch for punching holes in the range of φ0.8——φ1.6.
(2) When punching thick plates, please use a die that is one size larger than processing hole diameter. CAUTION: At this point, if you use a normal size die, it will cause damage to punch thread.
Example 1. Processing conditions in following table, although processing hole diameter corresponds to A-station mold, please use B-station mold.

Material	Plate thickness (mm)	Aperture (mm)
Mild steel (40kg/mm2)	6.0	8.2-12.7
Mild steel (40kg/mm2)	4.5	11.0-12.7
Stainless steel (60kg/mm2)	4.0	8.2-17.7

Example 2. For processing conditions in following table, although processing hole diameter corresponds to B-station mold, please use C-station mold.

Material	Plate thickness (mm)	Aperture (mm)
Mild steel (40kg/mm2)	6.0	22.9-31.7
Mild steel (40kg/mm2)	4.5	30.6-31.7
Stainless steel (60kg/mm2)	4.0	22.9-31.7

(3) For cutting edge of punch, ratio of minimum width to length should generally not be less than 1:10.
Example 3. For a rectangular punch, when cutting edge length is 80mm, the most suitable cutting edge width is ≥8mm.
(4) Relationship between minimum size of punch edge and thickness of plate. It is recommended that minimum dimension of cutting edge of punch is twice thickness of plate.

5. Sharpening of mold

1. Importance of mold sharpening

Regular sharpening of dies is guarantee of consistent punching quality. Regular sharpening of mold can not only improve service life of mold but also service life of machine. It is necessary to master correct sharpening time.

2. Specific characteristics of mold that need to be sharpened

For sharpening of mold, there is no strict number of blows to determine whether sharpening is required. It mainly depends on sharpness of cutting edge. It is mainly determined by following three factors:
(1) Check fillet of cutting edge. If radius of fillet reaches R0.1 mm (maximum R value shall not exceed 0.25 mm), sharpening is required.
(2) Check punching quality, is there any large burr?
(3) Judging whether sharpening is required by noise of machine stamping. If noise is abnormal when stamping with same pair of dies, it means that punch is blunt and needs to be sharpened.
Note: If edge of cutting edge is rounded or back of cutting edge is rough, sharpening should also be considered.

3. Method of sharpening

There are many ways to sharpen mold, which can be realized on a special sharpening machine or on a surface grinder. Sharpening frequency of punch and the lower die is generally 4:1, please adjust height of die after sharpening.
(1) Harm of incorrect sharpening method: Incorrect sharpening will aggravate rapid damage of mold edge, resulting in a greatly reduced number of strikes per sharpening.
(2) Benefits of correct sharpening method: sharpen mold regularly, quality and accuracy of punching can be kept stable. Cutting edge of mold is damaged slower and has a longer life.

4. Sharpening rules

Following factors should be considered when sharpening mold:
(1) Rounded corner of cutting edge depends on sharpness of cutting edge in the case of R0.1-0.25mm.
(2) Surface of grinding wheel should be cleaned.
(3) It is recommended to use a loose, coarse-grained, soft grinding wheel. Such as WA46KV
(4) Amount of grinding (knife cutting) should not exceed 0.013 mm. If amount of grinding is too large, surface of mold will be overheated, which is equivalent to annealing treatment, and mold will become soft, which will greatly reduce life of mold.
(5) Sufficient coolant must be added when sharpening.
(6) When grinding, punch and lower die should be fixed and stable, and special fixtures should be used.
(7) Sharpening amount of mold is certain. If this value is reached, punch will be scrapped. If you continue to use it, it is easy to cause damage to mold and machine, and gain outweighs gain.
(8) After sharpening, edge should be treated with oilstone to remove excessively sharp ridges.
(9) After sharpening, it should be cleaned, demagnetized and oiled.
Note: Sharpening amount of die mainly depends on thickness of plate being stamped.

6. Pay attention before using punch

1. Storage

(1) Wipe inside and outside of upper mold cover with a clean rag.
(2) Be careful not to scratch or dent surface when storing.
(3) Oiling to prevent rust.

2. Preparation before use

(1) Thoroughly clean upper die set before use.
(2) Check whether there are scratches or dents on the surface. If there is, remove it with an oil stone.
(3) Oil inside and outside.

3. Matters needing attention when installing punch on upper die sleeve

(1) Clean punch and oil its long handle.
(2) Insert punch into bottom of upper mold sleeve on large-station mold, and do not use force. Do not use a nylon hammer. When installing, punch cannot be fixed by tightening bolts on upper die sleeve, and bolts can only be tightened after punch is correctly positioned.

4. Install upper mold combination into turret

If you want to extend service life of mold, gap between outer diameter of upper mold sleeve and turret hole should be as small as possible. So please perform following procedure carefully.
(1) Clean keyway and inner diameter of turret bore and oil it.
(2) Adjust keyway of guide sleeve of upper die to match key of turret hole.
(3) Insert upper mold sleeve into tower hole straightly, and be careful not to have any inclination. Upper die guide bush should slide into turret hole by its own weight.
(4) If upper mold sleeve is tilted to one side, it can be gently tapped with a soft material tool such as a nylon hammer. Repeat tapping until upper die guide bush slides into correct position by its own weight.
Note: Do not use force on outer diameter of guide sleeve of upper die, but only on the top of punch. Do not knock on the top of upper mold sleeve, so as not to damage turret hole and shorten service life of individual stations.

7. Mold maintenance

If punch is bitten by material and cannot be taken out, please check according to following items.
1. Re-sharpening of punches and dies. A mold with a sharp edge can produce a beautiful cut surface, but a blunt edge requires additional punching force, and rough cross section of workpiece produces a great resistance, causing punch to be bitten by material.
2. Gap of mold. If gap of mold is not selected relative to thickness of plate, punch needs a lot of demoulding force when it is separated from material. If punch is bitten by material for this reason, please replace lower die with a reasonable clearance.
3. State of processed material. When material is dirty or has dirt, dirt adheres to mold, causing punch to be bitten by material and cannot be processed.
4. Materials with deformation. Warped material clamps punch after hole is punched, causing punch to bite. For warped materials, please flatten them before processing.
5. Excessive use of springs. Will make spring fatigue. Please always pay attention to check performance of spring.

8. Oiling

Amount of oil and number of oil injections depend on conditions of material to be processed. For rust-free and dirt-free materials such as cold-rolled steel sheets and corrosion-resistant steel sheets, mold should be filled with oil. Oil injection points are guide sleeve, oil injection port, contact surface between cutter body and guide sleeve, and lower mold. Oil with light machine oil.
For materials with rust and dirt, rust fine powder will be sucked between punch and guide sleeve during processing, resulting in dirt, which prevents punch from sliding freely in guide sleeve. In this case, if oil is applied, it will make rust easier It is stained, so when punching this material, on the contrary, wipe off oil, decompose it once a month, use gasoline (diesel) oil to remove dirt on punch and lower mold, and wipe it clean before reassembling. This will ensure that mold has good lubrication performance.

9. Problems and solutions that often occur during use of molds

Problem 1. Plate comes out of jaws

Reason	Solution
Incomplete unloading of mold	Using a sloped punch Apply lubricating fluid to the board Heavy Duty Mold

Problem 2. Mold wears seriously

Reason	Solution
Unreasonable mold clearance (too small)	Increase die clearance
Misalignment of upper and lower mold bases	Station adjustment, centering of upper and lower molds Turret level adjustment
Failure to replace worn mold guide components and turret inserts in time	Replace
Punch overheating	Add lubricating fluid to sheet Ensure lubrication between punch and die Use multiple sets of molds of same specification and size in same program
Improper sharpening method, resulting in annealing of mold, resulting in increased wear	Using soft abrasive grinding wheel Clean the grinding wheel frequently Small bite size Adequate coolant
Nibbling	Increase step Bridge nibbling

Question 3. Punch with material and punch sticking

Reason	Solution
Unreasonable mold clearance (too small)	Increase die clearance
Punch edge passivation	Timely sharpening
Poor lubrication	Improve lubrication conditions

Question 4. Scrap rebound

Reason	Solution
Die problem	Bulletproof lower die 10% reduction in hole clearance for small diameter holes Diameter is greater than 50mm, and gap is enlarged Increased scratches on cutting edge side of die
Punch	Increase depth of mold Install unloading polyurethane top bar Beveled edge

Problem 5. Difficulty in unloading

Reason	Solution
Unreasonable mold clearance (too small)	Increase die clearance
Punch wear	Timely sharpening
Spring fatigue	Replace spring
Punch sticking	Remove adhesions

Question 6. Stamping noise

Reason	Solution
Difficulty unloading	Increase die clearance Increase unloading force Stripper plate with soft surface
There is a problem with support of sheet on workbench and in turret	Using spherical support mold Reduce working size Increase working thickness
Sheet is too thick	Use oblique edge punch

10. Precautions for using special forming tools

1. Strokes of sliders of different types of machines are different, so attention should be paid to adjustment of closed height of forming mold.
2. It is necessary to ensure that molding is sufficient, so it needs to be adjusted carefully. Adjustment amount should not exceed 0.15mm each time. If adjustment amount is too large, it is easy to cause damage to machine and mold.
3. For stretch forming, please use light spring components to prevent tearing of sheet, or difficulty in unloading due to uneven deformation.
4. Install a spherical support mold around forming mold to prevent sheet from tilting.
5. Forming position should be as far away from clamp as possible.
6. Molding is best done at the end of processing program.
7. Be sure to ensure that plate is well lubricated.
8. When ordering, pay attention to problem of giving way to special forming tools. If distance between two forming tools is relatively close, please communicate with salesperson of our company.
9. Because forming tool needs a long unloading time, it is necessary to use a low speed during forming process, and it is best to have a delay.

11. Precautions for using a rectangular cutting knife

1. Step distance should be as large as possible, which should be greater than 80% of the entire tool length.
2. It is best to realize jumping nibbling through programming.
3. It is recommended to use a beveled edge mold.

12. How to punch holes without exceeding nominal force of machine

During production process, it is necessary to punch a round hole with a diameter larger than 114.3mm. Such a large hole would exceed nominal force limit of machine, especially for high shear strength materials. This problem can be solved by punching large-sized holes by multiple punching methods. Cutting punch force in half or more with a smaller tool size cut along a larger circumference can probably be done with most of tools you already have.

13. A simple method for punching large round holes

Mold of this convex lens can be made into radius size you need. If hole diameter exceeds nominal force of punch, we recommend using (A) scheme. Use this die to punch out perimeter of circle. If hole diameter can be punched within nominal force range of punch, then a radial mold and a convex lens mold can punch out required hole in four times without rotating mold (B)

14. Finally, it takes shape downwards

When selecting forming dies, downward forming operations should be avoided as this would take up too much vertical space and result in additional flattening or bending of sheet. Down forming can also sink into lower die and be pulled out of turret, however, if down forming is the only process option, then it should be done as final processing step on the sheet.

15. Prevent material distortion

If you need to punch a lot of holes in sheet and sheet doesn't stay flat, buildup of punching stress could be cause. When punching a hole, material around hole is stretched downward, which increases tensile stress on upper surface of sheet. Downstroke movement also leads to an increase in compressive stress on the lower surface of sheet. For a small number of punched holes, result is not obvious, but as number of punched holes increases, tensile and compressive stresses also multiply until plate is deformed.
One way to eliminate this distortion is to die cut every other hole, then go back and die remaining holes. This creates same stress on the sheet, but breaks down tensile/compressive stress build-up that would result from punching one after the other in the same direction. This also makes the first batch of holes share partial deformation effect of second batch of holes.

16. If your stainless steel flanging is deformed

Applying a high-quality forming lubricant to material before flange is made will allow material to separate from mold better and move smoothly across die surface during forming. This gives material a better opportunity to distribute stresses of being bent and stretched, preventing deformation on the sides of formed flange hole and wear on the bottom of flange hole.

17. Some suggestions for overcoming difficulty of unloading

1. Use a punch with a fine core rubber particle.
2. Increase clearance of lower die.
3. Check fatigue of spring.
4. Use heavy-duty molds.
5. Appropriately use oblique edge molds.
6. Lubricate plate.
7. Large-station molds need to be installed with polyurethane unloading head.

18. Main reason for rebound of waste

1. Sharpness of cutting edge. The larger fillet of cutting edge, the easier it is to cause scrap to bounce.
2. Modulus of mold. When stamping mold at each station, requirement for modulus of entry is certain, and modulus of entry is small, which is easy to cause waste to rebound.
3. Whether clearance of mold is reasonable. Unreasonable mold clearance can easily cause waste to rebound.
4. Whether there is oil on the surface of processed plate.

Gud Mould Industry Co., Ltd