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·In cold stamping processing, the material (metal or non-metal) is processed into parts (or semi-finished products). Stamping is a pressure processing method in which the material is applied at room temperature using a mold mounted on a press to cause separation or plastic deformation to obtain the required parts. The mold mounted on the press is assembled with mold accessories such as punch needles and then directly contacts the material (metal or non-metal), causing the material to separate or plastically deform, thereby obtaining the required parts. Stamping molds are indispensable process equipment for stamping production and are technology-intensive products. The quality, production efficiency and production cost of stamping parts are directly related to the mold design and the precision and quality of mold accessories. Below, the editor of Xianji.com will introduce to you the relevant knowledge of stamping molds, including: stamping mold structure, classification, types and characteristics, and design and production skills.
Stamping mold structure
The structure of hardware stamping molds can generally be divided into upper die and lower die. The upper die is composed of a mold handle (punch handle), a guide sleeve, a punch, a pad, a fixing plate, a screw, a pin, a mold base (upper support), and a material release plate. The lower mold is generally composed of a lower mold seat, a guide plate (side guide plate), a concave mold, a stop plate, a material bearing plate, a guide column, a screw, and a pin.
1. On top is an ordinary blanking mold, the product is a rectangle with three small round holes in the middle;
2. The punching composite punch is a rectangular body, which means to cut the material and remove the appearance of the product from the material. The surroundings of the cutting punch composite punch are also cutters, which are equivalent to the punch, so the surroundings cannot be chamfered. There are three small round holes in the middle of the cutting punch composite punch, which belongs to the cutting punch, which means that the three round holes in the middle of the product are punched out.
3. There is a square hole in the middle of the concave template, which belongs to the knife edge. The punching composite mould of the following material is a punch to punch out the product shape; the corresponding inner disassembly on the punching composite mould of the downcoming material is also called an inner disassembly plate or an inner disassembly plate. The figure is marked as "unloading block", which is actually the same. The function of the unloading block is to push the product out of the concave template; the unloading block also has another function, which is to press the material, press the material and then punch the three small round holes in the middle.
4. The "top-type punch" marked in the figure is actually a punch. It is combined with the three circular cutters on the cut-out punch composite punch to punch out the three small round holes in the intermediate product.
5. The function of the "fixed key" on the lower mold lower pad is to fix the cut-out punch composite punch to prevent it from jumping out of the mold as the mold rises, resulting in an accident.
6. The "unloading plate" marked on the lower die is commonly known as out-of-discharge. Its function is to remove the washed waste from the cut-out punch composite punch to prevent the waste from getting stuck on the cut-out punch composite punch.
Stamping mold classification
There are many forms of stamping molds, and the punch is classified according to three aspects: working nature, mold structure, and mold material.
1. Classification according to the nature of the process
1. Cutting die
A mold that causes the material to produce a separate mold along a closed or open contour line. Such as blanking die, punching die, cutting die, cutting die, edge die, cutting die, etc.
2. Bending die
Make the sheet blank or other blank bends bend along a straight line (bending line), thereby obtaining a mold for workpieces of a certain angle and shape.
3. Deep drawing mold
It is a mold that makes the sheet blank into an open hollow piece, or further changes the shape and size of the hollow piece.
4. Forming die
It is a mold that directly replicates the blank or semi-finished workpiece according to the shape of the convex and concave molds, while the material itself only produces local plastic deformation. Such as expansion die, shrink die, flaring die, undulating forming die, flange die, shaping die, etc.
5. Riveting mold
It is to borrow external forces to connect or overlap the parts in a certain order and manner to form a whole.
2. Classification according to the degree of process combination
1. Single process mold
A mold that only completes one stamping process in one stroke of the press.
2. Composite mold
There is only one station, and in one stroke of the press, two or more stamping processes are completed at the same station at the same time.
3. Progressive die (also called continuous die)
In the feeding direction of the blank, there are two or more work stations. In one stroke of the press, two or more stamping processes are completed successively at different work stations.
4. Transfer mode
It combines the characteristics of single-process molds and progressive molds, and uses a robot transfer system to realize rapid transfer of products within the mold, which can greatly improve product production efficiency, reduce product production costs, save material costs, and ensure stable and reliable quality.
3. Classification according to processing methods of products
According to different product processing methods, molds can be divided into five categories: punching and shearing molds, bending molds, drawing molds, forming molds and compression molds.
1. Punching and shearing mold:
The work is completed by shearing. Commonly used forms include shearing dies, blanking dies, punching dies, trimming dies, edge forming dies, drawing punches and punching dies.
2. Bending mold:
It bends a flat blank into an angled shape. Depending on the shape, accuracy and production volume of the part, there are many different types of molds, such as ordinary bending dies, cam bending dies, curling dies, arc bending dies, bending punching dies and twisting dies, etc.
3. Draw the mold:
The drawing mold is to make a flat blank into a bottomed seamless container.
4. Forming mold:
It refers to the use of various local deformation methods to change the shape of the blank. Its forms include convex forming dies, curling forming dies, necking forming dies, hole flange forming dies, and round edge forming dies.
5. Compression mold:
It uses strong pressure to flow and deform the metal blank into the required shape. Its types include extrusion dies, embossing dies, imprinting dies, and end-pressure dies.
Types and characteristics of stamping die materials
1. Carbon tool steel
The most commonly used carbon tool steels in molds are T8A, T10A, etc., which have the advantages of good processing performance and low price. However, the hardenability and red hardness are poor, the heat treatment deformation is large, and the load-bearing capacity is low.
2. Low alloy tool steel
Low alloy tool steel is based on carbon tool steel with an appropriate amount of alloying elements added. Compared with carbon tool steel, it reduces the tendency of quenching deformation and cracking, improves the hardenability of steel, and has better wear resistance. Low alloy steels used to make molds include CrWMn, 9Mn2V, 7CrSiMnMoV (code CH-1), 6CrNiSiMnMoV (code GD), etc.
3. High carbon and high chromium tool steel
Commonly used high carbon and high chromium tool steels include Cr12, Cr12MoV, and Cr12Mo1V1 (code D2). They have good hardenability, hardenability and wear resistance. The heat treatment deformation is very small. They are high wear-resistant micro-deformation mold steels, and their load-bearing capacity is second only to high-speed steel. However, the segregation of carbides is serious, and repeated upsetting (axial upsetting, radial pulling) and forging must be carried out to reduce the unevenness of carbides and improve performance.
4. High carbon medium chromium tool steel
High-carbon medium-chromium tool steels used for molds include Cr4W2MoV, Cr6WV, Cr5MoV, etc. They have low chromium content, few eutectic carbides, uniform carbide distribution, small heat treatment deformation, and good hardenability and dimensional stability. Compared with high carbon high chromium steel where carbide segregation is relatively serious, the performance is improved.
5. High speed steel
High-speed steel has the highest hardness, wear resistance and compressive strength among mold steels, and has a high load-bearing capacity. Commonly used in molds are W18Cr4V (code 8-4-1) and W6Mo5 Cr4V2 (code 6-5-4-2, US brand name M2) with less tungsten content, as well as the carbon-reduced and vanadium-reduced high-speed steel 6W6Mo5 Cr4V (code 6W6 or low carbon M2) developed to improve toughness. High-speed steel also needs to be modified to improve its carbide distribution.
6. Base steel
A small amount of other elements are added to the basic components of high-speed steel, and the carbon content is appropriately increased or decreased to improve the properties of the steel. Such steel types are collectively called matrix steel. They not only have the characteristics of high-speed steel, with certain wear resistance and hardness, but also have better fatigue strength and toughness than high-speed steel. They are high-strength and tough cold-work die steels, but the material cost is lower than high-speed steel. Commonly used base steels in molds include 6Cr4W3Mo2VNb (code 65Nb), 7Cr7Mo2V2Si (code LD), 5Cr4Mo3SiMnVAL (code 012AL), etc.
7. Carbide and steel-bonded carbide
Carbide has higher hardness and wear resistance than any other type of mold steel, but has poor flexural strength and toughness. The cemented carbide used for molds is tungsten-cobalt. For molds with low impact and high wear resistance requirements, cemented carbide with lower cobalt content can be used. For molds with high impact, cemented carbide with higher cobalt content can be used.
Stamping mold design and production skills
1. Information from the waste situation
Scrap is essentially the inverse image of the formed hole. That is, the same parts in opposite positions. By checking the scrap, you can determine whether the gap between the upper and lower molds is correct. If the gap is too large, the scrap will have a rough, undulating fracture surface and a narrow bright band area. The larger the gap, the larger the angle between the fracture surface and the bright zone area. If the gap is too small, the scrap will exhibit a small angle fracture surface and a wide bright band area.
Excessive gaps create holes with large curls and edge tears, leaving the profile with a thin edge sticking out slightly. Gaps that are too small create a band that curls slightly and tears at high angles, causing the profile to be more or less perpendicular to the material surface.
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 the mold life by increasing the gap is at the expense of the quality of the finished hole.
2. Selection of mold gap
The clearance of the mold is related to the type and thickness of the material being stamped. Unreasonable gaps can cause the following problems:
1. If the gap is too large, the burrs of the stamped workpiece will be relatively large and the stamping quality will be poor. If the gap is too small, although the punching quality is better, the wear of the mold will be serious, which will greatly reduce the service life of the mold and easily cause the punch to break.
2. If the gap is too large or too small, it is easy to cause adhesion on the punch material, resulting in material stripping during stamping. If the gap is too small, a vacuum will easily form between the bottom of the punch and the sheet material, resulting in scrap rebound.
3. A reasonable gap can extend the life of the mold, have good unloading effect, reduce burrs and flanges, keep the plate clean, have consistent hole diameters without scratching the plate, reduce the number of sharpening times, keep the plate straight, and position the punching holes accurately.
3. How to improve the service life of the mold
For users, increasing the service life of the mold can greatly reduce stamping costs. The factors that affect the service life of the mold are as follows:
1. Material type and thickness;
2. Whether to choose a reasonable lower die gap;
3. The structural form of the mold;
4. Whether the material is well lubricated during stamping;
5. Whether the mold has undergone special surface treatment;
6. Such as titanium plating, carbon titanium nitride;
7. Centering of the upper and lower turrets;
8. Adjust the reasonable use of gaskets;
9. Whether the inclined edge mold is appropriately used;
10. Whether the machine tool mold base has been worn;
4. Issues that should be paid attention to when punching holes of special sizes
1. For punching holes with a minimum hole diameter of φ0.8-φ1.6, please use a special punch.
2. When punching thick plates, please use a mold that is one size larger than the hole diameter. Note: At this time, if a normal size mold is used, the punch thread will be damaged.
3. The ratio of the minimum width to length of the punch cutting edge should generally not be less than 1:10.
4. The relationship between the minimum size of the punch cutting edge and the plate thickness. It is recommended that the minimum size of the punch cutting edge be 2 times the plate thickness.
5. Mold sharpening
1. The importance of mold sharpening
Regular sharpening of the mold ensures the consistency of punching quality. Regular sharpening of the mold can not only increase the service life of the mold but also the service life of the machine. The correct sharpening timing must be mastered.
2. Specific characteristics of molds that require sharpening
For mold sharpening, there is no strict number of blows to determine whether sharpening is required. Mainly depends on the sharpness of the cutting edge. It is mainly determined by the following three factors:
① Check the fillet of the cutting edge. If the fillet radius reaches R0.1 mm (the maximum R value shall not exceed 0.25 mm), it needs to be sharpened.
② Check the punching quality. Are there any large burrs?
③Judge whether sharpening is needed by the noise of machine stamping. If the noise is abnormal when the same die is stamped, it means that the punch is blunt and needs to be sharpened.
Note: If the edge of the cutting edge becomes rounded or the back of the cutting edge is rough, sharpening should also be considered.
3. Sharpening method
There are many methods for sharpening molds, which can be achieved by using a special sharpening machine or on a surface grinder. The frequency of punch and lower die sharpening is generally 4:1. Please adjust the height of the die after sharpening.
① The harm of incorrect sharpening methods: Incorrect sharpening will aggravate the rapid damage of the mold edge, resulting in a greatly reduced number of blows for each sharpening.
②Benefits of correct sharpening method: By sharpening the mold regularly, the quality and accuracy of punching can remain stable. The cutting edge of the mold is damaged more slowly and has a longer life.
4. Sharpening rules
The following factors should be considered when sharpening molds:
① When the edge radius is R0.1-0.25 mm, it depends on the sharpness of the edge.
②The surface of the grinding wheel must be cleaned.
③It is recommended to use a loose, coarse-grained and soft grinding wheel. Such as WA46KV
④The grinding amount (cutting amount) each time should not exceed 0.013 mm. Excessive grinding amount will cause the mold surface to overheat, which is equivalent to annealing treatment, the mold will become soft, and the life of the mold will be greatly reduced.
⑤Sufficient coolant must be added when sharpening.
⑥When grinding, ensure that the punch and lower die are fixed stably, and use special tooling fixtures.
⑦The sharpening amount of the mold is certain. If it reaches this value, the punch will be scrapped. If you continue to use it, it will easily cause damage to the mold and machine, and the gain will outweigh the loss.
⑧After sharpening, the edge should be treated with a whetstone to remove excessively sharp edges.
⑨After sharpening, clean, demagnetize and oil it.
Note: The amount of mold sharpening mainly depends on the thickness of the plate being stamped.
6. Pay attention before using the punch
1. Storage
① Use a clean rag to clean the inside and outside of the upper mold cover.
②Be careful not to have scratches or dents on the surface when storing.
③Oil to prevent rust.
2. Preparation before use
① Thoroughly clean the upper mold cover before use.
② Check whether there are scratches or dents on the surface. If there is, use a whetstone to remove it.
③ Oil the inside and outside.
3. Things to note when installing the punch on the upper die sleeve
①Clean the punch and oil its long handle.
② Insert the punch into the bottom of the upper die sleeve on the large station mold without using force. Do not use nylon hammer. During installation, the punch cannot be fixed by tightening the bolts on the upper die sleeve. The bolts can only be tightened after the punch is correctly positioned.
4. Install the upper mold into the turret
If you want to extend the service life of the mold, the gap between the outer diameter of the upper mold sleeve and the turret hole should be as small as possible. So please perform the following procedures carefully.
①Clean and oil the keyway and inner diameter of the turret hole.
②Adjust the keyway of the upper mold guide bush so that it matches the key of the turret hole.
③Insert the upper mold sleeve straightly into the tower hole, being careful not to have any inclination. The upper die guide bushing should slide into the turret hole by its own weight.
④ If the upper mold sleeve tilts to one side, you can use a soft material tool such as a nylon hammer to gently knock it straight and repeatedly until the upper mold guide sleeve slides into the correct position by its own weight.
Note: Do not apply force on the outer diameter of the upper mold guide sleeve, only on the top of the punch head. Do not knock the top of the upper mold sleeve to avoid damaging the turret hole and shortening the service life of individual stations.
7. Mold maintenance
If the punch is bitten by the material and cannot be removed, please check the following items.
1. Re-sharpening of punch and lower die. A mold with a sharp edge can produce a beautiful cut surface. A blunt edge requires additional punching force, and the workpiece has a rough cross-section, which creates a lot of resistance and causes the punch to be bitten by the material.
2. Mold clearance. If the gap of the mold is not selected appropriately relative to the plate thickness, the punch will require a large demoulding force when breaking away from the material. If the punch is bitten by the material for this reason, please replace the lower die with a reasonable clearance. Zhengquan Technology’s WeChat content is really good and worth paying attention to!!
3. The state of the processed materials. When the material is dirty or has dirt, the dirt adheres to the mold, causing the punch to be bitten by the material and unable to be processed.
4. Materials with deformation. The warped material will clamp the punch after punching the hole, causing the punch to bite. For warped materials, please smooth them before processing.
5. Excessive use of springs. Will cause spring fatigue. Please always check the performance of the spring.
8. Oil injection
The amount of oil and the number of oil injections depend on the conditions of the material being processed. For rust-free and dirt-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 bushing, the oil filling port, the contact surface between the cutter body and the guide bushing, the lower mold, etc. Use light engine oil.
For materials with rust and dirt, the rust powder will be sucked into the space between the punch and the guide bush during processing, resulting in dirt, which will prevent the punch from sliding freely in the guide bush. In this case, if oil is applied, the rust will be more likely to stick. Therefore, when punching this kind of material, the oil should be wiped clean, and it should be broken down once a month. Use gasoline (diesel) oil to remove the dirt on the punch and the lower die, and wipe them clean before reassembly. This ensures that the mold has good lubrication properties.
9. Common problems and solutions during the use of molds
Problem 1: The plate comes out of the clamping jaws
Reason: Incomplete mold unloading
Solution:
1. Use a sloped punch
2. Apply lubricant to the plate
3. Use heavy-duty molds
Problem 2: Severe mold wear
Reason: Unreasonable mold gap (too small)
Solution: Increase mold clearance
Reason: The upper and lower mold bases are not aligned
Solution:
1. Work position adjustment, upper and lower die alignment
2. Turret level adjustment
Reason: Failure to replace worn mold guide components and turret inserts in time
Solution: Replace
Reason: The punch is overheated
Solution:
1. Add lubricant to the sheet
2. Ensure lubrication between the punch and the lower die
3. Use multiple sets of molds with the same specifications and sizes in the same program
Reason: Improper sharpening method causes annealing of the mold, resulting in increased wear.
Solution:
1. Use soft abrasive grinding wheel
2. Clean the grinding wheel frequently
3. Small amount of knife consumption
4. Sufficient amount of coolant
Reason: small step distance
Solution:
1. Increase the step distance
2. Use bridge type stepping
Problem 3: Punch tape and punch adhesion
Reason: Unreasonable mold gap (too small)
Solution: Increase mold clearance
Reason: Blunt edge of punch
Solution: Sharpen in time
Reason: poor lubrication
Solution: Improve lubrication conditions
Problem 4. Scrap rebound
Reason: lower mold problem
Solution:
1. Use bulletproof material lower mold
2. For small diameter holes, the clearance is reduced by 10%
3. If the diameter is greater than 50.00 mm, the gap will be enlarged
4. Increased scratches on the cutting edge side of the die
Reason: punch aspect
Solution:
1. Increase the depth of mold insertion
2. Install the unloading polyurethane top rod
3. Adopt oblique cutting edge
Problem 5. Difficulty in unloading
Reason: Unreasonable mold gap (too small)
Solution: Increase mold clearance
Reason: Punch wear
Solution: Sharpen in time
Reason: spring fatigue
Solution: Replace the spring
Reason: Punch adhesion
Solution: Remove adhesions
Problem 6. Stamping noise
Reason: Difficulty in unloading
Solution:
1. Increase the lower die clearance and good lubrication
2. Increase the unloading force
3. Use a soft surface unloading plate
Reason: There is a problem with the support of the sheet on the workbench and in the turret
Solution:
1. Use spherical support mold
2. Reduce work size
3. Increase working thickness
4. Thick sheet
5. Use inclined edge punch
10. Precautions when using special molding tools
1. Different models of machine sliders have different strokes, so attention should be paid to the adjustment of the closing height of the mold.
2. It is necessary to ensure that the molding is sufficient, so it needs to be adjusted carefully. It is best not to exceed 0.15 mm each time. If the adjustment amount is too large, it will easily cause damage to the machine and the mold.
3. For stretch molding, please use lightweight spring components to prevent tearing of the sheet or difficulty in unloading due to uneven deformation.
4. Install a spherical support mold around the forming mold to prevent the sheet from tilting.
5. The molding position should be as far away from the clamp as possible.
6. Forming processing is best done at the end of the processing program.
7. Be sure to ensure good lubrication of the plate.
8. When ordering, pay attention to the issue of giving way to special molding tools. If the distance between the two molding tools is relatively close, please be sure to communicate with our salesperson.
9. Because the forming tool requires a long unloading time, low speed must be used during forming processing, and it is best to have a delay.
11. Precautions when using rectangular cutting knife
1. The step distance should be as large as possible, greater than 80% of the entire tool length.
2. It is best to implement jump stepping through programming.
3. It is recommended to use a beveled edge mold.
12. How to punch holes without exceeding the nominal force of the machine
During the production process, round holes larger than 114.3mm in diameter need to be punched. Such a large hole would exceed the nominal capacity limit of the machine, especially for high shear strength materials. This problem can be solved by punching large holes multiple times. Using a smaller die to cut along a large circle circumference can reduce the punching force by half or more, which is probably possible with most of the tools you already own.
13. A simple method for punching large round holes
The mold for this convex lens can be made to your desired radius size. If the hole diameter exceeds the nominal force of the punch, we recommend using option (A). Use this die to punch out the perimeter of the circle. If the hole diameter can be punched within the nominal force range of the punch, then a radial mold and a convex lens mold can punch the required holes in four times without rotating the mold (B)
14. Finally, it is formed downward.
When selecting a forming tool, down-forming operations should be avoided because they take up too much vertical space and require additional flattening or bending of the sheet. Downforming may also become trapped in the die and then pulled out of the turret; however, if downforming is the only process option, it should be used as the last step in processing the sheet.
15. Prevent material distortion
If you need to punch a large number of holes in a sheet and the sheet doesn't stay flat, the cause may be a build-up of stamping stress. When punching a hole, the material around the hole is stretched downward, which increases the tensile stress on the upper surface of the plate. The punching movement also causes the compressive stress on the lower surface of the plate to increase. For punching a small number of holes, the results are not obvious, but as the number of punched holes increases, the tensile stress and compressive stress also increase exponentially until the plate is deformed.
One way to eliminate this distortion is to punch every other hole and then go back and punch the remaining holes. This creates the same stresses in the sheet, but breaks up the tensile/compressive stress buildup caused by consecutive punching cuts one after the other in the same direction. This also allows the first batch of holes to share the partial deformation effect of the second batch of holes.
16. If your stainless steel flanging is deformed
Applying a high-quality forming lubricant to the material before making the flange will allow the material to better separate from the mold and move smoothly across the lower mold surface during forming. This gives the material a better chance to distribute the stress generated when it is bent and stretched, preventing deformation on the edge of the formed flange hole and wear at the bottom of the flange hole.
17. Some suggestions for overcoming unloading difficulties
1. Use a punch with fine core rubber particles;
2. Increase the gap between the lower mold;
3. Check the fatigue degree of the spring;
4. Use heavy-duty molds;
5. Appropriately use inclined edge molds;
6. Lubricate the plate;
7. Large-station molds need to install polyurethane discharge heads.
18. Main reasons for scrap rebound
1. The sharpness of the cutting edge: the larger the rounded corner of the cutting edge, the easier it is to cause the scrap to rebound;
2. The mold input amount of the mold: When stamping the mold at each station, the mold input amount is required to be certain. If the mold input amount is small, it is easy to cause the waste material to rebound;
3. Is the mold gap reasonable? Unreasonable mold gaps can easily cause waste materials to rebound;
4. Whether there is oil stain on the surface of the processed plate.
The above is the stamping die structure, classification, material types and characteristics, and design and production techniques introduced by the editor of Xianji.com. Stamping molds are the mother of industry. Most of today's products are produced with stamping molds. Only the high efficiency of stamping molds can achieve mass production, improve efficiency and reduce costs. In the current era of rapid development of China's industrialization process, the stamping mold industry is still a sunrise industry and an industry full of opportunities! Stamping molds are one of the most important cornerstones in the industrial field and play a vital role in the manufacturing industry. Even highly industrialized developed countries are inseparable from the development of molds. For example, in the United States and Japan, the mold industry still occupies an important position in the total industrial output value. The threshold for competition in the stamping mold industry is not high, and there are more than 30,000 mold manufacturing companies across the country. Obviously, the imbalance between supply and demand is one of the main problems in the development of the mold industry. In addition to internal competition, mold companies in developed countries have accelerated their overseas expansion, further intensifying competition.
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