The hardened mold can be sharpened in the usual manner. Surface hardening will reduce the wear of the mold when punching stainless steel plates, but it will not extend its service life. Proper lubrication, timely sharpening, and operation in accordance with regulations are effective methods.
At present, in the field of sheet metal stamping machininging, CNC turret punch presses are widely used due to their high punching speed, high machininging accuracy, strong mold versatility, and product flexibility. The die used in the CNC turret punching machine has high stamping speed due to its high precision and quality requirements. After the user selects a certain quality mold, the level of its use and maintenance directly affects the machininging quality of the workpiece and the service life of the mold. Mould is also an important link to control equipment operation costs. Therefore, learning and mastering some of this knowledge and applying it to practice will also play an important role in improving efficiency and reducing costs.
The following discusses some technical points that should be followed in the use and maintenance of CNC turret punch molds, and proposes corresponding solutions to actual problems, which may have a good guiding role for users.
1.Ensure the best mold clearance
The die clearance refers to the sum of the clearances on both sides of the punch entering the lower die. It is related to plate thickness, material and stamping machining. Selecting appropriate die clearance can ensure good punching quality, reduce burrs and subsidence, keep the plate flat, effectively prevent strip material, and extend the life of the mold.
By checking the condition of the stamping waste, you can determine whether the die clearance is appropriate. If the gap is too large, the waste material will have rough undulated fracture surfaces and smaller shiny surfaces. The larger the gap, the greater the angle formed by the fractured surface and the shiny surface. When punching, crimps and fractures will form, and even a thin-edge protrusion will appear. Conversely, if the gap is too small, the scrap material will have a small angle fracture surface and a large shiny surface.
When performing partial punching such as grooving, nibbling, and shearing, the lateral force will deflect the punch and cause the gap on one side to be too small. Sometimes the edge shift will cause the lower die to scratch and cause rapid wear on the upper and lower die.
When the die is punched with the best clearance, the fracture surface and the bright side of the waste material have the same angle and overlap with each other. This can minimize the punching force and the burr of the punching hole is very small.
2. Timely grinding can effectively extend the service life of the mold
If the workpiece has excessive burrs or abnormal noise during punching, the mold may be passivated. Check the punch and the lower die. When the cutting edge wears and produces an arc with a radius of about 0.10mm, it will be sharpened.
Practice has shown that often grinding a small amount of sharpening instead of waiting until it becomes impossible will not only maintain good workpiece quality, reduce punching force, but also extend the life of the mold more than doubled.
In addition to knowing when the tool is sharpened, it is especially important to master the correct sharpening method. The mold sharpening procedure is as follows:
1) When sharpening, hold the punch vertically in the V-groove or fixture of the magnetic chuck of the surface grinder, each grinding amount is 0.03 ~ 0.05mm, repeat grinding until the punch is sharp, the maximum grinding amount Generally 0.1 ~ 0.3mm.
2) Use sintered alumina grinding wheel with hardness D ~ J and abrasive grain size 46 ~ 60. It is best to choose a grinding wheel suitable for high-speed steel grinding.
3) When the grinding force is large or the mold is close to the grinding wheel, adding coolant can prevent the mold from overheating and cracking or annealing. You should choose a high-quality multipurpose coolant according to the manufacturer’s requirements.
4) The grinding wheel feeds 0.03 ~ 0.08mm downward, the lateral feed is 0.13 ~ 0.25mm, and the lateral feed rate is 2.5 ~ 3.8m / min.
5) After sharpening, grind the cutting edge with a whetstone to remove burrs, and grind a fillet with a radius of 0.03 ~ 0.05mm, which can prevent the cutting edge from cracking.
6) Demagnetize and spray lubricant to prevent rust.
3.Methods to eliminate and reduce sticky materials
Due to the pressure and heat during punching, the fine particles of the sheet will adhere to the surface of the punch, resulting in poor punching quality. The sticky material can be removed by grinding with fine oil stone, and the grinding direction should be the same as the direction of the punch movement, so that no further sticky material will be generated after light. Do not use coarse gauze cloth, etc., so as to avoid the rougher surface of the punch and sticky material.
Reasonable die clearance, good stamping machining, and necessary sheet lubrication will reduce the generation of sticky materials. To prevent overheating, lubrication is generally used, which will reduce friction. If you cannot lubricate or rebound the waste, you can take the following methods:
Alternate use of multiple punches of the same size in turn, which allows longer cooling time before being reused.
Stop using the overheated mold. Programmatically control the die change, interrupt its long repetitive work, or reduce its punching frequency.
4.Measures to prevent sheet deformation when punching a lot of holes
If many holes are punched in one plate, the plate cannot be kept flat due to the accumulation of punching stress. Each time the hole is punched, the material around the hole will be deformed downward, causing tensile stress on the upper surface of the sheet and compressive stress on the lower surface. For a small number of punching holes, the effect is not obvious, but as the number of punching holes increases, tensile and compressive stress accumulates somewhere until the material deforms.
One way to eliminate this kind of deformation is to die cut every other hole and then return to the remaining holes. Although stress may be generated in this way, the stress accumulation during sequential punching in the same direction will be relieved, and the stresses of the two sets of holes in the front and back will cancel each other, thereby preventing the deformation of the sheet.
5.Try to avoid punching through narrow strips
When the die is used to punch a sheet with a width smaller than the thickness of the sheet, the punch will be deformed due to the lateral force, the gap on one side will be too small or the wear will be aggravated, and the lower die will be scratched when it is severe, making the upper and lower die Also damaged.
It is not recommended to nibble narrow strips with a width less than 2.5 times the sheet thickness. When cutting through narrow strips, the sheet tends to bend into the opening of the lower die, instead of being completely cut off, and even wedging into the side of the die. If the above situation cannot be avoided, it is recommended to use a fully guided die with a backing plate to support the punch. Six, the surface hardening of the punch and its scope of application
Although heat treatment and surface coating can improve punch surface characteristics, it is not a general method to solve stamping problems and prolong die life. Generally speaking, the coating improves the hardness of the punch surface and improves the lubricity of the sides, but these advantages disappear after about 1,000 punches when stamping large tonnage, hard materials.
6.Surface hardened punches can be used for the following situations:
Soft or sticky materials (such as aluminum);
Thin abrasive materials (such as glass epoxy sheet);
Thin hard materials (such as stainless steel);
Frequent nibbling
In case of abnormal lubrication.
Surface hardening usually uses titanium plating, nitriding, and other methods. Its surface hardened layer has a molecular structure with a thickness of 12 to 60 μm. It is a part of the punch base, not just a coating.
The hardened mold can be sharpened in the usual manner. Surface hardening will reduce the wear of the mold when punching stainless steel plates, but it will not extend its service life. Proper lubrication, timely sharpening, and operation in accordance with regulations are effective methods.
7.Maintenance of the punch die position is not good for neutrality
If the alignment of the punch die position is not good, resulting in rapid passivation of the die and poor workpiece machininging quality, the following points can be repaired:
Check the level of the machine tool and readjust if necessary;
Check and lubricate the die holes and guide keys on the turntable, and repair them if there is any damage;
Clean the lower mold base of the turntable so that the lower mold can be accurately installed, and check the wear of the keys or key grooves, and replace if necessary;
Use a special mandrel to calibrate the mold station, and adjust if there is any deviation.
The above contents are for normal situations. In view of the fact that the specific types and specifications of punches and dies are different, users must also understand and summarize their experience in accordance with the actual situation to give full play to the best performance of the dies.
