Use and maintenance of CNC turret punching die
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At present, in the field of sheet metal stamping processing, CNC turret punch presses are widely used due to their fast stamping speed, high processing precision, strong mold versatility and flexible products. The mold used in the CNC turret punch press has a high punching speed due to its high precision and quality requirements. After purchasing a certain quality mold, the level of use and maintenance of the user directly affects the processing quality of the workpiece and the service life of the mold. Mold is also an important part of controlling equipment operating costs. Therefore, learning and mastering some of the knowledge in this area and applying it to the actual situation will also play an important role in improving efficiency and reducing costs.
The following is a discussion of some technical points that should be followed in the use and maintenance of CNC turret punching dies, and propose corresponding solutions to practical problems, which may have a good guiding role for users.
First, to ensure the best mold clearance
The mold gap refers to the sum of the gaps on both sides of the punch into the lower mold. It is related to the thickness of the plate, the material and the stamping process. The proper die clearance is used to ensure good punching quality, reduce burrs and collapse, keep the sheet flat, effectively prevent the material from being mixed and prolong the life of the mold.
By checking the condition of the stamped waste, it can be determined whether the mold gap is appropriate. If the gap is too large, the scrap will have a rough undulating fracture surface and a small shiny surface. The larger the gap, the larger the angle formed between the fracture surface and the shiny surface, the curling and fracture will occur during punching, and even a thin edge protrusion will appear. Conversely, if the gap is too small, the scrap will have a small angle of fracture and a large shiny surface.
When performing local punching such as grooving, nibbling, shearing, etc., the lateral force will deflect the punch and cause the unilateral clearance to be too small, and sometimes the edge offset may excessively scratch the lower die, resulting in rapid wear of the upper and lower dies.
When the mold is punched with the best clearance, the fracture surface and the shiny surface of the scrap have the same angle and overlap each other, so that the punching force is minimized and the punching burr is small.
Second, timely sharpening can effectively extend the service life of the mold
If the workpiece has excessive burrs or unusual noise during stamping, the mold may be passivated. Check the punch and the lower die. When the edge of the blade is worn to produce an arc with a radius of about 0.10 mm, it is sharpened.
Practice has shown that frequent micro-sharpening, rather than waiting for non-grinding, can not only maintain good workpiece quality, reduce punching force, but also prolong the life of the mold by more than one time.
In addition to knowing when the mold is sharpened, it is especially important to have 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. The grinding amount is 0.03~0.05mm each time, repeat grinding until the punch is sharp, the maximum grinding amount Generally 0.1~0.3mm.
2) Use sintered alumina grinding wheel, hardness D~J, abrasive grain size 46~60, preferably the grinding wheel suitable for high speed steel grinding.
3) When the grinding force is large or the mold is close to the grinding wheel, the coolant can be prevented from overheating and cracking or annealing. The high quality multi-purpose coolant should be selected according to the manufacturer's requirements.
4) The grinding wheel has a downward feed amount of 0.03~0.08 mm, a lateral feed rate of 0.13~0.25 mm, and a transverse feed rate of 2.5~3.8 m/min.
5) After sharpening, use the oil stone to sharpen the cutting edge, remove the burr, and grind the rounded corner with a radius of 0.03~0.05 mm to prevent the edge from cracking.
6) The punch is demagnetized and sprayed with oil to prevent rust.
Third, the method of eliminating and reducing the adhesive
Due to the pressure and heat during stamping, fine particles of the sheet are bonded to the surface of the punch, resulting in poor punch quality. The removal of the binder can be polished with a fine stone, and the direction of the grinding should be the same as the direction of the movement of the punch, so that further adhesion can be avoided after the light. Do not use roving or other sanding to avoid rougher surface and easier adhesive.
Proper mold clearance, good stamping process, and the necessary sheet lubrication will reduce the build-up of the binder. To prevent overheating, it is generally lubricated, which will reduce friction. If you are unable to lubricate or have a scrap back, you can do the following:
Alternate use of multiple punches of the same size in turn can have a longer cooling time before being reused.
Stop using the overheated mold. Programmatically change the mold, interrupt its long-term repetitive work, or reduce its punching frequency.
Fourth, measures to prevent sheet deformation when punching many holes
If a lot of holes are punched in one plate, the accumulated sheet due to the punching stress cannot be kept flat. At each punching, the material around the hole will deform downward, causing tensile stress on the upper surface of the sheet and compressive stress on the lower surface. For a small amount of punching, the effect is not obvious, but when the number of punching increases, the tensile and compressive stresses accumulate somewhere until the material is deformed.
One way to eliminate this type of deformation is to first punch every other hole and then return to the remaining hole. Although stress is generated in this way, the stress accumulation in the sequential pressing in the same direction is alleviated, and the stresses of the two groups of holes are offset each other, thereby preventing deformation of the sheet.
Fifth, try to avoid punching too narrow strips
When the die is used for punching the sheet with a width less than the thickness of the sheet, the punch will be bent and deformed due to the lateral force, so that the gap on one side is too small or the wear is intensified. In severe cases, the lower mold is scratched, and the upper and lower molds are made. Also damaged.
It is not recommended to step through narrow strips with a width less than 2.5 times the thickness of the sheet. When the narrow strip is cut, the sheet tends to bend into the lower mold opening instead of being completely cut off and even wedged into the side of the die. If this is not the case, it is recommended to use a full-guided mold with a backing plate to support the punch. Sixth, the surface hardening of the punch and its scope of application
Although heat treatment and surface coatings improve the surface characteristics of the punch, it is not a general method to solve the stamping problem and extend the life of the die. In general, the coating improves the surface hardness of the punch and improves the lubricity of the sides, but these advantages disappear after about 1000 stampings in large tonnage, hard material stamping.
6. A hardened punch can be used for the following situations:
a soft or sticky material (such as aluminum);
Thin abrasive materials (such as glass epoxy);
Thin hard material (such as stainless steel);
Rushing frequently;
Unnormal lubrication.
The surface hardening is usually carried out by means of titanium plating, nitriding, etc., and the surface hardened layer is a molecular structure having a thickness of 12 to 60 μm, which is a part of the punch base, not just a coating.
The case hardened mold can be sharpened in the usual manner. Surface hardening reduces the wear of the mold when it is punched with stainless steel, but it does not extend its service life. Proper lubrication, timely sharpening, and operation according to procedures are effective methods.
7. Repair of the punch mold position when the neutrality is not good.
If the centering of the punching die is not good, the mold is quickly passivated, and the workpiece processing quality is poor, and the following points can be overhauled:
Check the level of the machine and re-adjust if necessary;
Inspect and lubricate the die holes and guide keys on the turntable, and repair if damaged.
Clean the lower die holder of the turntable so that the lower die can be accurately installed and check the wear of the key or keyway and replace if necessary;
Use a special mandrel to calibrate the mold station and adjust it if there is a deviation.
The above is the usual situation. In view of the specific types and specifications of punching machines and molds, users should also know and summarize the experience in combination with the actual situation to give the best performance of the mold.