How to use  CNC punching machine
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How to use CNC punching machine

CNC punching machine is a device that automatically performs blanking and cutting of sheet material according to a pre-programmed processing program. A proper usage should not only ensure the processing of qualified parts that meet the design requirements, but also enable the CNC punching machine to be applied rationally and its performance to be fully utilized. In the process of using CNC punching machines, each company has its own method on how to better maintain the equipment. The following is a summary of the reasonable use of CNC punching machines by Jia Feng based on years of experience in sheet metal processing

Operation specification

The processing of sheet metal parts is inseparable from CNC punching technology, and the correct operation specification of CNC punching can not only make the processing smooth, but also maximize the utilization efficiency of the machine tool and greatly extend its service life. The following are the operation specifications of Jia Feng.

(1) Before using the CNC punching machine, remove objects that obstruct safety or work from the work area.

(2) Close the air compressor relief valve and turn on the air compressor power.

(3) Clean the table surface, turn on the power of the main machine, check the operation status of the air compressor for any noise and abnormalities, and check the air pressure.

(4) Enter the drawing making program and confirm that the tool required for this drawing is properly installed.

(5) When preparing the tool, 1) select the most suitable tool size. 2) calibrate the mold. 3) determine the clearance of the lower mold, the clearance is 0.2mm for the plate thickness below 1.2t, 0.3mm for the plate thickness between 1.5t and 1.6t, 0.4mm for the plate thickness of 2.0t, 0.5mm for the plate thickness of 2.3t, and 0.6mm for the plate thickness of 3.0t. If the material becomes aluminum or copper, the clearance will be one level, if there is no tool used above, in principle, it will not be punched, if it is urgent, the next level of standard can be used. 4) Measure the length of the upper die and decide the position of the loading tool (standard length: 74mm, oblique tool: 77mm). 5) Measure the length of the upper die and decide the position of the loading tool. 5) Determine the thickness of the lower die, 18mm for 30mm and 20mm for 60mm. 6) Select the correct intermediate ring, concave type below 31mm and flat type above 32mm. 7) Select the appropriate stripper plate (in principle, 3mm larger than the tool). After the die is assembled, check whether the upper and lower dies and stripper plates are oriented correctly, and correct the tool on the tooling calibrator.

(6) Put on the tooling die according to the tooling program.
(7) Prepare proper material.
(8) Start the programmed punching.
(9) The first sample punching is completed, measure if the dimensions of each part are the same as the drawing, if the burr is normal, if the process needs to be changed, if so, the program must be changed first (if there is still a continuous production of the material, keep the qualified parts and mark the material number in the appropriate place for the sample for future production).

(10) Before production, we must consider how to place the finished material to ensure quality and facilitate the next process; during production, we should always pay attention to the storage condition of the bottom material box (not too much, inconvenient to carry); the lubrication condition of the mold, and remove the residual chips on the table at any time (to avoid scratching the workpiece).

(11) In production, pay attention to whether the tool is off and broken; whether the burrs meet the requirements; whether the bed surface is neat; whether the processing object is scratched and pay attention to the sudden collision, off the material board off, etc.

(12) If the above situation occurs, you should immediately press the emergency stop switch, if there is a code displayed on the computer screen, then refer to the manual of each model to exclude. Otherwise, follow the general method to repair and re-produce after removing obstacles.

(13) Punching speed according to the material thickness, size and other factors to adjust the appropriate speed, and strive to achieve the highest wedding power.

(14) Production should be the next work project to be used in the mold (knife) tools, materials and other information ready, so that after the end of the work, can continue production in the shortest possible time (that is, to shorten the machine idle time, improve the rate of marriage).

(15) After the workpiece is completed and handed over to the next workstation, the correct quantity and precautions should be informed.

(16) After the machine stops working, it should be completed to clear the scrap box, collect the tool into the tool storage, adjust the bed to the middle position, air compressor air release, perform the first level (daily) maintenance, clean the surrounding environment to perform the first level (daily) maintenance, 1) check the lubrication point of the machine to see if there is lubricant. Whether it needs to be added. 2) Rub and lubricate the X-axis, Y-axis lubrication. 3) Clean the trash of the upper and lower die of C-axis. 4) Clean the residue of the gears and rack of the X-axis, Y-axis motor. 5) Check whether the electrical control panel has any loose function is normal. 6) Open the electrical panel door to check whether the electrical switch is normal.

Operation Tips

Ensure the best die clearance

Die clearance is the sum of the gap between the two sides as the punch enters the lower die. It is related to the plate thickness, material and stamping process. Choosing the right die clearance can ensure good punching quality, reduce burrs and collapse, keep the plate material flat, effectively prevent banding and prolong the life of the die.

The suitability of the die clearance can be determined by checking the stamping scrap. If the gap is too large, the scrap will have a rough and undulating fracture surface and a smaller shiny surface. The larger the gap, the greater the angle between the fracture surface and the shiny surface, which can result in rolled edges and fractures, or even a thin edge protrusion. Conversely, if the gap is too small, the scrap will have a small angle fracture surface and a large bright surface.

When making partial punching such as slotting, step punching, shearing, etc., the lateral force will deflect the punch and cause too little clearance on one side, and sometimes the edge deflection will scratch the lower die and cause rapid wear of the upper and lower dies.

When the die is punched with the best clearance, the fracture surface and the bright surface of the scrap have the same angle and coincide with each other, so that the punching force is minimized and the burr of the punch hole is small.

Timely sharpening can effectively extend the life of the die

If excessive burrs appear on the workpiece or abnormal noise is generated during punching, the die may be dulled. Check the punch and the lower die, and sharpen them when the edge of the edge is worn to a radius of about 0.10 mm.

Practice has shown that frequent sharpening in small amounts, rather than waiting until it is necessary, will not only maintain good workpiece quality and reduce the punching force, but will also more than double the life of the die.

In addition to knowing when to sharpen the die, it is especially important to master the correct sharpening method. The sharpening procedure is as follows: 1) Use sintered alumina grinding wheels with hardness D to J and abrasive grain size 46 to 60, preferably suitable for high-speed steel grinding. 2) When sharpening, clamp the punch vertically in the V-slot or fixture of the magnetic chuck of the surface grinder and grind 0.03 to 0.05mm at a time and repeat until the punch is sharp, the maximum grinding amount is generally 0.1 to 0.3mm.

3) When the grinding force is high or the die is close to the grinding wheel, adding coolant can prevent the die from overheating and cracking or annealing, and a high quality multi-purpose coolant should be used according to the manufacturer’s requirements.

4)The grinding wheel should be fed downward by 0.03-0.08mm, lateral feed by 0.13-0.25mm and lateral feed rate by 2.5-3.8m/min

5) After sharpening, polish the edge with oil stone to remove the burr and grind a rounded corner with a radius of 0.03-0.05mm, which can prevent the edge from chipping.

6) Demagnetize the punch and spray on lubricant to prevent rusting.

Methods to eliminate and reduce sticky material

Due to the pressure and heat during punching, fine particles of sheet material will be bonded to the punch surface, resulting in poor punching quality. The direction of polishing should be the same as the direction of punch movement, so that further sticky material will be avoided. Do not use coarse gauze, etc., to avoid rougher surface of the punch, which will make it easier for sticky material to appear. Reasonable die clearance, good stamping process, and necessary plate lubrication will reduce the generation of sticky material. Preventing overheating is generally done by lubrication, which will reduce friction. If lubrication is not possible or scrap rebound occurs, the following methods can be used.

Alternating multiple punches of the same size in rotation will give them a longer cooling time before being reused. Take the overheated die out of service. Interrupting their repetitive work for long periods of time or reducing their punching frequency by programming controlled die changes.

Measures to prevent sheet deformation when punching many holes

If many holes are punched in a sheet, the sheet will not remain flat due to the accumulation of punching stress. Each time a hole is punched, the material around the hole is deformed downward, resulting in tensile stress on the upper surface of the sheet and compressive stress on the lower surface. For a small number of punched holes, the effect is not significant, but when the number of punched holes increases, tensile and compressive stresses accumulate somewhere until the material is deformed.

One way to eliminate such deformation is to first punch every other hole and then return to punch the remaining holes. This also generates stresses, but relieves the accumulation of stresses when punching sequentially in the same direction, and also causes the stresses in the two sets of holes before and after to cancel each other out, thus preventing deformation of the sheet.

Avoid punching too narrow strips as much as possible

When the die is used to punch a sheet with width less than the thickness of the sheet, the punch will be bent and deformed due to the lateral force, which will cause the gap on one side to be too small or the wear to increase, and in serious cases, the lower die will be scratched and the upper and lower dies will be damaged at the same time.

It is recommended not to step punch narrow strips with width less than 2.5 times the thickness of the plate. When cutting narrow strips, the sheet will tend to bend into the opening of the lower die instead of being completely cut off, and may even wedge into the side of the die. If this cannot be avoided, it is recommended to use a fully guided die where the rewind plate supports the punch.

Surface hardening of punches and its application

Although heat treatment and surface coating can improve the surface characteristics of punches, they are not a general solution to punching problems and extend die life. Generally speaking, the coating increases the surface hardness of the punch and results in improved lubrication of the sides, but these advantages disappear after about 1,000 strokes when stamping large tonnage, hard materials.

Surface hardening punches can be used for the following situations: punching soft or sticky materials (e.g. aluminum); punching thin abrasive materials (e.g. glass epoxy sheets); punching thin hard materials (e.g. stainless steel); and frequent step punches.

The case of abnormal lubrication: surface hardening is usually done by titanium plating, nitriding, etc. The surface hardening layer is a molecular structure with a thickness of 12 to 60 μm, which is part of the punch substrate, not just a coating. Surface hardened dies can be sharpened in the usual way. The surface hardening will reduce the wear of the die when punching stainless steel plates, but it will not prolong its service life, while proper lubrication, timely sharpening and operation according to the rules are effective methods.

Overhaul when the alignment of the punching die is not good

If the alignment of the punching die position is not good, resulting in rapid die passivation and poor workpiece quality, the following points can be overhauled: check the level of the machine tool and readjust if necessary; check and lubricate the die hole and guide key on the turntable and repair any damage in time; clean the lower die seat of the turntable so that the lower die can be installed accurately and check the wear of the key or keyway and replace it if necessary; use a special mandrel to calibrate the die position and adjust it in time if there is any deviation.


The use of CNC punching machine is a discipline that needs to be constantly explored and flexibly applied in order to achieve the best use effect.



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