Mold use technology and maintenance level are important links to improve processing quality, mold service life and control equipment operation cost.
This post mainly discusses the problems often occurred in the use of NC turret punch die, and puts forward the corresponding technical points and precautions for die maintenance.
Common problems in use
Mold with material
Mold with material will cause waste rebound, and the influencing factors are:
(1) the sharpness of the die edge. The larger the fillet of the edge, the easier it is to cause waste rebound;
(2) the mold entry modulus is small, which is easy to cause waste rebound;
(3) whether the clearance of the mold is reasonable;
(4) whether there is much oil on the surface of the processed plate;
(5) fatigue damage of die spring;
(6) poor lubrication.
In the use of the die, the wear amount of each side of the die punch core will be different. Some parts have large scratches and wear faster, while some parts wear slower, especially on the thin and narrow rectangular die.
The main reasons for this problem are as follows:
(1) the turret design or machining accuracy of the machine tool cannot meet the requirements, especially the alignment of the die mounting base of the upper and lower turntables is not good;
(2) the design or machining accuracy of the mold cannot meet the requirements;
(3) the accuracy of the guide sleeve of the die punch is not up to standard;
(4) the die clearance is too large or too small;
(5) due to long-term use and wear, the mold mounting base or mold guide sleeve is not well aligned.
Fatigue damage of die spring
In the use and maintenance, the die spring of CNC turret punch is often easy to be ignored.
The spring specifications corresponding to different punch equipment and dies are also different. Different springs have different performance and service life, so they need to be maintained or replaced regularly.
Otherwise, it is easy to lead to the problem of mold with material or cause greater losses such as damage to the mold and guide sleeve.
Technical points of correct use of NC punch die
Optimum die clearance
Die clearance refers to the sum of the clearance on both sides when the punch enters the lower die.
The choice of die clearance depends on plate thickness, material and stamping process. Corresponding die clearance shall be selected for different plate thickness or material.
Too small or too large clearance will damage the die and affect the punching quality.
If the die clearance is properly selected, it can ensure good punching quality, reduce burr and collapse, keep the sheet flat, effectively prevent material carrying and prolong the service life of the die.
Die clearance is determined mainly by checking the stamping waste.
If the waste has rough undulating fracture surface and small bright surface, it indicates that the gap is too large.
The angle between the fracture surface and the bright surface is directly proportional to the gap.
The larger the gap is, the curling and fracture will be formed during punching, and even a thin edge protrusion will appear.
Methods of eliminating and reducing sticking
Due to the pressure and heat generated during stamping, the fine particles of the sheet will be bonded on the surface of the punch, thus affecting the quality of the punch.
Lubrication is generally used to prevent overheating and reduce friction.
If it is impossible to lubricate or waste rebound occurs, the method of stamping with punches of the same size can be adopted alternately.
Multiple punches stamping in turn can give each punch sufficient cooling time before use.
To remove the sticking material on the punch, fine oilstone can be used for grinding to avoid further sticking material.
The grinding direction shall be consistent with the movement direction of the punch.
Avoid grinding with coarse abrasive cloth to prevent the punch surface from becoming rougher and sticking again.
Measures to prevent sheet deformation when punching many holes
If a plate is punched with many holes, the plate will be deformed.
This is due to the accumulation of punching shear stress during each punching, and the material around the hole will deform downward, resulting in tensile stress on the upper surface and compressive stress on the lower surface.
When few holes are punched, this punching stress will not affect the quality of the plate, but when many holes are punched, the tensile stress and compressive stress on the upper and lower surfaces of the plate accumulate at a certain point, which will lead to the irregularity and deformation of the material.
The method to prevent this kind of deformation is to change the punching sequence of holes, punching every other hole, and then return to punching the remaining holes.
This can effectively reduce the stress accumulation during sequential stamping in the same direction.
Although this punching method will also produce stress, it will offset the stress of the front and rear groups of holes, so as to prevent the deformation of the sheet.
Avoid punching too narrow strips
When the die is used to cut the plate with the width less than the thickness of the plate, the punch will bend and deform due to the action of lateral force, while on the other side, the wear will be aggravated due to the small gap.
In serious cases, the lower die will be scratched or the upper and lower dies will be damaged at the same time.
In addition, when cutting too narrow strip, the sheet will not be completely cut off, but will tend to bend into the opening of the lower die, or even wedge into the side of the die.
The way to avoid this kind of die wear is to try to avoid narrow strip sheets with too small step width, especially those less than 2.5 times the thickness of the sheet.
If narrow blanking cannot be avoided, it is recommended to use a return plate or a fully guided die.
Different material molds shall be selected for plates of different materials
The surface hardening of punch usually adopts titanium plating, nitriding, etc. the surface hardening layer of punch is not only a surface coating, but also a part of punch matrix with a molecular structure with a thickness of 12 ~ 60μm.
Through surface hardening, the wear of the die will be reduced when punching special materials such as stainless steel plate, but the surface hardening of the die can not prolong its service life. The maintenance methods of the punch through surface hardening are still conventional methods such as proper lubrication, timely grinding and operation according to regulations.
The hardened mold can still be sharpened in the usual way.
Case hardened punches may be used in the following cases:
- Punching soft or viscous materials (such as aluminum);
- Thinned abrasive materials (such as glass epoxy sheet);
- Thinned hard materials (such as stainless steel);
- Frequent impact;
- Abnormal lubrication.
Maintenance in use
(1) The molds shall be cleaned and oiled regularly or in time.
The molds shall be strictly inspected before installation and use to remove dirt.
Add lubricating oil or stamping oil to the corresponding sliding parts and cutting edges of the die at regular intervals during production;
After production, the mold shall be comprehensively inspected and cleaned.
After cleaning, the anti-rust lubricating oil shall be applied in time, and the mould shall be sealed and stored to ensure the cleanness of the mould for normal use in the future.
(2) When installing the male and female dies on the rotary table, they should be installed in strict accordance with the installation process of the dies to avoid inconsistent installation direction of the male and female dies.
For those dies with installation direction requirements, they should be cautious to avoid accidents due to installation errors.
(3) The operating tool for installing the mold should be made of soft metal, such as aluminum or copper.
If the hardness of the operating tool is too high, the mold may be damaged by knocking, smashing and other actions during the installation process.
During transportation, protect the mold and handle it gently to avoid damage to the cutting edge and guide.
When replacing the mold and grinding, pay attention to safety before and after starting the equipment to prevent damage to the equipment, mold and personnel.
Maintenance after use
(1) Timely grinding:
The amount of edge grinding of punch die is limited. When the edge is worn, it should be grinded in time.
If it continues to be used, it will accelerate the edge wear, reduce the quality of punching parts and shorten the service life of the die.
Practice has proved that it is very important to grasp the appropriate grinding time.
Don’t wait until it is necessary to grind.
Regular micro grinding can not only reduce the blanking force and ensure good workpiece quality, but also double the service life of the die.
In addition, mastering the correct grinding method is also helpful to improve the service life of the die.
In order to prevent the mold from cracking or annealing due to overheating, the high-quality coolant required by the manufacturer shall be added during grinding;
After grinding, it is necessary to remove the burr of the edge with an oilstone and grind the edge into a flat fillet with a radius of 0.03 ~ 0.05mm, so as to prevent the edge from cracking.
In addition, the cutting edge surface cannot be magnetic, and demagnetization must be carried out to prevent material blockage;
Demagnetize the punch and spray lubricating oil to prevent rust.
(2) Timely replace the spring:
In the process of mold maintenance, spring and other elastic parts are most likely to be ignored, but the spring is often damaged by fracture and deformation.
The damaged spring must be replaced in time, and the spring with the same specification and model should be replaced to avoid affecting the use of the mold or damaging the mold due to the mismatch of parts.
(3) Check whether the fasteners are loose or whether the parts are damaged at any time.
Check the relationship and damage of the accessories of the mold installation base and other parts at any time.
Find and solve them in time to avoid loosening and displacement, resulting in mold damage and other accidents.