Introduction

The stability and reliability of punch machine tool performance are one of the important criteria for judging whether a machine tool is of high quality. Machine tool manufacturers are constantly pursuing the stability and reliability of the machine tool while pursuing the high performance of the machine tool. The same is true for CNC turret punch presses. Compared with foreign machine tools, domestic machine tools have a higher failure rate after a period of use. However, foreign machine tools such as German machine tools do a better job in this regard and have a higher reputation in the industry.

Similarly, when customers purchase more important machine tools, in most cases, they do not only consider the price but comprehensively measure the cost-effectiveness of a machine tool. Because of the same type of machine tool, the purchase price of the machine tool + the use cost of the machine tool + the maintenance and repair cost of the machine tool + the effective service life of the machine tool = the total cost. For a machine with a relatively high purchase price, if the performance is higher, the total cost will be much lower. From the point of view of the CNC turret punch press, the cost of mold use occupies a large proportion of the total cost. If the price of a CNC turret punch press is 1 million yuan, and the punch is working 8 hours a day, then its mold use for one year The cost is about 100,000 yuan; if the service life of the mold can be doubled, it will directly generate economic benefits of more than 100,000 yuan. Therefore, how to extend the service life of the mold must be the research direction of the punch manufacturer.

Problem analysis

The sequence of punching on a CNC turret punch press is as follows: ①The upper die just touches the sheet material → ②The upper mold begins to extrude the sheet material → ③The waste material falls, the punch returns to a certain depth, and the sheet material will move to the next position.

Among them, if the depth of entry into the mold is too shallow, there may be situations where the sheet cannot be punched and the scrap rebounds; while the depth of entry into the mold is too deep, it will reduce efficiency and mold stripping.

In the use of CNC turret punch presses, punches, turrets, and molds are the parts that intensively reflect the technical level and quality. The most common problems are the rebound of scrap and the stripping of molds. Scrap rebound and mold stripping often directly cause serious consequences such as rapid mold loss and workpiece damage, which affect the overall performance of the machine tool. Users often complain about poor mold usage, short life span, and easy picking of workpieces. In addition to the quality of the mold itself, improper use by users, and poor mold maintenance, the most important reason is the defect of the machine itself.

In order to solve the problem of scrap rebound and mold banding, punch manufacturers have conducted long-term research and adopted various methods, but the effect is not satisfactory and the problem cannot be solved fundamentally. Only a few high-end foreign manufacturers have added more effective functions, but they need to increase the hardware configuration and the cost is higher.

There are many reasons for scrap rebound and mold stripping. For the problem of scrap rebound, the main solution is to use an anti-rebound lower die, add ejector head to the punch, reduce the gap between the lower die, and adjust the depth of the mold. The main reasons for stripping are insufficient mold discharge force, too much depth of mannequin, small mold gap, the sharpness of the cutting edge, and reduction of the blow head. It is not difficult to find that the depth of the mold plays a very important role in it. In the actual use of the machine tool, due to factors such as the number of mold use and the use environment, each mold needs to be sharpened to a different degree, so the height of the mold is constantly changing. Take the high-speed CNC turret punch HPI3048-36 produced by our factory as an example. In theory, there are 36 mold heights in 36 stations, plus the height of the molds of different stations A, B, C, and D. The same (note: Nisshinbo machine tool punches can be changed according to the different positions of A, B, C, D, and there is no corresponding change after the height of each mold is changed.) In other words, there should be a preload point, bottom dead center, and feeding point corresponding to itself. However, the reality is that most domestic and foreign punch presses do not have this function. Generally, rotating the upper die nut is used to correct the change of die height (A, B station), but it cannot solve the problem fundamentally, and it will also cause the mold spring. New problems such as insufficient breaking and unloading force. Especially for some low-quality machine tool users, after grinding the mold, as long as the sheet material can be flushed down, the height of the mold is not adjusted at all. The serious consequences are obvious.

Only a few high-end manufacturers abroad have added mold height detection devices. When the height of the die changes, the position of the punch will change accordingly, which can better solve this problem, but it is necessary to increase the configuration and change the structure of the machine tool, which is costly.

In summary, it is not difficult to draw such a conclusion: To improve the cost performance of machine tools, increasing the service life of the mold is an important factor. To increase the service life of the mold, it is imperative to solve the problem of scrap rebound and mold stripping. Among them, adding the automatic punch adjustment function is a better choice.

Solutions

For the existing CNC turret punch press in our factory, this function can be realized without changing the mechanical structure or adding any hardware configuration. Here is an example of how to automatically change the preload height of the punch. The punch uses PLC programming (SIEMENS 840D system).

Mould station judgment:

NETWORK:1 (Judging that the current mold is A station mold)

L  MD  88

L  DB20.DBD  0

== R

=  M  51.0

NETWORK:2 (Judging that the current mold is B station mold)

L  MD  88

L  DB20.DBD  4

== R

=  M  51.1

NETWORK:3(Judging that the current mold is C station mold)

L  MD  88

L  DB20.DBD  8

== R

=  M  51.2

NETWORK:4(Judging that the current mold is D station mold)

L  MD  88

L  DB20.DBD  12

== R

=  M  51.3

NETWORK:5(modify punch data according to different stations)

M005:NOP  0

A  M  51.0

JC  M006

A  M  51.1

JC  M006

A  M  51.3

JC  M007

A  M  51.2

JC  M008

M006:L  DB21.DBW  144

T  DB57.DBW  2

JU  M009

M007 :L  DB21.DBW  144

L  130 ；(correction value)

-I

T  DB57.DBW  2

JU  M009

M008 :L  DB21.DBW  144

L 170 ；(correction value)

-I

T  DB57.DBW  2

M009:L  200 ；(send punch data)

T  DB140.DBW  48

L  DB57.DBW   2

T  DB140.DBW  50

L  DB21.DBW  150

T  DB140.DBW  56

L  DB21.DBW  156

T  DB140.DBW  58

L  MW  440

T  DB140.DBW  82

In this way, the preload height of the punch can be automatically adjusted according to different types of stations. Because the mold heights of the A and B stations are different from that of the C and D stations, the addition of this function can effectively avoid the occurrence of stripping.

Of course, you can also modify the punch data of other stations. For example, the punch height of each station can be corrected by this method. When the mold height changes, the correction value is put into the R parameter, and the system will adjust the punch height through the correction value to optimize the entire stamping action.

All processes will be processed by PLC, without affecting the programming format of the existing part program, and without increasing the cost of the machine tool, achieving the purpose of increasing the performance of the machine tool, improving the service life of the mold, and reducing the scrap rate of the workpiece.