Stamping dies: why always jumping scrap during high-speed precision blanking, do you know the reason?


The so-called jumping scrap refers to the phenomenon that the waste scrap punched into the concave die edge is carried out of the die surface by the punch when the continuous die is punching at high speed. Its existence will bring material or terminal crushing, thus affecting the quality of products, shorten the life of the die, reduce production efficiency, is the high-speed continuous punching production "taboo".

First, the reasons for the formation of jumping chips
1. Causes
The main reason for the formation of jumping chips is that in the high-speed continuous punching process (as shown in Figure 1), due to the high punching speed (up to 800m/s or more) and the impact of cutting oil and other factors in the punching process, so that a momentary local vacuum is formed between the punch and the waste chips, when the material is very thin, the weight of the waste chips itself and the sum of the friction force of the die edge on its less than the adsorption force of the punch, in the process of the rise of the punch, the waste chips will be adsorbed on the surface of the punch. The scrap will be adsorbed on the surface of the punch and rise with it, thus forming jumping chips.

2. Factors affecting jumping chips
There are many factors affecting the jumping chip, when the punch edge chipping or blunting, excessive amount of cutting oil, the material is very thin and the depth of the punch into the concave die is too short, etc., can cause jumping chip.
Second, the method of preventing and controlling jumping chips
1. Reduce the adsorption force between the punch and the waste chips
(1) open a groove on the punch, for a relatively large cross-section and regular symmetrical punch, a small groove can be ground in the middle to reduce its contact area with the waste chips (as shown in Figure 2).

(2) For punches with large cross-section and irregular shape, use a diamond grinding rod to grind some pits on them

(3) Grind the edge of the punch to the shape shown in Figure 4 or make a chamfer of 0.3mm.
(4) In the design, add a blowing hole in the punch for air blowing to prevent chip jumping.

(5) For the punch made of SKD11 material, a spring pin can be added to the punch when designing to prevent chip jumping.
2. Increase the friction force (clamping force) of the die edge on the scrap chips
(1)For block or combination die, use the "cover" pin about 1mm below the edge to increase the friction of the scrap in the die (clamping force).
(2) For process auxiliary steps, such as side edges, dividing station edges, etc., the shape of the scrap can be appropriately complicated to increase the clamping force of the scrap in the concave die, so as to prevent chip jumping.

(1)Vacuum cleaner is used to suck away the scrap to prevent chip jumping. Use vacuum cleaner at the bottom of the lower die to form negative pressure and suck away the scrap, which is also a good and effective way to prevent chip jumping as proved by experiment.
(2) For some small punches, when punching and cutting, attention should be paid to the fact that the falling mouth should not be too small, otherwise it will cause chip accumulation due to electrostatic absorption of waste materials.
(3) Keep the punch and concave die edge sharp, add cutting oil in appropriate amount, etc., also help to prevent chip jumping.
In short, the reasons affecting chip jumping are very complicated, and there are many ways to prevent it.