Material Dragging of Turret Punch Press: Cause Analysis and Solution

CNC turret punch has been widely used in sheet metal processing industry because of its fast speed, high precision and strong universality of molds.

It is suitable for small batch and multiple varieties.

It has very high requirements for the precision and quality of the mold.

In the process of NC turret punch processing products, the phenomenon of turret punch mold dragging material often occurs due to mold maintenance and other reasons.

In general, the material dragging is caused by the fact that under normal circumstances, the upper die punch cannot be separated from the plate in time or completely.

The harm of turret punch die dragging material to processing is: the upper die punch is damaged or broken, the clamp of turret punch and the plate being produced are damaged, and the protective cover of turret punch is damaged due to the deformation and curling of plate.

When the punching die of the NC punch continues to cut near the pad slag, the unloading guide sleeve will hit the pad slag into the surface of the sheet metal, resulting in the scrapping of the parts due to the unqualified size and surface quality.

The cushion slag falls on the lower rotary table, which makes the feeding hidden danger, and the plate will be scratched or even damaged.

Sometimes, due to the continuous generation of cushion slag, the cushion slag overlap exceeds the strength limit of the mold and damages the mold.

When there are many single pieces or small quantities of production, the scrap rate caused by cushion slag is significantly improved.

When half of the cushion slag is impacted at the lower die opening, it will cause material belt.

Causes of material dragging in turret punch die

1. Long term use of the mold leads to damage, fatigue or fracture of the spring of the mold.

2. The unloading force of stamping plate is greater than the spring force.

3. The cutting edge of the upper die is too deep during stamping.

4. There is too much resistance and no lubrication when the die sleeve and die core are pressed up and down.

5. The clearance of stamping die is wrong, and the waste after stamping rebounds.

6. The feeding speed is too fast and the spring is not sensitive.

7. The upper and lower die edges are passivated, so that the pushing force is greater than the returning force.

8. The upper die may have magnetism after grinding, or some plates may have weak magnetism, which makes the upper die produce magnetic attraction to the waste when working.

The method of solving the problem of turret punch die drag material

1. Check the spring regularly. If it is damaged or broken, replace the spring.

2. Adjust the stamping height of the die so that when the punch is closed, the punch will punch through the plate to 1 ~ 2mm.

3. Lubricate the mold sleeve and core regularly.

4. Check the gap between the upper and lower molds and grind the knife edge of the upper and lower molds, and clean the molds regularly.

5. Sharpen the die in time, do not make the die mouth too blunt, and demagnetize after sharpening.

Causes of steel plate being pulled off in stamping process

When the steel plate is pulled off, it shows that the steel plate moves at the clamp, and it shows that the clamping force of the clamp is not enough, resulting in pulling off.

In fact, there are many reasons.

(1) The upper die is not separated from the sheet material in time, resulting in material belt.

(2) The feeding modulus is not enough, and the steel plate is not washed down, resulting in pulling.

(3) When using the drawing die, the return of the die is not completely reset, and the steel plate is still on the die.

(4) The steel plate is uneven and bumped.

(5) The scrap rebounded and stuck the steel plate.

(6) The upper die or lower die mouth becomes blunt.

(7) There is a problem with the lower gear plate of the clamp.

Waste rebound and material dragging

Definition of waste rebound: the phenomenon that the upper die brings the blanking after punching out of the lower die mouth in the stamping process.

With material means that the upper mold core cannot be disengaged in time.

Treatment method:

(1) Increase the strength of the upper die return spring and replace it if necessary.

(2) Increase the die clearance to match the stamped steel plate.

(3) Increase the entry modulus, and the normal entry modulus is about 1mm.

(4) When using the drawing die, ensure that the working condition of the drawing die is good.

(5) Level the steel plate to avoid collision.

(6) Polyurethane return spring is added to the upper die to reduce the chance of waste rebound.

(7) Grind the upper and lower dies to make the die mouth sharp.

(8) Replace the lower gear plate of the clamp and tighten the screws. If the clamp is ineffective or loose, it shall be repaired in time to avoid affecting the machining accuracy.

The accuracy of X-axis and Y-axis is finally realized by clamping the steel plate with the clamp. If the clamp is loose, it will inevitably affect the machining accuracy.

Reasons for material status

(1) Whether the material surface is in good condition.

(2) Whether the direction of material adhesion layer is conducive to impact.

Reasons for programming

(1) Mold selection.

(2) Punching sequence and direction.

(3) Determination of impact size.

mold installation

Fig. 1 mold installation

inspection of rotary table punch

Fig 2 inspection of rotary table punch

Fig. 3 installation of mold

Analysis of common mold problems

The mold shall be installed firmly, and the angle of the upper and lower molds shall be correct to ensure that the mold works in good condition (Fig. 1).

Frequently check whether there are iron filings and sundries on the turret.

If there are iron filings and sundries on the turret, they are easy to fall into the turret, block them and damage the machine tool (Fig. 2).

When installing the die (Fig. 3), the operator shall put the keyway vertically, and shall not use a blunt tool to knock it in, otherwise the die will be stuck and damage the machine tool.

The mold shall be tightened firmly, and the upper and lower molds shall be aligned to ensure the correct position and ensure that the mold works in good condition.

The residue on the station, especially the indexing station, needs to be cleaned.

Damage of mold

Mold damage includes lower mold damage and paired upper mold damage (Fig. 4 and Fig. 5).

The cause of damage may be that it is not fully placed in the specified position when inserting the mold;

When turret rotates, it interferes and collides with the punch, resulting in die damage;

Excessive adjustment of punch height (in case of excessive grinding of upper die and lower die). The position of the corresponding primary key can ensure that the upper and lower molds are not misplaced.

damage of lower formwork

Fig 4 damage of lower formwork

Fig 5 upper mold damaged

Causes and Countermeasures of die fracture

The causes and Countermeasures of die fracture are shown in Table 1.

Table 1 causes and countermeasures of die fracture

Fracture condition

Causes and Countermeasures of die fracture

Causes and Countermeasures of die fracture

Causes and Countermeasures of die fracture

Observation position

Upper end of punch core

Punch appearance

Upper part of lower die

Analyze the reason

The punch core is hit directly

Strike away from the center of the punch

Fracture after crossing. Clear cross marks remain on the die. Note: at the moment of cross punching, the cutting edge does not necessarily break immediately. Due to the fracture inside the metal, it breaks during subsequent punching.


Punch core to avoid being hit directly

Avoid striking away from the center of the punch core

Alignment of upper and lower dies

Standard height of punch and lower die

When the lower die of the punch core is excessively ground, the insufficient cutting amount of the upper die to the lower die (Fig. 6) will lead to the floating of the waste (magnetism is one of the reasons for the floating of the waste).

The floating of waste will cause die fracture and abnormal wear. At this time, it is necessary to pad the gasket.

Continuous processing away from the center of the die will cause stress on one side of the die. This is related to the cause of die fracture.

Fig. 6 insufficient cut in amount of upper die to lower die

Abnormal wear and unilateral wear of die

When you observe the upper part of the lower die, you can usually see the stepping marks in both horizontal and vertical directions.

This die has only abnormal wear on the long side, and the wear of the upper and lower dies is the same.

The lateral stepping is the cause of the interference between the upper and lower dies, and the stepping trace is shown in Fig. 7.

Generally, you can see the stepping traces in both horizontal and vertical directions.

Fig. 7 step punch marks

Proof of transverse step punching: observe the waste (Fig. 8).

The waste is less than the width of the die, and the direction of the burr is not exactly the same (if one side is different from the other side), which can be proved to be transverse step punching.


Fig. 8 waste

material adhesion

Fig. 9 material adhesion

belt plate caused by adhesion

Fig. 10 drag plate caused by adhesion

Observe the cross-section condition of the waste before, after, left and right.

If the shear surface is not uniform, it is the cause of unilateral wear.

Material adhesion, plate dragging

See Fig. 9 and Fig. 10 for material adhesion and strip plate.

Observe the cutting section of waste materials and products.

Adhesion is easy to occur when the cutting section (bright belt) is too large.

Adhesion is inevitable in the use of molds.

The cause analysis of abnormal adhesion depends on the material, gap, processing procedure, use frequency, etc.

These have a great impact and are necessary conditions for analysis.

For the phenomenon with plate, the reason may be that the spring becomes lower, the spring force is insufficient, the lubrication is insufficient, etc;

Therefore, it is necessary to consider the same materials, products, processing procedures and whether the gap causes this kind of phenomenon before the problem occurs.

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