The Blanking Die of Automatic Uncoiling Line Scratches the Sheet Metal: How to Solve the Problem?

With the development of automobile industry, people have a deeper understanding of automobile manufacturing technology.

In order to manufacture high-quality automobiles, advanced equipment and technology must be provided.

In the past, blanking dies accounted for a small proportion of stamping dies in the development of automobile panels.

This is because the investment of automobile stamping dies accounts for a high proportion of the development cost of the whole vehicle.

In order to reduce the one-time investment in the early stage, automobile manufacturing enterprises often cancel the development of blanking dies and use square or rectangular blanks for forming.

In this way, although the early stage investment in die development is saved, the material consumption is increased.

At present, steel prices have risen sharply, and automobile manufacturers have gradually realized that in order to reduce the manufacturing cost of complete vehicles, it is necessary to improve the utilization rate of single vehicle materials.

Therefore, large automobile manufacturers have introduced uncoiling and blanking lines and put uncoiling and blanking molds and even swing shear molds into operation, which effectively avoids the bumps and scratches of sheet metal during uncoiling and blanking, so as to improve the quality of sheet metal;

At the same time, the use of automatic uncoiling and blanking can effectively reduce the occurrence of sheet metal scratch operator accidents;

The most obvious effect is that the application of uncoiling line increases the production beat to 60SPM, greatly reduces the labor intensity of workers and improves the production efficiency.

Description of the problem

In order to improve product quality, material utilization and production efficiency, our company has added a 630t automatic uncoiling and blanking line.

The newly-built uncoiling and blanking line has the functions of automatic uncoiling, leveling, continuous feeding, continuous shearing, automatic stacking and so on, as shown in Fig. 1.

process flow diagram of uncoiling and blanking line

Fig. 1 process flow diagram of uncoiling and blanking line

At present, the production beat of the new uncoiling line is 30 ~ 60SPM, which is much higher than the speed of the old line of 22 ~ 40SPM.

The improvement of production beat puts forward higher requirements for the manufacturing accuracy and reasonable structure design of the die.

The blanking die must be able to support the sheet metal with accurate positioning and smooth movement.

Its structure is very similar to that of ordinary blanking die.

Its upper die structure is the same as that of ordinary die, and the only difference is the lower die structure.

The lower die has a floating plate to transport the sheet metal, which can effectively prevent the friction and scratch between the sheet metal and the edge of the punch.

In the early stage of commissioning and production of 630t uncoiling and blanking line, surface scratches often occur on the sheet metal, which seriously affects the surface quality.

Due to the lack of investment in the cost of new blanking dies, the old dies need adaptive transformation to carry out normal production in the new uncoiling line.

At present, the biggest problem is the scratch of sheet metal, as shown in Fig. 2.

sheet scratch

Fig. 2 sheet scratch

Cause analysis of sheet metal scratch and deformation

The debugging results of the blanking die in the early stage show that the scratch position of the sheet metal is constantly changing and there is no rule to follow, which brings us some difficulty in finding the cause;

In the next two months of mold commissioning, we screened all factors that may cause sheet scratch.

Through on-site elimination and verification, we finally summarized the following four reasons.

Insert backrest cusp, contour high point

(1) The back of the cutting punch is not chamfered, and the insert is at a high point.

When the sheet metal moves at high speed, it will jump up and down, which is easy to contact with the back of the cutting punch;

If the back of the cutting punch is not rounded, there will be short-distance scratches on the sheet, as shown in Fig. 3.

fillet of insert knife back

Fig. 3 fillet of insert knife back

(2) High point in the guide wheel.

Most uncoiling and blanking dies will be equipped with a guide wheel on the feeding side, which can feed smoothly and prevent the sheet from colliding with the high point quickly;

The wheel in the guide wheel is fixed with an open bolt, which rotates with the roller.

The open bolt is higher than the roller and directly contacts the plate, thus scratching the plate, as shown in the red circle in Fig. 4.

the pin is higher than the roller

Fig. 4 the pin is higher than the roller

Sheet scratch caused by insufficient strength of feeding mechanism

(1) The strength of the feeding floating plate is insufficient and deformed, resulting in inconsistent height of the feeding roller;

The thickness of floating plate is generally 16 ~ 20mm;

The material is 45 steel, which is generally not quenched and tempered, has poor rigidity and hardness, and is very easy to deform.

If the floating plate warps upward at both ends (shown in the red circle in Fig. 5), the feeding height of some balls will also be raised, resulting in the ball scratching the plate;

If the two ends of the floating plate collapse downward (shown in the red circle in Fig. 5), the conveying height of the plate is less than the height of the punch edge, and the collision will occur.

Fig. 5 blanking die

(2) 6 ~ 10 leading blocks (shown in 6 yellow circles in Fig. 5) will be arranged on the floating plate and connected by welding.

Usually, the welded area will be locally deformed, which will affect the feeding height of the ball, and some high ball will cause Scratch of the plate.

Ball scratch

(1) Causes of ball manufacturing error:

At present, the domestic ball manufacturing accuracy error is large.

Field experience can determine that when the height error of the ball exceeds 0.1mm, it will cause obvious scratch to the sheet metal, and its quality is unacceptable.

(2) Material reason of ball

The ball is easy to rust in the environment with high humidity, and the rusted ball will directly scratch the sheet metal.

(3) The production environment of the blanking die is poor.

Powder and iron filings enter the ball, causing the ball to fail to rotate normally.

At this time, sliding friction will occur between the plate and the ball, and the plate will be scratched.

Scratch of support arm

(1) The material of the support arm is too hard and the sheet material is too soft;

In the process of high-speed transportation, the sheet metal rubs with the support arm, and the sheet metal is scratched.

(2) The spring at the bottom of the support arm is too hard.

When the sheet is sent to the support arm, because the spring strength at the bottom is too large and the lifting angle of the support arm is too large, the sheet will dive down through a large arc and have rapid friction with the ball, resulting in obvious friction marks, as shown in Fig. 6.

material supporting arm

Fig. 6 material supporting arm

Solution to sheet scratch

According to the original structure of the old mold, after many debugging scheme comparisons, we have determined the final solution, as shown in Fig. 7.

Fig. 7 layout of support arm

(1) Chamfer and polish all punch backs to avoid edge scratches.

(2) Replace all dead balls.

Before replacement, be sure to ensure that the replaced ball is equal to the original ball.

The height difference between the purchased ball and the original ball is 0.5mm.

The precision of the purchased ball is poor and the height is different, which greatly increases the difficulty of on-site debugging.

It needs to be continuously padded and adjusted to meet the same height.

(3) Reinstall the support arm.

The material supporting arm on the lower die has been lost.

The model of the material supporting arm is determined by looking up the digital model, and the new parts are purchased and replaced.

The spring at the bottom of the purchased material supporting arm is too high, and the spring with appropriate elasticity is selected again.

When the copper material supporting arm pushes up the sheet metal, there is no large arc dive, the feeding stability is good, and the sheet metal commissioning results show that there is no scratch.

(4) Add a thin pad or polyurethane under the ball.

The floating plate of the lower die is 16mm thick and has been used for 6 years.

Through the platform detection, local deformation has occurred, resulting in unequal ball height. The deformation of the floating plate can only be balanced by adding thin pad or polyurethane;

The height and installation position of polyurethane are confirmed through on-site commissioning, which effectively avoids the jumping and scratch of high-speed running sheet metal, as shown in Fig. 8.

layout of polyurethane block

Fig. 8 layout of polyurethane block


The sheet scratch of blanking die can also be effectively avoided in the early design.

First of all, the layout of uncoiling and blanking process is very important.

The insert design should avoid sharp corners as far as possible.

The insert back must be rounded and polished with a polishing machine.

Remember not to polish only with sandpaper, otherwise the board will be scratched if the roughness is unqualified.

Secondly, increase the strength and stiffness of the floating plate;

The support of the material support frame adopts the integral structure, that is, the integral material support frame is adopted.

If the steel plate is adopted, its thickness is 25mm, and the tempering is 30 ~ 40HRC, so as to prevent scratches caused by different heights of parts due to deformation.

Finally, a more scientific roller or brush is used to replace the existing ball.

The ball support belongs to point contact, while the roller and brush belong to surface contact, which effectively reduces the pressure of the support parts on the sheet metal;

Adding a support arm at a suitable place will greatly reduce the impact scratch of the ball caused by the instantaneous acceleration of the sheet metal.

In a word, a reasonable scheme can completely solve the sheet scratch of uncoiling and blanking die, improve the surface quality of blanking sheet and greatly reduce the economic loss caused by sheet scratch.

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