What is a claw stamping mold?
Claw stamping molds are also known as DRAW molds. Most used in the automotive industry, especially in mass stamping, create many parts that constitute the finished product.
DRAW is the metal-forming process in which the workpiece will be clamped (held) at the bezel, the rest of the workpiece will be pushed, forming an empty shape. Many people will easily confuse DRAW with the stretching process, but it's not. The clamped workpiece is still capable of shifting in the DRAW mold due to the traction between the elements of the metal plate greater than the friction force between the workpiece and the mold. As a result, the thickness of the metal plate will be less variable, unlike the stretching process.
Structure and how the claw stamping mold works
Draw mold consists of 3 main parts: Punch, Blank Holder and Die.
In this article, I make molds, while the steel to make molds is mainly S50C, in addition to in the molds, cutting, there are other types such as SS400, SKD11, SK3 …
How does the DRAW swipe stamping mold work?
The workpiece clamping force is generated from the cushion pin's thrust onto the Blank Holder, causing blank holder to go up and squeeze tightly into die. When stamped in large quantities (mass stamping), to avoid Blank Holder being shifted leading to unstable clamping force, cushion battery is replaced by Gas Cushion.
Specifically, people use instructions for Blank Holder. This case is a Draw mold, so it is usually heel guide (guided by the sliding plates).
Order of priority to choose the method of creating clamping force for BH from the point of view of efficiency and cost
- Cushion Battery – pushed by Cylinder in the stamping machine itself.
- Pros: Cheap, large push battery journey, simple mold texture, easy clamping force adjustment.
- Cons: The different stamping machines that lead to the battery cushion scheme are different so the molds are harder to fit into the other stamping machine.
- Gas Spring – Gas Springs
- Pros: A set of molds can be installed in different stamping machines, which can adjust the clamping force.
- Cons: Expensive, complex mold structure, larger BH journey (150mm or more) then high mold is unstable)
- Coil Spring – Steel Springs
- Pros: Cheap, easy to replace.
- Cons: Failure to adjust the clamping force, difficulty creating large clamping force, the journey is usually small, the clamping force gradually decreases with the number of uses so it is unstable.
- Urethan – Rubber Springs
- Pros: Very cheap, Large clamping force.
- Cons: Unable to adjust the grip force, the Journey is usually very small.
Note about spring selection
At this time the structure of the mold will be much more complicated.
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Advantages and disadvantages of claw stamping molds
The advantage of DRAW mold is that it can shape most of the details on the car's chassis, the product surface quality is high, there are few wrinkles, the thickness is not much changed.
The disadvantages are the large mold size, complex texture, large stamping workpiece size that costs the material, the ribs of the product are easy to deform warp.
For example, actually designing products with DRAW molds
Mr. Hao's share in Facebook Group Stamping molds and car jigs.
Looking at the product to be made seems simple, however it has a fairly large depth of up to 115mm. Also use CR340X material with a flow stress of up to 440MPa. Mr. Hao chose the draw mold design in advance to see if it was suitable or not. People who are learning mold design can refer to how to think about how to design so that the fewer stamping molds the better.
With the development of modern design simulation software as it is now, the design has been a lot faster. There is no need to design the surface of the mold that you can put the product directly into the simulation software. From there directly create the surface for the mold with both automatic and manual customization. This means that you can test it before the mold is designed to be completed. You can also perform a stamping operation to see if the output product has any problems.
The result is described as the photo below. As expected, a DRAW mold cannot be formed.
The image below shows the torn detail in 2 positions, and a large array in the middle of the product is wrinkled. In addition, many other warped positions. So we need to change the stamping process.
Method of reducing the depth of draw mold -> RESTRIKE
Now based on the experience I will try the draw mold depth reduction option first, then RESTRIKE again (RESTRIKE mold), my process will be as follows:
DRAW -> TRIM -> RESTRIKE -> TRIM
Learn more about TRIM molds
After selecting the process, Mr. Hao continued to put the stamping process on simulation. Without simulation software, it will definitely create a lot of waste.
When changing the stamping process and the depth of the DRAW mold, the profile of each mold must be reconstructed. It is not too difficult to make changes, because the tool software has already supported a lot.
Just follow the process created before, Mr. Hao has processed the shape of the embryo. The result is quite satisfactory is no tear, no wrinkles, only a little warping on the edge of the product.
The warped processing is quite complicated, so there will be an article shared more closely. If you're interested, you can sign up for an email to get notifications when a new article updates here.
After agreeing on the mold surface design, export draw and RESTRIKE mold surface data from the simulation software and put into cad software for further design. Then complete the other detailed structures of the 2 molds and take them to be manufactured.
Software should be used to design and simulate patterns
You should use software specialized for stamping simulation such as JSTAMP, AutoForm. These software works very quickly. If you have simulated before, when transferring to CAD software, there will be no need to edit.
Autoform software can export the results formability, thinning, wrinkles … There is no need for code. Very convenient and fast, reducing many operations in the design.
Explain a little to you why my mold looks so simple and somewhat rudimentary, it doesn't look like the molds you usually see. Here I want to convey the most important part of mold design that is the design of the stamping process (die layout) and the design of the mold stool surface. The more details are produced, the more complex the mold structure, but the face is still the same so you just handle the molding surface well, combined with a reasonable stamping process that will form only.
This mold is also only for stamping, not a large stamping mold, so the details are removed to reduce the design and fabrication time.
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