Bending sheet metal parts without marks and scratches could be a real headache for some of our customers with very simple solutions but they do not know about it. Let us start from the beginning.
Press brake bending is the “final” operation in production to get the complete part. At first, the raw part is cut with plasma, laser, punching press, waterjet, etc. as the flat piece, and only after bending it could be a part as it is planned and designed. For sure after bending could be some additional operations such as welding, painting, adding screws, etc. but bending is the process to provide the part the final shape and geometry.
If there were some edge defects on the part (for example burrs) they will be removed first. The same procedure for any operations with surfaces — finishing, grinding, satination, etc. — they will be probably made with deburring machines after the cutting and before bending.
So the prepared part after will come to bending press brake to be bent. The problem is that normally with standard classical metal press brake tools during the bending process, you will receive small friction and abrasion of the shoulders of the bottom dies and the metal of the part itself. For sure it is not good for the bending tools (you will have constant friction every time and if you have parts plated like the galvanic treatment you will also leave small particles on the tool during the bending process) and for sure it is not good for the part — you will have small scratches on both parts of the die.
Theoretically, if the part will go later to the painting it is not a problem. But if the surface is already prepared as we explained before it is the main problem for the parts. The most important could be for example polished and finished metal which is usually used for the production of the kitchen, restaurant, and medical furniture.
Necessary to note — this problem is actually for dies only. For punches and the internal surface of the bend, it is not important because it is inside and mainly not visible.
In the US market, there is a huge offer of urethane and polyurethane replacements for standard press brake tools which could be made as inserts in holders or as real complete tools to put in supports and these urethane tools are realized also for all main tooling systems like Promecam, WILA, Trumpf, etc.
Hard material provides small wear and long life use and because it is not metal it doesn’t leave marks.
The other experimental story could be to enlarge the radiuses of die shoulders but in practice, nobody uses this way — it is too complicated, no guarantees with the result and expanding of radius links to the bigger necessary flange for bending.
In Europe, various manufacturers offer also nylon materials for the same purposes but also are not very popular for standard bends. The same is for urethane — the critics for this are that during the wear of the material of urethane die it became more elastic, and softer and cannot allow the same repeatability of results during use. So for some applications, it could be not very important but sometimes it is requested.
So in Europe, we prefer to use bending film for press brake to obtain the constant result and, as well to use any standard tooling without any replacement. The thickness of bending film depends on the thicknesses, for example up to 2 mm of metal thickness, it is recommended to use 0,4–0,5 thickness of bending film. The use is very simple — you can attach it with special holders, magnets, or any fixation you will choose and you will bend it as normal standard bending. Once you see bending film frayed, worn out, thin, or any holes you will just replace it with new. It helps you remove any scratches and also positively affects the wear of the tools themselves.
Bending film is made with high-quality polyurethane with the requirements of the customer on width and thickness. Usually, it is up to 2 mm in thickness but could be more under special request. In Asia and Japan the big population for purposes of non-scratches bending gaining the special cloth. But there are no real studies on how it is better than film and what is, for example, the better economy in 1-meter costs. From one point of view, the cloth could be more flexible but when it is really not important it doesn’t make any advantages.
If the part has small burrs and no deburring activities are used (recommended but not presented in the factory) it is reasonable to bend the parts with burrs down and use the bending film as well. In this way, you can have more wear of the bending film of burrs but you will not make additional wear of the punch — the burrs can reduce the wear of the punch very fast it will be in the top direction.
The solution with bending film is very easy, economic, and effective and you will have your product exactly perfect without any visual defects.
This post is also published on @Medium