Better Communication, Better Bending
Bending is the most complex operation in metal fabrication, and good communication is critical. Unfortunately, engineers and operators often don’t discuss as much as they should before launching a job into production.
In many ways, lean manufacturing is all about flow, which includes fabricated parts and information about those parts. With bending in particular, efficient part flow can’t happen without the efficient flow of information.
Having a cheat sheet can do a world of good in the press brake, programming, and, especially, engineering departments. If an engineer knows what the shop’s tooling library can and cannot produce, they can prevent many headaches down the road.
What’s on the cheat sheet depends on the shop and the product mix. Generally, the cheat sheet should:
- Describe the basics of forming tonnages to ensure the job can be bent safely with the shop’s available tools and equipment.
- Describe the basics of bend allowances, bend deductions and blank sizes and how changing the inside bend radius affects all three.
- Note whether the brakes are bottoming or air bending. Most modern operations air-bend, so if the shop still relies on old charts developed for bottoming, operators in the brake department will continue to struggle, often just “making it work” the best they can.
The cheat sheet also should include minimum flange lengths, which usually can’t be less than 70 percent of the standard die width. Ideally, an engineer should look at a flange on a drawing, refer to the tooling library, and know whether it will work with the machines and tools the fabricator has on the floor.
They should also know the tooling shut heights and how they affect bend line access, such as deep box bends with return flanges. While the engineer might have to talk with the programmer or others to discuss forming options, such as using gooseneck punches, window punches, a punch with horns or anything else, the cheat sheet could at least spell out general guidelines. If the part has flange dimensions outside these limits, the engineer can discuss options with the programmer.
Finally, the cheat sheet should include what the shop deems to be reasonable linear and angular tolerances—achievable on any properly set up machine in the shop. Material thickness can vary from lot to lot. For efficient operation, the tolerances specified should consider that thickness variation.