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Sheet metal fabrication can be an art as much as a science.  With today’s bending, forming, and cutting machinery technologies, it’s hard to believe the skill set that’s still involved in producing sheet metal fabricated parts, assemblies and weldments.  Any good contract manufacturing company or sheet metal fabrication service provider will tell you that years of experience in metal fab are paramount.  The combination of seasoned sheet metal experts, new technology and the economic pressures of global competition has crafted a high skilled of sheet metal fabricators in the USA.  The wiley manufacturers that have survived through the overseas outsourcing era have a rich knowledge of low volume manufacturing techniques as well as high volume production manufacturing technology prowess.  We’ve canvassed some of our own experts to give up some insider tips on sheet metal fabrication.  Here’s just a few of the secrets that I was able to pry from their metal nicked hands.   

Metal Forming and Bend Radii

How you specify bend radius is important. Most sheet metal fabricators prefer that you design with a “Max” inside radius. That allows programming to vary the bend allowance to fit the tooling that will yield the best performance. For example, if you specify a max bend radius of .060, the fabricator can choose, .008, .032, or .060 tool to get the best results

When we “flatten out” a part in CAD in programming, one must adjust for bend allowance, by adding material to each bend to allow for the shrinkage of material during forming. The amount of material added is based on the tooling radius. Specifying a “Max” allows greater latitude, and sometimes allows us the ability to save parts that are on the edge of tolerance. Not all materials shrink the same.

Bump forming for bending curves into sheet metal

Bump forming is a process by which a part is formed with very small incremental angles. They require more “hits” per part but allow us to make parts with large radii using standard tooling. It can be done on either the Panel Bender or Brake. The larger the radius, the more susceptible it is to variation in material thickness, or tensile strength, because of the number of hits required. We often create profile gages to make sure we stay on track. Marketing loves a sleek radius, but there’s a cost. The part on the left was not the original design.

Slot and tabs for self locating

Use of slot and tab construction for self-locating mating parts in the middle of a part, or notch and tab at welded corners to help self-locate, and they help to restrain adjacent surfaces against weld shrinkage.  Using slot and tab techniques  will speed up assembly time and drastically improve repeatability, especially at production volumes.  Typically these features are not designed directly into the prints by the design engineer.  The fabricator and engineer will have to collaborate to ensure this is acceptable to the print and determine whether a note must be added to the prints to manufacture this way.  In our experience as a contract manufacturer, the answer is usually yes.

Cleco fasteners for temporary fastening

Cleco Fasteners, often known as Clecos or Clekos, which are temporary retractable rivets to hold surfaces together for welding. This requires additional holes in the mating parts for locating, that can be filled with weld after use.  Clecos are great for use in panels or any other area where speed and repeatability is a factor.  They come in many standard shapes and sizes, are readily available and can be installed with one hand.  Holes must be pre-drilled into the base material before the clecos can be installed.

BONUS: Welding Fabrication Quick Tips

  • On long seams weld in sections alternating back and forth along seam to reduce distortion. 
  • Allow for shrinkage when staging parts when possible. EX:  if there is a 90* angle stage parts slightly open utilize angularity tolerance to allow for shrinkage when corner seams are welded. 
  • Utilize tack welds when possible to reduce part movement prior to welding complete. 
  • When welding aluminum part cleanliness as well as filler rod cleanliness will have a significant impact on the quality of welds. especially during any testing requirements. 
  • Quality tooling and consumables (gas,filler rod,equipment,etc) aid in producing a quality weldment.
  • Tab and slot location features can assist in self locating component parts as well as squaring a corner seam
  • Purging argon through (inside) a stainless welded assembly can reduce inside weld discolor, impurities at the welded seam

Conclusion

After speaking with the folks in our sheet metal fabrication department, it’s easy to see why metal fabrications companies need to cherish the experts they have in house.  The experience that comes from years of welding, bending, forming is getting harder and harder to replace.  It’s important that articles like this exist to help keep the experience flowing around the industry.  But even more important is for good people like our readers to take this knowledge, use it for your own fabrications and weldments and expand your own knowledge base.  Whether you’re working at a high-end contract manufacturing operation like PEKO, or a 5 person metal fabrication outfit in rural USA, take some of these tips and apply them to your processes.

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