Laminate tooling, depression grooving, and more about bending sheet metal

This laminate die is comprised of 0.5-in.-thick sections of 304 stainless steel.

This month, I cover a range a topics from laminate tooling to 6061 aluminum tube and even ironworker operation. These come from readers across the country and around the globe.

As always, thanks for your questions. I’m honored to know that, thanks to the print magazine and the internet, my content reaches readers from far and sundry places. Keep the questions coming, never stop questioning the status quo, and never stop learning.

Question: How would you feel about a homemade, 4-in. V die for bending 0.75-in. 304 stainless steel round rod? The laminated sections would be made from 0.5-in.-thick 304 stainless steel, held together with 0.5- and 0.75-in. round bar plug welded on the ends.

Answer: That concept works well, and for the most part, you can make it out of hot-rolled pickled & oiled (HRP&O) punches, too, as the nose radius isn't too small for the applied tonnage. Of course, stainless steel can work well if you need something that wears less than HRP&O material.

Creating the pieces to laminate using a laser or waterjet is the only way to do an excellent job. The laser is preferred because the heat-affected zone at the cut edge will harden the HRP&O material and reduce wear. Know that once assembled, the individual pieces will still scratch the material you’re forming, but they won't dent the material you’re bending.

For the punches, scratches usually won't matter, but for the dies, scratches might. If your part has a finish requirement, protect the die with urethane film to eliminate the marks.

I assume you will be running a weld bead down the laminated pieces, and using the barstock is a great idea to keep the pieces in alignment before you do. Another way to align the individual components is to use a small-diameter punch to create a half-shear, where the slug is punched halfway out of the sheet. Then you only need to snap them together, clamp them, and run a weld bead. Whether adding a punching operation makes economic sense will depend on the equipment you are using and the amount of tooling you are building. Regardless, it's another option to consider.

Whatever option you choose, know that this laminated tooling concept should work. I have done it myself many times.

Question: Do you know an actual term that describes a depressed, groove-type breakable joint in sheet metal? That is, if a depressed groove is formed into a piece of sheet metal, the single piece of sheet metal can be bent in an up-and-down motion along the depressed groove until the sheet metal breaks and separates into two pieces.

Answer: To the best of my knowledge, this is called depression grooving. The process creates a V groove using a punch or die set to indent the sheet metal. The groove also can be made with a V-shaped rolling wheel pressed into the material, with the material on top of a solid flat surface. In either case, whether or not this produces a breakable joint is all a matter of penetration into the material.

That said, I know that some haven't had much luck with this way of grooving, as it tends to mark the parts up. One way that I think works better is to cut the V groove. That is, you remove material to create the V, which can be either a breakaway groove or a very sharp inside radius.

Question: I am building a flying ultralight using 6061-T6 aluminum tube with an outside diameter of 1.9 in. and an inside diameter of 1.5 in. I need to bend a few pieces about 10 degrees. Does the material need to be annealed before bending that small of an angle? And if so, do I need to retemper it to maintain its strength? I am unsure that the bend would need annealing with the small number of degrees to be bent. And I am uncertain if bending 10 degrees would work with the material's current tempered state.

Answer: I haven't worked a lot with tubing, but I have plenty of experience with 6061 sheets. On that note, I would say that a 10-degree bend should not be an issue for you. If it is giving you trouble, you can heat it a little without really annealing the material, and it should bend easily. Just do not get too carried away with the heating.

If you should need to retemper, the process is pretty easy to do, but I would refer you back to the material manufacturer for the specifics of time and temperature.

Question: I am a weld shop of one and need help learning how to operate a used press brake and ironworker I acquired. They have no manual, and I haven't been able to find anything online. I bent some 10-ga. material last week, and the results were spot on. However, I just conducted some test bends on another supplier's 10-ga. sheet, and nothing is correct.

Answer: Getting a used piece of equipment without operational or maintenance manuals is common. Even with new machines, the manuals can disappear. That being said, the best way to learn any equipment you are unfamiliar with is to contact the manufacturer directly. They should be able to provide you with detailed instructions on how to use their product. You can find their contact info on their website.

You can find a few books that cover both press brake and ironworker operator training. For press brakes, my latest textbook, "Bending Basics," is available through the Fabricators & Manufacturers Association (FMA). Ironworkers are a different animal, so I don't cover them in my book. Nonetheless, you can find great books available on the topic, and while not machine-specific, they will cover the basics. Additionally, you may want to reach out to other welders who have used or are familiar with the machines you purchased to get their advice on how to use it correctly.

Question: I’ve struggled to understand how the bend radius on a print (which I specify) correlates to tool selection. For example, we are currently having some issues with some parts made from 0.5-in. A36 material. For these parts, we use a punch with a 0.5-in. radius and a 4-in. die. Now, if I use the 20% rule and multiply the bottom die opening by 15% for steel, I get 0.6 in. But how does the operator know to use the 0.5-in.-radius punch if the print calls for a bend radius of 0.6 in.?

Answer: First, for the 20% rule to work, you must be air forming, where the inside bend radius is floated as a percentage of the die opening. Again, the name of the rule comes from how 304 stainless steel air bends, forming a radius that's between 20% and 22% of the die opening. Our baseline material is 60-KSI tensile-strength mild steel, which air forms a radius that's between 15% and 17% of the die opening. Sometimes, the range can be even wider due to variations in the material being bent. (Editor's Note: For more on the 20% rule and sharp bends, you can search the archives at TheFabricator.com.)

This isn't bottoming. Because we’re air forming, the punch radius only affects the bend if the nose radius exceeds the naturally floated bend radius. In this case, the bend will take on a new, larger radius. Conversely, if you use a very narrow punch, you’re more likely to bend sharp, meaning the punch tip will dig in and crease the bend line. If you’re bending sharp, you won't produce a good inside bend radius, and you’ll cause many other forming issues as well.

In the case you cited, a 0.5-in. punch nose would be the appropriate tool, as it gets as close as possible without exceeding the naturally floated bend radius. A punch nose with a 5/8-in. radius would be larger than the floated radius.

Again, if you are air forming, the radius is floated, and the punch essentially becomes a pushing unit. As long as you don't use a punch nose that exceeds the floated radius or one that's so narrow that you start to bend sharp, the exact punch nose radius you use isn't critical. In your case, whether you use a 0.5- or 0.375-in. punch, you’ll produce the same floated radius in the part.

If you are working with and calculating for the 0.6-in. radius and want to specify the operator to use the 0.5-in.-radius punch, specify it either on the print, in the paperwork, or on the setup sheet.