March 31, 2014
Prototyping a roll formed profile doesn’t have to be done in the conventional way, with hardened tooling and short runs made from long strips of material (or coil). American Roll Form uses butt-welded strips of steel, fed into a roll former outfitted with soft tooling, to prototype roll-formed sections. It uses a few other strategies that substantially reduce prototyping cost and lead-time.
As roll-formed profiles become more complex and tooling costs escalate, it becomes more critical than ever for engineers to make sure processes will work as intended before making a major investment in tooling. Even designs created with the best computer software, finite element analysis (FEA), or modeling program don’t always work quite as intended. Considering that some sections require a tooling investment in the tens of thousands of dollars, the OEM needs assurance that all aspects of design, fit, form, and function meet the necessary specifications.
FEA and computer programs are a good start, but experience and intuition play a role in developing a complex and cost-effective prototyping process to ensure the product will work as designed before investing in the finished tooling. With the economy tight and margins slim, OEMs can’t afford to pay twice for the same tooling; there is no room for error. The time to rework tooling may extend from days to weeks depending on the issues, often causing serious release delays and substantial cost overruns.
Techniques such as using soft tooling, bending parts on a press brake, and punching on a turret punch press can help to ensure that the part will perform when it is in production on a roll forming line. Such prototypes can be produced in a much shorter lead-time and at a drastically reduced cost compared to expensive custom tooling.
This doesn’t negate the need for FEA. In many cases, FEA reveals problem areas long before the first roll is cut. However, FEA isn’t perfect. Making an actual sample may be the only way to see if the design chosen will actually work. Samples can help guarantee the tooling outcome because of what is learned in the process.
Downstream processes can also cause complications. Using a roll forming line to make a profile is one thing; determining what will happen to that profile after holes are punched, notches are made, and other operations are run is something else altogether. All forming processes impart stresses to the workpiece; punching, piercing, and notching releases some of those stresses and changes the profile’s shape.
The lead-times for finished parts may be unacceptable when additional time is required to build machines, jigs, and fixtures. In this case, an actual sample made to print is essential to keep the project lead-times in the required time frame.
A recent example of this prototyping strategy involved an aluminum extrusion. The OEM wanted to comparethe cost and functionality of a roll formed part with the extrusions. The tooling cost—$65,000 for rolls, prepunch die, straightener, and cutoff die—was a hurdle.
The drawing specified a light-gauge section made from 0.035-in. G-90, hot-dip-galvanized steel. The part had three fairly straightforward 90-degree bends and two trickier complex radius bends. The part also had numerous holes in it, along with notches on the end where the radius bends were. The drawing allowed for virtually no end flare or deformation on the cut.
To prototype this part, the engineering team and toolmaker partners developed soft roll forming tools for initial forming and used a turret punch press and press brakes for the final forming.
The two big benefits of soft steel are cost and lead-time. It’s not heat-treated, which cuts the price significantly and reduces the lead-time from 10-12 weeks to 1-3 weeks. A side benefit is that the steel can be recycled after the proofing session is over.
Producing the Prototype. The engineering team determined that the roll formed portion of the part needed eight passes to get to spec. Turret punching could be used to create the required holes and end notches, and a press brake would make the three 90-degree bends. Based on this prototyping process, the OEM placed the order for the soft tooling, and the rolls were designed and made in just three weeks.
The engineering team proved the concept by ordering the material, punching and nibbling the necessary holes and slots, then butt welding the punched strips together. This was done so they would go through the soft tooling as if they were in coil form, ensuring a continuous flow of material through the rolls and simulating the roll forming process.
After the parts were rolled to print for both shape and tolerance, they were forwarded to the press brake for the final forming of the 90-degree bends. The quality control department verified that they were made to spec before they were delivered to the OEM.
Evaluating the Samples. Ultimately, the OEM received 20 samples of six different part lengths to test and try out in its final application. The OEM’s tests revealed that the roll formed part worked as well as the aluminum extrusion at a much lower cost. The OEM placed a production order for the final tooling with an annual part volume expected to exceed 750,000 feet of steel.
In the end, this sample run cost less than $8,000, saving 85 percent of the conventional prototype tooling cost.
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