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Picking a process

When faced with multiple processing options, how do manufacturers know which is the correct one?

Given the huge variety of metalworking techniques and technologies available to manufacturers today, choosing the most cost-effective approach to parts production can be a challenging

Some harder aluminums and curved profiles might make welding a better choice compared to bending.

task. One example of this is whether to bend a flange or to cut and weld it.

Perhaps your shop has a good handle on this question, but it seems there’s still a fair amount of confusion out there. When a member on a popular engineering forum asked his peer group for advice on this topic, the responses were all over the map (the names have been changed to protect the innocent):

  • WallyWelder claimed that welded joints are as strong or stronger than those that have been bent.
  • MaryLovesMetals argued that while the weld itself might be stronger, the heat-affected zone on either side negates any benefit.
  • Jimbo327 suggested that some materials work harden when bent and are therefore stronger.
  • BuckmasterDave pointed out that it’s cheaper to bend than weld.
  • ToolManTaylor countered this by saying it takes longer to set up the press brake than to “just weld the damn thing.”
  • SheetmetalSam said that bending introduces plastic strain, but noted that proper heat treating eliminates this potential failure point.
  • GoneFishing17 offered a succinct “it depends.”

To gain further professional insight, Techgen Media Group spoke with two industry experts. And although their answers contain more than a hint of “it depends,” they are insightful, nonetheless.

Deciding factors

A material’s formability and weldability are major factors in deciding on a manufacturing method. Other factors include available equipment and long-term project quantities and forecast projections.

“Many factors come into play with the design and fabrication of any part,” says Andrew Pfaller, segment manager for Miller Electric Mfg. LLC. “Certainly, a material’s formability and weldability are major factors in deciding on a manufacturing method, and shops should evaluate these as well as other factors, such as what equipment they have along with long-term project quantities and forecast projections.”

Brett Thompson, laser technologies and sales consulting manager at Trumpf Inc., agrees, but notes that bending is generally a less expensive process than welding. “Here again, the choice depends on the material, its thickness and the final part geometry, but where a bend might take just a few seconds to complete, a weld can require far more time. The grinding, straightening and polishing that likely goes with that weld, not to mention any thermal effects on the material, are additional considerations.”

This is why Trumpf offers education courses on part design and optimization, some of which focuses on ways to reduce welds. The company also offers software – TruTops Calculate – that calculates cycle times and manufacturing costs for parts and entire assemblies. Miller offers numerous training programs as well, some of which are designed to make customers more knowledgeable on the welding process and avoid some of the common industry misperceptions referenced earlier.

Yet Thompson is quick to point out that welding has its place. Obviously, the thicker the material, the more tonnage is required to bend it, eventually leaving shops with no choice but to cut and weld. The type of welding also plays a role in the decision-making process.

“Compared to MIG or stick welding, for example, laser welding is extremely fast,” he says. “And the higher speed means that the thermal input to the material is very minimal, so there’s little chance of weakness or brittleness around the weld. Those benefits, however, are offset somewhat by a higher investment cost and a need to fixture parts.”

The best move

Whatever the available options, Miller’s Pfaller points out that shops often have no choice in the matter. “For general industry work, it’s often left up to the fabricator how to best manufacture the part,” he says. “If they can form it, they’re likely going to try that first, assuming they have the in-house capability. But if the fabricator is doing work for the aerospace industry, for example, or another mission-critical application, more often than not, they’ll hear, ‘I want it made this specific way. Do you have the capabilities?’”

Part design plays a factor as well. “I’ve seen complex parts that simply can’t be completed on a press brake,” he adds. “In these instances, the shop typically does as many bends as possible and then welds the rest. And yet some materials – some of the harder aluminums, for instance – don’t bend very well, so welding might be the better choice. Each situation is somewhat unique.”

Thompson notes that material utilization should also be considered, especially when working with more expensive materials. If utilization is less than ideal, laser welding might be the more cost-effective approach. Similar arguments can be made for very short flange lengths or where a special tool is required and the job quantity doesn’t justify acquiring it.

Consider equipment

The transition from a punched or laser cut blank to precision bent part to laser welded finished component is shown.

And then there’s equipment. ToolMan Taylor’s complaints about setup time and suggestion to “just weld the damn thing” carry little weight on an automated press brake, one that can change its own tools  in a matter of minutes. And even though Trumpf is known for its high-quality press brakes, the growth of laser welding is changing the way manufacturers process parts.

“Welding at 200 ipm alters the equation somewhat,” Thompson says. “A NEMA enclosure, for instance, can often be produced for lower cost when only the profile is formed, but the sides are welded. This maximizes sheet utilization and decreases tooling complexity on the press brake.”

Pfaller points to another important technology. It’s not necessarily new, although it is rising in popularity: robotics.

“Whether TIG, plasma or laser, you need good upstream process control and tooling if you’re going to automate,” he says. “A human can manipulate the torch angle or adjust weld speeds based on a poor fit-up, but a robot can’t. That’s why it’s critical to have consistent parts going into a robotic cell if you expect consistent parts coming out. That’s true regardless of the material, thickness or part geometry or whether the part will be bent or welded.”

Miller Electric Mfg. LLC

Trumpf Inc.