October 10, 2011
These days the ironworker can play a role in production, thanks in part to the custom tooling available, as well as positioning and gauging systems that add accuracy, repeatability, and efficiency to the operation.
Since the inception of hydraulic ironworkers, the traditional machine came with at least three main tools: a punch for punching holes in plate or angle iron; a flat-bar shear for shearing plate usually up to 24 in. wide; and an angle shear for shearing angle iron to length. Many machines also have had built-in notchers for notching or nibbling into plate or angle iron.
That was about it. Shops had at least one ironworker for short-run or one-off jobs, and it was always a reliable workhorse for maintenance work. But the ironworker typically was not thought of as a production machine.
Today the hydraulic ironworker can indeed augment production. Two factors make this possible. One, the machine can accept various custom tools designed around parts or part families. Second, ironworkers now have positioning and gauging systems that add accuracy, repeatability, and efficiency to ironworker operation.
Consider a job shop bending department with two large press brakes, each with 8-foot-long beds. One press brake operator bends large side panels for a cabinet assembly, while at another brake an operator bottom-bends thin-gauge, 3-inch-wide brackets that go with that assembly. Meanwhile, work-in-process for another job—a stack of medium-sized panels—sits nearby. Welders and assemblers downstream have every component needed for the subassembly, except for one formed component— which is now WIP, sitting in front of the brake that's now bending tiny brackets.
To those uninitiated to fabrication, this makes for an odd sight: a massive brake bed with a narrow tool set near the middle. Such a setup might represent an unnecessary constraint, especially if an ironworker is sitting idle in the corner. An attachment would allow an ironworker to bend those small brackets and, ultimately, open this constraint in the bending department.
This scenario shows how an operation can match the demands of an application with the right machine. The CNC brake is a relatively advanced, expensive machine, and so has a higher operating cost (machine rate) than an ironworker. Bottom-bending those brackets ties up a machine that could be churning out complex air-bended components that require the press brake's ram repeatability and multiaxis, automated backgauging.
This isn't to say the hydraulic ironworker is inaccurate. Manual gauging on an ironworker can act just like a backgauge on a press brake. Narrow bending tool sets can be installed on either end of the ironworker, at the punching or notching station. Longer bending tool sets can be installed in the center, where the machine's angle shear would normally go (see Figure 1).
Ironworkers aren't limited to simple, straightforward bending either. Consider another operation involving rod bent into a narrow U shape with two 90-degree angles, creating a U-bolt. Space for the return flange would be so large that even an incredibly deep gooseneck punch couldn't accommodate it. So for this application, the operator uses a special punch with an open center, which provides space for the return flange to swing back during the second bend. In this setup, guides ensure the first and second bends are on the same plane (see Figure 2).
An ironworker with a custom bending tool set can excel at bottoming an offset or U-bend—but as with any forming machine, the ironworker must have adequate tonnage to make these forms in one hit. The ironworker usually offers between 2 and 7 in. of stroke height. Considering tonnage, many bending applications on an ironworker use a 2-in.-wide V-die opening for 0.25-in. material (using the traditional guideline of the die opening being eight times the material thickness). Occasionally an ironworker will have a 3- to 4-in.-wide die opening to bend 0.375- to 0.5-in. plate, but that normally is the thickest an ironworker will handle when bottoming.
An ironworker that air-bends can handle a variety of material thicknesses. Still, the limit switches in the hydraulics driving the ram are not as accurate as on a precision press brake. Precise air bending still is possible, however, with special tooling. For instance, a die with a solid stop at the bottom allows the ironworker to stroke down to the point where the material is formed, just as the machine bottoms on the stop. This enables the ironworker to air-bend precisely without relying on a precise stroke control.
Custom punching and notching tools allow an ironworker to cut complex geometries in angle iron and plate. For instance, one shop uses a specialty punch to broach a hex-head hole into predrilled bolt heads. These aren't 3-cent bolts found at the local hardware store, but instead specialized bolt heads that can be more than an inch in diameter. The operator drops the predrilled bolt head into a die designed specifically for the application. The die holds the bolt head in place while the hex-shaped tool descends to punch the hex-shaped hole into the head of the bolt. The slug material is forced down to the bottom of the predrilled hole. This is why, in this application, it is critical that the punch not overstroke (see Figures 3 and 4).
Ironworkers also can handle tube, as one shop demonstrates with a custom tube punching setup. This application involves welded tubes that make a T-joint. The tubes are preformed to match a coupler, and the design calls for an oval hole to be cut out of the cylindrical tube. On the ironworker, a tube is inserted over a custom mandrel, which supports the tube and also serves as the die. A punch then descends to cut that oval hole (see Figure 5).
Other special tools include cluster punches, which can cut complicated patterns in one hit. The tool design must consider slug removal; a four-hole cluster punch tool set must ensure all four slugs can be efficiently dropped out of the machine. These special punches make specific hole patterns; a four-hole punch makes a four-hole pattern in one hit. If an operator were to use the same tool to make only two holes, he could side-load and damage the tool.
How precise an ironworker is depends on several factors. In punching, it depends on how well the punch ram is guided, and this includes the amount of clearance between the punch and die. Some new machines have a 1⁄16-in. clearance, while others have 1⁄32 in. The greater the clearance, the looser the punching tolerance will be.
In many cases, tolerance problems arise not from the accuracy of the hole geometry itself but from the hole position. Standard tooling allows workers to position common hole locations precisely, such as in the four corners of a baseplate. But beyond the standard four-corner punch and similar setups, hole positioning has been a challenge on the ironworker. Traditionally, workers center-punched or chalked-out hole locations based on a template, then attempted to locate these holes with the ironworker punch ram, matching up holes by line of sight. This was slow, tedious work.
Today's programmable stops and X-Y positioning tables change the situation (see Figure 6). Consider a long plate requiring a series of irregularly spaced holes in a line, so that the near side of each hole is 2, 12, 22, and 24 in. away from the plate edge. A programmable system can position that plate precisely, moving 2 in. from the plate edge to punch the first hole, another 10 in. to punch the second, 10 in. again for the third hole, and then a final 2 in. for the last hole.
For the right application, accurate positioning together with custom tooling can help turn the ironworker into a viable production machine. It obviously cannot match the speed of more expensive machine tools, but often the cycle time of individual machines isn't the constraint.
The ironworker's cycle time may be slower, but is this a problem? Another machine may be more productive, but all of that productivity is wasted if the machine just piles a mountain of excess WIP downstream. In the right situation, the humble, relatively inexpensive ironworker can ensure workers downstream receive all parts of a subassembly exactly where and when they need them.
Images courtesy of Scotchman Industries.
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