Better tube bending cuts production time, improves consistency for heavy equipment manufacturer
CNC provides faster, better bends
After decades of using an old manual tube bender with no features, Kress Corp. took a huge leap in technology when it purchased a new bender with CNC, full-color interface, and stacked tooling capability. The result is a 10-fold productivity improvement.
Although the U.S. steel industry isn’t as large as it used to be, it still packs a punch. In 2012 U.S. steel companies produced 88.6 million tons of raw steel, which made the U.S. the third-largest raw steel producer in the world. The industry was larger and growing in 1965, with an output of 119 million tons, when Edward Kress founded Slagaway Corp. Kress’ idea was to design and build vehicles to lift, haul, and pour out slag pots, the enormous containers used in the basic oxygen furnace (BOF) steelmaking process.
It was a big ambition, but Kress was up to it. The Kress family had been involved in manufacturing transportation machinery for three generations. Kress Brothers Carriage Co. manufactured motorized fire trucks in the early decades of the 20th century, and Kress’ father Ralph had designed off-road haulers for the Dart Truck Co., Caterpillar, and LeTourneau.
Edward Kress initially focused on slag pot carriers. He later broadened the company’s product offerings (and renamed it Kress Corp.), branching out to design and manufacture other specialized vehicles for moving steel slabs, lifting stacking steel coils, hauling and dumping coal, and unloading railcars. It even manufactures specialized personnel carriers for researchers in Antarctica.
Despite the variety of machinery, Kress products have one thing in common: They are enormous. The payloads range from 600 to 400 tons and the engines develop from 400 to 2,100 horsepower. The cold-weather personnel carrier holds 60 people. The thickest components are made from 6-in.-thick plate. A single tire can cost as much as $40,000. In most cases, the driver climbs a ladder to enter the cab.
In an environment where everything is on a big scale, it’s understandable that small components would get short shrift. Indeed, for years the company’s hydraulic lines, cab ladders, and handrails were bent on a manual bender. Only recently did the company upgrade to a CNC tube bender.
Protractor, Level, and Intuition
The old manual bender left a lot to be desired. It held just one bending die and had no additional features. The bending staff had to use a manual protractor, fastened to the tube with locking pliers, to measure the rotation of every bend. To make a second bend in a different plane, they used a common bubble level to ensure the first bend was level before making the second bend. Getting it right was a slow, deliberate process, considering that some of the parts are 20 ft. long and contain up to 10 bends in several planes (see Figure 1).
It was hard to get it right every time. Compensating for springback was largely a matter of intuition, but tube can vary quite a bit from heat to heat, so even years of experience didn’t eliminate inconsistencies. Kress compensated by checking all of the tubular components on a coordinate measuring machine (CMM), but this added to the time needed to fill service orders and tied up the CMM quite a bit. It also revealed just how difficult accurate bending can be.
Seeing the Difference With CNC
The company’s decision to purchase a CNC tube bender resulted in a quantum leap in productivity. Comparing its new machine, a YLM model 50S2 ROSM-4A from J&S Machine, to its old machine is like, well, comparing a subcompact car to Kress’ cold-weather personnel carrier. Both can move passengers from point A to point B, but beyond that,there is no comparison.
The bending staff uses the machine’s interface to pull up the part drawing, or imports the drawing if it’s a new part. The next step is a simulation that shows how the tube will feed into the machine, and how the machine will bend it. This routine tracks the entire length of the tube, making sure that the end of the tube doesn’t crash into the bender (see Figure 2).
After loading the tube and ensuring the work area is clear, the bender operator initiates the bending sequence, and the machine proceeds to form the tube. After that’s done, he unloads the bender and loads the next tube.
This is a huge improvement over the old process.
- Then: After looking over the work order and pulling the corresponding part print, the machine operator would pore over the blueprint; figure out the bending sequence; then start the painstaking process of loading, clamping, bending, measuring, repositioning, leveling, bending, measuring, and so on.
Now: or a new part, the operator uses the bender’s software to import the CAD drawing; for an existing part, he enters the part number to pull up the program. After loading the tube into the machine and running a simulation to verify the tube won’t collide with the bender, he starts the bending sequence.
- Then: When changing sizes, the bender operator always had to change the bend die.
Now: The new machine holds a stack of tools; often the operator completes several work orders before changing the tooling. For example, it can bend a hydraulic system part (1/4 in. OD) and a handrail component (2 in. OD) without a tool change (see Figure 3).
Kress keeps the most commonly used die at the bottom because it is the least frequently replaced die.
- Then: It was impossible to determine interferences ahead of time. After making several bends, if interference looked likely, the operator often would have to remove the tube, turn it around, and bend from the other end. If that didn’t work, he’d have to try a different bending sequence.
Now: The bender’s simulation software looks for interferences to prevent collisions.
- Then: The manual protractor was fairly accurate, but not exact. A variance of just a degree or two on one bend followed by a degree or two on a subsequent bend would result in a poor fit. In some cases, especially long parts, the part wouldn’t fit at all, and would need to be rebent or scrapped.
Now: Every lot of tubing has unique characteristics, but within a single heat, the bend angle precision is approximately +/- 0.1 degree.
The cumulative benefit is the biggest benefit of all, which is the productivity enhancement. Kress estimates that the CNC machine is about 10 times faster than the manual process.
Another benefit is meeting its own manufacturing standards. Kress developed and uses a standard which keeps it on target for its products and, just as importantly, for the work it does for another OEM. The CNC machine enabled Kress to tighten up its manufacturing standards, improving its products and solidifying its business relationship with its customer.
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