December 2, 2013
When fabricator SF Tube Inc. noticed a falling productivity in its welding department, it discovered poorly cut tube that required an added step, end facing, before welding. The band saw blade was the culprit, which led to one change, a different brand, but ultimately a handful of improvements in productivity.
Nobody wants a demanding, high-maintenance machine. Any modern machine tool should be robust enough to run for long periods of time with little attention other than some regular downtime for cleaning and scheduled maintenance. The same goes for other items, such as consumables. After the decision is made to use a particular brand of welding wire, machine lubricant, or blasting media, it’s time to get back to work. Second-guessing decisions, doing additional research into the options, and changing course usually aren’t very productive activities.
However, the set-and-forget mindset can allow a small situation to grow into a substantial problem and then become a full-blown crisis. Often paying attention to the little things can prevent a minor problem from getting out of control and bringing a shop’s processes to a grinding halt, or at least a grinding slowdown.
This is what happened at SF Tube Inc., Hayward, Calif., when it traced a fabrication bottleneck back to its cutting operations. The company’s management realized it had overlooked the importance of an uncelebrated consumable in its cutting department, the humble band saw blade.
“Blade selection was almost an afterthought,” said Rafael Nuñez Jr., vice president of business development for SF Tube. “You don’t think too much about it until something goes wrong,” he said.
The downside is that when something goes wrong, it can go wrong in a big way. This was the case at SF Tube. The company cuts 85 to 90 percent of the tubing it handles, and some of it goes through the cutting area two or three times. Considering that the company processes about 30 miles of tubing per month, the cutting operation can have significant ramifications on how smoothly the shop runs (or doesn’t).
Small Problems, Big Ramifications. SF Tube’s staff didn’t have a problem when the saw had a fresh blade. A new blade would cut fast and square, and downstream processes would run like clockwork. As the blade started to wear, the deterioration in cut quality wasn’t immediately noticeable in the cutting operation. Management noticed problems elsewhere.
“We first noticed the problem in the welding process,” Nuñez said. “The time it takes to complete a weld increases as it takes more time to fill bigger gaps. Instead of finishing 18 assemblies per hour, the output falls, and eventually it drops to 12 parts per hour, and you know you have a problem.”
This problem is more severe on parts joined by orbital welding, an automated process that works well only if the gap is small and consistent.
“For one recurring project, we make long coils,” Nuñez said. “We start with 20-foot lengths of tube and butt-weld them, and in the end we have ¼ mile of tubing per a coil. When they’re finished, the coils are more than 13 ft. in diameter.” Sometimes this project barely got off the ground before problems cropped up.
Because shop space is limited, the welding is done outdoors (see Figure 1). In some cases, after the tube was cut and carried outdoors, the welding machine operators found that the tubes wouldn’t mate, so they had to stop what they were doing, carry the tubes back into the shop, and do an end-facing operation to square them up. The additional time for this got out of hand pretty quickly, increasing as much as 15 percent, according to Nuñez.
The saws are used for more than just the trim cuts before welding. They are also used to make initial (rough) cuts and final trim cuts, so deteriorating cut quality sent disruptive tremors throughout many of the company’s operations.
The other problem concerned blade life. A financially conservative company, SF Tube looks to maximize every dollar it spends, not just on equipment, but on consumables too. Management wasn’t satisfied with the blade life it was getting from its saw blades.
“The cut quality would deteriorate pretty quickly,” Nuñez said. SF Tube doesn’t claim to take it easy on its saw blades—it does quite a bit of work in stainless steel and heavy-wall mild steel pipe—but regardless, it tries to maximize the use it gets from every dollar it spends. The saw operator would try to make the blade last as long as he could, and make some adjustments to compensate as the blades wore. For many commercial products, this worked, because near-perfect cut quality wasn’t all that important. However, the company does quite a bit of work for industries that have tight tolerances, such as food and beverage, medical, and aerospace, and the saw operator’s tricks go only so far in preserving cut quality as the blade nears the end of its life cycle.
It also led to all sorts of other problems. As a blade wears, friction increases; over time it does less cutting and more pulling and tearing on thin-wall material. A dull blade can twist the tube in the vise, and if it’s a bent tube with just a small amount of surface area for the vise to grip, the twisting action can distort the tube’s shape. A bent tube rotating in a vise also poses a safety hazard if an equipment operator is nearby.
A final problem, related to the short blade life, was inventory replenishment. The blade supplier couldn’t keep up with the demand, according to Nuñez. SF Tube uses a kanban system and relies on consistent deliveries of consumable items, and the supplier would deliver fewer blades than he was obligated by the contract to deliver.
A representative for Simonds Intl. made SF Tube’s search for a new supplier easy when he dropped off a supply of sample blades.
“He gave us several blades to try out,” Nuñez said. “He also helped with process questions, machine optimization, and all the subtle issues that go along with fine-tuning a process like this.” It opened Nuñez’s eyes to the intricacies of sawing technology—proper blade material, tooth pitch, blade speed, and feed rate for starters, and related concerns, such as coolant selection and coolant flow rate. Coolant selection is especially critical at SF Tube because some of the machining centers cannot tolerate some of the saw coolants, Nuñez said.
SF Tube uses three of the company’s BroadBand® bimetal blades: 1⁄4 x 0.040 inch with variable 8/12 pitch; 1 x 0.040 in., 10/14 pitch; and ¾ x 0.040 in., 10/14 pitch. As the name implies, the series was developed to cut a broad selection of materials, such as aluminum, carbon steel, and stainless steel. According to Simonds, the combination of variable pitch and 8-degree positive angle extends the blade’s life cycle, provides smoother finishes, and reduces noise.
SF Tube also uses one of the company’s DieBand Plus® bimetal blades, ½ x 0.020 in., 10/14 pitch, an M42 high-speed-steel blade developed for toolrooms and shops that do a lot of contour cutting. Made with 8 percent cobalt high-speed wire on a high-tensile-strength spring steel backer, the blade’s teeth are hardened to 67-69 RC.
The first thing SF Tube noticed with the blade change was that it started getting a better value for its money. Based on the price and longevity, the company changed its practices, and it no longer relies on the saw operators to compensate for wearing blades and doesn’t have to use an end-facing operation to square up crooked cuts. When cut quality starts to deteriorate, the operator replaces the blade.
Second, it gets better results on thin-wall tubing. The blades stay sharp longer, so they cut longer, rather than biting into the wall.
Third, since SF Tube made the switch to the new blade, it found that, on some parts, the final trim cut was better quality than it expected. Now after the trim cut, the part is ready for deburring, eliminating an intermediate end-facing operation.
Fourth, inventory is no longer a problem; the new supplier delivers blades weekly in the quantities SF needs to keep its six saws running full-time.
Finally, SF Tube moved its other blade purchases to the new supplier, so it’s relying on a single supplier for bands, cold saw blades, and carbide-tipped blades; coolants for all of its cutting operations; and even deburring tools. This doesn’t result in a change that is easily measured in dollars and cents, but it does cut down on paperwork and simplifies the ordering process.
This isn’t the end of it. A rock thrown into a pool sends out ripples in all directions, and likewise, management at SF Tube has begun looking in all directions, trying to find additional efficiencies in nooks and crannies of its operation that have been overlooked.
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