April 2008 Edition

MACHINING CENTERS

From Bottleneck to Breakthrough

Replacing machinery on its last legs provided a boon in production and flexibility

"We had a bottleneck in our shop," Gregg DeCheck, manufacturing engineer for Twin Disc, Racine, WI, said. "We knew why the process was being held up - old machinery that couldn't keep up and forced us to rework parts."

Twin Disc was experiencing first-hand a problem with which other shops in the U.S. were struggling: an important process was hindered by worn-out, inefficient equipment.

"We won't ship a bad part," Tom Mutter, a CNC tool operator with 33 years of experience at Twin Disc, said. "Not only were the old machines slow, but we'd have to prove parts two and three times to make sure they were right. It really slowed down our progress.

"On top of that, we had limited flexibility. We couldn't stop what we were doing to start urgently-needed parts. That customer would be out of luck."

"We knew we needed a fix," DeCheck said. "More importantly, we knew we needed a reliable, efficient process upgrade that would allow us to cut parts for years without any issues. We choose a Makino MMC2 with two A110Es to break the bottleneck."

For 87 years Twin Disc has been developing, engineering, manufacturing and distributing power transmission products that make things work. The products it produced are seldom seen, but go into machines that contribute to modern life.

Twin Disc products are installed in the drivelines and powertrains of farm tractors, road pavers, cranes, mining trucks, oil rigs, logging equipment, firefighting and rescue vehicles, pleasure craft, fishing and work boats, pumps, turbines, and other products.

And Don't Spare the Horses

Most of these products made by Twin Disc manage and control the horsepower generated by internal combustion engines and electric motors. Where there's an industrial-strength vehicle or machine that requires conversion of horsepower, Twin Disc has a way to do it.

This experience has made Twin Disc an efficient business, letting it crank out thousands of parts each year for customers with demanding specifications and schedules. With many of its customers demanding customized parts, and some on a just-in-time schedule, Twin Disc found its process lagging in machining transmission housings.

"We knew the housings were holding up everything," DeCheck said. "Until the housing was complete, other processes had to wait. For a company like ours, with our manufacturing experience, a bottleneck is unacceptable."

Twin Disc reduced the process time from 14 hours to seven hours and experienced a 30 to 40 percent decrease in cycle times

The transmission housing setup was simple - two machines with two operators, each loading castings onto fixtures. There were six parts pallets, all loaded into the machines as they were ready to be cut.

After the part came off, it would go to layout where it was checked for accuracy. Often, Twin Disc had to put the part back on the machine at least once to fix imperfections - performing part setup, running a partial program to fix the flawed cuts, and then rechecking the part for accuracy.

When a part passed inspection, it was sent to the next stage.

"The old process was static," Mutter said. "If a request for an urgent part that was not already in progress came in, we were stuck. The process took so long and was so labor-intensive we couldn't afford to push parts to the head of the line unless it was absolutely necessary."

Inflexibility and Bottlenecks

Lack of flexibility left Twin Disc unable to meet the production schedule for the transmission housings, which meant other production processes, such as gearing, were forced to wait for housing production to clear.

"Hence the bottleneck," DeCheck, said. "We were always waiting for the housings before moving on. This was frustrating when there was an urgent need for a custom part. The lack of flexibility meant we sacrificed other parts to do the custom part.

"The old machinery was costing us time and money," DeCheck said. "As a fix, we tried to have one of the machines rebuilt. It didn't work like we hoped.

"The rebuild threw off the perpendicularity of the machine, making a bad problem even worse. The old machines wouldn't do what we needed to make the parts quickly and efficiently, while maintaining our high standard of quality," he said.

Twin Disc looked at many manufacturers' machines to replace their worn-out equipment. They focused on return on investment, as well as manufacturer reputation and financial stability.

"We didn' t want to buy a machine where the manufacturer could disappear tomorrow, discontinue the machine line, or do anything else that might jeopardize our ability to manufacture parts," DeCheck said. "We knew Makino's reputation of reliability, accuracy, and customer service, and we knew it wasn't going to disappear, so it would be around for service, upgrades, and new machines."

Twin Disc purchased a Makino Machining Complex 2 - MMC2 - from Makino, Auburn Hills, MI. The machining cell consisted of 22 pallets - 11 per machine - and two A100E horizontal machining centers, each with a 244-tool magazine.

The A100E's cutting feedrates and rapid traverse rates were 1,970 ipm. It came with Makino GI control feature for high feedrates and accuracy.

The MMC let Twin Disc load several parts onto fixtures, then machine automation did the rest of the work. All the operator had to do was load and unload parts.

Prime Example

"We have one large transmission housing that takes advantage of the new setup," Mutter said. "The housing starts out as a 1,600 lb casting. The final piece is 4-1/2'×4'×2'.

"The part requires multiple processes, including boring radial holes, milling mounting pads, drilling and tapping. We semi the bores first, then drill and tap all the faces. We mill and finish-turn a pilot diameter on the back to which the front housing connects with bolts. We also use techniques, such as circular interpolation and helical milling, so we don't have to use large boring bars."

The housing has bores 22" deep. It's big and complicated, but Twin Disc reduced the process time from 14 hours to seven hours with the MMC2 and the A-Series machines.

The company uses a 21" mill with a special shank to create deep bores to reduce vibration and chatter. All of the 21" counter-bores are done using the A100E.

"We use two mills on most cuts," Mutter said.

The use of two mills lets them run at high rpm and feedrate, taking off about 200 thousandths per pass.

"Our old machines didn't let us use this modern, highly-efficient tooling," he said. "The new machine cuts down production time.

"Next we do the finish work and drilling and tapping," he said. "We run high-performance drills at high speeds, which is faster than the standard milling we were doing. After we're done drilling and tapping all of our holes, we do the finish boring.

"As far as quality goes, all first-pieces off the machine are checked," Mutter said. "We check every bore and spot check caps and some of the other processes as they are running. The quality we're getting is excellent. We run government work with tight specs. With the Makinos we see a lot of perfect parts."

Going Deep

One of the biggest problems the company had with its previous equipment was with deep perpendicular bores of 5" or more where it had to hold a couple of tenths perpendicularity per inch.

"We couldn't pull that off on the old machines," Mutter said, "but with the A-100Es, we're getting it right every time."

"We've experienced a 30 to 40 percent decrease in cycle times on the housings, most of which came from reduced setups and faster feedrates," DeCheck said.

"We've been able to have operators double-up on machines, too, which saves a lot of time and money. We used to have to assign one person to each machine, but because we don't have to pull the part off the fixture for each new piece we put in, one operator can now handle two machines."

Twin Disc used to have two six-palleted machines dedicated to gear housings. These machines each had an operator, standing by to pull finished parts off the fixture and replace them with new parts, then pull the parts off and take them to layout for proving.

The company is finding the savings it expected, such as in machine uptime and cycle times. But, it also is finding savings of time and money in areas it didn't expect, such as tool life and tool changes.

"One of our primary concerns was reducing the amount of machine down time," DeCheck said. "Our older machines were ready to be retired, and were going down all the time. When we looked for a new CNC machine, we wanted reliability and speed."

The 22 pallets let the company cycle parts faster, keeping the machines cutting instead of stopping to have operators load and unload parts. Feedrates improved by 25 percent.

"The new machines increased our ability to feed from 158 ipm to more than 1,000 ipm, though we don't run them quite that fast all the time," DeCheck said.

Other Benefits

"The high-pressure coolant lets us get better tool life and better flush chips from the holes," he said. "The new boring tools let us save space in the magazine - we can cut most of the bores with the tools onboard. We can often mill-bore where we'd hand-bored in the past, an expensive and time consuming process."

A clear ROI was important to Twin Disc. It needed evidence that paying for a premium machine would provide a quick return through benefits as well as provide payback in the long-run.

"Because we were able to have one operator on two tools, from one-on-one, and because our speed improved, ROI wasn't hard to establish," DeCheck said.

The new machine also made short runs possible.

"Since we're a custom transmission shop, every job is different and every customer's work is different. Now we have the ability to switch from job to job on demand," he said.

"We might be in the middle of a run and someone would need two housings. In the old setup, the person who needed the housings was out of luck. Now, in a matter of a few minutes we can make the change and run the job. It's removed the bottleneck."

Twin Disc can have the parts sitting on the rack, have several orders opened and in partial operation, and switch back and forth between any of the open orders.

"We're running parts so fast that now we're having problems keeping up the supply of castings - we cut them faster than we can produce the raw pieces," Mutter said.

"We're looking into buying more machines to improve other processes in our shop," DeCheck said. "We hope to eliminate other bottlenecks.

"We're slowly moving more towards just-in-time production, as long as the equipment and people to support that are in place.

"Business is booming. Fortunately, we invested at the right time and are ready to handle business as it comes in the door." Makino

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