Cutting Tool Engineering
December 2011 / Volume 63 / Issue 12

Magnetic attraction

By CTE Staff

The TMF Center, Williamsport, Ind., machines big parts in large volumes. The shop employs 96 CNC machines to manufacture steel and cast iron components for mining and construction equipment. Running three shifts, 7 days a week, the facility’s capabilities also include flame cutting, welding, painting, grinding and heat treating. Part size and volume make efficient workhandling and workholding key factors in maximizing overall productivity.

The company’s effort to streamline production of a family of large 1080 steel side plates for asphalt roller machines is a good example. The shop makes seven versions of the plates, which measure 8 ' to 12 ' long, 1¼ " to 5 " thick and 2 ' to 2½ ' wide. The plant produces about 25 of the parts per day.

TMF had been using a series of 12 toe clamps to hold the side plates for machining. Repositioning the clamps for each different part in the family took about 2 hours. Then, changeover from one similar part to the next during machining required about 20 minutes. That included loosening the toe clamps, removing the part from the machine, clearing the chips, loading the next part and retightening the clamps.

According to Jeff Martin, plant manager, TMF is “always looking for process improvements.” Seeking a way to reduce setup and changeover time, the shop consulted with longtime supplier Techniks Inc., Indianapolis.

Greg Webb, vice president of sales for Techniks, said, “Our company has worked with TMF for more than 10 years, and they’ve grown accustomed to us through our toolholders and boring products.” To hold the side plates, Techniks suggested its MagVISE magnetic workholding.

Webb said magnetic workholding was a good fit for TMF. “Their parts are very large and unusually shaped, and they have a lot of different sizes. They really needed something modular in its design and setup.” The MagVISE system enables users to selectively place the magnets as needed, he added. TMF decided to use 15 MagVISE ECB 120 magnets to hold the side plates. A turn of a handle activates or deactivates a 7 "×4 "×4 " magnet. Each magnet provides a holding force of up to 2,640 lbs., depending on workpiece size and thickness.

Courtesy of Techniks

A TMF employee loads a large steel side plate onto an array of MagVISE ECB 120 magnets from Techniks.

To determine how to arrange the magnets on the machine table, shop personnel “laid all the parts on top of each other in ProE CAD software, then came up with the best pattern of magnets underneath the side plates to get maximum holding and maximum clearance for tools that go through the part,” Martin said.

With the magnets holding the side plates, individual setups for the seven different parts in the family were no longer necessary. Changeover time between machining of similar parts dropped from 20 to 5 minutes, most of which was consumed moving the parts to and from the machine.

“Now, when you release the magnets, the chips are free, so it takes a lot less time to blow them off the fixture,” Martin said. “Then you just turn a handle to lock each magnet down again. That’s what got us down to 5 minutes.”

TMF also uses MagVISE workholding on a large bridge mill for machining another group of asphalt roller components called screeds. The screeds are 4 ' to 10 ' long × 2½ ' wide × 5⁄8 " thick and made of AR400 steel. For this application, 11 magnets are bolted to each of two base plates that are mounted on the machine table with ball-lock fixtures. Because the base plates and magnets are removable, the shop can cut other parts on the machine.

“Putting the two base plates together gives us 22 units to run the length of the machine,” Martin said, adding that the shop has to use as many as possible to avoid side load shifting because machining includes milling three edges of the screed.

To handle the side loads, the magnets are fitted with a permanent stop against which the fourth, unmachined edge of the screed rests. A floating stop helps locate the screed when it is loaded into the machine.

“When we engage all the magnets, we remove that floating stop and mill the three sides,” Martin said, noting that the setup prevents part movement. He added that magnetic workholding also straightens any bow that may exist in a part before it is machined.

Techniks’ Webb said interest in magnetic workholding has grown over the last 2 years, attributing it to increased market awareness and a desire to avoid adding workers. “Companies want to look at every process they have and whittle away as much time as possible,” he said. “That’s where magnetic workholding is so strong, because part setup and changeover times can be reduced tremendously.” CTE

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