Magnetic attraction

Author Cutting Tool Engineering
Published
December 01,2011 - 11:15am

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END USER: The TMF Center, (765) 762-1000 CHALLENGE: Reduce setup and changeover times when machining large parts. SOLUTION: A modular magnetic workholding system. SOLUTION PROVIDER: Techniks Inc., (877) 354-3837, www.techniksusa.com

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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. 

TechniksTMFPrdT10-11.tif

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.”

Related Glossary Terms

  • boring

    boring

    Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

  • clearance

    clearance

    Space provided behind a tool’s land or relief to prevent rubbing and subsequent premature deterioration of the tool. See land; relief.

  • computer numerical control ( CNC)

    computer numerical control ( CNC)

    Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

  • computer-aided design ( CAD)

    computer-aided design ( CAD)

    Product-design functions performed with the help of computers and special software.

  • fixture

    fixture

    Device, often made in-house, that holds a specific workpiece. See jig; modular fixturing.

  • gang cutting ( milling)

    gang cutting ( milling)

    Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

  • grinding

    grinding

    Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

  • milling

    milling

    Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

  • milling machine ( mill)

    milling machine ( mill)

    Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.