Laws of attraction

Author Daniel McCann
Published
August 01,2009 - 12:00pm

Simon Barton sounds equal parts puzzled and frustrated at the state of electropermanent magnetic workholding in the U.S. “I was at IMTS [in Chicago] last year,” said Barton, head of engineering and sales for Alpha Workholding Solutions, Statesville, N.C. “We had a booth at the back of the hall with a big VF4 Haas machine that had magnets. We did the same sort of demonstration that we did at IMTS in 1994. And I would say that of the 800 or so companies that stopped by the booth, less than 5 percent actually were users of magnets.” Many of the other visitors, he continued, responded to the demonstration with an impressed, “‘You can do that with a magnet?’”

An Alpha Workholding Solutions permanent electromagnet in use during a through-workpiece application.​ Image courtesy of Alpha Workholding Solutions

Electronic Chucks

While permanent (nonelectronic) magnetic workholders have proven useful for light (12 " in diameter and less) applications, electronic magnet technology can easily handle larger jobs. About 3 " thick, the electromagnetic chucks are typically mounted on a pallet or tombstone. They range from 4 "×8 " to 6 '×10 ', and can weigh from 15 lbs. to 500 lbs. or more.

Two types of electronic magnets are available: electropermanent magnets (EPs), such as those manufactured by Alpha Workholding, and electromagnets.

EPs consist of two sets of permanent magnets: one set with poles that are electronically activated, and the other set with nonswitchable poles. Once charged with a single pulse of DC voltage, the activated magnets assume the same polarity as the permanent magnets, and the device is powered. The magnets retain their power until they’re electronically demagnetized by switching polarity. In the interim, there’s no need for connecting cables, and their portability is a commonly highlighted feature.

Electromagnets are made of an iron core encircled by an electronically charged coil, which creates a magnetic flux. Unlike EPs, electromagnets depend on a continuous source of electricity; thus, cabling is a necessity and heat is a constant. While a power outage is a threat with electromagnets, the risk can be limited with safety stops built into the controls. Electromagnets feature flexible holding power. Once charged, the EPs power can be increased, but in order to lessen clamping force the operator has to stop the operation and start over. By contrast, the electromagnet’s power can be adjusted without shutdowns.

While popular in Europe, electro- magnet workholding solutions have been slow to gain ground in this country. Some sources attribute their lackluster performance in the U.S. market to bad experiences stemming from misapplications. Yet companies that have adopted EPs and electromagnets are quick to endorse their cost savings and flexibility.

Time Saver

Several years ago, a North American die manufacturer (who asked to remain anonymous) launched a companywide effort to install the Alpha Workholding magnets on equipment throughout the facility, including its high-speed milling centers.

The company manufactures sheet dies ranging from 6 " to 16 ' long. It decided to adapt EPs to nearly all its machine tools, including more than a dozen grinders, 4-axis machining centers and 5-axis gantry mills.

The initial impetus for the new technology was to reduce setup time for grinding applications. For years, the company had used manual clamping systems—trap blocks, hold downs, standard studs and T-nuts in the table. Setups typically took 2 to 3 hours. With the EPs, prep time was down to 15 or 20 minutes.

Today, the company has several dozen EPs, most of them 3 "-thick incorporated into tables about 2 " wide and 14 " long, though they also have larger models. The magnets ranged in price from $3,000 to six figures, depending on size and customer requirements.

In addition to reducing setups, the company saw that the EPs improved grinding capabilities. When grinding guideways or broach rails about 3 " or 4 " wide, 8 " tall and about 170 " long, the firm was able to achieve 0.0002 " or 0.0003 " accuracy using magnetic holding. The company reported that such precision would nearly be impossible with a mechanical setup.

One problem Alpha Workholding takes special measures to eliminate is chips adhering to the workpiece. “We can manipulate our [magnetic] poles—putting magnetism where we want it and not where we don’t—in such a way that if people are drilling, turning or machining around the edges, chips won’t be a nuisance,” Barton said. “Somebody can send us a print, so that we can model that part and the magnet that we recommend for the application; we can then determine the [needed forces] and basically give them a guarantee that the part won’t move or vibrate, and there will be no problems with chips.”

Streamlined Operations

Last September, at its Warner Robins, Ga., facility, forklift attachment manufacturer Cascade Corp. added a Wen Technology permanent electromagnetic workholder as part of a streamlining project. Cascade adapted it to a newly acquired Mazak VTC655 vertical machining center. The aim was to make the equipment as autonomous as possible to enable one operator to oversee both the Mazak and an OKK machining center, which has pneumatic workholders.

“We make hydraulic attachments for forklifts,” said Ricky Schnable, Cascade staff manager. “The Mazak is for machining mounting holes into the side shifter. These holes are for mounting a new product introduced last year called a fork positioner, a device to locate the spread between forks.”

Dr. John Powell, president of Wen Technology Inc., Raleigh, N.C., explained that the magnet for the Cascade application holds the side shifter’s “steel rails with a section shaped like an S, which includes several different sections and a range of lengths. These rails require selective machining and drilling, and need to be presented to the spindle so that the diagonal portion of the S is at a controlled angle near vertical.

“We provided a customized, single-piece magnet that covered the machine table with four strips of magnetic poles running down its length. To support the part, machinable rails were installed along these magnetic strips, which are machined to fit the sections. Since there are no clamps between the parts, they could load four parts at once on a smaller machine—or twice as many as they could with mechanical clamping.”

With no clamp obstructions, deburring of the pieces is performed automatically inside the Mazak vs. manually outside the VMC. “That helped to eliminate operator involvement and was one of the things that sold us on the permanent electromagnets,” Schnable said.

Another feature of the Wen technology that proved attractive to Cascade is its ability to wash off chips in the machine. “We had Mazak add an M-code to control the magnets on and off,” Schnable said. The control “can actually demagnetize the part while it’s inside the machine, turn on the coolant, run it across the part, clean it of chips and wash off the table, so operators don’t have to clean fixtures when they come out of the machining center. This was another step that helped to eliminate operator involvement so they can run two machines. Also, operators don’t have to do clamping. We were accustomed to working with big, bulky clamps that had to be tightened down.”

One of the latest developments in EP technology is Wen’s dash-M control. Introduced in June, the device uses an internal microcontroller to detect problems—such as chips in the connector and crushed cables—and shuts down a machine before it short-circuits. “Our new dash-M technology is like antilock brakes or traction control for your car—a combination of avoidance and insurance,” Powell said. “The primary innovation is firmware that not only switches your chuck on and off, but simultaneously checks for fault conditions and actively attempts to protect both the control and the chuck connected to it. While the technology does not prevent chips getting into connectors, coolant in junction boxes or cables getting crushed by a forklift truck, it is effective at preventing these events from propagating into burnt controls, cooked chucks and serious downtime.”

The electromagnet Option

Not all companies that opt for electronic clamping choose EPs. Some firms, such as United Grinding Technologies, Miamisburg, Ohio, are sold on the benefits of electromagnetic chucks. For the past 12 years, the company has used O.S. Walker electromagnets on its Studer CNC grinders.

“Electromagnetic chucks offer you the flexibility of varying the amount of magnetism needed to hold the part,” said Don Hayes, project manager for the Studer Grinding Div. of United Grinding. Hayes’ division focuses on providing customers with ID and OD cylindrical grinding products. Companies commonly use electromagnets to hold bearing races and mold and die components when grinding.

Hayes illustrated the technology’s flexibility with a couple of scenarios. “Let’s say you have a part with a thin wall, which doesn’t have much surface contact to the magnet and you need to crank up your holding power, or you have a part that requires less grinding force and you want to crank down your holding power pressure—you can perform either with an electromagnet. It gives you more flexibility from part family to part family.”

Variable magnetic workholding also comes in handy when working with non-linear parts, said John Knight, sales representative for O.S. Walker, Worcester, Mass. “Because they can vary the power, they won’t suck the workpiece down to the magnet and take the bow out of it, for instance.” In addition, Knight said, because the magnetic lines of flux on the electromagnet pass through air more effectively than those generated by EPs, “electromagnets are less air-gap sensitive, meaning they hold better when parts are not flat.”

Setting up an electromagnetic workholding application takes just several minutes. “Again, one of the benefits of an electromagnetic chuck is you can turn your magnetism down,” Hayes said. “So you put the part on the face of the magnetic chuck, [adjust the] dial indicator, and as the workhead rotates, you can tap the part in and center it to where you want it. Obviously, while you’re dialing it in you want to be able to tap it around so you need lower holding power then. And once you have it dialed in, you crank up the power and you can do your grind.”

United Grinding integrates the electromagnetic chuck into its Studer controls; the two pieces of equipment, in effect, talk to each other, Hayes said. “For instance, if a chuck were to lose electrical supply or a part became loose, the machine would go into an E stop and retract. So the machine is always monitoring [an application]. When the machine is grinding, you cannot deactivate the magnetic chuck; it’s locked out. So even though we buy a controller, the magnetic chuck and the entire package from O.S. Walker, we integrate it into the machine so it becomes one. You cannot do a cycle start on the machine unless the chuck is energized; the two communicate back and forth, and that’s all part of our [own] safety links.” The ability to integrate the two pieces of equipment added to the Walker electromagnet’s appeal. “The big thing I would say about the chucks is that they allow a lot of flexibility,” Hayes said. CTE

Contributors

Alpha Workholding Solutions
(877) 217-6900
www.alphaworkholding.com

Cascade Corp.
(800) 227-2233
www.cascorp.com

Extrusion Dies Industries LLC
(715) 726-1201
www.extrusiondies.com

O.S. Walker
(508) 853-3232
www.walkermagnet.com

United Grinding Technologies
(937) 847-1214
www.grinding.com

Wen Technology Inc.
(919) 954-1004
www.wentechnology.com

Related Glossary Terms

  • broach

    broach

    Tapered tool, with a series of teeth of increasing length, that is pushed or pulled into a workpiece, successively removing small amounts of metal to enlarge a hole, slot or other opening to final size.

  • centers

    centers

    Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

  • chuck

    chuck

    Workholding device that affixes to a mill, lathe or drill-press spindle. It holds a tool or workpiece by one end, allowing it to be rotated. May also be fitted to the machine table to hold a workpiece. Two or more adjustable jaws actually hold the tool or part. May be actuated manually, pneumatically, hydraulically or electrically. See collet.

  • 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.

  • coolant

    coolant

    Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

  • cylindrical grinding

    cylindrical grinding

    Grinding operation in which the workpiece is rotated around a fixed axis while the grinding wheel is fed into the outside surface in controlled relation to the axis of rotation. The workpiece is usually cylindrical, but it may be tapered or curvilinear in profile. See centerless grinding; grinding.

  • extreme pressure additives ( EP)

    extreme pressure additives ( EP)

    Cutting-fluid additives (chlorine, sulfur or phosphorus compounds) that chemically react with the workpiece material to minimize chipwelding. Good for high-speed machining. See cutting fluid.

  • extrusion

    extrusion

    Conversion of an ingot or billet into lengths of uniform cross section by forcing metal to flow plastically through a die orifice.

  • flat ( screw flat)

    flat ( screw flat)

    Flat surface machined into the shank of a cutting tool for enhanced holding of the tool.

  • 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.

  • inner diameter ( ID)

    inner diameter ( ID)

    Dimension that defines the inside diameter of a cavity or hole. See OD, outer diameter.

  • machining center

    machining center

    CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.

  • magnetic chuck

    magnetic chuck

    Workholding device used on surface grinders and milling machines for holding ferrous parts with large, flat sides. Holding power may be provided by permanent magnets or by an electromagnetic system. See chuck.

  • 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.

  • outer diameter ( OD)

    outer diameter ( OD)

    Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.

  • sawing machine ( saw)

    sawing machine ( saw)

    Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).

  • tap

    tap

    Cylindrical tool that cuts internal threads and has flutes to remove chips and carry tapping fluid to the point of cut. Normally used on a drill press or tapping machine but also may be operated manually. See tapping.

  • turning

    turning

    Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

Author

Senior Editor

Daniel McCann is a former senior editor of Cutting Tool Engineering. Questions or comments may be directed to alanr@ctemedia.com.