Laws of attraction: Drilling Performance

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.”