A new technology that uses rapidly reversing magnetic pulses to relieve stress on metal may have applications for molds for the plastics industry. Don Debelak, vice president of marketing for Magnetic Processing Systems Inc. in Eden Prairie, Minn., said pulse magnetic technology uses the natural magnetism that exists in everything to relieve stress and lengthen the life of metal components. Current applications for PMT include cutting tools, drill bits, punch and stamping dies and finished goods such as gears, bearings and axles.
Specially designed magnetic pulses inside a small machine repeatedly magnetize a metal part in opposite directions. This causes the molecules to become active and shift, allowing defects in the steel structure to realign and correct themselves.
Treatment takes less than a minute and the result is a uniform atomic structure that is stronger and more resistant to chipping, cracking and fracturing, extending the life of a cutting tool by as much as three times, depending on the tool, the company said.
Elroy Bentz, owner of Bentz Tool Inc., a manufacturer of cutting tools in San Jose, Calif., said he uses the technology to treat all his cutting tools and is sold on its effectiveness.
``It doesn't reduce the wear factor, but it does help with the breakage problems,'' said Bentz, who performed his own test using PMT on various cutting tools to see what effect it had on tool life.
Bentz also treats all the cutters he regrinds with PMT, which he reports increases the useful life significantly.
Bentz said life extension of the tools varies from customer to customer, but his tools get an average of 10-15 percent longer life than cutting tools not treated. One of his customers reported the three-times-longer life, while others said they average a 20-30 percent longer life.
Metal parts or tools that have undergone heat treatment, grinding, machining or welding have experienced substantial improvement in fatigue life after PMT treatment, according to MPS.
Debelak said that although the machines being used in the treatment are stationary and can treat a part as large as 12 inches in diameter and of any length, development is under way on a hand-held unit to relieve stress in large injection molds.
David Barr, president of MPS, purchased the technology and equipment from Innovex Inc. in 1991. Since that time, he has refined the process, built larger machines and found new applications.
``Innovex had proven PMT works on small cutting tools, but we saw the opportunity to take the technology and extend it to higher-end products,'' Barr said. ``Instead of extending the life of a $25 drill bit, we'd rather extend the life of a $100,000 plastic injection mold.''
Typically, stress relief in molds is done through a heat process called annealing. However, said Debelak, annealing also can distort the mold because the entire mold must be heated. Taking the path of least resistance, PMT - a nonthermal process -just goes after those areas in the steel where there is a weakness or stress.
Because treatment time averages 42 seconds, as opposed to several hours for heat treatment, a molder or mold maker can reduce downtime.
The hand-held model, when it becomes available, will allow mold makers and molders to treat molds themselves without having to send the mold out for heat treating. Thus, the mold can be treated more often and the integrity of molded parts maintained.
A product also is being developed that will fit on a steel mold to relieve stress continuously during the molding process, Barr said.
Small cores and cavities can fit into the company's 12-inch-diameter machine at its service center, where it offers the treatment.
The firm also builds custom equipment for in-plant use.
Debelak said the company has more than 800 customers that use PMT in their operations in a variety of industries, including automotive, aerospace, appliance and machine tool.