Mold makers complain that mold steel has not kept up with advances in machining technology. Translate that to mean the latest and greatest computer numerically controlled milling machines can cut steel at a faster rate than the steel's properties will allow and still hold toler-ances. ``What [mold makers] would like is steel as hard as diamond, but [that] machines like aluminum,'' said Roy Hindle, marketing support manager for Uddeholm, a steel manufacturer in Rolling Meadows, Ill.
This concern stems largely from the fact that mold steel represents only 4-6 percent of the total cost of the mold, while machining time represents 60-65 percent of the total cost. The balance of the cost is design engineering.
Development of new mold steels has been relatively slow because the steel market is a conservative one, Hindle said.
``People, both mold makers and tooling engineers for [original equipment manufacturers], are reluctant to make changes as far as mold steels are concerned,'' he added.
Dennis Nowack, marketing director for Crucible Service Centers in Camillus, N.Y., agreed.
``Mold designers stick with what they know,'' he said. ``If they're used to P-20, they'll stick with P-20 because they know it, know what it will do and how it will act.''
He also said that perhaps the industry is too conservative.
``Our big task as a quality steel supplier is to try to be ahead of the game,'' Nowack said, ``to have the types of materials available that meet the changing requirements of both the OEM and the mold maker.''
Sometimes those involve two opposing forces.
``Demands of the mold makers and the end user of the mold are often different, and in some cases even contradictory,'' Hindle said. ``It's tough to satisfy both.''
Mold makers typically want to use a steel that machines fast and accurately, and can be welded and polished easily so that no witness lines show on the molded parts. Molders and OEMs often want the hardest, longest-lasting steel that resists abrasion and chemicals. There still is a reluctance among some mold makers to use stainless steel, primarily because it is not the easiest to machine.
Although there have been few true breakthroughs in mold steel, some steels use additives to create alloys that offer differing properties to suit specific requirements, said Dick Christopher, vice president of marketing for D-M-E Co. in Madison Heights, Mich.
``The most important thing we can do for steels is cut down on the amount of contaminants in the material and eliminate hard and soft spots,'' Christopher said.
Several of those interviewed pointed out that NAK 55 is probably the newest attempt to produce a steel that allows for ``free machining'' while maintaining hardness.
NAK 55 is an age-hardened steel produced by Daido Steel in Nagoya, Japan, and imported and distributed in the United States by International Mold Steel Inc. in Erlanger, Ky.
Thomas Schade, vice president and general manager of International Mold Steel, said NAK 55 is known for its stability and ability to hold tight toler-ances while machining as much as 50 percent faster than P-20, with a Rockwell hardness factor of 40.
Ion nitriding of NAK 55 produces a material of 62 Rockwell hardness, which is harder than SS 420 and has improved corrosion resistance.
Roland Krevitt, tooling engineer for Apple Computer Inc. in Cupertino, Calif., said he specifies NAK 55 for many of that company's tools. Its sulfur content makes the material good for free machining and it textures better than alternative steels, he said.
The newest development in steel, produced and patented by Sinto Ltd. in Nagoya, Japan, and sold by International Mold Steel, is Porcerax II, a porous stainless steel that ``breathes.'' Schade said it offers a new solution to difficult gas venting problems by actually allowing the gas to escape through the walls of the mold itself.
Schade said the material is excellent for parts that need venting in hard-to-vent areas, and allows the mold to run at a reduced injection pressure, which cuts down wear on the mold.
The material is a powdered sintered metal that is 25 percent air by volume, but machines much like SS 420. After machining, the surface is polished to reopen the holes.
Krevitt said he understands the reluctance of mold makers or original equipment manufacturers to use a new tool steel. When Krevitt first was introduced to PX5, another steel from Daido, he was working on a major new-product development program with a computer company in Taiwan for Apple.
Krevitt was given a sample of the material to test-machine and weld. After the test, Krevitt said, he found the toughness to be far better than that of P-20. The material's weldability without preheating or post-heating was a tremendous advantage.
``But to go from a sample to a $1.5 million tooling program is quite a leap,'' he said.
He admittedly was nervous about committing the program to a new steel. ``But, I love being a pioneer,'' and it worked out well, Krevitt said.
