Tool steels have historically been over-used for injection mold cores and cavities, simply because they've been both cheap and familiar. But soaring price tags on many tool steels, coupled with the push for more productive molding operations, is triggering an investigation of alternative mold construction materials. While not necessarily cheaper than steel on a price basis, these alternatives have thermal engineering or maintenance cost advantages that make them more attractive than ever. Copper alloys are one choice. They can speed the removal of heat from critical sections of the tool, potentially improving cycle times 20 to 50 percent and even improving the dimensional stability of the molded parts themselves. Look for more stainless steels, too. Stainless has always been the material of choice when molding acid-emitting resins, such as PVC. But now use of stainless is spreading, particularly for expensive tools, because corrosion-related maintenance efforts and costs are reduced through the life of the tool. Finally, important advances are also under development with aluminum mold materials, particularly in strength, surface hardness, corrosion resistance, and uniformity after heat treating (go to the Design News Materials Forum at http://rbi.ims.ca/4921-511 for more information). Here's a look at three recent mold materials that can serve as steel stand-ins:
Improved Stainless RoyAlloy is a new stainless mold-base steel, developed by Edro Specialty Steels, to overcome shortcomings associated with prehardened 420F (1.2085) stainless holder steels: a lack of toughness, unpredictable stability, inconsistent machinability and poor weldability. Edro says thermal treatments give the material improved dimensional stability after machining without the need for stress relieving. Simplified Plumbing The photo shows a MoldStar 90 beryllium-free copper alloy core for a 32-cavity mold running a polypropylene part used in a packaging application. "Because of the conductivity of the alloy, a water channel is cut only in the base of the core, in place of an intricate, small, water system normally needed had the material been tool steel," comments Cliff Moberg, president of Performance Alloys.
Molding Mounds MoldMAX V is a new copper-nickel-silicon-chrome alloy that has a hardness of 30 HRC and thermal conductivity approximately four to five times greater than P20 tool steel. The new grade is the second in a series of non-beryllium-copper alloys introduced by Brush Wellman. Moldmax XL is a copper-nickel-tin alloy with similar properties.
An envelope is a common packaging item, usually made of thin flat material. It is designed to contain a flat object, such as a letter or card.
Traditional envelopes are made from sheets of paper cut to one of three shapes: a rhombus, a short-arm cross, or a kite. These shapes allow for the creation of the envelope structure by folding the sheet sides around a central rectangular area. In this manner, a rectangle-faced enclosure is formed with an arrangement of four flaps on the reverse side.
Producing high-quality end-production metal parts with additive manufacturing for applications like aerospace and medical requires very tightly controlled processes and materials. New standards and guidelines for machines and processes, materials, and printed parts are underway from bodies such as ASTM International.
Engineers at the University of San Diego’s Jacobs School of Engineering have designed biobatteries on commercial tattoo paper, with an anode and cathode screen-printed on and modified to harvest energy from lactate in a person’s sweat.
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