One of the issues facing the moldmaker is choosing the right steel. In many cases the choice is made by the customer; however, in many other instances it is up to the moldmaker—Which alloy should I use? Which hardness? What about toughness?

Answers to these questions are often given by looking at the production process the molds are to be used in; the production material being handled by the mold, the lifetime requirements and many other factors. For example, the spray-formed steel allows for a better toughness, which creates the possibility for increasing hardness without compensation of toughness. But the moldmaker still needs to make the choice.

At this relatively early stage of spray-formed steel market penetration, the best suggestion is to contact some of the leading manufacturers for advice and help in selection of the right alloy and the right properties such as hardness and toughness.Another issue is machining. As spray-formed steel typically is harder and tougher than conventional steel, the machining processes can be more difficult.

At this relatively early stage of the spray-formed steel technology, it is hard to give general guidelines, but in a specific test case, machining costs were 25 percent higher than for conventional steel. However, in the same test case, the maintenance regrinding depth needed to refurbish the tools after use was only 0.1 mm for the spray-formed steel tool against 0.3 mm when using conventional steel. This is due to the more homogeneous structure of the spray-formed steel.

Spray-formed steel has been used in field tests as feed screws in extruding and injection molding processes.

At a German company extruding PA reinforced with 45 percent glass fibers, spray-formed steel containing 8.9 percent Vanadium was used for the screw elements. After the test period, the spray-formed steel showed 27 to 49 percent less wear compared to 10 percent Vanadium PM alloy used previously. This corresponds to 35 percent longer tool life. The PM alloy was already far better than traditional cast steel with respect to tool lifetime.

When longer screws are needed, spray-formed steel with a higher toughness is a better choice. In a field test at an American company, the alloy with 7.2 percent Vanadium mentioned above was tested against a 9 percent Vanadium PM alloy.

The test was carried out on feed screws used in an injection molding process for manufacturing plastic grinding wheels. The grinding wheels were made of a plastic reinforced with SiO2-particles. The feed screws were 50 to 80 mm in diameter and had a length of up to 2,500 mm.

After the test period, the spray-formed steel showed better lifetime figures than the 9 percent Vanadium PM alloy previously used. As a result, spray-formed steel is now being used as the standard steel for the feed screws at this American company.

As a final example, spray-formed steel was tested at an American company, which uses a small mold for steel powder compaction in order to produce a part used in the automotive industry.

Using spray-formed steel with 8.9 percent Vanadium for the mold, 10 to 15,000 parts could be produced before the mold had to be taken out for regrinding due to wear. This contrasts vastly to the traditional cemented carbide used previously, where only three to 4,000 parts could be produced before maintenance regrinding was needed. The failure mechanism in this case was both chipping and wear. As an additional benefit to the moldmaker and the mold repair shop, machining turned out to be easier and the spray-formed steel mold was more easily polished than the traditional one.

Even at this early stage of spray-formed steel market penetration, a vast number of tests have proven that molds and tools made of spray-formed steel last longer and are more resistant to wear—meaning less costs due to fewer renewal tool purchases, fewer tool change operations due to wear, less tool renewal production downtime, less maintenance grinding and less maintenance costs.

For the moldmaker, the steel shows excellent properties for mold construction and mold maintenance, even though machining in some cases may be more difficult. The biggest issue, however, is that the spray-formed steel is new to the moldmaker, so the best recommendation is to learn much more about this material of the future.