A trend is forming toward the greater use of high-strength, low-alloy (HSLA) steel for component manufacturing due to the fact that the high strength can result in lighter parts. While that is certainly most beneficial from the product-engineering point of view, there are some process considerations that need to be taken into account lest the production of these components be, well, let’s say “seriously compromised.”
Pat Ontrop, who is currently director of Aftermarket Products for the Minster Machine Co. (Minster, OH), a renowned manufacturer of presses, points out some of the considerations that must be made vis-à-vis HSLA steel and the pressroom. Fundamentally, he explains, the issue with HSLA steel is that it magnifies or amplifies any issues that may have existed when processing a previous non-HSLA steel. Simply, the higher-strength material means there are higher, more concentrated loads under compression. This can cause problems with regard to such things as reverse loading or off-center situations during forming.
One way to address the higher strength is through the use of higher tonnage presses. At Minster, Ontrop says, they’re also taking a fundamental look at machine design, such that areas are being addressed in order to accommodate HSLA steel. For example, he says that previously, the deflection rating was based on the die covering (front/back, left/right) about two-thirds the bed area. Now, thanks to design modifications, it’s just one-half, yet higher loads are accommodated. Previously, he says, presses were designed to handle a snap-through (or reverse loading or breakthrough loading) of 10 to 20%. Now they can handle 40%.
Certainly, not all press shops are going to be getting new equipment. Yet they may be stamping HSLA steel—whether they realize it or not. So Ontrop has some recommendations for people in these facilities. For one thing, he thinks that it is essential that they have tonnage monitors on their equipment. Which brings him to the point of people receiving HSLA steel and not realizing it. He explains that sometimes steel is ordered with a “minimum yield strength of X.” The steel meets the minimum requirements. It is the right gage. But because it is conceivably an HSLA material, when the processing occurs, it could cause an overload situation. (He is also a proponent of die sensors, regardless of the type of steel being processed.) Another item that he recommends people think about is material straighteners. Generally, it is a situation where straighteners are just thought of with regard to material thickness. But he points out that when HSLA materials are on the doc, it is a good thing to spec that straightener in terms of both material thickness and tensile strength. Otherwise, that straightener may not be doing a whole lot of straightening.