According to industry sources, the global market for high speed steel (HSS) cutting tools is expected to grow to more than $10 billion by 2020. Ricky Payling, product strategy manager for round tools at Dormer Pramet, looks at why HSS remains a popular option, the different compositions available and how the material has adapted to a fast-changing industry.
Despite the growing competition from solid carbide, HSS continues to be popular with manufacturers due to its high wear resistance and excellent hardness and toughness properties. HSS cutting tools are best suited to mass production environments where tool life, versatility, productivity and tool cost are of the highest importance to an end-user. It therefore still has a major part to play in efficient and reliable machining of many components.
Also, the current focus for a good product quality, which meets the customer application requirements at a cost-effective price, is proving attractive in the present global economic climate.
To support the growing worldwide demand for HSS, cutting tool manufacturers have committed extensive resources to this segment. This includes increased investment in not just new product development but also research and development activities, which has led to HSS tools becoming more reliable with a reduction in the number of defects, lower production costs and shorter lead-times. The addition of improved substrates, including powder metallurgy and coatings have been instrumental in further enhancing performance.
Across Dormer’s range of round tools, there are currently four different material types available; high speed steel, high speed cobalt (HSS-E), high speed steel/carbide (HSS HM) and HSS-E powder metallurgy steel (HSS-E PM). These materials are used across our assortment of drills, countersinks, reamers, taps and milling cutters.
A typical HSS composition features chromium (4%), tungsten (approx. 6%), molybdenum (up to 10%), vanadium (around 2%), cobalt (up to 9%) and carbon (1%). The different grade types depend on the varying levels of elements added.
Chromium improves hardenability and prevents scaling. Tungsten offers greater cutting efficiency and resistance to tempering, as well as improved hardness and high temperature strength. Molybdenum – a by-product of copper and tungsten production – also improves cutting efficiency and hardness, as well as resistance to tempering. Vanadium, which is present in many minerals, forms very hard carbides for good abrasive wear resistance, increases high temperature wear resistance and strength, as well as retention of hardness.
Cobalt improves heat resistance, retention of hardness and slightly improves heat conductivity, while carbon, increases wear resistance and is responsible for the basic hardness (approximately 62-65 Rc). The addition of 5-8% more cobalt to HSS improves strength and wear resistance. Typically, drills made with the addition of more cobalt are used in application specific operations.
HSS tools can resist vibrations, whatever the type of machine tool, even if rigidity has been lost over time and regardless of workpiece clamping conditions. It can prevent mechanical shocks at tooth level in milling operations and cope with varying lubrication conditions which may result in thermal changes.
Also, thanks to the inherent strength of HSS, tool manufacturers can produce extremely sharp cutting edges. This make it easier to machine difficult materials, offers less work hardening of austenitic stainless steels and nickel alloys, and gives a better surface quality and tolerances of machined parts.
As the metal is cut and not torn, it provides longer tool life with lower cutting-edge temperatures. It also requires lower cutting forces, which ultimately means less power consumption from the machine tool. From a tool life point of view, HSS performs very well with intermittent cutting applications – however, it has limited cutting speed range which is far lower when compared to carbide tools.
HSS may be an established cutting tool material, but it does not mean it has not been subject to constant development and improvements since it was first used back in the late 19th century. Dormer Pramet’s range of HSS substrates, for example, is anything but outdated. We have invested in powder technology to develop a material that provides better results.
HSS-E with powder metallurgy offers a higher content of alloy elements and a combination of unique properties to improve toughness, wear resistance and hardness. Using HSS-E-PM prolongs tool life, makes it more predictable, improves feed and speed performance, as well as helping to reduce chipping problems.
The most recent application of this powdered metallurgy technology is in Dormer’s Shark Line taps which are manufactured from a HSS-E-PM substrate specifically developed for taps to give the additional toughness required, consistently stable properties and superior grindability compared to conventional high-speed steels. These improved characteristics mean the taps have a more predictable and assured life.
Also, HSS-E and HSS-E-PM are excellent substrates for a variety of coatings, such as titanium nitride (TiN), titanium aluminium nitride (TiAlN), titanium carbon-nitride (TiCN), as well as multilayer coatings.
Coatings considerably improve tool life and further boost the performance of HSS tools in environments where productivity and speed and feed rates are high, as well as in dry operations and for machining of difficult materials.
They offer increased surface hardness for higher wear resistance, reduced friction for better chip creation, reduce cutting forces and less heat generation, crater wear resistance and improved surface quality of finished parts. TiAlN-coated HSS-E cutting tools, for example, are highly suited to dry machining of cast iron as this helps resist high temperatures, while TiAlN coated HSS-E-PM tools are suitable for the machining of titanium and nickel alloys.
In an age where users require reliable, consistent, versatile tools at a cost-effective price, high speed steel is still the ideal choice for many applications. As such, it can still hold its own in the marketplace against younger and more technically advanced materials.
If anything, HSS has over many years become stronger by adapting itself with new coatings, adjusting its composition and adding new technology, all helping to retain its position as a vital material in the metalcutting industry.
The cutting tool sector industry has always been a competitive landscape and HSS remains a key component to offering customers what has always been an essential requirement: choice.
An example of a real-world application comes with Dormer’s A553 high speed cobalt (HSS-E) drill, which has become a key component for a Swedish manufacturer.
Larssons Mechanical Workshop, founded in 1951, manufactures subcontracted metal products, as well as processing and assembly support for a wide range of industries. One particular job involved the machining of thousands of holes in its packaging machine rollers made from 2346 and 2333 stainless steel.
A 12mm diameter A553 drill – which features a TiAlN top coating and internal coolant – is used to drill thousands of holes to depths of up to 70mm, which equates to 70-75m of drilling.
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For Larssons, HSS is the preferred option as CNC operator, Gunnar Wistrand explains: “It is flexible drill that, unlike a carbide drill, is more forgiving if something happens. Another safety advantage of the A553 is that we can leave the machine without risk of failure.”
In this respect, the advantages far outweigh the disadvantages as Mr Wistrand confirms: “Utilising the A553, it takes an extra 30 seconds for each reel to be produced. However, the process is more predictable and changeover time is greatly reduced.
“The extra time it would take to change tools would cost us far more. Not changing the tool as frequently also eliminates any safety concerns associated this process.”
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