How traditional HSS tools meet the needs of today

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.

Cutting tools made from High Speed Steel (HSS) are witnessing a level of growth around the world which shows no signs of slowing down with the global market for HSS cutting tools expected to grow to more than USD 10 billion by 20201

This is a significant amount, especially when the current global market for the entire cutting tools industry is valued at around USD 18.5 billion. The increase is supported by a steady demand from key segments, such as automotive and construction, as well as heavy electrical and industrial equipment.

A POPULAR OPTION

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. This 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 (HSS), 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.

HSS COMPOSITION

A typical HSS composition features chromium (four percent), tungsten (approx. six percent), molybdenum (up to 10 percent), vanadium (around two percent), cobalt (up to nine percent) and carbon (one percent). 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 five to eight per cent more cobalt to HSS improves strength and wear resistance.

Typically, drills made with the addition of more cobalt are used in application specific operations.

ADVANTAGES

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 unique strength of High Speed Steels, 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, 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 tools.

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.

COATINGS AND SUBSTRATES

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 helps reduce chipping problems.

The most recent application of this powdered metallurgy technology is in Dormer’s Shark Line taps. They are manufactured from a HSS-E-PM substrate, specifically developed for taps to give the additional toughness required, consistently stable properties and superior grind-ability 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 Aluminum 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.

SUMMARY

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 market place against younger and more technically advanced materials.

If anything, HSS has over the 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 metal cutting industry. The cutting tool industry has always been a competitive landscape and HSS remains a key component to offering customers what has always been an essential requirement: choice.