Stainless steel: doubling milling speeds
Last year alone, according to estimates by the International Stainless Steel Forum (ISSF), more than 24 million tonnes of stainless steel were produced worldwide. Additionally, its proportion of the total steel production of 1.22 billion tonnes is steadily rising. Steel alloys of this kind are used for many different applications in very different industries as a result of their extreme corrosion resistance. When it comes to machining, however, the challenge always remains the same: these alloys subject tools to extreme stresses and strains. At the company ABZ Terodde in Bocholt, for example, large numbers of machine components are manufactured from stainless steel. LMT experts recently achieved a spectacular reduction in the company’s machining times for a pump housing using LMT Fette face milling cutters.
“Stainless steel is a challenge,” confirms Carsten Wegner, application engineer for cutting tools at LMT Fette. “Performance indicators that have a major influence on machines’ productivity, such as cutting speed and feed per tooth, frequently suffer when they come up against the alloy. As a result, many users are constantly on the lookout for new tool solutions,” says Wegner. Of course, the reasons for the extreme strain on these tools are found in the material properties of the stainless steel:
• Surface hardening can occur in many stainless steels during machining. Using the wrong tool can even lead to an extreme increase in the material’s hardness.
• Compared to other kinds of steel, stainless steels are generally worse at conducting the heat generated by the machining process. As a result, very high temperatures can build up on the tool’s cutting edge – with all the familiar disadvantages for tool life.
• Stainless steel’s high viscosity can also lead to an increase in torque during machining, which in turn increases the strain on the cutting tool.
- LMT Fette MultiEdge VA FMV45 face milling cutter
Dissatisfied with existing tools
This extremely demanding material is frequently used at ABZ Terodde. The small privately owned company in Bocholt produces components for the mechanical engineering industry. It manufactures parts for offshore wind turbines and production equipment used in the chemical industry. The reliability and durability of these components is especially important. For example, ABZ Terodde manufactures housings for a pump used to transport corrosive liquids and they are made of stainless steel, since it is best suited to coping with the extreme material stress. The production planners at ABZ Terodde used to deploy a 80-millimetre-diameter cutter to machine the housing. However, it could only achieve cutting speeds of 200 metres per minute (795 revolutions per minute). For a tool with eight teeth and a teeth feed of roughly 0.1 millimetres, this meant a feed rate of just 600 millimetres per minute. “Our customer just couldn’t be satisfied with these performance figures,” says Wegner.
As a result, LMT Fette machining experts recommended a machining strategy that eventually produced a real quantum leap in performance. It revolved around the LMT Fette MultiEdge VA FMV45 face milling cutter with an 80-millimetre diameter, equipped with indexable inserts made of LC440T cutting material. “Of course, we know the properties of the tool and the cutting material very precisely and therefore recommended that our partners at ABZ Terodde dramatically change the cutting parameters. The cutting speed was increased to 250 metres a minute and tooth feed to 0.22 millimetres. That meant a feed of 1,313 millimetres per minute with the MultiEdge’s six teeth. In a nutshell, it was possible to more than double the feed rate,” explains Wegner. These are incredible results, which far surpass those of the previous tool. It is therefore no surprise that the improved output immediately convinced the customer: “Overall, the machining involved in the production of a pump housing is now completed twice as fast and our cutting system has doubled the life distance of the tools used,” LMT Tool System team member Ralf Funke sums up the result.
Component quality without finishing
How do we explain the tool’s incredible performance? “From the very outset, application engineers, external sales staff and tool developers at LMT Fette worked closely together on the development of the MultiEdge. The experiences of our customers flowed directly into the design itself. Additionally, we have decades of experience of developing high-performance tools,” says Wegner. The result of this close collaboration is now becoming apparent in specific details. On one hand, the LMT developers have further optimized the areas of contact between the tool’s base plate and indexable inserts, which has significantly improved the stability of the indexable inserts. On the other hand, the new indexable inserts perform impressively as a result of a soft cutting action, which has substantially reduced noise.