Taking the hard line

Responding to customer requirements for the machining of increasingly sophisticated materials, tooling companies are looking to improve the performance of their tooling products through an increasing dedication towards the research and development of new carbide grades, cutter body designs and innovative tool coatings in order to deliver both improved tool life and higher productivity.

These developments are now being seen in machine shops around the world and have transformed the ability of tungsten carbide tooling systems to machine a multitude of materials such as titanium and heat resistant super alloys (HRSA). In fact, materials like titanium, nickel alloys and heat resistant stainless steels were once considered exotic and difficult to machine, but are now almost commonplace. And although they demand the right tools and techniques, these materials can be machined more reliably and with far higher productivity than was previously imagined.

Ceratizit has taken the decision to focus on niche industry segments and specific components, such as turbine blades, titanium aircraft structural components and engine rings in heat resistant super alloys, with the purpose of fully understanding these processes by concentrating its development programmes so that it can match tools to the customer requirements.

According to Ceratizit UK's key account technical manager, Nathan Paxton, cooperation with the company's aerospace customers operates on several levels.

“Supported by industry specialists from our parent company, Ceratizit UK works closely with its aerospace key account partners to obtain a full understanding of their current and future needs as they relate to our areas of interest,” he begins. “Our most commercially successful products are developed to meet this broad understanding of typical industry needs. For example, the general view that titanium machining was of large and increasing importance led to the development of dedicated titanium milling grade and field tests with an early version using the then best available coating - a commercially available open market PVD coating. This then led us to develop a unique in-house CVD version with higher hardness and a smoother surface that gave improved performance for the current grade CTC5240.

“Often a customer will ask us to develop a tool to meet a specific application need and later these prove to have wider applications for other companies in the industry. For example our wing skin milling system was originally designed for Gardner Aerospace in Hull, whilst our HSC-11 high speed aluminium milling system was developed in response to another UK customer who wanted indexable insert tools to replace solid carbide for smaller diameters down to 16mm.”

Cutting through the barriers

With machining test facilities located at its Reutte-based research and development centre in the Austrian state of Tyrol, Ceratizit collaborates with specialist universities, such as Zwickau in Germany that help provide more ‘blue sky' testing to overcome many of the customer headaches associated with the machining of sophisticated materials. The company also has several joint projects running to develop semi-special titanium machining solutions that may in future become standard ranges.

Paxton says that typically, it's a combination of material type and complex part geometry that can provide the biggest technology hurdles that customers sometimes struggle to overcome.

“The first golden rule for machining materials like titanium and nickel alloys is to ensure optimum stability, i.e. the workpiece is securely clamped on a rigid machine using short tools,” he continues. “However, the reality is often thin-walled, complex parts that can't be held easily, as well as long tool extensions and 5-axis machining. Therefore, the entire process demands serious consideration in doing as much machining as possible with good stability and then taking great care of the later stages.

“The second golden rule is to carefully optimise the chip thickness. The cutting edges of indexable inserts are reinforced with a small radius to minimise edge chipping. The size of this radius is chosen based on the intended application in terms of material and chip thickness. When faced with poor stability, it's all too easy to reduce the feed rate to the point that the chip thickness is around or even less than the edge rounding of the insert. This can lead to disaster with massive heat generation, work hardening of the surface, premature insert failure and possible damage to the workpiece. As well as choosing particularly tough and heat resistant carbide, we have developed two geometries, F40 and M31, to offer a good compromise of smooth cutting with low cutting forces but a stable edge suitable for medium and rough milling on heat resistant materials.”

As the manufacturing sector becomes more diversified and materials start to migrate from more specialist areas like aerospace into the general engineering sector where companies may not be so familiar with machining them, Ceratizit says in-depth application knowledge enables it to gain a competitive advantage in delivering major productivity gains. At the same time, it also sees opportunities for cross fertilisation in tooling development between industries.

“The complex and unstable components, exacting specifications and high-tech materials typical of the aerospace industry create perhaps the greatest challenge for cutting tool manufactures,” states Paxton. “However with expensive and safety critical components and often hugely expensive machine tools it is often very hard to carry out production trials and this can create a conservative attitude. Especially once processes are established, the view is often that the cost of testing new tools, revalidating processes, components and changing paperwork cannot be justified by any potential improvements.

“In theory, there is the possibility of making radical changes in the early stages of a project, but often the reality is that suppliers and even methods are carried over from similar work done previously. The restrictions are much lower for rough machining processes, but even here, people are often reluctant to consider change. Generally, the greatest obstacle is in persuading a prospective new customer that major improvements are possible.”

Paxton contrasts this situation with that of the power generation industry: “Turbine blade production involves the machining of similar materials to the aerospace industry with similar challenges relating to component stability,” he concludes. “However, production quantities are much higher, individual costs are far lower and, of course, there is no question of changes jeopardising flight safety. With intense cost competition between plants, there is the opportunity and incentive to constantly try new tools and methods and push tools to the absolute performance limit.”

This gives companies like Ceratizit a clear advantage as it has a strong position in both the aerospace and power generation industries with which to build on its experience from the turbine blade industry for roughing and semi-finishing aerospace components.

www.ceratizit.com