Cutting Tools Users and applications should drive tool engineering
A survey – jointly conducted by the Fraunhofer Institute for Production Technology and the Laboratory for Machine Tools at Aachen University – outlines requirements for improving cutting technologies.
Manufacturers using cutting technologies are confronted every day with demands for shorter lead times and lower production costs while also maintaining or surpassing existing quality standards. This matters especially with respect to materials that are difficult to machine, since these are often key to the development of high-performance product innovations. Cutting tools for drilling, turning and milling are exposed to high thermal and mechanical loads in when used to machine high-temperature-resistant and extremely hard materials such as nickel-based and titanium alloys, titanium aluminides and powder-metallurgical steel. What results is short tool lifetimes, long processing times and the poor-quality workpiece surfaces.
The Fraunhofer Institute for Production Technology (IPT) and the Laboratory for Machine Tools and Production Engineering (WZL) of the RWTH Aachen jointly conducted a survey in response to this challenge. The survey asked about development trends in the toolmaking industry relating to drilling, turning and milling operations, and its results provide an overview of toolmaking from the perspective of manufacturing companies. The research institutes polled some 150 companies, most of them users of cutting technologies, tool manufacturers or coaters. Others manufactured machine tools, materials, clamping systems or other systems. With its focus on companies directly confronting the new issues relating to machining, the survey promotes future development in tool engineering from the tool user’s point of view.
Selecting the most appropriate tool for each machining task is vitally important for ongoing optimisation of cutting processes. The Fraunhofer IPT and WZL survey highlights, among other things, trends in development toward tool geometries and coatings tailored to the requirements of specific machining tasks, along with the importance of innovative cutting materials.
However, most companies reported that their own approach tended to be unsystematic. The selection process is rarely conducted methodically, and employee expertise is not always utilised or even documented. This can delay process design and result in substantial costs. When long-serving employees leave the company, they take considerable knowledge away with them. Most survey respondents thus felt that the need for standardisation of process- and tool-design methods and for information regarding optimised tool geometries and coatings was enormous (see chart).
The tool geometry selected exerts a decisive influence on tool life and on the properties of machined parts. Coordinating the rake and clearance angles or the cutting-edge chamfer with a milling tool, for example, can achieve a significant improvement in operational characteristics. However, it is vital to harmonise the tool’s macro- and microgeometry with the requirements of the pertinent machining task, since this is the only way to ensure reliable improvement in process performance. In order to draw qualified conclusions in this context, the Fraunhofer IPT is researching selection of optimal tool geometries for diverse machining tasks within the EU-funded QuickPro collaborative project.
Qualifying optimum conditions of cutting-tool application is pivotal particularly in regard to the tool’s substrate material and coatings. It is vital to ensure that the tool and its coating are tailored to each other when difficult-to-cut materials are being machined. This enables tool life to be prolonged and the machine tool to be used in applications with higher process parameters.
In industrial practice, however, users often encounter nonuniform or nontransparent coatings that fail to fulfil their potential for efficiency. Commonly, incorrect coating application is at fault. This can result in performance fluctuations that are difficult to explain. When coating properties are not tailored precisely to the application requirements, there is no reliable improvement in tool performance.
Several important questions then confront the user: What are the advantages of tool coating? Which coating is best suited, economically and technologically, to this application? How should the machining process be designed in order to exploit the coating’s full benefits? (Through the Fraunhofer Project Centre for Coatings in Manufacturing, the Fraunhofer IPT is researching the answers to these questions collaboratively with coating experts from the Centre for Research and Technology Hellas in Thessaloniki, Greece.)
Almost all of the surveyed companies regard new cooling-lubricant strategies as important for driving improvement in machining processes. This is because lubricant strategies achieve their full process-efficiency potential only when they are fine-tuned to meet perfectly the requirements of the cutting tools being used. The principle applies to dry machining, minimum-quantity lubrication (MQL), flood, and high-pressure cooling strategies, as well as to cryogenic cooling. (Survey respondents ranked these as the most important cooling strategies.) Each approach has specific advantages and disadvantages, which must be weighed carefully when selecting the appropriate strategy for the operation at hand, in order to optimise process performance and production costs.
As expected, around two-thirds of the companies questioned ranked robustness, operator-friendliness and flexibility as the most important selection criteria for process monitoring systems. Surprisingly, however, 50% of them could not envisage the ways modern process monitoring systems could help them check on the purity of the cooling lubricant or assess various tribological systems in terms of cooling-lubricant strategy or coating technology. Functions of this nature are always useful when difficult-to-machine new materials are involved.
Quite a few respondents (75%) did not wish to spend more than €10,000 on a process monitoring system. Most of them expressed a preference for the system to be integrated within the machine control system.
Tool qualification and development thus are regarded as pivotal factors in further optimising cutting technology, particularly in the case of machining difficult materials. In addition, adapting the cooling-lubricant strategy to harmonise with the tool specification is rapidly gaining in importance. Finally, process monitoring systems will become more important in process design and control. They must, however, be robust, user-friendly and flexible.