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hp tooling 2020 #3

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  • Components
  • Processes
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  • Milling
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The journal of hp tooling is an english, global publication on all aspects of high precision tools, accessories and their applications.

processes Adhesive

processes Adhesive bonding: Opportunities for cutting tool manufacturers written by Michael Stroka, Thomas Götz and Andreas Gebhardt, Fraunhofer Institute for Manufacturing Engineering and Automation IPA Today, the German cutting tool industry, predominantly small and medium-sized enterprises (SMEs), faces multiple challenges. In order to continue to meet the customer requirements in terms of tool performance, sustainability and machining quality, new technologies must be taken into account. This helps to maintain market leadership in the competitive global environment. To encounter the challenges of producing high quality cutting tools with outstanding performance new technologies play a key role for the manufacturers. Within the framework of the project “Innovationsforum Zerspanwerkzeuge”, funded by the Federal Ministry of Education and Research (BMBF), suitable technologies and innovative solutions for SMEs were identified by the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. Alternative manufacturing methods for product and process optimization have to be considered in research and the development of new generations of cutting tools. Various types of cutting tool designs In the current state of technology, two different tool designs are used to manufacture milling tools. The cutting tool is on the one hand designed as a solid tool, in which the cutting part and the shank are machined (e.g. by grinding) from a monolithic cutting material (see figure 1a). On the other hand, a multi-part design is applied, in which figure 1, types of milling tools a) monolithic construction b) composite tool with bolted inserts c) composite tool with brazed inserts [Leuco AG] the shank is made from a tougher and cheaper base material and the cutting edges from a harder, more wear-resistant material (e.g. carbide, CBN). However, the latter procedure requires the two components to be joined together. The joint can be produced mechani cally by screwing or clamping (see figure 1b) or in a material-locking manner by soldering (see figure 1c) [Klocke and König 2007]. As regards end mills, the most common practice for providing a joint between the cutting edge and the base body is currently brazing at working temperatures of over 700° C. How ever, this restricts the selection of usable cutting materials. While some cutting materials are not suitable for a brazing process, others can be permanently damaged by high thermal stress [Stroka et al. 2018; Tigra GmbH 2018] such as diamond (PCD), which graphitizes at temperatures above 730° C [Tigra GmbH 2018]. In addition, high temperatures can lead to distortion of the cutting tools [Stroka et al. 2018]. Low-heat joining through the use of bonding technology Structural adhesives offer a competitive alternative to the established soldering process for the high-strength connection of cutting segments to tool bodies [Brand and Hustedt 2015; Stroka et al. 2018]. Bonding is a low-heat joining process using an adhesive. According to DIN 8593-8 (DIN 8593-8:2003-09) adhesives are non-metal materials which bond assembly parts by means of surface adhesion (adhesion through wetting and interlockability) and internal strength (cohesion through inter-molecular attraction). The functional principle of the adhesive bond is shown schematically in figure 2. A particular advantage of the joining process is the material independence of the joining partners, so that a large number of material combinations can be bonded with long-term stability, such as steel and carbide, PCD/CBN or cutting ceramics [Brockmann 2008; Luhn et al. 2012a; Moser et al. 2013]. Moreover, the low-heat joining process prevents changes in the microstructure and the formation of microcracks in the cutting material [Brockmann 2008]. Further adhesive applications in cutting tools can take other advantages like vibration dampening, corrosion protection or reduction of mass inertia due to lightweight construction [Doobe 2012]. In addition, the reworking costs for distortion and complex cleaning processes that arise during brazing are eliminated [Doobe 2012]. Given 24 no. 3, September 2020

processes cohesive power in the adhesive layer adherend 1 adhesive power between adhesive layer and substrate surface adherend 2 tion and im plement process control have to be taken into consideration when dimensioning the joint. To perform a high reproduction rate of the reachable joint strength automation processes are necessary. Otherwise, a failure in the bond could have a fatal impact both on the machine and its operator. An overview of the advantages and disadvantag es of adhesion technology is presented in table 1. figure 2 schematic representation of an adhesive bond [Habenicht 2009] the advantages mentioned above, such as the use of new cutting materials on circular blades (figure 3), the adhesive bonding technology could have a considerable impact on the cutting tool industry. table 1 advantages and disadvantages of adhesion technology [Habenicht 2009] advantages no thermally conditioned stress of the micro structure no thermally conditioned part deformation disadvantages surface preparation of the joining parts limited form stability under thermal loading However, the use of adhesives instead of brazing alloys also brings some disadvantages. The lower ther mal stability and the high effort to carry out surface preparafigure 3 different cutting materials on a circular saw blade possibility of joining different materials high dynamic stability; high vibration dampening accurate process control time influence of the whole procedure Current research in the field of the adhesive bonding of cutting tools Individual research projects have been carried out in recent years to prove the usability of adhesives for different cutting tool applications. tungsten carbide Darwish, for example, investigated the mechanical performance of bonded joints under thermal influence and the vibration dampening capability of milling tools with carbide tips and steel body. Bonded millers showed less wear, an improved surface roughness of the manufactured parts and only small differences in cutting forces. [Darwish and Davies 1989] Two funded projects in 2003 and 2007 (IGF no. 12792 N and 15028 N) used adhesives to join diamond-segments on circular blanks for stone-working applications. They also investigated optimized joint geometries with finite-element methods and developed a partially automated maintenance module. Moreover, successful cutting of granite was carried out. [Stehr et al. 2003; Stehr 2004; N.N. 2010] SiAlON-ceramic [Fraunhofer IPA, photographer Rainer Bez] Bonded saw bands for stone-working were investigated in the IGF project no. 17193 N and cutting trials were successfully performed. In this context, new joint geometries, capable adhesives and surface treatment were taken into account. [Kohl et al. 2014; Kohl et al. 2015; Schwarte 2015] no. 3, September 2020 25

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