Papers

ICMCTF2005 Session G4/E5: Coatings for Cutting and Forming Tools, and Green Manufacturing Applications

Monday, May 2, 2005 10:30 AM in Room Royal Palm 1-3

Monday Morning

Start	Invited?	Item
10:30 AM		G4/E5-1 About the Pulsed Sputtering Technology to Apply Advanced Tribological Coatings to High Precision Bearing Components G. Erkens, R. Cremer, T. Rasa (CemeCon AG, Germany); G. Spachtholz, Ch. Brecher (WZL University of Aachen, Germany) Pulsed DC sputtering processes and mid frequency plasmas are gaining increasing attention in a wide range of different application. Innovative PVD coatings deposited with these technologies led to a significant reduction of wear and friction and to a tremendous increase in performance of modern cutting tools and highly loaded components. High precision bearings represent a class of such components. The demands on e.g. spindle bearing systems are increasing as the performances of innovative cutting machines increase. A component in general has to be coated if the given material and surface can not stand the increasing external loads in modern machines. This is also valid for hybrid bearings as the weak part still remains the steel race. Plasma enhanced sputtering by means of pulsed DC also in combination with mf PACVD leads to nano-structured coatings with high adhesion and best surface finish even at low deposition temperatures on various substrate materials. The pulsed process technique to apply nano-structured and graded carbon based tribological coatings on functional surfaces at low temperature will be illustrated. The high performance tribological coatings and the properties will be presented with respect to the increasing demands of modern components, machine parts and in particular of high precision bearings.
10:50 AM		G4/E5-2 Multi-Functional Multi-Component PVD Coatings for Cutting Tools M. Kathrein (CERATIZIT Austria GmbH, Austria); C. Michotte, M. Penoy (CERATIZIT Luxembourg S.a.r.l., Luxembourg); P. Polcik (PLANSEE Ag, Austria); C. Mitterer (University of Leoben, Austria) Highly wear resistant PVD coatings are well established in cutting operations. Further efforts to improve the cutting performance need to be focused on all relevant wear mechanisms. Thus, the relevant objectives are an enhancement of the abrasive wear resistance, toughness, oxidation resistance, and the reduction of friction. The aim of this work was to investigate properties and cutting performance of new multi-functional multi-component PVD coatings based on Ti_1-xAl_xN applied to cutting tools. A commercial PVD unit was used to deposit coatings from powder metallurgically prepared multi-component targets. Coating structure and chemical composition were characterized using scanning electron microscopy (SEM), wavelength-dispersive electron probe microanalysis (EPMA), glow discharge optical spectrometry (GDOS) and X-ray diffraction (XRD). Coating hardness and tribological properties were evaluated by Vickers micro-indentation, ball-on-disc tribometer and cutting tests. The results show a remarkable influence of additional elements in these Ti_1-xAl_xN coatings on the properties. An example of a complex alloyed multi-functional coating is shown in detail. Alloying with elements like V resulted in a significantly increased lifetime in various cutting applications. Furthermore, the advantages and restrictions of powder metallurgically produced multi-component targets for sputter- and arc-PVD processes are demonstrated.
11:10 AM		G4/E5-3 CVD Diamond Tool Performance in Metal Matrix Composite Machining Y.K. Chou, J. Liu (University of Alabama) Metal matrix composites (MMC) have found steadily increasing applications in the industry such as automotive. MMC is considered as one of difficult-to-machine materials due to rapid tool wear, high cutting temperatures, and inconsistent part quality, etc. Because of abrasive nature of the reinforced phase in MMC, diamond tools are the only candidates suitable for MMC machining. Due to its lower cost and flexible in shape, diamond coatings have been widely used to replace polycrystalline diamond tools. MMC machining by diamond coated tools is still full of open questions, pertaining to assessment of machining and thermal aspects. In this study, commercial CVD diamond tools, ~30 microns thick, on tungsten carbide substrates, were evaluated by outside diameter turning of aluminum-matrix composite bars (A359 with 15% SiC particles). Cutting conditions ranged from 2 to 6 m/s of cutting speed and 0.05 to 0.2 mm/rev feed, and a 2 mm depth of cut. Tool wear and part surface finish were analyzed for the tool performance study. Cutting forces and chip-tool contact area were measured for the cutting tool temperature analysis, by finite element simulation. Cutting temperatures were also acquired to validate the thermal model. The results show that tool wear is rather sensitive to the cutting speed and the dominant wear feature is detaching of the diamond film on the flank wear-land surface, after some steady wear. The delaminated structures on the worn surface suggested the bonding is critical to tool performance. On the other hand, the cutting temperature seems to have a decisive effect on the coating detaching process and thus tool performance. A thermal management device, heat-pipe, has been used to alleviate cutting temperatures in CVD diamond machining of composite. The preliminary results promise remarkable tool wear reduction, also tool temperature decreasing confirmed by thermal analysis and verified by tool temperature measurements.
11:30 AM		G4/E5-4 Non-Stick Coatings in Polymer Processing P. Navabpour (Loughborough University, United Kingdom); D.G. Teer (Teer Coatings Ltd., United Kingdom); D.J. Hitt, M. Gilbert (Loughborough University, United Kingdom) Processing of polymers involves physical contact between polymer and metal tools during various stages such as mixing and moulding. A major problem during polymer processing is the adhesion of polymer and/or its additives to tools. Various factors can influence adhesion. These include processing conditions (e.g. temperature, shear rate); composition and crystal structure of the tool surface material; surface energy and surface roughness. Surface properties of the tools used in polymer processing can be modified by coating low surface energy materials on the surface in order to reduce adhesion. This work presents an investigation in the application of physical vapour deposition (PVD) coatings for reducing adhesion of polymers to tools. Several coatings were prepared onto stainless steel sheets using the PVD process. The crystal structure and surface energy of the coatings were analysed using X-ray diffraction and by measuring contact angles, respectively. Adhesion of a number of thermoplastic and thermosetting polymers against the coated surfaces was evaluated. Specimens for adhesion studies were prepared by compression moulding of polymer onto coated steel sheets. The stress required for separating the polymer from the coated surface and the amount of residue on the surface after separation of polymer were used to indicate the effectiveness of coating in reducing adhesion. A study of the relationships between adhesion and coating characteristics was then carried out.
11:50 AM		G4/E5-5 Cutting Performance Improvement Through Micro-Blasting on Well-Adherent PVD Films on Cemented Carbides Inserts K.-D. Bouzakis (Aristoteles University of Thessaloniki, Greece); G. Skordaris, I. Mirisidis, N. Michailidis (Laboratory for Machine Tools and Manufacturing Engineering, Greece); G. Erkens (CemeCon AG, Germany) Through micro-blasting on cemented carbides substrates, a cutting performance improvement can be achieved, mainly due to coating adhesion enhancement. On the other hand micro-blasting directly on PVD-coatings, under certain circumstances, may also lead to a further impressive tool life increasing. The objective of the described investigations was to detect optimum substrate and PVD-film mechanical treatment combinations, enabling a cutting performance enhancement of the coated tools. The coating and substrate strength properties modifications due to micro-blasting were determined by means of a finite element methods (FEM) supported evaluation of nanoindentation measurements results. Moreover, the alterations of substrate and coating surface macro and micro-topomorphies, induced by micro-blasting were registered and evaluated. The obtained roughness characteristics can be associated to the holding strength of the individual carbide grains by the Co-binder and to the film adhesion. The latter was characterized by means of the inclined impact test, which enables the determination of the coating removal propagation, when vertical and tangential loads on the film surface are simultaneously exercised. The cutting performance of the applied inserts was checked systematically in milling. The related experimental results were elucidated by means of the FEM simulation of the cutting process, enabling the consideration of graded coating and substrate strength properties as well as film adhesion alterations, due to substrate surface tompomorphy modifications. The investigations showed that a significant tool life enlargement can be achieved through the conduction of micro-blasting on coatings, deposited on substrates with optimized roughness.
12:10 PM		G4/E5-6 Performance of Low Friction Coatings in the Dry Drilling of Automotive Al-Si Alloys N. Wain (University of Warwick, United Kingdom); N.R. Thomas, S. Hickman (Teer Coatings Ltd., United Kingdom); J. Wallbank (University of Warwick, United Kingdom); D.G. Teer (Teer Coatings Ltd., United Kingdom) Due to the high financial and environmental cost of cutting fluids, there is a considerable driving force in many machining industries for a reduction in their use. However, any such reduction will be commercially acceptable only if the overall performance of machining operations can be maintained in dry conditions. This might be achieved through the use of low-friction coatings on cutting tools. TiB₂-based coatings have been promoted as effective in improving the performance of tools used to machine Al alloys¹. In this work such coatings were deposited on high-speed steel drills by closed-field unbalanced magnetron sputter ion plating. Further drills were coated with low-friction Graphit-iC^TM, Dymon-iC^TM or MoST^TM coatings, and others left uncoated. These were tested in the dry drilling of automotive Al-Si alloys. The measured performance criteria were the tool lifetime and the dimensional accuracy of the drilled hole. End-of-tool-life in most cases was brought about by blockage of the drill flutes with adherent Al. Results show that, while all the coatings offer significant improvements over uncoated tools, exceptional results were achieved using the Graphit-iC^TM coating. When compared to TiB₂-coated tools in air-cooled conditions this coating improved tool life by over 400% and reduced the number of undersized holes by a similar amount. EDX analysis of used tools revealed that the coatings survived intact; therefore the improvements in performance are probably due to the reduced adhesion between the coatings and the aluminium. ¹ Berger, M., et al., Surface and Coatings Technology 149, 14-20 (2002).