Papers

ICMCTF1998 Session G5: Hard Coating Applications: Cutting, Forming and Autolubricated Tools

Thursday, April 30, 1998 8:30 AM in Room Town & Country

Thursday Morning

Start	Invited?	Item
8:30 AM		G5-1 A TiAlN Coating Texture Sets New Performance Standards H. Curtins (Platit Ltd., Switzerland); D. Franchi (Ferioli & Gianotti S.p.A., Italy); J. Rechberger (Vilab Ltd., Switzerland) For some niche applications multilayer alloy tool coatings have shown remarkable machining results. However in industrial use most of these coatings have failed to demonstrate reliable performance. Extensive development work with very discriminating testing programs has lead to a new family of Al-based alloy coatings. The novelty of these high performance coatings lies in their textured structure. With the Platit cathodic arc technology it has become possible to deposit multilayer alloy coatings with very specific crystallographically preferred structures. For TiAlN coatings for example a new structure with <311> texture has been achieved. This coating texture has become the key factor for outstanding tool performance. A very high level of reliability could be proved in, for example, difficult industrial deep hole drilling applications with restircted lubrication.
9:10 AM		G5-3 Wear and Cutting Performance of Coated Microdrills F.H.W. Loeffler (Institution, Germany) Drills with a diameter of less than 1.2 mm are used for a number of different applications in manufacturing of electronic parts. In industrial practice they are in a machine tool together with more than 2000 single drills of different diameter. For some machines it is not possible to change the numbers of turns for the individual diameters. So the cutting conditions are also different in these cases. The study describes the existing wear of coated and uncoated microdrills. The drills were coated by using different PVD techniques and various coating materials. The interpretation for the various behavior of the coated drills includes not only the materials but also the coating and cutting conditions.
9:30 AM		G5-4 PVD Hard Coating Applications Update D.T. Quinto, R. Wild (Balzers Limited, Liechtenstein) The wide acceptance of PVD hard coatings has now confirmed earlier predictions of their technological competitiveness relative to CVD coating and conventional surface treatment processes. Increasingly successful applications realized with new generation PVD-coated tools demonstrate the flexibility for tailoring the coating material design to particular metalcutting conditions. Multilayer PVD types -- of TiN, TiCN, TiAlN -- have been developed with the requisite microhardness and control of coating microstructure and internal stress state. Thus coated tool designs may address high speed cutting and dry machining demands. Beyond cutting tool applications, related PVD hard coatings i.e. CrC, CrN, WC/C, have improved the performance of molds, dies and punches in metalworking and plastic forming operations as well as precision components undergoing sliding wear. Industrial case studies illustrate these points and current technology limitations will also be discussed.
10:10 AM		G5-6 Failure Mechanisms of Multi- and Mono-layer PVD Coatings in Interrupted Cutting Processes K.-D. Bouzakis (University of Thessaloniki, Greece); N. Vidakis (University of Tehssaloniki, Greece); T. Leyendecker, G. Erkens, H.-G. Fuss, R. Wenke (CemeCon GmbH, Germany) The failure mechanisms of PVD coatings in interrupted cutting processes are comprehensively detected in this paper. The wear and the fatigue behaviour of multilayer and single coatings on high speed steel are investigated experimentally in milling and analytically through a Finite Elements Method (FEM) simulation of the cutting process. The initiation and progress of the tool failure is depicted through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) microspectral investigations of the used cutting edges. Furthermore the FEM simulation of the contact between the tool and the workpiece enables a quantitative description of the influence of mechanical and thermal stress components on the tool failure. Hereby, existing critical coating fatigue stresses and experimentally derived technological cutting data were considered.
10:30 AM		G5-7 Investigation of New Arc PVD Coatings in the System Ti-Hf-C-N E. Lugscheider, O. Knotek, H. Zimmermann, S. Stricker (Werkstoffwissenschaften, Germany) Present research work in machining determined by ecological and economical reasons is focussed on working without cooling and lubrication, high speed cutting (HSC), near net shape and hard maching. To achieve the desired aims in productivity and quality modern high performance machining tools as well as the adapted tooling machines and process parameters are necessary. Especially the machining of tempered or austenitic steels requires complex mechanical, thermal and tribological properties from the applied tools. Since conventional high speed steel or cemented carbide cutting materials often can not fulfill these high demands, new efficient cutting tools has to be developed. It was alrady proved, that coatings in the system Ti-Hf-C-N deposited with the arc PVD process are well suited for the demands of modern machining applications due to their special thermophysical properties. The deposition of quaternary coating systems requires a multiude of coating parameters to be optimized. In this study the influence of deposition parameters (e.g. bias voltage, reactive gas pressure, etc.) on the properties of the coatings were investigated. Especially the dependence of multilayer structures and different carbon carrier gases on the coating characteristics were examined. For the evaluation of the coating adhesion two test methods, the Rockwell-C test and the scratch test, were compared.
10:50 AM		G5-8 Crystalline Aluminum Oxide Layers on Steel Workpieces F. Fietzke (Frauenhofer Institut Elektronenstrahl- und Plasmatechnik, FEP, Germany); K. Goedicke (Frauenhofer Institut Elektronenstraho- und Plasmatechnik, FEP, Germany); T. Wuensche (Frauenhofer Institut Elektronenstrahl- und Plasmatechnik, FEP, Germany) Up to now crystalline aluminum oxide has found only a minor application as hard coating, despite of its outstanding properties like transparency, high hardness, low friction coefficient and chemical inertness. This fact can be explained by its problematic deposition conditions: either one uses CVD or PVD processes with a workpiece temperature of 1000^°C or one will obtain amorphous layers with unacceptable low hardness and chemical inertness. Beyond it the deposition rate is low. The introduction of reactive Pulse Magnetron Sputtering at medium frequencies (PMS) allows to overcome both application barriers for crystalline aluminum oxide layers. With Dual Magnetron Systems a long-term-stable process at a deposition rate of more than 10 microns per hour can be obtained. Additionally, caused by the high pulse plasma density, a key was found to deposit fully crystalline Al₂O₃ layers onto steel at relatively low temperatures. Presented in the paper are crystalline aluminum oxide layers deposited onto steel substrates using the PMS process at workpiece temperatures of 400 to 700^°C. Potential fields of application are discussed and economical calculations concerning the production costs and the attainable benefits are made.
11:10 AM		G5-9 A Hard and Soft Tool Coating Reaches Out for New Frontiers J. Rechberger (Vilab Ltd., Switzerland); D. Franchi (FERIOLI & GIANOTTI S.p.A., Italy); H. Curtins (Platit Ltd., Switzerland) Todays design and manufacturing trends push tools to new limits: Higher speeds and feeds, fewer machinining steps, reduced coolants and higher precision finish. Often unstable "go/no go" situations occur because the conventional tools are running at their limits. With todays newest tool coatings some of the traditional limits have been overcome. Especially the new generation of Al-based hard coatings with a textured structure in combination with soft solid lubricant tool coatings have produced astonishing results. A major area being the dry and semi dry machining for the automotive industry. In particular forming with extreme contact geometries and deep hole drilling. A reliable day to day production in these areas does not tolerate compromise solutions but requires a carefully tuned optimal hard and soft coating combination. In particular a well defined interface between hard and soft coating. Milestones on the industrial development path of such a new coating combination will be presented which includes validity aspects of traditional coating characterization tests.
11:30 AM		G5-10 Advanced Soft Tool Coatings and Their Complex Mechanisms of Operations J. Rechberger (Vilab Ltd., Switzerland); H. Curtins (Platit Ltd., Switzerland); D. Franchi (FERIOLI & GIANOTTI S.p.A., Italy) Soft lubricant based tool coatings have shown a tremendous impact on industrial mahcining and forming operations. Depending on the application field these modern coatings allow to drastically improve tool life, production speeds, workpiece surface finish, chip flow and environmental aspects. To a first approach most of these benefits have been attributed to the low coefficient of friction of these coatings. However, the vast experience with the soft tool coatings over the past seven years has brought many new aspects of these coatings into the picture including the important role of the interface. It has been recognized that the bulk properties of the coating alone do not play the key role. Particularly the traditional tribological model tests do not reflect coating performance on a tool. In some instances they are even contradicting and demonstrate the complexity of this new tool coating technology
11:50 AM		G5-11 Use of DLC Coatings in Lubrication Reduced Metal Forming K.H. Taube, T. Michler (Fraunhofer Institute for Surface Engineering and Thin Films, Germany) DLC coatings are well known for their high hardness and wear resistance. Their low values of dry friction coefficient against many metals and the minimum transfer of metals to the coating e. g. in ball on disk tests make them very interesting candidates for a large range of industrial applications. Therefor they have already found a rather broad application for force transmitting machine parts like bearings or gears. This work describes results from the use of DLC coatings in metal forming. Variations of carbon based coatings like pure DLC and metal containing DLC (MeC) coatings have been tested in stripe drawing, deep drawing, bending, punching and massive forming of steel and aluminum. By the use of DLC coated tools necessary amounts of lubricating agents can be significantly reduced, even with critical metals like stainless steel and aluminum. Nonlubricated deep drawing of stainless steel and clinching of aluminum was possible with optimized coatings. In lubrication reduced steel forming applications life time increases by a factor of two and more could be reached by pure, hard DLC. In certain cases, where especially an excellent adherence of the coating is needed, also MeC coatings have shown good results. In aluminum forming interestingly the less wear resistant pure DLC coatings showed the smallest tendency to cold welding. Methods for deposition of the coatings as RF PACVD for pure DLC and DC Magnetron reactive PVD for MeC are shortly described. Hardness, wear resistance and adhesion of the coatings are compared to their behavior under service. Conclusions for laboratory quality control for tool coatings are drawn.