Hard and Hybrid Coatings: Cutting, Forming, Autolubricated Tools and Machine Parts

Friday, April 14, 2000 1:30 PM in Room Town & Country

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1:30 PM G4-2-1 Oxidation Characteristics and Technical Properties of Chromium-based PVD-hardcoatings for use in Semisolid Forming Tools
Th. Hornig, E. Lugscheider, K. Bobzin, St. Bärwulf (University of Technology Aachen, Germany)
Dies for SSM-forming suffer from multiple combinations of wear mechanisms. The modes of wear are similar to that occuring at tools for pressure die casting. One of the most important problems for semisolid processes with Aluminum is the sticking of the produced components in the die. Chromium based PVD-coatings are found to give satisfying solutions for pressure die casting tools. Their coefficients of thermal expanse are matched to those of tool steels as well as they form stable oxide scales protecting against surface interaction with the molten metal. The paper presents the effect of oxidation as a concrete mean for reducing the sticking of Aluminum on tools surfaces. Therefore hardcoatings of CrC, CrN and CrAlN were characterized in their oxidation behavior and their thermal shock resistance. The surface energies of differently oxidized specimens were measured and set into relation to the oxidation atmosphere. Clear correlations between the oxidation state and the surface energies were found. It will be shown that the stresses in the films were also influenced by the state of oxidation. The course of oxidation was investigated by in-situ XRD-measurements in grazing incidence modification. Finally the technological performance of the coatings was tested by high temperature wear tests and impact testing. The oxide scale was found to have a strong influence on the technical performance especially against wear at high temperatures.
1:50 PM G4-2-2 Towards a New Generation of Coated Hobs
F. Rabezzana (Metec Technologies, Italy); H. Berndt, B. Zorn (Saazor Wälztechnik, Germany); G. Vergnano (Fratelli Vergnano, Italy); D. Franchi (Ferioli & Gianotti, Italy); J. Kohlemainen (Diarc, Finland); F. Curtins (Blösch AG, Switzerland); C. Banvoy (PSA Peugeot Citroen, France); J. Picot (ENSAM); C. Rech, M.A. Djouadi (ENSAM, France); A. Rozen, E. Bergmann (Geneva School of Engineering, Switzerland); A. Guglielmo (ILM-CNR)
Hobs had been technology leaders for the introduction of PVD coatings on tools. They play this role again in the current technology shift to dry cutting. Different combinations of hard coatings and selflubricating coatings have been tested on segmented hobs produced from M23 and integral hobs made from ASP 23. Two laboratory cutting tests - grooving with a flywheel and face milling of a slab with a hob and a field test were compared The field test was a consecutive roughing and finishing operation on the gear of the secondary axle of a passenger car gear box. Most coatings were combinations of commercially available hard and selflubricating coatings: TiN, TiCxN1-x, TixAl1-xN, MoS2, CrC/C and amorphous diamond. They were compared with the newly developped coatings c-MoxTi1-xN, and composites based on bichalcogenides. Coating composition, structure, morphology, thickness and adhesion were measured with standard methods prior to the trials. The mechanical properties of the bichalcogenide composites were further investigated by nanoindentation with differential loading. The differences of the 3 machining operations and the impact of these differnces on the rating of the coatings are discussed. The relation of these rankings with the mechanical and tribological properties of the coatings is analysed qualitatively.
2:10 PM G4-2-3 Application of Hard Coatings to Gear Hobbing : Elaboration of Tests Procedure and Wear Mechanism Analysis in Field Tests
J. Rech, M.A. Djouadi, J. Picot (ENSAM, France); A. Guglielmo (ILM-CNR, France)
Coating technology is one means of achieving a crucial enhancement in tool performance especially in hobs that had been the first tools to be coated in a big scale. Nevertheless no deep analysis of wear mechanism have been done on field machines. The bifunctional coatings : combinaison of a tough hard and refractory coatings with a self lubricant coating with a good thermochemical and abrasion resistance but a lower hardness are very interesting since it's difficult to get a simple coating having all these characteristics. The use of bilayers raises several problems, so, in order to investigate the behaviour of these bifunctional coatings hobs have been coated by PVD methods. After elaboration of a procedure for hobs testing, field tests have been performed. Results of tool life tests and investigations of tool wear mechanisms for different coated hobs will be presented and discussed.
2:30 PM G4-2-4 A Drilling Test with Particular Reproducibility
A. Rozen, E. Bergmann (Geneva School of Engineering, Switzerland)
We have developped a new drilling procedure based on the procedures previously developped by Dröse et al. and Schulz and Mathies. Previous drill tests were made in cast steels, either 42CrMo4 or X155CrMoV5 1. Shifting to a powder metallurgical steel with higher abrasion resistance and using modern NC equipment, we were able to reduce the spread between repetitive tests to 1 - 2 holes for tools coated in the same batch under identical conditions . This high reproducibility opens the way for investigations into the impact of details of process parameters and loading procedures on coating performance hitherto hidden by the spread in the test results. The high costs of the working material are compensated by a decrease in the number of holes by a factor of 8 when compared with the X155CrMoV 5 1. The test has been introduced successfully as an independent confidential benchmarking for different vendors. The failure mode analysis seems consistent with a model, where uncoated surfaces are subject to strong adhesive wear (galling).
2:50 PM G4-2-5 Acoustic Emission And Motor Current Study Of Drilling With Minimum Cooling
J.R.T. Branco (Fundação Centro Tecnológico De Minas Gerais- Cetec, Brazil); J.M. Vieira (Universidade Estadual de São Carlos, Brazil)
There has been an increasing interest for dry machining. For this purpose, MoS@sub2@ and hard carbon coatings are being developed for various cutting operations. Since drilling provides an inexpensive means to investigate the performance of cutting materials, including the effects of coatings, and due to the interest in real time monitoring the wear process, the present study was carried out. Acoustic emission - AE and motor current - MC, were monitored during drilling of AISI D3 with high-speed drills coated with TiN, TiCN, hard carbon and MoS@sub2@. The drilling MC and AE in the range of 10 kHz to 1000 kHz frequency were analyzed as a function of drilling depth for holes along each drill life test. Drill wear was analyzed by light and scanning electron microscopy, combined with 3D profilometry. The effect of coatings on AE parameters were analyzed at different cutting stages, as distinguished by AE.
3:30 PM G4-2-7 No Title Listed
W. Fritsch (RWTh Aachen, Germany); M. Sarwar (University of Northhumbria at Newcastle, Univted Kingdom); H. Schulz (Balzers AG, Liechtenstein)
We have developped a new drilling procedure based on the procedures previously developped by Dröse et al. and Schulz and Mathies. Previous drill tests were made in cast steels, either 42CrMo4 or X155CrMoV5 1. Shifting to a powder metallurgical steel with higher abrasion resistance and using modern NC equipment, we were able to reduce the spread between repetitive tests to 1 - 2 holes for tools coated in the same batch under identical conditions . This high reproducibility opens the way for investigations into the impact of details of process parameters and loading procedures on coating performance hitherto hidden by the spread in the test results. The high costs of the working material are compensated by a decrease in the number of holes by a factor of 8 when compared with the X155CrMoV 5 1. The test has been introduced successfully as an independent confidential benchmarking for different vendors. The failure mode analysis seems consistent with a model, where uncoated surfaces are subject to strong adhesive wear (galling).
3:50 PM G4-2-8 Improvement of Cutting Performance of PVD Coated HM Inserts in Chipboard Milling, Considering Chip Formation
K.-D. Bouzakis, A. Siganos, G. Koutoupas (Laboratory for Machine Tools and Manufacturing Engineering, Mechanical Engineering Dept., Aristoteles University of Thessaloniki, 54006, Greece); P. Nikolakakis (DROMEAS S.A., Serres Industrial Area , 62121 Serres, Greece)
Based on the experience gained utilizing coated HM tools in metal cutting, an investigation was carried out in order to asses the performance of such tools in chipboard milling. Within the framework of this project, a series of uncoated and coated HM cutting inserts, pretreated through grit-blasting, under various blasting pressure conditions, were examined. The wear mechanism and the effect of substrate pre-treatment were experimentally investigated by means of wear monitoring, by means of Scanning Electron Microscopy (SEM). The whole procedure was aided by cutting force measurements and FEM simulation of the cutting process, so that the cutting loads occurring in chipboard milling could be determined, taking into account the chip formation mechanism. The loading data obtained by the aforementioned numerical-experimental procedure, were used in a simulation of the tool loading, by means of FEM, thus making it possible to calculate the stress distribution within the cutting insert, and investigate its influence on the wear mechanism. The results obtained indicated that adhesion strength is of major importance for coated tools used in chipboard milling. Tools that had no pretreatment in order to remove the undesired squeezed and smeared Co binder phase, that counteracts a good adhesion between the substrate and the coating, behaved alike the uncoated ones. On the contrary, tools with substrate pre-treated through grit blasting, and, therefore, with better adhesion properties, worn considerably less, being able to preserve their coating longer. Furthermore, the investigation carried out showed that higher blasting pressures led to longer tool lives and, therefore, enhanced tool performance.