ICMCTF2006 Session E5/G4: Tribological Studies of Coatings for Green Manufacturing and Dry Machining
Monday, May 1, 2006 10:30 AM in Sunrise
E5/G4-1 Chlorine Implanted TiCN Coating for Protection of Steel Moving Parts from Severe Dry Wear
T.A. Aizawa (University of Toronto, Canada); T.S. Sumitomo (University of Tokyo, Japan)
Various steel parts in the industrial products experience severe wearing in dry. In the case of moving parts in the compressors, protective coating is indispensable to improve the dry wear resistance even in the high sliding speed range. Different from the lubricated wear, low friction coefficient as well as low wear volumes are required in the materials design for this type of coating. TiCN coating is employed here as a base coating material to investigate the effect of chlorine implantation on the improvement of dry wear resistance and to describe the dry wearing behavior with comparison to solid lubrication by MoS@sub 2@. TiCN layer with the thickness of 2 µm was coated onto SKH51 sample with the intermediate buffer of titanium by using the hollow cathode ion plating. Chlorine was implanted into this coating with different doses. Pellet-on-disc method was utilized to measure the variation of friction coefficient in air with increasing the normal pressure. The sliding velocity is kept constant, 10.4 m/s. Normal pressure is monotonically increased up to 14.8 MPa by 0. 37 MPa/s. For comparison, MoS@sub 2@-sputtered high-Si aluminum alloy pellet samples were also used to describe the dry wearing mode. Without chlorine implantation, every TiCN-coated sample broke away within 10 seconds. This short duration of dry sliding with low friction coefficient is much improved by chlorine implantation: low friction duration can be at least doubled or more by chlorine implantation. Compared to MoS@sub 2@ sputtering, nearly the same friction coefficient of µ = 0.05 to 0.1 can be attained; this proves that self-lubrication via Cl-implantation provides solid-lubrication mode in dry wearing. Further optimization of base ceramic coatings leads to attain better dry wearing state than MoS@sub 2@-lubrication.
E5/G4-3 Nanocrystalline Diamond Coated Micro-End Mills for Micro/Meso-Scale Manufacturing
P. Heaney, A.V. Sumant, F. Pfefferkorn, R.W. Carpick (University of Wisconsin-Madison)
There is growing interest in high precision machining to fabricate miniaturized parts for medical devices, micro-satellites, and the optical industry with meso-scale machine tool systems (mMTs) which utilize tools with diameters ranging from 10 to 500 microns. This technology complements standard Si-MEMS fabrication processes with its ability to directly produce true 3D structures with high accuracy, low cost, and short cycle time. One of the important aspects of micro-end milling which influences precision machining is the choice of tool materials. Presently, tungsten carbide (WC) with cobalt binder is widely used as a standard material. However, it suffers from a number of drawbacks such as limited operational life, difficulty in machining adhesive metals such as aluminum and copper, and poor surface finish. We have developed a new approach in coating existing tungsten carbide micro-end mills with nanocrystalline diamond (NCD) coatings using the Hot Filament Chemical Vapor Deposition (HF-CVD) technique. We have developed a seeding method to obtain uniform conformal NCD coatings on 300 micron diameter WC micro-end mills. The performance of the uncoated and NCD coated tools have been evaluated by performing machining experiments on 6061-T6 Aluminum. The test procedure involves machining a channel and measuring the cutting forces, tool wear, surface roughness, and burr formation. The initial test results show significant improvement in the tool life, extremely low wear, little adhesion of the metal to the tool, and a significant reduction in the cutting forces. This translates into achieving a smooth surface finish and dry machining at high speed with little or no burr formation. Since no lubricants are required during machining and the formation of metal burrs is greatly reduced, this approach greatly reduces the environmental impact of the micro-machining process and therefore offers a great promise for micro and meso-scale manufacturing applications.
E5/G4-4 Influence of AlCrN-Based PVD Coating Properties on Wear Mechanisms in Metal Cutting
C. Gey, V.H. Derflinger, J.L. Endrino (Balzers Ltd., Liechtenstein); G.A. Fontalvo (University of Leoben, Austria)
PVD coatings deposited by cathodic arc evaporation have for years played a key role in the functionality of high quality cutting tools. For the development of a new coating system the relevant coating properties have to be identified in order to receive longer tool lives and/or to allow higher material removal rates. This paper deals with the description of mechanical and physical coating properties with regard to the wear mechanisms prevalent on the tool, including microhardness, oxidation resistance and thermal conductivity at temperature. The focus here is placed on commercially available AlCrN-based coating systems especially on a monolithic variant for milling applications as well as on a multilayer structure for drilling applications. Different wear mechanisms can be detected by these modifications, which help to understand the relationship of cutting process loads and wear progression with regards to coating properties.