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So far ultraprecision diamond machining of steel molds for optical applications is not possible because of excessive wear of the applied diamond tools. This article discusses a thermochemical approach for steel machining with single crystal diamond tools as well as the process of material modification. Ultraprecision raster milling experiments for the nitrided carbon steel C45 ͑AISI 1045͒ and the tempering steel 42CrMo4 ͑AISI 4140͒ are presented. In both materials a surface roughness of RaϽ 10 nm could be achieved. The observed flank wear of the cutting tools was VBϽ 2 m for all experiments after cutting work pieces with a diameter of 30 mm.

Micro milling is an appropriate technology for the flexible production of precise micro molds with complex shapes for metal forming processes (e.g. micro deep drawing). Besides high form accuracy micro ball end milling also provides a specific surface topography which can enhance the tribological behavior during the forming processes. This paper is focusing on the tribological behavior of micro structured surfaces generated by micro milling compared to smooth surfaces. The coefficient of friction was investigated on a pin-on-disc test stand for different materials. The results of the tribological tests suggest a relationship between micro structure and coefficient of friction. Finally, the correlations between machining parameters and tribological behavior will be discussed.

A novel conditioning technique to precisely and effectively condition the nickel electroplated mono-layer coarse-grained diamond grinding wheel of 91m grain size was developed to fabricate a Diamond Micro Tool Array (DMTA) in ductile machining of brittle materials. During the fabricating process, a copper bonded diamond grinding wheels (91m grain size) dressed by ELID (electrolytic in-process dressing) was applied as a conditioner, a force transducer was used to monitor the conditioning force, and a coaxial optical distance measurement system was used to insitu monitor the modified wheel surface status. The experimental result indicates that the newly developed conditioning technique is applicable and feasible to generate required wheel topography of less than 2μm run-out error and grain geometries. The taper cutting test on BK7 proves the fabricated DMTA is capable of realizing ductile machining of brittle materials.

Ultra precision machining processes generate surfaces in optical quality and with sub-micron form accuracies. These specifications can be realised by applying single crystal diamond tools with nanometric edge sharpness. Typical workpiece materials are non-ferrous metals which can be machined without significant tool wear. But for optical mould making these materials have disadvantages regarding tool life in injection moulding of plastics. Alternatively diamond cutting of thermo-chemically treated steel is a new way to machine hardened steel moulds. This paper presents results from the machining of two thermo-chemically treated steel alloys. Analyzing and evaluating the machining results regarding surface integrity will lead to recommendations for the ultra precision machining of nitrocarburized steels. The influence of the thermo-chemically generated compound layer composition on surface quality and tool wear has been investigated. Therefore, diamond turning experiments have been carried out on a five axes ultra precision lathe in different depth beneath the surface. Here, both steels can be machined in optical surface quality with a surface roughness Sa < 10 nm, but the achievable surface quality strongly depends on the depth beneath the surface in which the machining takes place. The results show that with increasing depth beneath the surface the roughness values increase as well. Therefore, diamond machining at the edge between compound layer and diffusion layer has to be avoided to gain the best possible surface quality.Today it is believed that the high wear rate of single crystal diamond tools results from the high chemical affinity between the iron atoms of the steel and the carbon atoms of the diamond tool. An explanation proposed by Evans and Paul is that the un-paired electrons in the d-shell of the iron react with the electrons in the p-shell of the carbon [1]. This reaction causes breakage of covalent bonds in the diamond lattice leading finally to catastrophic diamond tool wear. Further results could be found in a study by Shimada et al. who explored the wear mechanism under different ambient temperatures [2]. In the past many different approaches for reducing diamond tool wear have been made. For example, cryogenic turning where the contact point between tool and workpiece is cooled with liquid nitrogen. Evans found a reduction of the wear rate when turning 440V steel at cryogenic temperatures [3]. Casstevens reports about a wear reducing effect in turning under a carbon saturated gas atmosphere [4]. Moriwaki developed an ultrasonic assisted cutting process where the diamond tool oscillates with 20 kHz along the cutting direction which leads to an increase of tool life [5]. Shamoto realized an ultrasonic vibration tool with three degrees of freedom for the machining of sculptured surfaces [6]. Klocke reports that the applied frequency in ultrasonic assisted tuning is a main factor. With an increased frequency the surface finish is improved, and the cutting process is stabilized [7]. These approaches...