Hiroyuki Hanyu

Dry and semi-dry machining using finely crystallized diamond coating cutting tools

Finely crystallized diamond coatings with smooth surfaces have recently been developed by the authors. In the present study, shaft tools with these new coatings were applied to dry and semi-dry machining of highly adherent aluminum alloys whose efficient means of dry machining have not yet been established for. In comparison to the case of conventional diamond coatings with rough surfaces, more than four times longer durability of drills was realized in perfectly dry condition. In the case of minimum quantity of lubricant condition, the lifetime was found again to be more than four times longer and successfully achieved the largest improvement of diamond-coated drills ever reported in semi-dry condition.

New diamond coating with finely crystallized smooth surface for the tools to achieve fine surface finish of non-ferrous metals

In spite of many significant advantages of diamond coated cutting tools, rough surface with large crystal grains prevented them from usage for finishing process. In this study, a new smooth diamond coating with finely crystallized diamond on the surface was developed, whose roughness is less than 1 μm. Endmills with this coating was subjected to cutting tests for the performance of finishing non-ferrous alloys. Roughness of finished workpiece surface was less than 1 μm maximum value, which was as small as that could be achieved by using non-coated cemented carbide endmills. Anti-wear property and durability were not spoiled by these changes in coating morphologies.

Recycling technique for CVD diamond coated cutting tools

Due to the thinness of the films produced by Chemical Vapor Deposition (CVD), a cutting operation should be discontinued if the diamond-coated tool shows even a small amount of abrasion or wear on the substrate surface. For that reason, a recycling technique for CVD diamond-coated cutting tools is being sought with keen interest. In this paper, we propose a new technique for recycling CVD diamond cutting tools by completely removing the worn thin film from the tool and then applying a new film to the de-coated surface. We then performed durability-cutting tests and compared the results of a re-coated diamond tool with a newly coated diamond tool. The effectiveness of this technique was authenticated by the cutting tests.

Development of Ultra Fine Crystalline Diamond Film and Some Applications

We would like to report on the development of our new ultra fine crystalline CVD diamond film and some applications. CVD Diamond films have good wear resistance, but the crystal size is too large. Therefore, in case of application of diamond films for cutting tools, we cannot get fine surface finish on work materials. Recently we succeed in production ultra fine crystalline CVD diamond film and various cutting tools as taps, drills and end mills. Aluminum alloys have lately been consumed more than ever in airplanes and automobiles for the purpose of decreasing the weight of structural materials.Copper alloys are used for the electrode of electric discharge machines (EDM) recently. EDM electrodes are required fine surface finish because the surface quality of mold depends on accuracy of EDM electrodes. Soft materials such as aluminum and copper alloys have high viscosity and additionally activity. So during cutting aluminum and copper alloys we have sometimes adhesion between cutting tools and work pieces. Diamond film on tools is able to improve the reactivity to aluminum and copper alloys. But up to now the diamond film has a lot of course crystal and tend to supply rough surface finish on work pieces. We developed ultra fine crystalline diamond film on end mills by plasma chemical vapor deposition (CVD) method. Now our aircraft, automotive and molding customers can get smooth surface finish of work pieces.Keeping ISO14001, we recommend oil free cutting with ultra fine crystalline diamond coated cutting tools. Here I introduce background of the development and cutting examples with new fine diamond coated end mills.

Optimization of cutting edge shapes for the development of high performance diamond coated drills.

Recently, due to the increasing amount of aluminum machined in the automobile industry, there has arisen a corresponding need for tools to perform efficient and effective aluminum processing. For the machining of aluminum alloy that contains a large amount of silicon, highly wear-resistant cutting tools such as diamond coated ones are needed. Because high silicon aluminum alloy contains silicon particles dispersed in the matrix of aluminum, which quickly wear the tools. However, diamond coatings on cutting edges are easily broken off by the mechanical collision against the particles. Under anew concept of reducing the stress in diamond coatings on cutting edges, we tried to optimize the construction of coated drills by changing the shape of cutting edges and coating thickness. Shape of thinning and helix angle were selected as the parameters to optimize the shape of drills. The drills with negative angel of thinning and 20 degree helix angle showed the best performance including durability. By putting together the results above, the diamond-coated drills with optimized structure were newly developed. Their performance appeared to be satisfactory in cutting high silicon aluminum alloy from 12 to 23% silicon content.

De-coating Technique for CVD Diamond Coatings and Evaluation of Performance for Recycled Cutting Tools.

For the recycling of CVD (chemical vapor deposition) diamond coated cutting tools, a mechanical method, where old films were partly ground and re-coated, has been conducted. However, because of some problems it is not considered as an effective method. In order to overcome these difficulties, the authors have recently proposed a new technique for de-coating the diamond coatings on tools completly by combustion in a high temperature. This article clarifies the mechanism of the de-coating method, and proposes the treatment method for tools with different coating lengths. The examples of treatment conditions for de-coating obtained from the test results are reported in this paper. The durability cutting tests were performed with the regenerated tools. Finally the effectiveness of this technique was verified by the cutting tests.