The engineblock production lines need high speed tapping with tungsten carbide taps. In the tapping process, the machining precision and the tool life of taps are directly influenced by tapping forces. And the parameter optimization of tap structures is also correlated with the variation of tapping forces. Therefore, the study of tapping forces is necessary in developing new style taps. Several experiments about some novel carbide taps are performed on a vertical machining center by a Kistler dynamometer system in blind tapping both gray cast iron and ductile cast iron. And the variations of tapping forces are analyzed in tapping-in and tapping-out periods. It indicates that cutting forces hardly vary with the tap wear in tapping cast iron. Contrarily, tapping forces are closely correlated with the holding method. Besides, it also depends on the helix angle, the flute numbers and the plasticity of the work material to some extent.
To select high performance milling tools with optimum geometry structure suitable for machining hardened steel SKD11, geometry structures of tools are optimized. Four kinds of TiAlN coated cemented carbide tools are developed. The milling performance in high-speed milling hardened steel SKD11 by using these four kinds of tools is evaluated through the aspects of cutting force, cutting vibration, chip deformation, tool life, and tool wear mechanism, thus determining the optimum milling tool. The tool life of the optimum tool is 3 times of that of other tool, and the cutting force and vibration decrease by 70% compared with that of other tools. It has the most stable cutting performance.
Two new AlTiN coated cemented carbide drills with Al content of 40% and 55% in weight are developed for high efficiency dry drilling of 40Cr. By studying tool durability, machined hole quality, tool wear mechanism, chip deformation, and lubrication, the dry drilling performance of the two kinds of coated drills is analyzed. Experimental results show that the AlTiN coated drills are suitable for high efficiency dry drilling and can obtain higher quality of machined holes. The tool durability of the drill with 55% Al content is 1. 3 times of that of the drill with 40% Al content at the cutting speed of 90 m/min. The wear mechanism of two AlTiN coatings are studied in experiments. During dry drilling process, oxidative wear appears in both two kinds of drills. The oxide film is formed on the top of the coated drill containing Al content of 55%. And the oxide film helps to increase its high temperature resistance and decrease the coating flaking, thus the drill is failed because of coating subsidence. The drill with less Al content is failed due to peeling and breakage. The lubricated condition in dry drilling is improved by the high Al content coating. It helps to reduce the cutting deformation and benefits to improve the quality of machined holes. The AlTiN coating with higher Al content shows longer tool life and higher quality of machined holes in high efficiency dry drilling. Its tool life increases by 30% compared with that of the coating with less Al content.
To evaluate the new designed cutting tools for high-efficiency milling of the hardened die steel SKD11,surface integrities of millers with different geometric structures are analyzed, considering the surface roughness, micrograph of chips, surface microhardness, residual stress and metallurgical texture of the surface layer. The in fluences of geometric characteristics of different cutting tools and their wear characteristics on the surface integrity are studied. Results show that the milling tool with rake angle; 5 of the hardened diesteel. The generation of saw-tooth chips is depressed when a reasonable positive rake angle is selected. And the compressive residual stress is induced on the machined surface in milling the hardened die steel. The occurrence of surface softening is postponed by increasing the clearance angle and reducing the tool flank wear.
