This dissertation, "A Study of Tool Life and Machinability Parameters in High Speed Milling of Hardened Die Steels" by Caotan, Niu, 牛草坛, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A study of tool life and machinability parameters in high speed milling of hardened die steels submitted by NIU Cao Tan for the degree of Master of Philosophy at The University of Hong Kong in August 2007 Traditionally, moulds and dies used in manufacturing industries are made by machining alloy steels in their soft state to form the required mould. This is then followed by applying heat treatment process to increase the mould's surface hardness for obtaining better wear resistant property. The modern approach of making moulds and dies is to machine hardened alloy steels directly by applying High Speed Machining (HSM) technology. This new machining method not only eliminates the need for post-machined heat treatment process but also reduces machining time and improves machined surface quality. However, use of high cutting speed is associated with faster tool wear. A challenge of using HSM is therefore in the determination of appropriate machining process parameters for obtaining longer cutter tool life. Since relating few previous studies have considered this aspect, the answers to this challenge would be very useful for planning machining operation. This thesis has four main objectives: 1) to investigate the effects of employing different tool path orientations and cutting speeds on tool life, tool wear, cutting forces and surface finish when performing high speed finish milling on hardened (>HRc40) die steel with the use of cemented carbide ball-end milling cutter; 2) to obtain the cutting characteristics when applying zig-zag tool path pattern on inclined surface machining; 3) to simulate more realistic machining by milling the inclined surface under interrupted cutting conditions; and 4) to investigate the effects of using ball-end milling cutters with different geometries on tool life and relevant machinability parameters when performing HSM on inclined surface in interrupted cutting conditions. To achieve these objectives, a series of machining experiments were designed and conducted to implement the defined objectives. Various sophisticated instruments and measuring systems were employed to monitor and measure cutting force, surface roughness and tool wear. The experimental results showed that the tool life was significantly influenced by tool path orientation, cutting speed and tool path pattern. The longest tool life was achieved when using horizontal upward tool path orientation, one-directional tool path pattern, and with a cutting speed of 377 m/min. The resultant cutting force was found to increase with the increase of tool wear and cutting speed. The relationship between machined surface roughness and tool wear was not clearly observed. High frequency of cutting interruption did not affect the cutting performance of the VF-2SB ball-end milling cutter significantly. Therefore, the cutting performance when the VF-2SB ball-end milling cutter was used in these tests is similar to that of the actual cutting process. Due to its bigger helix angle and rake angle, the VF-2SDB ball-end milling cutter had a shorter tool life and produced a poorer surface finish than the VF- 2SB ball-end milling cutter. (Word counts of the Abstract = 440) DOI: 10.5353/th_b3955717 Subjects: Reliability (Engineering)Tool-steel - TestingMilling machinery