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Hot forming processes of complex parts with small cavities demand high-performance tools made of hardened steels. Their surface can be tribologically modified in order to control the material flow for improving the mold filling of functional elements. Surface structuring here offers great potential for adjusting the frictional properties and thus controlling the material flow in forming processes. In this study, high-feed milling (HFM) of surface structures in hot work tool steel (HWS) components is investigated. The process performance was determined by cutting force measurements and tool life tests. The achievable surface topography was measured and evaluated in terms of structure quality and roughness parameters, and friction properties were derived based on the results. In a hot ring compression test, the influence of certain structure variants on the material flow was analyzed. The results conclude that HFM is a suitable process for structuring HWS components with constant structure quality and low tool wear. In addition, a variety of structures showed significant influence on the hot ring compression test. This indicates a relevant potential of HFM for the modification of hardened tool surfaces to improve the performance of hot forming processes and increase the manufactural quality and productivity. [ABSTRACT FROM AUTHOR]

In the present research, an innovative testing method, specifically developed to characterize the tool steels under creep-fatigue conditions, was carried out on a TQ1 (X36CrMoV5-2) hot-work tool steel in cooperation with Constellium R&D center. The experimental campaign consisted of different testing conditions, and most of the specimens were nitrided to account for the specific surface state of the tools. Tests were performed on a 100 kN MTS fatigue machine equipped with a heating furnace. A creep-fatigue loading type was applied to the specimens, i.e., a cyclic load with a dwell time, in order to properly reproduce the conditions acting on extrusion tools and dies. Under a constant temperature of 520 °C, the effects of four different load levels and two different values of dwell times were evaluated. In addition, selected test conditions were replicated with specimens not nitrided with the aim to evaluate and quantify the influence of the superficial treatment. Final results were presented in terms of fatigue diagram of the TQ1 steel and compared to the performances of the H11 tool steel tested in a previous research by the same authors. [ABSTRACT FROM AUTHOR]

The surface finish of machined parts is known to have considerable effect on some properties such as wear resistance and fatigue strength. Thus, the quality of the surface has a significant importance for evaluating the productivity of machine tools, and mechanical parts. In this paper, the effects of cutting speed, feed rate, depth of cut and workpiece hardness on surface roughness, cutting pressure, and cutting power in the hard turning of hardened AISI H11 (X38CrMoV5-1) using CBN7020 tools were experimentally investigated. The response surface methodology (RSM) and analysis of variance (ANOVA) were used to check the validity of quadratic regression model and to determine the significant parameter affecting the output responses. The mathematical models for output parameters have been developed using Box-Behnken design with 29 runs. The results indicated that the surface roughness parameters are influenced principally by the feed rate and workpiece hardness while the depth of cut has no significant influence. In addition, cutting speed is the main influencing factor on the cutting power. Also, the results show that the tool life is influenced principally by the cutting speed and in the second level by the feed rate. [ABSTRACT FROM AUTHOR]

This experimental study is conducted to determine statistical models of cutting forces in hard turning of AISI H11 hot work tool steel (∼ 50 HRC). This steel is free from tungsten on Cr-Mo-V basis, insensitive to temperature changes and having a high wear resistance. It is employed for the manufacture of highly stressed diecasting moulds and inserts with high tool life expectancy, plastic moulds subject to high stress, helicopter rotor blades and forging dies. The workpiece is machined by a mixed ceramic tool (insert CC650 of chemical composition 70%AlO+30%TiC) under dry conditions. Based on 3 full factorial design, a total of 27 tests were carried out. The range of each parameter is set at three different levels, namely low, medium and high. Mathematical models were deduced by software Minitab (multiple linear regression and response surface methodology) in order to express the influence degree of the main cutting variables such as cutting speed, feed rate and depth of cut on cutting force components. These models would be helpful in selecting cutting variables for optimization of hard cutting process. The results indicate that the depth of cut is the dominant factor affecting cutting force components. The feed rate influences tangential cutting force more than radial and axial forces. The cutting speed affects radial force more than tangential and axial forces. [ABSTRACT FROM AUTHOR]