Sun Fanghong

Experimental research on the dynamic characteristics of the cutting temperature in the process of high-speed milling

Abstract The cutting temperature is a key factor which directly affects cutting tool wear, workpiece surface integrity and machining precision in the high speed machining (HSM) process. The purpose of this paper is to present an inverse heat-transfer model considering three-dimensional transient heat conduction to calculate the heat flux and the temperature distribution on the tool–workpiece interface in the high speed milling process. The model was set up by a finite element method based on Beck’s inverse heat-conduction theory and was verified by numerical simulations and a series of experiments which aimed to obtain the surface temperature data of a thin-walled workpiece with the aid of an infrared thermometer and the tool–workpiece interface temperature by an embedded artificial thermocouple. The dynamic characteristics of the cutting temperature in high-speed milling aluminum alloy were studied systematically. The numerical simulation results revealed that there was a close agreement between the calculated temperature value and the measured temperature value of the cutting interface in high-speed milling of aluminum alloy. The inverse heat-conduction method can be used to estimate the heat flux flowing into the workpiece and the temperature distribution on the tool–workpiece interface. Using the infrared thermometer as a remote sensor can solve the problem of measuring the temperature in high-speed milling and also it can be used as an approach to reveal the cutting mechanism of high-speed milling. There exists a critical cutting speed in the high-speed milling aluminum alloy. The value of this critical speed will be different for the different cutting conditions. Constant feed per tooth must be kept in high-speed milling to efficiently suppress excessive heat generation while obtaining a high material removal rate, especially for machining difficult to-cut materials with a thin-wall construction. The average tool–workpiece interface temperature is influenced by the thickness of the workpiece. The related temperature distributions will be very beneficial to the optimal construction design for the thin-wall parts used in the aeronautics and astronautics as well as die and mold industries.

Studies on the grinding characteristics of directionally solidified nickel-based superalloy

Abstract Directionally solidified nickel-based superalloy DZ4 is a kind of very important structural material nowadays produced domestically. Grinding burn usually occurs in the grinding process, thus being an obstacle to further promoting grinding efficiency and grinding precision. This paper has discovered the grinding mechanism of this new type superalloy on the basis of systematic analyses of the variable characteristics: the grinding force, grinding temperature, topography of the ground surface, hardness distribution of the surface layer, as well as morphology of the surface layer from a metallographical viewpoint. The results will be beneficial in the grinding of this new type superalloy with high efficiency and high precision.

Improved adhesion of diamond coating on cobalt-cemented tungsten carbide hardmetal by using pulsed-UV-laser substrate surface pretreatment

Abstract Pulsed-UV-laser surface ablation has been applied in substrate pretreatment in order to obtain good adhesion of diamond coating grown on cobalt-cemented tungsten carbide hardmetal. The dependence of diamond coating’s adhesion on different shots of pulsed-UV-laser substrate pretreatment has been studied experimentally. The results were compared with diamond coating deposited by using traditional acid-etching substrate pretreatment. It was shown that adhesion of diamond coating grown on tungsten carbide hardmetal has been greatly improved by using pulsed-UV-laser substrate pretreatment. The corresponding laser pretreatment condition for the optimal adhesion of diamond coatings was finally obtained. It has been demonstrated that pulsed-UV-laser substrate pretreatment should be a feasible and effective method for improving adhesion of diamond coating on cobalt-cemented tungsten carbide hardmetal. It is the characteristic surface morphology produced by pulsed-UV-laser surface ablation that subsequently results in this improved adhesion of diamond coating grown on tungsten carbide hardmetal. The number of laser shots being used in substrate pretreatment has a great influence to the adhesion of diamond coating deposited on tungsten carbide hardmetal. One should always apply proper number of laser shots in pulsed-UV-laser substrate pretreatment when seeking for the optimal adhesion of diamond coating on tungsten carbide hardmetal. In this work, the corresponding number of laser shots for the optimal adhesion of diamond coating has found to be 300 laser shots.

Diamond-coated tube drawing die optimization using finite element model simulation and response surface methodology

Diamond-coated drawing dies are considered as the next generation of drawing dies for their unique characteristics, such as high hardness, wear resistance, low friction and thermal conductivity in the cold drawing process. In order to utilize the superior characteristics of diamond coatings toward improving the drawing performance, modified typed drawing die is developed to minimize the diameter shrinkage. Finite element model simulation is used to simulate the low carbon steel tube sinking drawing process, using a two-dimensional axi-symmetric elastic–plastic element model. The parameters of tube drawing die, such as the main reduction zone α1, the semi-angle of the secondary reduction zone α2 and the length of the secondary reduction zone L, are considered. Based on the simulation results, the cause of diameter shrinkage is studied. The influence of parameters of tube drawing dies on the diameter shrinkage is investigated using the response surface methodology. The gained equation reveals that L is the most significant parameter.

Optimization of depositing uniform and wear resistant diamond films on massive mechanical seals

Purpose This study is focused on depositing uniform, wear resistant as well as easily-polished diamond coatings on massive mechanical seals in a large-scaled vacuum chamber, in the purpose of obtaining diamond coated mechanical seals with improved sealing performance and considerable cost. Design/methodology/approach The computational fluid dynamics (CFD) simulation test and its corresponding deposition experiment are carried out to improve the uniformity of diamond films on massive mechanical seals. The polishing properties and sealing performance of three different diamond films (MCD, NCD and MNCD) coated mechanical seals and uncoated mechanical seals are comparatively studied by the polishing tests and dynamic seal tests to obtain the optimized diamond coaitng type on the mechanical seals. Findings The substrate rotation and four gas outlets distribution is helpful for depositing uniform diamond coatings on massive mechanical seals. The MNCD coated mechanical seal shows the advantages of high polishing...