Advanced Materials Research Vol. 1136

Abstract: In this paper, molecular dynamics (MD) model is explored to study single-crystal nickel micro-nanomachining mechanism. Accordingly, LAMMPS would implement the simulation of nanometric cutting process, and snapshots at different steps are obtained by VMD and OVITO. On this basis, a reasonable explanation is given to the forming mechanism of chip and surface machined in the machining process of single-crystal nickel. The result of work-piece temperature distribution shows that there is a temperature gradient around the machining zone, where chip part achieved the highest temperature. Moreover, a large number of dislocations are observed. Part of dislocation atoms move forward and generate the chips, taking a lot of heat. Another part of dislocation atoms combine with the work-piece surface atoms with elastic recovery, and form the machined surface.

Abstract: Carbon fiber reinforced plastic (CFRP) are used for various aircraft structural components because of their superior mechanical and physical properties such as high specific strength, high specific stiffness, etc. In order for CFRP materials to be used in aircraft structures or machine elements, high quality holes must be created on them efficiently. However, it is difficult for conventional methods such as drilling, helical milling and so on to meet the requirements. Therefore, this study proposes a novel method for creating holes on CFRP products. This method is just performed by tilting the workpiece at a certain angle on the basis of conventional helical milling (CHM) and hence called tilt helical milling (THM). In this paper, the processing principle of the THM is described in detail at first. An experimental apparatus is then constructed by installing a work holding unit produced in house onto a CNC milling machine. Finally, experiments are carried out on the apparatus. The obtained experimental results demonstrated that the THM is capable of creating holes on CFRP with lower burrs and chippings formation compared with those by CHM. By this new method, high quality holes could be obtained with high efficiency compared with conventional methods.

Abstract: Single crystal Ni₃Al-based superalloy has excellent comprehensive performance.To study the micro-milling surface quality of Ni₃Al-based superalloy, this article used two-edged carbide alloy micro-milling tool with 0.8mm diameter, then orthogonal experiment of three factors and five levels was implemented to the micro-milling of typical single crystal Ni₃Al-based superalloy IC10. The primary and secondary factors of the impact on the micro-milling surface quality were found from spindle speed, feed rate, milling depth by range analysis, and the ideal cutting process parameters combination was optimized and obtained, then its cutting mechanism and the reason of affecting the surface quality were analyzed. The experiment result has certain guiding significance to the micro-milling mechanism of single crystal superalloy.

Abstract: In recent years, the demand for carbon fiber reinforced plastics (CFRP), which have excellent mechanical properties, is increasing in various fields. In particular, the amount of CFRP used accounts for more than 50% of the body structure weight of the state-of-the-art airplanes. Moreover, in such airplanes, stack material, which is a combination of CFRP and titanium alloy (Ti-alloy), is frequently used. Therefore, a novel high-efficiency end-milling technology for cutting CFRP and Ti-alloy simultaneously is required. It is known that for restraining the occurrence of tool wear, diamond coating, which has high hardness, is useful. On the other hand, in the case of machining of Ti-alloy, several problems arise due to the machining heat. Consequently, in this study, we focus on cBN (cubic boron nitride). In order to compare diamond coating and cBN, end-mills, which were electroplated diamond grains, were also fabricated. In this study, as a cutting experiment, side milling of stack material, which is a combination of CFRP and Ti-6Al-4V, was carried out using the fabricated tools. Then, we discuss their cutting performance by measuring the CFRP temperature and chip temperature, tool wear, surface roughness, and surface integrity. As a result, it could be expected to precisely cut the stack material with the fabricated electroplated cBN end-mill. However, it is seen that improvement of the tool shape or the electrodeposition process is required.

Abstract: An innovative cutting method, constant load feeding method, is proposed as a high precision secondary working tool in CFRP cutting. The constant load feeding can restrain the occurrence of cutting defects such as burr and scuffing in a diamond saw cutting. The combining of constant load feeding with point contact eliminated most of the cutting defects even in the CFRP cutting with a low rigidity cutting tool like the diamond saw blade. In addition, there was no apparent cutting damage on the cutting surface obtained from the drilling with constant load feeding. These facts indicate that the self-generated feed rate in the constant load feeding would be the optimal feed rate to realize a defect-free drilling of CFRP composites.

Abstract: The cutting heat, during the process of drilling fiber reinforced resin matrix composites, has a significant effect on the quality and the tool wear. In this paper, based on the homogenization hypothesis of the material and the finite difference method, a temperature field model for drilling unidirectional Kevlar composites was developed. During the drilling process, the heat source formed by cutting edge and chisel edge can be seen as a conical heat source. The results show that the temperature field distribution is ellipse away from the drilling zone with the longer axis paralleling to the fiber direction and changes close to the drilling zone.

Abstract: Ultra-precision fly cutting machines have long been the hardest one to compliant and induce great focus of researchers. In this paper, a surface topography model is proposed to predict the surface generation in an ultra-precision fly cutting machine. The building of surface topography model is based on the trace of the tool tip. With the 3D surface profile simulations of workpieces, several influencing factors of surface topography, especially the factors related to micro waviness error, are studied.

Abstract: As a measure to perform a burnishing process easily on an NC lathe, the authors propose a new method using a flank face positioned in a few millimeters lower part of the nose cutting edge of a tool. In the experiment, giving a fixed depth of burnishing (t=1, 2 and 4μm/pass), the carbon steel workpiece (S45C) of φ30mm which had been turned at V=200m/min and f=0.15mm/rev was burnished by predefined number of times. As a result, the surface roughness improved in nearly proportion to the total depth of burnishing and the roughness value of Rz≈10μm measured after turning could be improved to Rz≈2.5μm. Utilizing the feed control with an accuracy level of micron meters of the NC lathe, an attempt to control the dimensional accuracy of the workpiece diameter in the order of micron meters was also made. As a result, the workpiece radius came down constantly by 0.6~0.8 times in proportion to the tool depth of burnishing (t=1μm/pass), which reveals that the dimensional accuracy of the workpiece diameter could be controlled by the proposed burnishing process utilizing a fixed depth of burnishing system. Using the same burnishing process, circularity of the workpiece Δr could be improved to Δr≈2μm from Δr≈4μm measured after turning.

Abstract: Cutting force and temperature are the two chief factors affecting bone rehabilitation during bone cutting in many orthopedic surgeries. To reveal new knowledge of thermal and force when milling cortical bone, slotting experiments were carried on high-speed milling platform. Cutting force and temperature were measured during the milling process. The effects of cutting inputs on cutting thermal and force were researched in detail. The results showed that: feed rate and spindle speed had a great impact on the milling temperature, while the milling force was mainly influenced by spindle speed. A feed rate of 1.0-1.4 mm/s is recommended to obtain preferable milling force and temperature, and a larger feed rate of 1.2-1.4 mm/s is advised to use with a lower spindle speed (8000-20000 r/min), while a smaller feed rate of 1.0-1.2 mm/s should be chosen when spindle speed was between 20000-40000 r/min. Feeding parallel to the growth direction of the cortical bone can significantly reduce the milling temperature, but there was no obvious change in milling force. The lowest cutting temperature obtained during the experiment was around 50 °C without coolant, which was acceptable for orthopedic surgeries.

Abstract: Bone drilling commonly exists in clinical practice and the heat and force generated by the drilling process has a huge impact on the surgery effect and the recovery of patients. High speed drilling, proved to have less injury and be more efficient when compared to the traditional low speed drilling, is considered to be the development direction of bone drilling-related surgeries. In order to make a further study of the controlling of the heat and force during the bone drilling process, the experiment designed to examine the influence of the diamond coating has been conducted and the result indicates that the diamond coating generally has little influence on the drilling force, however, it can increase the drilling temperature to a certain extent which indicates that the diamond coating is not suitable to apply to bone drills under the conditions of the conducted experiments. The result of this research could be of some help to the development of new kinds of medical drills.