Advanced Materials Research Vols. 69-70

Abstract: To improve efficiency in ultra-precision lapping germanium (Ge) substrate, a new ultra-precise process technology is introduced in this paper. Two steps ultra-precise process were semi bonded abrasive lapping in rough machining, and CMP process in finish machining. A good surface quality workpiece was obtained in semi bonded abrasive lapping process efficiently. Several machining parameters were compared and applied. After CMP process, the mirror-like surface of Ge substrate was obtained.

Abstract: Due to different datum position and inevitable distortion from the linear friction welding process, the nominal CAD model from the design stage is no longer suitable for the use of the final NC machining, and that is the main problem for precisely machining complex blisk. In this paper, an adaptive machining approach based on adaptive process model for high precision manufacturing of blisk is proposed and developed. Comparing the nominal model with the inspection result, adaptive process model is reconstructed to describe workpiece localization, allowance distribution and composite error compensation for NC machining of blisk accurately. Firstly, the transformation matrix for allowance optimization is searched fleetly by genetic algorithm with constraint conditions. Secondly, using the cross-section curve blending and deformation compensation method, adaptive model for shape distortion is constructed to solve the part-to-part variation machining problem and to realize precision machining for complex geometry blisk. Finally, based on the adaptive process model, tool paths used for the last NC machining process can then be adaptively generated to implement the different processes work. Example shows that the adaptive machining technology of blisk is feasible and the result is of high precision and efficiency.

Abstract: High Speed Machining (HSM) has been proved to be useful in the machining of many materials. This research is concerned with the performance of HSM in the milling of Ti-6.5Al-2Zr-1Mo-1V (TA15) titanium alloy. The tool life and wear mechanism of the milling tool under different cutting speed were investigated, and the influences of cutting speed on the surface integrity and fatigue property of the machined part were studied. According to the experimental results, acceptable tool life can be obtained in a speed range up to 200m/min. The results also show that increasing cutting speed can help to improve the surface integrity and fatigue property of the machined part.

Abstract: Using grey system theory in axiomatic design of high speed face milling cutter, the structural design method of cutter was investigated. The problem of parameter interaction and function coupling in axiomatic design of cutter was solved using the analysis method of grey cluster, and realized the reconstruction of design matrix and collaborative design planning. Results show that there is not design loop which exists in the development of high speed milling cutter, the effects of simplifying design process, shortening design cycle and improving collaborative design are validated in development of high speed face milling cutter. Results of experiments indicate that cutting vibration of high speed face milling cutter using structural design method is depressed, the cutters with higher safety and cutting stability, and their cutting performance have met the requirement of high speed milling.

Abstract: NURBS interpolation has many advantages over the traditional linear or circular interpolation in high-speed machining. The existing work in this regard focuses on adaptive feed interpolation considering the chord error constraints and tangent acceleration limits. However, regardless of the dynamic characteristics of individual axis, performance will inevitably suffer when the system is called upon to execute a complex trajectory beyond the range of its capabilities. The intent of the present work is to provide an optimal feed interpolation method respecting both the chord error constraint and the drive constraint of each axis. A look-ahead scheme is applied with a moving window to augment the calculation efficiency for real-time application. Simulations are performed to verify the resulting feedrate, acc/dec profiles and the real-time performance of the proposed interpolator.

Abstract: This paper gives the details of High Speed Milling experiments with AISI 52100 steel (HRC52) by using coated carbide end mills. Cutting force and Surface roughness data are presented. The effects of cutting speeds (1000-8000rpm), widths of cut (0.05-0.4mm) and cutting conditions (dry cutting and dry cutting with air coolant) are investigated. The results show that in high speed milling of hardened steels, when cutting speed surpasses a critical value, cutting forces decrease as cutting speed increasing; and the increasing of widths of cut causes the increase of cutting forces approximately linearly; surface roughness does not experience obvious increase or decrease and has a minimum in a specific condition; the machining results of dry cutting with air.

Abstract: In five-axis high speed milling of freeform surface with ball-end cutters, unwanted machining results are usually introduced by some error effects. Hence precise modeling and simulation of milled sculptured surfaces topography and roughness is the key to obtain optimal process parameters, satisfactory surface quality and high machining efficiency. In this paper, a predictive model for sculptured surface topography and roughness of ball-end milling is developed. Firstly, a mathematical model including both the relative motion of the cutter-workpiece couple and some influential factors on machined surface quality such as the tool runout, tool deflection and tool wear is proposed, and subsequently the analytical form of the tool swept envelope is derived by means of homogeneous coordinate transformation. Then the minimal z-values of the corresponding points lied in discrete cutting edges model and Z-map workpiece model are used to update the workpiece surface topography and to calculate 3D surface roughness. Finally, the simulation algorithm is realized with Matlab software. A series of machining tests on 3Cr2MoNi steel are conducted to validate the model, and the machined surface topography is found in good accordance with the simulation result.

Abstract: In this paper, FEM is used to simulate the three stages of catastrophic shear occurrence, expansion and shear band formation when serrated chips are formed under adiabatic shear behavior in high-speed machining of hardened steel GCr15 with PCBN tool. By comparing data of simulation and experiment on chip morphology characters, it is indicated that they are in good accordance. Hereby, the author has analyzed strain and temperature distribution in adiabatic shear band, and dynamic characters of cutting force . The research results show that adiabatic shear band begins from tool tip and extends to workpiece free surface, and it is characterized by large strain and high temperature. In addition, it results from adiabatic shear behavior that cutting force waves regularly in a numerical range.

Abstract: High speed machining (HSM) is finding wider applications due to its economic advantages, such as faster material removal rates, and its technological merits, such as improved surface finish. Nevertheless, the application of HSM also brings about some undesirable results. For example, the tool life and surface integrity of a machined component are greatly affected by the large amount of heat generated, but heat dissipation during an HSM has not been well understood. This paper aims to achieve a quantitative understanding of the heat dissipation in HSM using a bar turning configuration. Based on the calorimetric method and utilizing water as the heat transfer medium, the temperature rise in water was measured to determine the fractions of heat dissipated into the chips, the tool and the workpiece during machining. The obtained results show that the chips take the largest portion of the heat generated and this fraction increases with the increase in feed.

Abstract: High nickel-base alloy, such as G3, is famous for its corrosion resistant, high intensity and other characteristic, which is popular in petroleum extraction and other heavy industry. However its poor machinability is a big obstacle to launching this material in its application. This paper introduces the poor machinability and tool wear behavior in turning high nickel-base alloy-G3. Based on rough and finished turning, turning experiments were carried out according on cutting speed, cutting depth, coolant and etc. some improved processes were suggested. This paper will be beneficial and guidable in turning high nickel-base alloy and other similar high nickel-base alloy or stainless steel.