Advanced Materials Research Vol. 1136

Abstract: In grinding process, the grinding wheel profiles are copied to workpiece surface. Therefore, the finished workpiece surface can be estimated by the grinding wheel surfaces. In this paper, new measuring method of the distribution of cutting edge in grinding wheel surface by two AE sensors is proposed. From experimental results, it is confirmed that the distribution of cutting edges in wheel surface can be measured easily by the proposed method compared to another measuring method.

Abstract: Infrared thermographic technology has attracted the attention of various industrial fields. We therefore focus on it as a novel tool temperature monitoring method to improve the end-milling conditions of difficult-to-cut materials. However, it is difficult to measure tool temperature under coolant conditions because coolant prevents the monitoring of end-mill tool surfaces. Thus, we developed a novel temperature monitoring method by applying a pore electric discharge machining process to place a thermocouple sensor in the end-mill tool and by using a wireless telegraphic multifunctional tool holder to directly measure the internal temperature of the end-mill tool under rotation. We evaluated internal temperature distribution under various end-milling conditions on the basis of multipoint simultaneous measurements and discussed the influence of forced convection heat transfer on the internal temperature of the tool under various rotating conditions. In addition, we used a finite element method to analyze unsteady heat conduction on the basis of temperature measurement by high-speed video infrared thermography and compared the results with those of the wireless telegraphic multifunctional tool holder to demonstrate its validity and usefulness.

Abstract: The use of electron microscopy and power-monitoring during grinding was investigated in terms of evaluating the fracture and wear characteristics and chip-formation mechanisms of abrasive grains and bond formulations. Diamond abrasives and fused, sintered and sintered triangular-shaped aluminum-oxide abrasives were evaluated. Power was shown to be a useful tool in determining the chip-formation mechanisms and the extent of grit fracture, particularly in triangular-shaped abrasive. Conclusions were supported by electron-microscope analysis. Power was also used to evaluate low-cost vs. premium diamond. Practical recommendations are given for evaluating grit, wheel and bond performance both in the laboratory and in production.

Abstract: High-precision aspheric surfaces are generally measured using interferometer with a computer-generated holograms (CGH), which has a wavy line pattern fabricated onto a glass substrate. CGH patterns are generally made using lithographic techniques that was developed for semiconductor industry. Patterns can be subsequently etched into glass substrate using reactive ion or chemical etching. The accuracy of the drawn pattern on a CGH decides the accuracy of the measurement. Draw pattern error mainly includes the line-width deviation and its position error. In this paper, the influences of defocus of drawing laser and the wet-etching processes on the line-width were firstly investigated. On the other hand, the position error under different line-width was obtained by analyzing the relationship of line-width error and the position error. Based on the above-obtained results, a CGH having a diameter of 80 mm and the minimum line-width of 1.8 μm was successfully fabricated. Testing results showed that the wavefront error was only 3.79 nm, significantly higher than the commercial-available ones. The fabricated CGH is expected to use in the high-precision measurement of asphercal surfaces.

Abstract: Grinding is a machining technology for plane surfaces and cylindrical surfaces in general. In comparison with cutting, higher accuracy can be provided and it is easier to manufacture high-hardness materials using grinding. However, the grinding wheel surface state changes during grinding, and grazing, clogging and shedding may then lead to problems. As these problems degrade the accuracy and productivity of grinding and the surface integrity of the work material, it is important to select an appropriate grinding condition to avoid the problems. In this study, a novel in-process system for monitoring the grinding wheel surface temperature and grinding state in real time, was proposed. A thermocouple is embedded in the grinding wheel in the developed system. The measured temperature data are transmitted to the external terminal equipment by a wireless transmitter built into the tool shank. Grinding wheel surface temperature was measured on four kinds of grinding wheels using the developed system. As a result, the grinding wheel surface temperature was measured successfully. In addition, it was clarified that the temperature transition largely depends on the grinding state.

Abstract: The blade is one of the key part of aero engine because its shape precision and surface quality significantly influence the performance, efficiency and reliability of the engine. The blade surface is generally obtained by precision finishing process, which is a repeated work of profile error measurement, profile error calculation and error correction manufacturing. For profile error calculation, the matching of measurement points and ideal blade surface must be firstly performed. However there is few detailed work reported on matching algorithm. In this paper, a new matching algorithm for profile error calculation was proposed. Firstly, the coarse matching method based on characteristics of blade section curves between measurement points and its corresponding ideal section curve was studied. Then the Sigular Value Decomposition (SVD)-Iterative Closest Point (ICP) precision matching method was adopted to improve the matching precision. After that, the weight calculation method was applied to balance the profile errors among different section curves. Simulation work was performed to validate the proposed matching algorithm. Results shows that micrometer-order matching accuracy of the blade section curves could be obtained through the above-mentioned three matching steps.

Abstract: Chatter vibration generated by coupling a work-piece, machine tools, and cutting tool is a serious problem for engineers. A regular pattern forms the machined surface when chatter vibration occurs. There must be a direct relationship between the relative displacement and machined surface. We propose a method for controlling chatter vibration of end-milling from a machined surface. Hammering tests were first carried out to determine the natural frequencies of machine tools and the tool system, which are likely to be the cause of vibration. We also propose a technique of applying reverse analysis to end-milling surfaces. The machined surface is assumed to include an essential index to easily control chatter vibration at the factory. We found that chatter vibration occurs near the frequency of the cutting tool, tool holder, and their coupling, not at the natural frequency, and the chatter vibration frequency can be calculated by analyzing the surface pattern and cutting conditions. Moreover, the proposed method was effective in analyzing chatter vibrations including more than two kinds of natural frequencies at the same time.

Abstract: The cutting force is widely regarded as being the most valuable information when observing a metal cutting process. Considering practicability, indirect cutting force measurement methods which forego additional sensors have been studied in academic field. Disturbance observer-based cutting force estimation method was known as a typical example, and its validity was verified in linear motor driven stage. However, accurate cutting force estimation is still difficult in ball-screw driven stage because of non-linear friction and resonance. In this study, feasibility of sensorless cutting force estimation was verified by using large scale commercial machine tool. Considering that the motion of rotational and translational elements independently, cutting force observer (CFOB) was modeled as two-degree-of-freedom system. The CFOB was mounted to control systems of both stage and spindle head which were driven by ball-screw and servo motor. While friction force and torque have non-linear position dependence, high repeatability was confirmed. Thus, their non-linearity could be attenuated by identifying friction force and torque beforehand machining operation. From experimental results, it was shown that tooth-pass frequency and second harmonics component of the cutting forces could be estimated accurately by using the CFOB. The results were acquired from control systems of both stage and spindle head.

Abstract: It is frequently the case that the feed rate indicated in a numerical control (NC) program does not obtain in actual machining processes and the cutting tool does not path the points indicated in the NC. A reason underlying such problems is that control gains are not optimized, which causes issues with acceleration and deceleration in the control of machine tools. To address these problems, in this paper, we propose a method for the optimization of control gains using the MATLAB and Simulink software by considering the weight of the workpiece, the controlling distance, and the controlling speed. Simulations confirmed the effectiveness of our proposed optimization.

Abstract: Increasing the wafer diameter from φ300 mm to φ450 mm is required to enhance semiconductor devices productivity. A high-stiffness rotary grinding machine equipped with water hydrostatic bearings was developed for a φ450 mm silicon wafer. The grinding machine has an upper structure consisting of a wheel spindle system and a lower structure consisting of a rotary worktable system. The spindle shaft creates both rotary and axial feeding motion. The upper and lower structures are clamped together rigidly by three kinematic couplings. A higher loop stiffness is required for the grinding machine because grinding the larger wafer requires a higher grinding force. This paper investigates the loop stiffness of the developed wafer grinding machine.