Materials Science Forum Vols. 836-837

Abstract: Low carbon steel (AISI1020) strips with grain refinement were successfully produced by large strain extrusion machining (LSEM).A finite element simulation was performed to make comprehensible the deformation behavior of LSEM process. The influence of annealing temperature and annealing time on the microstructure and mechanical properties of strips was investigated by two sets of heat treatments and Vickers hardness test. As a result, strips can maintain high hardness under 400°C but start losing it as the temperature increased to 500°C and above. When annealED at 300°C for 1~9h, hardness of strips can maintain at almost the same level as that before annealing. Obvious hardening was found when annealing at 200~300°C mainly because of the dislocations atresia. Despite of the anneal-hardening behavior, these results indicated that the extruded AISI1020 strip has a good thermal stability at temperature below 400°C.

Abstract: This paper resolved CNC turret punch cause vibration phenomenon in the course of processing sheet,analysis of its dynamic characteristics of the beam servo feed mechanism, using the method of constrained modal analysis.Through the establishment of finite element model exactly for the servo beam and setting the boundary elastic restraint stiffness, solving the natural frequencies and mode shapes of the servo beam under boundary constraints and loading conditions. Constraints modal analysis results are consistent with experimental monitoring results of CNC turret punch servo beam. This modeling methodology and results of the analysis has a high practical value for CNC turret punch dynamic characteristics analysis and structural optimization design.

Abstract: The first step to predict the milling stability is to identify the dynamic characteristics of cutting process. And the mass loading effects of removal material play an important role on the dynamic characteristics of milling process for thin-walled parts, such as impeller, turbine blades and automobile components, which is changing with cutting time or tool position. Therefore, how to identify the instantaneous dynamic characteristics of milling process is one of the most significant problems. In the paper, a structural dynamic modification method with variable mass to predict the instantaneous dynamic characteristics of multi-axis milling thin-walled workpiece with complex curved surface is proposed. The proposed method takes into account the variations of dynamics characteristics of workpiece with the tool position and material removal. And the material cutting process is regarded as the structural dynamic modifications of cutting system, the instantaneous dynamic characteristics of which can be estimated by the extended Sherman-Morrison-Woodbury formula to obtain the corrected frequency response function (FRF). Experiments were carried out to obtain the instantaneous dynamics of a thin-walled workpiece and the results were verified by finite element method (FEM).

Abstract: As technology develops, the aviation structures become more and more complex and consist of more difficult-to-machine features. In order to evaluate the cutting tool performance, it is necessary to design a testing thin-walled benchmark with some typical difficult-to-machine features which are extracted from complex integrated components used in aviation. Firstly, the models with different typical features were designed and optimized using UG NX. Then, based on the analysis of process of typical features, the specific processing strategies of testing benchmarks were proposed. Finally, the process was analog simulated with CAM to evaluate whether it was qualified for machining. The results would make preparations for the evaluation of different cutting tool performance.

Abstract: Grinding is a material removing process with undefined cutting edges. The high numbers of grains participating during the chip formation are continuously subjected to non-uniform wear and topography changes. This behavior typifies a highly non-stationary process. Capturing the whole process in a simulation and predicting the work results is difficult. For this reason are In-process monitoring techniques a suitable approach to address this issue. In this paper a wireless In-process monitoring system is presented. The system is mounted on the grinding hub and detects the dynamic behavior of the wheel during the grinding process. A full bridge with strain gauges located close to the abrasive layer has been used to give instantaneous feedback concerning normal force and wheel deformation during each wheel revolution. This technique enables a continuously monitoring and improving of the grinding process, hence a more efficient and sustainable use of the abrasive layer. Experiment results are presented which demonstrate the ability of the ‘intelligent’ wheel to monitor grinding processes and to improve the machine performance.

Abstract: In order to get an accurate online measurement for the transient cutting temperature in precision, in an ultra-precision cutting process,a temperature measuring device should be assessed whether it can obtain precise magnitude readings and variables of which are measured accurately. The just produced thin-film thermocouple used to measure tool cutting temperature must be correctly calibrated[3,4] , however traditional calibrating process problems rely on manual operation completely with lots of problems such as low efficiency, high labor intensity and large error. this paper proposes an automatic calibration system for thin-film thermocouple by using temperature measuring furnace, data acquisition card and computer-based software. The system makes an automatically and intelligently calibration process. By using a high-precision data acquisition card and precision amplifier circuit, eight thermocouples can be calibrated at the same time automatically which effectively shortens the calibration time and improves the accuracy. Use temperature metering furnace to control data acquisition. Secondary error from using standard thermocouple and other methods to collect the temperature metering furnace real-time temperature is eliminated. The system software modules consist of data reading, data processing, data display, database operation, data query and report generation module. The experimental results show that nonlinear fitting error is less than 0.6% within the temperature measurement range, which meets the requirement of the secondary precision of thermocouple error. This paper intends to provide a new calibration method for thermocouple temperature measurement tool development and production[7].

Abstract: Blades are important components of aviation-engine, with complex shape and high precision machining. The radius of curvature of the leading and trailing edges of the precision forging blades is small and the curvature changes fast. In this paper, the adaptive machining scheme about the leading/trailing edge of the precision forging blade is proposed. Firstly, the measurement model based on theoretical model of the blade is established. Secondly, according to the measurement model, the measurement path planning is proposed. Thirdly, measurement data processing and registration, then blade model reconstructed to generate the new NC code for machining.

Abstract: Machine tool vibrations cause uncomfortable noise, may damage the edges of cutting tools or certain parts of machine tools, but most importantly, they always have negative effect on the quality of the machined surface of workpieces. These vibrations are especially intricate in case of milling processes where complex tool geometries are used, like helical, serrated, non-uniform pitch angles, and so on. During the milling process, the arising vibrations include free, forced, self-excited, and even parametrically forced vibrations together with their different combinations. Regarding surface quality, the most harmful is the self-excited one called chatter, which is related to the regenerative effect of the cutting process. Its relation to machined surface quality is demonstrated in an industrial case study. The modelling and the corresponding cutting stability are presented in case of a helical tool applied for milling with large axial immersions. The extremely rich spectrum of the measured vibration signals are analyzed by means of model-based predictions, and the results are compared with the spectral properties of the corresponding machined surfaces. The conclusions open the way for new kinds of chatter identification.

Abstract: In this paper, experiment investigation is conducted on the machinability when ball milling A880 gas turbine blade profile. Cutting force spectrum acquired online is used to optimize the cutting parameters. The results indicate that cutting force signal in time domain and frequency domain can reveal the cutting stability, which provides an experimental guideline for gas turbine blades manufacturing.

Abstract: With the development of the high-speed and high-precision CNC machine tools, the interaction between mechanical system and servo drive torque in the feed system becomes more and more serious which affects the surface quality of the workpiece. In this paper, taking a small-sized vertical milling center as the research object, the characteristics of servo torque and mechanical system are analyzed, respectively. Then the influence of electromechanical matching on the tracking fluctuation of the feed system is discussed. Furthermore, aiming at the surface roughness of the workpiece, the influence of the interaction between servo torque and mechanical system on the surface quality of the workpiece is analyzed under different milling ways. Finally, a large number of experiments are carried out to verify the analysis above. At last, the optimization methods of machining precision based on electromechanical matching are put forward. It can be found that in the high-speed machining, the servo torque has lots of harmonics which act on the mechanical system with kinds of modals, leading to the vibration. The surface quality of the workpiece will be deteriorated rapidly when the mode of vibration is consistent with the sensitive direction of machining error. The surface quality of the workpiece can be significantly improved through optimizing the feed velocity and the processing method and realizing the electromechanical matching.