Prediction Methods and Experimental Techniques for Chatter Avoidance in Turning Systems: A Review

The general trend towards lightweight components and stronger but difficult to machine materials leads to a higher probability of vibrations in machining systems. Amongst them, chatter vibrations are an old enemy for machinists with the most dramatic cases resulting in machine-tool failure, accelerated tool wear and tool breakage or part rejection due to unacceptable surface finish. To avoid vibrations, process designers tend to command conservative parameters limiting productivity. Among the different machining processes, turning is responsible of a great amount of the chip volume removed worldwide. This paper reports some of the main efforts from the scientific literature to predict stability and to avoid chatter with special emphasis on turning systems. There are different techniques and approaches to reduce and to avoid chatter effects. The objective of the paper is to summarize the current state of research in this hot topic, particularly (1) the mechanistic, analytical, and numerical methods for stability prediction in turning; (2) the available techniques for chatter detection and control; (3) the main active and passive techniques.

Concept and proof for an all-silicon MEMS micro speaker utilizing air chambers

MEMS-based micro speakers are attractive candidates as sound transducers for smart devices, particularly wearables and hearables. For such devices, high sound pressure levels, low harmonic distortion and low power consumption are required for industrial, consumer and medical applications. The ability to integrate with microelectronic circuitry, as well as scalable batch production to enable low unit costs, are the key factors benchmarking a technology. The Nanoscopic Electrostatic Drive based, novel micro speaker concept presented in this work essentially comprises in-plane, electrostatic bending actuators, and uses the chip volume rather than the its surface for sound generation. We describe the principle, design, fabrication, and first characterization results. Various design options and governing equations are given and discussed. In a standard acoustical test setup (ear simulator), a MEMS micro speaker generated a sound pressure level of 69 dB at 500 Hz with a total harmonic distortion of 4.4%, thus proving the concept. Further potential on sound pressure as well as linearity improvement is outlined. We expect that the described methods can be used to enhance and design other MEMS devices and foster modeling and simulation approaches.

Single Grain Scratch Tests to Determine Elastic and Plastic Material Behavior in Grinding

This paper presents an overview of kinematic simulations in grinding. Up to now the simulations are carried out under the assumption of an ideal cutting process. Therefore, the simulation results are not exactly identical to the experimental results. For this reason, the simulation needs to be enhanced with the plastic material flow during cutting. To explain this behavior, single grain scratch experiments were conducted to detect the different sources of influence on the plastic deformation and on the pile-up. First, in the experiments the grain shapes as well as the cutting speeds were varied. To take the effect of different grain shapes into account, three different grains were used. The effect of the cutting speed was investigated at cutting speeds ranging from 60 to 120 m/s. The results were evaluated with a confocal microscope. To quantify the results of the efficiency of the cutting process, the relative chip volume parameter was used.

Recent Advances and Future Perspectives in a Grinding Wheel with Defined Grain Pattern

It is achieved that abrasive grains could be ordered on the surface of a grinding wheel using modern manufacturing methods. The excellent feature of a grain-arranged grinding wheel is that it can increase the proportion of active grains, improve the cutting efficiency, increase the chip volume space, effectively reduce the grinding temperature, prolong the service life of the grinding wheel and improve the surface finish of workpiece. Consequently, in the area of academic and industry the research of a grain-arranged grinding wheel has become a hot research topic, and more and more scholars focus on the research of the grain-arranged grinding wheel. In this paper, distribution patterns of abrasive grains were introduced; molding techniques for distributing abrasive grains were summed up; progress in research and future research trends of a grain-arranged grinding wheel was presented.