Jeong-Du Kim

Theoretical analysis of micro-cutting characteristics in ultra-precision machining

Abstract The physics of the micro-cutting process at very small depths of cut (1 μm or less) is not well understood despite the successful development of ultra-precision machining technology. Sliding along the clearance face of the tool due to the elastic recovery of the workpiece and plowing due to the tool edge radius may become important in the micro-cutting range. To obtain a clear understanding of these two factors, an orthogonal cutting model, the so-called RECM (round-edge cutting model), is suggested.

Simulation for the prediction of surface-accuracy in magnetic abrasive machining

A new machining technique, magnetic abrasive machining which uses magnetic force as a machining pressure, has been developed recently for the efficient and precision finishing of surfaces. The process is controllable because the machining pressure is controlled only by the current that is input to the coil of solenoid, but it needs the monitoring of the surface roughness for the automation of the process and for the achieving of machining efficiency by preventing over-finishing of the surface. For this, in the present study, the surface roughness is predicted as a function of finishing time by a model that has been derived from the removed volume of material. Thus, it is possible, from the surface-roughness model, to predict the time when existing scratches are completely removed. The simulation results are confirmed by comparing them with the experimental results of previous papers.

Micro surface phenomenon of ductile cutting in the ultrasonic vibration cutting of optical plastics

Abstract Mirror-surface machining is a very important technology in the manufacturing of precision parts, especially optical parts. At the present time these are parts produced by multi-processes, i.e. grinding and polishing, which are inefficient. In this study, ultrasonic vibration cutting as a substitute for such processes in the precision machining of optical plastics (CR-39) which have been used for optical lenses is suggested and experimented upon. To analyze the characteristics of surfaces machined by ultrasonic vibration cutting in the ductile mode, wavelength spectrum analysis is carried out and the micro-structure is compared with that of conventional cutting. As a result, in micro cutting by ultrasonic vibration, it was confirmed that surfaces of ductile cutting are obtained, for depths of cut of less than 2.7 μm.

Development of a magnetic abrasive jet machining system for precision internal polishing of circular tubes

Abstract A recently developed finishing process using a rotating magnetic field is known to be very efficient for the finishing of parts such as vacuum tubes, sanitary tubes, etc. which are difficult to be finished by conventional finishing methods as they are generally curved tubes. However, the finishing system using a rotating magnetic field has the defect that the cross-section of the workpiece can only be circular because of the internal rotating tool. Therefore, a new finishing process for workpieces of non-circular cross-section is required. Magnetic abrasive jet machining is a new concept in finishing processes, being a precision internal finishing method using a working fluid mixed with magnetic abrasives, which is jetted into the internal surface of the tube, with magnetic poles being provided on the external surface of the tube. In this study, the new-concept finishing process, or the magnetic abrasive jet machining system, was developed. The machining conditions were predicted using simulation and some characteristics of the finishing process were analyzed.

Study on magnetic polishing of free-form surfaces

Magnetic polishing technology applicable to free-form surfaces such as the die/mold manufacturing field, has been studied using two types of magnetic polishing tool. Finishing efficiency and final surface roughness can be satisfactorily achieved at the same time by magnetic polishing using two types of magnetic polishing tool. One is an abrasive wheel type and the other is a magnetic brush type. The possibility of free-form surface polishing has been confirmed by use of the magnetic polishing technology because it has flexibility of profiling and does not need any complex tool-path control, with respect to workpiece surfaces. Magnetic force was estimated and measured. A two-stage magnetic polishing experiment has been executed using the magnetic polishing tools and mini CNC milling machine without tool-path control. A realization of efficient polishing of curved surfaces is possible using the two-stage magnetic polishing method, and it was also confirmed that automation of free-form surface polishing is possible by this method.

High-spend machining of aluminium using diamond endmills

Milling experiments on aluminum alloy were carried out using a laboratory-designed diamond endmill. The machining of aluminium alloy using a conventional tool at a conventional cutting speed generally results in short tool-life, poor surface quality and poor edge finishes because of the formation of built-up edges and burrs. The machining technology of aluminum alloy surfaces with a good surface finish and edge finishing is very important and required in many industries. The experimental results reveal the possibility of machining a mirror-like aluminum alloy without built-up edges and burrs using the designed diamond endmill at high speed.

Characteristics of chip generation by ultrasonic vibration cutting with extremely low cutting velocity

Recently, mirror-surface machining of brittle materials such as ferrite, glass, and optical plastics has become more important, as these materials are used in optical communications and precision devices. Non-ferrous metals such as aluminium and copper were readily turned with diamond tools, but as the need for both infra-red and reflective optics escalated, the need to machine brittle materials arose. In this paper, ultrasonic vibration cutting at 20 kHz at extremely low cutting velocity for the precision machining of brittle plastics used for optical lenses is suggested and tested. The mechanism of chip generation, and characteristics of surfaces in the ductile mode, machined by ultrasonic vibration cutting are investigated. As a result, when micro cutting by ultrasonic vibration, it was confirmed that the chips generated by ductile mode cutting are obtained at 1/40 of the critical cutting velocity of the ultrasonic vibration cutting system, which is an extremely low cutting velocity.

A study of the ultrasonic-vibration cutting of carbon-fiber reinforced plastics

Abstract In the use of carbon-fiber reinforced plastics it is often necessary to cut the components, but the cutting of CFRP is usually made difficult by delamination of the composites and by a short tool life. In this paper, the machinability of CFRP by means of ultrasonic-vibration cutting is investigated experimentally. The experimental results have led to the trial application of ultrasonic-vibration cutting, which has been verified to be highly effective in terms of cutting force and surface quality.

Development of a micro-depth control system for an ultra-precision lathe using a piezo-electric actuator

Abstract Micro-positioning systems using piezo-electric actuators have very wide applications, for example as in ultra-precision machine tools, optical devices and measurement systems In order to keep a high-precision displacement resolution, they use a position sensor and feed back the error. From the practical point of view, high-resolution displacement sensor systems are very expensive and it is difficult to guarantee such sensitive sensors to work properly in the hard operational environment of industry. In this study, a micro-depth control system which does not require a position sensor but which uses piezoelectric voltage feedback has been developed. It is driven by hysteresis—considering a reference input voltage which is calculated by computer, and then uses actuator/sensor characteristics of piezo-electric materials. Results of experiments indicate a fast and stable response of the micro-positioning system and suggest it is an efficient technique for controlling the piezo-electric actuator.

Development of a combined-type tool dynamometer with a piezo-film accelerometer for an ultra-precision lathe

Abstract The cutting force is the most important variable by means of which to understand the mechanics of ultra-precision machining. However, most tool dynamometers monitor the static cutting force, although it is necessary to measure the dynamic cutting force to clarify the machinability of the material, the formation of the chip, chatter and the wear of the tool. In this research, a combined-type tool dynamometer which can measure the static cutting force and the dynamic cutting force together by use of strain gauges and a piezo-film accelerometer has been developed. An analysis of the dynamometer has also been carried out.