Seoung Hwan Lee

Optimisation of cutting parameters for burr minimization in face-milling operations

Burrs formed during face milling operations can be very difficult to characterize since there exist several parameters which have complex combined effects that affect the cutting process. Many researchers have attempted to predict burr characteristics including burr size and shape, using various experimental parameters such as cutting speed, feed rate, in-plane exit angle, and number of inserts. However, the results of these studies tend to be limited to a specific process parameter range and to certain materials. In this paper, the Taguchi method--which is a systematic optimisation method for design and analysis of experiments--is introduced to acquire optimum cutting conditions for burr minimization. In addition, analysis of variance (ANOVA) is employed to study more detailed performance characteristics. Experimental verifications are provided to show the effectiveness of this approach.

Run-to-run process control of magnetic abrasive finishing using bonded abrasive particles

In this study, magnetic abrasive finishing, a polishing method using novel bonded magnetic abrasive particles, is implemented in the nanometer-scale surface polishing of STAVAX (S136) die steel workpieces, which are widely used for precision lens molds. With the aid of run-to-run control, a process control method, nanometer-scale mold surface quality is achieved and maintained over multiple runs. A specially designed magnetic quill equipped with an electromagnet was connected to a computer numerical control machining center to construct the polishing setup. Based on Preston’s equation and a set of preliminary experiments, design of experiment and analysis of variance were used to select and evaluate the relevant control parameters for the process. The finishing results show that the magnetic abrasive finishing has a nanometer-scale finishing capability (down to 8 nm surface roughness). Under run-to-run control with the selected parameters, the surface roughness values were successfully maintained below the target values (10 and 50 nm for Ra and Rmax, respectively), which shows that the proposed magnetic abrasive finishing scheme is readily adaptable to ultraprecision polishing applications, which are subject to disturbances for a relatively long period of time.

Classification and prediction of burr formation in micro drilling of ductile metals

In the micro drilling of precision miniature holes, the formation of exit burrs is a topic of interest, especially for ductile materials. Because such burrs are difficult to remove, it is important to be able to predict various burr types and to employ burr minimisation schemes that consider burrs’ micro-scale characteristics. In the present work, an artificial neural network (ANN) was used to predict the formation of burrs in the micro drilling of copper and brass, along with burr formation/optimisation analysis specialised for micro drills. The influence of cutting conditions, including cutting speed, feed and drill diameter, upon exit micro burr characteristics such as burr size and type was observed, analysed and classified. Based on the results, an empirical equation to predict micro burr height is proposed herein. The classification results were compared with conventional burr cases using burr control charts. Then, micro burr types were predicted by means of an ANN, using the influential parameters as input vectors. The usefulness of the proposed scheme was demonstrated by comparing the experimental and prediction/analysis results.

Monitoring of Brittle-Ductile Transition during AFM Machining Using Acoustic Emission

An atomic force microscope (AFM) with suitable tips has been used for nano fabrication/nanometric machining purposes. In this paper, acoustic emission (AE) was introduced to monitor the nanometric machining of a brittle material (silicon) using AFM. In the experiments, AE responses were sampled, as the tip load was linearly increased (ramped load), to investigate machining characteristics during continuous movement. By analyzing the experimental results, it can be concluded that measured AE energy is sensitive to changes in the mechanism of material removal including the ductile-brittle transition during nanometric machining. The critical depth of cut value for the transition is evaluated and discussed.

Analysis of precision deburring using a laser —An experimental study and FEM simulation

The purpose of this study is to develop an effective methods for automated deburring of precision components. A high power laser is proposed as a deburring tool for complex part edges and burrs. For the laser experiments, rectangular-shaped carbon steel and stainless steel machined specimens with burr along one side were prepared. A 1500 Watts CO2 laser was used to remove burrs on the workpieces. The prediction of the heat affected zone (HAZ) and cutting profile of laser-deburred parts using finite element method is presented and compared with the experimental results. This study shows that the finite element method (FEM) analysis can effectively predict the thermal affected zone of the material and that the technique can be applied to precision components.

Investigation of the contact force distribution and dynamic behaviour of an automobile windshield wiper blade system

The structural behaviour of a windshield wiper system and the dynamic behaviour of the wiper rubber blade are investigated using finite element analysis. Non-linear contact analysis was performed to examine the influences of the structural design variables such as the curvature of the primary beam, the thickness of the yoke, the rotational angle of the yoke and the thickness of the steel beam on the distribution of the contact force along the blade length, and the effects of the vertical load and the coefficient of friction on the vibrational behaviour of the blade were investigated using transient dynamic analysis. Experimental validation was conducted by measuring the contact force distribution and the vibrational behaviour of the rubber blade. The experimental data and the simulated results show good agreement. The contact force distribution is sensitive to changes in the primary beam’s curvature, the yoke’s rotational angle and the steel beam’s thickness. The vertical load and the coefficient of friction both have significant influences on the vibrational behaviour of the rubber blade. It is found that the proper combination of the variables investigated allows a more uniform contact force distribution and less vibration and thereby improves the performance of the wiper blade. These analyses demonstrate the variables that influence the wiper blade behaviour and should provide key insight into means for improving the wiper performance.

Application of optical force measurement to mode characterization of atomic force microscopy nanomachining

Atomic force microscopy is often used not only to acquire the sample surface topography at the subnanometer scale but also to measure forces on the surface during imaging. This study aims to develop a practical measurement scheme of the actual scratching forces exerted during atomic force microscopy nanoscratching using a simple optical microscope setup. The measurement results are utilized to analyze the mode characteristics of atomic force microscopy nanomachining. Unlike typical atomic force microscopy force measurement methods using position-sensitive detector signal analysis, the optically measured atomic force microscopy cantilever deformation data using varying input (normal) forces along with information on the cantilever stiffness were used to estimate the components of the actual force exerted during nanomachining without using complex data interpolation methods. Scratching experiments were performed on Si(100) workpieces, and the estimated real force values were compared with the experimental data from atomic force microscopy nanomachining for each input force and corresponding scratch depth. Frictional coefficients and in-process acoustic emission monitoring results were also used to conduct an in-depth analysis of the actual force results. It is shown that the estimation results are meaningfully close to both the theoretical evaluations and the scratching experimental data as the scratch depth changes. Moreover, the force data are shown to have the ability to detect mode transitions such as the elastic–plastic and the plowing–cutting transitions during nanomachining, which validates the utility of this approach.

Analysis and monitoring of mode transitions during afm nanomachining of IZO-Coated pyrex glass

ABSTRACT The goal of this research is to investigate and monitor machining mode transitions during nanoscale scratching of IZO-coated Pyrex glasses using atomic force microscope (AFM). Among the AFM nanomachining mode features, which include elastic/plastic deformations and crack generation, pile-up (by ploughing) is a key surface phenomenon that can represent plastic deformation characteristics, such as a sign of chip making. Moreover, because the pile-up formation mechanism of coated materials is reported to be distinct from that of bulk materials, the examination of pile-up in coated materials is challenging, along with brittle transition (crack initiation). In this research, the pile-up formation and crack initiation, that occur during nanoscratching, were examined and analyzed near the coating-substrate (glass) boundary. In addition, acoustic emission (AE), a sensing scheme with nanoscale sensitivity, was introduced to detect significant machining state variations and mode transitions. Experimental and analysis results indicate that the proposed scheme is viable for characterizing/monitoring the nanoscale machining of coated materials.

The five-degree of freedom stitching method of areal surface data for high precision and large area measurement

In this research, a five-degree of freedom (5-d.o.f.) stitching method is proposed which is implemented by calculating the 5-d.o.f. relative position and orientation between small areas of 3D profile data acquired with high resolution. The relative position and orientation is calculated from the data of the overlap area for adjacent measured areas by using the least squares method and the cross correlation function. Furthermore, a data synchronizing algorithm is also proposed for the case in which a specimen is measured by different instruments. To verify practical application of the stitching method and the synchronizing algorithm, a multi-probe optical measuring instrument was developed.

Characterization of Magnetic Abrasive Finishing Using Sensor Fusion

In configuring an automated polishing system, a monitoring scheme to estimate the surface roughness is necessary. In this study, a precision polishing process, magnetic abrasive finishing (MAF), along with an in-process monitoring setup was investigated. A magnetic tooling is connected to a CNC machining to polish the surface of stavax(S136) die steel workpieces. During finishing experiments, both AE signals and force signals were sampled and analysed. The finishing results show that MAF has nano scale finishing capability (upto 8nm in surface roughenss) and the sensor signals have strong correlations with the parameters such as gap between the tool and workpiece , feed rate and abrasive size. In addition, the signals were utilized as the input parameters of artificial neural networks to predict generated surface roughness. Among the three netwoks constructed -AE rms input, force input, AE+force input- the ANN with sensor fusion (AE+force) produced most stable results. From above, it has been shown that the proposed sensor fusion scheme is appropriate for the monitoring and prediction of the nano scale precision finishing process 기호설명 µ : 마찰계수 w : 단면폭 F : 수직연마력 V : 입자속도 R : 입자반경 A