• Journal of the Korean Society for Precision Engineering
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• v.24 no.6
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• pp.131-137
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• 2007

In metal casting process, it is very difficult to predict the form accuracy of cast part and reduce repeatability error. In this study, the variations of form accuracy were measured in the process of metal cast prototyping, where RP part is manufactured from CAD model in the first, and then, wax part is cast in the vacuum environment using the RP part as master model, and finally metal prototype is cast using ceramic mold and the wax part as pattern. To investigate the variations of form accuracy, the averages and standard deviations of error distribution of the parts measured by 3D scanner were compared. It was observed that the biggest shrinkage is generated during the extraction of wax part in the second step and the biggest deterioration of form accuracy is generated during the metal part casting in the last step.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.4
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• pp.57-63
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• 2003

Machining information such as form accuracy and surface roughness is an important factor for manufacturing precise parts. To this regard, OMM (On the Machine Measurement) has been researched for last several decades to alternate CMM (Coordinate Measurement Machine) process. In this research, the OMM system with a laser displacement sensor was developed for measuring form accuracy and surface roughness of the machined workpiece on the machine tool. The surface roughness was estimated comparing the sensory signal with the reference data measured from master specimen. Also, form accuracy was determined from the moving averaged raw data. In addition, the geometric error map constructed beforehand using the geometric errors of the machine tool was used to compensate the obtained form accuracy. The overall performance was compared with CMM result, and verified the feasibility of the measurement system.

• Design & Manufacturing
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• v.17 no.2
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• pp.15-21
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• 2023

In this study, a diamond turning machine and a laser-assisted machining module were utilized for the complex combined cutting of aspheric shapes and fine patterns on the surface of high-hardness brittle material, silicon. The analysis of material's form accuracy and corrective machining was conducted based on key factors such as laser output, rotational speed, feed rate, and cutting depth to achieve form accuracy below 1 ㎛ and surface roughness below 0.1 ㎛. The cutting condition and corrective machining methods were investigated to achieve the desired form accuracy and surface roughness. The rotational speed of the spindle and the linear feed rate of the diamond turning machine were varied in five stages for the cutting condition test. Surface roughness and form accuracy were measured using both a contact surface profilometer and a non-contact surface profilometer. The experimental results revealed a tendency of improved surface roughness with increased rotational speed of the workpiece, and the best surface roughness and form accuracy were observed at a feed rate of 5 mm/min. Furthermore, based on the cutting condition experiments, corrective machining was performed. The experimental results demonstrated an improvement in form accuracy from 0.94 ㎛ to 0.31 ㎛ and a significant reduction in the average value of the surface roughness curve from 0.234 ㎛ to 0.061 ㎛. This research serves as a foundation for future studies focusing on the machinability in relation to laser output parameters.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.68-74
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• 1999

One of the recent changes in machining technology is rapid application of micro- and high precision grinding processes. A fine groove generation is necessary for the fabrication of optic, electronic and semiconductor parts, and achieved by chemical or mechanical processes. Slot grinding is very efficient for the generation of micro ordered groove with hard and brittle materials. As slot grinding is continuous, the ground depth become gradually shallow because of wheel wear. The form accuracy become worse from the increase of ground slot width by the loading phenomena at wheel side, results on chipping damage of the workpiece. The experiments achieve to the enhancement of the form accuracy and chipping free of the brittle materials using V shaped cast iron bonded diamond wheels. In this study we focused on the investigation of the effect of the high pressure air jet on the grinding characteristics. As a results, we found that the high pressure air jet is very effective on the reductions of the wheel wear, enhancement of the form accuracy.

• Journal of the Korean Society for Precision Engineering
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• v.4 no.2
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• pp.36-46
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• 1987

An optical technique using laser for non-contact measurement of surface roughness and form accuracy of ground surfaces is presented. It is found that, when a ground surface is illuminated by a beam of laser light, the roughness height and slope distribution has significant influence on the pattern of reflection and it maintains an unique Gaussian distribution relationship with the surface roughness. The principle idea of the optical measurement system is therefore monitor the radiation, and then calibrate it in process against surface roughness by means of necessary digital data processing. On the other hand, measuring the form accuracy of a ground surface is accomplished by using a triangular method, which is based on observing the movement of an image of a spot of light projected onto the surface. The image is focused, through a series of lenses for magnification, on a photodetector array lf line configur- ation. Then the relative movement of image and consequently the form accuracy of the surface can be obtained through appropriate calibration procedures. Experimental test showed that the optical roughness measurement technique suggested in this work is very efficient for most industrial applications being capable of monitoring the roughness heights ranging 0.1 to 0.6 .$\mu$m CLA values. And form accuracy can be measured in process with a resolution of 10 .$\mu$m.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.6
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• pp.138-145
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• 2007

Among various rapid prototyping processes, stereo-lithography process which can manufacture transparent prototype is known to be the greatest in the form & dimensional accuracy and surface roughness. In this paper, bench mark tests of 4 stereo-lithography-type rapid prototyping apparatus were carried out using transparent materials. The test includes measurement of mechanical properties, form accuracy, building speed and manufacturing cost. It was observed that ViperPRO of 3D systems is advantageous in the mechanical properties and building speed, RM600011 of CMET in sub-milli scale form accuracy and manufacturing cost, and relatively economical Eden500V of Objet is great in tensile strength at room temperature.

• English Language & Literature Teaching
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• v.11 no.1
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• pp.77-98
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• 2005

The purpose of the study is to investigate whether focus-on-form instruction is effective in promoting accuracy in writing and to make some suggestions regarding education in business English writing. For this purpose, an experiment, of which the participants were 29 college sophomores taking a course in business English, was made. The learners received instruction in the English nouns followed by modificatory phrases or clauses through the focus-on-form techniques, feedback and explicit explanation. The results were as follows: First, the learners who received focus-on-form instruction improved accuracy in writing. Second, there was a correlation between the learners' English proficiency levels and the effects of focus-on-form instruction. Third, the high level learners showed more positive attitude toward focus-on-form instruction than the low level ones. To promote accuracy in written business communication, the following suggestions were made on the basis of the results: First, focus-on-form instruction should be incorporated into a content-based business English class. Second, repeated focus-on-form instruction is needed. Third, learners' English proficiency levels should be taken into account when focus-on-form instruction is given.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.10
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• pp.31-40
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• 2003

In this paper, optimal cutting condition to minimize the form error in side wall machining with a flat end mill is studied. Cutting forces and tool deflection are calculated considering surface shape generated by the previous cutting such as roughing. Using the form error prediction method from tool deflection, optimal cutting condition considering form accuracy is investigated. Also, the effects of tool teeth number, tool geometry and cutting conditions on form error are analyzed. The characteristics and the difference of generated surface shape in up and down milling are discussed and over-cut free condition in up milling is presented. Form error reduction method through successive up and down milling is also suggested. The effectiveness and usefulness of the presented method are verified from a series of cutting experiments under various cutting conditions. It is confirmed that form error prediction from tool deflection in side wall machining can be used in optimal cutting condition selection and real time surface error simulation for CAD/CAM systems. This study also contributes to cutting process optimization for the improvement of form accuracy especially in precision die and mold manufacturing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.44-48
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• 1996

This paper describes the effects of thermal deformation in electromagnetic chuck on the grinding accuracy. Gringing process is the last machining process and decisive in saving past other machining cost. The thermal deformation of grinding machine is unavoidable and affect seriously ginding accuracy. The thermaldeformation of electromagnetic chuck is one of important thermal problems. Heat generation of magnetic chuck is analyzed and measured. The temperature disturibution in chuck is elliptical form with high temperature in center of chuck. The thermal deformation form of chuck is changed with time to mountain form. The grinding experiment shows that the thermal deformation of magnetic chuck influence strongly machining accuracy as much as the headstock

• English Language & Literature Teaching
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• v.13 no.2
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• pp.63-90
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• 2007

The present study investigated what combination of three form-focused options - explicit explanation, production practice, and corrective feedback - may be effective in helping low-proficiency learners improve accuracy in communicative writing. The subjects were 34 Korean university students enrolled in 'Business English 1' and the study lasted 11 weeks. The relative clause structure was selected as the target structure. The study found that the combination of explicit explanation, sentence-level production practice, communicative writing practice, and recasts had a significantly greater effect on improved accuracy than the combination of communicative writing practice and recasts and that of explicit explanation, communicative writing practice, and recasts. Because the second and third combinations didn't lead to significantly improved accuracy, it can be concluded that of the form-focused options forming the first combination sentence-level production practice made a decisive contribution to the significant increase in accuracy. It also found that the provision of self-correcting opportunities before providing recasts on errors committed in sentence-level production practice resulted in significantly greater accuracy in communicative writing than the provision of recasts alone on them. The results of the study suggest that we should make low-proficiency Korean learners have sentence-level production practice which is intensive and focused and make them self-correct targeted errors before providing them with narrowly focused recasts in order to help them to improve writing accuracy.