• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.972-978
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• 2004

Forward slip is an important parameter often used in rolling-speed control models for tandem hot strip rolling mills. In a hot strip mill, on-line measurement of strip speed is inherently very difficult. Therefore, for the set-up of the finishing mill, a forward slip model is used to calculate the strip speed from roll circumferential velocity at each mill stand. Due to its complexity, most previous researches have used semi-empirical methods in determining values for the forward slip. Although these investigations may be useful in process design and control, they do not have a theoretical basis. In the present study, a better forward slip model has been developed, which provides for a better set-up and more precise control of the mill. Factors such as neutral point, friction coefficient, width spread, shape of deformation zone in the roll bite are incorporated into the model. Implementation of the new forward slip model for the control of a 7-stand hot strip tandem rolling mill shows significant improvement in roll speed set-up accuracy.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.10
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• pp.212-220
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• 2002

The finishing process for die and mold manufacturing is very important because it influences the final quality of products. Injection molds need higher quality surface than general purpose dies and molds. Conventional polishing can not make mold surface down to nanometer roughness efficiently because of their loading and glazing. This paper focused on the development of fixed abrasive pad using water swelling mechanism of polymer binder network. Self-conditioning was recognized as the long term polishing stabilization tool without any loading or glazing because water makes fixed abrasives free by swelling of the pad. Consequently, stable nano-polishing process has been applied on the injection mold, from the experimental results with polished surface roughness of Ra 15.1nm on STD-11 die steel.

• Design & Manufacturing
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• v.12 no.2
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• pp.16-21
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• 2018

Recently, as the demand for high-precision parts increases due to industrial development, a machine tool system for ultra-precision machining and polishing has been actively developed. As a result, there is an increasing demand for ultra-precision surface roughness along with dimensional processing. However, due to the increase in processing time due to the demand for ultra-precise surfaces and enormous facility investment, it is difficult to secure competitiveness. The polishing process using the abrasive film in super precision machining has been applied to machines, electronic devices, aerospace, and medical fields. Super finishing using the abrasive film which is applied in the industrial field recently can achieve high surface roughness in a short time. Super finishing using the abrasive film which is applied in the industrial field recently can achieve high surface roughness in a short time. Also, application of industrial field is increasing due to advantages such as low noise and low dust. Recently, researches on stainless steel having strong resistance to corrosion, heat resistance, heat resistance, toughness and weldability have been actively conducted with respect to the nuclear energy industry or marine development. Therefore, in this study, surface roughness and residual stress were measured after SUS304 polishing using dynamic analysis of film polishing apparatus and polishing film.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.2
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• pp.86-92
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• 2021

Usually, the die-cast components used in small mobile devices require finishing processes, such as computer numerically controlled coating. In such cases, porosity is the most important defect. The shape of the molten aluminum that passes through the runner and gate in a mold is the one of the factors that influences gas porosity. To define the spurt index, which numerically indicates the shape of molten aluminum after the gate, Reynolds number and Ohnesorge number are used. Before die fabrication, computer-aided engineering analysis is performed to optimize the filling pattern. Finally, X-ray and surface inspection are performed after casting and machining to evaluate how the spurt index affects porosity and other product parameters. Based on the results obtained herein, a new gating system design process is suggested.

• Textile Coloration and Finishing
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• v.23 no.4
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• pp.304-311
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• 2011

For sound absorption and sound insulation in automobile industry, the sound absorption materials based on meltblown nonwovens were prepared by SMS (spunbond-meltblown-spunbond) technique. And the sound absorption coefficient (${\alpha}$) of the meltblown nonwoven, produced with isotatic-polypropylene(PP), was examined for the various processing conditions such as die-to-collector distance(DCD), nonwoven weight(GSM), and air suction conditions. The meltblown nonwoven for sound absorption materials was composed of bulky microfiber web, increasing with increases in weight and DCD. The sound absorption coefficient(${\alpha}$) was excellent as a sound absorption materials of PAD type composed of SMS(spunbond-meltblownspunbond) nonwovens.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1784-1788
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• 2003

For the improvement of geometrical accuracy in end milling, cutting method and cutting condition selection are investigated in this paper. As machining processes are composed of several steps such as roughing, semi-finishing. and finishing, cutting forces and tool deflection are calculated considering surface shape generated by the previous cutting. The effects of tool teeth numbers, tool geometry, and cutting conditions on the form error are analyzed. Using the from error prediction method from tool deflection, cutting condition for geometrical accuracy improvement is discussed. The characteristics and the difference of generated surface shape in up and down milling are dealt with and over-cut free condition in up milling is presented. The form error reduction method by alternating up and down milling is also suggested. The effectiveness of the presented method is examined from a set of cutting tests under various cutting conditions. This research contributes to cutting process optimization for the geometrical accuracy improvement in die and mold manufacture.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.5
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• pp.59-66
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• 2003

This study suggests the new ultraprecision finishing techniques for micro die and mold parts using magnetic field-assisted polishing. Conventional magnetic abrasives have several disadvantages, which are missing of abrasive particle and inequal mixture between magnetic particle and abrasive particle. Therefore, bonded magnetic abrasive particles are fabricated by several method. For example, plasma melting and direct bonding. Carbonyl iron powder is used as magnetic particle there silicon carbide and alumina are abrasive particles. Developed magnetic abrasives are analyzed using SEM. Feasibility of magnetic abrasive and polishing performance of this magnetic abrasive particles also have been investigated. After polishing, surface roughness of workpiece is reduced from 85.4 ㎚ Ra to 9 ㎚ RA.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.1
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• pp.45-51
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• 2002

To reduce the cost and increase reliability of die and mold products, automation of the finishing (polishing) process is essential. A major element of automation is a reliable database and a knowledge base for polishing status. This paper presents a polishing expert system which can determine optimal polishing sequences and conditions by using an empirical formula and an experimental database. The simplex method was used for the curve fittings of the experimental results. Also a graphical user interface, which visualizes the optimized results, was developed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.98-102
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• 1994

There are many difficulties in automatic polishing for die & mold surfaces. Even though the process has been studied in the past 15 years, it has not been achieved yet, but by the process of actual hand work of well-skilled workers. A new magentic assisted polishing process, which is one of the potential method for automation of surface finishing has been studied in the past 10 years by colleagues. The process has many merits, but on the other hand also has demerits, one being low efficiency of gridability by comparision with grinding wheel polish. Therefore, some attempts were tried to improve the grindability by adopting electropolishing, ultra-high speed milling, 5-axis controlled machine etc... most recently by collegues. This study also aims to improve the efficiency of polishing by introducing the easily-polished shape surface milling method equalizing the tool feed per tooth to the pick feed. This milling method was experimentally confirmed to have sufficient grindability to polish milled surface (with 10 .mu. mRmax surface roughness) into mirror surface (with 0.4 .mu. mRmax surface roughness).

• The Journal of Korean Academy of Prosthodontics
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• v.36 no.6
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• pp.888-899
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• 1998

In-Ceram system is one of contemporary esthetic all ceramic restorations and has relatively high flexural strength. The purpose of this study was to evaluate the marginal fidelity according to type of resin cement and measuring position, and to evaluate fracture strength according to type of resin cement. In this study, twenty seven In-Ceram crowns were fabricated on the metal master die of prepared maxillary right central incisor and devided into three groups. All specimens were cemented with Panavia 21 (group PV), Super-bond (group SB) and Lute-it (group LI) on the metal master die. After cementation, specimens were measured marginal gap between the margin of the In-Ceram crown and the finishing line of metal master die by using a stereomicroscope (SZ-ST, Olympus, Japan). Marginal gaps were recorded at the labial, lingual, mesial and distal measuring points on the metal master die. For the mesurement of fracture strength, lingual surfaces of cemented specimens were loaded at a distance of 1mm from incisal edge by using the Autograph S-2000 (Shimadzu, Japan). The results of marginal fidelity and fracture strength were statistically analyzed with the SPSS version 8.0 programs. The results of this study were as follows: 1. In comparison of marginal fidelity according to the measuring points, there was no significant difference. 2. The marginal fidelity according to the type of resin cement was decreased in order of group $LI\;(63.75{\mu}m),\;SB\;(77.78{\mu}m),\;PV\;(86.53{\mu}m)$, and there was significant difference between group LI and PV (p<0.05). 3. The fracture strength according to the type of resin cement was showed descending order of group $LI\;(60.00kg/cm^2),\;SB\;(56.80kg/cm^2),\;PV\;(56.11kg/m^2)$, but there was no significant difference.