• Design & Manufacturing
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• 제15권4호
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• pp.37-42
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• 2021

The tube necking process increases the thickness of the material, and some of the tube necking products require cutting on the inside of the formed product as a post-process. In order to prevent over-cutting or un-cutting due to increased thickness during cutting, it is necessary to know in advance the increase in thickness after forming. Therefore, in this study, the thickness change according to the tube necking was observed. Aluminum 3003-F and 6061-O were used for the materials used in the experiment, and necking was carried out up to 50% of the outer diameter of the tube through five processes. The two materials were formed under the same conditions, and the thickness of three points was observed in each process. In addition, the thickness increase of the two materials was compared, and the trend of thickness increase according to the cumulative necking ratio was observed. As a result of the experiment, both materials had the smallest thickness at the end of the formed product. In addition, as a result of comparing the thickness measurement values of the two materials, the maximum difference was 0.1mm, indicating that there was no difference in thickness between the two materials.

• 한국재료학회지
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• 제31권11호
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• pp.601-607
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• 2021

Laser cladding a surface treatment process that grants superior characteristics such as toughness, hardness, and corrosion resistance to the surface, and rebuilds cracked molds; as such, it can be a strong tool to prolong service life of mold steel. Furthermore, compared with the other similar coating processes - thermal spray, etc., laser cladding provides superior bonding strength and precision coating on a local area. In this study, surface characteristics are studied after laser cladding of low carbon steel using 18%Cr-2.5%Ni-Fe powder (Rockit404), known for its high hardness and excellent corrosion resistance. A diode laser with wavelength of 900-1070 nm is adopted as laser source under argon atmosphere; electrical power for the laser cladding process is 5, 6, and 10 kW. Fundamental surface characteristics such as crossectional microstructure and hardness profile are observed and measured, and special evaluation, such as a soldering test with molten ALDC12 alloy, is conducted to investigate the corrosion resistance characteristics. As a result of the die-soldering test by immersion of low carbon alloy steel in ALDC12 molten metal, the clad layer's soldering thickness decreases.

• Design & Manufacturing
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• 제16권4호
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• pp.46-51
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• 2022

The piercing process of creating holes in sheet metals for mechanical fastening generates high shear force. Real-time monitoring technology could predict tool damage and product defects due to this severe condition, but there are few applications for piercing high-strength aluminum. In this study, we analyzed the load signal to predict the punch's wear level during the process with a piezoelectric sensor installed piercing tool. Experiments were conducted on Al6061 T6 with a thickness of 3.0 mm using piercing punches whose edge angle was controlled by reflecting the wear level. The piercing load increases proportionally with the level of tool wear. For example, the maximum piercing load of the wear-shaped punch with the tip angle controlled at 6 degrees increased by 14% compared to the normal-shaped punch under the typical clearance of 6.7% of the aluminum piercing tool. In addition, the tool wear level increased compression during the down-stroke, which is caused by lateral force due to the decrease in the diameter of pierced holes. Our study showed the predictability of the wear level of punches through the recognition of changes in characteristic elements of the load signal during the piercing process.

• 한국정밀공학회지
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• 제13권3호
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• pp.110-122
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• 1996

Finite element analysis tool was developed to analyze the casting process. Generally, casting process consists of mold filling and solidification. Both filling and solidication process were simulated simultaneously to investigate the effects of process variables and to predict the defect. At filling process, thermal coupling was especially considered to investigate thermal history of material during the filling stage. And thermal condition at the final stage of filling is used as the initial conditions in a solidification process for the exact simullation of the actual casting processes. At mold filling process, Lagragian-type finite element method with automatic remeshing scheme was used to find the material flow. A perturbation method with artificial viscosity is adopted to avoid numerical instability in low viscous fluid. At solidification process, enthalpy-based finite element method was used to solove the heat transfer problem with phase change. And elastic stress analysis has been performed to predict the thermal residual stress. Through the FE analysis, solidification time, position of solidus line, liquidus line and thermal residual stress are found. Through the study, the importance of combined analysis has been emphasized. Finite element tools developed in this study will be used process design of casting process and may be basic structure for total CAE system of castings which will be constructed afterward.

• 한국표면공학회지
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• 제56권5호
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• pp.328-334
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• 2023

The carbon-based films have various properties, which have been widely applied in industrial application. However, it has critical drawback for poor adhesion between films and metal substrate. In the present work, we have deposited carbon-based films on injection mold steel by plasma assisted chemical vapor deposition (PACVD). In order to improve adhesion, prior to film deposition, the substrate was nitriding-treated using PACVD. And its effect on the adhesion was investigated. Due to the pre-nitriding, the amorphous carbon nitride (a-CN:H) films presented 10 times higher adhesion (34.9 N) than that of un-nitirided. In addition, a friction coefficient was decreased from 0.29 to 0.15 for the amorphous carbon (a-C:H) due to improved adhesion. The obtained results demonstrated that pre-nitriding considerably improved the adhesion, and the relationship among adhesion, hardness, and surface roughness was discussed in detail.

• Design & Manufacturing
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• 제18권2호
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• pp.23-28
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• 2024

The automobile industry is a wide range of related industries, including parts manufacturing and vehicle assembly, press processing is an essential element in making automobiles. Press processing is a processing method for metal sheets that has relatively high dimensional and shape precision and is suitable for mass production. It refers to processing by attaching a special tool, a mold, to a press machine. Recently, the automobile industry is attempting to reduce the weight of automobiles in order to reduce carbon emissions due to global warming, and the use of high-strength steel sheets, which are lighter than general structural steel sheets, is a natural trend. Shear processing is required to use high-strength steel, and the shape of the shear surface created by shear processing has a significant impact on the quality of the automobile. Therefore, various methods are being attempted to improve the share surface during shear processing. Among them, shaving processing is a method of shearing the primary shearing area again, and it is difficult to obtain an accurate answer because complex deformation occurs in the microscopic shear area. Therefore, in this study, the effect of machining allowance on shaving processing was analyzed using the finite element method using high-strength steel plate (SPFH590), and the differences were compared and examined through actual experiments under the same conditions.

• 헤리티지:역사와 과학
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• 제47권4호
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• pp.224-243
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• 2014

"용재총화", "천공개물", "The Korean Review"등의 고문헌을 통하여 청동유물 제작에 사용된 소재, 거푸집, 합금 등의 주조기술을 확인하였다. 상평통보 복원 주조실험은 "The Korean Review"를 기초한 주물사주조법을 적용하여 황동, 청동 소재의 모전판(母錢版, 鑄錢版)을 제작하였다. 거푸집은 본기(本器)틀과 목틀, 주물사로 구성되는데 본기틀은 주물사를 담는 바깥 틀의 재질에 따라 목틀과 쇠틀로 나뉘며, 주물사는 옅은 황색의 전북 이리사를 사용했다. 주물사주조법으로 상평통보 복원에 사용된 모합금 성분비를 살펴보면, 황동은 "The Korean Review" 기록의 성분비인 Cu 60%, Zn 30%, Pb 10%를 근거로 삼았으며, 실제 복원에는 합금 시 아연과 납이 기화되어 성분비율이 감소될 것을 감안하여 Cu 60%, Zn 35%, Pb 15%로 설정하였다. 청동은 청주시 신봉동유적 출토 해동 통보의 성분비인 Cu 80%, Sn 6%, Pb 14%를 근거로 하였으며, 실제 복원에는 Cu 80%, Sn 11%, Pb 19%로 설정하였다. 주물사주조법에 의한 상평통보 복원은 목재로 부전(父錢)을 먼저 제작하고 목틀과 본기쇠틀을 이용한 거푸집 만들기, 합금, 주조하기, 모전 만들기 등의 과정으로 모전판(母錢版, 鑄錢版)을 복원하였다. 복원된 상평통보의 모합금과 1차 주조, 2차 주조물의 성분분석을 실시한 결과 청동 모합금은 구리는 약 5%가 증가하고 납은 약 4% 손실되었으며, 황동 모합금은 구리는 약 5%가 증가하고 납은 약 4%, 아연은 12%은 감소하여 아연의 손실률이 큰 것을 알 수 있다. 1차, 2차 모전판의 EDS 분석결과 청동 모전판은 1차에 비해 2차에서 납이, 황동 모전판은 아연이 낮게 나온 것은 1차 모전판의 용융과정에서 납과 아연이 기화된 결과로 보인다. 또한 청동과 황동의 모합금과 1차, 2차 주전판의 미세조직에서는 ${\alpha}$상과 크고 작은 납 편석물이 보이고, 황동 모전판에서만 불순물로 보이는 Al, Si 등이 확인되었다.

• 구강회복응용과학지
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• 제22권2호
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• pp.193-202
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• 2006

Objective To evaluate the influence of water storage on the mechanical properties of dental adhesives over 1 and 3 months. Materials and Methods Adhesive resin sheets were prepared by pouring either All-bond 2(AB), Clearfil SE Bond(SE) into a mold measuring $15{\times}15{\times}0.9mm$. After solvent in primer evaporation, the adhesives were light-cured and removed from the mold and divided in two pieces, trimmed to hourglass shape that were used to determine the micro-tensile strength(MTS). Another hourglass shaped metal mold measuring $2.0{\times}1.5mm$ in cross-section area was made to determine the Young's modulus(E). Adhesive specimens for Young's modulus(E) were prepared in the same method. Specimens were stored at $37^{\circ}C$ in distilled water and tested after 1 and 3 months. The data were analyzed by one-way ANOVA and Tukey's test. Results Water storage significantly decreased the micro-tensile strength(MTS) of AB and SE specimens after 1 and 3 months(P<0.05). The Young's modulus(E) were also decreased after water storage for 1 and 3 months, but statistically not significant in each group of AB and SE group respectively. Conclusions Long-term exposure of adhesive resin to water can cause reduction of mechanical properties. It may compromise resin/dentin bonds and affect longevity of restorations.

• Corrosion Science and Technology
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• 제11권6호
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• pp.280-285
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• 2012

Aluminum is on active metal, but it is well known that its oxide film plays a role as protective barrier which is comparatively stable in air and neutral aqueous solution. Thus, aluminum alloys have been widely applied in architectural trim, cold & hot-water storage vessels and piping etc., furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston because of its properties of temperature and wear resistance. In recent years, the oil price is getting higher and higher, thus the using of low quality oil has been significantly increased in engines of ship and vehicle. Therefore it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and prolong its lifetime. In this study, the effect of solution and tempering heat treatment to corrosion and wear resistance is investigated with electrochemical method and measurement of hardness. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment and exhibited the highest value of hardness with tempering heat treatment temperature at $190^{\circ}C$ for 24hrs. Furthermore, corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. As a result, it is suggested that the optimum heat treatment to improve both corrosion and wear resistance is tempering heat treatment temperature at $190^{\circ}C$ for 16hrs.

• Design & Manufacturing
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• 제11권3호
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• pp.46-50
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• 2017

Press processing is one of the best machining methods capable of mass production, satisfying dimensional, shape and quality among the methods of processing a metal plate. Among them, Fine blanking is a method of obtaining a precise cross-section such as machining of the shear surface shape. In this research, Using SCP-1 and SHP-1 materials. The deformation behaviors of the material flow affecting the die height of the shear section in accordance with the position of the V-ring in the Fine blanking were compared and analyzed. Result of interpretation, It was confirmed that the force acts on the position where the material flow direction accurately forms the die roll that the material of SCP-1 is at a position of 1.5 mm and the material of SHP-1 is at 2.0 mm. As a result, it was confirmed that the state of fo1111ing the shear surface by the V-ring was excellent. Using analysis results, In the experiment, the height of the die roll was considered by applying The position of the V-ring was 1.5 mm in SCP-1 and 2.0 mm in SHP-1. As a result of comparing the height of the die rolls, the height values of the die rolls were different from each other, It has been considered that the tendency of the die rolls to coincide with each other. It is considered that the difference of the die roll height is caused by the pressure input of the V-ring. In this study, the deformation behavior of the material(In addition to the position of the V-ring, the flow direction of the material depends on the shape of the V-ring and the Indentation amount) is considered to be an important factor in determining die roll height.