• 한국정밀공학회지
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• 제14권10호
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• pp.157-163
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• 1997

The needs to machine hardened steels with high productivity and good sufrace integrity have been increased in the dies & molds industry. This paper presents some experimental results on the CBN ball endmilling for hardened tool steel. This investigation concerns on the effects of cutting fluids, cutting speed, and feed on the cutting performance such as cutting forces, tool wear, and surface finish. The wear of CBN ball endmill for each cutting conditions were also examined through the microscopic observation. It has been found that the higher cutting speeds with cutting fluids result in better cutting performance.

• Journal of Welding and Joining
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• 제34권1호
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• pp.21-25
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• 2016

The automotive vehicle is made through the following processes such as press shop, welding shop, paint shop, and general assembly. Among them, the most important process to determine the quality of the car body is the welding process. Generally, more than 400 pressed panels are welded to make BIW (Body In White) by using the RSW (Resistance Spot Welding) and GMAW (Gas Metal Arc Welding). Recently, as the needs of light-weight material due to the $CO_2$ emission issue and fuel efficiency, new joining technologies for aluminum, CFRP (Carbon Fiber Reinforced Plastic) and etc. are needed. Aluminum parts are assembled by the spot welding, clinching, and SPR (Self Piercing Rivet) and friction stir welding process. Structural adhesive boning is another main joining method for light-weight materials. For example, one piece aluminum shock absorber housing part is made by die casting process and is assembled with conventional steel part by SPR and adhesive bond. Another way to reduce the amount of the car body weight is to use AHSS (Advanced High Strength Steel) panel including hot stamping boron alloyed steel. As the new materials are introduced to car body joining, productivity and quality have become more critical. Productivity improvement technology and adaptive welding control are essential technology for the future manufacturing environment.

• 한국재료학회지
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• 제20권4호
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• pp.194-198
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• 2010

Cubic boron nitride (c-BN) is a promising material for use in many potential applications because of its outstanding physical properties such as high thermal stability, high abrasive wear resistance, and super hardness. Even though 316L austenitic stainless steel (STS) has poor wear resistance causing it to be toxic in the body due to wear and material chips, 316L STS has been used for implant biomaterials in orthopedics due to its good corrosion resistance and mechanical properties. Therefore, in the present study, c-BN films with a $B_4C$ layer were applied to a 316L STS specimen in order to improve its wear resistance. The deposition of the c-BN films was performed using an r.f. (13.56 MHz) magnetron sputtering system with a $B_4C$ target. The coating layers were characterized using XPS and SEM, and the mechanical properties were investigated using a nanoindenter. The friction coefficient of the c-BN coated 316L STS steel was obtained using a pin-on-disk according to the ASTM G163-99. The thickness of the obtained c-BN and $B_4C$ were about 220 nm and 630 nm, respectively. The high resolution XPS spectra analysis of B1s and N1s revealed that the c-BN film was mainly composed of $sp^3$ BN bonds. The hardness and elastic modulus of the c-BN measured by the nanoindenter were 46.8 GPa and 345.7 GPa, respectively. The friction coefficient of the c-BN coated 316L STS was decreased from 3.5 to 1.6. The wear property of the c-BN coated 316L STS was enhanced by a factor of two.

• 한국세라믹학회지
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• 제43권6호
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• pp.358-361
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• 2006

A two-step plasma-assisted boronizing process was carried out on the AISI 1045 steel substrate to reduce the pore density introduced by a conventional single plasma boronizing process. The specimens were plasma boronized for 1 h at $650^{\circ}C$ and subsequently far 7 h at $800^{\circ}C$ in an atmosphere of $BCl_3-H_2-Ar$. The boride layer thickness was parabolic in boronizing time, a high HV reading of 1540 was found up to the boride layer thickness of $25{\mu}m$. It was found that the morphology of the boride layer prepared by the two-step boronizing process was changed from a columnar to a tooth-like structure and the pores in the borided steel were eliminated completely in comparison to those synthesized by the conventional single boronizing process, implying that it is highly applicable for enhancing the dense and compact coating properties of the low-alloy steel.

• Design & Manufacturing
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• 제17권2호
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• pp.22-26
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• 2023

As Light-Emitting Diodes(LEDs) continue to advance in performance, their application in automotive lamps is increasing. Automotive LEDs utilize light guides not only for aesthetics but also to control light quantity and direction. Light guides employ patterns of a few hundred micrometers(㎛) to regulate the light, and the surface roughness(Ra) of these patterns can reach tens of nanometers(nm). Given that these light guides are produced through injection molding, mold processing technology with high surface quality micro-patterns is required. This study serves as a preliminary investigation into the development of high surface quality micro-pattern processing technology. It examines the surface roughness of the workpiece based on the cutting direction of the pattern and the cutting fluid type when cutting micro-patterns on STAVAX steel using cubic Boron Nitride(cBN) tools. The experiments involved machining a step-shaped micro-pattern with a height of 60 ㎛ and a pitch of 400 ㎛ in a 22×22 mm area under identical cutting conditions, with only the cutting direction and cutting fluid type being varied. The machining results of four cases were compared, encompassing two cases of cutting direction(parallel to the pattern, orthogonal to the pattern) and two cases of cutting fluid type (flood, mist). Consequently, the Ra value was found to be the highest(Ra 128.33 nm) when machining with the flood type in parallel to the pattern, while it was the lowest(Ra 95.22 nm) when machining with the mist type orthogonal to the pattern. These findings confirm that there is a difference of up to 25.8 % in the Ra value depending on the cutting direction and cutting fluid type.

• 소성∙가공
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• 제32권2호
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• pp.81-86
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• 2023

The hot stamping process is widely used for high strength of vehicle parts, with heating 900 ℃ or higher in a furnace and in-die quenching to achieve strength above 1.5 GPa of the quenchable boron alloyed steel 22MnB5. First of all, the hot stamping process consisted of heating, forming, quenching and trimming. In the trimming process case, the laser method has been conventionally adopted. For laser trimming process, it has the problems pertaining to low productivity and high cost while the hot stamping process, accordingly the trimming process need to investigate the research for alternative method. In order to overcome these issues, many research groups have studied the mechanical trim solution on the hot stamped parts at high temperature. In this study, the mechanical piercing was performed during the hot stamping process at the high temperature for overcome the disadvantages of laser cutting. Also, the process parameters such as piercing time after die closing, clearances of between die and punch were controlled for obtaining the reasonable shear characteristics.

• 대한기계학회논문집A
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• 제34권6호
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• pp.797-803
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• 2010

자동차의 측면 충돌시 승객을 보호하고자 박판재를 이용하여 자동차의 도어 임팩트빔을 핫스탬핑공법을 이용하여 개발하였다. 핫스탬핑 기술은 차량의 차체 강성을 증가시킬 뿐만 아니라 차체 중량 및 부품 수 축소로 인한 공정의 감소도 가능하게 한다. 핫스탬핑 시편을 제작하고, 기계적 물성시험을 수행하여 물성 데이터를 확보하였다. 핫스탬핑 임팩트빔의 성형해석및 구조해석을 이용한 최적 설계를 수행하여 기존 파이프형태의 임팩트빔보다 강도는 102% 향상되고, 중량은 34% 감소된 핫스탬핑 임팩트빔을 개발하였다.

• 한국강구조학회 논문집
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• 제12권3호통권46호
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• pp.291-302
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• 2000

복합적층 구조물에서 복합재료는 그 자체의 높은 강성, 강도와 내구성등의 특성을 갖고 있을 뿐 아니라, 구조물의 역학적 특성에 따라 얼마든지 재료의 특성을 합리적으로 구성하여 배치할 수 있는 매우 우수한 장점이 있다. 본 연구에서는 등분포로 재하된 복합적층경사판의 처짐에 관한 해석으로서 복합적층 경사판의 처짐을 나타내는 단일 4차 편미분방정식을 3개의 종속변수를 갖는 3원2차 연립방정식을 이용하여 해석하는 수치해석 법을 제시하였으며, 대칭 앵글-플라이 각도로 적층, 역대칭 앵글-플라이 각도로 적층, 비대칭 앵글-플라이 각도로 적층한 경우에 처짐과 단면력을 비교 검토하였다.

• 한국재료학회지
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• 제6권8호
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• pp.841-851
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• 1996

최근의 연구에 의하면 직접 소입강에서 미량의 베이나이트상의 생성이 확인되었다. 마르텐사이트 변태전에 생성된 베이나이트상은 마르텐사이트의 패킷을 미세화시키고 입도 미세화로 기계적 성질을 향상시킨다고 한다. 본 연구에서는 미량 합금 원소로 Mo, B 등을 첨가한 강을 $1200^{\circ}C$에서 단조하여 물에 직접 소입한 후, 베이나이트상의 분율을 조절하기 위해 베이나이트 변태 온도에서 일정시간 유지하는 열처리 과정을 거쳐 생성된 베이나이트상의 분율과 기계적 성질간의 관계를 고찰하였다. 이로써 마르텐사이트와 베이나이트 혼합 조직의 강도와 인성을 증가시키는 효과적인 베이나이트 분율을 조사한 후에, 직접 소입시에 이와 같은 분율의 베이나이트 함량으로 조절할 수 있는 방법을 제시하여 고강도 고인성형 직접 소입강의 개발에 활용하고자 한다.

• Steel and Composite Structures
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• 재36권6호
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• pp.671-687
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• 2020

The aim of this research is to analyze buckling and bending behavior of a sandwich Reddy beam with porous core and composite face sheets reinforced by boron nitride nanotubes (BNNTs) and shape memory alloy (SMA) wires resting on Vlasov's foundation. To this end, first, displacement field's equations are written based on the higher-order shear deformation theory (HSDT). And also, to model the SMA wire properties, constitutive equation of Brinson is used. Then, by utilizing the principle of minimum potential energy, the governing equations are derived and also, Navier's analytical solution is applied to solve the governing equations of the sandwich beam. The effect of some important parameters such as SMA temperature, the volume fraction of SMA, the coefficient of porosity, different patterns of BNNTs and porous distributions on the behavior of buckling and bending of the sandwich beam are investigated. The obtained results show that when SMA wires are in martensite phase, the maximum deflection of the sandwich beam decreases and the critical buckling load increases significantly. Furthermore, the porosity coefficient plays an important role in the maximum deflection and the critical buckling load. It is concluded that increasing porosity coefficient, regardless of porous distribution, leads to an increase in the critical buckling load and a decrease in the maximum deflection of the sandwich beam.