B.D. Joo

Laser surface hardening of AISI H13 tool steel

被尝试答案作为产生的热用 200 W 纤维激光变硬和微观结构的精炼改进表面坚硬并且通过固体穿 AISI H13 工具钢的性质采购原料。激光的坚硬融化了地区被调查。为了识别热的效果，在融化地区的激光上输入，扫描条件被控制。结果显示出那，同样收到的 AISI H13 工具钢的坚硬是近似，在激光表面以后的 Hv 240，和坚硬加热处理在 Hv 480510 附近。变硬的深度和宽度随输入使用了的热的增加被增加。试验性的结果的申请将在 tooling 工业被考虑。

Application of direct laser metal tooling for AISI H13 tool steel

In the die industry, it is commonly agreed that residual tool life can be successfully extended by timely repair of damaged surfaces. Traditionally, the main repair process is tungsten inert gas (TIG) welding, but a new process called direct laser metal tooling (DLMT) emerges. DLMT is a manual process, of which results depend on the materials of the powders and tools, the laser process and parameters. This technology is a direct-metal freeform fabrication technique in which a 200 W fiber laser is used. AISI H13 tool steel is a suitable material for die casting tools because of the high resistance to thermal fatigue and dimensional stability. In this research, AISI H13 tool steel was melted with metal powder by fiber laser. Before melting AISI H13, the powders were analyzed with XRF equipment. Then, hardness distribution of laser melted zone was investigated. The microstructure in laser melted zone was discussed. In order to identify the effect of particle size of powder on the melted zone, two types of particle sizes of powders were used. Experimental results show that the mold repair process using DLMT can be applied in the mold repair industry.

Flow characteristics of aluminum coated boron steel in hot press forming

Abstract The flow characteristics of aluminum coated boron steel in hot press forming were investigated. Furthermore, the effects of aluminum coated layer on press forming were analyzed during deep drawing. The results show that aluminum coated boron steel exhibits a high sensitivity on temperature and strain rate. Aluminum coating layer appears in surface flaking in a temperature range of 700–800 °C, but smooth surface is formed above 900 °C.

Deformation analysis for cold rolling of Al-Cu double layered sheet by physical modeling and finite element method

The deformation characteristics of Al-Cu double layered sheet during rolling with various process parameters were studied by both a physical modeling technique and the finite element method. Physical modeling and the finite element method are complementary, due to their different advantages and limitations. Physical modeling simulates metal forming operations by using a model workpiece under conditions similar to those in actual production. The deformation characteristics of double layered sheet during rolling were also simulated using a commercial finite element code, FORGE™. The effects of process parameters, such as total reduction ratio, initial thickness ratio and differential speed ratio on the rolling characteristics were the primary focus of the investigation. In addition, an analytical model for double layered sheet rolling is also proposed with the use of a force-thickness diagram. From the results, the effect of the process parameters on the rolling of the Al-Cu double layered sheet has been determined.

Characterization of deposited layer fabricated by direct laser melting process

Deposition dimensions are important in the final applications of products made by direct laser melting (DLM). This investigation used a 200 W fiber laser to produce single-line beads from stainless steel 316L powder using a variety of different energy distributions. To investigate the deposited layer, deposition width, height, penetration depth, and side surface roughness were measured. In order to validate the effectiveness of the two main process parameters (laser power and scan rate), multi-layered beads were fabricated by the sequential layering of single lines. It was found that with an increase in linear energy density, the wetting angle was reduced, and the average roughness was also increased with linear energy density. An equation that predicts the deposition height for a multi-layered bead is proposed and experimentally validated in this study. For deposited layer applications, the material properties of the deposited layer, such as contact angle, interfacial contact resistance, and flexural strength are estimated. The rougher deposited layers show higher contact angle and interfacial contact resistance. The flexural strength of the DLM fabricated specimen is above 250 MPa.

Hydroforming of flanged tubular part

Tube hydroforming is the technology that utilizes hydraulic pressure to form a tube into desired shapes inside die cavities. Recently, tube hydroforming technology draws attentions of automotive industries due to its advantages such as weight reduction, increased strength, improved quality and reduced tooling cost. Hydroformed automotive parts used as structural components in vehicle body frame or subframe often have to be structurally joined at some point. Therefore it is useful if the hydroformed automotive parts can be given a localized attachment flange. In this study, a tube hydroformed product which has flange has been formed at various processing conditions. To accomplish successful flange hydroforming process, thorough investigation on proper combination of process parameters such as internal hydraulic pressure and tool geometry has been performed. For the process design FE analysis was performed with Dynaform 5.5. With optimized die parting angle and circumferential expansion ratio, hydroforming experiments to form flange were performed and forming characteristics at various process conditions were analyzed. The results show that flanged parts can be successfully produced by tube hydroforming process.

Effect of Laser Parameters on Sintered Powder Morphology

Selective laser sintering is a kind of rapid prototyping process whereby a three-dimensional part is built layerwise by laser scanning a powder. This process is highly influenced by powder and laser parameters such as laser power, scan rate, spot size and layer thickness. Therefore a study on fabricating a line with Fe-Ni-Cr powder on AISI H13 tool steel has been performed by selective laser sintering. In this study, fabrication was performed by experimental facilities consisting of a 200W fiber laser which can be focused to 0.08 mm and atmospheric chamber which can control atmospheric pressure with argon. The line was fabricated with various laser power, scan rate and layer thickness. Line width and surface quality were investigated. With power increase or layer thickness decrease, line width was decreased and line surface quality was improved with scan rate optimization.

Characterization of the aluminium coating layer in the hot press forming of boron steel

Abstract Hot press forming allows geometrically complex parts to be easily formed from boron steel blanks. The rapid cooling after forming produces a product with extremely high strength. To prevent the blanks from oxidizing and decarburizing during heating, forming, and subsequent press cooling, the boron steel is supplied with an aluminium-based coating. This surface coating influences the formability of the component and the quality of the final product. The main purpose of the present research is to characterize the changes in the aluminium-coated layer on a boron steel during hot press forming. To characterize the evolution of the coated layer, experiments for hot press forming were conducted under various conditions that simulated a production process. Test specimens were heated to temperatures between 810 and 930 °C and were then press hardened. The aluminium-coated layer develops four distinct microstructural regions: (a) a diffusion zone; (b) an aluminium—iron (Al—Fe) zone I; (c) a low-aluminium zone (LAZ); and (d) an Al—Fe zone II. The band-like LAZ is clearly observable in the temperature range of 810 to 870 °C and becomes sparsely dispersed at temperatures above 900 °C. The microcracking behaviour of the aluminium-coated layer during forming was also analysed with both bending and deep-drawing tests. The strain concentration in the softer LAZ is found to be closely connected to both microcracking and exfoliation of the coated layer during the press forming.

Effect of Process Parameters on Hydroforming Characteristics of a Rectangular Shape Flange

Hydroforming has attracted the attention of manufacturing industries for vehicles and transportation systems. A wide range of products such as subframes, camshafts, radiator frames, axles and crankshafts are made by the hydroforming process. Hydroformed parts often need to be structurally joined to other components during assembly. Therefore it is useful if the hydroformed automotive parts can be attached with a localized flange. In this study, a hydroforming process to produce a rectangular shape flange is proposed. FE analysis to form the flanged rectangular shape was performed by Dynaform 5.5. The hydroforming characteristics at various die aspect ratios and feeding conditions were analyzed and optimal process conditions which can avoid defects are suggested. For validation purposes, hydroforming experiments to form the flange were conducted with the optimized conditions. The results show that the flanged parts can be successfully formed with a hydroforming process without additional processing steps.

A Study on Forming Characteristics of Roll Forming Process with High Strength Steel

Roll forming is a kind of sheet metal forming process used to manufacture long sheet metal products with constant cross section. Recently, roll forming technology draws attentions of automotive industries due to its various advantages, such as high production speed, reduced tooling cost and improved quality. In automotive industries, roll formed automotive parts used as structural components in vehicle body frame or sub frame and high strength steel becomes more common to improve safety and fuel efficiency. However, when roll forming process is performed with high strength steel, rolling forming defects, such as spring back, buckling and scratch should be considered more carefully. In this study, efforts to avoid roll forming defects and to optimize forming parameters were performed. FE analysis was performed with high strength steels using commercially available simulation software, COPRA-RF™ and SHAPE-RF™. Forming characteristics were analyzed and roll flower model and proper roll-pass sequences were suggested by analyzing longitudinal strain and deformation behavior. This study provided considerable experience about roll forming process design that using high strength steel.