S.S. Kang

Effect of tool temperature on the reduction of the springback of aluminum sheets

Abstract The effect of tool temperature on the reduction of springback amount of aluminum 1050 sheet has been investigated in this study. As the springback phenomenon is caused by elastic recovery of deformed sheet, the control of elastic recovery is important in decreasing the amount of springback. Therefore, any combination of tool temperature that can reduce elastic recovery can be effective in reducing the amount of springback. The experimental verification of U-bent aluminum 1050 sheet shows that the combination of hot die and cold punch can reduce the amount of springback up to 20% when compared to conventional room temperature bending test.

Finite element investigation on spring-back characteristics in sheet metal U-bending process

Abstract The most prominent feature of sheet metal forming process is an elastic recovery phenomenon during unloading which leads to spring-back and sidewall curl. Accordingly, it has been a crucial research subject for designing bending tools securing the dimension precision of products. However, the elastic recovery is not only associated with various tool parameters but also hard to predict accurately owing to the complex material deformation behavior. This paper aims at the numerical investigation on spring-back characteristics to the major process parameters. For this goal, we employ the updated Lagrangian thermo-elastoplastic finite element method to a plane-strain sheet metal U-bending process. A description of process formulation and finite element approximation is also presented.

A study on a die wear model considering thermal softening: (I) Construction of the wear model

The service life of tools in metal forming process is to a large extent limited by wear, fatigue fracture and plastic deformation. In elevated temperature forming processes wear is the predominant factor for tool operating life. To predict tool life by wear Achards model is generally applied. Usually hardness of die is considered to be a function of temperature. But hardness of die is a function of not only tem-perature but also operating time of die. To consider softening of die by repeated operation it is necessary to express hardness of die by a function of a function of temperature and time. By experiment of reheating of die softening curve was obtained and applied to suggest modified Archards Model in which hardness is a function of main tempering curve.

A study on die wear model considering thermal softening (II): Application of the suggested wear model

In bulk metal forming processes prediction of tool life is very important for saving production cost and achieving good material properties. Generally the service life of tools in metal forming process is limited to a large extent by wear, fracture and plastic deformation of tools. In case of hot and warm forging processes tool life depends on wear over 70%. In this study finite element analyses are con-ducted to warm and hot forging by adopting suggested wear model. By comparison of simulation and eal profile of die suggested wear model. By comparison of simulation and real profile of die suggested model is verified.

Estimation of hole flangeability for high strength steel plates

Abstract Hole flanging experiments are performed on flat circular plates with a hole in the center to investigate the fracture and lip shape behaviors of TRIP steels and ferrite–bainite duplex (F+B) steels. The conventional hole flanging process is limited to a certain limit hole diameter below which failure will ensue during the hole expansion. In the hole flanging, deformation by lip or fracture by petalling may occur when sheets are struck by punches of various shapes and high circumferential strains are induced in the deforming material. Fracture of the plate during hole flanging is mainly caused by lip fracture that results from multiple localized neckings that take place around the hole periphery where straining is most severe. F+B steel has better hole flangeability than TRIP steel in the viewpoint of minimum hole diameter, while in the viewpoint of lip shape accuracy and lip height TRIP steel has better formability than F+B steel. Both criteria are proved to be valuable indices to estimate the hole flangeability of high strength steel.

Application of computer-aided process planning system for non-axisymmetric deep drawing products

Abstract A computer-aided process planning system for rotationally symmetric deep drawing products has been developed. The application for non-axisymmetric components however has not been reported yet. Thus, this study investigates process sequence design and constructs a computer-aided process planning system for non-axisymmetric deep drawing products with elliptical shape. The system developed consists of three modules. The first one is three-dimensional modeling module to calculate surface area for non-axisymmetric products. The second one is a blank design module that creates an oval-shaped blank with the identical surface area. The third one is a process planning module based on production rules that play the best important roles in an expert system for manufacturing. The production rules are generated and upgraded by interviewing field engineers. Especially, drawing coefficient, punch and die radii for elliptical shape products are considered as main design parameters.

A study on resistance welding in steel sheets using a tailor-welded blank (1st report): Evaluation of upset weldability and formability

Abstract A press formability analysis of welded parts was studied in the current work, using a tailor-welded blank. For a body panel produced by the press forming of parts welded by the tailor-welded blank method, the following conditions are demanded: (1) The strength of the welded parts must be higher than those of the base metals. (2) After the welding, severe welding deformation must be avoided. (3) The press formability of the welded parts is similar to that of the base metals. (4) The reproductibility of the welding must be high. There are numerous welding methods satisfying these conditions, but the purpose of this study is to investigate the upset weldability and formability of a particular kind of material (SPCC). SPCC steel sheet shows good weldability and formability under some welding conditions. The experimental results are discussed by the evaluation of the results obtained from the tensile test, the hardness test, the microstructure and the Erichsen cup test. The formability of upset welded SPCC steel sheet as evaluated by the Erichsen cup test was little lower than that of the parent material.

Synthesis and mechanical evaluation of nanocomposite coating layer of nc-TiN/a-Si3N4 on SKD 11 steel by sputtering

In this work, Ti–Si–N coating layer, one of promising nitride coatings to extend the life time of forming tools and other mechanical components, were deposited on SKD 11 steel substrate by a DC reactive magnetron sputtering technique. The coating layer was revealed nanocomposites, consisting of nano-sized TiN crystallites embedded in an amorphous matrix of Si3N4. Such microstructural characteristics of Ti–Si–N coating layer resulted in a significant improvement of hardness compared to common TiN coatings. Friction coefficient and wear rate of the coating layer significantly decreased with increase of relative humidity. The self-lubricating tribo-layers such as SiO2/Si(OH)2 played an important role in the wear behavior of the Ti–Si–N coating layer. It was found from our experimental results that the tribological behaviors of the Ti–Si–N coating layer were dependent on the factors affecting the tribochemical reaction, i.e., Si content and relative humidity rather than the hardness of coating layer.

A study on the development of a substitution process by powder metallurgy in automobile parts

Abstract Powder metallurgy processes using sintering are able to form net-shaped products and have been used widely in the production of automobile parts to improve productivity. However, the toughness of powder products is generally poor because they contain pores. Therefore, forged products are used in parts subjected to severe fatigue loads, but in the case of powder products having high toughness, they could substitute for forged products. In this study, the choice of powder materials and production processes, including mixing, compaction, sintering, and heat treatment are studied to produce the clutch disc spline hub of an automobile. For this, three types of materials are selected and processed and the mechanical properties and microstructure of the sample are investigated, along with the performance of a dynamic test carried out under real conditions.

A study on the improvement of formability for elliptical deep drawing processes

Abstract The punch and die corner radii, the lubricant condition, the working speed, the blank-holding force, the friction force and the clearance change the formability of the deep drawing process. In general, sheet metal forming may involve stretching, drawing or various combinations of these basic modes of deformation. The influence of the punch and die corner radii is of great importance in the design of sheet metal working processes. Recently, most of the research for the sheet metal deep drawing process has been performed on the formability of an axisymmetric shape, but there are not any concrete reports on the formability of a non-axisymmetric shape. In addition, the conventional corner radii of the punch and die have been determined by trial-and-error using industrial experience and post-processing tests, and only approximate corner radii of the punch and die have been presented. In order to obtain the optimal products in the deep drawing process, elliptical deep drawing tests were carried out with several corner radii of the punch and die. In this study, the optimal corner radii of the punch and die in the deep drawing process with a non-axisymmetric blank shape are proposed. Research has been carried out using diverse technologies including experimentation and the finite element method.