B.J. Kim

Experimental Analysis for the Tubular Hydroformability of Aluminum Alloys at Elevated Temperatures

Aluminum alloys have a high potential for weight reduction in automotive and other applications, but they have a relatively low tubular hydroformability at room temperature. Hot working processes are commonly used for bulk metal forming, such as forging and rolling, but rare in sheet metal forming like hydroforming. The hydroformability of aluminum alloys can however be enhanced significantly at elevated temperatures. In this study, the hydroformability of aluminum alloys at elevated temperatures has therefore been investigated by using a specially designed induction heating system. The formability characteristics at high temperatures were obtained by a T-fitting forming test as well as a free bulge test. The effects of the process parameters such as an internal pressure and temperature on tubular forming limits have mainly been investigated and the results are presented in this paper

Optimization of Tube Hydroforming Process by Using Fuzzy Expert System

In the tube hydroforming process, a tube is placed into the die cavity and the ends of the tube are sealed by fixing the axial cylinder piston into the ends. Then the tube is pressurized with a hydraulic fluid and simultaneously the axial cylinders move to feed the material into the expansion zone. In this study, the empirical and the quantitative relationship between process parameters and hydroformabillity are analyzed by fuzzy rules. Fuzzy expert system is an advanced expert system which uses fuzzy rule and approximate reasoning. Many process parameters are converted to the quantitative relationship by use of approximate reasoning of fuzzy expert system.

The Effects of the Heating Conditions on the Hydro-Formability of the Aluminum Alloys at High Temperatures

Modern automobiles are built with a steadily increasing variety of materials and semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature of the specimen very quickly. The specimen applied to the test is AA6061 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of AA6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.

Web Based Shape Inspection System for the Forging Products Having Complicated Shapes

The outer race of the constant velocity(CV) joint is an important load-supporting automotive part, which transmits torque between the transmission and the wheel. The outer race is difficult to be forged, because its shape is very complex and the required dimensional tolerances are very stringent. Therefore, the internet based shape inspection system is developed in this study to provide quick and accurate measuring data. Proposed system uses mechanical displacement sensors to measure the shape of CV joint that has six inner ball grooves, and commercially available Lab- View program is used to process measured data into the dimensional shape. Developed program provides a simple user interface that enables users to have real-time access of data measured from industrial production lines. Furthermore, the measured data can be exchanged via the internet between users and forging system operators. A java applet helped the system connection via internet. A data, IP access, is transmitted to the packet by TCP/IP. Our proposed system has many advantages over current measuring systems including fast and efficient data processing by real-time measuring, and system flexibility.

Effect of the Surface Defects on Hydroformability of Aluminum Alloys

Extruded aluminum alloys, which are highly versatile, have relatively modest prototyping cost, good strength and corrosion resistance. Because there is no weld seam, the circumferential mechanical properties may be uniform and advantageous for hydroforming. However, surface defects such as die lines and pick-up can be generated during the extrusion especially due to imperfections on the die surface. In this study, the extent of the crack propagation caused by die lines is evaluated according to the deformed shape of the tube in hydroforming process. And when forming a extruded aluminum tube, the deformed surface of the tube frequently becomes rougher with increasing plastic strain. This is well known as orange peel phenomenon and it has a significantly effect not only on the surface quality of a final product but also on the forming limit. To evaluate the effects of the orange peel on the hydroformability, the inter-stage polishing has been performed. Through the several tests including hydroforming test, the effect of surface defects on the hydroformabilities are well defined.

Effect of Heat Treatment Conditions on Tube Hydroformability

Tube hydroforming provides a number of advantages over conventional stamping process, including fewer secondary operations, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength and stiffness. It can produce wide range of products such as sub-frame, engine cradle, and exhaust manifold. In this study, the effect of heat treatment conditions, such as post seam annealing(PSA) and bright annealing(BA), on the ovality and hydro-formability of steel tubes has been investigated. Hydroformability has been estimated as the bulging height obtained depending on the various process parameters such as an internal pressure, axial feeding, and heat treatment conditions. The ovality and forming height were found to strongly depend on material properties after heat treatments.

Machining Characteristics of Tool Steels Manufactured by Electro Slag Casting Process

Machining characteristics of tool steels manufactured by electro slag casting process has been investigated in this study. For the estimation of machinability, turning and drilling tests are carried out. The chip shapes at various velocities are investigated for the comparison of turning workabilities of tool steels because the chip shapes reflect characteristics of cutting resistance. In case of drilling test, feed motor currents measured by a hall sensor are used as a measure for the drilling resistance. The machining characteristics of the tool steels are strongly correlated with tensile properties, such as tensile strength, hardness, and ductility. In case of turning workability, it was found to be favoured by the higher tensile strength, while the opposite is true far the drilling workability. The electro-slag casted materials show better turning workability in the viewpoint of chip shapes and, the quenching-tempered electro-slag casted material has relatively better drilling machinability than that of the annealed one.