Pan-Ki Seo

Determination of Die Design Rules for Semi-Solid Die Casting Process and Its Experimental Investigation

Die design rule for semi-solid die casting (SSDC) with A356 electromagnetic stirring (EMS) aluminum alloy, was proposed. The die design rule included inspection of machine, part requirements, parting line determination, sleeve, plunger, gating system, overflow, air vent, ejector pin, and heating line design. The specification of gating system, overflow, air vent, plunger tip, and sleeve suitable for respective part were regulated. Two steps die system of lower-positioned gate and three steps die system of center-positioned gate were manufactured for 4 automobile suspension parts, based on the die design rule. For the sound filling pattern and solidification behavior, injection speeds of 4 parts were summarized to the interval (from V1 to V4). As a result of observing the microstructure of 4 parts after T6 heat treatment, primary Al-α phase was globularized and fine Si particles were distributed around the grain boundary. The mechanical properties of 4 parts with T6 heat treatment were investigated and showed ultimate tensile strength (UTS) of 330 MPa, yield strength (YS) of 250 MPa, and elongation of 7.5% as average.

Fabrication of Rheological Material with Rotational Pressure Type Equipment

Many rheocasting processes had been proposed because of the difficulty of recycling, the limit of material, and the high cost of raw material in thixocasting. But, these rheocasting processes also had disadvantages such as the high initial investment cost and the lower mechanical properties than thixocasting. In this study, a continuous fabrication of rheological material with pressure rotation equipment was newly devised to overcome the disadvantages of rheocasting process. In order to investigate the thixoformability, reheating experiments were carried out with the material fabricated by the newly devised equipment.

Computer Aided Simulation of the Rheology Forging Process for Aluminum Alloys and its Experimental Investigation

Rheology forming is a novel processing method of semi-solid processing, which is different from traditional mold forging and conventional casting process. The rheological behavior of metallic alloys containing both solid and liquid phases was investigated with the low and high solid fraction ranges. Its obvious advantages are easier to produce complex work pieces because of excellent forming ability, more flexible to shape, and more compact in the inner quality for its high pressure. This research paper presents the theory of the rheology forming process and the results of the finite element simulation of rheology forming for aluminum alloys. In this proposed theoretical models for the rheology forming process involve simultaneous calculations performed with solid phase deformation and the liquid phase flow analysis. To analyze the rheology process, the new flow stress curves of rheology aluminum alloys and the viscosity for the simulation of two-phase flow phenomena have been proposed with as a function of temperature.

Phase Transformation Die Casting Process for Manufacturing a Thin-Type Product and Its Mechanical Performance Assessment

Thixo die casting of Al alloy is suitable for complicated large parts of the near net shape with less defect and excellent mechanical properties in comparison with conventional liquid metal die casting processes. To manufacture products with high performance, the reheating conditions, the casting plan, the die design, the injection conditions, the defect analysis, and the quantitative evaluation of mechanical properties are required. Al-Si binary alloys like A356 and A357 suitable for the thixo die casting process (phase transformation die casting process), which have outstanding fluidity, have been employed to completely fill the die cavity during forming. Thus, in the current work, the phase transformation die casting experiments using hypoeutectic A356 alloys were conducted for a variety of injection conditions and pressurization conditions. Finally, the ultimate tensile strength (UTS) and yield strength (YS) as well as the elongation of the thixo die cast component were evaluated in terms of both mechanical and metallurgical points of view.

Development of trimming die with 1.2 GPa steel grade

Abstract In order to reduce the weight and to improve the crash performance of the vehicle, advanced high-strength steel of DP980 and CP1180 has been widely used in the automotive industry. However, the high-strength steel in the press parts causes severe tool wear or failures, such as adhesion, chipping and fracture at the tool cutting area during the shearing process. These result in the excess burr which deteriorates the tool life and causes serious problem in the product quality. The objective of this study was to evaluate the effect of the characteristic of sheared surface on the die material and surface treatment conditions at the shearing process with 1.2 GPa steel grade. The characteristics of sheared surface were evaluated after the shearing process of 60,000 strokes. A burr height was measured using the illuminometer. Also, tool wear of failures was analysed through observing microstructure. The shearing conditions such as die material, heat treatment and process parameter of clearance and pad force were determined as a result of the experiment analysis. The effectiveness was evaluated to manufacture the trimming die of sill side with 1.2 GPa steel grade.

The effect of inclined angle and positioning on the sheared edge in mechanical trimming using hot half-trimming of 22MnB5

Abstract Hot-stamped parts using 22MnB5 sheet have been increasingly applied to the automotive body-in-white to reduce weight with high crashworthiness. The drawn panel should be trimmed by high-priced laser cutting or press trimming to be a complete part. The authors previously suggested the hot half-trimming method to achieve the press trimming of the hot-stamped part with extremely high strength. In this study, the effect of inclined trimming angle and positioning error of the trimmed part within the clearance on the sheared edge has been investigated. The analytical and experimental results of trimming considering inclined angle and positioning error showed that the quality of sheared edge is improved with the increase in inclined angle and practically allowable burr below 0.1 μm appears regardless of the clearance in subsequent mechanical trimming process.

The Effect of Stirring Current and Stirring Time on Microstructure and Mechanical Properties in Rheo Die Casting Process

Semisolid processing is now becoming of greater interest for the production of various parts than pressure die casting. In the rheo die casting process, the important thing is to control the solid particles behavior during the rheo die casting process. So, in this paper, to find out the effect of stirring current and stirring time on the microstructure and mechanical properties, rheo die casting experiments were performed according to the stirring current such as 0, 20, 40 and 60 A and the stirring time such as 20, 40 and 60 sec. The results to the experimental conditions were analyzed.

Development of Horizontal Reheating System for Semi-Solid Die Casting and Its Microstructure Evaluation

The parts manufactured by die casting process usually contain liquid segregation and porosities. To solve these problems, the semi-solid forming process has been applied. The process enables material in the semi-solid state to be completely filled, and parts with the complicated shape to be fabricated by applying relatively low pressure. This process is necessary in order to control the microstructure of the billet as well as to achieve the desired semi-solid billet state. In this study, a horizontal high-frequency induction heating device which can be fabricated by semi-solid forming irrespective of a billets size was developed. A globular structure of the reheated billet and a billets temperature distribution during the reheating process for A356 were investigated.

Microstructural Characterization of Rheology Material Fabricated by Rotational Barrel Type

The new rheology fabrication process has been developed to rheo die casting and rheo forming process. The barrel type equipment, which could continuously fabricate the rheology material, was specially designed to have a function to control cooling rate, shear rate and temperature. During the continuous rotation of barrel with a constant temperature, the shear rate is controlled with the rotation speed. The barrel surface has both the induction heating system and the cooling system to control the temperature of molten metal. By using this system, the effect of the rotation speed and the rotation time on the microstructure was widely examined. The possibility for the rheoforming process was investigated with microstructural characteristic.

Continuous Fabrication Process of Grain Controlled Aluminum Material for Rheology Forming and Its Microstructural Evaluation

In rheo forming process, slurry making is very important factor because the microstructure of slurry affects the quality of final products. Therefore, to control the microstructure of slurry, slurry making by new rheo die casting was studied. To continuously fabricate grain controlled material, cup was cleaned and heated up to about 200°C to prevent the abrupt decrease of molten metal and transferred to the slurry making machine. In slurry making machine, molten metal was poured into a preheated cup and the initial temperature was about 650°C.The used material, in this experiments, was A356 aluminum alloy. In the 4 cooling stages, a respective air cooling time was changed from 5 sec to 60 sec to make slurry temperature below 600°C. High frequency induction heating was given during about 55 seconds. After these processes, grain controlled aluminum material was made. In new rheocasting method, processes parameters are degree of overheat in molten metal, cooling condition, high frequency induction heating condition and cup temperature. Microstructures according to these parameters were observed. By image analysis, solid fraction, equivalent diameter and roundness of grain were investigated and discussed. Finally, to find out mechanical properties of grain controlled aluminum part by rheo die casting, tensile tests were carried out to the T6 heat treatment. Introduction In semi-solid forming process, there are two processes such as thixo forming and rheo forming. It is reported that semi-solid forming process has many advantages like longer die life, good mechanical properties and energy saving compared to the conventional forming process [1-2]. Materials fabricated by continuous casting process with electromagnetic system are used in thixo forming. Therefore, the cost of feedstock material is very high. Also, in mass production of thixo forming product, there are disadvantages such as limited selection of alloy, billet reheating cost, non-destructive control cost, the difficulty of scrap recycling and billet loss during reheating process. On the contrary, the rheo forming process on-demand slurry like not only cast alloy but also structural alloy can be used and the recycling of scrap is much easier [3]. In the rheo forming process, molten alloy is directly cooled from the liquid state to the mushy state. Therefore, reheating process can be removed compared to the thixo forming process. Grain controlled material was made by mainly 3 steps like pouring, cooling and heat adjustment. These steps are included many process parameters. Pouring temperature is lower than that of conventional casting process. During pouring, molten metal is solidified at the surface of pouring cup. Grain can be controlled as globular microstructure by air blow cooling. Finally, the temperature of slurry is adjusted as proper temperature for rheo die casting by high frequency induction heating [4]. In this paper, to overcome the disadvantages of thixo forming process and apply the rheo forming process, continuous fabrication process of grain controlled aluminum material with above-mentioned three steps has been studied. Key Engineering Materials Online: 2004-10-15 ISSN: 1662-9795, Vols. 274-276, pp 547-552 doi:10.4028/www.scientific.net/KEM.274-276.547