Key Engineering Materials Vols. 622-623

Abstract: Two alloys of steel containing nominally 0.45C-1.0Si-2.0Mn-0.8Al and 1.2Al were cast in open air induction furnace. Dilatation testing was carried out to recognize the effect on Aluminum on the different critically transformation temperatures. The alloys were hot forged at 1200°C and then subjected to different cooling rates. Mechanical testing was carried out at room temperature. Optical and SEM microstructure were observed. X-ray diffraction was conducted to observe the microstructure constituents.

Abstract: The paper presents selected aspects of analysis cold micro-forging process of a screw made of austenitic stainless steel, concerning relation between strain and hardness. Strain hardening character of a material in consecutive forming operations was analyzed experimentally by the measurement of hardness distribution made on longitudinal axial sections of screws. The relationship between hardness and effective strain (hardness curve) was determined, which made it possible to obtain strain distributions in different regions of a material subjected to cold deformation on the basis of strain distribution numerically estimated with FEM simulation performed using QForm2D/3D commercial software. Conclusions were formulated concerning strain inhomogeneity and strain-hardening intensity with respect to the correlation between strain and hardness. It was also concluded, that nonuniformity of hardening rate in a bulk can lead to local variations in flow stress and eventually, to occurrence of the metal flow related defects, which was illustrated with a case study of cold heading of self-tapping screw of AISI 304Cu stainless steel, with large head diameter to shank diameter ratio. In order to validate the obtained results, the same method was used for analysis of hardness development in steel 19MnB4.

Abstract: Parts having a strength distribution were produced from tailor friction-welded billets consisting of steel bars having different quenchabilities. Chrome steel SCr420 and mild steel S25C bars having high and low quenchabilities, respectively, were joined by friction welding. The tailor friction-welded billets were forged, and then quenched so as to have a strength distribution. The cold formability of the tailored billet was first examined from simple compression in the normal and tangential directions to the joint. No cracks appeared even for an 80% reduction in height in the compression. In a tensile test of the 80% reduced billet, the softer S25C side was fractured and the interface was not fractured. The tailor billets have enough cold formability. The thermal influence around the joint of the tailor friction-welded billets was eliminated by annealing, and thus inhomogeneous deformation around the joint in forging was prevented. A shaft having a high strength flange and a connecting rod having high strength and machinability were produced by forging and quenching of the tailored billet.

Abstract: The hot ring compression test of chrome steel covered with an oxide scale film is carried out to examine the effects of the oxide scale film on the hot forging characteristics. For changing the chemical compositions of the oxide scale, the oxide scale film is generated at air or steam atmosphere. The nominal coefficient of shear friction of the chrome steel covered with the oxide scale film is estimated from the plastic deformation behavior during the ring compression test. The estimated coefficient of shear friction of the chrome steel covered with the oxide scale film is found to be lower than that of the chrome steel without the oxide scale film. Furthermore, the oxide scale generated at steam atmosphere provides lower friction characteristics in comparison with the oxide scale generated at air atmosphere. The mechanism of the reduction of friction with the oxide scale is discussed.

Abstract: A hot spline forming process of die-quenched gear drums using resistance heating of a side wall of a cup formed by cold deep drawing and ironing was developed. The side wall having uniform cross-sectional area is resistance-heated by passage of the current in the axial direction, the heated side wall of the drawn cup is ironed and is finally die-quenched. The gear drum was successfully formed and the hardness was between 400 and 500 HV. Not only the formability was improved but also the formed dram was hardly oxidised because of rapid resistance heating.

Abstract: Isothermal forging is a near-net shape forming technology for manufacturing complex titanium alloy components. In order to characterize the workability of Ti-6Al-4V alloy during isothermal forging process, the material properties of Ti-6Al-4V alloy were investigated by isothermal compression tests under different strain rate-temperature, where the temperature range is 850~1000 °C and strain rate range is 0.001~0.05s⁻¹. The obtained flow stress-strain data was used to develop the Arrhenius constitutive model of which material constants considered the compensation of strain. The developed constitutive model was used to simulate the isothermal forging process of Ti-6Al-4V alloy component by finite element (FE) based numerical method. The metal flow and potential defect locations were predicted by numerical simulation. Furthermore, the relevant simulation results were compared with the product in industrial workshop to demonstrate the validity of material constitutive model. Keywords: Isothermal forging; Ti-6Al-4V alloy; Hot compression test; Arrhenius constitutive model; FE analysis; Model validation;

Abstract: This paper presents the experimental research results concerning a new method of forming of brackets with a triangular rib. The forging process of products with ribs was conducted applying a three-slide forging press (TSFP) on material model in the form of lead plates. During the experiment, the influence of the process particular parameters on the obtained products quality was analyzed. On the basis of the research results the main failure modes of the material during processing were determined. The limiting value of the plate upsetting coefficient depending on its length was given. Considering conducted research works, it was stated that it is possible to form such brackets forgings in TSFP in accordance with the worked out method.

Abstract: This study introduces a new approach of direct recycling using the hot press forging process that eliminates the two intermediate processes of cold-compact and pre-heating. This method leads to low energy consumption without intervening the metallurgical processes. In this study, the optimum of machined chips from high speed milling is recycled by hot press forging. The mechanical properties and surface integrity of the different chips were investigated. The performance of recycled aluminium AA 6061 chips in the mechanical and physical properties were compared with the original aluminium billet. Response surface methodology (RSM) was used to develop mathematical model of the effects on pre-compaction cycle, holding time and suitable pressure significant to the process. It is hoped that, utilization of primary metal could be fully utilized by direct recycling technique (hot press forging) introduced in this study and at the same time developing a sustainable manufacturing process technology for future needs.

Abstract: Open die hot forging has a wide industrial application on deforming ingot into billet with desired dimension and qualified internal microstructure. An example open die forging process of Ti-6Al-4V ingot is selected herein. A 3D FE-based numerical method was used to investigate the open die forging process with respect to the real working conditions. The simulation results were validated by the collected experimental process parameters from the forging system. Moreover, design of experiment method is adopted regarding the variation of process parameters to reveal the effects of critical factors on product deformation and quality characteristics. Results show that the process parameters including press speed, feed and reduction has significant effect on the workpiece deformation and effective strain which represents the forged billet formability and quality. Improved process parameters method is suggested with respect to the experienced benchmark based on the sensitivity analysis. Keywords: Open die forging; Ti-6Al-4V alloy; Sensitivity analysis; Process parameter; Numerical simulation;

Abstract: Solution heat treatment, forming and in-die quenching (HFQ) is a patented process to form complex shape metal components at a high efficiency and a low cost. Conventional experiment approaches to determine forming limit curves (FLCs) at different strain paths are not applicable for the HFQ forming process. A novel biaxial tensile test rig is designed to overcome the difficulties and determine the FLCs at high temperatures based on the commercial Gleeble machine. This test device employs the circle plate and connecting rod mechanism in order to achieve different strain states, such as uniaxial tension, plane strain and biaxial tension. Resistance heating and air cooling are adopted to obtain an isothermal environment and to control cooling rates in Gleeble respectively. The designs of the cruciform specimen for this test are also introduced in this paper.