Applied Mechanics and Materials Vol. 889

Abstract: In the present work, the process of interaction of an abrasive particle with the surface of a component is modeled in the framework of dynamic problems of the theory of thermoelasticity, considering plastic deformation, friction and wear of the surface in the contact region. Two boundary contact problems are considered. The first problem deals with the contact interaction of an element of an abrasive particle in the form of a truncated cone and the surface of a part. The circle of smaller diameter of the cone contacts the surface of the part taking into account the friction and plastic deformation of this surface. Kinematic or force boundary conditions are applied to the circle of greater diameter. In the case of kinematic conditions, the normal and tangential displacements of the circle and its rotation are specified. In the case of force conditions, the force and moment are given. In the second task, the hard stamp slides at a constant speed along the flat boundary of the workpiece, the value of the die insertion is set. In the contact area, the sliding friction force is expressed through normal pressure and heating due to the friction and wear. The stress and temperature fields near the contact region are investigated.

Abstract: A new heat treatment procedure is proposed to remove the strong texture microstructure of JIS type G4051 S45C rolled steel, thus making ease for further machining process and hardening to obtain higher hardness and grain homogeneousness over the common heat treatment procedure. This procedure includes annealing and normalising process and is applied for f14x20 mm samples. By annealing process at approximate 840 to 880°C for 2 to 6 hours, the strong texture has been improved by about 30-40% in comparison to the conventional crystallization process. By normalising process at 880°C and 920°C for 15 minutes, the strong texture has almost treated. The grain size along the rolling direction (RD) and traverse direction (TD) are in the range of 15 to 50 μm.

Abstract: In this research work, the result of the effects of technological parameters on surface roughness in extrusion bars of aluminum alloy were pesented. The results of this study may be used for choosing optimal parameters of extrusion process so that surface quality of extruded bar was improved.

Abstract: The aim of this paper is to present the simulation and experiment of the welding butt-joint aluminum alloys to low carbon steel using Visual-weld software and the metal inert gas (MIG) welding process. The workpiece is set up in a virtual environment with an area of 150 x 70 x 5 mm, a welding speed at 3.5 mm/s, and a heating source of 2.5 kW. The finite element method (FEM) is used as a powerful tool in simulating, calculating and predicting the welding stress and distortion at the early stage of the design process and development of welding products. The metallurgical process, deformation, hardness, etc. are investigated using the FEM in Sysweld software. The microstructure of the intermetallic layer is observed using scanning electron microscopy. The hardness of the intermetallic layer is examined using Vickers hardness testing. Tensile strength and bending strength are examined by tensile and compress multimeter equipment. To improve the quality of the aluminum/steel welds, the IMCs layer should be as small as possible. The experimental results are better if the welding current of range of 95 – 100 A and the welding speed is from 3.5 to 4 mm/s.

Abstract: Porosity, hardness, and adhesion mainly affect the performance of thermal spray coating and significantly depend on spray parameters. Therefore, determining value of the spray parameters and their effects on the coating properties are always taken into consideration. This paper studies optimization as well as evaluates influences of HVOF spray parameters which include powder feed rate (M), rotational speed of the details per minute (N) and step movement of the nozzle per revolution (S) to the adhesion, porosity, micro-hardness of Cr₃C₂ - 20(80Ni20Cr) coating on 40Cr steel shaft substrate. Taguchi experimental design L9 combined with analysis of variance (ANOVA) was used to determine optimum spray parameters and percentage of effect of each spray parameter on properties of the coating. From obtained results, the optimal spray parameters are m = 35 g.min^-1, n = 130 rpm, S = 6 mm for the highest hardness coating of 658.2 HV; with m = 45g.min^-1, n = 130rpm, S = 3 mm for the smallest porosity of 1.27%; with m = 35g.min^-1, n = 130 rpm, S = 3 mm for the coating with a maximum adhesion of 44.07 MPa. The percent effects of the parameters m, n, S to adhesion, porosity and hardness were (2.8%, 33.6%, 63.6%), (0.1%, 1.3%, 98.6%), (32.7%, 43.3%, 24%), respectively. The percent effects of spray parameters on corresponding coating property allows adjustment of spray parameters to obtain the desired coating. Verified experiment results shows that the results are reliable. Taguchi method and ANOVA can find optimal parameters of the HVOF spray to acquire high-performance coating.

Abstract: Wear and soldering are the two common failure types of high pressure die casting molds. Surface treatment solutions are often offered to limit these two forms of failure. In this study, the authors compared the average frictional force occurring when the die casting core was removed from the aluminum block to evaluate the effect of the chromium nitride and titanium nitride coating on the friction properties of the mold surface. Experience had shown that hard nitride coating significantly reduced the friction between the core and castings by aluminum alloys as well as significantly reduced the amount of adhesive applied on the mold surface. The experiment also showed that the coating of chromium nitride also reduced the level of damage to the core surface in real working conditions.

Abstract: The DC magnetron sputtering is often used for fabricating thin hard coatings for a wide range of industrial applications. The technique allows using DC power for deposition low or non-conductive films from metal target without using expensive RF power for insulation target. However, the performance of DC reactive sputtering is affected significantly by a phenomenon namely target poisoning. When the target poisoning occurs, coating is formed not only on substrate surface but also on target surface, which results in the reduction of deposition rate and coating properties. This paper presents a study on poisoning of Ti target during TiN coating deposition in the Ar + N₂ atmosphere. Results showed that the target poisoning state is impressed dramatically by partial pressure and flow rate of nitrogen gas. In poisoning mode, the deposition rate was reduced significantly compared to that in the metal mode. In addition, the formed TiN coating exhibited a non-stoichiometric and low adhesion to the substrate.

Abstract: This paper presents experimental studied results about surface roughness during end milling SKD11 steel under room temperature and work-piece preheated condition. Conventional samples were first performed. The samples which are same technical parameters were then performed at elevated temperatures to evaluate effective of heating process on the surface roughness. Orthogonal array Taguchi method was used to experimental design. The results showed that the surface quality of product was significantly improved under thermal - assisted milling. The surface roughness model during machining at room and elevated temperatures were evaluated and showed a good agreement with result of experiments.

Abstract: In the traditional mold manufacturing process, manual methods are mostly used to design, fabricate and then perform forming test to find out the reasonable processing mode for the product. Thanks to the development of technology, the forming design can be greatly reduced by using commercial software. This study uses a combination of ABAQUS software and TAGUCHI algorithms to calculate and design products. By using simulation tool, the fracture, safety, wrinkles as well as stress and strain on the surface of the product can be easily predicted after forming process. So that, the forming process were firstly simulated and executed on the software to find out important parameters. The variance analysis (ANOVA) was then performed to assess the effect of each parameter. Finally, the optimum solution for the product was selected based on ranking levels of each parameter.

Abstract: Aluminum 7000 series have been widely used in the aircraft and aerospace applications owing to its advantages of lightweight, high strength, and excellent corrosion resistance. Recently, the sheets have been applied in the automotive engineering in order to reduce the weight of commercial cars. For this demand, press forming is a common forming method used to produce a designed automotive part. However, springback is one of the main reasons to limit applications of the aluminum 7000 series. This study develops several material models that consider important material behavior including Young's modulus, Bauchinger's effect, and material anisotropy on springback prediction for the tested material. These models have been implemented in ABAQUS software to analysis a bending process and estimate springback amount. As a result, the effects of each material behavior on springback were clarified. Based on simulation results, it is found that correctly capturing the Bauchinger's effect is the major key to the success of springback prediction for such kind of material.