مجله مهندسی ساخت و تولید ایران
سال هفتم شماره 4 (تیر 1399)

In recent years, 3D printing methods (additive manufacturing) have been attracted in research centers and industry. Among several 3D printing processes, fused deposition modeling (FDM) was more popular. In this method, plastic filaments were used for rapid prototyping or manufacture of a structural part. In this research, composite filaments compounded by a polymeric matrix and different volume fraction of aluminum oxide (alumina), were produced. Mechanical and physical properties of printed parts by these filaments were evaluated. Tensile test results showed that with increase of the volume fraction of alumina, tensile strengths were decreased because of inter layer voids. For 20% volumetric of alumina, tensile strength was decreased up to 70%. But in compression test, compressive strength was decreased 74% with increase of alumina till 10% and then compressive strength increased. Also, heat deflection temperature test was conducted and 11% decrease in heat deflection temperature was obtained, because of lower strengths of composites. Thermogravimetric analysis (TGA) showed that with increase of alumina, thermal stability of printed parts was increased. Linear shrinkage was measured for printed part in three directions and anisotropic shrinkage was explained. Also with increase of alumina till 15% volumetric, hardness was decreased to 27% and after that the hardness was increased a little. With increase of alumina till 20% volumetric, warpage of parts was decreased to 91%.

A simple definition of functional graded material (FGM) includes composite with inhomogeneous micro-structure that made by at least two components. The properties of FGMs vary along the the material thickness. The centrifugal procedure is a useful method to fabricate a FGM material. Different parameters of centrifugal method effect on the distribution of the reinforcement material. In this study, copper, iron, SiC and alumina powders were used as reinforcements and a polyester resin employed as the matrix. In manufacturing process of mentioned materials, powders with specific volumetric ratio, mixed with the resin and poured into the rotary mold. By attention to centrifugal force, powder paricles found specific position in the resin. Captured images from the surface of fabricated FGM tubes and distribution of particles were analysed by image processing. Three point bending tests were used to measure the strength of material according to ASTM D790 standard. The results showed that the rotational speed of mold is the most effective parameter on the distribution of reinforcement particles. Therefore, by increasing the speed from 250 to 500 rpm, slope of distribution of reinforcement particles increased. The results of the bending test showed that employment of reinforcement particles with more strength and volume led to increase the strength and module of fabricated FGMs.

Severe plastic deformation processes have been developed for the fabrication of material with proper mechanical properties over the past decade. The Extrusion process with Equal Channel Angular Pressing as a new process is able to apply a severe plastic deformation due to two continuous shear regions with higher strain rates and more homogeneous strain distribution compared to some of the SPD processes like ECAP. In this study, a new process of severe plastic deformation is introduced and fabricating an high strength AA1050 specimen was investigated experimentally and numerically which led to presenting an effective parameter of this process. It has been shown with using this new process, it is possible to fabricate samples with a higher strain rate and more homogeneous distribution compare with conventional ECAP and extrusion, and the limitation of the high length sample was significantly reduced than the conventional ECAP which friction with the die wall prevents it from continuing. It has been shown that the fabricated sample of one pass of this process has a 50% increasing in yield strength than the annealing sample, which indicates the high efficiency of this process.

Nowadays, with the advancement of materials science and the production of materials with special properties such as super alloys, composites and ceramics used in advanced industries, the use of traditional machining methods for the production of these parts is not possible. Therefore, the use of modern methods has been considered. One of these methods, which has the ability to add to traditional cutting processes, is the use of ultrasonic vibrations during the machining process. In this paper, analytical relations have been derived to calculate machining forces associated with ultrasonic vibration based on the undeformed chip thickness. Then numerical simulation of ultrasonic assisted milling process is performed by applying the vibrations to the workpiece in the feed direction by using the ABAQUS finite element software and the machining forces are determined. The results obtained by analytical and numerical data show that the use of ultrasonic vibrations can change the direction of movement of the tool and change the thickness of the undeformed chip and thus reduce the machining forces in the milling process. Also, based on the results, it was found that there is a good agreement between the results obtained from analytical analysis and 3D FEM modeling in macro scale.

Friction stir processing is a solid-state method used for local homogenization, grain structure refinement, and improvement of mechanical properties of metallic materials. Through this method, AA5456/SiO2/5-15p nanocomposites were produced in the present research. The average particle size of the reinforcements was 20 nm. The processing parameters included the constant traverse of 8 mm/min and rotational speeds of 800 and 2500 rpm. The microstructural examinations were carried out using the optical and scanning electron microscopies. The results showed that the average grain size of the stir zone reduced by incorporation of the reinforcing particles into the matrix. It was also observed that the increase in the rotational speed results in a decrease in the grain size of the stir zone. The mechanical properties of the friction stir processed composites were also evaluated by the microhardness and tensile testing. It was revealed that the microhardness is increased from 80 to 170 HV when the rotational speed increases. The tensile test results showed an improved strength from 130 to 210 MPa for samples with lower percentages of reinforcements.

In this research, wear behavior of a TRIP steel and a DP steel from two different heat treatments was investigated on a high-strength low-alloy steel. Reciprocating wear tests were performed at a force of one kg with a constant linear velocity of 0.1 m/s. Wear samples were studied by SEM with point analysis. To study type of phases formed, XRD was used. The results showed that during the wear process, TRIP steel had more weight loss than DP steel, and in TRIP steel, the rate of change in weight decreased significantly during the wear process due to the transformation of the remaining austenite phase to martensite. In the DP steel, due to severe difference in ferrite and martensitic hardness, a more uniform wear surface was produced. Also, experiments showed that Fe2O3 oxide was formed in steel DP and Fe2O3 and Fe3O4 in steel TRIP, which increased the amount of iron oxide in steel TRIP compared to DP steel. Ultimately, the wear mechanism of both steel, delamination and oxidation wear were detected.