مجله مهندسی ساخت و تولید ایران
سال دهم شماره 5 (امرداد 1402)

In this study a new severe plastic deformation method named noncircular thin section cyclic extrusion–compression (NCTS-CEC) is proposed for processing ultrafine-grained noncircular thin section beams. In this technique, the total length of noncircular L shaped section is passed through a neck zone and experiences severe plastic strains. Therefore, the high amount of accumulated plastic strain could be imposed by repeating the number of process cycles. In the first section of study, the AM60 Magnesium alloy is inserted into die and deformed by punch in different cycles. The observations by optical and SEM microscopes showed the formation of about 5 μm fine grains from the initial value of 75 μm after processing by two cycles of the NCTS-CEC. Also, the mechanical properties including yield strength, UTS, elongation and microhardness are evaluated at different cycles of NCTS-CEC processing. The obtained results showed the increase of yield strength and UTS to 136.9MPa and 286.7 MPa from the initial values of 89.5 MPa and 227.3 MPa, respectively. The Vickers microhardness is increased to 89HV from the initial value of 54HV at the end of second cycle. Also, the elongation of processed sample is increased to 14.4% from 11.3% due to texture evolution, grain refinement and breakage of brittle eutectic phases at the end of second cycle. The cellular automaton (CA) finite element method was implemented to simulate the process to predict the microstructure evolution of AM60. The obtained results from cellular automaton finite element (CAFE) and experimental methods were in good agreement.

In the process of molding parts using the plastic injection molding method, it is key essential to apply appropriate parameters in order to produce a qualified product. The purpose of this paper is to choose helpful production parameters and optimize them for molding eight different parts made from Polyetherimide. In the beginning, based on the previous research and the capabilities of Mold Flow software, appropriate process parameters were chosen. These parameters were: melt temperature, mold surface temperature, packing pressure and coolant inlet temperature. The simulations in Mold Flow software were done based on Taguchi’s L25 orthogonal array. Afterward, the critical and comparable results including: volumetric shrinkage, sink mark, warpage and the percentage of frozen volume in parts were exported from the simulations. Eventually, the optimizations were made based on these results by applying the gray relational analysis. The optimizing results show that in all distinguishing coefficients of the gray relational analysis (0.1 to 0.9), the melt temperature was 360 °c, the mold surface temperature was 140 °c, the packing pressure was 100% of the injection pressure and the coolant inlet temperature was 12.5 °c lower than the mold surface temperature of the most optimized ones. Also based on the ANOVA results, in all difference indices, parameters of melt temperature and packing pressure were respectively the most effective.

In this article, ultrasonic welding of thermoplastic composites has been studied with an emphasis on weldability and joint quality evaluation, heat generation and joint formation, and the effect of welding force, vibration amplitude, fiber direction, horn displacement has been investigated. In this research, composites including PA6 and unidirectional pre-impregnated glass fibers, in two types of lay-outs (90/90/0/0)s and (0/90/-45/45/90/0)s with an energy director of flat shape with a thickness of 0.14 mm. Three vibration amplitudes of 51.8, 74.5 and 86.2 μm and welding force of 300, 500 and 1000 N with three welding times of 300, 500 and 900 ms are considered. The results of the test show that the highest welding strength of 25.5 MPa was obtained, which occurs in the vibration amplitude of 86.2 μm and the welding force of 500 N and the welding time of 500 ms. It can also be seen that the amount of maximum power consumption is affected by vibration amplitude and welding force, and by changing the direction of the fibers of the first layer of the composite from 90 degrees to 0 degrees, the welding strength increases more than twice.

In this study, the production of nanocomposite samples was investigated using digital light processing (DLP). First, the effect of the thickness of the printing layer in three values of 50, 75, and 100 micrometers on the tensile properties of neat and composite resin samples as well as the printing time was investigated. Next, by adding different amounts of aluminum oxide nanopowder with a particle size of 50 nm to the resin, the effect of different percentages of nanopowder on the mechanical properties of the samples, including tensile strength and wear resistance, was investigated. The results showed that samples with less layer thickness have better strength than samples with more layer thickness. By reducing the thickness of the layer from 100 to 75 and 50 micrometers, the tensile strength in neat samples increases by 4 and 8.55%, respectively. Also, with the increase of alumina up to 2% by weight, the tensile strength first decreases, and then with the continued increase in the number of reinforcing particles, the tensile strength improves, so that finally, with 8% by weight of alumina, the tensile strength shows an increase of nearly 16% compared to the neat resin sample. . In addition, with the increase in the weight percentage of alumina in the nanocomposite, the wear resistance first weakens and then improves, and finally (similar to the tensile strength) at 8 weight percent of reinforcing particles, the specific wear rate decreases by nearly 67% compared to the neat resin sample.

7075 aluminum alloy, with a high strength-to-weight ratio and good impact strength, is one of the useful materials in the aerospace and automotive industries. However, this alloy has limitations such as poor formability, high spring back at low temperatures, and thermal distortion during hot forming. To overcome these limitations, a thermomechanical process including solution heat treatment, forming, and quenching in the die can be used. In this research, for producing a U-shape part with a depth of 30 mm, a 7075 sheet with a thickness of 2 mm was first subjected to solution heat treatment at a temperature of 480 ℃, and then was immediately transferred to a cooling die to be formed at a temperature of 4 ℃ under a hold time of 20 seconds. Finally, the part was artificially aged to improve its mechanical properties. A finite element simulation of the process using the ABAQUS software was also performed. Good dimensional accuracy and absence of rupture in the final U part, close agreement between the experimental and simulation results, an acceptable 25% reduction in elongation, very close tensile strength to the base material, and microhardness equal to 95% of the base material are the results of this research.

The wires used in the wire EDM process are of great importance in this new machining process as the cutting agent of the workpiece. Factors such as the diameter of these wires, their material, and their manufacturing method make their production simply not possible. In the upcoming research, a widely used type of Chinese wire in the domestic industry has been selected, examined, and analyzed. In the early stages of the research, the Chinese wire sample was elementally analyzed and its compounds were extracted, then it was subjected to a tensile test and its mechanical properties were also extracted. In the next steps, the wire was made with the aim of making a Chinese model by two methods of casting and extrusion and was again subjected to chemical analysis and tensile test. Also, in the final stage, all the wires made on the wire EDM machine were put under the same parameters and conditions and tested on a piece of work. The important innovation of the current research is in making wire EDM wire by extrusion method for mass production inside the country. The manufactured wire sample has up to 80% more strength than Chinese wire and is also 10 times softer than that, which increases the strength and softness of the wire leading to greater resistance of the wire and reducing the possibility of its tearing during machining operations.