مجله مهندسی ساخت و تولید ایران
سال هفتم شماره 8 (آبان 1399)

In vacuum forming process, determining the optimum conditions and selecting the appropriate values of parameters improves the dimensional and physical quality of the components and reduces waste and discarded parts during the manufacturing process. In this research, the ABS sheet with 2 mm thickness was selected and the mold was made from aluminum, then the experimental tests were performed by varying the initial sheet thickness (4 and 5 mm), Six temperature times ("315,"330 ,"345 و"360, "375, "390) and direction of feeding the sheet (vertical or horizontal for extruding). After 3D-measurement of vacuum components, the influence of the values and conditions of the parameters on the thickness and thermal shrinkage changes were studied. Increasing the heating time resulted in improved flow and steady distribution of sheet thickness, While the minimum changes of thickness (up to 2%) for the vacuum of the 4 mm sheet happened in heating time of 345", and for the vacuum of the 5mm sheet occurred in heating time of 390", and minimum thermal shrinkage (0.3%) was seen in heating time of 315" for 4 mm sheet by feeding vertical to the direction of extrudes. By changing the primary thickness of the sheets from 4mm to 5 mm, thickness variations reduced but the thermal shrinkage increased up to 0.9%. The vertical position of extruded materials chained structure with vacuum orientation caused the layers slippage resistance on each other and led to decreased thickness variations from 35% to zero and also reduced thermal shrinkage from 1.2 to 0.3 %.

Wheel loading in the grinding process is inevitable due to the chips arrangement separated from the surface of the workpiece in the gap between the grains. The amount of this loading depends on the factors such as workpiece material, grinding parameters, coolant-lubricant conditions and wheel surface topography. Determining the time to remove the chips from the wheel surface is one of the important variables in the grinding process, preventing the chips from sticking to the surface of the wheel and thus increasing the roughness of the surface. There are several methods for analyzing and monitoring the condition of wheel surface. In this study the influence of dressing condition and coolant-lubricant environments on the wheel surface loading has been investigated using image processing in python software. Using the examination of wheel surface images in pre and post grinding process of Inconel 738 under various condition of coolant-lubricant, optimal conditions for grinding wheel surface topography as well as workpiece feed rate are provided to prevent excessive loading.

Recently many researches are being conducted on flying robots. One field is to design the flapping kinematics to achieve better performance and maneuverability. Better maneuverability is achievable via variable wing geometry and for better performance, the effect of wing’s angle of attack can be considered. Positive effect of angle of attack is studied before however, variations of angle of attack in a flapping cycle is the main subject in this paper. Three dimensional model of wing and body is inserted in ANSYS-FLUENT and aerodynamic lift force is simulated and calculated. Each wing is modeled as a two-part mechanism with relative motion. Comparing to previous studies, wings’ angle of attack periodically changes which is more similar to natural flapping and improves efficiency. Change rate of this variations is equal to flapping frequency. At first numerical simulations are verified by a previous study on a wing with fixed angle of attack. Then the wing with variable angle of attack is numerically simulated. Results show that an improvement of the lift force for more than ten percent is achievable by this method.

Single point incremental forming is one of the novel processes in forming of metallic sheets that has created high forming levels in sheet by local plastic deformation. In this paper, new tool based on incremental forming principles is introduced for production of cylindrical flange. Using this tool for forming of the flange, the manual milling machine is used instead of milling machine equipped with computer numerical control (CNC). Forming of flange wall is accomplished by a new tool that includes two forming punches. Tool shank is fixed on milling machine spindle and the value of eccentricity determines the final diameter of flange. Movement of rotary tool is simple and downward with defined step. The results show that flanges with specified diameters can be formed by using this method very fast. Increasing the diameter of the primary hole created on the sheet increases the flange height but also increases the thinning. Increasing rotational speed results in forming flanges with higher height but increasing vertical feed rate of tool decreases the flange height.

Wire electrical discharge turning (WEDT) is one of the relatively new areas of research in machining. The main reason for using WEDT is the lack of contact between the tool and the workpiece during the cutting process, which makes the workpiece hardness and brittleness not a limiting factor for cutting. For WEDT it is necessary to add a rotating mechanism to the wire cut device to rotate the workpiece while holding it. In this paper, the effect of current intensity and feed rate on surface roughness and fatigue life of workpiece Mo40 is investigated using design of experiments with response surface method and the effect of each input parameters is determined using analysis of variance. According to the results of the experimental experiments, with increasing table feed and current intensity, surface finish and fatigue life of the workpiece decrease. Feed rate with 87 and 75% effect on surface roughness and fatigue life, respectively, is the determining parameter. The lowest surface roughness (1.63 µm) and the highest fatigue life (85613 rev) were obtained using values of 1 ampere for current and 0.4 mm/min for feed rate in the WEDT process, but in other experiments of the WEDT process, the surface roughness is higher and the fatigue life is less than that of the conventional turning. The average surface roughness in the WEDT process is 52% higher than that of conventional turning, and the average fatigue life of the workpiece in the WEDT process is 16.8% lower than that of conventional tuning.

The present study investigates the effects of adding 2.5 wt,% of chromium on the phase transformation, microstructure, and mechanical properties of an advanced medium-manganese high-strength steel containing 4.5 wt.% of manganese. The addition of chromium enhanced the hardenability and a fully martensitic structure formed after the hot-rolling process and air-cooling the rolled sheet and consequently austenitization and rapid cooling which are part of the production route of medium-manganese steel sheets was eliminated. Also, the addition of chromium made it possible to choose higher annealing temperatures because of transforming the carbide phases into carbides stable at higher temperatures. The investigation of the microstructure, phases, and hardness verified the formation of martensite with a Vickers hardness of 461 after hot rolling. Performing intercritical annealing at 700°C for 10 min caused the austenite phase to return to the structure and produced satisfactory mechanical properties, including an ultimate tensile strength of 940 MPa and an elongation of 17%. The reverse austenite phase, the considerable reduction in hardness, and the enhancement of elongation after annealing verified the intercritical annealing process.