مجله مهندسی ساخت و تولید ایران
سال ششم شماره 3 (امرداد و شهریور 1398)

Mechanical recycling of wood products is a step towards maintaining environmental resources and reducing pollution. One of the problems of repeated recycling is the change in physical and mechanical properties, including changes in the molecular structure of products. In this research, in order to analyze the redox molecular structure, a granule of plast with a weight ratio of 70% high density polyethylene is prepared by extruding method and is injected in 5 cycles. Experimental experiments were carried out at a 60-bar injection pressure and a 70-bar retaining pressure and a second pressure time of 2 seconds. Molecular flow rates and crystalline percentages were tested to investigate the molecular structure of the recovered samples. High-density polyethylene with high chain length, with recycling and chain breakage, increased molecular weight, increased viscosity, which reduced the flow rate of molten material in recycled samples. The damage caused by the continuity of the chains and the loss of power between the chains causes an increase in the molten flow rate of 2.8 gr / 10min and the conversion of the semi crystalline molecular structure to amorphous and the reduction of the percentage of crystalline by 30% Is. Increasing the recycling cycle reduces the destruction time to 9.3 minutes in recycled samples

In this paper, a novel fabrication technique for functionally graded materials (FGMs) to have a programmed and continuous material pouring is presented. Microscopic examination and studying the desired gradient in various samples as well as studying the effects of volume fraction of constituents on microstructure, relative density and micro-hardness of the samples are other investigations presented in this article. The fabricated samples are made of Al powder as the matrix and Alumina (Al2O3) ceramic particles as the reinforcement. Functional gradient of Alumina particles distribution in the Al matrix along a cylindrical sample was applied using a novel material pouring device. After pouring the powder mixture with 10, 15, and 20 vol% of reinforcement into the die, various compacting pressures of 100, 200, 400, and 500 MPa were applied to the sample and sintering process under 700 oC temperature was carried out. The results show acceptable accuracy of the material pouring device after examining the distribution of reinforced particles. As well, it is obtained that as the volume fraction of Alumina particles increase, the relative density decreases and the Vickers micro-hardness enhances. So that, the most hardness in 20% Alumina sample is observed about 95.8 HV. In addition, as the compacting pressure increases, the relative density enhances up to 96%. In Al-15 vol% Al2O3 sample, increasing the compacting pressure from 200 to 500 MPa caused an improvement in micro-hardness by about 200%.

Jamming is defined as sudden and unwanted immobilization of workpiece during its loading/unloading into the fixture. Investigation of workpiece jamming in fixture and prediction of its occurrence during fixture design process may induce to modification of the fixturing plan, reduction of the fixture fabrication costs and decreasing of the jamming-related consequences. The present study focuses on the numerical investigation of workpiece jamming in fixture using block and palm case study and comparison of its results to the theoretical predictions. For this purpose, numerical analysis of block and palm case study is conducted using Adams® software. Results of numerical analysis represent that jamming is occurred for block by traveling of distance equal to 0.754 on the horizontal surface. Numerical results are compared to the theoretical predictions. Theories for prediction of jamming incorporate two main methods; first, development of dynamics equation for calculation of velocity and acceleration at the contact points and second, the minimum norm principle. Agreement of the numerical results to the predictions of the first-category theoretical analyses (calculation of the velocity and acceleration at the contact points) confirmed the accuracy of the numerical results. Also, effects of the parameters including coefficient of friction between the workpiece and base plate, angular velocity of palm and mass of block are studied on the block’s jamming distance.

Cooling/lubricant fluids are typically used in machining processes to reduce the tool-workpiece friction, decrease machining heat and improve surface quality. In recent years, however, several laws have been used in place to protect human health and environment, requiring industry to reduce coolants consumption and expand the use of low-risk and renewable ones. For this reason, a recent new lubrication technique called minimum quantity lubrication (MQL) has been developed for the machining processes. Vegetable oils are kinds of bio-based lubricants and have a significant capacity to be used in MQL due to their environmentally friendly and renewable properties. Stainless steels are considered to be difficult to machining materials and hence their machinability improvement has always been the subject of research. In this investigation, the effects of MQL and type of lubricant in the milling process of martensitic stainless steel EN 1.4903 have been studied. For this purpose, one type of vegetable oil derived from sesame seeds in two conditions including non-additive (pure) and with antioxidant additives, as well as one type of mineral oil have been applied in the experiments. Then, milling force, surface roughness and surface texture have been evaluated. Also, in order to compare the results with other lubrication methods, the tests have been performed under dry and wet conditions. The results show that the MQL compared to the conventional lubrication methods increases the machinability of stainless steel by reducing forces and improving surface quality. Moreover, the type of oil applied has a great influence on the process outputs.

The Researchers seeking to expand the capabilities of robots have begun looking to biological systems for inspiration. One particularly agile creature, the gecko lizard, is remarkably adept at maneuvering across both flat and vertical surfaces. The study of the gecko’s adhesive system has informed the design of several synthetic adhesives in recent years. These low consuming energy adhesives had a successful performance in climbing robots and robotic grippers. The existing grippers mainly use tendon mechanism for transmitting force inside the gripper and electrical motors for actuating the gripper. This paper concentrates on design and fabrication of a new gripper which uses solenoid for actuation, and Scuttt-Russel mechanism instead of tendon mechanism for transmitting force. The new gripper is more robust and cheaper than existing grippers. To verify the applicability of proposed gripper, experiments were conducted on a variety of substrates that demonstrated the gripper’s successful operation. Experimental results demonstrated 4.6, 4.5 and 4 kPa average normal adhesion pressure on the surface of acrylic, steel and glass respectively. Also, maximum measured adhesion increased 20% in comparison with previous tendon gripper. The results illustrate that a Solenoid actuator with Scott-Russel mechanism has the potential to be used as a new actuator in gecko-inspired gripper.

In this paper, according to slab method an analytical model is presented to study asymmetrical rolling process of unbounded clad sheets; in which, based on the process conditions, both of the two frictional models, including constant shear frictional model and coulomb frictional model, are applied. In the proposed model, vertical sides of the slabs include non-uniform normal stresses and shear stresses distribution. Equilibrium and yield equations for each portion of upper and lower sheets in the quaternary zones of deformation region are extracted by considering assumptions such as, large contact angle and utilization of new stress field, which is tried to be as near as possible to the real situation. Then, the bonding point position of the sheets, as well as, the upper and lower neutral points’ position, are determined. Moreover, the trend of the most important process quantities such as, pressure, force and torque of the process which are influenced by the sheet thickness reduction, ratio of speeds and work rolls radii, are investigated. Additionally, the proposed model is studied via finite element process simulation using ABAQUS software. Eventually, the results of the proposed model is compared with the analytical and experimental results of other researchers.