مجله مهندسی ساخت و تولید ایران
سال ششم شماره 6 (آذر 1398)

In this article, indentation process of damaged drinking water pipelines, repaired by polyester resin, are experimentally investigated while they are under two different conditions of constant and variable inner pressures. For this purpose, a mechanical defect is machined in pipe wall, and then, damaged part of the tube is repaired by the polyester resin. Then, to inject water into the tube and create different pressures, shut down two-end tube is connected to a hydraulic circuit. Then, the specimen with a certain inner pressure is placed into the universal testing machine between a rigid platen and a cylindrical punch. By applying the lateral force on the specimen, indentation test is performed in quasi-static condition; and it continues up to considering the first leakage effect in the repaired zone. In one type of the tests, inner pressure is kept in a constant value during indentation progress; and in the other type, inner pressure increases, slowly, due to indenting the tube wall. In each test, initial pressure, sample deformation mode, ultimate displacement of the punch, ultimate force, and energy absorption are measured; and in the variable pressure tests, ultimate pressure is also recorded. The variable pressure experiments show that when initial pressure increases, ultimate displacement of the punch, ultimate force and energy absorption decreases.; while, in the constant pressure experiments, by increasing the constant inner pressure up to 14 bar, ultimate displacement, ultimate force and absorbed energy increases and then in lieu of higher inner pressure, the mentioned parameters follow a decreasing trend.

Chatter is undesirable self-exciting vibration that occurs during machining process and could cause damage to the tool and the machine and surface finish of the workpiece. This phenomenon is generated from interaction of the tool and workpiece during cutting process and is one of the limiting factors for achieving a high cutting rate. In this paper, the effect of clamping of tool and workpiece on stability lobes of the milling process is investigated by employing a four degrees of freedom model of tool and workpiece. For this reason, the dynamic of cutting process is modeled through a set of coupled delay differential equations by considering regenerative chatter and loss of contact effect. Structural parameters of this model are measured by using the modal test in different clamping torques of the tool and the workpiece. Simulated stability lobes diagram is constructed based on full-discretization method. To validate the presented model, half immersion up-milling cuts were performed, and the limit values of axial depth of cut in different tool and workpiece clamping are determined experimentally for two different spindle speeds. The results indicated a good agreement between the stability lobes diagram obtained by FDM method and the experimental limit values. In addition, the results showed that the torque of clamping tool and workpiece have effect on the boundary of the stability lobes, that is, the increase of torque clamping lead to increment of the minimum critical cutting depth and reduces amplitude of vibration in stable and unstable cases over determined time interval.

Welded sheets are made by butt connecting of the base plates in various welding methods. These sheets are called tailor welded blanks, welded sheets (TWBs). Due to their many benefits, they have found many uses in various parts of the industry. In this Research, the formability and effect of weld line of TWBs of St12 and St14 in thicknesses of 1 mm and 1.5 mm in single point incremental forming in the form of a truncated pyramid has been investigated. At first, the maximum depth that can be shaped in single point incremental forming of a truncated pyramid from each of the base plates for different values of wall angle was obtained and the critical wall angle for each of them was determined. Then, the incremental forming of the truncated pyramid was done using welded sheets at the critical wall angle of the base plates. In this regard, TWBs were considered with different layouts and combinations of base plates. To investigate the effect of weld line on forming depth, each combination was prepared in two weld directions of 0 and 45⁰ relative to the rolling direction. The experiment results showed that the fracture depth of TWBs with 45⁰ was reduced by an average of 14% compared to TWBs in the rolling direction. Furthermore, the average depth of the TWBs at the average critical wall angle of the base plates decreases to about 25% compared to the base plates. Therefore, the TWBs should be formed at their critical wall angles.

In the milling of sculptured surfaces, cutting forces and the final part accuracy can be affected by surfaces curvatures. In this paper, an analytical formulation containing the explicit form of the principal curvatures of the surface is developed for extracting the engagement boundaries between a ball-end mill and a sculptured surface, and the effect of surface curvatures on the milling forces is investigated. To this end, first, a mechanistic cutting force model is presented for calculating the milling forces acting on a ball-end tool. Orthogonal to oblique cutting technique is used to calculate the cutting force coefficients, and the model is verified by comparing the predicted milling forces with the existing ones in the literature. Then, parametric studies are performed to investigate the effects of cutting depth and surface curvatures on the milling forces. The results show that at a constant cutting depth, the milling forces are more influenced by the surface curvatures at the concave and saddle regions of the surface in comparison with the convex regions. Furthermore, for constant values of curvatures, the effect of surface curvatures on the milling forces increases as the cutting depth decreases. In other words, as the cutting depth decreases, neglecting the effect of surface curvatures results in more relative error in the calculated milling forces. Furthermore, the obtained results show that the surface curvature perpendicular to the feed direction has more influence on the milling forces than the curvature in the feed direction.

The laminate composite plates are a candidate to delaminate when subjected to stresses concentration during the drilling operation. In this paper, the influence of drill feed rate and diameter in the delamination of composite plates is studied by experimental tests. For this purpose a carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) plates with different thickness are made in laboratory and drilling is done for the 54 different drilling condition cases. Based on digital images processing (DIP) for the drilled surfaces, an image of the damaged area was used to measure the delaminated area and then compare the results. Optimum feed rate is obtained as 200 mm/min for CFRP and 125 mm/min for GFRP with the spindle speed of 800 rpm. By increasing the thickness of the composites, there is a decrease in the delamination, so that by increasing the thickness of the CFRP and the GFRP to 4 mm, with increasing diameter of the drilling tool, the area of the damage region in the same feed rate has decreased. In most cases, a directly proportional relationship was confirmed between an area of damage region and the feed rate.

In this paper, thermo-mechanical behavior of the welding process was analyzed to determine the effect of preheating on the distortion magnitude and distribution in dissimilar joints. By using a verified finite element model, an efficient user subroutine was developed to consider the effects of phase transformation. In order to verify the model, experimental data for dissimilar joints, obtained by CMM measuring device method, were utilized. Good agreement was observed between the finite element and experimental data. The results indicated that the developed computational method is an effective tool to predict the distortion of dissimilar weld joints. The present finite element model was developed in a butt-welded plate to consider the effect of the preheating. It was observed that the increasing of the preheating temperature magnitude of distribution decreased on the carbon steel and stainless steel sides. Moreover, by increasing the preheating temperature more than special temperature range the preheating has no meaningful effect on the distortion on the both side of joint. Whatever, the preheating temperature become asymmetric in dissimilar joints, effect of the preheating on the distortion reduction is negligible on the carbon steel side but it has important effect on the stainless steel side. By increasing the preheating temperature invariably the carbon steel side has distortion of welding less than stainless steel side because of that’s high thermal coefficient.