Sharif Digital Repository

Inaccuracies in workpiece location lead to errors in position and orientation of machined features on the workpiece, and strongly affect the assemblability and the quality of the product. The accurate positioning of workpiece on a fixture is influenced by rigid body displacements and rotations of the workpiece due to several errors (e.g. geometric radial and position errors in locators and manufacturing tolerances of the workpiece). In this paper, an efficient approach is introduced for analysis and compensation errors in the workpiece-fixture-cutting tool system. A new mathematical formulation of workpiece-fixture modelling is proposed to establish the relationship between the locating... 

Fixtures play a key role in locating workpieces to manufacture high quality products within many processes of the product lifecycle. Inaccuracies in workpiece location lead to errors in position and orientation of machined features on the workpiece, and strongly affect the assemblability and the final quality of the product. The accurate positioning of workpiece on a fixture is influenced by rigid body displacements and rotations of the workpiece. In this paper, a systematic approach is introduced to investigate the located workpiece position errors. A new mathematical formulation of fixture locators modeling is proposed to establish the relationship between the workpiece position error and... 

This study concentrates on the effects of weld sequence and welding fixtures on distribution and magnitude of induced arc welding residual stresses built up in butt-joint of Gas Tungsten Arc Welding (GTAW) AA5251 plates. Aluminum plates have been welded under different welding conditions and then, longitudinal and transverse residual stresses were measured in different points of the welded plates employing hole-drilling technique. The results indicate that welding sequence significantly alters the distributions of both longitudinal and transverse residual stresses while the changing in the weld sequence leads to 44% decrease in longitudinal residual stress. Besides, both the geometry of weld... 

The purpose of this work is to assess the effect of welding fixtures on distributions and values of residual stresses during Gas Tungsten Arc Welding (GTAW). The butt-joint GTAW of AA5251 plate is investigated using a transient thermo-mechanical analysis performed by the finite element program, ABAQUS. The model considers two different welding conditions including unconstrained and perfectly constrained conditions while macro examination and residual stress measurements by implementing hole drilling techniques are utilized to evaluate the predictions. The results show that the utilizing of a welding fixture alters the temperature field within the plate being welded and the depth of the weld... 

Effects of zinc layer on microstructure and mechanical behavior of resistance spot welds of aluminum to galvanized (GS-Al joint) and low carbon steel (PS-Al joint) were explored. The results showed that although nugget 'volume' in PS-Al joint was larger, the nugget 'diameters' of PS-Al and GS-Al joints were almost the same in size since the melted zinc layer was pushed toward the outer regions of the nugget. Melting and evaporation of zinc coat led to reduction of Al-Fe intermetallic layer thickness. Presence of zinc also reduced the fixture-induced tensile stress. Utilizing carbon steel fixtures during welding caused a sensible vibration in the joint members. The vibration resulted in... 

Fretting fatigue occurs in engineering applications where two interacting surfaces are subjected to fluctuating forces. The fluctuating forces occasionally act as a combined loading condition. The present paper investigates fretting fatigue behaviour of 316L stainless steel under such combined (i.e. tensile and bending) loading conditions. A new fixture was developed in order to apply bending and tensile loads simultaneously. Using this fixture, the effect of different bending-to-tension ratios was investigated. The results showed that increasing the contribution of bending load improves fretting fatigue life. On the other hand, increasing grain size decreases fretting fatigue life.... 

Tolerance analysis is essential for estimation of final error of key product characteristic (KPC) in a mechanical assembly caused by errors in production and assembly of individual parts. Many mechanical assemblies, especially in automotive and aerospace industries, include sheet metal parts with a small ratio of thickness to width or length. Such parts are substantially flexible and thus, are prone to large errors due to elastic deformations during assembly production. Phenomena such as deformation due to fixture force, spring back, welding distortion and so on are common to such parts. Unlike tolerance analysis of rigid parts, here, the elastic deformation of the parts plays a significant...