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As vacuum suction cups are widely used in stamping plants, it becomes urgent and important to understand their performance and failure mode. Vacuum suction cups are employed to lift, move, and place sheet metal instead of human hands. Occasionally the vacuum cups would fail and drop parts, even it would cause expensive delays in the production line. In this research, several types of vacuum cups have been studies and compared experimentally. A new tensile device and test method was developed to measure the pulling force and deformation of vacuum cups. The digital image correlation technique has been adopted to capture and analyze the contour, deformation and strain of the cups under different working conditions. The experimental results revealed that the relevant influential parameters include cup type, pulling force angles, vacuum levels, sheet metal curvatures, etc.

In this paper, an emphasis is put on describing the elastic and plastic deformation behavior of the bolted joint. The bolt material is assumed to be plastic hardening. A nonlinear combined stress model is established for a typical bolted joint for the purpose of studying its behavior under a yield tightening. The combined effect of axial and torsional stresses in the tightened threaded fastener is considered. A new approach for yield tightening under ideal plastic bolt was proposed, and the effects of the thread and bearing frictional coefficients on the clamp load prediction are evaluated. The prediction precision of deformation behavior of the bolted joint under yield tightening for the strain hardening bolt material are studied experimentally.

Spot Welding is an important welding technique which is widely used in automotive and aerospace industry. One of the keys of checking the quality of the welds is measuring the size of the nugget. In this paper, the Shearographic technique is utilized to test weld joint samples under the thermal loading condition. The goal is to identify the different group of the nuggets (i.e. small, middle, and large sizes, which indicate the quality of spot welds). In the experiments, the sample under test is fixed by a magnet method from behind at the four edges. Thermal loading was applied in the back side and the sample is inspected using the digital Shearographic system in the front side. Results show the great possibility of classifying the nugget size into three groups and the measurement is well repeatable.

In this paper, a finite element methodology is given in which finite element models of a three-weld Al-Cu plate is created with support and loading conditions emulating those seen in an optical lab. Harmonic response is sought for the models under the presumption that various defective welds are present. The numerical results are carefully examined to determine the guideline frequency range so the actual optical experiment can be carried out more efficiently.

In today's light-weight vehicles, the strength of spot welds plays an important role in overall product integrity, reliability and customer satisfaction. Naturally, there is a need for a quick and reliable technique to inspect the quality of the welds. In the past, the primary quality control tests for detecting weld defects are the destructive chisel test and peel test [1]. The non-destructive evaluation (NDE) method currently used in industry is based on ultrasonic inspection [2, 3, 4]. The technique is not always successful in evaluating the nugget size, nor is it effective in detecting the so-called “cold” or “stick” welds. Therefore, it is necessary to develop a precise and reliable noncontact NDE method for spot welds. There have been numerous studies in predicting the weld nugget size by considering the spot-weld process [5, 6].

This study investigates the effect of Teflon and adhesive coatings on the torque-tension relationship and the self-loosening performance of threaded fasteners. Two Teflon insulation coatings and one locking adhesive are considered. The torque-tension relationship is established for coated and uncoated fasteners for both tightening and loosening. Finally, the fasteners are tested to determine their self-loosening performance under cyclic transverse loads. A computer controlled fastener tightening system is used to establish the torque-tension relationship during tightening. The coefficients of thread and bearing friction, and the overall nut factor are measured. The breakaway loosening torque of tightened bolts, along with the coefficients of thread and underhead friction and nut factor are investigated. A modified Junker machine is used to evaluate the self-loosening performance of fasteners with various coatings.

This study investigates the effect of the fasteners threads dimensional variation within the conformance tolerance limits on the self-loosening of threaded fasteners that are subjected to cyclic transverse service loads. A test setup is developed in order to simulate cyclic transverse service loads, and monitor the fastener clamp load loss and rotation in real-time during the test. The tested fasteners are used in one of the critical safety joints in a DaimlerChrysler vehicle. The tested thread dimensional parameters are the major diameter, the minor diameter, the pitch diameter, thread pitch, and thread profile angle. These parameters are measured optically. A set of conforming fasteners are selected and tested for self loosening. The self-loosening results are used to construct a model that fits the data points that are obtained experimentally. After that, the developed model is used to estimate the effect of each factor and its interaction with other factors on the self-loosening.

In this paper, the effect of bearing friction and the hole clearance on the out-of-plane surface deformation in bolted joints is studied. Series of clamp load-deformation correlations are established for different lubrication conditions and hole clearance values by using both FEA and experiment methods. To study the effect of bearing friction coefficient, values that range from 0.1 to 0.4 are adopted in the FEA model. Three lubrication conditions are used in experiments; namely, clean bolts, oil lubricated bolts and grease lubricated bolts. In order to investigate the effect of hole clearance, four different hole diameters are used in FEA model with M8 bolts; namely, 8.8mm, 9mm, 9.25mm and 9.7mm, three of them are used in the experiments. Experiments are conducted on a single-bolt joint made of an aluminum plate that is fastened with an M8 class 10.9 button head socket screw.

This paper investigates the reliability of tightening automotive weld studs, using experimental techniques. During the nut installation on weld studs, only a small amount of the applied torque is used to produce the required clamp load in the joint. While a large amount of the input torque is lost in overcoming friction between the sliding surfaces. Large scatter in the stud tension often results from the normal friction variations. As a result, the weld stud becomes more susceptible to a pull-through failure mode especially in thin sheet metal applications. The torque-angle signature during stud tightening is analyzed to assess the strength and quality of the weld stud joint. The effect of the weld stud thread type, stud coating, sheet metal thickness and stud material on the torque-tension relationship of weld studs is investigated. An experimental procedure and test set up are proposed to test weld studs.

Vehicle weight reduction is a significant challenge for the modern automotive industry. In recent years, the amount of vehicular components constructed from aluminum alloy has increased due to its light weighting capabilities. Automotive manufacturing processes, predominantly those utilizing various stamping applications, require a thorough understanding of aluminum fracture predictions methods, in order to accurately simulate the process using Finite Element Method (FEM) software or use it in automotive engineering manufacture. This paper presents the strain distribution of A5182 aluminum samples after punch impact under various conditions by Digital Image Correlation (DIC) system, its software also measured the complete strain history, in addition to sample curvature after it was impacted; therefore obtaining the data required to determine the amount of side-wall-curl (Aluminum sheet springback) present after formation.

Weld Joints are widely used in automotive and aerospace industry. The main issue in the weld joints is the quality inspection to detect the disconnection in the welded area. In this paper, Shearographic technique with dynamic excitation is introduced to test the weld joints. In the experiments, the coupons are of 4 very thin layers of metal sheets welded together. The goal is to find out if there are any disconnections between the layers. They are clamped and then excited by a PZT actuator from behind. A real time digital Shearographic system with a self-refreshed reference image technology has been developed to display the measuring result, i.e. shearogram. A big range of driving frequencies is scanned to find the proper frequency and amplitude that can help to identify the disconnections. The results show that when the driving frequency reaches the resonance frequency, there will be big amplitude and thus a fringe pattern becomes visible on the coupon surface.

A multi-sensor Digital Image Correlation (DIC) system is employed to measure the deformation of metal specimens during tensile tests. The multi-sensor DIC system is capable of providing high quality contour and deformation data of a 3D object. Methodology and advantages of the multi-sensor DIC system is introduced. Tests have been done on steel and aluminum specimens to prove the performance of the system. With the help of the multi-sensor DIC system, we proposed our approaches to determine the forming limit based on shape change around the necking area instead of calculate the FLD based on the in-plane strains. With the employed system, all measurements are done post-deformation, no testing controlling mechanism, such as load force control or touching control, is required. The extracted data is analyzed and the result shows a possibility that we may be able to improve current technique for Forming Limit Diagram (FLD) measurement.

This study investigates the effect of fastener coating, tightening speed, and repeated tightening on the torque-tension relationship, and on the coefficients of thread and underhead friction. Selected coatings provide three distinctly different levels of friction between threads and under the rotating fastener head; these coatings are assigned a low, medium, or high friction designation. Due to the fact that the torque-tension relationship is highly sensitive to normal variations in friction, the findings of this study would improve the reliability and safety of bolted assemblies, especially in critical applications. For the three selected coatings, the experimental procedure determines the coefficients of thread and underhead bearing friction as well as the overall fasteners torque-tension relationship at two tightening speeds for three fastener sizes with fine and coarse threads. Additionally, the effect of repeated tightening is examined.

An experimental study is presented in order to determine the effect of tightening speed on clamp load distribution in a gasketed steel joint. Two gasket materials are considered, namely, Styrene Butadiene Rubber and Flexible Graphite. Flange tightening is achieved using a multiple spindle fastening system that has speed and torque controls; the fastening system is also capable of performing simultaneous tightening of all fasteners using other advanced control modes such as torque-turn or torque-to-yield strategies. Two tightening patterns are investigated, namely, simultaneous tightening of all bolts and individual tightening of one bolt at a time following a star pattern. The tightening speed in this study ranges from 1 rpm to 100 rpm. Clamp load loss due to the combined effects of gasket creep relaxation and elastic interaction is investigated.

Light-weighting vehicles cause an increase in Aluminum Alloy stamping processes in the Automotive Industry. Surface finish and lubricants of aluminum alloy (AA) sheet play an important role in the deep drawing processes as they can affect the friction condition between the die and the sheet. This paper aims to develop a reliable and practical laboratory test method to experimentally investigate the influence of surface finish, lubricant conditions, draw-bead clearances and pulling speed on the frictional sliding behavior of AA 6XXX sheet metal. A new double-beads draw-bead-simulator (DBS) system was used to conduct the simulated test to determine the frictional behavior of an aluminium alloy with three surface lubricant conditions: mill finish (MF) with oil lube, electric discharge texture (EDT) finish with oil lube and mill finish (MF) with dry lube (DL).

In this paper, an optical method for inspecting the bolt tension is presented. This method uses 3-D Electronic Speckle Pattern Interferometry (ESPI) technique to measure and monitor the deformation field on the surface of the clamped member, and to establish a reliable correlation with the bolt tension. A new torque-deformation tension control concept is presented on the basis of this deformation - bolt tension relationship. Because the relationship between the bolt tension and deformation is independent of the frictional variables of the bolt, the inspection and control accuracy by this optical method is more reliable than relying on the torque-tension relationship. This experimental study is completed on a bolted joint. The relationship between the in-plane deformation on a clamped pin and the bolt tension is established. The method for eliminating the effect of the rotation on the deformation measurement is provided.

Spot Welding is now widely used in the fabrication of sheet metals, mainly due to the cost and time considerations. Spot welds are found in nearly all products where sheet metal is joined. Examples range from a single metal toolbox to nearly 10,000 spot welds found in a typical passenger car. Obviously the quality of the spot weld has a direct impact on the quality of the product. The problem of estimating the spot-weld quality is an important component in quality control. If the weld nuggets are improperly or incompletely formed, or the area surrounding the nugget is smaller than required, the structural integrity of the entire part may be uncertain. Furthermore these inconsistencies are usually internal and are seldom visible to Optical Inspection. This study is focused on the non-destructive evaluation of the spot welds using “Digital Shearography”.

A nonlinear model is established for the clamp load analysis of tightened bolted joints that are subjected to a separating service load that is cyclic in nature. The analysis takes into account the strain hardening of the bolt material to determine its behavior beyond the elastic limit. The bolt tension versus elongation curves during the tightening are established. The clamp load loss is determined due to the permanent set in the fastener after a cyclic separating force has been removed. The fastener material with strain hardening plastic behavior is used for modeling the behavior of the bolted joint system. The effect of some non-dimensional variables on the amount of clamp load loss is investigated. Analytical results are presented for a range of stiffness ratios that simulate both soft and hard joint applications.

A V-engine high pressure fuel pipe have experienced several failures during dyno engine validations at brazed joints due to combination of static and dynamic engine loads. The braze fillet experience high local stress concentration with large gradients and it was critical to capture strain contour at this spot to properly understand the failure. Strain gauges was used to measure strain but was incapable of capturing the braze fillet due to the small fillet radius and lack of real estate to install the gauge (braze fillet radius ~ 0.10 mm). A whole field optical experiment method Digital Image Correlation was utilized to successfully captured strain contour at area of interest and results fed back to computational model.

The coefficient of friction between surfaces is an important criterion for predicting metal behavior during sheet metal stamping processes. This research introduces an innovative technique to find the coefficient of friction on a lubricated aluminum sheet metal surface by simulating the industrial manufacturing stamping process while using 3D digital image correlation (3D-DIC) to track the deformation. During testing, a 5000 series aluminum specimen is placed inside a Stretch-Bend-Draw Simulator (SBDS), which operates with a tensile machine to create a stretch and bend effect. The friction coefficient at the contact point between an alloy sheet metal and a punch tool is calculated using an empirical equation previously developed. In order to solve for the unknown friction coefficient, the load force and the drawback force are both required. The tensile machine software only provides the load force applied on the specimen by the load cell.