Search Results

The objective of the study is to investigate the effect of current pulsation frequency on the weld bead microstructure, segregation and hardness of Hastelloy C-2000 weldments. Bead on Plate (BoP) welds were made by using Pulsed Current Gas Tungsten Arc Welding method (PCGTAW) at eleven different frequencies. The weld bead width and depth of penetration was measured with the help of Dinolite macro analyzer. The microstructure of weldments are further examined through optical microscope and Scanning Electron Microscopy (SEM) to identify the type of grain, grain coarsening and extent of the Heat Affected Zone (HAZ). The grain structure turn into finer and equiaxed in all cases and there was an optimum frequency range over which the significant grain refinement was observed. Microsegregation of alloying elements were computed with the aid of Energy Dispersive X-ray Spectroscopy (EDS). Vickers Hardness Tester was used to measure the hardness of the weld samples at ambient conditions.

In the present work, fabrication of similar Stainless Steel (SS) 304 joints by Nd-YAG Laser Welding Process (LWP) was done. A novel approach was attempted in this study. Welding was performed on dual sides of the plate (top and bottom) for a better mixture of micro powder particles in the weld pool region to achieve maximum depth of penetration, which is not easily possible in a single-sided LWP. High depth of penetration during fabrication of joints, significantly improved the mixture ratio of molten steel with reinforced micro powder particles. Al2O3 micro powder particles were reinforced in the weld pool region through the drilling process with varying depth ratios, and a moderate gap was maintained between each hole. The effects of Al2O3 on the microstructure and mechanical properties were studied and elaborated. Totally 12 samples were fabricated and joining was performed keeping the frequency as constant and varying laser power, travel speed for all the trials.

The Oil Hardening Non Shrinking (OHNS) die steel refers to a variety of carbon and alloy steels that are particularly well-suited for making tools. Though these steels are weldable, there is risk of crack formation. But, this can be avoided with convinced specifications like pre heating, proper choice of electrode etc., In the present work, OHNS die steel is welded with three different electrodes. The chosen electrodes were mild steel electrode, E312-16 chromium based electrode and E-NiCrFe-3 nickel based electrode. The OHNS steel is welded with these three electrodes and the welded specimens were examined for hot cracking tendency and mechanical properties of the joint. The hot cracking tendency was assessed by Houldcroft’s weldability test (Fishbone test). All the three electrodes proved the good results in terms of hot crack resistance and the specimen welded with E312-16 chromium based electrode provides good mechanical properties.

Many methods have been developed to evaluate the fatigue life of structures when the joints are as per ideal case. But if the joints are loosening, it leads to increase in loading on the other members which causes failures. Most commonly in commercial vehicle segment welding joint & bolting joints are most popular ones. It is very easy to find out bolts strength & loosening effect in static conditions. But when vehicle is moving (i.e. dynamic condition), same method cannot be used. For this we have developed methodology to predict the bolts loosening in dynamic condition using vibration data. Similarly, loading may differ on the structural members if the welds are failing in dynamic conditions. To overcome this problem, in our organization we have a solution. Of course to simulate welding failures fatigue analysis is mandatory. We are using notch-stress approach for evaluating the welding strength of the joint.

This paper deals with vehicle door 120-degree joint rust issue and water leak faced in most of SUV cars. Generally based on vehicle segment its styling curves and exterior design are defined. A Sedan or Hatchback is provided with curves to show its fluidic design but a SUV is provided with Straight lines to show its aggressive look. In existing condition door frame Joint has sharp joints where weld bead is added to prevent rust in joint area, but still improper seating of weather strip on weld bead cause water leak. Door’s A Pillar Frame and Horizontal Frame match at 120 degree joint edges are chamfered straight to match perfectly. Weld bead runs over the matching profile to join it. But weld bead project over the Frame surface and affects weather strip seating & results in poor sealing. Adhesive added for better sealing also follows the same path on bead and create a path way for water entry. Thus in long run this water stagnates and cause chronic rust issues in frame.

Virtual validation of automobile components poses a huge challenge and needs continuous process improvements. One of such challenge in FE modelling of welds and understanding its behavior with respect to physical behavior. With the ongoing development of BSVI line of products in commercial vehicle industry, the virtual validation needs to be accurate and close to the physical behavior of the components. The learning and challenges faced during the previous development is implemented in the current study for weld simulation and correlation activity. The brackets welded to the power train components is taken as a challenge in the present work. Initially weld model was depicted in the CAD and was analyzed in CAE by providing proper FE connection. This practice had lot of flaws, approximations due to perpendicularity and flatness concerns in the models leading to consuming a lot of time in model preparation.

In recent years, there has been a rapid growing demand for laser brazing in the transportation industry for automotive-Body in White (BIW), steel sheet assembly. Implementation of laser brazing is aimed primarily to improve productivity, quality of joints and cost. Laser brazing works by filling the opening amongst two substrates by melting the filler wire with the help of laser beam (used as a heat source), whereas in conventional resistance spot welding, contacting metal surface points are joined by the heat obtained from resistance to electric current. BIW is essentially a welded metal structure which is meant to provide durability and crashworthiness to the vehicle and is conventionally assembled using resistance spot welding process. The BIW structure comprises of various steel grades having varying thicknesses, compositions, microstructures and mechanical properties.

The main objective of the exhaust system is to offer a leakage proof, noise proof, safe route for exhaust gases from engine to tailpipe, where they are released into the environment, while also processing them to meet the emission norms. New stringent emission norms demand ‘near-zero’ leakage exhaust systems, throughout vehicle life bringing the joints into focus as they are highly susceptible to leakage. Needless to say, this necessitates them to endure not only structural but also the environmental loads, throughout their life. Thus, the fatigue life or durability tests become the most critical part of the exhaust system development. Test acceleration and result correlation (for life prediction), to meet the stringent project timelines and stricter environmental norms are the key considerations for developing a new testing methodology. Quality of accelerated tests is ensured by deploying all possible multiple loads, to simulate real-life conditions.

According to the increasing demands for light-weight design in the automotive industry, the use of thinner and lighter materials such as aluminum alloys for automotive parts has led to significant weight reduction. The joining of these materials has required development of new technologies in joining/fastening rather than welding. Flow drill screwing is one of the latest technologies created to fasten sheet metal panels. This paper discusses results of an evaluation of fatigue characteristics of flow drill screw (FDS) joints based on experimental data and observations from the literature. It was observed that the important fatigue-related geometric parameters of FDS joints were the gap between sheets and the extruded (or bulged) zone during screwing. Major failure modes were observed such as sheet failures where cracks grow from the inner surface of the sheet and around the extruded zone.

It has been well-documented in academic literature that, when subjected to compressive cyclic loading (R = -∞), weldments can experience fatigue failure. However, unlike non-welded components, it has been shown that mean stress has a negligible impact on the fatigue life of welds (Gurney, 1979). Currently, most analytical weld prediction methods neglect the influence of mean stress and instead focus only on the relationship between the stress (or strain) amplitude and the respective number of cycles to failure.

Automakers generally recommend not to weld structural parts after a vehicle crash, and these should be replaced as a whole part in case of a crash event. Sectioning of these members is also not recommended and use of the repair manual is mandatory in case of fracture of such parts. However, repair shops may not adhere to these instructions and use incorrect repair procedures on these members which would modify their strength properties. This study analyses the impact of welding structural members in a vehicle like the A-pillar which use Ultra-High Strength Steels (UHSS) for reducing the weight of the vehicle and improving the crashworthiness of the structure. The research conducted in this paper highlights the differences in the crash performance of a repaired vehicle as opposed to baseline injury values for the vehicle.

In automotive Body-In-White (BIW) structures, stiffness and the fatigue behavior is greatly influenced by the properties of its joints. Spot welding is one of the most widely used process for joining of sheet metals in BIW. Spot weld fatigue life under Accelerated Durability Test (ADT) is crucial for durability performance of BIW structures. Experience of BIW validations highlighted more number of spot weld failures in CAE when compared to actual tests. Hence, lot of iterations in the form of design modifications are required to be carried out to make these spot welds meet the targets which increases design & development time as well as cost. Current practice uses force-based approach for predicting spot weld fatigue life in CAE. To improve the spot weld fatigue life correlation, extensive study has been carried out on the approaches used for calculating spot weld fatigue life, namely force & stress-based approaches.

A major barrier, preventing RFSSW from use by manufacturers, is the long cycle time that has been historically associated with making a weld. In order for RFSSW to become a readily implementable welding solution, cycle times must be reduced to an acceptable level, similar to that of well developed, competing spot joining processes. In the present work, an investigation of the RFSSW process is conducted to evaluate factors that have traditionally prevented the process from achieving fast cycle times. Within this investigation, the relationship between cycle time and joint quality is explored, as is the meaning and measurement of cycle time in the RFSSW process. Claims and general sentiment found in prior literature are challenged regarding the potential for high-speed RFSSW joints to be made.

Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). In this paper, two different injection molding tests were completed. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line region. Tensile samples were cut at different locations along the weld line on the injection molded plaques. The test results showed that both UTS and fracture strain increase when the sample locations are away from the insert. This trend is attributed to different meeting angles. Second, standard ISO tensile bars with and without weld line were injection molded to identify the size of the weld line affected zone. A FEA model was built in ABAQUS, where the tensile sample was divided into two different regions, the solid region and the weld line affected region.

Welding processes are complex in nature. They affect the mechanical properties of a weldment in and around the welding joint (in the heat affected zone: HAZ), causing deformation and inducing high level of residual stress and plastic strain which are detrimental to the weldment performance. After welding some materials soften while others harden in the heat affected zone, depending on the process heat input, the thickness of the material and its chemical composition. Traditionally, finite element (FE) performance analyses (crash, rupture, fatigue, static and dynamic tests) of weldments are performed without accounting for the effects of welding processes and as such the real performance of a weldment is not accurately predicted. On one hand, if base material properties are used to represent a weldment which hardens in the heat affected zone, the performance analysis results would be too conservative which would hinder/limit potential weight reduction strategies.

Spot Welds are a category of welds used extensively in automotive structures, normally for metals. The fatigue analysis of such spot welds can be evaluated using (a) the Point 2 Point (P2P) method where a beam or bar is used to connect the 2 surfaces being joined, (b) a more modern approach where the 1D element is replaced with an “equivalent” brick element, or (c) a third approach that falls somewhere between where a “spider” and circular ring of elements, is used to represent the spot weld. In all 3 cases there is an assumption that the cross section is circular. For some specialist cases such as plastic connectors, the cross section is not circular so a new user defined weld is proposed. This paper will describe the approach that is based on the concept that a user generated tensor line can be used (equivalent to the theoretical Force/Moment to stress algorithms built into the P2P approach) along with special S-N curves create for different joint shapes.

This paper presents preliminary result in a flexible fixture solution for airframe assembly comprising a modular steel framework called Box-joint and flexible tooling modules called Hexapods. The solution is comprises a framework that is screwed together instead of welding beams together, which enables re-building the framework when performing change-over in a more extensive reconfiguration. The Hexapods are parallel legged passive fixture stands that can change their configuration to facilitate easy setup in a change-over between handle different assemblies. A solution to configure the Hexapods manually is described. The investment cost can be kept low by using a metrology system to provide for high accuracy in the tool configuration process instead of using precision parts in the fixture system.

This paper presents preliminary result in a flexible fixture solution for airframe assembly comprising a modular steel framework called Box-joint and flexible tooling modules called Hexapods. The solution is comprises a framework that is screwed together instead of welding beams together, which enables re-building the framework when performing change-over in a more extensive reconfiguration. The Hexapods are parallel legged passive fixture stands that can change their configuration to facilitate easy setup in a change-over between handle different assemblies. A solution to configure the Hexapods manually is described. The investment cost can be kept low by using a metrology system to provide for high accuracy in the tool configuration process instead of using precision parts in the fixture system.

In the aircraft industry, joining technologies get more and more important, because they represent a high expense factor when components have to be assembled. Riveting is the current state-of-the-art joining method due to its very safe and robust application. However it is a time and weight consuming technology as it requires overlapping sections that have to be drilled in order to place the rivets in up to three rows. Thus, the aircraft industry currently evaluates several welding technologies to reduce production and maintenance cost as well as the weight of aircrafts for longer range and higher efficiency. Friction Stir Welding (FSW) represents an innovative joining technology that allows the welding of all aluminium alloys of interest with excellent seam properties and with thicknesses from 0.3 mm up to 50 mm and more. The substitution of automated riveting by FSW can lead to a significant reduction of process time and a cost reduction of up to 20 %.

Many of the vehicle components are manufactured by sheet metal forming process together with joining methods like the spot or seam weld, which will cause work hardening and thermal deformations in the products. As result, undesirable residual stresses, uneven thickness distribution and weld notches can be generated in the final product. Since the fatigue life of an automotive component depends on the manufacturing effects, much care should be given on the estimation of the process effects. In this study, fatigue life of a vehicle suspension component is estimated with finite element methods with considering the stamping and welding process effects. Residual stress distribution due to work hardening and thermal deformation is obtained, and used in determining the fatigue life as the mean stress effect. The simulation result is compared with test result and it shows the fatigue life is affected much more by welding rather than stamping.