Important Joining Technology Research Articles

Automatic identification framework of the geometric parameters on self-piercing riveting cross-section using deep learning

Self-piercing riveting (SPR) is one of the most important joining technologies used in light-weight vehicle body manufacturing. Traditionally, SPR joints are developed through trial-and-error tests on various rivet and die combinations. Given the hundreds of rivets and dies available in SPR joint design, huge combinations exist in the full solution space. How to optimize the joining process at a low cost with high reliability is critical both for new material, new vehicle and new production line development. Instead of relying on experience-based physical testing, data-driven approach has been believed to be a promising way for future automotive manufacturing and design. However, the lack of effective data acquisition and accurate characterization methods for joints becomes a barrier, which limits the volume and availability of joining data. In present research, an automatic identification framework of the geometric parameters on SPR cross-sections using deep learning is proposed, which integrates an innovated and complete flow from the image pre-process to postprocess. Firstly, cross-section images are transformed into material segmentation maps using deep learning. Then critical control point of a cross-section is identified accurately, and totally 9 key geometrical parameters are measured based on the locations and combinations of control points. The present research shows that SOLOv2 and Unet are the best models for SPR cross-section image segmentation. The proposed framework could provide high accurate measurement results (average error < 0.02 mm) with a very short process time (within secs), laying a solid foundation for data-driven design and optimization of joining processes within the whole design space at vehicle level.

Fatigue properties of self‐piercing riveted multi‐rivet joints in steel and aluminum sheets

AbstractSelf‐piercing riveting (SPR) is an important joining technology for connecting steel and aluminum sheets. In this paper, AA6111 aluminum alloy and DP780 high‐strength steel were adopted to study the influence of fatigue on remaining static strength and energy absorption properties on self‐piercing riveting multi‐rivet joints. The results showed that energy absorption capacity of the specimens decreased significantly after high cycle fatigue. Fatigue reduced the remaining static lap shear strength of riveted specimens. Scanning electron microscopy (SEM) was used to analyze the cross section of fatigue specimens fractured by static tension. The results showed that fretting wear was found at the contact area between rivet and aluminum sheets. Fatigue bands and fatigue cracks appeared in fatigue specimens after high cycle fatigue, while those with low cycle fatigue specimens did not appear. Small cracks weaken the strength of the aluminum sheet, resulting in the static tensile strength of the riveted specimen with high cycle fatigue is lower than that of other fatigue specimens.

Increasing flexibility of self-pierce riveting using numerical and statistical methods

Abstract Self-pierce riveting with semi-tubular rivets (SPR-ST) is currently the most important joining technology for modern mixed-material car body constructions. In these body designs a multitude of material and thickness combinations occurs and for many of these combinations individual parameters of the SPR-ST process like the rivet length and die geometry have to be determined. This paper shows an approach to increase the flexibility of the SPR-ST process by the determination of the process parameters using FEM simulations in combination with statistical methods. In the described investigations one parameter set is derived for the SPR-ST process from seven different material combinations with steel and aluminum materials. For each material combination a simulation model is validated by the comparison of the joint geometry and force-stroke diagram from the experimental reference joints with the results from the process simulation. On the basis of the validated simulation models, numerical sensitivity analyses are carried out for each material combination to investigate the correlations between the process parameters die geometry and rivet length with important quality characteristics of the joint like interlock, minimal thickness of the die-sided sheet and joining force. With the knowledge of these studies computed process optimizations are carried out, in order to define one die geometry to join all seven material combinations in good quality, so a tool changing is no longer required. The reduction from seven to only one optimized SPR-ST tool saves costs as well as processing time and production space.

COMPARISON OF FRICTION STIRS WELDING TECHNIQUE WITH CONVENTIONAL WELDING METHODS

In 1991 the welding institute (TWI) invented abstract friction stir welding(FSW) method which is an innovative solid state material joining. In the last two decade this method is one of the most important joining technologies. In aerospace and automotive industries for their joining requirements these methods are using, which mainly focus on the joining of aluminum alloys. The joining of aluminum alloys by conventional welding processes can sometimes cause serious problems. Presence of segregation and porosities and including loss of alloying elements are the difficulties recognized during the solidification process and structure. The troubles existing during the solidification related with the convention fusion welding processes can overcome by the friction stir welding which offers an alternative through solid-state bonding.

The influence of deformation conditions in solid-state aluminium welding processes on the resulting weld strength

Solid bonding of aluminium is an important joining technology with applications in fabrication, forming and new low-carbon recycling routes. The influence of deformation conditions on the strength of the resulting weld has yet to be fully assessed, preventing optimization of current processes and development of new ones.In this work, an extensive literature review identifies the deformation parameters important to weld strength: interface strain, strain rate, normal contact stress, temperature and shear. The film theory of bonding is used to derive a model that quantifies the relevance of these parameters to the weld strength. This model is then evaluated using an experiment in which the interface strain and normal contact stress are decoupled, and the friction hills between both the tooling and the samples and between the samples themselves minimized. Neither the model nor the experiments deal with samples that have undergone mechanical surface preparation (for example, scratch brushing) prior to bonding.The experiments show that a minimum strain is required for bonding. Increasing the temperature, normal contact stress or shear stress can reduce this minimum strain. A normal contact stress above the materials’ uniaxial yield stress is necessary to produce a strong bond. Increasing the strain rate has little affect on the weld strength for bonds created at low temperatures, but can significantly reduce the strength of bonds created at higher temperatures.The proposed model correctly predicts these trends; however, for higher temperatures it underestimates bond strengths and the influence of strain rate, suggesting that diffusion mechanisms increase the strength of bonds created at higher temperatures.

Influence of the temperature cycle on local distortions in car panels caused by hot curing epoxies

Adhesive bonding is becoming a more and more important joining technology in automotive industry. Hot curing epoxy adhesives are often used for structural bonds of car body shells. The cure process of the adhesive, however, can cause panel surface distortions. These distortions can occur close to the bond-line (local distortions) or concern the whole geometry of a part (global distortions). In order to avoid these defects, a fundamental understanding of how distortions develop is needed. In this work, the development of distortions is monitored over entire temperature cycles by means of a displacement measurement. The focus is on how different cure temperatures and heating rates affect the development and the final state of local distortions. It was found that distortions can already develop in the heating phase before the cure temperature is reached. Changes in the heating rate influence the development of distortions.

Stress Relaxation and Fatigue Characterisation of Eutectic SnPb Solder Alloy

Soldering is the most important joining technology in the semiconductor industry, especially for IC chip packaging. The binary eutectic SnPb alloy had been in used for decades, before regulations and restriction on the usage of lead in solders was imposed. Thus, replacing SnPb solder alloy with Pb-free solders has also been an issue in the electronic industry. The previously used SnPb alloy was in used due to several reasons, namely (a) it has low melting temperature (183oC) and solidified at a single temperature to form eutectoid composition, (b) binary in composition and is readily available commercially and (c) many researches had been undertaken in the previous decades. Creep, stress relaxation and fatigue tests were conducted on eutectic SnPb solder alloy in order to study the alloy mechanical characteristics, and hence a suitable Pb-free solder alloy could be chosen as a replacement alloy. In this study, creep, stress relaxation and fatigue tests were conducted on eutectic SnPb solder alloy at 30oC and 50oC, respectively. The study showed that stress relaxation in the alloy decayed instantaneously to zero-value when cycling was done at R=-1 and that cycling was done at 600 cycle per minute (CPM) which enable fatigue test to be conducted on the bulk solder alloy. A non-zero stress relaxation value will result in the alloy to failed predominantly due to creep and fatigue failure will not be observed.

Description of failure modes in welded components operating in the creep regime

Welding is one of the most important joining technologies in modern process and power plant construction. At present, martensitic heat resistant 9–12% chromium steels are one of the favored materials used for high temperature components, because of their good weldability, excellent hot workability and high creep strength. Nevertheless, under service conditions, for a number of these martensitic steels, the fine grained or intercritical heat affected zone (HAZ3) has the poorest creep strength since the heat input of the welding affects the microstructure of this zone. Furthermore the stress situation and multiaxiality of the stress state in the weld region changes permanently due to creep and relaxation. Experimental results show a strong influence of the factor of multiaxiality of the stress state on the creep behaviour of components especially of welded components. This paper gives a phenomenological description of the specific damage and failure behaviour of creep loaded welds. The previously mentioned time dependent stress — strain situation in weldments will be discussed and the influence of the multiaxiality of the stress state will be identified. Basic possibilities to avoid premature failure in the HAZ region are shown such as the optimum heat treatment of the base metal (BM) prior to welding, the variation of the welding methods and the optimization of the welding geometry and the deposit materials.

Simulation of welded aluminium automotive components

A successful lightweight construction can only be achieved by an optimised combination of material selection, design and fabrication. When aluminium alloys are used for lightweight components, welding is one of the most important joining technologies.