Joining Speed Research Articles

Influence of the process time on a self-piercing riveting process with tumbling kinematic

The increasing significance of ecological responsibility, stricter political regulations and economic objectives are driving innovation in research fields such as lightweight construction. One of the most important popular methods is the use of multi-material systems. Due to the different geometric and mechanical properties of the various materials used, resource efficient applications and utilizations are possible. Great challenges arise for the joining processes to realize these multi-material systems, since conventional joining processes reach their limits. In the field of mechanical joining processes, there are continuously new approaches, such as superimposing the punch in a self-piercing riveting process with a tumbling kinematic, to increase the number of adaptable process parameters and enhance the process control. Through various preliminary tests, a good understanding of the process has been developed, which allows to directly control the geometric joint parameters by configuring the tumbling strategy. A major challenge, particularly with regard to future industrial applications, is the process time, which is comparatively high due to the tumbling kinematics. In the investigations, a reduction of approximately 90% of the process time is targeted by adapting the joining and tumbling strategy. Therefore, the correlation of the traverse velocity and the tumbling velocity are examined in a gradual series of experiments. To represent realistic applications, the experiments are carried out with a dual-phase steel and a precipitation-hardening aluminum alloy. For identifying the influence of the process parameters on the joining process, a constant rivet–die combination is applied. Further, the examination of force–displacement curves is conducted. Moreover, the determination of geometric joint parameters is reliant upon macrographs to assess the influence of the joining time on the geometric joint formation. The test results show that a significant increase in joining speed with a resulting reduction in process time is feasible. Although the joining properties are affected, reliable joining is possible. In particular, the shaft thickness of the rivet is influenced by the varying proportion of the tumbling process in the joining operation and increases with higher joining speeds.

Achievement of high-strength Al/CFRP hybrid joint via high-speed friction stir lap joining and laser texturing pretreatment parameters variation

This paper presents the achievement of a high-strength Al/CFRP hybrid joint through a high-speed friction stir lap joining process, combined with variations in laser surface texturing pretreatment parameters. The study examined the impact of laser surface texturing parameters by varying the depth, interval distance and width of the laser texture. By adjusting laser texturing parameters, the softened PA66 was fully infused into the textured grooves on the aluminum surface, leading to a significant reduction in interfacial voids and cracks in Al/CFRP. The preliminary tensile shear test showed that the hybrid joint broke at the CFRP base material, indicating that the laser texturing exhibited excellent Al/CFRP interface strengthening ability. Further compression shear tests were applied to reveal the actual interfacial load-carrying performance for comparison. The maximum shear strength of 25.5−1.34+0.7 MPa was achieved at a joining speed of 3000 mm/min. Additionally, a mathematical model was proposed to assess the strengthening impact of laser texturing parameters, considering micro-texture geometry and interfacial defects. The tearing of PA66, detachment of carbon fibers, and the breakage of carbon fibers were the three primary types of fracture modes identified at the Al/CFRP interface. The joining mechanism revealed that both mechanical interlocking and the chemical bonding of Al-O-C contributed to the increase in joint shear strength. This study presents a credible method for producing high-strength Al/CFRP lightweight structures.

Development of double-sided friction stir welding of advanced high strength steel sheets

Double-sided friction stir welding (FSW), performed with a pair of rotation tools, was studied in an attempt to increase the joining speed when applied to welding of automotive advanced high-strength steels (AHSS). The experiments were performed on butt joint of 1.6-mm-thick 1180 MPa grade steel sheets, and sound welds were obtained when the travel speed was no more than 4 m/min, fairly comparable with laser beam welding (LBW), one of the conventional automotive welding processes. It was clarified by experimental and numerical analyses that the enhancement in travel speed was due to the unique material flow interactively developed by a pair of rotation tools. Double-sided FSW was performed at 3 m/min of joining speed on butt joint of dissimilar steel sheets in a combination of 1.5 GPa and 590 MPa grades. The mechanical properties of the welded joints were evaluated by tensile, V-bending and Erichsen tests comparing with LBW, which verified that double-sided FSW exhibited sufficient mechanical properties for the press-forming to produce automotive parts. A prototype automotive part was successfully fabricated using the tailor-welded blank welded with double-sided FSW, which demonstrates its applicability to automotive production.

Joining Photovoltaic Cell Connection Strips Using Ultra-Acoustic Wave - Resistive Hybrid Heating System

The manufacture of photovoltaic panels for the production of sustainable energy also involves the stage of electrical connection of the cells in the panel structure. This electrical connection is made by soldering of copper strips on the negative electrode of the cell. During the bonding process, due to the temperature of approximately 220-240°C at which the connecting strip is continuously heated, cracking processes of the upper layer of glass from the cell surface were identified. For this reason, it is necessary either to heat to lower temperatures, a solution that is not viable due to the melting temperature of the solder alloy which usually exceeds 210°C, or a different dosing of the heat flux. The solution proposed in the paper is to create a variable heat flux that allows the melting of the solder alloy, but at the same time to reduce the thermal load of the glass support layer. Through the proposed variant, the energy dosing is done with the help of a heating system consisting of two sources, an ultra-acoustic energy source and a classical resistive source. The resistive source provides an amount of energy to ensure a temperature in the range of 60-140°C, the difference to the melting point of the solder alloy being transferred locally by ultrasonic pulses. Research has highlighted the need to limit the range of values of the pressure of the circular sonotrode, which positively influences the mechanical stress of the photovoltaic cell, but also leads to a reduction in the joining speed. The dosing of the two components of the total energy, the one coming from the resistive source and the one coming from the ultra-acoustic vibration source is decisive for the efficiency of the joining process and for the quality of the soldered joint. Microscopic analyses revealed micro-cracks of the glass surface layer at forces higher than 100 N. Areas with lack of soldering for resistive heating at temperatures lower than 130oC were highlighted, the difference of 90-110°C being achieved by the contribution of ultra-acoustic energy.

Study of steel-aluminium joining under the influence of current waveforms using advanced CMT process variants

ABSTRACT In the conventional GMAW process, increasing weld deposition increases the heat input, which adversely affects the steel-aluminum joint performance due to the brittle IMC layer growth. In the present work, advanced CMT variants in AA6061-T6 and galvannealed steel joining were investigated. All Fe-Al joints are made at a constant joining speed and wire feed rate with CMT process variants, viz. CMT-Standard, CMT-Advanced, CMT-Pulsed, and CMT-Pulsed-Advanced. The influence of current and voltage characteristics of process variants on the thermal profile, joint profile, IMC layer morphology, and mechanical properties of the joint was studied. The welding arc and molten droplet transfer phenomena were explained using recorded welding current and voltage waveforms synchronized with welding arc images. The FE-SEM, EDS, and XRD analyses were performed to confirm the phases and morphology of the IMC layer. The results show that the localized heating due to positive current pulses in CMT-Pulsed and CMT-Pulsed-Advanced processes affects the IMC layer morphology and induces cracks at the Fe-Al joints’ root, leading to low shear tensile strength. The crack-free joints were observed with the CMT-Standard and CMT-Advanced processes. Also, with an increase in the positive CMT cycle in the CMT-Advanced process, heat input decreases and shear tensile strength increases.

Joining aluminium and poly(lactic acid) specimens by laser beam – a feasibility study

In this article, our main aim is to demonstrate and prove that it is feasible to join aluminium and poly(lactic acid) (PLA) specimens by laser beam. We investigated the effects of structuring the surface of the aluminium specimens with corundum blasting and joining speed and used three types of PLA (with the same D-lactide content but different average molecular weights) to investigate the effect of the viscosity of the polymer melt on the load-bearing capacity of the joints. Joined aluminium-PLA specimens were successfully manufactured and examined with standard lap-shear tests. We found that both surface structuring, joining speed and the type of PLA material influenced the load-bearing capacity of the aluminium-PLA joint.

Influence of wire feed rate to speed ratio on arc stability and characteristics of cold metal transfer weld–brazed dissimilar joints

To explore the influence of wire feed rate (WFR) to speed ratio on arc stability, interfacial microstructure and mechanical properties, cold metal transfer (CMT) weld-brazed lap joints of aluminium alloy (AA5052) to dual-phase (DP780) steel were formed at a constant optimized heat input of 80 J/mm. Cyclic representation of recorded voltage and current showed that joining process was comparatively less stable at high WFR to speed combinations. At high WFR and higher speed combinations, greater spatial variations in intermetallic compound (IMC) layer thickness due to spilling of τ5-Fe2Al7.4Si phase and higher porosity in the bead reduced the resistance to failure of the joints especially in the case of AlSi12 filler. Addition of Si successfully increased the wettability of the joints and also reduced the average thickness of the IMC layer at the interface. Formation of hard and brittle orthorhombic η-Fe2Al5 and monoclinic θ-FeAl3 compounds was observed for pure Al filler whereas less brittle ternary Fe-Al-Si intermetallic phases formed with Si-enriched fillers. Three modes of failure, in the Al heat-affected zone (HAZ) (due to softening), bead (due to porosity) and interface (due to poor wettability/increased brittleness), were observed during shear tensile testing. The joints formed using AlSi5 filler at lower joining speed and low WFR combinations, i.e. high WFR/speed ratio, showed higher and consistent mechanical properties.

Experimental investigations and numerical prediction on the effect of shielding area and post flow time in the GTAW of CP Ti sheets

In this study, bead on plate (BoP) trials are conducted on 2-mm thick commercially pure titanium (CP Ti) sheets by gas tungsten arc welding (GTAW) process. Welding current (75–105 A) and joining speed (250–300 mm/min) are taken as the variables. In the weld samples’ appearance of the surface, colorizations are noticed for understanding the role of shielding gas. BoP trials are subjected to metallographic examination to measure weld profiles. These measured values are fed as input for the Goldak double ellipsoidal model to performing the GTAW process. For BoP trials, temperature profile and Iso-surface contours along the moving heat source direction are taken at various time intervals. From the temperature history, shielding area and post flow time are identified. A shielding arrangement is fabricated and implemented based on these bead profile and temperature profile history. After the successful fabrication of shielding arrangement, experimental butt joints are made by GTAW process to verify the efficiency of shielding arrangement. Bead profile of experimentally fabricated 1.6-mm and 2-mm butt joints are compared and verified against the finite element model results. Moreover, cupping test is conducted to analyze the ductility of the joints. The maximum elongation of 96.10% is measured for 1.6-mm face out joints from cupping test.

Effect of silane coupling on the joint characteristics of friction lap joined Al alloy/CFRP

ABSTRACTDissimilar materials joining of an A5052 plate and a carbon fibre reinforced thermoplastic (CFRTP), which consisted of polyamide 6 (PA6) with 20 wt% carbon fibre addition, was performed using friction lap joining (FLJ) with the Al alloy plate as a top and the CFRTP plate as a bottom. The joint characteristics were evaluated to investigate effects of the surface treatment by the silane coupling treatment for A5052 and the joining speed on the joining properties. The joint strength was increased by inducing the silane coupling treatment for the A5052 plate surface. The tensile shear fracture load of the silane coupling treated FLJ joint increased by increasing the joining speed up to 6.67 mm/s and then decreased. The maximum tensile shear fracture load of 5.0 kN was obtained at the joining speed of 6.67 mm/s, and the fracture occurred at the CFRTP base plate with the joint efficiency of 97%. The shear strength of the joint interface of the joint formed at the joining speed of 1.67 mm/s, which fractured at the joining interface by the tensile shear test, was estimated to be about 19 MPa. The covalent bondings between the A5052 plate and the silane coupling layer, and the silane coupling layer and the CFRTP plate were indicated by inducing the silane coupling treatment.

CFRTP and stainless steel laser joining: Thermal defects analysis and joining parameters optimization

Experiments with different joining parameters were carried out on fiber laser welding system to explore the mechanism of CFRTP/stainless steel joining and the influence of the parameters on the joining quality. The thermal defect and the microstructure of the joint was tested by SEM, EDS. The joint strength and the thermal defect zone width was measured by the tensile tester and the laser confocal microscope, respectively. The influence of parameters such as the laser power, the joining speed and the clamper pressure on the stainless steel surface thermal defect and the joint strength was analyzed. The result showed that the thermal defect on the stainless steel surface would change metal’s mechanical properties and reduce its service life. A chemical bonding was found between the CFRTP and the stainless steel besides the physical bonding and the mechanical bonding. The highest shear stress was obtained as the laser power, the joining speed and the clamper pressure is 280 W, 4 mm/s and 0.15 MPa, respectively.

Direct joining of oxygen-free copper and carbon-fiber-reinforced plastic by friction lap joining

Oxygen-free copper (Cu) was successfully joined to carbon-fiber-reinforced thermoplastic (CFRTP, polyamide 6 with 20wt% carbon fiber addition) by friction lap joining (FLJ) at joining speeds of 200–1600mm/min with a constant rotation rate of 1500rpm and a nominal plunge depth of 0.9mm. It is the first time to report the joining of CFRTP to Cu by FLJ. As the joining speed increased, the tensile shear force (TSF) of joints increased first, and decreased thereafter. The maximum TSF could reach 2.3kN (15mm in width). Hydrogen bonding formed between the amide group of CFRTP and the thin Cu2O layer on the Cu surface, which mainly contributed to the joint bonding. The influence factors of the TSF of the joints at different joining speeds were discussed. The TSF was mainly affected by the joining area, the degradation of the plastic matrix and the number and the size of bubbles. As the joining speed increased, the influence factors varied as follows: the joining area increased first and then decreased; the degradation of the plastic matrix and the number and the size of bubbles decreased. The maximum TSF was the comprehensive result of the relatively large joining area, small degradation of the plastic matrix and small number and sizes of bubbles.

Development of butt welding of polymeric materials based on softening and stirring effects by hot tool

In this study, new butt welding technique was proposed to join polymeric materials in which the polymeric material is softened by a heated tool due to the Joule effect heating of the electric current flow through the tool, and the coalescence of material is done by the stirring action due to the tool rotation. A 3 mm-thick Polycarbonate (PC) sheets were joined in various joining conditions, from which joining mechanism, mechanical properties of joints and process parameters affecting joint performance were investigated. In the experiments, in situ observation with a CCD camera and material temperature measurement during the process, as well as the observation of surface appearance and cross section of the joint and tensile test were performed for these purposes. It was shown from the in situ observation and material temperature measurement that the molten and softened region is formed around the weld tool. It was also shown that sufficient heat input was required to form sound joints with acceptable performance, which depended upon the joining speed and amount of electric current flow through the tool. The observation of joint appearance and cross section revealed that the joint with comparable thickness to base material was obtained under the condition of revolution pitch below 0.08 mm, defined by the ratio of joining speed to tool rotation. It is noticed that joints obtained from the proper conditions have the same mechanical properties as the base material, and that the process parameters of this method were tool rotation speed, welding speed and amount of electric current. These results suggest proposed method is useful for joining the polymeric materials.

摩擦重ね接合によるステンレス鋼と炭素繊維強化熱可塑性樹脂との異材接合

The effect of joining speed on the joining strength of the dissimilar materials joint of the SUS304/ carbon fiber reinforced thermoplastic (CFRTP) was investigated. SUS304 plates (150mm×75mm×2.0mm) and CFRTP (consisted of PA6 matrix and 20wt% carbon fiber) plates (150mm×75mm×3.0mm) were joined by friction lap joining (FLJ) using rotational WC-Co tool. Different joining speeds in the range from 1.67mm/s - 16.7mm/s and the tool rotation speed of 8.33 s-1 were selected as processing conditions. Direct joining of SUS304/CFRTP was accomplished at all of joining speeds by FLJ. The tensile shear strength of the joint increased with increasing joining speed up to 3.33mm/s, however, it decreased from the joining speed of 3.33mm/s to 16.7mm/s. The interfacial fracture occurred at all of joining speeds. The fractured surface analysis of SUS304 revealed that teared fragments from the CFRTP base plate were bonded to SUS304. At the lower joining speed, the excessive heat input caused thermal decomposition of PA6 from the matrix of CFRTP resulted bubbles; the joint strength was decreased because of these bubbles. The shortage of the heat input at the higher joining speed caused insufficient wetting of molten PA6 to SUS304, which resulted in the decreased strength of the joint.

Laser-Based Joining of Thermoplastics to Metals: Influence of Varied Ambient Conditions on Joint Performance and Microstructure

Laser-based joining of thermoplastics to metals shows a great potential for functional design especially in terms of lightweight constructions. In the joining process, the joining speed and the energy per unit length, respectively, show an influence on time-temperature profiles measured in the joining zone. The time-temperature profile affects the joining zone and consequently the joint behavior in mechanical testing. In the current investigation, the joining zone was characterized by the melting layer. Moreover, the mechanical properties of the joint by tensile shear testing and the fracture mode were investigated. Based on the results obtained, three sets of joining speeds/energies per unit length with different mechanical behaviors were selected for further investigations under varied ambient conditions. Thereby, the influence of outdoor weathering as well as aging above the glass transition temperature of the plastic part on the joint’s performance was compared with the nonaged joints.

Microstructures and mechanical properties of friction stir welded lap joints of commercially pure titanium and 304 stainless steel

Friction stir welding was performed to accomplish dissimilar lap joining of commercially pure titanium (CP-Ti) to 304 stainless steel (SUS304). The joining speed was varied from 25 to 100mmmin−1. At a joining speed of 50mmmin−1, the morphology of the interface was a flat and simple interfacial reaction layer whose thickness was less than 1μm. The reaction layer consisted of four layers: β-Ti (+ ω-Ti), Ti2Ni, FeTi+Fe2Ti, and σ-FeCr, listed in order from the CP-Ti side to the SUS304 side. At a joining speed of 25mmmin−1, the interface consisted of a macroscopically mixed and laminated structure approximately 300μm thick consisting of multiple reaction layers. During the tensile shear test, joint fractures occurred in the CP-Ti base material at every joining speed. However, during the peel test, joint fractures occurred at the joint interface.

Direct joining of carbon-fiber–reinforced plastic to an aluminum alloy using friction lap joining

A carbon-fiber–reinforced thermoplastic (polyamide 6 with 20wt.% carbon fiber addition) and an aluminum alloy (A5052) were joined using friction lap joining. The joint characteristics were evaluated to investigate the effects of A5052 surface treatments and the joining speed on the joint properties. Carbon-fiber–reinforced thermoplastic and A5052 were joined via an interfacial magnesium oxide layer. Surface grinding of the A5052 generated the aluminum hydroxide on the alloy surface and increased the tensile shear strength of the joint. The tensile shear strength increased as the joining speed increased from 100 to 1600mmmin−1, and decreased thereafter.

Optimization of Laser Transmission Joining Process Parameters on Joint Strength of PET and 316 L Stainless Steel Joint Using Response Surface Methodology

The objective of the present work is to study the effects of laser power, joining speed, and stand-off distance on the joint strength of PET and 316 L stainless steel joint. The process parameters were optimized using response methodology for achieving good joint strength. The central composite design (CCD) has been utilized to plan the experiments and response surface methodology (RSM) is employed to develop mathematical model between laser transmission joining parameters and desired response (joint strength). From the ANOVA (analysis of variance), it was concluded that laser power is contributing more and it is followed by joining speed and stand-off distance. In the range of process parameters, the result shows that laser power increases and joint strength increases. Whereas joining speed increases, joint strength increases. The joint strength increases with the increase of the stand-off distance until it reaches the center value; the joint strength then starts to decrease with the increase of stand-off distance beyond the center limit. Optimum values of laser power, joining speed, and stand-off distance were found to be 18 watt, 100 mm/min, and 2 mm to get the maximum joint strength (predicted: 88.48 MPa). There was approximately 3.37% error in the experimental and modeled results of joint strength.

Development and benchmarking of HTTP-based multivision video server using fast stream joiner

High functionality and interactivity of video services are strongly desired. Earlier reports have presented an encoding scheme and a fast joining scheme for interactive multivision video streaming systems. Together, they enable numerous users to access any view area interactively at any desired resolution. The joining means the combination of multiple streams into a single video stream. The server joins pre-encoded multiple streams into one bitstream according to a user request; then the server transmits it simultaneously to many clients. This structure obviates complexity at the client terminal because the client terminal simply receives and decodes the single stream. This paper describes implementation of an actual HTTP-based streaming server by embedding the stream joiner module into a widely available HTTP server. The contribution of this paper is that the joining speed of the server surpasses the necessary speed attained with practical network equipment connecting to the server. Results of experiments described in this paper underscore the proposed method's effectiveness.

ANALYSIS OF THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF DUAL PHASE STEEL UNDER THE EFFECTS OF DIFFERENT BRAZING RATES

ABSTRACTEnvironmental, concerns regarding reducing CO2 emissions and the drive of having better fuel economy have already enthused the car manufacturer to use the weight materials having better mechanical properties. Automotive industry has shown a great interest in Dual Phase steels due to the possibility of reducing weight of vehicles and increasing the passenger safety at a very competitive cost. Automotive applications unavoidably entail welding and joining in the manufacturing process and the fatigue resistance of welded joints due to the integrity and safety requirements. The variation of welding parameters (voltage, current and speed of welding) affects weld performance, mechanical, and metallurgical properties.The CMT (Cold Metal Transfer) braze welding is a relatively new technology that partially decouples the arc electrical transients from the filler wire feed rate. It allows reducing the heat required for welding and permits higher joining speeds.The aim of this work is to study the interfacial microstructures and intermetallic compounds produced by cold metal transfer welding of two plates of galvanized DP600 dual phase steel with CuSi3 as filler metal. The study was performed by applying a CMT braze welding with three different joining speeds. The welded microstructures and microhardness were determined and related to the welding process conditions.A small HAZ, constituted by martensite, bainite and coarse ferrite grains, has been highlighted. Furthermore, an intermetallic Fe-Si-Cu compound layer formed at the interface between steel and filler metal. The joining speed sways the size of ZTA since the heat input Q affects the phase transformation in the weld and heat affected zoneThis parameter also affects the thickness of the compound layer and the size of precipitates in the filler metal, likewise the mechanical characteristics. The fracture starts at the interface steel-copper where intermetallic compounds formed.

Laser-Mig Hybrid Welding of aluminium to steel — A straightforward analytical model for wetting length

Laser-MIG hybrid welding was recently suggested as a feasible process for joining of aluminium to steel for both structural as well as tailored blank applications. In this process, the aluminium is molten to create a brazed bond to the zinc-coated steel sheet, which remains solid. Using thin-sheet materials in a thickness range of approximately 1 mm in butt joint configuration, this process allows a joining speed of more than 100 mm/s at a laser power of 4 kW whilst retaining some gap bridging ability. In such a case, the wetting length of the aluminium melt on the top and bottom sides of the zinc-coated steel sheet is of significance for the properties of the joint. Therefore, an understanding of the parameters governing wetting length is required. To promote this understanding, a model to calculate wetting length in dependence of processing conditions is suggested. Based on the assumption that there is a correlation between the temperature field on the steel sheet and wetting length, an analytical model for the temperature field is developed and correlated with experimental results on the material combination AA6016 T4 (thickness 1.15 mm) and DC05+ZE (1 mm). Both model and experiments show that the wetting length is correlated to the melting isotherm of the zinc coating (provided a sufficient amount of melt is created). These results shall contribute to an improved understanding of the process.