Design of Fully Automatic Specification Selection System for Resistance Welding Equipment

A system for fully automatic selection of welding specifications in resistance welding equipment has been developed to address the problem of workers frequently choosing the wrong specifications during manual welding of multiple parts on a single machine in automobile factories. The system incorporates an automatic recognition system for different workpiece materials using the added machine fixture,visual detection system for nuts and bolts,and secondary graphical confirmation to ensure the correctness of specification calling. This system achieves reliable,fully automatic selection of welding specifications in resistance welding equipment and has shown significant effects in improving welding quality for massproduced workpieces,while solving the problem of specification calling errors that can occur with traditional methods involving process charts and code adjustments. This system is particularly suitable for promoting applications in manual welding of multiple parts on a single machine in automobile factories,ensuring correct specification calling and welding quality.

The effect of activating fluxes on the cathode spots in the activating TIG welding

The cathode spots are a common phenomenon in the TIG(tungsten inert gas)welding process.However,it is rarely observed in the activating TIG welding process.This research is mainly focused on the effect of activating flux on cathode spots in the activating TIG welding.The characteristics and behaviors of cathode spots were investigated in activating TIG welding by the high-speed camera and the spectrograph.Three kinds of oxide(TiO_(2),SiO_(2),MnO_(2))and two halide(MnCl_(2),CaF_(2))activating fluxes are used in the activating TIG welding process.The results show that differ from the TIG welding,the oxide activating flux increases the number of cathode spots and decreases the velocity.The effect is the opposite for the halide activating flux.Moreover,the number of spots no longer varies with the current except TiO2 activating flux.As the temperature of the weld pool surface increases the spot moves away from the center.But this rule is not valid when silica and manganese compounds activating fluxes are used.The variation of cathode spots is caused by the oxide film reformed and the distribution of weld slag.The formation mechanism of cathode spots might be the impact of ions on the cathode surface and the strong electric field formed near the cathode surface.

Friction stir keyholeless spot welding of AZ31 Mg alloy-mild steel

Friction stir keyholeless spot welding（FSKSW） using a retractable pin for 1.0 mm thick galvanized mild steel and 3 mm thick AZ31 B magnesium alloy in a lap configuration was investigated.The process variables were optimized in terms of the joint strength.The effects of the stacking sequence on joint formation and the joining mechanism of FSKSW AZ31B-to-mild steel joints were also analyzed.It shows that the process window and joint strength are strongly influenced by the stacking sequence of the workpieces.While the process window is narrow and unstable for FSKSW of a magnesium-to-steel stack-up,a desirable process was established for the steel-to-magnesium stacking sequence,a desirable process and higher strength joint can be got when the steel-to-magnesium stacking sequence.XRD phase and EPMA analyses of the FSKSW joint showed that the intermetallic compounds are formed at the steel-to-magnesium interface,and the element diffusion between the mild steel and AZ31 B magnesium alloy revealed that the joining methods for FSKSW joints is the main mechanical joining along with certain metallurgical bonding.

Multi-field dynamic modeling and numerical simulation of aluminum alloy resistance spot welding

In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.

Study of joining mechanism of ABS polymer and steel/aluminum by resistance spot welding

The joining of metal and polymer is an increasingly important method to get lightweight components in the development of manufacturing industry- nowadays. In this artiele, metal and polymer lap joint was achieved by means of resistance spot welding （RSW） and ultrasonic assistance welding （UAW）. The joining mechanism of lap joint was analyzed by OM, TEM on microstructure at the interface of lap joints and XPS and IR spectra was discussed based on the following different ones： mechanical-interlocking, diffusion bond and coordination bond. The results showed that it was the combined action that played an important role in the effective joining work. Besides, ultrasonic assistance was used in the study to aid welding process based on its high-frequency ultrasonic vibration, which made joints shaping better and improved tensile strength visibly contrast to joints with the same lower heat input parameters.

Numerical simulation on temperature field for resistance spot welding of non-equal thickness stainless steel

An axisymmetric finite element model is developed to simulate the temperature field of resistant spot welding according to the process characters of nugget formation of non equal stainless steel sheets. A simulation method of the interaction of electrical and thermal factors is presented. The spot welding process of nugget formation is simulated using hard and soft welding technique norms. The heating characters of soft and hard norms determine the differences in the process of nugget formation and determine the finally shape and offset of nugget. Experimental verification shows that the model prediction agrees well with the practical.

Ultrasonic C-scan Detection for Stainless Steel Spot Welding Based on Wavelet Package Analysis

An ultrasonic test of spot welding for stainless steel is conducted. Based on wavelet packet decomposition, the ultrasonic echo signal has been analyzed deeply in time - frequency domain, which can easily distinguish the nugget from the corona bond. The 2D C-scan images produced by ultrasonic C scan which contribute to quantitatively calculate the nugget diameter for the computer are further analyzed. The spot welding nugget diameter can be automatically obtained by image enhancement, edge detection and equivalent diameter algorithm procedure. The ultrasonic detection values in this paper show good agreement with the metallographic measured values. The mean value of normal distribution curve is 0.006 67, and the standard deviation is 0.087 11. Ultrasonic C-scan test based on wavelet packet signal analysis is of high accuracy and stability.

Comparative study of resistance spot welding performance between cold-rolled DP980 and Q&P980 steels

Advanced high strength steel (AHSS) has been widely used in the automobile industry.The resistance spot welding performance of DP980 and Q&P980 steels was studied through comparing the two steels’welding current range,tensile shear strength (TSS),cross tension strength (CTS),weld spots’microhardness,etc.The following conclusions were achieved:It is easy for both DP980 and Q&P980 steels to get a nugget size bigger than 4 mm,they all have welding current ranges exceeding 2 kA and high weld strength.

DETECTION METHOD OF SPOT WELDING BASED ON MULTI-INFORMATION FUSION AND FRACTAL

A novel detection method of support vector machine （SVM） based on fractal dimension of signals is presented. And models of SVM are made based on nugget size defects of spot welding. Classification using these trained SVM models is done to signals of spot welding. It is shown from effect of different SVM models that these models with different inputs. In detection of defects, these models with inputs including sound signal have a high percentage of accuracy, the detection accuracy of these models with inputs including voltage signal will reduce. So the SVM models based on fractal dimensions of sound are some optimal nondestructive detection ones. At last a comparison between SVM detection model and ANNS detection model is researched which indicates that SVM is a more effective measure than Artificial neural networks in detection of nugget size defects during spot welding.

Numerical simulation of deep cryogenic treatment electrode tip temperature for spot welding aluminum alloy

Deep cryogenic treatment technology of electrodes is put forward to improve electrode life of resistance spot welding of aluminum alloy LF2. Deep cryogenic treatment makes electrode life for spot welding aluminum alloy improve. The specific resistivity of the deep cryogenic treatment electrodes is tested and experimental results show that specific resistivity is decreased sharply. The temperature field and the influence of deep cryogenic treatment on the electrode tip temperature during spot welding aluminium alloy is studied by numerical simulation method with the software ANSYS. The axisymmetric finite element model of mechanical, thermal and electrical coupled analysis of spot welding process is developed. The numerical simulation results show that the influence of deep cryogenic treatment on electrode tip temperature is very large.

Microstructure and mechanical properties of Mg-to-Al dissimilar welded joints with an Ag interlayer using ultrasonic spot welding

Lightweight ZEK100-0 Mg alloy and A16022-T43 Al alloy with an Ag interlayer were joined via ultrasonic spot welding(USW),focusing on the microstructural change and tensile lap shear strength of the welded joints in relation to welding energy.Mg/Al interface was superseded by Mg/Ag and Al/Ag interfaces,and unfavorable Mg门A-intermetallic compound was eliminated.Ag foil was observed to be intact in the nugget center,while it was broken or dissolved at the nugget edge at high welding energy levels.The diffusion layer at the Mg/Ag interface consisted of two distinctive sub-layers:Mg3Ag intermetallic compound adjoining Ag foil,and Mg3Ag-l-Mg eutectic structure adjacent to Mg.Only a thin diffusion layer consisting mainly of Ag3Al occurred al lhe Al/Ag interface.The tensile lap shear strength first increased,reached its peak value,and then decreased with increasing welding energy.The shear strength achieved in the present study was〜31%higher than that of the joint without interlayer.Interfacial failure occurred at all energy levels,with Ag foil particles or fragments being stuck on both Mg and Al sides due to its intense interaction with Mg and Al via accelerated diffusion during USW.The results obtained pave the way for the challenging dissimilar welding between Mg and Al alloys.

Dissimilar ultrasonic spot welding of Mg-Al and Mg-high strength low alloy steel

Sound dissimilar lap joints were achieved via ultrasonic spot welding （USW）, which is a solid-state joining technique. The addition of Sn interlayer during USW effectively blocked the formation of brittle Al12Mg17 intermetallic compound in the Mg-Al dissimilar joints without interlayer, and led to the presence of a distinctive composite-like Sn and Mg2Sn eutectic structure in both Mg- Al and Mg-high strength low alloy （HSLA） steel joints. The lap shear strength of both types of dissimilar joints with a Sn interlayer was significantly higher than that of the corresponding dissimilar joints without interlayer. Failure during the tensile lap shear tests occurred mainly in the mode of cohesive failure in the Mg- Al dissimilar joints and in the mode of partial cohesive failure and partial nugget pull-out in the Mg-HSLA steel dissimilar joints.

Effect of deep cryogenic treatment on mechanical behavior of a Cu-Cr-Zr alloy for electrodes of spot welding

The effects of deep cryogenic treatment on mechanical behavior of a Cu-Cr-Zr alloy for electrodes of spot welding were investigated employing Brinell-hardness testing unit, abrasion examination machine, electronic almighty testing machine and X-ray stress analyzer. Tensile fracture surfaces of the alloy were characterized by scanning electronic microscope （SEM） with energy dispersive X-ray spectroscopy （EDS）. The results showed that, after deep cryogenic treatment, σb and σ0.2 increased 23 MPa and 21 MPa respectively, the wear rate of the alloy exhibited the trend of decrease with the decreasing temperature and increasing time of deep cryogenic treatment, and the surface residual stress of the alloy was partially eliminated by deep cryogenic treatment.

Visual sensing and morphological image processing of weld pool in laser spot welding

A visual sensing system was established to monitor the weld pool in laser spot welding. The top-hat and bottom-hat transformation algorithms based on mathematical morphology were used to compensate for non-uniform contrast of weld pool edge. Moreover, the canny edge detector was applied to extract the weld paol profile. The edge detected results show that the morphological operation is obviously superior to the traditional contrast enhancement method. In addition, the combination of dilation and erosion was applied to eliminate the irrelevant edge details, and the smooth weld pool edge was acquired. Based on the image processing technology described above, the dynamic process of weld pool diameter during laser spot welding was obtained.

Development of liquid-nitrogen-cooling friction stir spot welding for AZ31 magnesium alloy joints

A liquid-nitrogen-cooling friction stir spot welding(C-FSSW) technology was developed for welding AZ31 magnesium alloy sheets. The liquid-nitrogen cooling degraded the deformability of the welded materials such that the width of interfacial cracks increased with increasing cooling time. The grain size of the stirred zone(SZ) and the heat-affected zone(HAZ) of the C-FSSW-welded joints decreased, whereas that of the thermomechanically affected zone(TMAZ) increased with increasing cooling time. The maximum tensile shear load of the C-FSSW-welded joints welded with a cooling time of 5 or 7 s was larger than that of the friction stir spot welding(FSSW)-welded joint, and the tensile shear load decreased with increasing cooling time. The microhardness of the C-FSSW-welded joints was greater than that of the FSSW-welded joint. Moreover, the microhardness of the SZ and the HAZ of the C-FSSW-welded joints increased, whereas that of the TMAZ decreased, with increasing cooling time.

Microstructure and properties of probeless friction stir spot welding of AZ31 magnesium alloy joints

The AZ31 magnesium alloy with a thickness of 1.8 mm was welded by the probeless friction stir spot welding process without Zn interlayer.The influence of process parameters on joint microstructure and mechanical properties was investigated by using different rotating speeds and dwell time.Microstructure of joints is divided into three regions:stir zone,thermomechanically-affected zone and heat-affected zone.With the increase of rotation speed and dwell time,the depth of stir zone gradually increases,and hook defects extend from the interface of two plates to the surface of the upper plate.The tensile shear strength of joints and two fracture modes(shear fracture and plug fracture)are closely related to hook defects.The maximum tensile shear strength of the joint is 4.22 kN when rotation speed and dwell time are 1180 r/min and 9 s,respectively.Microhardness value and its fluctuation in upper sheet are evidently higher than those of the lower sheet.

Numerical and Experimental Study on Nugget Formation Process in Resistance Spot Welding of Aluminum Alloy

The weld nugget formation in the resistance spot welding(RSW) of aluminum alloy was investigated in the present study. The nugget formation process was directly observed by using a digital high-speed camera. Numerical simulation was also employed to investigate the nugget formation process. The results showed that for the RSW of two aluminum alloy sheets, a nugget was first formed in the workpiece/workpiece(W/W) interface and grew along the radial direction and axial direction of the sheets, and then it became a large elliptical nugget. For the RSW of three aluminum alloy sheets, two small nuggets were firstly formed in two W/W interfaces and grew along the axial direction and radial direction; finally they fused into one nugget. Besides, there existed a critical welding time, after which the nugget size remained nearly unchanged. This indicates that a long welding time is unnecessary for the RSW of aluminum alloy. In addition, the calculated nugget radius was compared with the experimental results, which showed that the simulation results agreed well with the experimental results.

SPOT WELDING QUALITY FUZZY CONTROL SYSTEM BASED ON MULTISENSOR INFORMATION FUSION

The multisensor information fusion technology is adopted for real time measuring the four parameters which are connected closely with the weld nugget size（welding current, electrode displacement, dynamic resistance, welding time）, thus much more original information is obtained. In this way, the difficulty caused by measuring indirectly weld nugget size can be decreased in spot welding quality control, and the stability of spot welding quality can be improved. According to this method, two-dimensional fuzzy controllers are designed with the information fusion result as input and the thyristor control signal as output. The spot welding experimental results indicate that the spot welding quality intelligent control method based on multiscnsor information fusion technology can compensate the influence caused by variable factors in welding process and ensure the stability of welding quality.

Application of the wavelet packet and its energy spectrum to identify nugget splash during the aluminum alloys spot welding

Nugget splash during aluminum alloys spot welding has a detrimental effect on weld nugget integrity, strength and durability of the welded joints. This investigation is performed to identify nugget splash from voltage signals because these are easily accessible on-line. In the present work, we propose a novel method based on the wavelet packet transform and its energy spectrum for pattern recognition of splash signal. The result demonstrates that this novel method is more accuracy and a useful way of monitoring the spot welding quality.

Expulsion characterization in resistance spot welding by means of a hardness mapping technique

Expulsion is an undesired event during resistance spot welding because the weld quality deteriorates. It is the ejection of molten metal from the weld nugget which usually occurs due to applying a high current for a short welding time. Expulsion has a significant impact on the final yield strength of the weld, thus the detection and characterization of expulsion events is significant for the quality assurance of resistance spot welds. In this study, hardness mapping, using a scanning hardness machine, was used as a quality assurance technique for re- sistance spot welding. Hardness tests were conducted on a resistance spot welded sample to prepare a hardness map. The test results showed good correlation between the hardness map and metallographic cross sections. The technique also provided further fundamental understand- ing of the resistance spot welding process, especially regarding the occurrence of expulsion in the nugget.