Important Welding Parameters Research Articles

Effect of tool pin profile on mechanical and microstructural properties of cooling assisted friction stir welding of AA6063-T6 weld joint

ABSTRACT Experiments have been performed in air and cooling-assisted condition with three tool pin profiles i.e. square, triangular and threaded cylinder. In this study, an effort has been made to comprehend how the mechanical characteristics, micro-hardness, and microstructure of friction stir welded AA6063-T6 joints are affected by in-process cooling, tool profiles, tool dimensions, and process parameters. For friction stir welding with cooling assistance, process parameters were optimised. For higher tensile and impact strength, a square tool profile with a shoulder to pin diameter ratio of 3:1 is found to be the most effective. The most important welding parameter was found to be rotations per minute (rpm). Microstructural analysis reveals finer grain size and a significant increase in microhardness in the weld nugget zone with cooling assisted FSW.

Experimental investigation and optimization of IRB6700 ABB robot spot welding process parameters

In this study, the influence of robot spot welding parameters on the tensile shear strength of the weld joints was investigated. The experimentation was planned using Taguchi orthogonal array approach and the experiments were conducted on the IRB6700 Asea Brown Boveri (ABB) Robot Spot Welding machine. The important spot welding parameters studied in this work are electrode forces, welding currents, and welding times. The optimum IRB6700 ABB robot spot weld parameters were determined by using analysis of the Signal-to-Noise (S/N) ratio. The result shows that the parameter electrode force is having a maximum influence on the weld joint tensile shear strength in stainless steel and mild steel material, 58.51% and 70.95%, respectively. The confirmation experiment shows that the spot weld joint tensile shear strength can be improved by selecting a suitable range of spot weld parameters.

Effect of ultrasonic welding process parameters on peel strength of membranes for tents

Ultrasonic welding is a universal, clean, and secure alternative joining method. Alternative joining technologies are used increasingly to fulfill specific functional requirements of the seam, such as fluid impermeability to achieve positive bonding during the assembly of technical textiles. In this research, the effect of important ultrasonic welding parameters on peel strength and weld seam thickness was investigated for flexible and lightweight textile material, which is a valuable innovative hybrid textile for technical applications like architectural, construction, and protective textiles. Three main welding parameters with three different levels were selected based on the preliminary test results of 6 and 12 mm welding widths, and a superimposed type of seam was applied. Light scanning microscopic images were used to examine the effective weld locations and their morphology at the joining interface. The parametric influence of ultrasonic welding technique on-seam quality and their tendencies in the relationship were analyzed. Optimized peel strength yielding parametric levels were also assessed numerically. The result shows that the optimal peel strength value was obtained at a welding speed of 2.318 m/min, power of 119.382 W, and pressure force of 349.729 N for a 12 mm welding width. The weld seam thickness had an inverse relationship with the peel strength, and a higher amount of thickness was reduced to 12 mm welding width than 6 mm. Microscopic cross-sectional image of weld seam indicated that a compressed yarn between the coating material at higher welding power and pressure force in lower welding speed. A nonlinear quadratic numerical model was developed to predict the peel strength, and their results were close to the regressed diagonal line against the actual points. The statistical analysis was carried out to show the significant effect of process parameters on peel strength, whereby the obtained results were statistically significant.

Effect of explosive welding parameters on Al/LCS interface cladded by low velocity of detonation explosive welding (LVEW) process

Interfacial properties govern the metallurgical and mechanical behaviour of welded specimens. Hence to study the effect of different parameters on weld interface is an important aspect to bring the desired output properties for various applications. In this study, a newly developed low velocity of detonation explosive welding (LVEW) process was applied to clad aluminium (Al) and low carbon steel (LCS) plates. Loading ratio (R) and stand-off distance (SD) were adopted for this study, as these two mostly affect the welding behaviour and act as important welding parameters. Microstructural examination as well as mechanical tests were performed. Three kinds of morphology were observed at the weld interface, i.e. large waves (LW), small irregular waves (SIW) and smooth flat interface (SFI), where SIW and SFI contribute interface devoid of voids, intermetallic and melting pockets. But at higher R and SD, AlFe and Al2Fe intermetallic were observed in non-continuous form in micron range. Elemental analysis confirmed the local diffusion with very thin diffusion thickness of 0.8–2 μm. Micro-hardness profile discloses the shock hardening effects across the vicinity of the weld interface, where an increase in hardness value was above the parent value. Chisel test and shear strength test also confirmed the good quality of bonding, while in shear fracture study, dimple structure was dominated in all the specimens. All these observations concluded that for cladding Al/LCS, LVEW process is best suitable and further, the practicability of these welded plates was checked by fabricating components like bi-metallic O-ring (push-fit type), hollow cylinder and bolts.

Research on the optimization of welding parameters in high-frequency induction welding pipeline

In this paper, numerical simulation and finite element analysis were applied to optimize the important parameters including V-type joint and current frequency for high-frequency induction welding. The coupling of the 3D harmonic electromagnetic field and 3D transient temperature field was analyzed by establishing the physical file of the electromagnetic field and temperature field in high-frequency induction welding. The influence of important welding parameters on the temperature field distribution in the welding area was obtained by using a single control variable method. In the temperature field, the size of the V-type joint determines the heating efficiency, and the current frequency affects the heat produced by the eddy current. The numerical simulation results were verified by the analysis of the actual production experimental results and a good process parameter group was summarized. The shape of the slit between the different V-type joint parameters and the centerline of the squeeze roll showed that the relationship of the welding image and the welding quality and provided a solution for real-time online monitoring of welding quality.

Model-based parameter optimization for arc welding process simulation

This paper presents a model-based parameter optimization for simulating a metal-inert gas welding process. The computational model used in this study is based on computational fluid dynamics methods and implemented using the finite volume approach on a 3D computational domain. The wire electrode, the arc plasma and the workpiece are treated as a self-consistent system. Important welding parameters, including arc current, wire feed rate, workpiece thickness, welding speed and geometry, as well as the metal alloy types used for the wire and workpiece, were implemented as adjustable parameters. By tuning these parameters, the performance of the arc welding can be predicted, and different settings can be compared to optimize welding performance.A benchmarking study of the arc model against experimental measurements is presented to demonstrate the model's capabilities in the prediction of the weld pool changes and thermal dynamics involved in the welding process. Two numerical case studies are presented to demonstrate the use of the model-based optimization to quantify welding pool variations with the change in welding parameters. The first case study is the determination of the optimal arc current and welding speed settings for different workpiece thicknesses. The optimization process shows that the predictions are not only in agreement with established experimental welding experience on the direct relationship between workpiece thickness and arc current, but more importantly quantify this relationship for a given workpiece thickness. The second case study focuses on the welding parameters optimization for different metal alloys. The comparison suggests that the welding parameters suitable for some aluminium alloys are less likely to be successful in welding magnesium alloys. A further model validation of Mg alloy AZ31 welding shows an agreement with experimental measurements. The work presented shows the potential of model-based parameter optimization to assist process engineers in the practical improvement of the welding process.

Experiments on formation mechanism of root humping in high-power laser autogenous welding of thick plates with stainless steels

Deep penetration laser welding is an efficient and effective way to produce the heavy section structure. Deep penetration can be achieved by high-power autogenous laser welding; however, it poses a significant challenge in obtaining good quality of welds, which are free of imperfects such as root hump, under-fill, and collapse. It is partially attributed to a lacking of understanding on the formation of imperfects. In this paper, we looked into the formation mechanism of root humping experimentally. The laser autogenous welding were implemented using a 10 kW fiber laser on thick stainless steel plates. A high-speed imaging system was applied to observe the metallic vapor and molten pool flow during the welding process. The formation mechanism of root humping with different focal positions were analyzed and discussed. The results showed that the most important welding parameter was the focal position; it had a strong effect on the formation of root hump; it affected the penetration mode of laser keyhole welding. The root hump had a large volume and were generated periodically when a positive defocus was applied. When a negative defocus was applied, the root hump had a small volume and with no obvious periodicity. On the other hand, the welding speed could be optimized to suppress root hump only when a negative defocus was applied. Finally, applying a bottom shielding gases played a positive role in reducing root hump. The results from our study provides the evidences to develop the strategies to suppress root hump during high-power laser autogenous welding on thick metal plates.

The effect of shoulder coupling on the residual stress and hardness distribution in AA7050 friction stir butt welds

The effect of shoulder coupling in friction stir welding (FSW) on the distribution of residual stresses, microstructure and hardness has been investigated by comparing welds manufactured with a conventional tool, using different levels of downforce, to joints produced using a stationary shoulder (SSFSW). The welds were produced in AA7050-T7651 6.35 mm plate with the same travel speed and similar power levels. Reducing the tool downforce in FSW led to a decrease in the overall shoulder input power, but a minimal reduction in the weld zone hardness and peak residual stresses. In contrast, relative to FSWs made with a similar input power, the stationary shoulder led to much more significant microstructure and property changes including a reduction in the HAZ width, an increase in the minimum weld zone hardness level and a significant reduction in the peak tensile residual stresses (by ~ 25%). With SSFSW, the improvement found in the hardness and residual stress distribution from eliminating the energy dissipated by the tool shoulder could be directly correlated to a reduction in the weld temperature and narrowing of the thermal field, which reduced the size of the HAZ and region of plastic misfit responsible for the weld residual stresses. By comparing the results with previous work it was found that, apart from using a stationary shoulder, the most important welding parameter affecting the weld zone peak tensile stresses was the travel speed, with longitudinal residual stresses doubling upon increasing the travel speed from 100 to 400 mm/min.

Performance Prediction for Ultrasonic Spot Welds of Short Carbon Fiber-Reinforced Composites Under Shear Loading

Ultrasonic welding is a well-known technique for joining thermoplastics and has recently been introduced to joining carbon fiber-reinforced composites (CFRC). However, suitable models for predicting joint performance have not yet been established. At present, most failure models for bonded composites are built based on uniform adhesive joints, which assume constant joint properties. Nevertheless, the joint properties of ultrasonic spot welds for CFRC are variable, which depend on the input welding parameters. In this paper, the effect of welding energy, which is the most important welding parameter, on the joint properties is investigated. Then, a surface-based cohesive performance model based on mode-II (in-plane) shear loading is developed to predict the joint performance, wherein the critical fracture parameters in the model are described via the functions of welding energy. After comparing the simulated results with experiments, the model is proven feasible in predicting the joint properties of the ultrasonic spot welds under shear loading condition, and hence, a mix-mode cohesive-zone model is practical to predict the joint performance under any loading conditions with the predicted fracture parameters.

Investigation properties of high frequency welded steel pipes for natural gas transportation made of X60 steel

Basic idea in this research work is to check prescribed quality requirement of steel pipes welded by implementation of high frequency contact welding process (HFCW). These pipes are intended for natural gas transportation. As a raw material for pipes production was used X60M steel coils with thickness of 6.5 mm. Outer diameter of pipe is Φ508 and length 12000 mm. Preliminary welding procedure is given based on personal experience and technical knowledge. Special attention was paid to the most important welding parameters: current frequency, voltage and welding speed. After performing of welding additional heat treatment (normalization) of the welded pipes (joints) was performed at the temperature of 900ºC. In order to confirm proposed welding technology, complex investigations were performed. As first chemical analysis of base metal was performed. Nondestructive testing encompass visual inspection, and ultrasound testing of pipes, while destructive testing consists of tensile testing, bend testing and hardness measurement. Besides, for analysis of micro and macro structure of welded joint metallographic investigation was made. Hydrostatic test and flattening test as technological investigations were performed too. Carried investigations confirmed that produced pipes with predicted welding parameters completely fulfilled standard requirement, and serial production of ordered pipes for natural gas transportation was realized.

An Experimental Insight on the Selection of the Tool Tilt Angle for Friction Stir Welding of 7075 T651 Aluminum Alloys

Objectives: To determine the optimum tool tilt angle for friction stir welding (FSW) Al 7075-T651 alloy plates by investigating the mechanical and metallurgical properties of the joints. Methods/Statistical Analysis: Al 7075-T651 plates of 6.5mm thickness are welded varying the tool tilt angle from 0 to 6 degrees. The mechanical properties like tensile strength and microhardness are evaluated. The testing of tensile specimens is done as per ASTM E8 M-04 standards. The Vickers hardness has been investigated at the weld center in the transverse direction. The microstructural changes occurring are studied with the help of metallographic inspection. Scanning electron microscopy (SEM) has been adopted to evaluate the fracture mode of the tensile specimens. Findings: An important welding parameter in FSW that influences the welding quality is the tool tilt angle. In this paper the results of Al 7075-T651 joints welded by FSW with varying tilt angle are investigated for their mechanical strength and metallurgical properties. Evaluation of the tensile strength is carried out and put in relation with the microstructure investigations. From the experimental analysis it is observed that the weld joints made with two degree tool tilt angle are defects free resulting into the best mechanical and metallurgical properties compared to other joints. The fracture surface examination with the scanning electron microscope shows that the fracture surface of the joints are largely governed by the change in the tilt angles. The observations of fracture surface under SEM shows that the joint made with two degree tilt angle failed in a ductile mode whereas all the other joints failed in brittle mode. Application/Improvements: 7000 series aluminum alloys are a family of alloys that are practically unweldable by fusion welding processes. FSW procedure can be economically utilized to weld such alloys. This study will benefit to direct the selection of tool tilt angle during FSW of Al 7075 T651 plates.

철도차량 적용을 위한 Al alloy(A6005)-Mg alloy(AZ61) 이종소재 마찰교반용접 특성 연구

본 연구에서는 이종소재 A6005-AZ61 접합을 위하여 마찰교반용접의 툴 삽입 위치와 모재의 냉각 유 무에 따라 용접부 특성을 분석하였다. 다른 용접 조건들인 툴 회전속도와 이송속도는 500rpm-30mm/min으로 고정하고 Advancing side에 알루미늄 합금(A6005), Retreating side에 마그네슘 합금(AZ61)을 배치하여 용접을 진행하였다. 용접은 여섯 가지 케이스를 진행하였다. 용접부 특성을 관찰하기 위하여 인장 시험을 진행하고, 광학현미경을 사용하여 용접부의 미세조직을 관찰하였다. 인장시험 결과 마그네슘 합금 방향으로 툴을 1mm 이동시키고 모재에 냉각을 시킨 조건에서 강도가 가장 높게 나타났다. 동일한 용접 조건에서 냉각을 한 경우에 냉각을 하지 않은 것 보다 강도가 약 2배 높게 측정되었다. 툴의 위치는 용접부 중심에서 알루미늄 합금 방향으로 1.7mm, 마그네슘 합금 방향으로 1.7mm 이동시켜 과도한 편심을 적용한 용접 조건에서는 교반이 잘 이루어지지 않아 용접부의 건전성이 가장 좋지 않았다. 과도한 편심을 적용한 용접 조건에서는 교반이 잘 이루어지지 않아 용접부의 건전성이 가장 좋지 않았다. 본 연구를 통해 A6005-AZ61 이종 마찰교반용접시 용접속도와 툴 회전속도만큼 모재의 온도 조절과 툴 삽입위치가 중요한 용접변수임을 확인 하였다. In this study, the welding characteristics of friction stir welding were investigated in accordance with the tool plunge position and cooling to the base materials for the joining of dissimilar materials (A6005-AZ61). Other different welding conditions, such as the tool rotation speed and welding speed, were fixed to 500rpm-30mm/min, respectively, and welding was then carried out by placing the Mg alloy (AZ61) on the advancing side and Al alloy(A6005) on the retreating side. Welding was conducted under six different conditions. To investigate the welding characteristic, tensile test and microstructure observations using an optical microscope were carried out. As the tensile test result, the maximum strength appeared under the condition in which the tool is moved 1 mm to the Mg alloy direction and cooling to the base materials. Under the same welding conditions, the strength with cooling was approximately two times higher than that without cooling. The tool was located in each direction of 1.7 mm from the weld line. Therefore, in the excessive off-set of tool position, the welding integrity was in an extremely poor condition due to the lack of stirring. This study was confirmed by the A6005-AZ61 dissimilar friction stir welding the welding speed and the tool rotation speed. In addition, the temperature control and tool plunge position are important welding parameters.

A Review of Similar and Dissimilar Micro-joining of Nitinol

NiTinol belongs to a class of smart materials which has a wide range of applications in the field of automotive, aerospace, biomedical, robotics, etc., owing to the growing trend in miniaturization of components. Micro-joining is becoming one of the important and familiar processes in the fabrication of miniaturized components. Recently, effective micro-joining of thin sheets has been gaining a lot of interest among researchers. In this article, the research and progress in micro-joining of NiTinol to itself and other metals are reviewed at different aspects. To date, laser welding, tungsten inert gas welding, and resistance welding have been used to a large extent in investigating the weldability of NiTinol alloys. Some important welding parameters used in micro joining by various researchers and their effects on weld qualities are detailed in this review. Metallurgical aspects, mechanical properties and corrosion aspects of micro-joined NiTinol sheets/wires are discussed. The aim of this report is to review the recent progress in micro-joining of NiTinol and to provide a basis for follow-on research.

Effects of welding parameters on weld pool characteristics and shape in hybrid laser-TIG welding of AA6082 aluminum alloy: numerical and experimental studies

The effects of three important welding parameters including laser power, welding current and welding speed on the weld pool characteristics, shape and dimensions in hybrid laser-TIG welding of AA6082 aluminum alloy are studied by numerical, experimental, and statistical approaches. For this aim, first, a 3D numerical model is used to simulate heat transfer and fluid flow in the weld pool and then resultant weld shape for various welding conditions. Besides, a set of experiments are performed to validate and calibrate the model. Finally, analysis of variance (ANOVA) method is applied to investigate more precisely how welding parameters affect weld dimensions. The simulation results show with increasing the laser power and welding current and decreasing the welding speed, the Marangoni and buoyancy forces increase. With increasing the laser power, the weld depth increases more significantly than the weld width. The weld half width increases with increasing the welding current, whereas the weld pool depth is relatively unchanged. Furthermore, with increasing the welding speed, both weld pool depth and half width decrease with similar slope. Generally, the presented model showed a good capability to predict the weld geometry and characteristics under various applied welding conditions which can reduce number of needed experiments.

Parametric study of transient temperature distribution in FSW of 304L stainless steel

Three-dimensional nonlinear thermal simulations are carried out for the friction stir welding (FSW) of 304L stainless steel using finite element analysis software—COMSOL® Multiphysics. Based on published experimental data of transient temperature for the Stainless Steel 304L, the thermal numerical simulation is verified. Cases of parametric sweeps for a few important welding parameters like normal force (5–50 kN), rotational speed (200–1500 RPM), shoulder radius (10–50 mm), and translational speed (0.5–3 mm s−1) are analyzed at three specific locations for the friction stir welding process. The objective of this analysis is to study the effect on transient temperature during the welding operation with varying parameters. The validated model is extended to parametric study of variation of transient temperature with shoulder radius and normal force that have not yet been experimentally validated. Transient temperature is an important factor for successful fusion of metal. The simulation shows an increasing trend of the peak temperature with increasing tool rotational speed, decreasing travel speed, increasing shoulder radius, and increasing normal force. This analysis can assist in choosing optimum welding parameters for successful welding under various constraints and for prediction and control of heat-affected zone.

Effects of Dwell-Time and Plunge Speed during Micro Friction Stir Spot Welding on Mechanical Properties of Thin Aluminum A1100 Welds

Friction Stir Welding is a relatively new technique for joining metal. In some cases on aluminum joining, FSW gives better results compared with the arc welding processes, including the quality of welds and produces less distortion. The purpose of this study is to analyze the effect of high speed tool rotation on micro Friction Stir Spot Welding (μFSSW) to the shear fracture load of the welds. Response Surface Methods was used to analyze μFSSW parameters with the response. The welding material was Aluminum A1100, with thickness of 0.4 mm. The tool was made of HSS material which was shaped by micro grinding process. Tool shoulder diameter is 4 mm, and the pin diameter 1.5 mm with length of pin is 0.6 mm. The spindle speed is fixed at 33,000 rpm. The parameters that varied were the plunge speed (2 mm/min, 3 mm/min, 4 mm/min), and dwell time-1 (0 s, 2 s, 4 s) and variable of dwell time-2 (0 s, 2 s, 4 s). From the results of experiment and analysis, it is shown that the important welding parameter in high speed μFSSW process is dwell time-2.

Single-sided laser beam welding of a dissimilar AA2024–AA7050 T-joint

Abstract In the aircraft industry double-sided laser beam welding of skin–stringer joints is an approved method for producing defect-free welds. But due to limited accessibility – as for the welding of skin–clip joints – the applicability of this method is limited. Therefore single-sided laser beam welding of T-joints becomes necessary. This also implies a reduction of the manufacturing effort. However, the main obstacle for the use of single-sided welding of T-joints is the occurrence of weld defects. An additional complexity represents the combination of dissimilar and hard-to-weld aluminium alloys – like Al–Cu and Al–Zn alloys. These alloys offer a high strength-to-density ratio, but are also associated with distinct weldability problems especially for fusion welding techniques like laser beam welding. The present study demonstrates how to overcome the weldability problems during single-sided laser beam welding of a dissimilar T-joint made of AA2024 and AA7050. For this purpose a high-power fibre laser with a large beam diameter is used. Important welding parameters are identified and adjusted for achieving defect-free welds. The obtained joints are compared to double-sided welded joints made of typical aircraft aluminium alloys. In this regard single-sided welded joints showed the expected differing weld seam appearance, but comparable mechanical properties.

EFFECT OF PROCESS PARAMETERS ON TENSILE STRENGTH IN GAS METAL ARC WELDED JOINTS AA7075-T6 ALUMINUM ALLOY BY USING REGRESSION AND RESPONSE SURFACE MODEL

Aluminum and its alloys have been used in recent times due to their light weight, moderate strength and good corrosion resistance. Aluminum alloy 7075-T6 has been researched upon especially as a potential candidate for aircraft material. This alloy is difficult to weld using conventional welding techniques like GTAW and GMAW. An attempt has been made in this paper to weld 7075-T6 alloy using GMAW with argon as a shielding gas. The welding experiment was carried out on Odor, Chennai and tensile strength tested on Ministry of Micro and small and Medium Enterprises Testing Center, Government of India, Chennai for the purpose of improving tensile strength. In order to formulate the equation between important welding parameters like current (I), Voltage (V), Welding Speed (WS) and Gas flow (GS) (predictors) and tensile strength (response) so that multiple regression as chosen and validated this model SPSS 16 and formulated the transfer function with interaction between predictors reported by Minitab 15.

Effects of High Speed Tool Rotation in Micro Friction Stir Spot Welding of Aluminum A1100

Technology of Friction Stir Welding (FSW) is a relatively new technique for joining metal. In some cases on Aluminum joining, FSW gives better results compared with the arc welding processes, including the quality of welds and less distortion. The purpose of this study is to analyze the parameters effect of high speed tool rotation on micro Friction Stir Spot Welding (μFSSW) to the shear strength of welds. In this case, Aluminum material A1100, with thickness of 0.4 mm was used. Tool material of HSS material was shaped with micro grinding process. The spindle speed was fixed at 30000 rpm. Tool shoulder diameter was 3 mm, and a length of pin was 0.7 mm. The parameter variations used in this study were the variable of pin diameter (1.5 mm, 2.0 mm, and 2.5 mm), a variable of plunge speed (2 mm/min, 4 mm/min, 6 mm/min), and the variable of dwell time (2 seconds, 4 seconds, 6 seconds). Where the variation of these parameters will affect to the mechanical properties of welds (as response) was the shear strength. Response Surface Methods (RSM) was used to analyze μFSSW parameters with the shear strength of welds. From the result of experiment and analysis, it is shown that the important welding parameters in high speed μFSSW process are pin diameter and plunge speed.

Effects of Welding Parameters in Micro Friction Stir Lap Welding of Aluminum A1100

Technology of Friction Stir Welding (FSW) as a technique for joining metal is relatively new. In some cases on Aluminum joining, FSW gives better results compared with the Arc Welding processes, including the quality of welds and less distortion. FSW can even use milling machine or drilling machine, by replacing the tools and the appropriate accessories. The purpose of this study is to analyze the effect of process parameters on micro Friction Stir Lap Welding to the tensile load of welds. In this case, Aluminum material A1100, with thickness of 0.4 mm was used. Tool material of HSS material was shaped with micro grinding process. Tool shoulder diameter was 3 mm, while the diameter pin was 2 mm and a length of pin was 0.7 mm. The parameter variations used in this study were the variable of spindle speed (2300, 2600, and 2900 rpm), variable of tooltilt angle (0, 1, 2 degree) and a variable of Feed rate (50, 60, 70 mm/min). Where the variation of these parameters will affect to the mechanical properties of welds (as response) was the tensile load. Analysis and optimization parameters between the micro FSLW parameters with the tensile load of welds, is used a Response Surface Methods (RSM). From the result of experiment and analysis, it is shown that the important welding parameter in Micro Friction Stir Lap welding process is tilt angle.