Armando Joaquin

Resistance Spot Welding (RSW) of Advanced High Strength Steels (AHSS) for Automotive Body Construction

There has been a substantial increase in the use of advanced high strength steel in automotive structures in the last few years. The usage of these materials is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are getting popular with superior mechanical properties and weight advantages compared to mild steel materials. These new materials have significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application in future vehicle programs. Due to high strength nature of AHSS materials, higher weld forces and longer weld times are needed to weld AHSS materials. In this paper, weld lobe development for DP600, and DP780 steels are discussed. DP600 steels were joined with two different weld equipments and three different electrodes and their influence on mechanical properties are discussed. Development work on the effect of weld tips on button size, and shrinkage voids due to different welding variables is discussed. DP780 EG steel (1.0 mm) is also joined to itself. The weld lobes, mechanical properties (tensile shear and cross tension), cross-section examination, and microhardness of 1.0 mm DP780 EG to 1.0 mm DP780 EG weld joint results are discussed.Copyright

Metal Inert Gas (MIG) Welding Process Optimization for Joining Aluminum 5754 Sheet Material Using OTC/Daihen Equipment

The development of lightweight vehicles, in particular aluminum intensive vehicles, require significant manufacturing process development for joining and assembling aluminum structures. Currently, 5xxx and 6xxx aluminum alloys are being used in various structural applications in a number of lightweight vehicles worldwide. Various joining methods, such as MIG, Laser and adhesive bonding have been investigated as technology enables for high volume joining of 5xxx, and 6xxx series alloys. In this study, metal inert gas (MIG) welding is used to join 5754 non-heat-treatable alloy sheet products. The objective of this study is to develop optimum weld process parameters for non-heat-treatable 5754 aluminum alloys. The MIG welding equipment used in this study is an OTC/Daihen CPD-350 welding systems and DR-4000 pulse power supply. The factors selected to understand the influence of weld process parameters on the mechanical properties and metallurgy (weld penetration) include power input (torch speed, voltage, current, wire feed), pulse frequency, and gas flow rate. Test coupons used in this study were based on a single lap configuration. A full factorial design of experiment (DOE) was conducted to understand the main and interaction effects on joint failure and weld penetration. The joint strengths and weld penetrations are measured for various operating ranges of weld factors. Post weld analysis indicates, power input and gas flow rate are the two signficant factors (statistically) based on lap shear load to failure and weld penentration data. There were no 2-way or 3-way interaction effects observed in ths weld study. Based on the joint strength and weld penetration, optimum weld process factors were determined.Copyright

Static Tensile Strength of Gas Metal Arc Welded (GMAW) Joints of Uncoated Dual Phase 600 (DP600) Steels

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive steels for automobile makers. The usage of AHSS steels is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. These new steels have significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures due to Heat affected Zones (HAZ) at the weld joint. In this study Gas Metal Arc Welding (GMAW) of a lap joint configuration consisting of 1.5 mm uncoated DP600 to itself was investigated. The objective of the study was to understand the wire feed rate and torch speed influence on lap joint strength. A two factor, two level, full factorial design of experiment (DOE) was conducted to understand the wire feed and torch speed influence on tensile strength. In order to understand the curvature effect, center point was also considered in the experiment. Based on the statistical analysis, wire feed rate was the only significant factor on static tensile strength. Metallurgical properties of the lap joints were evaluated using optical microscopy. Significant hardness drop of 40% was observed at the HAZ.Copyright

Gas Metal Arc Welding (GMAW) Process Optimization for Uncoated Dual Phase 600 Material Combination With Aluminized Coated and Uncoated Boron Steels for Automotive Body Structural Applications

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive steels for automobile makers. The usage of AHSS steels is projected to grow significantly in the next 5–10 years as new safety and fuel economy regulations are enacted. These new steels pose significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. In this paper, Gas Metal Arc Welding (GMAW) of uncoated DP 600 and boron (coated and uncoated boron) steels were investigated. In the first study, 2.0 mm DP 600 and 2.0 mm uncoated boron lap joints (Joint #1 and #2) were investigated. In the second study, 1.00 mm DP 600 and 2.0 mm USIBOR (aluminized coated boron) lap joints (Joint # 3 and #4) were investigated. Static and fatigue tests were conducted on the four joint configurations. The effects of steel stack-ups and microhardness distribution along the tensile stress flow direction of the joints on fatigue performance defined by fatigue life as well as crack initiation site and propagation path were analyzed. Metallurgical properties of the dissimilar metal lap joints were evaluated using optical microscopy. The boron steel shows a significant drop in hardness at the heat affected zone (HAZ) as compared to the DP600 steel side. It was found that for the 2.0 mm DP600 and 2.0 mm boron steel dissimilar joint, fatigue life of the joint is better when boron steel was on the top of the joint (Joint #2). However, in the case of 1.0 mm DP 600 and 2.0 mm USIBOR lap joint, the fatigue life of the joint is better when 1.0 mm DP 600 was on the top of the joint (Joint # 3). Ductility of boron steel and significant HAZ softening in boron steel are believed to be the key factors for the fatigue failure at the boron steel side (in all four joint configurations).Copyright

Laser Hybrid Welding of Uncoated Boron Steel for Automotive Body Construction

The automotive industry is in constant pursuit of alternative materials and processes to address the ever changing needs of their customer and the environment. This paper presents findings from a study using a laser hybrid process (laser with Gas Metal Arc Welding) to join uncoated boron steel. In order to understand the affect from laser hybrid joining process, bead on plate experiments were conducted using 1.0 mm, 1.5 mm and 2.0 mm thick coupons. Further, one lap joint configuration was also investigated using the 1.5 mm thick coupons. Based on the test results, a significant reduction in tensile strength was observed at the Heat Affected Zone (HAZ).Copyright

Influence of Metal Inert Gas (MIG) Welding Factors Wire Feed Rate and Weld Travel Speed on Aluminum Weld Joint Strength

The purpose of the study was to understand effects of weld travel speed and wire feed rate in metal inert gas (MIG) welding on the aluminum materials joint strength. Initial experiments indicated a noticeable positive effect of travel speed on weld strength with an over 95% statistical significance. Nonetheless further experimentation at a significantly lower wire feed rate proved the opposite with similar statistical significance. A negative effect of welding travel speed on joint strength was measured at lower wire feed rates. In order to understand the weld travel and wire feed rate on the joint strength, a Design of Experiment (DOE) was conducted. For this experiment, weld system process factors were set constant (wave control, gas flow rate, torch angle, trim and wave type) except for travel speed and wire feed rate. A two-factor two-level full factorial design of experiment (DOE) was conducted in order to understand the effects of these two factors on weld strength. Additional welding at higher wire feed rates were conducted in order to confirmed the trend found. Results showed travel speed effects on joint strength as a result of its direct interaction with wire feed rate. This occurrence can have significant economic implications if proven to be repeatable and will be the subject of this and future MIG welding studies as they relate to aluminum structures.Copyright

Dimensional Variation Analysis of T-Node Joints Using Aluminum 6063-T52 Extrusion Material in Gas Metal Arc Welding (GMAW) Joining Process

The development of manufacturing processes for joining and assembling of lightweight aluminum vehicles requires detailed process capability studies as well as dimensional variation analysis studies to ensure process controls are in place. These manufacturing processes not only have to provide cycle time viability but also need to maintain or surpass product safety and quality. T-Nodes joint designs are an integral of aluminum architectures based on hybrid designs, i.e those fabricated from mixed aluminum products consisting of castings, stampings and extrusions. The purpose of this study was to find optimum parameters for minimum distortion for the gas metal arc welding (GMAW) of 6063-T52 T-Nodes. The welding factors considered were locators (4-way and 2-way pins verses net surfaces), the welding equiment process factors (power input, pulse frequency, gas flow rate, torch angle and arc intensity), the use of simultaneous welding, and welding sequence order. A partial factorial design of experiment (DOE) was conducted to understand the effects of these factors on T-node joint distortions. A total of 14 points were considered for dimensional distortion measurements. Results showed power (heat) input is the only statiscally significant factor on joint distortion. Locators type as well as welding sequence and simultaneous welding also had a measurable affect on part deviation during welding.Copyright

Finite Element Modeling of Spot Welding for Advanced High Strength Steels (AHSS)

Weldability is a critical enabler for application of new grades of steel, which have found widespread applications in the auto industry to meet new safety regulations and reduce weight of vehicles. There are a wide variety of these grades of steel which are being used across the industry. Even within a OEM the number of material and gauge combinations becomes quite large. This requires a considerable amount of testing to prove out welding feasibility of these steels. This paper discusses the use of a finite element method (FEM) to model spot welding of DP600 and correlates the results with experiments. Improved accuracy and confidence in these tools can provide a way to better understand the physics of the process and improve the weldability of these steels in a cost effective manner.Copyright

Laser Hybrid Welding of Advanced High Strength Steels (AHSS) for Automotive Body Construction

In response to demands for improved safety standards and fuel economy, automotive OEMs have shown an increased interest for using light weight materials with greater strength. Advanced High Strength Steels (AHSS) have gained popularity due to their superior mechanical properties and weight advantages, as compared to mild steel materials. Welding of AHSS materials remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. Currently, various fusion welding processes such as Metal Inert Gas (MIG), Laser and Laser Hybrid are used on mild steel applications. The Laser and Laser Hybrid weld processes continue to gain popularity in automotive applications due to their ability to provide structural integrity and manufacturing efficiency. In laser welding, only a light source is used to join materials together. In laser hybrid, both a light source and metal filler are used to join the materials. In this paper, the laser hybrid joining process on AHSS materials (DP780 and Boron) is investigated. Influence of heat from Laser Hybrid welding process and its effect on the steel is discussed.Copyright