Sergio Angotti

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

Influence of Lubricants on Advanced High Strength Steel Tubes in Bending Process

To reach safety, emissions, and cost objectives, manufacturers of automotive body structural components shape thin gauge, high strength steel tube using a series of manufacturing steps that often include bending, preforming and hydroforming. Challenging grades and bend severity require a sensitive optimization of the tubular bending process. Lubricants play a significant role in establishing a successful bending process. In this study, the performance of two lubricants, Hydrodraw 551 and HFO 20, were investigated for bending Dual Phase 780 (DP780) and High Strength Low Alloy 350 (HSLA350) thin-walled steel tubes. Formability success was evaluated in terms of wrinkling, thinning strain and final geometry. Lubricant performance was found to be sensitive to grade and application site. HFO 20 was found to be a poor choice for bending DP780 tube.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

Resistance Spot Welding (RSW) Process Optimization for Uncoated 1.0 mm Boron to Uncoated 1.0 mm Boron for Automotive Applications

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 the introduction of new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are gaining popularity due to their superior mechanical properties and weight advantages, as compared to mild steels. These new materials also pose significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application on future vehicle programs. Due to the 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 1.0 mm uncoated boron to 1.0 mm uncoated boron 2T stack-up combination is discussed. Weld lobes were developed with Mid Frequency Direct Current (MFDC) equipment, ISO type B-16 tip, constant weld force of 3.43 kN (770 lbf), hold time of 5 cycles and the weld times were varied 10, 13 and 16 cycles. Based on the tensile, cross-tension and nugget data, there were no correlations were observed between tensile load and button size and also between cross-tension and button size. Microhardness data assessment found heat affected zone (HAZ) at the weld nugget area and similar HAZ was observed for all the welding cycles. The weld lobes, mechanical properties (tensile shear and cross-tension), cross-section examination, and microhardness of 1.0 mm boron to 1.0 mm boron 2T stack-up results are discussed.Copyright

Resistance Spot Welding (RSW) Process Optimization for Uncoated 2.0mm Dual Phase 780 to 2.0 mm Uncoated 2.0 mm Dual Phase 780 (DP780) Steel for Automotive Applications

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. This work is in support of lightweight structures development and during the weld development phase various gages of coated and uncoated AHSS materials (DP780, DP980, TRIP780, Boron, Algoma 700B) were investigated. Both 2T and 3T stack-up conditions were investigated. Also, some combination of AHSS materials with High Strength Low Alloy (HSLA) and Bake Hardenable 210 (BH210) electro galvanized (EG) steels were also investigated. In this paper, weld lobe development for 2.0 mm DP780 bare to 2.0 mm DP780 bare 2T stack-up combination is discussed. Weld lobes were developed with Mid Frequency Direct Current (MFDC) equipment, ISO type B-20 tip, constant weld force of 6.36 kN (1430 lbf), hold time of 5 cycles and the weld times were varied 21, 24 and 27 cycles. Based on the tensile, cross-tension and nugget data, there were no correlations were observed between tensile load and button size and also between cross-tension and button size. Weld cross section data indicated heat affected zone (HAZ) at the weld nugget area and hardness drop of 17% was observed at the HAZ area. Irrespective of weld cycles, similar HAZ was observed close to the weld nugget. The weld lobes, mechanical properties (tensile shear and cross tension), cross-section examination, and microhardness of 2.0 mm DP780 bare to 2.0 mm DP780 bare weld 2T stack-up results are discussed.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