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A New Testing Method to Evaluate Edge Cracking With Considerations of The Shear Clearance and Press Speed

EWI, Inc.-Jiahui Gu, Laura Zoller, Hyunok Kim
  • Technical Paper
  • 2020-01-0758
To be published on 2020-04-14 by SAE International in United States
As the automotive industry increasingly adopts the more use of Advanced High Strength Steel (AHSS) for the vehicle light-weighting and crashworthiness, the edge cracking issue continuously increases in stamping AHSS. Different lab-scale test methods such as the ISO standard hole-expansion test and the half specimen dome test are available to evaluate edge formability. However, none of these lab-scale testing methods fully considers production conditions such as various shear clearances, part complexity, and shearing speed associated with the mechanical or hydraulic press operation. To address these limitations of the available testing methods, a new punching and stamping test was developed. This paper introduces the simulation and experimental approach in developing this unique testing method to design the peanut-shaped hole that is the most sensitive to edge cracking in stamping. Three different sheet materials, DP780, 980 GEN3, and aluminum 6022-T4 were tested to validate the reliability of the newly developed testing method. Selected materials were punched with two different shear clearances between 10~20% that are commonly used for industrial applications. Also, two different press motions, conventional mechanical…
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EDGE-QUALITY EFFECTS ON MECHANICAL PROPERTIES OF STAMPED NON-ORIENTED ELECTRICAL STEEL

General Motors LLC-Peggy Jones, Margarita Thompson, Yew Sum Leong, Paul Crepeau
General Motors Technical Center India-Virupakshappa Lakkonavar, Swaroop Kavi
  • Technical Paper
  • 2020-01-1072
To be published on 2020-04-14 by SAE International in United States
The market for electric vehicles and hybrid electric vehicles is expected to grow in the coming years, which is increasing interest in design optimization of electric motors for automotive applications. Under demanding duty cycles, the moving part within a motor, the rotor, may experience varying stresses induced by centrifugal force, a necessary condition for fatigue. Rotors contain hundreds of electrical steel laminations produced by stamping, which creates a characteristic edge structure comprising rollover, shear and tear zones, plus a burr. Fatigue properties are commonly reported with specimens having polished edges. Since surface condition is known to affect fatigue strength, an experiment was conducted to determine the effect of sample preparation in stamped specimens. Tensile properties were unaffected by polishing. In contrast, polishing was shown to increase fatigue strength by approximately 10-20% in the range of 105-107 cycles to failure.
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Investigation of Fracture Behavior of Deep Drawn Automotive Part affected by Thinning with Shell Finite Elements

General Motors LLC-Hwawon Lee, Shengjian li, Hui-Min (Emmy) Huang, Parvath Police
  • Technical Paper
  • 2020-01-0208
To be published on 2020-04-14 by SAE International in United States
In the recent decades, tremendous effort has been made in automotive industry to reduce vehicle mass and development costs for the purpose of improving fuel economy and building safer vehicles that previous generations of vehicles cannot match.An accurate modeling approach of sheet metal fracture behavior under plastic deformation is one of the key parameters affecting optimal vehicle development process. FLD (Forming Limit Diagram) approach, which plays an important role in judging forming severity, has been widely used in forming industry, and localized necking is the dominant mechanism leading to fracture in sheet metal forming and crash events.FLD is limited only to deal with the onset of localized necking and could not predict shear fracture. Therefore, it is essential to develop accurate fracture criteria beyond FLD for vehicle development. To enhance the accuracy of crash simulations, forming results from stamping process are generally introduced to consider work hardening and thinning/thickening of a stamped part during the simulations. However, fracture criteria are only applied to the original design thickness, not the change in the gage thickness after…
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Application of Laminated Steels for Stamped Bumpers

FCA US LLC-Eric Edwin Herz
Material Sciences Corp.-Justin Putti, Matt Murphy
  • Technical Paper
  • 2020-01-1055
To be published on 2020-04-14 by SAE International in United States
Light-weight solutions for stamped steel components that exhibit the same or similar appearance properties for purposes of authentic feel and perception to customers will play a critical role as the goal of reaching maximum fuel efficiency for large vehicles continues. This paper outlines the potential uses for laminated steel or “MSC Smart Steel®” in large stamped steel bumpers that would normally be stamped with thick sheet metal in order to meet vehicle level functional objectives. The paper presents the investigation of the one for one drop in capabilities of MSC Smart Steel® material to existing stamping dies, special processing considerations while manufacturing, vehicle level performance comparisons, and class “A” coating options and process needs. Most of all, it will highlight the significant vehicle weight saving benefits and opportunities as compared to current production stamped steel bumpers.
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Structural Performance Comparison between 980MPa Generation 3 Steel and Press Hardened Steel Applied in the Body-in-White A and B-Pillar Parts

General Motors LLC-Andre Pereira, Adam Ballard, Rajmouli Komarivelli, Haoming Li
United States Steel Corp.-Vasant Pednekar, Guofei Chen
  • Technical Paper
  • 2020-01-0537
To be published on 2020-04-14 by SAE International in United States
Commercially available Generation 3 (GEN3) advanced high strength steels (AHSS) have inherent capability of replacing press hardened steels (PHS) using cold stamping processes. 980 GEN3 AHSS is a cold stampable steel with 980 MPa minimum tensile strength that exhibits an excellent combination of formability and strength. Hot forming of PHS requires elevated temperatures (> 800°C) to enable complex deep sections. 980 GEN3 AHSS presents similar formability as 590 DP material, allowing engineers to design complex geometries similar to PHS material; however, its cold formability provides implied potential process cost savings in automotive applications. The increase in post-forming yield strength of GEN3 AHSS due to work and bake hardening contributes strongly toward crash performance in energy absorption and intrusion resistance. The viability of using cold stamped 980 GEN3 AHSS as a replacement for PHS has often been challenged due to concerns about formability and capability to meet final crash performance targets. To address these concerns, A-pillar and B-pillar parts were successfully cold stamped using U. S. Steel 980 GEN3 AHSS and assembled in a prototype mid-size…
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Tracking Panel Movement during Stamping Process using Advanced Optical Technology

Oakland University-Bicheng Guo, Xiaowan Zheng, Boyang Zhang, Rong Wang, Lianxiang Yang
  • Technical Paper
  • 2020-01-0541
To be published on 2020-04-14 by SAE International in United States
The metal panel is comprehensively applied in the automotive industry. A significant issue for the metal panel is the deflection when did the movement in the press line of the stamping process. Unpredictable deflection could result in the cut off of press line. In order to control the deflection in a safe zone, Finite element tools are used to simulate the panel transform process. However, the simulation needs experimental validation where conventional displacement measurement techniques could not satisfy the requirement of vast filed displacement and accuracy point tracking. In this study, multi-camera digital image correlation (DIC) systems have been developed to track a panel movement in the press line of the stamping process. There are some advantages for applying the DIC system, which is non-contact, full-field, high accuracy, and direct measurement techniques that provide the evaluation displacement of the metal panel and press line. Nevertheless, the traditional stereo DIC system (with two cameras) has a limited field of view, and the multi-camera DIC system expands the field of view and enables the measurement of panel…
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3rd Generation AHSS Virtual and Physical Stamping Evaluation

FCA US LLC-Bryan Macek
United States Steel Corporation-Justin Lutz
  • Technical Paper
  • 2020-01-0757
To be published on 2020-04-14 by SAE International in United States
Developing lightweight, stiff and crash-resistant vehicle body structures requires a balance between part geometry and material properties. High strength materials suitable for crash resistance impose geometry limitations on depth of draw, radii and wall angles that reduce geometric efficiency. The introduction of 3rd generation Advanced High Strength Steels (AHSS) can potentially change the relationship between strength and geometry and enable simultaneous improvements in both. This paper will demonstrate applicability of 3rd generation AHSS with higher strength and ductility to replace the 780 MPa Dual Phase steel in a sill reinforcement on the current Jeep Cherokee. The focus will be on formability, beginning with virtual simulation and continuing through a demonstration run on the current production stamping tools and press.
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Bake Hardening Behavior of DP, TBF, and PHS Steels with Ultimate Tensile Strengths Exceeding 1 GPa

Colorado School of Mines-Brandon W. Blesi, Charles Smith, David K. Matlock, Emmanuel De Moor
  • Technical Paper
  • 2020-01-0536
To be published on 2020-04-14 by SAE International in United States
Third generation advanced high strength steels (AHSS) have been developed combining high strength and formability, allowing for lightweighting of vehicle structural components. These AHSS components are exposed to paint baking operations ranging in time and temperature to cure the applied paint. The paint baking treatment, combined with straining induced from part forming, may lead to increased in-service component performance due to a strengthening mechanism known as bake hardening. This study aims to quantify the bake hardening behavior of select AHSS grades. Materials investigated were press hardenable steels (PHS) 1500 and 2000; transformation induced plasticity (TRIP) aided bainitic ferrite (TBF) 1000 and 1200; and dual phase (DP) 1000. The number designations of these grades refer to minimum as-received ultimate tensile strengths in MPa. Paint baking was simulated using industrially relevant times and temperatures from 15 to 60 min and 120 to 200 °C, respectively. Samples were prestrained 0, 2, or 5 pct to replicate part forming. Bake hardening values ranging from 90 to 140 MPa were observed for DP and TBF grades that were prestrained 2…
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Measurement and Evaluation of Vacuum Suction Cups using Digital Image Correlation

Oakland University-Wan Xu, Boyang Zhang, Rong Wang, Wen Ma, Bicheng Guo, Lianxiang Yang
  • Technical Paper
  • 2020-01-0542
To be published on 2020-04-14 by SAE International in United States
As vacuum suction cups are widely used in stamping plants, it becomes urgent and important to understand their performance and failure modes. Vacuum suction cups are employed to lift, move, and place sheet metal instead of human’s hands. Occasionally the vacuum cups would fail and drop parts, even it would cause expensive delays in the production line. In this research, several types of vacuum cups have been studies and compared experimentally. A new tensile device and test method was developed to measure the pulling force and deformation of vacuum cups. The digital image correlation technique has been adopted to capture and analyze the contour, deformation and strain of the cups under different working conditions. The experimental results revealed that the relevant influential parameters include cup type, pulling force angles, vacuum levels, sheet metal curvatures, etc. Also, the deformation distribution and history of the cups denote the weak part and failure mechanism during operation. Moreover, this work could help designers and operators thoroughly understanding the performance of vacuum suction cups and greatly improved in further work.
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Advancements of Superplastic Forming and Diffusion Bonding of Titanium Alloys for Heat Critical Aerospace Applications

The Boeing Company-Eve Taylor Burkhart, Larry Hefti
  • Technical Paper
  • 2020-01-0033
Published 2020-03-10 by SAE International in United States
Titanium’s high strength-to-weight ratio and corrosion resistance makes it ideal for many aerospace applications, especially in heat critical zones. Superplastic Forming (SPF) can be used to form titanium into near-net, complex shapes without springback. The process uses a machined die where inert gas is applied uniformly to the metal sheet, forming the part into the die cavity. Standard titanium alpha-beta alloys, such as 6Al-4V, form at temperatures between 900 and 925°C (1650-1700°F). Recent efforts have demonstrated alloys that form at lower temperatures ranging between 760 and 790°C (1400-1450°F). Lowering the forming temperature reduces the amount of alpha case that forms on the part, which must be removed. This provides an opportunity of starting with a lower gauge material. Lower forming temperatures also limit the amount of oxidation and wear on the tool and increase the life of certain press components, such as heaters and platens. A variation of this process is SPF combined with Diffusion Bonding (SPF/DB) of two or more titanium sheets to produce integrally stiffened structures with limited fasteners and less weight than…
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