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Technical Paper

A Practical Failure Limit for Sheared Edge Stretching of Automotive Body Panels

2010-04-12
2010-01-0986
Edge cracking is one of the major formability concerns in advanced high strength steel (AHSS) stamping. Although finite element analysis (FEA) together with the Forming Limit Diagram has been widely used, it has not effectively predicted edge cracking. Primary problems in developing a methodology to insure that parts are safe from edge cracking are the lack of an effective failure criterion and a simple and accurate measurement method that is not only usable in both die tryout and production but also can be verified by finite element analysis. The intent of this study is to develop a methodology to ensure that parts with internal cutouts, such as a body side panel can be produced without edge cracking. During tryout and production, edge cracking has traditionally been detected by visual examination, but this approach is not adequate for ensuring freedom from edge cracking.
Technical Paper

Monotonic and Fatigue Behavior of Magnesium Extrusion Alloy AM30: An International Benchmark Test in the “Magnesium Front End Research and Development Project”

2010-04-12
2010-01-0407
Magnesium alloys are the lightest structural metal and recently attention has been focused on using them for structural automotive components. Fatigue and durability studies are essential in the design of these load-bearing components. In 2006, a large multinational research effort, Magnesium Front End Research & Development (MFERD), was launched involving researchers from Canada, China and the US. The MFERD project is intended to investigate the applicability of Mg alloys as lightweight materials for automotive body structures. The participating institutions in fatigue and durability studies were the University of Waterloo and Ryerson University from Canada, Institute of Metal Research (IMR) from China, and Mississippi State University, Westmorland, General Motors Corporation, Ford Motor Company and Chrysler Group LLC from the United States.
Technical Paper

Austempering Process for Carburized Low Alloy Steels

2013-04-08
2013-01-0949
There is a continual need to apply heat treatment processes in innovative ways to optimize material performance. One such application studied in this research is carburizing followed by austempering of low carbon alloy steels, AISI 8620, AISI 8822 and AISI 4320, to produce components with high strength and toughness. This heat treatment process was applied in two steps; first, carburization of the surface of the parts, second, the samples were quenched from austenitic temperature at a rate fast enough to avoid the formation of ferrite or pearlite and then held at a temperature just above the martensite starting temperature to partially or fully form bainite. Any austenite which was not transformed during austempering, upon further cooling formed martensite or was present as retained austenite.
Technical Paper

Correlation Study on Parameters Affecting Springback Phenomenon in Stamping Simulation

2013-04-08
2013-01-1169
Springback is a major phenomenon in sheet metal forming process that has to be tackled to achieve the desired product with greater dimensional accuracy. Springback occurs due to elastic recovery of sheet metal after the stamping process. The automobile industry is gradually moving from use of conventional steels to advanced high strength steels (AHSS) for their light weight and greater strength properties; however AHSS possesses greater springback effect due to higher elastic limit which proves to be difficult to deal with the springback effect. Hence it is imperative that the counter measures are taken to minimize the springback effect. The purpose of the study is to showcase various factors that influence the prediction of springback phenomenon. In this study the simulation results are compared with scanned data of actual stamped panels and their deviation is studied.
Technical Paper

Die Wear Estimation in Automotive Sheet Metal Stamping

2013-04-08
2013-01-1171
Automotive industry's migration to usage of HSS (High Strength Steels), AHSS (Advance High Strength Steels) from conventional steels for their low weight and high strength properties has had its significant effects on die wear. The unpredictability of die wear can pose manufacturing issues, for example, undesirable tool life. Hence die wear has been gaining immense attention and lot of research work has been carried out to provide a die wear prediction method. This paper focuses on the method of estimating wear mathematically based on the mechanics behind die wear phenomenon. This is also an effort to study wear on die for an automotive component in critical areas for which the amount of wear are calculated. This study is further to be correlated with production data from die maintenance record, explicit measurement of die wear, etc., to validate the estimation.
Technical Paper

Optimization of High-Volume Warm Forming for Lightweight Sheet

2013-04-08
2013-01-1170
Traditional warm forming of aluminum refers to sheet forming in the temperature range of 200°C to 350°C using heated, matched die sets similar to conventional stamping. While the benefits of this process can include design freedom, improved dimensional capability and potentially reduced cycle times, the process is complex and requires expensive, heated dies. The objective of this work was to develop a warm forming process that both retains the benefits of traditional warm forming while allowing for the use of lower-cost tooling. Enhanced formability characteristics of aluminum sheet have been observed when there is a prescribed temperature difference between the die and the sheet; often referred to as a non-isothermal condition. This work, which was supported by the USCAR-AMD initiative, demonstrated the benefits of the non-isothermal warm forming approach on a full-scale door inner panel. Finite element analysis was used to guide the design of the die face and blank shape.
Technical Paper

Evaluation of Metal Gainers for Advanced High Strength Steel Flanging

2014-04-01
2014-01-0985
Forming a metal gainer is a common technique used to gather material in a high stretch region along an edge in preparation for a subsequent flanging operation. This technique has proven to be successful for mild steels, but needs to be evaluated for the applicability to advanced high strength steels (AHSS). The Auto/Steel Partnership High Strength Stamping Team launched a project for this study. Experimental trials were conducted on gainer forming, trimming and flanging. Twelve (12) AHSS have been tested with tensile strengths ranging from 460 to 1240 MPa. Edge stretch limits for flanging have been evaluated and compared to flanging without gainers. Different trimming and flanging approaches have also been tried. The results show that metal gainers are not advantageous for flanging of higher strength AHSS.
Journal Article

Development of Corrosion Testing Protocols for Magnesium Alloys and Magnesium-Intensive Subassemblies

2013-04-08
2013-01-0978
Corrosion tendency is one of the major inhibitors for increased use of magnesium alloys in automotive structural applications. Moreover, systematic or standardized methods for evaluation of both general and galvanic corrosion of magnesium alloys, either as individual components or eventually as entire subassemblies, remains elusive, and receives little attention from professional and standardization bodies. This work reports outcomes from an effort underway within the U.S. Automotive Materials Partnership - ‘USAMP’ (Chrysler, Ford and GM) directed toward enabling technologies and knowledge base for the design and fabrication of magnesium-intensive subassemblies intended for automotive “front end” applications. In particular, subassemblies consisting of three different grades of magnesium (die cast, sheet and extrusion) and receiving a typical corrosion protective coating were subjected to cyclic corrosion tests as employed by each OEM in the consortium.
Journal Article

Fatigue Based Lightweight Optimization of a Pickup Cargo Box with Advanced High Strength Steels

2014-04-01
2014-01-0913
Advanced high strength steels (AHSS) offer a good balance of strength, durability, crash energy absorption and formability. Applications of AHSS for lightweight designs of automotive structures are accelerating in recent years to meet the tough new CAFE standard for vehicle fuel economy by 2025. At the same time, the new generation pickup cargo box is to be designed for a dramatic increase in payload. Upgrading the box material from conventional mild steels to AHSS is necessary to meet the conflicting requirements of vehicle light weighting and higher payload. In this paper, typical AHSS grades such as DP590 and DP780 were applied to selected components of the pickup cargo box for weight reduction while meeting the design targets for fatigue, strength and local stiffness.
Journal Article

Fatigue Life Prediction of an Automobile Cradle Mount

2013-04-08
2013-01-1009
Elastomers have large reversible elastic deformation, good damping and high energy absorption capabilities. Due to these characteristics along with low cost of manufacturing, elastomeric components are widely used in many industries and applications, including in automobiles. These components are typically subjected to complex multiaxial and variable amplitude cyclic loads during their service life. Therefore, fatigue failure and life prediction are important issues in the design and analyses of these components. Availability of an effective CAE technique to evaluate fatigue damage and to predict fatigue life under complex loading conditions is a valuable tool for such analysis. This paper discusses a general CAE analytical technique for durability analysis and life prediction of elastomeric components. The methodology is then illustrated and verified by using experimental fatigue test results from an automobile cradle mount.
Journal Article

Fatigue Life Predictions under General Multiaxial Loading Based on Simple Material Properties

2011-04-12
2011-01-0487
A procedure for fatigue life estimation of components and structures under variable amplitude multiaxial loadings based on simple and commonly available material properties is presented. Different aspects of the analysis consisting of load cycle counting method, plasticity model, fatigue damage parameter, and cumulative damage rule are presented. The only needed material properties for the proposed procedure are hardness and monotonic and axial cyclic deformation properties (HB, K, n, K′ and n′). Rainflow cycle counting method is used for identifying number of cycles. Non-proportional cyclic hardening is estimated from monotonic and axial cyclic deformation behaviors. A critical plane approach is used to quantify fatigue damage under variable amplitude multiaxial loading, where only material hardness is used to estimate the fatigue curve, and where the needed deformation response is estimated based on Tanaka's non-proportionality parameter.
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