Influence of Die Materials on the Microstructural Evolution of HSS Sheets in Hot Stamping

2011 ◽  
Vol 473 ◽  
pp. 201-208 ◽  
Author(s):  
Andrea Ghiotti ◽  
Stefania Bruschi ◽  
Daniele Pellegrini
Keyword(s):  
Hot Stamping ◽  
Sheet Thickness ◽  
High Strength Steels ◽  
High Strength ◽  
Process Conditions ◽  
Main Process ◽  
Metal Sheets ◽  
Die Materials ◽  
Set Up ◽  
Tools Wear

Hot stamping of High Strength Steels sheets is gaining more and more popularity, particularly in the automotive industry, due to the sound microstructures achieved at the end of the process. The significant improvement of the mechanical properties achieved in the process enables to reduce the initial sheet thickness in favour of cost and fuel consumption reduction. However, a martensitic microstructure implies significant drawbacks in final trimming and cutting operations, which becomes more difficult and expensive due to tools wear and high blanking forces. This paper aims at investigating the performances of non-metallic materials to be used in heated dies, in order to inhibit the martensite formation by locally reducing the sheet cooling rate. To analyze the influence of the main process parameters, a new experimental set-up was designed and developed in a laboratory environment that allow applying controlled pressure and temperatures to HSS metal sheets. An analytical model was set-up in order to evaluate the influence of process conditions on the cooling profiles in different areas of the specimen. Accordingly, experiments were carried out to investigate the material behaviour when cooled in the different conditions. The experimentally acquired temperatures were analyzed and evaluated together with hardness measurements of metal sheets in order to assess the feasibility of the proposed approach in producing microstructurally-tailored components.

Investigation on the Numerical Simulation of Hot Stamping of Advanced High Strength Steels

2011 ◽  
Vol 189-193 ◽  
pp. 2144-2147 ◽  
Author(s):  
Li Min Wang ◽  
Tian Rui Zhou ◽  
Li Juan Wang ◽  
Xiao Ling Yang
Keyword(s):  
Finite Element ◽  
Hot Stamping ◽  
High Strength Steels ◽  
High Strength ◽  
Material Model ◽  
Element Analysis ◽  
Advanced High Strength Steels ◽  
Element Simulation ◽  
The Finite Element Analysis ◽  
Set Up

Hot stamping represents an innovative manufacturing process for forming of advanced high strength steels, implying a sheet at austenite temperature being rapidly cooled down and formed into a die at the same time (quenching). This affords the opportunity to manufacture components with complex geometric shapes, high strength and a minimum of springback which currently find applications as crash relevant components in the automotive industry. With regard to the numerical modeling of the process, the knowledge of thermal and thermo-mechanical properties of the material is required. The material model under hot stamping condition of advanced high strength steel should be set up. The Finite Element Analysis is an essential precondition for a good process design including all process parameters. This paper presents the finite element simulation of a hot stamping process and describes a number of procedures for the simulation of hot stamping. In addition, the development direction is pointed out at the end of this paper.

scholarly journals Forming a Flanged Hole When Quenching Press-Hardened Steel for Mechanical Fastening

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 721
Author(s):  
Yongjun Jeon ◽  
Hyunseok Choi ◽  
Dongearn Kim
Keyword(s):  
Hot Stamping ◽  
High Strength Steels ◽  
High Strength ◽  
Expansion Ratio ◽  
Hardened Steel ◽  
Continuous Increase ◽  
Pilot Hole ◽  
Experimental Apparatus ◽  
Mechanical Fastening ◽  
Hole Flanging

The recent stringent regulations on vehicle safety and reducing CO2 emissions have led to a continuous increase in the application of press-hardened steel (PHS) in automobiles. Similar to other high-strength steels, assembling PHS components using the common welding techniques employed in automotive production lines is significantly difficult because of the surface coating layers and the additives within. This difficulty in post-processing, attributed to its high strength, also limits the mechanical fastening of PHS components. Therefore, this study aims to develop a process for forming a structure enabling mechanical fastening by sequentially applying piercing and hole-flanging operations during the hot stamping process. Our experimental apparatus was designed to perform the hole-flanging operation after the piercing operation within a single stroke at a specific temperature during the quenching process of PHS. At high temperatures of 440 °C or higher, the hole-flanging process was conducted in a direction opposite to that of the piercing operation for creating the pilot hole. An extruded collar with a height of 8.0 mm and a diameter of 17.5 mm was achieved, which is hole expansion ratio(HER) of 82.5%.

scholarly journals Tribological Behavior of Laser Textured Hot Stamping Dies

2016 ◽  
Vol 2016 ◽  
pp. 1-15 ◽  
Author(s):  
Andre Shihomatsu ◽  
Sergio Tonini Button ◽  
Iris Bento da Silva
Keyword(s):  
Surface Topography ◽  
High Pressures ◽  
Hot Stamping ◽  
High Strength Steels ◽  
High Strength ◽  
Experimental Tests ◽  
Textured Surface ◽  
Laser Texturing ◽  
Stamping Dies ◽  
Before And After

Hot stamping of high strength steels has been continuously developed in the automotive industry to improve mechanical properties and surface quality of stamped components. One of the main challenges faced by researchers and technicians is to improve stamping dies lifetime by reducing the wear caused by high pressures and temperatures present during the process. This paper analyzes the laser texturing of hot stamping dies and discusses how different surfaces textures influence the lubrication and wear mechanisms. To this purpose, experimental tests and numerical simulation were carried out to define the die region to be texturized and to characterize the textured surface topography before and after hot stamping tests with a 3D surface profilometer and scanning electron microscopy. Results showed that laser texturing influences the lubrication at the interface die-hot sheet and improves die lifetime. In this work, the best texture presented dimples with the highest diameter, depth, and spacing, with the surface topography and dimples morphology practically preserved after the hot stamping tests.

Expulsion Intensity Monitoring and Modeling in Resistance Spot Welding Based on Electrode Displacement Signals

2020 ◽  
Author(s):  
Yu-Jun Xia ◽  
Yan Shen ◽  
Lang Zhou ◽  
Yong-Bing Li
Keyword(s):  
Resistance Spot Welding ◽  
Spot Welding ◽  
Low Carbon Steel ◽  
Sheet Thickness ◽  
High Strength Steels ◽  
High Strength ◽  
Material Strength ◽  
Low Carbon ◽  
Resistance Spot ◽  
Electrode Displacement

Abstract Weld expulsion is one of the most common welding defects during resistance spot welding (RSW) process especially for high strength steels (HSS). In order to control and eventually eliminate weld expulsion in production, accurate assessment of the expulsion severity should be the first step and is urgently required. Among the existing methods, real-time monitoring of RSW-related process signals has become a promising approach to actualize the online evaluation of weld expulsion. However, the inherent correlation between the process signals and the expulsion intensity is still unclear. In this work, a commonly used process signal, namely the electrode displacement and its instantaneous behavior when expulsion occurs are systematically studied. Based upon experiments with various electrodes and workpieces, a nonlinear relation between the weight of expelled metal and the sudden displacement drop accompanied by the occurrence of weld expulsion is observed, which is mainly influenced by electrode tip geometry but not by material strength or sheet thickness. The intrinsic relationship between this specific signal feature and the magnitude of expulsion is further explored through geometrical analysis, and a modified analytical model for online expulsion evaluation is finally proposed. It is shown that the improved model could be applied to domed electrodes with different tip geometries and varying workpieces ranging from low carbon steel to HSS. The error of expulsion estimation could be limited within ±20.4 mg (±2σ) at a 95% confidence level. This study may contribute to the online control of weld expulsion to the minimum level.

scholarly journals Parametric Investigation of Effect of Abnormal Process Conditions on Self-Piercing Riveting

2020 ◽  
Vol 10 (7) ◽  
pp. 2520 ◽  
Author(s):  
Taek-Eon Jeong ◽  
Dong-Hyuck Kam ◽  
Cheolhee Kim
Keyword(s):  
Process Parameters ◽  
Dissimilar Materials ◽  
High Strength ◽  
Process Conditions ◽  
Al Alloy ◽  
Main Process ◽  
Cross Sectional ◽  
Practical Applications ◽  
Parametric Investigation ◽  
Offset Distance

Self-piercing riveting (SPR) is one of the mechanical joining processes, and its application to Al/Fe dissimilar materials combination, which is hard to weld, is expanding in the automotive industry. The main process parameters in SPR are types of rivet and die, setting force, and rivet setting speed. Previously, the relationship between the main process parameters and output parameters such as cross-sectional characteristics and joint strength has been studied to optimize the SPR process. In practical applications, there are unexpected and abnormal process conditions such as poor fit-up, angular misalignment, edge offset distance, and inaccurate setting and pre-clamping forces, and their effects on the joining quality have not been discussed. In this study, parametric investigation was performed using an experimental design on SPR joints for 1 mm-thick high strength steel (590 DP) and 2 mm-thick Al alloy (Al5052-H32). The main effect of each level of the abnormal process parameters on the output parameters was statistically investigated, and the analysis of variance was performed for each abnormal process parameter. In the range of abnormal process conditions applied, the set force was the most significant factor affecting the output parameters, and the effect of pre-clamping force on the output parameters was the least significant.

Characterization of Heat Transfer Coefficients of Tool Materials and Tool Coatings for Hot Stamping of Boron-Manganese Steels

2010 ◽  
Vol 438 ◽  
pp. 81-88 ◽  
Author(s):  
Michael Wieland ◽  
Marion Merklein
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Hot Stamping ◽  
High Strength Steels ◽  
High Strength ◽  
Tool Steels ◽  
Transfer Coefficients ◽  
Element Analysis ◽  
Coated Tool

One characteristic of hot stamping of ultra high strength steels is the high wear rate of the used tools which leads to shorter tool life. Coatings improving wear resistance can increase the lifetime of the used tools but process relevant data such as the heat transfer capability of coated tool steels are missing. Within this paper the heat transfer capabilities of coated tool steels for the hot stamping processes are determined. Therefore different coating systems based on AlCrN are applied on the tool steels and the pressure dependent heat transfer coefficient is determined using process relevant conditions. As semi-finished blank the hot stamping steel 22MnB5 with an aluminum-silicon pre-coating is used. With respect to a finite element analysis of the forming operation of the hot stamping process the heat transfer coefficient represents an important input data for the process layout.

FE Simulation Models for Hot Stamping an Automobile Component with Tailor-Welded High-Strength Steels

2016 ◽  
Vol 25 (5) ◽  
pp. 1709-1721 ◽  
Author(s):  
Bingtao Tang ◽  
Qiaoling Wang ◽  
Zhaohui Wei ◽  
Xianju Meng ◽  
Zhengjun Yuan
Keyword(s):  
Fe Simulation ◽  
Hot Stamping ◽  
High Strength Steels ◽  
Simulation Models ◽  
High Strength
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