Special Issue "Hot, Warm and Cold Stamping of High Strength Steel and Aluminium Alloy Parts"

A special issue of Journal of Manufacturing and Materials Processing (ISSN 2504-4494).

Deadline for manuscript submissions: closed (30 June 2020).

Special Issue Editors

Prof. Dr. Ken-ichiro Mori
Website SciProfiles
Guest Editor
Department of Mechanical Engineering, Toyohashi University of Technology, Tempaku, Toyohashi, Aichi 400-8580, Japan
Interests: sheet metal forming; hot stamping; forging; joining; 3D printing
Prof. Dr. Tomoyoshi Maeno
Website
Guest Editor
Division of Systems Research, Faculty of Engineering, Yokohama National University, Yokohama, Kanagawa, 240-8501, Japan
Interests: metal forming

Special Issue Information

Dear Colleagues,

To improve the fuel efficiency of automobiles, the use of lightweight materials increases. High strength steel sheets have the advantages of low costs and a huge amount of production. The strength of the steel sheets increases, and that of ultra-high strength steel sheets exceeds 1 GPa. The application of the ultra-high strength steel sheets to body-in-white widely expands with rise in crash safety standards of automobiles, and these sheets are conventionally cold-stamped. To improve the drawbacks for the high strength steel sheets, warm stamping processes are tried. In hot stamping of quenchable steel sheets, high strength steel parts having a tensile strength of 1500 MPa can be produced under a low forming load. On the other hand, for high strength aluminum alloy sheets, not only cold stamping but also warm and hot stamping are attractive due to the improvement of springback and formability.

Prof. Dr. Ken-ichiro Mori
Prof. Dr. Tomoyoshi Maeno
Guest Editors

Manuscript Submission Information

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Published Papers (8 papers)

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Research

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Open AccessArticle
Minimisation of Heating Time for Full Hardening in Hot Stamping Using Direct Resistance Heating
J. Manuf. Mater. Process. 2020, 4(3), 80; https://doi.org/10.3390/jmmp4030080 - 07 Aug 2020
Abstract
To obtain enough hardness of the die-quenched products after hot stamping using direct resistance heating, the effects of the electrifying condition and initial microstructure of the quenchable steel sheet on hardness were examined in a hot bending experiment. The steel sheet was heated [...] Read more.
To obtain enough hardness of the die-quenched products after hot stamping using direct resistance heating, the effects of the electrifying condition and initial microstructure of the quenchable steel sheet on hardness were examined in a hot bending experiment. The steel sheet was heated up to 900 °C in 3 to 10 s. The required heating time was shortened by normalising heat treatment due to the fine grain size of the sheet. The standard deviation of the hardness of the sheet heated to 900 °C in 3.2 s without temperature holding at the austenitising temperature was 12 HV, whereas the deviation reduced to 5 HV for temperature holding at the austenitising temperature of 3 s. Full article
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Open AccessCommunication
Hemming with Pre-Bent Inner Sheet for Joining Ultra-High Strength Steel Sheets of Automobile Parts
J. Manuf. Mater. Process. 2020, 4(3), 77; https://doi.org/10.3390/jmmp4030077 - 25 Jul 2020
Abstract
In order to join two ultra-high strength steel sheets with low ductility for automobile parts, a joining process by hemming with a pre-bent inner sheet was developed. In this joining, the pre-bent inner sheet instead of the conventional flat inner sheet was used [...] Read more.
In order to join two ultra-high strength steel sheets with low ductility for automobile parts, a joining process by hemming with a pre-bent inner sheet was developed. In this joining, the pre-bent inner sheet instead of the conventional flat inner sheet was used to relax the deformation concentration of the outer sheet. Although 780 MPa steel sheets were joined without the pre-bent inner sheet, a fracture in the outer sheet occurred in joining the 980 MPa sheets due to the low ductility of the sheets. The 980 MPa and 1180 MPa sheets were successfully joined by hemming with the pre-bent inner sheet. In this process, the deformation of the upper sheet was relaxed by contacting with the inner sheet, and then the strain on the outer surface reduced. Although softening around a weld nugget occurred by heating in the conventional welded joint, work-hardening occurred in the hemmed joint. The joint strength was investigated and then the peel strength of the hemmed sheets was about a half of the welded one. It was found that the hemming process with the pre-bent inner sheet was effective for joining ultra-high strength steel sheets with low ductility. Full article
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Open AccessArticle
Investigation and Modeling of the Preheating Effects on Precipitation and Hot Flow Behavior for Forming High Strength AA7075 at Elevated Temperatures
J. Manuf. Mater. Process. 2020, 4(3), 76; https://doi.org/10.3390/jmmp4030076 - 23 Jul 2020
Cited by 1
Abstract
Preheating is the first but critical step for hot stamping high strength precipitate hardened aluminum alloys. To thoroughly understand the effects of preheating conditions—i.e., preheating rate and heating temperature—on the strength and hot deformation of aluminum alloys, a series of thermal–mechanical tests was [...] Read more.
Preheating is the first but critical step for hot stamping high strength precipitate hardened aluminum alloys. To thoroughly understand the effects of preheating conditions—i.e., preheating rate and heating temperature—on the strength and hot deformation of aluminum alloys, a series of thermal–mechanical tests was performed to determine the post-hardness evolution and hot flow behaviors. Typical microstructures with different preheating conditions were also observed through transmission electron microscopy (TEM), with which a unified model of both hot flow and strength based on key microstructural variables was developed, enabling the successful prediction of macroscopic properties using different preheating strategies. The results have shown that for high strength AA7075 at the T6 condition, the dominant mechanism of precipitate evolution with increasing temperature is the coarsening of precipitates first, followed by dissolution when they exceed a critical temperature. A higher heating rate results in a slower coarsening and a relatively higher strength level. In addition, the flow stress of hot deformation is also higher using a quick heating rate, with more significant softening and reduced ductility. Full article
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Open AccessArticle
Localized Laser Dispersing of Titanium-Based Particles for Improving the Tribological Performance of Hot Stamping Tools
J. Manuf. Mater. Process. 2020, 4(3), 68; https://doi.org/10.3390/jmmp4030068 - 08 Jul 2020
Abstract
Within the scope of this work, a new surface engineering technology named laser implantation has been investigated, in order to improve the tribological performance of hot stamping tools. This technique is based on manufacturing highly wear-resistant, separated, and elevated microfeatures by embedding hard [...] Read more.
Within the scope of this work, a new surface engineering technology named laser implantation has been investigated, in order to improve the tribological performance of hot stamping tools. This technique is based on manufacturing highly wear-resistant, separated, and elevated microfeatures by embedding hard ceramic particles into the tool surface via pulsed laser radiation. Hence, the topography and material properties of the tool are modified, which influences the thermal and tribological interactions at the blank-die interface. To verify these assumptions and to clarify the cause–effect relations, different titanium-based particles (TiB2, TiC, TiN) were laser-implanted and subsequently analyzed regarding to their geometrical shape and mechanical properties. Afterwards, quenching tests as well as tribological experiments were carried out by using titanium-diboride as the most promising implantation material for reducing the tribological load due to high hardness value of the generated implants. Compared to conventional tooling systems, the modified tool surfaces revealed a significantly higher wear resistance as well as reduced friction forces while offering the possibility to adjust the thermal interactions at the blank-die interface. Based on these results, a tailored tool surface modification can be pursued in future research work, in order to enhance the effectiveness of the hot stamping technology. Full article
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Open AccessArticle
Characterization of Thermomechanical Boundary Conditions of a Martensitic Steel for a FAST Forming Process
J. Manuf. Mater. Process. 2020, 4(2), 57; https://doi.org/10.3390/jmmp4020057 - 20 Jun 2020
Abstract
The present work characterized and modelled the interfacial heat transfer coefficient and friction coefficient of a non-alloy martensitic steel, for a novel Fast light Alloy Stamping Technology (FAST) process. These models were validated through temperature evolution, thickness distribution and springback measurements on experimentally [...] Read more.
The present work characterized and modelled the interfacial heat transfer coefficient and friction coefficient of a non-alloy martensitic steel, for a novel Fast light Alloy Stamping Technology (FAST) process. These models were validated through temperature evolution, thickness distribution and springback measurements on experimentally formed demonstrator components, which were conducted on a pilot production line and showed close agreement, with less than 10% variation from experimental results. The developed models and finite element simulations presented in this work demonstrate that non-isothermal processes can be precisely simulated with implementation of the accurate thermomechanical boundary conditions. Full article
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Open AccessCommunication
Hot Gas Forming of Aluminum Alloy Tubes Using Flame Heating
J. Manuf. Mater. Process. 2020, 4(2), 56; https://doi.org/10.3390/jmmp4020056 - 16 Jun 2020
Cited by 1
Abstract
Hot metal gas forming (HMGF) is a desirable way for the automotive industry to produce complex metallic parts with poor formability, such as aluminum alloys. A simple hot gas forming method was developed to form aluminum alloy tubes using flame heating. An aluminum [...] Read more.
Hot metal gas forming (HMGF) is a desirable way for the automotive industry to produce complex metallic parts with poor formability, such as aluminum alloys. A simple hot gas forming method was developed to form aluminum alloy tubes using flame heating. An aluminum alloy tube was heated by a flame torch while the tube was rotated and compressed using a lathe machine and simultaneously pressurized with a constant air pressure. The effects of the internal pressure and axial feeding on expansion and wall thickness distribution were examined. The results showed that the proposed gas forming method was effective for forming aluminum alloy tubes. It was also indicated that axial feeding is a vital parameter to prevent reductions in wall thickness by supplying the material flow during the forming process. Full article
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Open AccessArticle
Evaluation of Prediction Accuracy for Anisotropic Yield Functions Using Cruciform Hole Expansion Test
J. Manuf. Mater. Process. 2020, 4(2), 43; https://doi.org/10.3390/jmmp4020043 - 03 May 2020
Cited by 1
Abstract
To evaluate the prediction accuracy of the anisotropic yield function, we propose an original cruciform hole expansion test. Displacements on two axes were applied to the cruciform specimens with a hole in the center. The thickness strain in the region near the hole [...] Read more.
To evaluate the prediction accuracy of the anisotropic yield function, we propose an original cruciform hole expansion test. Displacements on two axes were applied to the cruciform specimens with a hole in the center. The thickness strain in the region near the hole was compared to the simulation results. Because this forming test is free of friction and bending, it is an appropriate method to assess the anisotropic yield function without the influences of friction or the Bauschinger effect, or the need to consider the stress-strain curve in high-strain region. Hill1948, YLD2000-2D, and spline yield function which is an improved version of the Vegter model were selected, and 6000 series aluminum alloy sheets (A6116-T4) were used in this study. The parameter identification method of the spline yield function also proposed in this paper using the pseudo plane strain tensile test and optimization software. As a result, the spline yield function has better predictive accuracy than the conventional anisotropic yield functions Hill1948 and YLD2000-2D. Full article
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Review

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Open AccessReview
Review of Shearing Processes of High Strength Steel Sheets
J. Manuf. Mater. Process. 2020, 4(2), 54; https://doi.org/10.3390/jmmp4020054 - 07 Jun 2020
Cited by 1
Abstract
Shearing processes of high strength steel sheets increasingly applied to lightweight automobile parts were reviewed. With the increase in strength of the high strength steel sheets, shearing operations become hard. First, the sheared edge quality in shearing of high strength steel sheets and [...] Read more.
Shearing processes of high strength steel sheets increasingly applied to lightweight automobile parts were reviewed. With the increase in strength of the high strength steel sheets, shearing operations become hard. First, the sheared edge quality in shearing of high strength steel sheets and the effects on the formability and fatigue strength were shown. Next, ironing processes with a taper punch and a punched slug, a slight clearance punching with a punch having a small round corner and a thickening process of the sheared edge were explained as processes for improving the sheared edge quality. Finally, hydrogen-induced delayed fractures of cold-sheared ultra-high strength steel sheets and of hot-trimmed parts were evaluated. Full article
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