| 1. |
- Jarfors, Anders E.W. 1963-, et al.
(author)
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On the Use of Conformal Cooling in High-Pressure Die-Casting and Semisolid Casting
- 2021
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In: Technologies. - : MDPI. - 2227-7080. ; 9:2
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Journal article (peer-reviewed)abstract
- Today, tool life in high pressure die casting (HPDC) is of growing interest. A common agreement is that die life is primarily decided by the thermal load and temperature gradients in the die materials. Conformal cooling with the growth of additive manufacturing has raised interest as a means of extending die life. In the current paper, conformal cooling channels’ performance and effect on the thermal cycle in high-pressure die casting and rheocasting are investigated for conventional HPDC and semisolid processing. It was found that conformal cooling aids die temperature reduction, and the use of die spray may be reduced and support the die-life extension. For the die filling, the increased temperature was possibly counterproductive. Instead, it was found that the main focus for conformal cooling should be focused to manage temperature around the in-let bushing and possibly the runner system. Due to the possible higher inlet pressures for semisolid casting, particular benefits could be seen.
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| 2. |
- Yuan, Miwen, 1990, et al.
(author)
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A Case Study for a Worn Tool Steel in the Hot Stamping Process
- 2023
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In: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 22, s. 1065-1075
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Journal article (peer-reviewed)abstract
- A good understanding of failure mechanisms can help us improve the lifetime of the dies. This paper presents a case study investigating the wear behavior of a QRO90 die insert utilized for stamping uncoated boron-alloyed high-strength steel sheets. Topography and microstructure were characterized by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), hardness measurement and X-ray photoelectron spectroscopy (XPS). Severe galling due to accumulated layers transferred from the boron-alloyed steel workpieces occurred on the die surface. Material softening was detected in the sublayer of the tool steel (up to ∼200 μm). In addition, white layers with a in a thickness of 1-2 μm were frequently observed on the surface of the round corner of the tool. The main wear mechanisms are discussed. Galling caused by surface softening and the spallation of white layers are considered to be the primary wear mechanisms for the tool.
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| 3. |
- Yuan, Miwen, 1990, et al.
(author)
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Characteristics of a modified H13 hot-work tool steel fabricated by means of laser beam powder bed fusion
- 2022
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In: Materials Science & Engineering. - : Elsevier Ltd. - 0921-5093 .- 1873-4936. ; 831
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Journal article (peer-reviewed)abstract
- In the present study, a modified H13 hot-work tool steel (M-H13) was fabricated by laser beam powder bed fusion (LB-PBF). The effect of two types of post processing, direct tempering from as-built condition (DT) and conventional quenching followed by tempering (QT), on the microstructure and mechanical properties was evaluated. The typical microstructure in QT condition was tempered martensite with carbides along lath boundaries. In DT condition, melt pool boundaries and cellular structure from as-built condition were still observed. While comparable tensile properties and hardness were obtained, DT samples exhibited significantly lower impact toughness compared to QT samples. This was attributed to the difference in work hardening ability and strain rate sensitivity originating from different microstructures obtained under these two heat treatment conditions. The study was also focused on the softening behavior and the correlation with the microstructure of the two post treatments at the elevated temperatures. It was found that the DT samples showed lower thermal softening compared to QT samples. The evolution of carbides was discussed based on the microanalysis results and the JMatPro simulation. © 2021 The Authors
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| 4. |
- Yuan, Miwen, 1990, et al.
(author)
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Softening Behavior of a Cold Work Tool Steel and High-Boron Tool Steel Fabricated by Directed Energy Deposition
- 2024
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In: Steel Research International. - 1869-344X .- 1611-3683. ; 95:3
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Journal article (peer-reviewed)abstract
- Prolonging the life of hot stamping dies in the automotive industry is challenging. Surface modification is an effective way to improve the durability of the dies. In this study, two tool steel grades, one cold work tool steel (V4E) and one high-boron tool steel (HBS), are deposited on a tool steel substrate using directed energy deposition, followed by tempering. Softening behavior at high temperatures of 550 and 600 °C is investigated. In the key findings, it is revealed that both steels exhibit remarkable hardness, surpassing the substrate even after extended exposure to high temperatures. HBS shows excellent softening resistance in terms of hardness at 550 °C but experiences a significant drop at 600 °C. V4E demonstrates an overall superior softening resistance due to its thermal stable MC (M represents metal) carbides and the relatively stable dislocation density. Microstructural analysis highlights some unique features, such as borides in HBS and dendritic structures in V4E. In this study, the correlation between microstructure characteristics and hardness evolution is revealed, providing some insights into how these materials resist softening to enhance the longevity and performance of hot stamping dies.
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| 5. |
- Yuan, Miwen, 1990, et al.
(author)
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Study of defects in directed energy deposited Vanadis 4 Extra tool steel
- 2022
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In: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 76, s. 419-427
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Journal article (peer-reviewed)abstract
- A cold work tool steel with varied number of layers was deposited on a substrate of hot work tool steel for hard-facing by directed energy deposition technique. This study deals with the defects and microstructure in the as-cladded tool steels. Defects, including pores and cracks, were found in the deposited zone, the number of which increased with the building height or number of layers deposited. Large irregular pores were mainly located at the lower regions of the deposited layers. The formation of this type of pores was attributed to the segregation of alloy elements on the pore surface and insufficient heat input. Non-equilibrium eutectic microstructure was a characteristic feature in the regions adjacent to the pores. Cracking, on the other hand, tended to occur in the upper part of the deposited layers. Two important contributing factors were identified for cracking. The first one was the microstructural gradient, which was modified from fine cellular dendrite to columnar dendrite when moving from the bottom to the top deposited layer. Second, the deposited cold work tool steel exhibited a relatively large temperature range of solidification, as simulated by Thermocalc software, leading to high sensitivity to hot cracking.
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