| 1. |
- Holmberg, Jonas, 1976-, et al.
(författare)
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A detailed investigation of residual stresses after milling Inconel 718 using typical production parameters for assessment of affected depth
- 2020
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Ingår i: Materials Today Communications. - : Elsevier Ltd. - 2352-4928. ; 24
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Tidskriftsartikel (refereegranskat)abstract
- Production of superalloy gas turbine parts involves time consuming milling operations typically performed in a sequence from rough to finish milling. Rough milling using ceramic inserts allows high removal rates but causes severe sub-surface impact. A relatively large allowance is therefore left for subsequent cemented carbide milling. With increased knowledge of the affected depth it will be possible to reduce the machining allowance and increase efficiency of the manufacturing process. Milling Inconel 718 using typical production parameters has been investigated using new and worn ceramic and cemented carbide inserts. Residual stresses in a milled slot were measured by x-ray diffraction. Stresses were measured laterally across the slot and below the surface, to study the depth affected by milling. The most important result from this work is the development of a framework concerning how to evaluate the affected depth for a milling operation. The evaluation of a single milled slot shows great potential for determining the optimum allowance for machining. Our results show that the residual stresses are greatly affected by the ceramic and cemented carbide milling; both regarding depth as well as distribution across the milled slot. It has been shown that it is important to consider that the stresses across a milled slot are the highest in the center of the slot and gradually decrease toward the edges. Different inserts, ceramic and cemented carbide, and tool wear, alter how the stresses are distributed across the slot and the affected depth.
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| 2. |
- Holmberg, Jonas, 1976-
(författare)
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High volumetric machining strategies for superalloy gasturbine components : Comparing conventional and nonconventional machining methods for efficient manufacturing
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a strong industrial driving force to find alternative manufacturing technologies in order to make the production of aero engine components of superalloys even more efficient than it is today. Introducing new and nonconventional machining technologies, as well as enhanced utilisation of today's high volumetric manufacturing, allows taking a leap to increase the material removal rate and the productivity. However, the final goal is to meet there quirements set for today's machined surfaces.The objective with the present work has been performed to show how the conventional, Milling, and the non-conventional machining methods, Abrasive Water Jet Machining, AWJM, Laser Beam Machining, LBM, and Electrical Discharge Machining, EDM, affect the surface integrity. This knowledge can beused to define and optimise different manufacturing alternatives for existing orfuture production.The results show that it is possible to use the rough milling to a greater extent if the impact on residuals stresses and deformation is used when determine the machining allowance. This could have a great impact on the productivity. However, further improvement of the productivity requires an alternative method. For this reason, EDM and AWJM was evaluated and shown to be suitable alternatives to today's manufacturing methods, but both methods require post processing. The results showed that a combination of two post processes is required for addressing issues with residue, topography and residual stresses.The most promising and effective manufacturing strategy would be EDM or AWJM for rough machining followed by post processing either by finish millingor post processing by means of High-Pressure Water Jet Cleaning and shot peening. If EDM and AWJM are to be considered as finish machining operations, further development of the two methods are required.
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| 3. |
- Holmberg, Jonas, 1976-, et al.
(författare)
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Selection of milling strategy based on surface integrity investigations of highly deformed Alloy 718 after ceramic and cemented carbide milling
- 2020
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Ingår i: Journal of Manufacturing Processes. - : Elsevier Ltd. - 1526-6125. ; 58, s. 193-207
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Tidskriftsartikel (refereegranskat)abstract
- High speed milling with ceramic indexable inserts is a current practice for manufacturing of gas turbine components in superalloys since it allows for high material removal rates. Ceramic milling is used for rough milling, which is followed by cemented carbide semi- and finish milling. The tool motion play an important role on the resulting surface integrity. The machining strategy of up or down milling will induce different degree of residual stresses and deformations. Increased knowledge of selecting the machining strategy with lowest impact will promote improved productivity by using ceramic milling to a greater extent based on the affected depth. The main objective in this work has been to correlate the residual stresses and deformations to promote a greater utilization of ceramic milling while still producing surfaces with acceptable properties. Prior investigations have shown that ceramic milling induce very high tensile stresses in the surface, exceeding the material's nominal yield strength. A second objective has been to explain these stress levels by thorough investigations of the deformation after milling. In this study, milling tests with new and worn ceramic and cemented carbide inserts have been performed in Alloy 718. The topography, residual stresses, deformation and hardness have been investigated for up, centre and down milling. Residual stress measurements were performed using X-ray diffraction, followed by evaluation of hardness and deformation, using hardness testing, light optical microscopy as well as electron back scattering diffraction (EBSD). These results have been used to determine an appropriate milling strategy based on lowest possible impact in respect to residual stresses and deformation. The results show a high degree of deformation after milling that differs for the up, centre and down milling. Based on these results, it is shown that up milling is preferable for new inserts but as the inserts wear out, down milling becomes more suitable since a lower degree of deformation and residual stress impact was observed. EBSD and hardness testing showed that the milling, especially ceramic milling, caused severe deformation of the surfaces resulting in grain refinement to a nano-crystalline level. This is most likely the explanation for the prevalence of the high tensile stresses without distorting or causing failure. © 2020 The Authors
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| 4. |
- Tamil Alagan, Nageswaran, 1990-, et al.
(författare)
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Coolant boiling and cavitation wear : a new tool wear mechanism on WC tools in machining Alloy 718 with high-pressure coolant
- 2020
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 452-453
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, research interest in liquid coolant media applied to the tool–workpiece interface (the tertiary shear zone) has grown considerably. In particular, attention has increased for work where the media has been applied under high-pressure. This is most likely triggered by the positive results reported on similar applications, but with coolant media directed towards the rake face of the cutting tool (the secondary shear zone). The most typical applications have not surprisingly been related to the machining of Heat Resistant Super Alloys (HRSA) or other “difficult to machine” alloys where the main intention has been to extend tool life and improve surface finish through reduced shear zone temperatures. Concurrently, these achievements have revealed a knowledge gap and unlocked a new research area in understanding the effects and influences of coolant media applied on super-heated surfaces under high-pressure conditions. The aim of this study is to investigate the “coolant boiling and cavitation” phenomena that emerges during the application of coolant under high-pressure to the flank face of an uncoated WC tool while turning Alloy 718. The experimental campaign was conducted in three aspects: varying flank (coolant media) pressure; varying spiral cutting length (SCL); and varying cutting speed. The results revealed that the location and size of the coolant-boiling region correlated with flank wear, coolant pressure and vapour pressure of the coolant at the investigated pressure levels. Further, the results showed that coolant applied with a lower pressure than the vapour pressure of the coolant itself caused the “Leidenfrost” effect. This then acts as a coolant media barrier and effectively reduces the heat transport from the cutting zone. Further, erosion pits were observed on small areas of the cutting tool, resembling the typical signs of cavitation (usually found in much different applications such as pumps and propellers). The discovered wear mechanism denoted as “Cavitation Wear” was used as base for the discussion aimed to deepen the understanding of the conditions close to the sliding interface between the tool and the workpiece. Even though “Cavitation Wear” has been widely reported in hydraulic systems like pumps and water turbines, it is a new phenomenon to be seen on cutting tools while using high-pressure flank cooling. © 2020 The Authors
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| 5. |
- Werke, Mats, et al.
(författare)
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Minimising machining distortions with support from adaptive fixtures and adjustment of the NC-code
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim was to develop and test an adaptive fixture concept with a modified hydraulic chuck from System 3R. The conclusion is that the chuck may be a good concept for adjusting machining distortions but further development is recommended. Further, a literature survey concerning responsive fixtures for CNC-machining is presented. In addition, a virtual approach for compensation of machining distortions was tested. A framework of LS-Dyna algorithms for springback compensation after sheet metal forming was tested on a use case. The study indicates that the concept can be applied for NC-code optimisation on solid geometries with a complex manufacturing process chain composed of e.g. forging, heat treatment and proceeding machining processes. The deformations after machining were notably reduced in this numerical survey. Also virtual concepts for calculation of material removal strategies and clamping force analysis is suggested and demonstrated. The project was carried out with the support of physical experiments with an adaptive fixture and simulation with FEM based on the contour method.
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