| 1. |
- Cedergren, Stefan, 1982, et al.
(författare)
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The effects of grain size and feed rate on notch wear and burr formation in wrought Alloy 718
- 2013
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Ingår i: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 67:5-8, s. 1501-1507
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Tidskriftsartikel (refereegranskat)abstract
- The effect of two different workpiece material grain sizes, 16 and 127 μm, on the depth-of-cut notch wear, chip morphology, and burr formation was studied in a turning operation. A material from the same batch of wrought superalloy Alloy 718 was heat-treated to achieve the two microstructures. The machining was performed at two feed rates, 0.1 and 0.2 mm/revolution. Uncoated cemented carbide tools were used. Both grain size and feed rate were found to influence the chip morphology and the sideflow which were also associated with both the notch wear and the burr formation. The effect of the grain size on the notch wear was larger than that of the feed rate under the tested conditions, with larger grains being more detrimental than smaller ones.
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| 2. |
- Cedergren, Stefan, 1982, et al.
(författare)
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Influence of deformed surface layer when machining wrought alloy 718 in an annealed and in a pre-strained condition
- 2014
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Ingår i: 8th International Symposium on Superalloy 718 and Derivatives 2014; Pittsburgh; United States; 28 September 2014 through 1 October 2014. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781634396424 ; , s. 263-271
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Konferensbidrag (refereegranskat)abstract
- Superalloys are difficult to cut, mainly due to their preserved strength at elevated temperatures and their exceptional work hardening, where the latter results in a deformed layer on the machined surface. The thickness and degree of deformation of this layer depends on several parameters, such as cutting speed, uncut chip thickness, tool material and edge geometry. This layer enters the cutting zone of subsequent revolutions in turning or in milling. Under certain circumstances, as when the uncut chip thickness is small, all deformation at subsequent machining takes place within the deformed layer. The same phenomenon may occur at the outer edge of the cutting zone where the unrestricted material flow leads to burr formation. The deformed layer at the outer edge is suggested as the cause for notch wear often found when machining Superalloys. In this paper the effect of deformed layer on machining is examined through controlled experiments on the material in to different states of strain; in the annealed state without any remaining strain and with a substantial amount introduced by tensile straining. The results showed that cutting forces were reduced when pre-straining the material. Tool wear was similar in both materials, with large scatter due to built-up edge formation.
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| 3. |
- Cedergren, Stefan, 1982
(författare)
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Influence of Material Variations on Machinability - Machining Difficult-to-Machine Alloys
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study is to investigate the effect of work material variations on machinability. Improved knowledge in this respect supports the development of sustainable production both from resource and economical points of view.The properties of work materials vary greatly depending on how they were manufactured. Castings generally have coarse microstructure compared to wrought material, where the added thermo-mechanical processing steps in the latter produce finer microstructure. Local within-part variations in microstructure are found in both castings and wrought material. In cast material this varies due to factors such as undercooling and cooling rate. In wrought material local variations in process parameters, such as deformation and temperature produce different microstructures.Within-process variations during machining also exist, where surfaces deformed during cutting are left to subsequent cuts. The same occurs when machining sheet metal, where degree of deformation also may vary due to local variations in strain. In this work differences in both microstructure and deformation has been investigated for three work materials; nickel-iron based Alloy 718, titanium alloy Ti-6Al-4V and the stainless steel 316L. It was found that coarse microstructures result in anisotropic chip formation, where chips had a non-periodic serrated appearance in both Alloy 718 and Ti-6Al-4V. Both alloys are known to produce continuous chips at low feed rates and cutting speeds, with a transition to serrated chips as these parameters are increased, due to instability in the cutting process. The serrations due to this instability show a more periodic appearance, clearly distinguishable to the serrations due to anisotropy.In Alloy 718 coarse microstructure was also found to produce large burrs, that were continuously built-up during machining, as well as increase notch wear at the depth-of-cut on the cutting tool. In Ti-6Al-4V the anisotropic chip formation behavior found in coarse microstructure was connected to orientations of alpha colonies, i.e. where some orientations produce highly localized deformation and others were homogeneously deformed at all feed rates and speeds investigated. Chip breakability was found to increase with size of alpha colonies, aided by the colonies that had highly localized deformation. The influence of the less periodic serrations found in coarse microstructure was also found to produce vibrations over a wider cutting speed range compared to the periodic serrations in finer microstructures.In both Alloy 718 and stainless steel 316L cutting forces were reduced when the work material had been deformed prior to machining, compared to annealed material.
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| 4. |
- Cedergren, Stefan, 1982
(författare)
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Influence of Microstructure on Chip Formation - Machining Aero Engine Alloys
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aero engine materials such as nickel-iron and titanium based alloys are known to be very difficult to machine. They are also known to produce shear-localized chips; a type of chip which is associated with both an increase of the tool wear and the vibration levels during machining. Robust machining operations are crucial for maintaining high productivity in the machining shop and variations in the actual work material, e.g. between batches or when the material supplier is changed, are known causes for unwanted disturbances. It goes without saying that a deeper understanding of how the work material microstructure interacts with the machining operation will lead to more robust processes. The aim of this work was to increase the understanding of how the microstructure of work material influences shear-localized chip formation. This was studied through transverse and orthogonal turning in two alloys, the superalloy Alloy 718 and the titanium alloy Ti-6Al-4V, for both of which the microstructure was varied by means of heat treatment. It was found that if the microstructures were finer than the uncut chip thickness, the machining behaviour was isotropic with a gradual increase of the shear-localization in chips when the cutting speed was increased in Alloy 718, and when feed rate was increased in Ti-6Al-4V. However, when the size of the microstructural constituents was increased through heat treatments and to be in the same order of magnitude as the chip thickness, anisotropic effects were found. The result was serrated chips at all cutting speeds in the case of Alloy 718, due to anisotropic deformation of grains at low speeds and with an increased influence of shear localization at higher speeds. The amount of shear localization was found to vary with the crystallographic orientation. In Ti-6Al-4V the orientation of the lamellar structure in the coarse Widmanstätten microstructure type affected the shear localization and this anisotropy could explain the presence of large lamellae in chips even at low feed rate.
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| 5. |
- Cedergren, Stefan, 1982, et al.
(författare)
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Influence of work material microstructure on vibrations when machining cast Ti-6Al-4V
- 2016
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Ingår i: The International Journal of Advanced Manufacturing Technology. - London : Springer. - 0268-3768 .- 1433-3015. ; 84:9-12, s. 2277-2291
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Tidskriftsartikel (refereegranskat)abstract
- Titanium alloys are known to produce shear-localized chips during machining, resulting in cyclic variations in cutting forces which in turn could cause severe problems with vibrations. However, at low cutting speeds and feed rates, continuous chips are formed, with an increase in both parameters favoring the transition to shear-localized chips. This transition is affected by work material microstructure, where a coarse microstructure gives anisotropic effects, e.g., when the size of alpha colonies is on the same order of magnitude as the primary cutting zone. The change in chip morphology with an increase in cutting parameters will then be dependent on the orientation of alpha colonies within the cutting zone. The microstructure of work material can show large variations depending on product form, e.g., cast, wrought, or sheet material, thus affecting whether the chip formation is isotropic or anisotropic. Other sources of variations also exist that can be found within the same component, such as segregation of alloying elements and differences in thermo-mechanical history during processing due to geometry. In this study, the interaction between work material microstructure, process parameters, and the machining system’s structural characteristics is studied. The aim is to further increase the knowledge about vibrations during machining of titanium and the role of microstructure and machining system properties. Different microstructures were produced by adding boron to cast Ti-6Al-4V material, where the resulting colony sizes gave both isotropic and anisotropic chip formation within the chosen cutting data range. The machining systems dynamic properties were varied by using different tool overhangs, thereby simulating different configurations of natural frequencies and stiffness. The results show the influence of both microstructure and machining system’s structural characteristics on the dynamic response of the system for different process parameters. This information can be used to increase robustness of machining operations taking into consideration this three-way relationship.
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| 6. |
- Cedergren, Stefan, 1982, et al.
(författare)
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On the Influence of Work Material Microstructure on Chip Formation, Cutting Forces and Acoustic Emission when Machining Ti-6Al-4V
- 2013
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 12, s. 55-60
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Konferensbidrag (refereegranskat)abstract
- The influence of heat treatment of work material on chip formation, when machining Ti-6Al-4V, was studied through microstructural investigation of chips, as well as response on cutting forces and acoustic emission. Three different microstructures were investigated; equiaxed, bimodal and Widmanstätten. It is well known that machining of titanium produces shear localized chips at all industrially practical cutting speeds and feed rates, however there is also a transition from aperiodic to periodic sawtooth chip formation. The feed rate was varied at constant cutting speed to study this transition from aperiodic to periodic saw-tooth chips in the three microstructures. Face turning cutting tests were used when sensor signals were collected. The results from this investigation stress the importance to consider work material microstructure when studying the chip formation process, and its impact on cutting forces and acoustic emission, when machining Ti-6Al-4V.
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| 7. |
- Fotedar, Sunney, 1989, et al.
(författare)
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A criterion space decomposition approach to generalized tri-objective tactical resource allocation
- 2023
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Ingår i: Computational Management Science. - : Springer Science and Business Media LLC. - 1619-697X .- 1619-6988. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a tri-objective mixed-integer linear programming model of the tactical resource allocation problem with inventories, called the generalized tactical resource allocation problem (GTRAP). We propose a specialized criterion space decomposition strategy, in which the projected two-dimensional criterion space is partitioned and the corresponding sub-problems are solved in parallel by application of the quadrant shrinking method (QSM) (Boland in Eur J Oper Res 260(3):873–885, 2017) for identifying non-dominated points. To obtain an efficient implementation of the parallel variant of the QSM we suggest some modifications to reduce redundancies. Our approach is tailored for the GTRAP and is shown to have superior computational performance as compared to using the QSM without parallelization when applied to industrial instances.
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| 8. |
- Fotedar, Sunney, 1989, et al.
(författare)
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Mathematical optimization of the tactical allocation of machining resources for an efficient capacity utilization in aerospace component manufacturing
- 2019
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Ingår i: Proceedings of the 10th Aerospace Technology Congress. - : Linköping University Electronic Press. - 1650-3686 .- 1650-3740. - 9789175190068 ; , s. 183-188
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Konferensbidrag (refereegranskat)abstract
- In the aerospace industry, with low volumes and many products, there is a critical need to efficiently use available manufacturing resources. Currently, at GKN Aerospace, resource allocation decisions that in many cases will last for several years are to some extent made with a short-term focus so as to minimize machining time, which results in a too high load on the most capable machines, and too low load on the less capable ones. This creates an imbalance in capacity utilization that leads to unnecessary queuing at some machines, resulting in long lead times and in an increase in tied-up capital. Tactical resource allocation on the medium to long-range planning horizon (six months to several years) aims to address this issue by allocating resources to meet the predicted future demand as effectively as possible, in order to ensure long range profitability. Our intent is to use mathematical optimization to find the best possible allocations.
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| 9. |
- Hoier, Philipp, 1988, et al.
(författare)
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Microstructural characteristics of Alloy 718 and Waspaloy and their influence on flank wear during turning
- 2018
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 400-401, s. 184-193
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Tidskriftsartikel (refereegranskat)abstract
- The present study deals with the influence of the microstructures of two wrought superalloys on the flank wear of uncoated cemented tungsten carbide tools in turning. Tool life tests have been performed in order to compare the flank wear development during machining of Alloy 718 and Waspaloy. Additionally, microstructural aspects, such as hardness, grain size as well as types and quantities of hard, abrasive phases have been determined and compared for both machined superalloy workpieces. The results show that Alloy 718 is associated with faster flank wear progression as compared with Waspaloy. The difference in wear is not likely to be the result of higher thermal and mechanical loads on the tool during machining Alloy 718. Characterization of obtained flank wear topographies after removal of adhered workpiece material revealed that abrasive wear is the dominant wear mechanism during machining both superalloys with the investigated cutting parameters. Varying extents of abrasive tool wear during cutting of the two alloys are therefore the likely reason for the different wear rates. In connection to that, significantly larger quantities of hard phases, specifically primary MC-type carbides and TiN-inclusions were found in the Alloy 718 workpiece which can explain the faster flank wear progression during machining this alloy.
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| 10. |
- Hultman, Hugo, et al.
(författare)
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Identification of variation sources for high precision fabrication in a digital twin context
- 2020
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Ingår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE). ; 2B-2020
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Konferensbidrag (refereegranskat)abstract
- The aerospace industry is increasing its focus on fabrication in manufacturing, foregoing large castings to instead assemble and join smaller parts into final products. This increases the total amount of geometrical variation introduced during the production process, since the unique variation from each individual part can add to a propagating effect putting the final assembled product outside of tolerance limits. Geometry assurance and variation simulation has traditionally been applied as a part of the design process to develop robust manufacturing concepts that are as insensitive as possible to variation. A concept for geometry assurance has been proposed where variation simulation is conducted for each individual assembly using real measurements from incoming parts, making it possible to make adaptive adjustments to production parameters to optimize results. It is however not feasible to measure and simulate every aspect of the process. This paper provides a summary of relevant sources of geometrical variation for a high precision fabrication process, based on input from a fabrication process in the aerospace industry. Variation sources are analyzed and discussed from an industrial perspective, putting them in the context of an actual fabrication process as well as in the context of digital twins for geometry assurance.
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