| 1. |
- Agmell, Mathias, et al.
(författare)
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Development of a simulation model to study tool loads in pcBN when machining AISI 316L
- 2018
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Ingår i: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 96:5-8, s. 2853-2865
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the development of a FE-simulation model to predict the mechanical stresses and thermal loads that a cutting tool of polycrystalline cubic boron nitride (pcBN) is subjected to, when machining AISI 316L. The serrated chip formation of AISI 316L has a major impact on the periodic loads acting on the cutting tool. Therefore, it is vital to correctly model this serrated chip formation. One of the major difficulties with FE-simulations of metal cutting is that the extreme deformations in the workpiece material, often leads to a highly distorted mesh. This paper uses the Coupled Eulerian-Lagrangian (CEL) formulation in Abaqus/Explicit, where the workpiece is modelled with the Eulerian formulation and the cutting tool by the Lagrangian one. This CEL formulation enables to completely avoid mesh distortion. To capture the chip serration process, the workpiece material is described with the Johnson-Cook damage model. The FE-simulation results are validated via comparison of the modelled cutting forces, chip serration frequency, and contact length against experimental ones.
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| 2. |
- Agmell, Mathias, et al.
(författare)
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Investigation of mechanical and thermal loads in pcBN tooling during machining of Inconel 718
- 2020
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Ingår i: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 107, s. 1451-1462
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates machining superalloy Inconel 718 with polycrystalline cubic boron nitride (pcBN) tooling both numerically and experimentally. Particular attention is given to mechanical and thermal stresses in the cutting tool arising from segmented chip formation and associated forces and temperatures. The temperature dependence of the mechanical properties of pcBN has been investigated and incorporated into a numerical model. In order to capture the dynamic loads due to a serrated chip formation, the Johnson–Cook damage model has been used. The extreme deformations during a machining process often results in a numerical difficulties due to a distorted elements. This paper uses the coupled Eulerian–Lagrangian (CEL) formulation in Abaqus/Explicit, where the workpiece is modelled with the Eulerian formulation and the cutting tool by the Lagrangian one. This CEL formulation enables to completely avoid mesh distortion. The finite element simulation results are validated via comparison of the modelled static and dynamic cutting forces and thermal loads induced into the cutting tool. The numerical model predicts a temperature of 1100–1200 ∘C at the cutting interface, which is in line with experimental determined data. The principal stresses at the rake up to 300 MPa are recorded, whereas higher level of stresses up to 450 MPa are found in the notch region of the tool, well correlated with experimental observation.
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| 3. |
- Agmell, Mathias, et al.
(författare)
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The Influence the Uncut Chip Thickness has on the Stagnation Point in Orthogonal Cutting
- 2017
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Ingår i: 16th CIRP Conference on Modelling of Machining Operations (16th CIRP CMMO). - : Elsevier BV. - 2212-8271. - 9781510842762 ; 58, s. 13-18
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Konferensbidrag (refereegranskat)abstract
- The effect of cutting data on the stagnation zone of a machining operation is of great interest since it governs the material flow around the cutting edge. The material flow has a significant influence on the mechanical properties of the machined surface. This paper presents a numerical model that is able to determine the effect that the uncut chip thickness has on the stagnation zone and the connection between the stagnation zone and the deformation layer in the machined subsurface.
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| 4. |
- Huuki, Juha, et al.
(författare)
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Process limitation of ultrasonic burnishing for commercially available martensitic stainless steel
- 2020
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 51, s. 885-889
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Konferensbidrag (refereegranskat)abstract
- Ultrasonic burnishing is attracting ever-greater interest as a surface finishing process. Although the popularity of this method in manufacturing industry remains limited, research is being conducted to explore both the detailed aspects and the limitations of this method. Tangential misalignment is one of most influential parameters in determining the mechanical properties induced by ultrasonic burnishing. This study investigates the effect of tangential misalignment on the ultrasonic burnishing of martensitic stainless steel (Stavax) and the surface integrity of the processed workpiece. Both negative and positive misalignments (from 0° to 5°) angles were tested. Macro hardness, instrumental micro hardness and surface roughnesses were measured. The results revealed that at higher tangential misalignment (>5° and along the negative side), ultrasonic burnishing cannot be performed for this material. It was found that with an increase in misalignment, hardness and surface roughness increased. Instrumental micro hardness measured from the burnished end, through the depth, revealed that hardness started decreasing from 60 µm towards the center of shaft. This indicates that beside ultrasonic burnishing has induced surface hardness, effect of hardness has been induced up to 60 µm. Considering the previous literature on ultrasonic burnishing, it appears that the potential of ultrasonic burnishing has some limitations depending on the material properties.
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| 5. |
- Laakso, Sampsa, 1983
(författare)
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Damage does not cut it - Saturated damage in FEM modelling of metal cutting breaks the simulation but not the chip
- 2020
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 51, s. 806-811
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Konferensbidrag (refereegranskat)abstract
- Damage models are used in metal cutting simulations to adjust the flow stress and to enable the serrated chip formation and chip breakage. The models describe the rupture strain of the material that is a function of temperature, stress, strain and strain rate. When a damage parameter in the model reaches a critical value, the flow stress of the material decreases to a predetermined fraction. Damage models show good results in predicting the cutting forces, chip thickness and serration frequency, but using them has serious disadvantages. First, damage models describe rupture strain, that is valid in metal cutting for chip breakage, but not for damage softening or chip serration, since those are based on adiabatic shear banding. Second point, shown in this paper, when material has reached the critical damage, the saturated model doesn't perform as intended. The damage model is saturated in simulations with multiple cutting passes. The initial cut deforms the layer under the tool. The same layer is then cut during the next cutting pass. During this cut, the damage model is already saturated. The damage model issues are relevant to all machining simulations because all machining processes include the multiple cutting passes.
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| 6. |
- Laakso, Sampsa, 1983, et al.
(författare)
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Evaluation of subcooled MQL in cBN hard turning of powder-based Cr-Mo-V tool steel using simulations and experiments
- 2022
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Ingår i: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 118:1-2, s. 511-531
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Tidskriftsartikel (refereegranskat)abstract
- Metal cutting fluids for improved cooling and lubrication are an environmental risk and a health risk for workers. Minimizing water consumption in industry is also a goal for a more sustainable production. Therefore, metal cutting emulsions that contain hazardous additives and consume considerable amounts of water are being replaced with more sustainable metal cutting fluids and delivery systems, like vegetable oils that are delivered in small aerosol droplets, i.e., via minimum quantity lubrication (MQL). Since the volume of the cutting fluid in MQL is small, the cooling capacity of MQL is not optimal. In order to improve the cooling capacity of the MQL, the spray can be subcooled using liquid nitrogen. This paper investigates subcooled MQL with machining simulations and experiments. The simulations provide complementary information to the experiments, which would be otherwise difficult to obtain, e.g., thermal behavior in the tool-chip contact and residual strains on the workpiece surface. The cBN hard turning simulations and experiments are done for powder-based Cr-Mo-V tool steel, Uddeholm Vanadis 8 using MQL subcooled to −10 °C and regular MQL at room temperature. The cutting forces and tool wear are measured from the experiments that are used as the calibration factor for the simulations. After calibration, the simulations are used to evaluate the thermal effects of the subcooled MQL, and the surface residual strains on the workpiece. The simulations are in good agreement with the experiments in terms of chip morphology and cutting forces. The cutting experiments and simulations show that there is only a small difference between the subcooled MQL and regular MQL regarding the wear behavior, cutting forces, or process temperatures. The simulations predict substantial residual plastic strain on the workpiece surface after machining. The surface deformations are shown to have significant effect on the simulated cutting forces after the initial tool pass, an outcome that has major implications for inverse material modeling.
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| 7. |
- Laakso, Sampsa, et al.
(författare)
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Multi-objective testing of different brass alloy components for DFM
- 2019
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Ingår i: 52nd CIRP Conference on Manufacturing Systems (CMS), Ljubljana, Slovenia, June 12-14, 2019. - : Elsevier BV. - 2212-8271. ; 81, s. 127-132
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the differences of leaded and low-lead brasses in terms of mechanical and thermal properties, machinability and product strength using physical testing and simulations. The information can be used in companies for Design for Manufacturability (DFM) while designing processes for lead free brass. The novelty of this research is to combine data from different testing methods to a unified model that can be used in both cutting simulations and product simulations.
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| 8. |
- Laakso, Sampsa Vili Antero
(författare)
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Heat matters when matter heats – The effect of temperature-dependent material properties on metal cutting simulations
- 2017
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Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 27, s. 261-275
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Tidskriftsartikel (refereegranskat)abstract
- The goal of metal cutting research is to predict process conditions accurately with a model or a simulation, in order to optimize and develop the processes. Development of such a model requires understanding of multiple branches of physics and engineering such as continuum mechanics, thermodynamics, tribology and materials science. For an accurate model, each aspect of the process must be modelled properly, or at least the effects of a certain phenomenon must be shown to be negligible. This paper investigates the effect of the temperature dependence of material properties on metal cutting simulations for three different engineering materials: AISI 1045 steel, AISI 7075 aluminium and AISI 304 stainless steel. It is generally accepted that the flow stress of metals is dependent on the temperature, but modulus of elasticity, thermal expansion, heat capacity and thermal conductivity are often considered constants and their effect is considered negligible. In this study, orthogonal turning of the materials is simulated with constant material properties and material properties that are functions of temperature. Each material property combination is simulated to test their effect on the results to investigate the individual and interdependent effects. Based on the results, a general guideline can be formed regarding the importance of heat capacity, thermal conductivity, modulus of elasticity and heat transfer.
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| 9. |
- Laakso, Sampsa V.A., et al.
(författare)
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The correct way of splitting tools - Optimization of instrument design for measuring contact stress distribution
- 2018
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 25, s. 97-102
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Tidskriftsartikel (refereegranskat)abstract
- Contact stress on the tool has been measured with a split-tool apparatus that has a poor resolution of the stress distribution, and with photoelastic tools that cannot be used with real cutting parameters since the materials are too weak. This paper presents an improved split-tool design allowing continuous stress distribution dataset instead of discreet steps by using a tilted separation plane between the tool tip and the tool body. This paper optimizes the separation plane angle with 3D-FEM to minimize deflection.
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| 10. |
- Laakso, Sampsa V.A., et al.
(författare)
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The mystery of missing feed force — The effect of friction models, flank wear and ploughing on feed force in metal cutting simulations
- 2018
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Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 33, s. 268-277
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Tidskriftsartikel (refereegranskat)abstract
- Underestimated feed force is a known systematic error in cutting simulations. It is considered a consequence of inaccurate friction models, but there are indicators that friction is not the only reason for the error. In some cases, the value of Coulomb friction must be over 1.0 to compensate for the feed force and such values cause over-estimated chip thickness for example. In turning, the ploughing force of the tool is affected by the feed velocity, which changes with the work diameter when cutting speed is constant. In addition, the edge geometry of the tool affect the ploughing force. In this paper, friction, edge geometry and the plough force are investigated with experiments and simulations to identify their effect on feed force.
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