| 1. |
- Andersson, Daniel C., et al.
(författare)
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A Numerical Study of Material Parameter Sensitivity in the Production of Hard Metal Components Using Powder Compaction
- 2014
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Ingår i: Journal of materials engineering and performance (Print). - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 23:6, s. 2199-2208
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Tidskriftsartikel (refereegranskat)abstract
- Modeling of hard metal powder inserts is analyzed based on a continuum mechanics approach. In particular, one commonly used cutting insert geometry is studied. For a given advanced constitutive description of the powder material, the material parameter space required to accurately model the mechanical behavior is determined. These findings are then compared with the corresponding parameter space that can possibly be determined from a combined numerical/experimental analysis of uniaxial die powder compaction utilizing inverse modeling. The analysis is pertinent to a particular WC/Co powder and the finite element method is used in the numerical investigations of the mechanical behavior of the cutting insert.
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| 2. |
- Rosenblad, Louise, et al.
(författare)
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An Experimental Investigation of the Solid State Sintering of Cemented Carbides Aiming for Mechanical Constitutive Modelling
- 2023
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Ingår i: Crystals. - : MDPI. - 2073-4352. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- The densification of cemented carbides during sintering was studied using an existing constitutive model based on powder particle size and material composition. In the present analysis, we study how well the constitutive model can capture the experimental results of a dilatometer test. Three experiments were performed, where the only difference was the transition between the debinding and sintering process. From magnetic measurements, it is concluded that the carbon level in the specimen is affected by changes to the experimental setup. It is shown, using parameter adjustments, that the constitutive model is more suited for a certain experimental setup and carbon level, which is a limitation of the model. In order to capture the mechanical behaviour under different experimental conditions, further constitutive modelling relevant to the carbon level is recommended.
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| 3. |
- Rosenblad, Louise, et al.
(författare)
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Constitutive Modelling Of Solid State Sintering Of Cemented Carbides
- 2022
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Ingår i: World PM 2022 Congress Proceedings. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- From a previously developed constitutive model for cemented carbide, the powder size- and configuration can be used to simulate the densification during the sintering process. However, small differences in experimental execution cannot be accounted for in the simulation, making the model sensitive. Here, we study how well the developed constitutive model can capture the experimental results of a dilatometer test. Three different experiments were performed where the only difference was the transition between the debinding and sintering process. From parameter adjustments, it is seen that the constitutive model is more suited for a certain experimental setup, which is a limitation of the model.
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| 4. |
- Rosenblad, Louise, et al.
(författare)
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Parametric dependency of a constitutive model describing solid state sintering of cemented carbides
- 2022
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 403, s. 117407-
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on an inverse modelling approach, using FEM to simulate the sintering of WC-Co powder using a continuum model. From a previously developed constitutive model of cemented carbide, the dependency of the material parameters is investigated in a sensitivity study. A value of sensitivity is assigned to all the material parameters and calculated at different steps in the sintering process, which represent its importance for capturing the shrinkage during sintering. The approach is that only the more sensitive parameters should be fitted when changing experimental setup or material composition, leaving the less important parameters constant, resulting in fewer tests and iterations. This approach is tested in an optimization of WC-Co powder sintering cycle, where the shrinkage curve is experimentally determined. It is concluded that some of the material parameters play a minor role in the modelling and could be set as constants in an optimization. The constitutive material model alone is unable to capture all features that appeared in the shrinkage curve during the experiment. Improvements of the model are discussed. An additional investigation, performed without heating rate dependency, shows that the remaining material parameters could compensate for the omitted heating rate for a known sintering cycle without losing accuracy.
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| 5. |
- Salmi, Kristin, et al.
(författare)
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Correlation Between Granule Strength and Green Strength at Compaction of Cemented Carbide Powder Materials
- 2021
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 30:12, s. 9078-9083
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Tidskriftsartikel (refereegranskat)abstract
- The correlation between granule strength and green strength of hard metal powders is examined. The approach is based on experiments and numerics. In the latter case, a Design of Experiment software is used. The granule strength of the powder (particle) is determined by GFP-measurements (“Granularfestigkeits-Prüfsystem”). During this test, a single particle is pressed from one side until breakage. The corresponding measurements of the green strength are done using three-point bend (3PB) testing. The experimental results show that the pressing agent has a strong influence on the behavior of both quantities. The statistical evaluation shows that the relation between the two strength properties is very close to linear with coefficient of determination R2 taking on the value 0.97. This of course indicates that it is possible to get information about one of the properties for a similar set of materials by experimentally determining the other one. This is of substantial practical importance as for one thing it can limit the amount of testing required. Even though the present investigation is pertinent to hard metal powders, the results could be of value for many other types of powder materials.
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| 6. |
- Staf, Hjalmar, et al.
(författare)
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An Analysis of the Stress State in Powder Compacts during Unloading, Emphasizing the Influence from Different Frictional Models
- 2023
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Ingår i: Applied Sciences. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2076-3417. ; 13:22
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Tidskriftsartikel (refereegranskat)abstract
- Finite element (FE) simulations are frequently used nowadays in order to analyse powder compaction and sintering, for example, when determining the shape of a cutting blank insert. Such analyses also make it possible to determine in detail the stress state in a powder compact during loading and unloading. This is certainly important as (residual) tensile stresses can lead to cracking, either after unloading or during the subsequent sintering step. The magnitude of plastic deformation is also an issue here. Concerning the stress state in the powder compact, the frictional behaviour (between walls and powder compact) is of great importance. For this reason, in the present study, two frictional models are implemented into a commercial FE software, and numerical results based on the stress state before and during unloading are derived. The two friction models produce quite different results, and it is obvious that the frictional behaviour at powder pressing has to be carefully accounted for in order to achieve results of high accuracy.
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| 7. |
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| 8. |
- Staf, Hjalmar, et al.
(författare)
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Determination of the Frictional Behavior at Compaction of Powder Materials Consisting of Spray-Dried Granules
- 2018
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 27:3, s. 1308-1317
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Tidskriftsartikel (refereegranskat)abstract
- The frictional behavior during powder compaction and ejection is studied using an instrumented die with eight radial sensors. The average friction over the total powder pillar is used to determine a local friction coefficient at each sensor. By comparing forces at compaction with forces at ejection, it can be shown that the Coulomb's friction coefficient can be described as a function of normal pressure. Also stick phenomena has been investigated in order to assess its influence on the determination of the local friction coefficient.
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| 9. |
- Staf, Hjalmar, et al.
(författare)
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Determining the density distribution in cemented carbide powder compacts using 3D neutron imaging
- 2019
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Ingår i: Powder Technology. - : Elsevier. - 0032-5910 .- 1873-328X. ; 354, s. 584-590
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Tidskriftsartikel (refereegranskat)abstract
- Spray-dried refractory carbide and metal powder mixtures, containing tungsten carbide, is compacted and sintered during the production of conventional cutting tool inserts. Since friction between the pressing tool and the powder gives rise to density gradients in the powder compact, shrinkage during sintering is uneven. The shape of the sintered blank is important and can be predicted with finite element (FE) simulations. To validate the simulation of the pressing procedure, the density gradients in the powder compacts must be measured with a high spatial resolution. Since tungsten has a high atomic number, it is hard to penetrate with X-rays and even cold neutrons. We show here that by using a polychromatic beam of thermal neutrons, along with beam-hardening correction, such measurements can be successfully realized. The obtained results show good agreement with corresponding FE-simulations. Also, deliberate differences in the compaction process could be verified with the neutron measurements.
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| 10. |
- Staf, Hjalmar, et al.
(författare)
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Evaluation of an advanced powder-die frictional model
- 2020
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Ingår i: Powder Technology. - : ELSEVIER. - 0032-5910 .- 1873-328X. ; 363, s. 569-574
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Tidskriftsartikel (refereegranskat)abstract
- It is known that the shape of a cutting insert blank, after pressing and sintering, can be predicted with finite element (FE) simulations. It is also known that such simulations have the potential to save costs and time when used for press tool compensation. However, in such simulations (and in a real situation), the frictional behaviour has a great influence on the results. Therefore, in this study, two frictional models are discussed and implemented into a commercial FE-program. The results from the different frictional descriptions, when for instance analysing density after compaction, shows a clear difference. It can be concluded that the frictional behaviour at powder pressing has to be modelled in detail, also at low forces.
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