| 1. |
|
|
| 2. |
- Devotta, Ashwin Moris, 1984-, et al.
(author)
-
Predicting Continuous Chip to Segmented Chip Transition in Orthogonal Cutting of C45E Steel through Damage Modeling
- 2020
-
In: Metals. - : MDPI. - 2075-4701. ; 10:4
-
Journal article (peer-reviewed)abstract
- Machining process modeling has been an active endeavor for more than a century and it has been reported to be able to predict industrially relevant process outcomes. Recent advances in the fundamental understanding of material behavior and material modeling aids in improving the sustainability of industrial machining process. In this work, the flow stress behavior of C45E steel is modeled by modifying the well-known Johnson-Cook model that incorporates the dynamic strain aging (DSA) influence. The modification is based on the Voyiadjis-Abed-Rusinek (VAR) material model approach. The modified JC model provides the possibility for the first time to include DSA influence in chip formation simulations. The transition from continuous to segmented chip for varying rake angle and feed at constant cutting velocity is predicted while using the ductile damage modeling approach with two different fracture initiation strain models (Autenrieth fracture initiation strain model and Karp fracture initiation strain model). The result shows that chip segmentation intensity and frequency is sensitive to fracture initiation strain models. The Autenrieth fracture initiation strain model can predict the transition from continuous to segmented chip qualitatively. The study shows the transition from continuous chip to segmented chip for varying feed rates and rake angles for the first time. The study highlights the need for material testing at strain, strain rate, and temperature prevalent in the machining process for the development of flow stress and fracture models.
|
|
| 3. |
- Holmberg, Jonas, 1976-
(author)
-
High volumetric machining strategies for superalloy gasturbine components : Comparing conventional and nonconventional machining methods for efficient manufacturing
- 2020
-
Doctoral thesis (other academic/artistic)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.
|
|
| 4. |
- Holmberg, Jonas, 1976-, et al.
(author)
-
Selection of milling strategy based on surface integrity investigations of highly deformed Alloy 718 after ceramic and cemented carbide milling
- 2020
-
In: Journal of Manufacturing Processes. - : Elsevier Ltd. - 1526-6125. ; 58, s. 193-207
-
Journal article (peer-reviewed)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
|
|
| 5. |
- Holmberg, Jonas, 1976-, et al.
(author)
-
Surface integrity investigation to determine rough milling effects for assessment of machining allowance for subsequent finish milling of alloy 718
- 2021
-
In: Journal of Manufacturing and Materials Processing. - : MDPI AG. - 2504-4494. ; 5:2
-
Journal article (peer-reviewed)abstract
- The planned material volume to be removed from a blank to create the final shape of a part is commonly referred to as allowance. Determination of machining allowance is essential and has a great impact on productivity. The objective of the present work is to use a case study to investigate how a prior rough milling operation affects the finish machined surface and, after that, to use this knowledge to design a methodology for how to assess the machining allowance for subsequent milling operations based on residual stresses. Subsequent milling operations were performed to study the final surface integrity across a milled slot. This was done by rough ceramic milling followed by finish milling in seven subsequent steps. The results show that the up-, centre and down-milling induce different stresses and impact depths. Employing the developed methodology, the depth where the directional influence of the milling process diminishes has been shown to be a suitable minimum limit for the allowance. At this depth, the plastic flow causing severe deformation is not present anymore. It was shown that the centre of the milled slot has the deepest impact depth of 500 µm, up-milling caused an intermediate impact depth of 400 µm followed by down milling with an impact depth of 300 µm. With merged envelope profiles, it was shown that the effects from rough ceramic milling are gone after 3 finish milling passes, with a total depth of cut of 150 µm. © 2021 by the authors.
|
|
| 6. |
- Holmberg, Jonas, 1976-, et al.
(author)
-
Surface integrity investigations for prediction of fatigue properties after machining of alloy 718
- 2021
-
In: International Journal of Fatigue. - : Elsevier Ltd. - 0142-1123 .- 1879-3452. ; 144
-
Journal article (peer-reviewed)abstract
- Fatigue performance is crucial for gas turbine components, and it is greatly affected by the manufacturing processes. Ability to predict the expected fatigue life of a component based on surface integrity has been the objective in this work, enabling new processing methods. Alloy 718 samples were prepared by different machining setups, evaluated in fatigue testing and surface integrity investigations. These results generated two predictive statistical multi-variate regression models. The fatigue correlated well with roughness, residual stresses and deformation. The two models showed great potential, which encourages further exploration to fine-tune the procedure for the particular case. © 2020 The Authors
|
|
| 7. |
- Magnevall, Martin, et al.
(author)
-
Improved cutting force measurements in milling using inverse filtering
- 2016
-
In: Proceedings of the 34th IMAC, A Conference and Exposition on Structural Dynamics 2016. - Cham : Springer. - 9783319300863 - 9783319300870 ; , s. 1-11
-
Conference paper (peer-reviewed)abstract
- Accurate estimates of cutting forces in metal cutting are important in the evaluation of e.g. different cutting tool geometries and concepts. However, dynamic influences from the measurement system affect the measurement result and may make the obtained cutting force data erroneous and misleading. This paper presents a method to construct an inverse filter which compensates for the dynamic influences from the measurement system. Using the suggested approach, unwanted dynamic effects from the measurement system can be counteracted. By applying the inverse filter it is possible to retain information related to the cutting forces at higher frequencies than possible with unfiltered data. The advantage of using the proposed method is illustrated by comparing simulated, inverse-and low-pass filtered cutting forces to unfiltered forces at different cutting speeds. The results indicate that inverse filtering can increase the usable frequency range of the force dynamometer and thereby provide more accurate and reliable results compared to both low-pass and unfiltered force measurements. © The Society for Experimental Mechanics, Inc. 2016.
|
|
| 8. |
- Parsian, Amir, et al.
(author)
-
Minimizing the Negative Effects of Coolant Channels on the Torsional and Torsional-Axial Stiffness of Drills
- 2021
-
In: Metals. - : MDPI. - 2075-4701. ; 11:9, s. 1473-1473
-
Journal article (peer-reviewed)abstract
- Coolant channels allow internal coolant delivery to the cutting region and significantly improve drilling, but these channels also reduce the torsional and torsional-axial stiffness of the drills. Such a reduction in stiffness can degrade the quality of the drilled holes. The evacuation of cutting chips and the delivery of the cutting fluid put strict geometrical restrictions on the cross-section design of the drill. This necessitates careful selection and optimization of features such as the geometry of the coolant channels. This paper presents a new method that uses Prandtl’s stress function to predict the torsional and torsional-axial stiffness values. Using this method drills with one central channel are compared to those with two eccentric coolant channels, which shows that with the same cross-section area, the reduction of axial and torsional-axial stiffness is notably smaller for the design with two eccentric channels compared to a single central channel. The stress function method is further used to select the appropriate location of the eccentric coolant channels to minimize the loss of torsional and torsional-axial stiffness. These results are verified by comparison to the results of three-dimensional finite element analyses.
|
|
| 9. |
- Tamil Alagan, Nageswaran, 1990-, et al.
(author)
-
High-pressure flank cooling and chip morphology in turning Alloy 718
- 2021
-
In: CIRP - Journal of Manufacturing Science and Technology. - : Elsevier Ltd. - 1755-5817 .- 1878-0016. ; 35, s. 659-674
-
Journal article (peer-reviewed)abstract
- The use of cutting fluids is commonly considered a necessity while machining Heat Resistant Super Alloys (HRSA). Specifically, cutting fluids applied under high-pressure, which for many decades have been the solution for the most demanding applications. The results might be diverse and vary between applications, but typically leads to improved tool life, enhanced chip breakability, lower temperature in the cutting zone and better surface quality of the finished product. The available high-pressure cutting fluid delivery systems are usually designed with the intention to improve the cutting fluid penetration at the vicinity of the cutting edge on the rake face side of the insert. However, there has been limited interest in investigating high-pressure cutting fluid applied to its flank face. Both specifically and in combination with cutting fluid directed to the rake face. In this study, the focus has been to investigate the chip formation process during the turning of Alloy 718 (Inconel 718). Particularly, for a defined turning operation where high-pressure cutting fluid is applied to the flank side as well as the rake side of an uncoated carbide insert. Several combinations of pressure levels and jet directions were investigated. The corresponding effects on the tool-chip contact zone and chip characteristics were studied for two cutting speeds. The results of the investigation showed a substantial improvement in lowering the tool-chip contact area at a rake pressure of 16 MPa. At which pressure, additional cutting fluid applied to the flank at a moderate pressure of 8 MPa had no dominant effect on chip formation (chip break). However, flank cooling of the cutting zone supports chip segmentation and thus indirectly chip breakability. For cutting fluid applied to the rake side at a more moderate pressure of 8 MPa, more prominent effects on the insert became apparent when additional cutting fluid was applied to the flank side. This was particularly noticeable when cutting fluid was directed towards the flank side of the insert at the same pressure level as the cutting fluid applied towards its rake face. The additional thermal transfer was seen to have a significant effect on the material deformation phenomena in the primary shear zone (lowering shear angle) as well as the sliding and sticking conditions of the tool-chip interface. Based on the evidence from this study, it can be concluded that cutting fluid applied towards the flank side of the insert has a significant impact on the cutting process. In particular, if applied in combination with a rake pressure at a similar level, in this case, 8 MPa. © 2021 The Authors
|
|
