| 1. |
- Berglund, Johan C, 1978, et al.
(författare)
-
Detailed evaluation of topographical effects of Hirtisation post-processing on electron beam powder bed fusion (PBF-EB) manufactured Ti-6Al-4V component
- 2024
-
Ingår i: Precision Engineering. - : Elsevier Inc.. - 0141-6359 .- 1873-2372. ; 85, s. 319-327
-
Tidskriftsartikel (refereegranskat)abstract
- Metal additive manufacturing surface topographies are complex and challenging to characterise due to e.g. steep local slopes, re-entrant features, varying reflectivity and features of interest in vastly different scale ranges. Nevertheless, average height parameters such as Ra or Sa are commonly used as sole parameters for characterisation. In this paper, a novel method for selecting relevant parameters for evaluation is proposed and demonstrated using a case study where the smoothing effects after three processing steps of the electro chemical post-process Hirtisation of a metal AM surface are quantified. The method uses a combination of conventional areal texture parameters, multiscale analysis and statistics and can be used to efficiently achieve a detailed and more relevant surface topography characterisation. It was found that the three process steps have different effects on the surface topography regarding the types and sizes of features that were affected. In total, Sdq was reduced by 97 %, S5v was reduced by 81 % and Sa was reduced by 78 %. A surface texture with much lower average roughness, less deep pits and less steep slopes was produced, which is expected to be beneficial for improved fatigue properties.
|
|
| 2. |
- Dunaj, Pawe, et al.
(författare)
-
Modeling the dynamic interaction between machine tools and their foundations
- 2024
-
Ingår i: Precision engineering. - : Elsevier BV. - 0141-6359 .- 1873-2372. ; 89, s. 451-472
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of a machine tool is directly influenced by the characteristics of the floor, subsoil, and their interaction with the installed machine. Installing a machine tool in its operational environment poses a distinct challenge that bridges mechanical and civil engineering disciplines. This interdisciplinary issue is often overlooked within the individual separate disciplines. However, effectively addressing this challenge requires a comprehensive understanding of mechanical and civil engineering principles. To address this problem, the present study proposes a method for improved modeling of the dynamic properties of the machine tool by considering the foundation and the subsoil on which it is installed. The method is based on finite element modeling. Linear models of the system components and the connections between them were used. These, supplemented with damping expressed by complex stiffness, made it possible to determine the natural frequencies, mode shapes, and frequency response functions (based on which the transmissibilities were obtained). Based on the experimentally verified models of vertical and horizontal lathes, the sensitivity analysis aimed at estimating the impact of changes in system parameters on vibration transmissibility for a floor-type and a block-type foundation was conducted. Thus, it was possible to identify those machine tool-support-foundation-subsoil system parameters that had the most significant impacts on the vibration's transmissibility. After analyzing the cases discussed, it became evident that the transmissibility of vibrations is primarily influenced by two key factors. First and foremost, the properties of the structural loop of the machine tool played a significant role. Additionally, the characteristics of the subsoil on which the foundation was situated emerged as a crucial determinant in the observed vibration transmissibility.
|
|
| 3. |
- Theissen, Nikolas Alexander, 1992-, et al.
(författare)
-
Measurement for the identification of static and quasi-static rotational stiffness
- 2021
-
Ingår i: Precision engineering. - : Elsevier BV. - 0141-6359 .- 1873-2372. ; 72, s. 215-223
-
Tidskriftsartikel (refereegranskat)abstract
- Machine tool calibration can be employed to optimise tool path trajectories through on- and off-line compensation of anticipated deflections, which result from a process plan, and to assess the machine tools capability to comply with the geometric dimensions and tolerances of a process plan.This work presents a measurement for the identification of static and quasi-static rotational stiffness of a rotational joint of 5-axis machining centres. This work shall serve as a basis towards the calibration of translational as well as rotational stiffness of 5-axis machining centres. The novelty of this work lies partly in the measurement procedure for the quasi-static rotational stiffness, which relies on multiple circular trajectories, as well as in the comparison of the static and quasi-static rotational stiffness of machine tools, which is usually identified using finite element approaches. The measurement procedure for the static rotational stiffness consists of inducing a static load directly, from an overhead factory crane, to a single rotational joint and measuring its deflection with both three LVDTsLinear Variable Differential Transformers (LVDTs) as well as three Non-Contact Capacitive Probes (NCCPs). While the measurement for the quasi-static rotational stiffness induces quasi-static loads indirectly from the Loaded Double Ball Bar, with different magnitudes and radii from the axis of rotation, between the tool centre point and the machine tool table. The quasi-static measurement procedure measures the deflection with both three LVDTs as well as three NCCPs while the spindle tracks circular trajectories inscribed by the movement of the rotary axis. The measurement procedures are implemented in two case studies on 5-axis machining centres with significantly different kinematic configurations to be able to highlight and discuss the limitations of the applicability of the method. The presented method works well for machining centres with symmetric and acceptably with asymmetric structures due to the corresponding symmetry of the deflection field.Finally, the manuscript concludes with a contextualisation of the introduced measurement procedure towards fully calibrated machine tool models, i.e. translation and rotation as well as static and dynamic, which together with customised post-processors and process models, might form the future basis of a stiffness volumetric compensation system.
|
|
| 4. |
- Kadivar, Mohammadali, 1987, et al.
(författare)
-
Modeling of micro-grinding forces considering dressing parameters and tool deflection
- 2021
-
Ingår i: Precision Engineering. - : Elsevier BV. - 0141-6359. ; 67, s. 269-281
-
Tidskriftsartikel (refereegranskat)abstract
- The prediction of cutting forces is critical for the control and optimization of machining processes. This paper is concerned with developing prediction model for cutting forces in micro-grinding. The approach is based on the probabilistic distribution of undeformed chip thickness. This distribution is a function of the process kinematics, properties of the workpiece, and micro-topography of the grinding tool. A Rayleigh probability density function is used to determine the distribution of the maximum chip thickness as an independent parameter. The prediction model further includes the effect of dressing parameters. The integration of the dressing model enables the prediction of static grain density of the grinding tool at various radial dressing depths. The tool deflection is also considered in order to account for the actual depth of cut in the modeling process. The dynamic cutting-edge density as a function of the static grain density, the local tool deflection, elastic deformation, and process kinematics can hence be calculated. Once the chip thickness is calculated, the single-grain forces for individual abrasive grains are predicted and the specific tangential and normal grinding forces simulated. The simulation results are experimentally validated via cutting-force measurements in micro-grinding of Ti6Al4V. The results show that the model can predict the tangential and normal grinding forces with a mean accuracy of 10% and 30%, respectively. The observed cutting forces further imply that the flow stress of the material did not change with changing the cutting speed and the cutting strain rate. Moreover, it was observed that the depth of cut and grinding feed rate had the same neutral effect on the resultant grinding forces.
|
|
| 5. |
- Kadivar, Mohammadali, 1987, et al.
(författare)
-
The role of specific energy in micro-grinding of titanium alloy
- 2021
-
Ingår i: Precision Engineering. - : Elsevier BV. - 0141-6359. ; 72, s. 172-183
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is concerned with understanding the role of specific energy in micro-grinding of conventional and additively manufactured Ti6Al4V. The effects of grinding and dressing parameters, cooling-lubrication conditions, and the directions of material build-up are studied. It is demonstrated that the minimum specific energy in single grain tests is independent of the material-fabrication method. The lowest measured specific energy obtained is 11.5 J/mm3 for both workpiece materials. The direction of material build-up influenced the process only when grinding with low aggressiveness, where 20% higher specific energy was observed. Similar specific energies were obtained for oil-lubricated and dry conditions, indicating that lubrication had minimal effect. The effects of the diamond concentration in the wheel and the dressing parameters were also investigated. Comparable specific energies were observed for wheels with C150 and C200 concentrations. The specific energy was found being predominantly influenced by dressing. Coarse dressing conditions produced 18% lower specific energy and, therefore, a more efficient micro-grinding process.
|
|
| 6. |
- Laspas, Theodoros, et al.
(författare)
-
Novel methodology for the measurement and identification for quasi-static stiffness of five-axis machine tools
- 2020
-
Ingår i: Precision Engineering. - : Elsevier BV. - 0141-6359. ; 65, s. 164-170
-
Tidskriftsartikel (refereegranskat)abstract
- Stiffness is an important characteristic of production machinery, as it contributes to its ability to precisely maintain the pose between a tool center point with respect to a workpiece under load. For machine tools, it directly affects the geometric dimensions and surface properties of the parts, i.e. how closely the parts match their design drawings. This work presents a novel measurement procedure to measure and identify full translational stiffness matrices of 5-axis machining centers using quasi-static circular trajectories. The measurement procedure consists of inducing quasi-static loads, which vary in magnitude and direction, at the tool center point of the machine tool using the Loaded Double Ball Bar and measuring the displacement with three Linear Variable Differential Transformers while the spindle tracks the circular trajectories inscribed by the movement of the rotary axis. The work outlines and quantifies the main components of the uncertainty budget related to the measurement of the translational stiffness matrices. The measurement procedure is implemented in a case study on a 5-axis machining center. Finally, the manuscript concludes with a discussion on the utility value of the translational stiffness matrix for the design and operation of machine tools as well as the possibility to expand the measurement procedure to a calibration procedure for 5-axis machining centers to analyze the translational and rotational stiffness.
|
|
