CERES :: Browsing by Author "Hönnige, Jan Roman"

Browsing by Author "Hönnige, Jan Roman"

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Open Access
Analytical model for distortion prediction in wire plus arc additive manufacturing
(Materials Research Forum, 2018-10-05) Hönnige, Jan Roman; Colegrove, Paul A.; Williams, Stewart W.
An analytical model was developed to predict bending distortion of the base-plate caused by residual stresses in additively manufactured metal deposits. This avoids timeconsuming numerical simulations for a fast estimation of the expected distortion. Distortion is the product of the geometry factor K, which is determined by the cross-section of substrate and deposit, and the material and process factor S, which is the quotient of residual stress and the Young’s Modulus. A critical wall height can be calculated for which the structure distorts the most. This critical height is typically less than 2.5 times the thickness of the substrate. Higher walls increase the stiffness of the cross-section and reduce the distortion with increasing height.
Open Access
Application of bulk deformation methods for microstructural and material property improvement and residual stress and distortion control in additively manufactured components
(Elsevier, 2016-11-08) Colegrove, Paul A.; Donoghue, Jack; Martina, Filomeno; Gu, Jianglong; Prangnell, Philip B.; Hönnige, Jan Roman
Many additively manufactured (AM) materials have properties that are inferior to their wrought counterparts, which impedes industrial implementation of the technology. Bulk deformation methods, such as rolling, applied in-process during AM can provide significant benefits including reducing residual stresses and distortion, and grain refinement. The latter is particularly beneficial for titanium alloys where the normally seen large prior β grains are converted to a fine equiaxed structure – giving isotropic mechanical properties that can be better than the wrought material. The technique is also beneficial for aluminium alloys where it enables a dramatic reduction in porosity and improved ductility.
Open Access
Compression behaviour of wire+ arc additive manufactured structures
(MDPI, 2021-05-27) Abbaszadeh, Masoud; Ventzke, Volker; Neto, Leonor; Riekehr, Stefan; Martina, Filomeno; Kashaev, Nikolai; Hönnige, Jan Roman; Williams, Stewart; Klusemann, Benjamin
Increasing demand for producing large-scale metal components via additive manufacturing requires relatively high building rate processes, such as wire + arc additive manufacturing (WAAM). For the industrial implementation of this technology, a throughout understanding of material behaviour is needed. In the present work, structures of Ti-6Al-4V, AA2319 and S355JR steel fabricated by means of WAAM were investigated and compared with respect to their mechanical and microstructural properties, in particular under compression loading. The microstructure of WAAM specimens is assessed by scanning electron microscopy, electron back-scatter diffraction, and optical microscopy. In Ti-6Al-4V, the results show that the presence of the basal and prismatic crystal planes in normal direction lead to an anisotropic behaviour under compression. Although AA2319 shows initially an isotropic plastic behaviour, the directional porosity distribution leads to an anisotropic behaviour at final stages of the compression tests before failure. In S355JR steel, isotropic mechanical behaviour is observed due to the presence of a relatively homogeneous microstructure. Microhardness is related to grain morphology variations, where higher hardness near the inter-layer grain boundaries for Ti-6Al-4V and AA2319 as well as within the refined regions in S355JR steel is observed. In summary, this study analyzes and compares the behaviour of three different materials fabricated by WAAM under compression loading, an important loading condition in mechanical post-processing techniques of WAAM structures, such as rolling. In this regard, the data can also be utilized for future modelling activities in this direction.
Open Access
Control of residual stress and distortion in aluminium wire + arc additive manufacture with rolling
(Elsevier, 2018-06-25) Hönnige, Jan Roman; Colegrove, Paul A.; Ganguly, Supriyo; Eimer, Eloise; Kabra, S.; Williams, Stewart W.
The aluminium alloy wire 2319 is commonly used for Wire + Arc Additive Manufacturing (WAAM). It is oversaturated with copper, like other alloys of the precipitation hardening 2### series, which are used for structural applications in aviation. Residual stress and distortion are one of the biggest challanges in metal additive manufacturing, however this topic is not widely investigated for aluminium alloys. Neutron diffraction measurements showed that the as-built component can contain constant tensile residual stresses along the height of the wall, which can reach the materials' yield strength. These stresses cause bending distortion after unclamping the part from the build platform. Two different rolling techniques were used to control residual stress and distortion. Vertical rolling was applied inter-pass on top of the wall to deform each layer after its deposition. This technique virtually elimiated the distortion, but produced a characteristic residual stress profile. Side rolling instead was applied on the side surface of the wall, after it has been completed. This technique was even more effective and even inverted the distortion. An interesting observation from the neutron diffraction measurements of the stress-free reference was the significantly larger FCC aluminium unit cell dimension in the inter-pass rolled walls as compared to the as-build condition. This is a result of less copper in solid solution with aluminium, indicating greater precipitation and thus, potentially contibuting to improve the strenght of the material.
Open Access
Data for the paper "residual stress and texture control in Ti-6Al-4V wire + arc additively manufactured intersections by stress relief and rolling"
(Cranfield University, 2018-05-02 13:58) Hönnige, Jan Roman ; Ganguly, Supriyo; Colegrove, Paul; Williams, Stewart; Lik Lee, Tung; Fitzpatrick, Michael E.; Ahmed, Bilal
Data supporting the paper: "residual stress and texture control in Ti-6Al-4V wire + arc additively manufactured intersections by stress relief and rolling".
Open Access
The effectiveness of grain refinement by machine hammer peening in high deposition rate wire-arc AM Ti-6Al-4V
(Springer, 2020-05-06) Hönnige, Jan Roman ; Davis, Alec E.; Ho, A.; Kennedy, Jacob R.; Neto, Leonor; Prangnell, Philip B.; Williams, Stewart W.
Surface deformation, applied in-process by machine hammer peening (MHP), has the potential to refine the coarse columnar β-grain structures normally found in high deposition rate Wire-Arc Additive Manufacturing (WAAM) processes with Ti alloys like Ti-6Al-4V. Effective refinement, as well as a reduction in texture strength, has been achieved in relatively thick sections and to a depth that is greater than that expected from the surface deformation induced by MHP. By application of MHP to each deposition track, the average β-grain size could be reduced from cm’s to less than 0.5 mm. Systematic experiments have been performed to investigate the origin of this interesting effect, which included ‘stop-action’ trials and separation of the strain and temperature gradients induced by the two process steps. The maximum depth of the plastic deformation from MHP required to generate new β-grain orientations was determined by electron backscatter diffraction local average misorientation analysis to be < 0.5 mm, which was less than the melt pool depth in the WAAM process. Nevertheless, new β-grain orientations were observed to form within the peened layer ahead of the approaching heat source as the peak temperature rose above the β transus, which then grew into the less deformed core of the wall as the temperature rose. This allowed the new grain orientations to penetrate deeper than the melt pool depth and survive to act as substrates for epitaxial growth at the fusion boundary during solidification, resulting in significant grain refinement
Open Access
Interpass rolling of Ti-6Al-4V wire + arc additively manufactured features for microstructural refinement
(Elsevier, 2018-03-05) McAndrew, Anthony R.; Alvarez Rosales, Marta; Colegrove, Paul A.; Hönnige, Jan Roman; Ho, Alistair; Fayolle, Romain; Eyitayo, Kamal; Stan, Ioan; Sukrongpang, Punyawee; Crochemore, Antoine; Pinter, Zsolt
In-process deformation methods such as rolling can be used to refine the large columnar grains that form when wire + arc additively manufacturing (WAAM) titanium alloys. Due to the laterally restrained geometry, application to thick walls and intersecting features required the development of a new ‘inverted profile’ roller. A larger radii roller increased the extent of the recrystallised area, providing a more uniform grain size, and higher loads increased the amount of refinement. Electron backscatter diffraction showed that the majority of the strain is generated toward the edges of the rolled groove, up to 3 mm below the rolled surface. These results will help facilitate future optimisation of the rolling process and industrialisation of WAAM for large-scale titanium components.
Open Access
Mechanical properties enhancement of additive manufactured Ti-6Al-4V by machine hammer peening
(Springer , 2019-07-31) Williams, Stewart W.; Ding, Jialuo; Hönnige, Jan Roman; Martina, Filomeno; Neto, Leonor
Wire + Arc Additive Manufacturing (WAAM) is a technology potentially offering reduction of material wastage, costs and shorter lead-times. It is being considered as a technology that could replace conventional manufacturing processes of Ti-6Al-4V, such as machining from wrought or forged materials. However, WAAM Ti-6Al-4V is characterized by coarse β-grains, which can extend through several deposited layers resulting in strong texture and anisotropy. As a solution, inter-pass cold rolling has been proven to promote grain refinement, texture modification and improvement of material strength by plastically deforming the material between each deposited layer. Nevertheless, with the increased interest in the WAAM technology, the complexity and size of the deposited parts has increased, and its application can be hindered by the low speed and complex/costly equipment required to perform rolling at this scale. Therefore, Machine Hammer Peening (MHP) has been studied as an alternative cold work process. MHP can be used robotically, offering greater flexibility and speed, and it can be applied easily to any large-scale geometry. Similarly to rolling, MHP is applied between each deposited layer with the new ECOROLL peening machine and, consequently, it is possible to eliminate texturing and reduce the β-grains size from centimeters long to approximately 1 to 2 mm. This effect is studied for thin and thick walls and no considerable change in grain size is observed, proving the applicability of MHP to large components. The yield strength and ultimate tensile strength increases to 907 MPa and 993 MPa, respectively, while still having excellent ductility. This grain refinement may also improve fatigue life and induce a decrease in crack propagation rate. In this study, it has been shown that MHP is a suitable process for WAAM Ti-6Al-4V applications, can be applied robotically and the grain refinement induced by very small plastic deformations can increase mechanical properties.
Open Access
Numerical analysis of heat transfer and fluid flow in multilayer deposition of PAW-based wire and arc additive manufacturing
(Elsevier, 2018-04-05) Bai, Xingwang; Colegrove, Paul A.; Ding, Jialuo; Zhou, Xiangman; Diao, Chenglei; Bridgeman, Philippe; Hönnige, Jan Roman; Zhang, Haiou; Williams, Stewart W.
A three-dimensional numerical model has been developed to investigate the fluid flow and heat transfer behaviors in multilayer deposition of plasma arc welding (PAW) based wire and arc additive manufacture (WAAM). The volume of fluid (VOF) and porosity enthalpy methods are employed to track the molten pool free surface and solidification front, respectively. A modified double ellipsoidal heat source model is utilized to ensure constant arc heat input in calculation in the case that molten pool surface dynamically changes. Transient simulations were conducted for the 1st, 2nd and 21st layer depositions. The shape and size of deposited bead and weld pool were predicted and compared with experimental results. The results show that for each layer of deposition the Marangoni force plays the most important role in affecting fluid flow, conduction is the dominant method of heat dissipation compared to convection and radiation to the air. As the layer number increases, the length and width of molten pool and the width of deposited bead increase, whilst the layer height decreases. However these dimensions remain constant when the deposited part is sufficiently high. In high layer deposition, where side support is absent, the depth of the molten pool at the rear part is almost flat in the Y direction. The profile of the deposited bead is mainly determined by static pressure caused by gravity and surface tension pressure, therefore the bead profile is nearly circular. The simulated profiles and size dimensions of deposited bead and molten pool were validated with experimental weld appearance, cross-sectional images and process camera images. The simulated results are in good agreement with experimental results.
Open Access
Numerical investigation of the effect of rolling on the localized stress and strain induction for wire + arc additive manufactured structures
(Springer , 2019-08-16) Abbaszadeh, Masoud; Hönnige, Jan Roman; Filomeno, Martina; Kashaev, Nikolai; Colegrove, Paul A.; Williams, Stewart W.; Klusemann, Benjamin
Cold rolling can be used in-process or post-process to improve microstructure, mechanical properties and residual stress in directed-energy-deposition techniques, such as the high deposition rate wire + arc additive manufacturing (WAAM) process. Finite element simulations of the rolling process are employed to investigate the effect of rolling parameters, in particular rolling load and roller profile radius on the residual stress field as well as plastic strain distribution for the profiled roller. The results show the response to rolling of commonly used structural metals in WAAM, i.e., AA2319, S335JR steel and Ti-6Al-4V, taking into account the presence of residual stresses. The rolling load leads to changes in the location and the maximum value of the compressive residual stresses, as well as the depth of the compressive residual stresses. However, the roller profile radius only changes the maximum value of these compressive residual stresses. Changing the rolling load influences the equivalent plastic strain close to the top surface of the wall as well as in deeper areas, whereas the influence of the roller profile radius is negligible. The plastic strain distribution is virtually unaffected by the initial residual stresses prior to rolling. Finally, design curves were generated from the simulations for different materials, suggesting ideal rolling load and roller profile combinations for microstructural improvement requiring certain plastic strains at a specific depth of the additive structure.
Open Access
Numerical study of rolling process on the plastic strain distribution in wire + arc additive manufactured Ti-6Al-4V
(AIP, 2019-07-02) Abbaszadeh, Masoud; Hönnige, Jan Roman; Filomeno, Martina; Kashaev, Nikolai ; Williams, Stewart W.; Klusemann, Benjamin
Wire+arc additive manufacturing (WAAM) is an additive manufacturing (AM) process that employs wire as the feedstock and an arc as energy source, to construct near net-shape components at high build rates. Ti-6Al-4V deposits typically form large columnar prior β grains that can grow through the entire component height, leading to anisotropy and lower mechanical properties, compared to the equivalent wrought alloy. Cold-working techniques such as rolling can be used to promote grain refinement in Ti-6Al-4V WAAM parts, thus increasing strength and eliminating anisotropy concomitantly. Additionally, rolling can be beneficial in terms of reduction of residual stress and distortion. The aim of this study is to illustrate the effect of rolling process parameters on the plastic deformation characteristics in Ti-6Al-4V WAAM structures. To produce a certain refinement of the microstructure, a certain amount of strain is typically required; thus suitable design guidelines for practical applications are needed. The effect of different rolling process parameters, in particular, rolling load and roller profile radius on the plastic strain distribution is investigated based on the finite element method. From a numerical point of view, the effect of the stiffness of the roller is investigated, e.g. deformable vs. rigid roller. Results indicate that for an identical rolling load, the deformable roller produces lower equivalent plastic strains due to its own elastic deformation. Additionally, a lower friction coefficient produces higher equivalent plastic strains near the top surface but, it has an insignificant effect on the plastic deformation further away from the top surface. However, numerically the computation time significantly increased for a higher friction coefficient. Larger roller profile radii lead to lower plastic strain near the top surface, but simultaneously had nearly no noticeable effect on plastic strains at deeper depth. In addition, the effect of interspace between rollers on the uniformity of the plastic strain during multi-pass rolling was investigated for a selected example. The results show that a higher uniform plastic strain distribution is obtained when the interspace between two rollers is equal to the residual width of the groove produced by a single rolling pass
Open Access
Quantification of strain fields and grain refinement in Ti-6Al-4V inter-pass rolled wire-arc AM by EBSD misorientation analysis
(Elsevier, 2020-09-25) Davis, Alec E.; Hönnige, Jan Roman; Martina, Filomeno; Prangnell, Philip B.
Inter-pass deformation is an effective method for refining the coarse β-grain structure normally produced in high-deposition-rate additive manufacturing processes, like wire-arc additive manufacturing. The effectiveness of applying contoured surface rolling deformation tracks to each added layer has been studied by developing, and applying, a large-area SEM-based strain mapping technique. This technique is based on calibration of the average point-to-point Local Average Misorientation (LAM) of α-phase lamellar variants in EBSD orientation data to the local effective plastic strain. Although limited in the strain range that can be measured, the technique has proven to be very effective for identifying the size and depth of the plastic zone induced by surface rolling, as well as the local strain distribution, up to a saturation limit of ~12%. The strain fields mapped showed a close correlation to the region and level of recrystallization that occurred in the deformation zones during rapid re-heating through the β transus. The β recrystallization identified was consistent with the local strain distribution within the plastic zones measured by the LAM method and previous work on the recrystallization mechanisms operating in WAAM inter-pass deformation processes.
Open Access
Residual stress and texture control in Ti-6Al-4V wire + arc additively manufactured intersections by stress relief and rolling
(Elsevier, 2018-04-08) Hönnige, Jan Roman; Colegrove, Paul A.; Ahmad, Bilal; Fitzpatrick, Michael E.; Ganguly, Supriyo; Lee, Tung Lik; Williams, Stewart W.
Additively manufactured intersections have the theoretical risk to contain hydrostatic tensile residual stresses, which eventually cannot be thermally stress relieved. The stresses in Ti-6Al-4V wire + arc additively manufactured (WAAM) intersections are lower compared to single pass walls and stresses in continuous walls are larger compared to discontinuous walls with otherwise identical geometry. Thermal stress relief was found to virtually eliminate them. Inter-pass rolling can yield the desired grain refinement, without having any noteworthy influence on the development of residual stresses. The strain measurement itself by neutron diffraction is facilitated by the refined microstructure, because the otherwise textured microstructure produces anisotropic peak intensity, not allowing Pawley refinement. Without rolling, the {101¯1} and {101¯3} family of hcp planes are the only ones that diffract consistently in the three principal directions.
Open Access
Study of residual stress and microstructural evolution in as-deposited and inter-pass rolled wire plus arc additively manufactured Inconel 718 alloy after ageing treatment
(Elsevier, 2020-10-14) Hönnige, Jan Roman; Er Seow, Cui; Ganguly, Supriyo; Xua, Xiangfang; Cabeza, Sandra; Coules, Harry E.; Williams, Stewart
The manufacture of structural components made from nickel-based super alloys would benefit from the commercial advantages of Wire + Arc Additive Manufacturing (WAAM), as it is commonly expensive to process using other conventional techniques. The two major challenges of WAAM are process residual stress and undesired microstructure. Residual stress causes part distortion and build failures, while the as-deposited microstructure does not allow the common heat-treatment to be effective in achieving the desired mechanical properties. This paper focuses on understanding the microstructural features, phase formation and three-dimensional residual stress state variation in as-deposited and inter-pass rolled conditions and after solutionising, quenching and ageing. The thermal history from successive deposition and cold working were correlated to the phase formation and macro residual stress formation and subsequent evolution. The {311} family of crystallographic planes were used as atomic strain gauge to determine the macrostrain and analysis of three dimensional stress state in different processing conditions. The measured strain were corrected for the compositional variation by measuring EDM machined d0 specimens manufactured under similar processing conditions. While the as-deposited part show significant stress redistribution and distortion after removal from the main fixture, inter-pass rolling was found to reduce part distortion significantly, the residual stress profile after inter-pass rolling showed highest tensile magnitude near the substrate while near the top of the deposit it was compressive as can be expected from the rolling process. The other two beneficial effects of inter-pass rolling on the microstructure are mitigation of the formation of undesired Laves-phase, thereby improving the response to solution treatment and aging together with significantly reduced grain size and texture. The application of inter-pass rolling reduces the potential part complexity, which however does not prevent the manufacture of common candidate parts, which are typically 1-to-1 replacements of forged, cast or machined from solid
Open Access
Thermo-mechanical control of residual stress, distortion and microstructure in wire + arc additively manufactured Ti-6Al-4V.
(2018) Hönnige, Jan Roman; Colegrove, Paul A.; Williams, Stewart W.
Wire + arc additive manufacturing (WAAM), unlike most other additive techniques, targets the manufacture of near-net-shape parts for large-scale structural components with medium complexity. WAAM is of special interest for the aerospace industry for reducing lead-time, material and process costs. Ti−6Al−4V is one alloy that could potentially benefit most from the advantages of WAAM, due to high material and process costs, and is therefore the main scope of this research. The manufacture of critical-use components for civil aviation requires a high process control to provide consistently strong and isotropic mechanical properties, as well as the elimination of residual stresses. Cold work can manipulate and counteract residual stresses caused by the additive process. When applied between two layers (i.e. between the deposition passes → interpass) it was found to refine the microstructure and thereby significantly improve the mechanical properties. So far it was only understood that it can theoretically control both residual stress and microstructure, but the science behind the process and how different parameters influence the effectiveness was only proposed. The present research demonstrates how cold work can be used effectively to address both issues, by identifying the process-relevant mechanisms. Before manipulating residual stresses, their development needed to be investigated Behaviour that had only been predicted using numerical simulations was measured for the first time using neutron diffraction and contour method stress determination techniques. This behaviour includes the development of residual stress during the deposition of straight walls and intersections, stress redistribution upon distortion after unclamping and the potential of thermal stress relief. Analogies to previous findings on steel helped explain the findings. The knowledge of stress development finally helped the development of an analytical model to predict residual stress and distortion, as well as stress redistribution upon unclamping. The performance and parameters of plastic deformation strategies were investigated using various characterisation techniques. Those include hardness mapping, residual stress measurements using hole-drilling and the contour method, electron-backscatter-diffraction (EBSD) plastic strain mapping, heat treatment, as well as numerical simulations to compare against the respective measurement techniques. The methodology allowed the development of parameters that produce the required amount of plastic deformation into the required depth of the material, for different thermal histories. Even though 6 % to 8 % of plastic strain can allow reorientation and the development of finer grains, 12 % of plastic strain or more is probably required to achieve a desired grain size. This value is equivalent to 4° lattice misorientation using an EBSD strain mapping technique and it is equivalent to an increase of hardness by at least20 HV. Different rolling and one alternative cold working techniques were investigated to address both individual issues, residual stress and microstructure. Side rolling was found to be far more effective on controlling residual stress and distortion than vertical interpass rolling. Profiled vertical inter-pass rolling on the other hand is far more effective to refine the microstructure and improve mechanical properties than flat rolling. Machine Hammer Peening is an alternative cold working techniques that offers a much higher degree of freedom compared to rolling. The proof of concept to integrate peening into additive manufacturing was successful. However, available machine hammer peening tools do not supply the impact energy required to be at eye level with rolling. It is estimated that approximately 5000 mJ would be required to be as effective as rolling with 70 kN. The fast thermal cycle within the heat affected zone during the additive deposition was measured for the first time at different locations, which allowed conclusions regarding the respective and local development of the microstructure. It furthermore helped to better understand the grain refinement mechanism, and the influence of thermal cycles on subsequent undesired grain growth. The research findings can be applied to develop effective inter-pass cold work strategies for arbitrary thermal cycles and they are sufficient to validate numerical simulations to design better process parameters more efficiently.
Open Access
Thermo-mechanical control of residual stress, distortion and microstructure in Wire and ARC additively manufactured Ti-6Al-4V
(2018-04) Hönnige, Jan Roman ; Colegrove, Paul A.; Williams, Stewart W.
Wire + arc additive manufacturing (WAAM), unlike most other additive techniques, targets the manufacture of near-net-shape parts for large-scale structural components with medium complexity. WAAM is of special interest for the aerospace industry for reducing lead-time, material and process costs. Ti−6Al−4V is one alloy that could potentially benefit most from the advantages of WAAM, due to high material and process costs, and is therefore the main scope of this research. The manufacture of critical-use components for civil aviation requires a high process control to provide consistently strong and isotropic mechanical properties, as well as the elimination of residual stresses. Cold work can manipulate and counteract residual stresses caused by the additive process. When applied between two layers (i.e. between the deposition passes → interpass) it was found to refine the microstructure and thereby significantly improve the mechanical properties. So far it was only understood that it can theoretically control both residual stress and microstructure, but the science behind the process and how different parameters influence the effectiveness was only proposed. The present research demonstrates how cold work can be used effectively to address both issues, by identifying the process-relevant mechanisms. Before manipulating residual stresses, their development needed to be investigated Behaviour that had only been predicted using numerical simulations was measured for the first time using neutron diffraction and contour method stress determination techniques. This behaviour includes the development of residual stress during the deposition of straight walls and intersections, stress redistribution upon distortion after unclamping and the potential of thermal stress relief. Analogies to previous findings on steel helped explain the findings. The knowledge of stress development finally helped the development of an analytical model to predict residual stress and distortion, as well as stress redistribution upon unclamping. The performance and parameters of plastic deformation strategies were investigated using various characterisation techniques. Those include hardness mapping, residual stress measurements using hole-drilling and the contour method, electron-backscatter-diffraction (EBSD) plastic strain mapping, heat treatment, as well as numerical simulations to compare against the respective measurement techniques. The methodology allowed the development of parameters that produce the required amount of plastic deformation into the required depth of the material, for different thermal histories. Even though 6 % to 8 % of plastic strain can allow reorientation and the development of finer grains, 12 % of plastic strain or more is probably required to achieve a desired grain size. This value is equivalent to 4° lattice misorientation using an EBSD strain mapping technique and it is equivalent to an increase of hardness by at least 20 HV. Different rolling and one alternative cold working techniques were investigated to address both individual issues, residual stress and microstructure. Side rolling was found to be far more effective on controlling residual stress and distortion than vertical inter-pass rolling. Profiled vertical inter-pass rolling on the other hand is far more effective to refine the microstructure and improve mechanical properties than flat rolling. Machine Hammer Peening is an alternative cold working techniques that offers a much higher degree of freedom compared to rolling. The proof of concept to integrate peening into additive manufacturing was successful. However, available machine hammer peening tools do not supply the impact energy required to be at eye level with rolling. It is estimated that approximately 5000 mJ would be required to be as effective as rolling with 70 kN. The fast thermal cycle within the heat affected zone during the additive deposition was measured for the first time at different locations, which allowed conclusions regarding the respective and local development of the microstructure. It furthermore helped to better understand the grain refinement mechanism, and the influence of thermal cycles on subsequent undesired grain growth. The research findings can be applied to develop effective inter-pass cold work strategies for arbitrary thermal cycles and they are sufficient to validate numerical simulations to design better process parameters more efficiently.

Browsing by Author "Hönnige, Jan Roman"

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