CERES :: Browsing by Author "Colegrove, Paul A."

Browsing by Author "Colegrove, Paul A."

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Open Access
2D linear friction weld modelling of a Ti-6Al-4V T-joint
(Technological Educational Institute of Eastern Macedonia and Thrace, 2015) Lee, Lucie Alexandra; McAndrew, Anthony; Buhr, Clement; Beamish, K. A.; Colegrove, Paul A.
Most examples of linear friction weld process models have focused on joining two identically shaped workpieces. This article reports on the development of a 2D model, using the DEFORM finite element package, to investigate the joining of a rectangular Ti-6Al-4V workpiece to a plate of the same material. The work focuses on how this geometry affects the material flow, thermal fields and interface contaminant removal. The results showed that the material flow and thermal fields were not even across the two workpieces. This resulted in more material expulsion being required to remove the interface contaminants from the weld line when compared to joining two identically shaped workpieces. The model also showed that the flash curves away from the weld due to the rectangular upstand "burrowing" into the base plate.Understanding these critical relationships between the geometry and process outputs is crucial for further industrial implementation of the LFW process.
Open Access
3D modelling of Ti–6Al–4V linear friction welds
(Taylor & Francis, 2016-12-05) McAndrew, Anthony; Colegrove, Paul A.; Buhr, Clement
Linear friction welding (LFW) is a solid-state joining process that significantly reduces manufacturing costs when fabricating Ti–6Al–4V aircraft components. This article describes the development of a novel 3D LFW process model for joining Ti–6Al–4V. Displacement histories were taken from experiments and used as modelling inputs; herein is the novelty of the approach, which resulted in decreased computational time and memory storage requirements. In general, the models captured the experimental weld phenomena and showed that the thermo-mechanically affected zone and interface temperature are reduced when the workpieces are oscillated along the shorter of the two interface contact dimensions. Moreover, the models showed that unbonded regions occur at the corners of the weld interface, which are eliminated by increasing the burn-off.
Open Access
Additive manufacturing applications in Defence Support Services: current practices and framework for implementation
(Springer Verlag (Germany), 2017-02-21) Busachi, Alessandro; Erkoyuncu, John Ahmet; Colegrove, Paul A.; Drake, R.; Watts, C.; Wilding, S.
This research investigates through a systems approach, “Additive Manufacturing” (AM) applications in “Defence Support Services” (DS2). AM technology is gaining increasing interest by DS2 providers, given its ability of rapid, delocalised and flexible manufacturing. From a literature review and interviews with industrial and academic experts, it is apparent that there is a lack of research on AM applications in DS2. This paper’s contribution is represented by the following which has been validated extensively by industrial and academic experts: (1) DS2 current practices conceptual models, (2) a framework for AM implementation and (3) preliminary results of a next generation DS2 based on AM. To carry out the research, a Soft System Methodology was adopted. Results from the research increased the confidence of the disruptive potential of AM within the DS2 context. The main benefits outlined are (1) an increased support to the availability given a reduced response time, (2) reduced supply chain complexity given only supplies of raw materials such as powder and wire, (3) reduced platform inventory levels, providing more space and (4) reduced delivery time of the component as the AM can be located near to the point of use. Nevertheless, more research has to be carried out to quantify the benefits outlined. This requirement provides the basis for the future research work which consists in developing a software tool (based on the framework) for experimentation purpose which is able to dynamically simulate different scenarios and outline data on availability, cost and time of service delivered.
Open Access
Alternative friction stir welding technology for titanium–6Al–4V propellant tanks within the space industry
(Maney Publishing (T&F), 2017-02-24) Brassington, W. D. P.; Colegrove, Paul A.
Friction stir welding (FSW) offers an appealing solid state joining alternative to traditional fusion welding techniques for titanium alloys because it reduces problems associated with high temperature processing. Propellant tanks are a critical component of every spacecraft and contain several weld seams and a prime candidate for this innovative technology. This paper reviews the current technological maturity of FSW relative to titanium alloys and considers the application with respect to a pressure vessel. FSW is currently in a period of significant investment by large engineering companies and international research institutions. The technology is advancing and evolving to cater for high temperature alloys. Stationary shoulder FSW and hybrid techniques show promising potential with respect to Ti–6Al–4V. The tool material and limited process window for this material are restrictive factors at present but can be overcome with future development.
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
Analytical process model for wire + arc additive manufacturing
(Elsevier, 2018-04-03) Ríos, Sergio; Colegrove, Paul A.; Martina, Filomeno; Williams, Stewart W.
An analytical process model for predicting the layer height and wall width from the process parameters was developed for wire + arc additive manufacture of Ti-6Al-4V, which includes inter-pass temperature and material properties. Capillarity theory predicted that cylindrical deposits were produced where the wall width was less than 12 mm (radius <6 mm) due to the large value of the surface tension. Power was predicted with an accuracy of ±20% for a wide range of conditions for pulsed TIG and plasma deposition. Interesting differences in the power requirements were observed where a surface depression was produced with the plasma process due to differences in melting efficiency and/or convection effects. Finally, it was estimated the impact of controlling the workpiece temperature on the accuracy of the deposit geometry.
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, J.; Martina, Filomeno; Gu, Jianglong; Prangnell, P. B.; Honnige, Jan
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
Arc instabilities during split anode calorimetry with the TIG welding process
(Springer, 2018-03-29) Egerland, Stephan; Colegrove, Paul A.; Williams, Stewart W.
Split anode calorimetry investigations of tungsten inert gas (TIG) arcs were conducted using a large-diameter shielding gas nozzle. Some conditions displayed arc symmetry whilst others proved distinctly asymmetric. The variation of welding current and electrode tip to workpiece distance (ETWD) was studied. Decreasing the ETWD was found to increase the current density towards the arc axis but similar to a previous study of the authors, Gaussian distributions were not observed. The gas nozzle was designed to produce laminar gas flow and sound shielding behaviour; however, anode surface oxidation was found after welding, presumably caused by shielding gas contaminated with oxygen through the welding sequence. Therefore, axial arc symmetry was influenced by random effects. The conditions and reasons for the observed phenomena are explored within this paper.
Open Access
Characterisation of residual stress state and distortion in welded plates stress engineered by local mechanical tensioning
(Transtec Publications; 1999, 2014-01-01T00:00:00Z) Ganguly, Supriyo; Wescott, A.; Nagy, T.; Colegrove, Paul A.; Williams, Stewart W.
Local mechanical tensioning is one of the most efficient and industrially relevant stress engineering techniques to modify weld residual stress field and subsequently reduce buckling distortion. However, application of rolling load and its magnitude need to be optimised for an energy efficient rolling process. In the present study gas metal arc butt welded plates of low carbon mild steel were rolled by a dual roller in different rolling configuration (top and reverse side rolling) and with different magnitude of rolling load. All the plates were rolled post welding. Residual strain profiles of the post weld rolled plates were measured, using the SALSA strain scanner, and the inplane stress were characterized. Average distortion of the rolled plates was correlated with the residual stress state. Reverse rolling was found to be more effective in removing distortion while the stress profile did not show any significant reduction of the peak stress.
Open Access
Characterising the effects of high-pressure rolling on residual stress in structural steel welds
(Cranfield University, 2012-09-12) Coules, Harry E.; Colegrove, Paul A.
The large residual stresses which occur in welded objects are an unavoidable consequence of the non-uniform cycle of thermal strain inherent in most welding processes. Furthermore, the particular distributions of residual stress which are characteristic of welding can adversely influence several material and structural failure mechanisms, including fatigue fracture, elastic fracture and buckling. This thesis describes an experimental investigation into the use of localised high-pressure rolling of the weld seam for the purpose of residual stress reduction in steel welds. In preliminary experiments, it is demonstrated that the transient stresses which occur in an object while part of it is welded or rolled, can be inferred from strain measurements taken during the process. Furthermore, such measurements can be used to estimate the resulting residual stresses. Good agreement is observed between residual stress distributions found using this method and determined using neutron diffraction. The effect of rolling on residual stress in structural steel welds is then investigated using both of these measurement techniques. Rolling is shown to greatly reduce tensile residual stress at the weld seam, even introducing compressive stress when a greater rolling force is used. However, this is only the case when rolling is applied post-weld: by contrast, methods involving rolling prior to or during welding do not improve the residual stress distribution. It is proposed, on the basis of transient stress measurements, that this is because the deformation which occurs in a weld during cooling greatly exceeds its yield strain, and so any effect of high-temperature deformation on residual stress is subsequently erased. Other effects of rolling on the properties of a weld have also been studied. Using mechanical tests and microstructural analysis it is shown that while post-weld rolling causes work-hardening of structural steel welds, rolling the weld at high temperature results in refinement of the weld microstructure, also hardening it. The effect of roller geometry on residual stress and fatigue life of rolled specimens has been investigated: the induced residual stress distribution is relatively insensitive to the roller’s crosssectional profile, while the fatigue life is shown to be reduced by post-weld rolling. The implications of these findings for the practical implementation of weld rolling, along with many other applied aspects of the process are discussed. While rolling is undoubtedly a useful and highly effective tool for residual stress mitigation in welds, its secondary effects should always be carefully considered.
Open Access
Comparison of joining efficiency and residual stresses in laser and laser hybrid welding
(2011-04-01T00:00:00Z) Suder, Wojciech; Ganguly, Supriyo; Williams, Stewart W.; Paradowska, A. M.; Colegrove, Paul A.
Laser welding is a high energy density process, which can produce welds with less energy input and thereby lower residual stress generation compared to arc welding processes. However, the narrow beam dimension makes it extremely sensitive in terms of fit up tolerance. This causes a problem in achieving high quality welds. Laser with arc hybrid process overcomes such issues. In this paper, longitudinal residual strains were compared for autogenous laser welding and laser/TIG hybrid processes. Joining efficiency, which is defined by the penetration depth achieved per unit of energy input, was correlated with the residual strain generation. It has been shown that to achieve a specific penetration depth, there is an optimum welding condition for each of the welding processes, which will give minimum tensile residual stress generation. The results imply that for the same penetration depth, hybrid process resulted in similar to 50% higher tensile longitudinal domain compared to autogenous laser.
Open Access
A computationally efficient thermal modelling approach of the linear friction welding process
(Elsevier, 2017-09-14) Buhr, Clement; Colegrove, Paul A.; McAndrew, Anthony
Numerical models used to simulate LFW rely on the modelling of the oscillations to generate heat. As a consequence, simulations are time consuming, making analysis of 3D geometries difficult. To address this, a model was developed of a Ti-6Al–4 V LFW that applied the weld heat at the interface and ignored the material deformation and expulsion which was captured by sequentially removing row of elements. The model captured the experimental trends and showed that the maximum interface temperature was achieved when a burn-off rate of between 2 and 3 mm/s occurred. Moreover, the models showed that the interface temperature is reduced when a weld is produced with a higher pressure and when the workpieces are oscillated along the shorter of the two interface dimensions. This modelling approach provides a computationally efficient foundation for subsequent residual stress modelling, which is of interest to end users of the process.
Open Access
Control of residual stress and distortion in aluminium wire + arc additive manufacture with rolling
(Elsevier, 2018-06-25) Honnige, Jan; 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
Defining next-generation additive manufacturing applications for the Ministry of Defence (MoD)
(Elsevier, 2016-11-02) Busachi, Alessandro; Erkoyuncu, John Ahmet; Colegrove, Paul A.; Drake, Richard; Watts, Chris; Martina, Filomeno
“Additive Manufacturing” (AM) is an emerging, highly promising and disruptive technology which is catching the attention of the Defence sector due to the versatility it is offering. Through the combination of design freedom, technology compactness and high deposition rates, technology stakeholders can potentially exploit rapid, delocalized and flexible production. Having the capability to produce highly tailored, fully dense, potentially optimized products, on demand and next to the point of use makes this emerging and immature technology a game changer in the “Defence Support Service” (DS2) sector. Furthermore, if the technology is exploited for the Royal Navy, featured with extended and disrupted supply chains, the benefits are very promising. While most of the AM research and efforts are focusing on the manufacturing/process and design opportunities/topology optimization, this paper aims to provide a creative but educated and validated forecast on what AM can do for the Royal Navy in the future. This paper aims to define the most promising next generation Additive Manufacturing applications for the Royal Navy in the 2025 – 2035 decade. A multidisciplinary methodology has been developed to structure this exploratory applied research study. Moreover, different experts of the UK Defence Value Chain have been involved for primary research and for verification/validation purposes. While major concerns have been raised on process/product qualification and current AM capabilities, the results show that there is a strong confidence on the disruptive potential of AM to be applied in front-end of DS2 systems to support “Complex Engineering Systems” in the future. While this paper provides only next-generation AM applications for RN, substantial conceptual development work has to be carried out to define an AM based system which is able to, firstly satisfy the “spares demands” of a platform and secondly is able to perform in critical environments such as at sea.
Open Access
Design of an empirical process model and algorithm for the Tungsten Inert Gas wire+arc additive manufacture of TI-6AL-4V components
(University of Texas, 2013-08-31) Martina, Filomeno; Williams, Stewart W.; Colegrove, Paul A.
In the wire+arc additive manufacture process parameters can be varied to achieve a wide range of deposit widths, as well as layer heights. Pulsed Tungsten Inert Gas was chosen as the deposition process. A working envelope was developed, which ensures unfeasible parameters combinations are excluded from the algorithm. Thanks to an extensive use of a statistically designed experiment, it was possible to produce process equations through linear regression, for both wall width and layer height. These equations are extremely useful for automating the process and reducing the buy-to-fly ratio. For a given layer height process parameters can be selected to achieve the required layer width while maximising productivity.
Open Access
Designing a WAAM based manufacturing system for defence applications
(Elsevier, 2015-10-09) Busachi, Alessandro; Erkoyuncu, John Ahmet; Colegrove, Paul A.; Martina, Filomeno; Ding, Jialuo
Current developments in “Wire+Arc Additive Manufacturing” (WAAM) have demonstrated the suitability of the technology for rapid, delocalized and flexible manufacturing. Providing a defence platform with the ability of on-board WAAM capability, would give the platform unique advantages such as improved availability of its systems and ability to recover its capability after being subject to shock. This paper aims to investigate WAAM technology and define a WAAM based manufacturing system for In-platform applications.
Open Access
Development of a numerical modelling approach to predict residual stresses in Ti-6Al-4V linear fraction welds.
(2017-12) Buhr, Clement; Colegrove, Paul A.; McAndrew, Anthony
Linear friction welding (LFW) is a solid-state joining process which has been successfully implemented to manufacture bladed-disks, chains and near-net shape components. During welding, large residual stresses are created as a consequence of a non-uniform heating of the component which can severely affect the integrity of the structure. Experimental measurement of residual stresses and temperatures on linear friction welds is difficult, so researchers have used modelling to provide a better understanding of these important characteristics. Models developed in the literature, replicate the welding process by including the oscillation of the workpieces, resulting in long computational times. Therefore, numerical models are mostly confined to 2D geometry and complex geometry cases such as keystone or bladed-disk welds are rarely considered. This thesis focuses on the development and validation of computational models capable of predicting the residual stress field developed in Ti-6Al-4V LFW without modelling the complex mechanical mixing occurring at the weld interface. Using a sequentially coupled thermo-mechanical analysis on a 3D model defined in ABAQUS, the heat was applied at the weld interface using the average heat flux post-processed from the machine data obtained during welding trials, for all the phases. The material deformation was ignored and the material expulsion is accounted for by sequentially removing rows of elements. The models were validated against thermocouples, neutron diffraction and contour method measurements. The shearing occurring at the interface while welding was found to have little effect on the final residual stress field and therefore can be omitted. The residual stress field was found to be driven by the temperature profile obtained at the end of welding, prior to cooling and by the weld interface dimensions. A low weld interface temperature, shallow thermal gradient across the weld and small weld interface dimensions should be sought to minimise the residual stress magnitude. Therefore, a low burn-off rate obtained with reduced welding frequency, amplitude and applied force should be used; however the impact of using these parameters on the microstructure and material properties may need to be considered. The modelling approach was successfully implemented on a blisk LFW and its peculiar geometry was found to have little effect on the residual stress field as the peak magnitude is driven by the overall length of the part and the thermal profile prior to cooling. Several cycles of post-weld heat treatment were also investigated for the blisk weld. The results showed that all post-weld heat treatments reduced the residual stresses, however the differences between the heat treatments on the resulting stress field was minimal. In conclusion, the thesis presents an innovative computationally efficient modelling approach capable of predicting the residual stresses within standard and complex geometry LFW.
Open Access
Development of a numerical modelling approach to predict residual stresses in Ti-6Al-4V linear friction welds
(2017-12) Buhr, Clement; Colegrove, Paul A.; McAndrew, Anthony
Linear friction welding (LFW) is a solid-state joining process which has been successfully implemented to manufacture bladed-disks, chains and near-net shape components. During welding, large residual stresses are created as a consequence of a non-uniform heating of the component which can severely affect the integrity of the structure. Experimental measurement of residual stresses and temperatures on linear friction welds is difficult, so researchers have used modelling to provide a better understanding of these important characteristics. Models developed in the literature, replicate the welding process by including the oscillation of the workpieces, resulting in long computational times. Therefore, numerical models are mostly confined to 2D geometry and complex geometry cases such as keystone or bladed-disk welds are rarely considered. This thesis focuses on the development and validation of computational models capable of predicting the residual stress field developed in Ti-6Al-4V LFW without modelling the complex mechanical mixing occurring at the weld interface. Using a sequentially coupled thermo-mechanical analysis on a 3D model defined in ABAQUS, the heat was applied at the weld interface using the average heat flux post-processed from the machine data obtained during welding trials, for all the phases. The material deformation was ignored and the material expulsion is accounted for by sequentially removing rows of elements. The models were validated against thermocouples, neutron diffraction and contour method measurements. The shearing occurring at the interface while welding was found to have little effect on the final residual stress field and therefore can be omitted. The residual stress field was found to be driven by the temperature profile obtained at the end of welding, prior to cooling and by the weld interface dimensions. A low weld interface temperature, shallow thermal gradient across the weld and small weld interface dimensions should be sought to minimise the residual stress magnitude. Therefore, a low burn-off rate obtained with reduced welding frequency, amplitude and applied force should be used; however the impact of using these parameters on the microstructure and material properties may need to be considered. The modelling approach was successfully implemented on a blisk LFW and its peculiar geometry was found to have little effect on the residual stress field as the peak magnitude is driven by the overall length of the part and the thermal profile prior to cooling. Several cycles of post-weld heat treatment were also investigated for the blisk weld. The results showed that all post-weld heat treatments reduced the residual stresses, however the differences between the heat treatments on the resulting stress field was minimal. In conclusion, the thesis presents an innovative computationally efficient modelling approach capable of predicting the residual stresses within standard and complex geometry LFW.
Open Access
Development of weld repair methods for Rene 80 nickel based superalloy
(Cranfield University, 2012-03) Rush, Matthew T.; Colegrove, Paul A.
Nickel based superalloys are an integral material for gas turbines, where their excellent high temperature mechanical properties and corrosion resistance are utilised. Due to the increasing costs of raw materials, manufacturers are interested in repairing in-service and manufacturing defects in components. Unfortunately, superalloys such as Rene 80 are highly susceptible to welding defects such as liquation cracking and post-weld heat treatment cracking, which make repair welding highly difficult. The aim of the research in this thesis was to develop an improved understanding of welding defect production in nickel-based superalloys. In particular, the effect of repair process and its parameters were examined, with the ultimate aim to produce crack-free repair welds. The main theme of the work involved a large parametric study of the process parameter effects on welding defects in Rene 80 using a high power fibre laser. This work determined an optimised range of parameters which reduced the incidence of cracking. Furthermore, this work also identified a key relationship between the weld bead geometry aspect ratio and the incidence of cracking. This relationship was studied using neutron diffraction to determine the differences in strain and residual stresses between two welds with identical heat input but different geometry. An in-depth investigation of the cracks within the material, identified that as-welded cracks formed via liquation of secondary phases such as carbides, γ/γ’ eutectics, and secondary gamma prime. The post weld heat treatment cracks formed by the strain-age mechanism in Rene 80. From this work, a novel repair procedure avoiding the complications associated with using lower strength filler metal was developed, based on the optimised welding parameters. Finally, a number of advanced low heat input welding processes were also investigated for repair of superalloys.
Open Access
Effect of nitrogen in backing gas on duplex root weld properties of heavy-walled pipe
(Springer, 2016-04-22) Sales, A. M.; Westin, E. M.; Colegrove, Paul A.
Duplex stainless steels are increasingly used for offshore subsea components as the technology allows for deeper recovery of oil and gas reserves. Alloy UNS S31803 (EN 1.4462/UNS S32205) combines high strength with good resistance to pitting and crevice corrosion. This grade is alloyed with nitrogen and has good weldability. For heavy-walled process piping intended for subsea sour service, the properties of the root pass are of high importance. For this reason, the effect of using nitrogen in the backing gas was investigated. Test pieces were manually welded with the gas tungsten arc welding (GTAW) process using an ER2209 filler wire. Tensile, bending and hardness testing was carried out and showed acceptable results across all specimens. Higher contents of nitrogen in the backing gas showed more austenite formation and a significant increase in pitting corrosion resistance when compared with pure argon. With Ar + 2 % N2, there was no pitting, but a small weight loss of 1.7 g/m2 was measured. 10 % N2 was required to pass both the corrosion tests ASTM G48 Method A (4 g/m2) and ASTM A923 (1 g/m2). The highest average impact toughness was achieved with pure nitrogen as the backing gas.