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Purpose The paper reports an investigation into the mechanical behaviour of hybrid components produced by combining the capabilities of metal injection moulding (MIM) with the laser-based powder bed fusion (PBF) process to produce small series of hybrid components. The research investigates systematically the mechanical properties and the performance of the MIM/PBF interfaces in such hybrid components. Design/methodology/approach The MIM process is employed to fabricate relatively lower cost preforms in higher quantities, whereas the PBF technology is deployed to build on them sections that can be personalised, customised or functionalised to meet specific technical requirements. Findings The results are discussed, and conclusions are made about the mechanical performance of such hybrid components produced in batches and also about the production efficiency of the investigated hybrid manufacturing (HM) route. The obtained results show that the proposed HM route can produce hybrid MIM/PBF components with consistent mechanical properties and interface performance which comply with the American Society for Testing and Materials (ASTM) standards. Originality/value The manufacturing of hybrid components, especially by combining the capabilities of additive manufacturing processes with cost-effective complementary technologies, is designed to be exploited by industry because they can offer flexibility and cost advantages in producing small series of customisable products. The findings of this research will contribute to further develop the state of the art in regards to the manufacturing and optimisation of hybrid components.

Hybrid manufacture of components by combining capabilities of replication and additive manufacturing processes offer a flexible and sustainable route for producing cost-effectively small batches of metal parts. At present, there are open issues related to surface integrity and performance of such parts, especially when utilising them in safety critical applications. The research presented in this paper investigates the ductility amplification of hybrid components produced using metal injection moulding to preform and then build on them customisable sections by laser-based powder bed fusion. The properties of such hybrid components are studied and optimised through the use of non-conventional post treatment techniques. In particular, hot isostatic pressing (HIP) is employed to improve mechanical strength and to produce hybrid components that have consistent properties across batches and throughout the samples, minimising microstructural heterogeneities between fabrication processes. Thus, the investigated post-processing method can offer an extended service life of hybrid components, especially when operating under severe conditions. The optimised post treatment was found to increase the hybrid components’ strength compared to as-built ones by 68% and ~11% in yield strength (YS) and ultimate tensile strength (UTS), respectively. Subsequently, leading to a great pitting resistance, thus, making HIP samples suitable for corrosive environments. The advantages of the HIP treatments in comparison to the conventional heat treatment of hybrid components are discussed and also some potential application areas are proposed.

High stiffness fracture fixation devices inducing absolute stability, activate inefficient primary healing and stress shielding. Taking High Tibial Osteotomy as a representative example, review of the clinical literature and mapping the fracture healing process revealed two physically contradicting requirements, which are only partially met by current techniques. Stiffness of the fixation is required immediately after fracture, however in the remodelling phase this can cause stress shielding. Stability is required immediately after fracture, however in the ossification phase less stability is required to stimulate secondary (and more efficient) healing. This study evaluates the use of the TRIZ Inventive Design Principles to overcome these physical contradictions. Six designs concepts were evaluated, of which the Macro-Geometry stiffness modulated design was ranked the highest. This was achieved through spatial decomposition of the problem utilising the Inventive Principles of Asymmetry, Extraction and Local Quality. This study offer perspectives on how to increase the patient specificity of fixation utilising the increased topology freedom of design for additive manufacture (AM).

It is generally recognised that electron beam melted (EBM) Ti-6Al-4V alloys exhibit a microstructural gradient along the build direction, but there have been some inconsistent experimental observations and debate as to the origin and magnitude of this effect. Here we present an unambiguous evaluation of this microstructural gradient and associated mechanical property along the EBM build direction on purpose-built round bar RB samples with build height of 380 mm and rectangular plate RP samples with build height of 120 mm. Columnar prior β grain width was found to increase (from 86 ± 38 to 154 ± 56 µm in RB and from 79 ± 34 to 122 ± 56 µm in RP samples) with the build height and the similar increase was also observed for α lath width (from 0.58 ± 24 to 0.87 ± 33 µm in RB and from 1.50 ± 45 to 1.80 ± 49 µm in RP samples). These observations can be attributed to the thermal gradient in the powder bed that produced a cooling rate gradient along the build height. The measured α lath width variation along the build height followed a log-normal distribution. The graded microstructure resulted in a decrease in micro-hardness which correlated very well with the mean α lath width by following a Hall-Petch relation.

Purpose – This paper aims to investigate the effects on material properties of layer-by-layer application of pressure during fabrication of polymeric parts by additive manufacturing (AM). Although AM, also known popularly as 3D printing, has set a new standard for ease of use and minimal restraint on geometric complexity, the mechanical part properties do not generally compare with conventional manufacturing processes. Contrary to other types of polymer processing, AM systems do not normally use (in-process) pressure during part consolidation. Design/methodology/approach – Tensile specimens were produced in Somos 201 using conventional laser sintering (LS) and selective laser printing (SLP) – a process under development in the UK, which incorporates the use of pressure to assist layer consolidation. Findings – Mechanical testing demonstrated the potential to additively manufacture parts with significantly improved microstructure and mechanical properties which match or exceed conventional processing. For example, the average elongation at break and ultimate tensile strength of a conventionally laser-sintered thermoplastic elastomer (Somos 201) increased from 136 ± 28 per cent and 4.9 ± 0.4 MPa, to 513 ± 35 per cent and 10.4 ± 0.4 MPa, respectively, when each layer was fused with in-process application of pressure (126 ± 9 kPa) by SLP. Research limitations/implications – These results are based on relatively small sample size, but despite this, the trends observed are of significant importance to the elimination of voids and porosity in polymeric parts. Practical implications – Layerwise application of pressure should be investigated further for defect elimination in AM. Originality/value – This is the first study on the effects of layerwise application of pressure in combination with area-wide fusing.

Additive manufacturing (AM) offers a number of benefits over conventional manufacturing, giving an increased design freedom and the opportunity to integrate multiple components, saving weight. The rigorous standard for material integrity set by the Aerospace sector necessitates the development of systems to ensure quality. Laser ultrasonic testing (LU) is a non-contact inspection technique which has been proposed as suitable for in-situ monitoring of additive manufacturing processes, as measurements can be taken at elevated temperatures. This paper will show the capability of this technique for assuring material quality in metal AM parts and compare LU with x-ray computed tomography (XCT).

The authors acknowledge the significant support provided by researchers from the Materials Centre, Department of Chemistry, University of Leicester (Dr Harris, Robert C., Dr Juma, Jamil ‎ and particularly Karl S. Ryder, Professor of Physical Chemistry). The affiliation of co-author A.A.Al-Barzinjy at time of submission of the article and duration of the experimental work, was the Materials Centre, Department of Chemistry, University of Leicester. The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. This three-level three-factor full factorial study describes the effects of electropolishing using deep eutectic solvents on the surface roughness of re-melted 316L stainless steel samples produced by the selective laser melting (SLM) powder bed fusion additive manufacturing method. An improvement in the surface finish of re-melted stainless steel 316L parts was achieved by optimizing the processing parameters for a relatively environmentally friendly electropolishing process using a Choline Chloride ionic electrolyte. The results show that further improvement of the response value-average surface roughness (Ra) can be obtained by electropolishing after re-melting to yield a 75% improvement compared to the as-built Ra. The best Ra value was less than 0.5 lm, obtained with a potential of 4 V, maintained for 30 min at 40 C. Electropolishing has been shown to be effective at removing the residual oxide film formed during the remelting process. The material dissolution during the process is not homogenous and is directed preferentially toward the iron and nickel, leaving the surface rich in chromium with potentially enhanced properties. The re-melted and polished surface of the samples gave an approximately 20% improvement in fatigue life at low stresses (approximately 570 MPa). The results of the study demonstrate that a combination of re-melting and electropolishing provides a flexible method for surface texture improvement which is capable of delivering a significant improvement in surface finish while holding the dimensional accuracy of parts within an acceptable range.

In this work, the effects of re-melting parameters for postprocessing the surface texture of Additively Manufactured parts using a statistical approach are investigated. This paper focuses on improving the final surface texture of stainless steel (316L) parts, built using a Renishaw SLM 125 machine. This machine employs a fiber laser to fuse fine powder on a layer-by-layer basis to generate three-dimensional parts. The samples were produced using varying angles of inclination in order to generate range of surface roughness between 8 and 20 µm. Laser re-melting (LR) as post-processing was performed in order to investigate surface roughness through optimization of parameters. The re-melting process was carried out using a custom-made hybrid laser re-cladding machine, which uses a 200 W fiber laser. Optimized processing parameters were based on statistical analysis within a Design of Experiment framework, from which a model was then constructed. The results indicate that the best obtainable final surface roughness is about 1.4 µm ± 10%. This figure was obtained when laser power of about 180 W was used, to give energy density between 2200 and 2700 J/cm2 for the re-melting process. Overall, the obtained results indicate LR as a post-build process has the capacity to improve surface finishing of SLM components up to 80%, compared with the initial manufactured surface.

Lastform, a three year EPSRC (IMI) programme, has investigated metallic laminating techniques to produce large‐scale production capable tooling. This work is intended as an overview of the research and development performed at the University of Warwick’s Warwick manufacturing Group. The programme was a collaboration between seven industrial partners and three universities with each university having a discreet area of research. The focus at Warwick was to establish robust methods of joining metal sheets to form tools for different production processes. Bonding mediums, test parts for process evaluation, sample tools and production tools are described. The advantages of metal laminating for different processes are evaluated. Results include reduced lead‐time and cost savings and enhanced processing capability by the use of conformable heating or cooling channels.

The subject of this paper is the assessment of the thermal and mechanical properties of Invar steel coatings, deposited using electric arc spraying, and the correlation of these properties to the spray parameters and processes used to offer coatings with characteristics appropriate to the requirements of tools used in the fabrication of precision polymer matrix composite work pieces. In particular, two processing methods, inert and air atomization, and three arc spray gun configurations (air cap design) were evaluated. The low coefficient of thermal expansion (CTE) properties of Invar are maintained in the spray-deposited coatings using both high velocity oxy-fuel (HVOF) and air-atomized arc spraying, although HVOF coatings have significantly lower CTE and greater durability than those deposited by arc spraying. The mechanical properties of the coatings are low compared to bulk Invar, regardless of the spray parameters and hardware used. Inert arc spraying affords more consistent coating characteristics but this comes with a compromised durability. The spray hardware was found to be more significant in determining the coating properties than the parameters employed.

The intention of this paper is to describe some of the activities undertaken by the Warwick Manufacturing Group towards an EPSRC/Industrially funded research programme called LASTFORM. The aim of the programme is to produce LArge Scale Tooling FOr Rapid Manufacture, predominantly in the Aerospace industry. At Warwick the method adopted was to LASER cut metal laminations to correspond to slices taken from a CAD model. The laminates were then joined to provide a near net shape of the required tool. Warwick’s main contribution to the programme was to investigate the various ways of joining these laminations together so as to withstand the production environment. The outline methodology is described and includes material selection, test procedures and the manufacture of simple and more complex tools. The paper concludes that LASTFORM tooling is suitable for a number of different processes at both low and high temperatures. Cost savings, lead time reductions and opportunities to add value to the tools is demonstrated.

The Tooling and Casting subgroup of the European Action on Rapid Prototyping (EARP) has undertaken a project to investigate the problems associated with using rapid prototype models as sacrificial patterns for investment casting. The accuracy and surface finish of the models and the castings were also assessed so that a comparison could be made. Models from each process were manufactured by different members of EARP and then three foundries were each given a set of models to convert to castings. Observes that one of the oldest metal manufacturing techniques, which dates back to 4000‐6000 BC, is being used with one of the most modern ‐ rapid prototyping.

Although significant progress has been made toward digital printing of electronics using inkjet technologies, the potential of laser printing for digital fabrication has been largely overlooked. Despite their speed and resolution capabilities toner-based systems are often regarded as incapable of handling conductive materials. This research reports recent laser printing development and its potential to replace conventional printed circuit board manufacturing steps, including conductive track deposition. The research had a dual focus, demonstrating proof of concept with conventional office laser printers (for artwork masks, etch resists, and seed layers for overplating), and used industrial laser printers with developmental toners to support direct production of electronics (conductive tracks, dielectric layers, and legends). The results confirm that laser printing can complement other digital printing approaches for directly depositing resists and conductive tracks. This work was done in collaboration with Quartz Technical Services Ltd., Merlin Flex-Ability Ltd., CTG PrintTEC GmBH and ZEAC. The UK Technology Strategy Board funding is gratefully acknowledged for funding a portion of the work reported herein.

The maximum energy dissipation principle can be successfully applied to describe a range of basic nonlinear models. The application of the general variational framework [29] , [30] , [31] has been illustrated for basic linear schemes. The study presented in the paper shows how the kinetic processes at this level of the biomolecular and biophysical phenomena can be effectively described in terms of the maximum energy dissipation principle and its variational formulation. On the basis of this approach, a range of Lagrangians was proposed for basic nonlinear dissipative kinetic models. The results of this study show that the framework is in agreement with nonlinear equilibrium thermodynamics.

PurposeThe purpose of this paper is to ascertain the stab resistance characteristics of a series of planar and articulated laser sintered (LS) samples, in accordance with the United Kingdom Home Office Scientific Development Branch (HOSDB) Body Armour Standard – Publication 39/07.Design/methodology/approachA series of LS planar samples were manufactured using an EOS P100 Formiga system, manufactured from 100 per cent virgin or a 50:50 mix of recycled and virgin Nylon (PA2200), ranging in thickness from 1‐10 mm. All planar samples were stab tested to the HOSDB knife‐resistance (KR) level one impact energy of 24 Joules, using an in‐house manufactured HOSDB guided rail drop test impact rig and standardised knives. Penetration through the underside of each sample was measured and recorded. These results were then used to develop an articulated, additive manufactured (AM) scale textile – LS from a 50:50 mix of recycled and virgin PA2200 powder. These samples were then tested using the aforementioned impact rig and stab impact energy.FindingsThe research demonstrated that while virgin PA2200 sample required a minimum thickness of 8 mm to achieve stab‐resistance below the HOSDB maximum penetration limit of 7 mm, this figure can be reduced to 5.6 mm when manufacturing LS planar samples from a 50:50 mix of virgin and recycled PA2200. Results from stab testing the articulated samples indicated a successful AM textile‐like design, with a maximum knife penetration of 1.6 mm – below the 7 mm HOSDB limit.Originality/valueThe paper describes a unique application of AM technologies for the manufacture of high‐performance stab resistant AM textiles.

This paper describes the use of a non-contact structured light scanning technique, computer aided design (CAD) and additive manufacturing (AM) to produce a burns pressure therapy splint, also known as mask or conformer. Masks such as this are used in the treatment of hypertrophic scars resulting from burns injuries. The case study described here is of a nine year old girl with significant hypertrophic scars to her face, especially her nasal bridge. Non-contact structured light scanning was used to capture accurate data of the patients face. This data was then post processed and used to produce a model of the patients face using the three dimensional printing processes from Z Corporation. The plaster model formed was then used to generate a former on which a polyethylene tetrephthalate glycol (PETG) mask was vacuum formed. The results illustrate the benefits and effectiveness in terms of accuracy of adopting an integrated surface scanning, CAD and AM approach for easier intervention and treatment.

A quantitative understanding of the bone remodeling process is of considerable biomedical and practical biotechnological interest to support the application of layer manufacturing techniques to produce scaffolds for surgical applications. Osteoclasts and osteoblasts play a principal role in different models of the bone multicellular unit operating in bone and display a rich spectrum of behaviour. The goal of this work is to show that it is possible to capture the cyclic dynamics of operating cells. The central idea of the mathematical model is that the regulatory nature of osteocytes is the basis of the cyclic-like behaviour associated with the system (remodeling process)as a whole. We developed this model taking due account of the apoptosis of osteocytes as a possible regulation loop in bone remodeling control. By applying the ordinary differential equations technique to the model, we show cyclic modes over a wide range of constants that have clear biological relevance. Simulations show that for a particular range of constants the model exhibits a torus-like quasi-steady state. Further investigation into these simulations indicates the existence of a surface in the osteoclasts-osteoblasts-osteocytes-bone space, that could be interpreted as a conservative value confirming the substrate-energy regenerative capability of the bone remodeling system. It is suggested that the nature of this recovering potential is directed against both mechanical and biochemical damage to the bone.

To help to understand the modelling process that occurs when a scaffold is implanted it is vital to understand the rather complex bone remodelling process prevalent in native bone. We have formulated a mathematical model that predicts osteoactivity both in scaffolds, as well as in bone in vivo and could set a basis for the more detailed allosteric models. The model is extended towards a bio-cybernetic vision of basic multicellular unit (BMU) action, when some of the regulation loops have been modified to reflect the allosteric control mechanisms, developed by Michaels–Menten, Hill, Koshland–Nemethy–Filmer, Monod–Wyman–Changeux. By implementation of this approach a four-dimensional system was obtained that shows steady cyclic behaviour using a wide range of constants with clear biological meaning. We have observed that a local steady state appears as a limiting cycle in multi-dimensional phase space and this is discussed in this paper. Physiological interpretation of this limiting four-dimension cycle possibly related to a conservative-like value has been proposed. Analysis and simulation of the model has shown an analogy between this conservative value, as a kind of substrate-energy regenerative potential of the bone remodelling system with a molecular nature, and to the classical physical value — energy. This dynamic recovery potential is directed against both mechanical and biomechanical damage to the bone. Furthermore, the current model has credibility when compared to the normal bone remodelling process. In the framework of widely recognised Hill mechanisms of allosteric regulation the cyclic attractor, described formerly for a pure cellular model, prevails for different forms of feedback control. This result indicates the viability of the proposed existence of a conservative value (analogous to energy) that characterises the recovery potential of the bone remodelling cycle. Linear stability analysis has been performed in order to determine the robustness of the basic state, however, additional work is required to study a wider range of constants.

One approach to developing a mathematical model that predicts osteoactivity both in bio-scaffolds, as well as the in bone tissue in vivo, is based on a bio-cybernetic vision of basic multicellular unit (BMU) action. In the case of the model presented in this paper, some of the loops of regulation have been modified to reflect the range of allosteric control mechanisms: Michaelis–Menten, Hill, Adair, Koshland–Nemethy–Filmer (KNF), Monod–Wyman–Changeux (MWC). This approach has resulted in a four-dimensional system that shows steady cyclic behaviour using a range of constants with clear biological meaning. The initial findings suggesting that a steady state appears as a cycle in multidimensional phase space and this is discussed in this paper. The existence of this cycle in the osteoclasts–osteoblasts–osteocytes–bone subspace indicates that there is a conservative value along steady trajectories for this dynamic system. Biophysical interpretation of this conservative value has been proposed as a kind of substrate-energy regenerative potential of the bone remodelling system with a similarity to the classical physical value—energy. Such a recovery “potential” is directed against both mechanical and biomechanical damage to the bone. The current model has credibility when compared to the normal bone remodelling process. In the framework of widely recognised Michaelis–Menten mechanisms of allosteric regulation the cyclic attractor, described formerly for a pure cellular model, prevails for different forms of feedback control. This finding demonstrates the viability of the suggestion of the subsistence of conservative value (analogous to energy) that characterises the recovery potential of the bone remodelling cycle. The results indicate that the robust behaviour of the model is maintained from the simple cellular level to the molecular biochemical level of regulation.

Biological parameters, such as bone resorption and formation constants, are important variables to achieve optimised hard tissue scaffolds design. To help to understand the modelling process that occurs when a scaffold is implanted it is vital to understand the rather complex bone remodeling process prevalent in native bone. One approach to developing a mathematical model that predicts osteoactivity both in scaffolds, as well as in bone in vivo, is based on a bio-cybernetic vision of basic multicellular unit (BMU) action – Komarova et al. (2003) . In the case of the model presented in this paper, an additional loop of regulation based on osteocyte activity has been added. This approach has resulted in a four-dimensional system, which shows steady-quasi-cyclic behaviour using a particular range of constants with real biological meaning. The initial findings suggesting that the basic steady-state appears as a torus in multidimensional phase space have been discussed. The existence of this surface in the osteoclasts–osteoblasts-osteocytes-bone subspace indicates that there is a first integral for this dynamic system. Biological and physical interpretation of this integral as a conservative value has been proposed. It is possible to draw an analogy between this conservative value, as a kind of substrate–energy regenerative potential of the bone remodeling system with a molecular nature, to the classical physical value (energy). There are clear indications that there is recovering potential within the BMU that results in a steady operating genetically predominated bone remodeling process. This recovering potential is directed against both mechanical and biomechanical damage to the bone. The current model has credibility when compared to the normal bone remodeling process. However, additional work is required to study a wider range of constants.

Thermal spraying methods have been mooted as a method of manufacturing tooling for many years and yet they have not made a significant in-road into this market. Generally, recent metal spraying research has focussed on the manufacture of small, high-pressure tools (for example, for automotive injection moulding tools). However, the metal spray process really lends itself to the manufacture of large tooling where it can compete more effectively against alternatives such as machining. The 3-year, £ 750k, IMI Spray Mould Programme, funded jointly by EPSRC (IMI) and the industrial partners: Airbus, BAE SYSTEMS, Bombardier Aerospace Shorts, A.T. Poeton, Rover Group, and Sulzer Metco, commenced in June 1997. The aim of this research is to develop a method of manufacturing tooling for composite aerospace components, particularly large primary structures over 15 m in length. This paper will present the results of this research programme, including technical data comparing both the technical and economic advantages of this novel approach to tool construction.

Rapid laminating methods predates rapid prototyping by several years, indeed the first work on laminated tooling by Professor Nakagawa was initially published in the late 1980s. Since then, Nakagawa’s team has been joined by a number of other research groups, with interest being boosted by the advent of rapid prototyping. This paper presents some of the finding of a 3 years study undertaken to investigate the use of laminated steel tooling for a range of automotive and aerospace production processes. The results of the programme are illustrated using production tooling for injection moulding of automotive components. The benefits of laminated tooling are shown, not just in terms of reduced cost and lead-times but perhaps more importantly, through reduced cycle times and improved part quality by the use of conformal cooling.

A diverse range of Rapid Prototyping, or layer manufacturing techniques have evolved since the introduction of the firstprocess in the late 1980's. Many, although not all, rapid prototyping processes rely on lasers to provide a localised andcontrollable source of light for curing a liquid photopolymer or heat to fuse thermoplastic powders to form objects. This

Traditionally investment casting of biomedical implants has utilized the lost wax process, this paper is an investigation into the possibilities of casting small lots of custom specific medical implants directly and indirectly from various rapid prototyping & tooling techniques. Small batch quantities for quick turn arounds cost and lead times are the main contributing factors for the purpose of this investigation. To directly produce parts means that a RP model will be used in the place of the wax pattern in the investment casting process. To indirectly produce parts means that a mould, which has been generated from RP&T techniques, will be used to manufacture wax patterns that will then in turn be used to investment cast the parts. The device to be manufactured is a non-sterile, referred to as ‘trial’ prosthetic implant. The implant is used by the operating surgeon to check the ‘fit’ of the cavity that will be made to receive the prosthesis plus bone cement that will be used to fix the implant in place.

This work was performed within IMI Spray Mould, an EPSRC joint funded programme, aimed at developing a manufacturing route for large aerospace composite forming tooling, based on metal spray technologies. Assesses the mechanical properties of Invar steel coatings, deposited using electric arc spraying, and correlates these properties to the spray parameters and processes used so as to offer coatings with characteristics appropriate to the tooling requirements. In particular, two processing methods, inert and air atomisation, and three arc spray gun configurations (air cap design) are evaluated. The mechanical properties of the coatings are found to be low compared to bulk Invar, regardless of the spray parameters and hardware used. Inert arc spraying affords more consistent coating characteristics but this comes with a compromised durability. The spray hardware is found to be more significant in determining the coating properties than the parameters employed.