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Metal Powder-based Additive Manufacturing

Wednesday 11th October 2017

For the first time, this year’s Enlighten Conference will feature a programme dedicated to metal powder-based additive manufacturing (AM). The aim of the programme is to provide a platform for technical discussion of areas related to metal powder based AM processes and to encourage better communication and co-operation between leading and upcoming academics and industrialists in the field. The programme is open to all metal powder based AM processes, including selective laser melting, electron beam melting and direct energy deposition.


09.00 Registration  
09.15 Welcome and opening remarks  

SESSION 1: Materials & Processes for Metal Additive Manufacturing

Chair : Professor Ian Ashcroft

09.20 Crystal growth and the development of new alloys for additive manufacturing
Dr Son Pham, Imperial College London, UK

Making high quality and reliable metals still remains one of the biggest challenges in additive manufacturing (AM) of metals. One of the main reasons is due to the lack of indepth understanding of microstructures in AM metals. In particular, rapid cooling in AM leads to unique microstructures that are very different to those formed during slow cooling in other manufacturing processes. In this study, we present our fundamental study to understand the crystal growth in rapid cooling of 316L steel made by AM and how the crystal microstructures evolve during the repeated deposition of materials. Crystal grains in meltpools are seen to epitaxially grow from existing grains in the substrate. The rapid cooling results in extremely fine rod-like solidification cells that are strikingly different to the dendritic microstructures seen in cast metals. It is found that the direction of existing cells and the new thermal gradient are two governing variables for the growth of crystals in the new meltpool, leading to the branching or the nucleation of new cells at the meltpool boundaries. The understandings of crystal growth in rapid cooling and crystal evolution provide valuable information for selection of more suitable alloys for AM, and being integrated in machine learning subroutines to help search new alloys for additive manufacturing. As a result, we propose to print a high entropy alloy (HEA). Preliminary results show that the HEA alloy can be printed with very high consolidation and offers outstanding mechanical properties.

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09.40 Process optimisation of Selective Laser Melting (SLM) biomedical components: production of ankle prostheses with lattice structures
Dr Alessandro Fortunato, Università di Bologna, Italy

A study of SLM manufactured Cobalt Chromium Molybdenum personalized ankle implants is presented. A wide-ranging experimental campaign has been carried out on high density SLM prosthesis components to correlate process parameters to mechanical properties, roughness, geometric accuracy, and wear and corrosion resistance. The results highlight the fact that two different sets of parameters are needed to optimize separately final properties of CoCrMo components. High fluence in fact is necessary to obtain high density and mechanical strength, whereas low fluence is necessary for good geometric tolerance, and better wear and corrosion resistance. An optimized “double fluence” process strategy has also been employed to produce real endoprosthetic implants for kinematic testing to investigate the functional performance of the articular surface. Subsequently, osseointegration has been considered by designing the bone-implant interface to facilitate cellular proliferation and reduce stress shielding. Several lattice structures with different reproducible geometries have been mechanically tested to evaluate strength and stiffness. The structures most compatible with the properties of the bone have then been chosen for preliminary biologic studies, with cell viability observed after 24 hours and after 2 weeks. A complete prototype of total ankle prosthesis has been fabricated eventually to show the overall potentials of SLM in biomedical applications.

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10.00 Additive manufacturing of compact heat exchangers: A case study on waste heat recovery heat exchangers
Dr Ahmed Hussein, HiETA Technologies Ltd, UK

Metal Additive Manufacturing (AM) technologies in particular powder bed fusion processes such as Selective Laser Melting (SLM) are capable of producing complex metallic features directly from CAD model without the need of tooling. The design freedom and inherent surface roughness associated with the process means that high heat transfer geometries can be used in the heat exchanger core, thus significantly reducing its size and weight in comparison to conventional surfaces. This is combined with the ability to make tailored manifold shapes that minimise the flow maldistributions. This paper will present a case study on condenser and evaporator units manufactured for waste heat recovery system (WHR). The WHR used works on the principle of inverted Brayton cycle by rejected exhaust heat of 2L petrol into series of heat exchanger units. The units were processed in SLM using Inconel625 metal powder with particle size range of 10-60 μm. This material was selected for its suitability in heat exchanger applications at elevated temperature up to 800C. Optimal core geometry was selected for this application based on CFD optimisation and experimental validation. The heat exchanger channels were inspected and standard pressure leak tests were performed. The heat exchanger units were tested both separately and in a full system bench test. The results show that high compact, low volume, and lightweight heat exchanger can be achieved using AM technology. The unit effectiveness exceeds 95% dropping the exhaust temperatures from 750C to 14C.

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10.20 Overview of metal AM and lattice structure research
Dr Ian Maskery, University of Nottingham, UK
10.30 Refreshment break  
10.50 Alloys and powder feedstock for metal AM and investigation of process-microstructure-property relationships
Prof. Maurizio Vedani, Polytechnic University of Milan

Additive manufacturing represents a very attractive fabrication route for tools and dies considering the advantages offered by the ease of generation of complex shapes and by the ability of implementing conformal cooling channels into parts.

The conventional tool steels processed by traditional routes (e.g. in cast or wrought forms) feature complex microstructures that allow to withstand heavy working condition against wear, thermal and mechanical loads, but also make them very sensitive to processing condition. For the same reasons, tool steels in powder form are considered as challenging to be processed by selective laser melting or direct deposition techniques. In light of this scenario, new materials would be required for the tool industry, featuring suitable service performance but also good processability by SLM and other AM techniques.

The present contribution is aimed at reviewing the properties of some popular alloy steels used in AM for the tooling industry. The peculiar effects induced by the SLM processing (fast solidification rate and rapid solid state cooling) are described. Opportunities for manipulation of the microstructure for the development of new steels will be discussed and examples of improved alloys will be given accordingly.

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11.10 Melt pool modelling, simulation and experimental validation for SLM
Dr Ir. Wessel Wits, University of Twente, Netherlands

SLM parts are built by successively melting layers of powder in a powder bed. Process parameters are often optimized experimentally by laser scanning a number of single tracks and subsequently determining which settings lead to a good compromise between quality and build speed. However, experimentation only does not yield the necessary insights into the physical processes behind the results. Therefore, the laser interaction with the powder bed must be modelled to describe the melt pool behaviour that occurs during the laser melting process. Energy absorption and heat conduction are modelled to determine the temperature distribution and characteristics of the melt pool for various process parameters such as laser power, scan speed, powder layer thickness, etc. The numerical model and simulations have been validated using measurement data obtained from SLM experiments using titanium alloy Ti6Al4V. Melt pool modelling can be used to predict SLM process parameters ranges for which single tracks are of good quality. Moreover, the simulated temperature distribution can also serve as input for methods predicting part deformation due to residual stresses.

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11.30 Industrialisation of laser-based AM
Utkarsha Ankalkhope, Manufacturing Technology Centre (MTC), UK

Laser based metal additive manufacturing (AM) technologies are divided into two main categories: Powder Bed Fusion (PBF) and Directed Energy Deposition (DED). In recent years, PBF has demonstrated its potential for high value, low volume and niche industrial applications. It is capable of producing complex shapes and innovative designs, which cannot be manufactured by conventional manufacturing processes. Conversely, DED has demonstrated its niche for manufacture of near net shape components with improved speed and buy-to-fly ratio.

Even though the wide range of industrial sectors have appreciated the importance and adoption of these processes, it is taking longer to industrialise them for final production due to some of the challenges listed below,

- Robust AM process simulation to aid in distortion prediction and correction
- Real-time monitoring and closed-loop feedback to reduce defects
- Integration of AM process into the existing production workflow
- Certification and validation of AM components
- Quality control and assurance documentation

The National Centre for Additive Manufacturing at the Manufacturing Technology Centre (MTC), in Coventry, is helping industrialise AM and enabling companies to implement AM for their business. This presentation will explain the key challenges and the work being done to accelerate the industrialisation of laser based AM processes for end-use applications.

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11.50 Investigation on the effect of laser parameters and scan strategy on residual stress created in SLM using simulation
Luke Parry, Added Scientific Ltd, UK
12.00 Lunch break  
  Afternoon venue : Media Centre  

SESSION 2: Sources and systems for laser additive manufacturing of materials

Chair : Prof. Johannes Henrich Schleifenbaum

12.55 Introduction to afternoon  
13.00 KEYNOTE:
High-power diode laser sources for materials processing
Dr Klaus Kleine, Coherent Inc., USA

Beam sources for metal additive manufacturing – status quo and requirements
Christian Hinke, Research Campus, Digital Photonic Production (Germany)

14.00 Alternative beam sources and machine concepts for Laser Powder Bed Fusion
Florian Eibl, Fraunhofer Institute for Laser Technology, Germany
14.20 Refreshment break in the exhibition hall  
15.00 Low SMILE vertical stacked laser bars enable KW modular line lasers
Dr Chung-en Zah, Chief Technology Officer, Focuslight, China
15.20 Monolithically wavelength-stabilized high power diode lasers
Dr Paul Crump, Ferdinand-Braun-Institut, Germany
15.40 Poster Introduction  
16.10 POSTER SESSION - in exhibition hall  
17.05 Networking  


The 2017 Conference and Industry Programme, run by Enlighten Meetings with its partners, covers application and technology advances, innovations and emerging technologies.

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Prof. Ian Ashcroft (Co-chair)
University of Nottingham

Prof. Johannes Henrich Schleifenbaum (Co-chair)
Fraunhofer Institute for Laser Technology, RWTH Aachen University


Dr Wilhelm Meiners
Fraunhofer Institute for Laser Technology

Christian Hinke
RWTH Aachen University

Dr Wessel W. Wits

University of Twente

Dr Alessandro Fortunato

University of Bologna

Ian Brooks

Moog Inc., UK.

Prof. Iain Todd

University of Sheffield

Dr David Brackett

Manufacturing Technology Centre

Dr Adam Clare

University of Nottingham

Prof. Chris Tuck

University of Nottingham