Technical Insight: Laser Metal Deposition

Laser metal deposition (LMD) is an additive manufacturing method that uses a high-powered laser to create a melt pool onto a substrate into which metal powders (although ceramics can also be used) are fed. The heat of the pool melts the powder materials so that they are fusion-bonded to the substrate. By repeating the process to set geometries it is possible to build parts layer-by-layer.

TWI has extensive experience in additive manufacturing processes including laser metal deposition, supporting industry through a range of different projects and building a breadth of industry experience and research as a trusted source of technical excellence.

Although TWI’s work includes providing direct and confidential support for individual Industrial Member companies, we also conduct projects as part of our ongoing Core Research Programme (CRP) that aim to advance processes and technologies for the wider benefit of our Members.

Core Research Programme (CRP) Projects

Example CRP projects undertaken at TWI related to the laser metal deposition process include…

- Optimisation of Direct Laser Metal Deposition of Alloy 718

To aid the uptake of direct metal laser deposition (DMLD) we created a CRP project to help establish a link between the process parameters used, the microstructure created, and the properties of the deposit, providing the necessary information for reliable part design, particularly for the aerospace industry. To this end, our experts conducted a programme of work to deliver relevant data on the performance of DLMD deposits of alloy 718. Alloy 718 was chosen as a well-established material that was already in widespread use, with applications in many areas of aeroengine design. Furthermore, alloy 718 components can be very large and thus offer some of the greatest savings (through repair or additive manufacture). It was also the baseline from which other polycrystalline alloys are judged. This CRP project assessed the performance of direct metal laser deposits for additive manufacture or repair purposes and established links between performance, observed weld quality, and detailed microstructure. This provided quantitative data that could be employed for modelling the microstructural development of direct metal laser repair deposits, as well as providing guidance for effective DMLD additive manufacture and repair of alloy 718 and similar materials.

- Mechanical Performance of Laser Metal Deposited Alloy 718

TWI’s earlier research into additive manufactured alloy 718 was extended with a further CRP project to provide mechanical performance data of LMD alloy 718. This would allow our team to optimise process parameters based on performance rather than metallurgical quality. Rectangular blocks of ally 718 were deposited on 316L stainless steel plates (Figure 1.) and subjected to direct two-stage heat treatment, with two parameters being developed for investigation; high energy input (HEI) and low energy input (LEI). Wrought alloy 718 was used as a benchmark for the LMD part tensile and fatigue testing (Figure 2), while creep rupture testing was also performed.

- Titanium 5553/811 Laser Metal Deposition for Aerospace Use

Also investigating LMD for the aerospace industry was a CRP project that examined the suitability of two titanium alloys (Ti-8Al-1Mo-1V (Ti-811), and Ti-5Al-5V-5Mo-3Cr (Ti-5553)) for laser metal deposition. Our team used the nickel-based alloy, Mar-M247, as a candidate material due to its high aluminium and titanium content which makes it very susceptible to crack formation and propagation during high temperature processing. This would open a pathway to the repair and refurbishment of aerospace components manufactured from modern high-strength alloys with the potential for substantial cost savings on the overhaul of high-cost components. The results were compared for the titanium alloys and Mar-M247, which was found to be impossible to deposit without severe cracking using any parameter combination.

Joint Industry Projects

Our Joint Industry Projects (JIPs) allow interested parties to come together as project sponsors in return for exclusive access to the research results and the opportunity to shape the direction of the project. These allow us to focus on specific challenges that impact particular industries and areas of interest to similar organisations.

- Certification of Laser Powder Additive Manufactured Components for Industrial Adoption in the Energy and Offshore Sectors

Working in partnership with Lloyd’s Register Energy, TWI aligned R&D with real-world practices to provide industry product certification guidelines to aid the industrial adoption of additive manufacturing (AM) technologies, including LMD, for the energy and offshore sectors. In addition to identifying potential applications for the AM processes, the project saw practical work conducted to determine optimum build parameters and the required inspection activities to certify components identified by the project sponsors and create industry-ready guidelines.

Public-Funded Projects

In addition, our expertise has been used on a range of public-funded projects, where we typically worked as part of a wider consortium of industry and academic experts to solve challenges of national or international industrial interest.

- Innovative Inspection Techniques for Laser Powder Deposition Quality Control

The European Commission-funded INTRAPID project was created to deliver three non-destructive testing (NDT) techniques for the inspection of parts and components created through additive manufacturing, with a particular focus on LMD.

- Additive Manufacturing for Wear and Corrosion Applications

https://www.twi-global.com/what-we-do/research-and-technology/research-programmes/public-funded-projects/amcor

Also funded by the European Commission, the collaborative AMCOR project worked to develop and demonstrate LMD manufacturing systems for the deposition of functional graded coatings (FGM) and 3D features onto metallic components supplied by industry that are subjected to in-service wear and corrosion. This was supported by the development, production and testing of mixed powder combinations for coatings suitability.

- Scale-up of Additive Manufacturing with Materials Manipulation Processing for Higher Performance and Reducing Waste in Manufacturing and Repair

The Scamper project, funded by Innovate UK, sought to address the problem of material waste in the aerospace sector, where up to 90% of material was being wasted during part manufacturing. LMD was seen as a solution to this problem via the direct manufacture of complex components in an expanded range of metallic alloys. This would also prove beneficial for repair, while the project partners also sought to improve LMD technology in terms of suitable materials, production rate and size of components.

Industrial Member Support and Research Projects

Our experts also undertake support and research projects for the benefit of specific Industrial Members. Many of these projects are necessarily confidential in nature, with the outcomes being provided directly to the Member in question. However, there are some examples that we are able to share…

- Innovative Laser Technology Restores the Iconic Spitfire

TWI was contacted by the Aircraft Restoration Company (ARC) who were restoring a Second World War Spitfire at Duxford Aerodrome in Cambridgeshire when a crack was detected in the landing gear suspension link. Our experts recommended high power LMD to deliver a crack free repair with a minimum effect on the properties of the original component material. The parameters for the repair were tested on a scrap part provided by ARC. Because the material grade used for the original Spitfire manufacture was now obsolete, we identified a modern high tensile steel that was available as a metal powder and closely matched the original for composition and material properties. Following an NDT inspection of the defect to determine the extent of the cracking, the defective material was machined away, allowing us to deliver a crack free repair of the landing gear component (Figures 3-5).

- Powder Metal Repair Process

TWI worked alongside a leading aircraft engine manufacturer to develop direct metal laser deposition (DMLD) for the repair of blades and seal segments (Figure 6).

- Repairing Worn Shafts using Laser Metal Deposition

We were contacted by an Industrial Member company to conduct a programme of work to apply LMD to both new and worn shafts from industrial rotating equipment. Having assessed the repair requirements and determined that LMD was the best solution to the challenge, TWI produced cladded test pieces for analysis using an agreed deposit geometry. One shaft was supplied specifically for experimenting with process parameters, which allowed us to produce a welding procedure specification for the client’s approval. This specification was then used for the repair of the two worn shafts (Figure 7).

- Repair of Hydraulic Pump Shafts

Rotherham-based SME, Hydraulic Pumps (UK) Ltd contacted TWI to solve a challenge related to the repair of hydraulic units. Due to the aggressive operating conditions in which they operate, parts typically suffer from severe wear and damage. However, some of the components are either obsolete or have high costs and lead times for replacements. We were able to recommend LMD as a potential solution, allowing parts that would have been scrapped to be repaired and returned to service. The low heat nature of LMD means that the material properties of the highly alloyed carbon steels used for hydraulic pump components are unaffected by the process, completing the repair without affecting the strength of the part and without the likelihood of significant distortion. The process was tested on damaged pump shafts (Figure 8) that were repaired using LMD (Figure 9) and returned to Hydraulic Pumps (UK) Ltd where the deposited material was machined back to original size and tolerance and the repaired parts were fitted back into their original casings and subjected to a range of tests before being dispatched to customers for extended use.

- Profiling the Master of Suspense using Large Scale LMD

An unusual demonstration of TWI’s expertise in LMD occurred when we were invited to display a 3D printed component at the International Digital Sculpture and Engineered Forms Exhibition in Austin, Texas, a showcase of original 3D-printed artworks from around the world created by pioneers in the digital arts and engineered functional forms.

TWI was originally invited to display a helicopter combustion chamber casing made through LMD (Figure 10). However, our experts decided to build something more befitting an art exhibition and so created a Rubin vase that was quite possibly one of the largest thin-walled net shape components built by LMD at the time, standing nearly 400mm tall with a consistent wall thickness of 0.9mm. The design was modelled on the facial profile of Alfred Hitchcock and the LMD process used was an approach developed by TWI, where the precise synchronisation of the movements of rotation and tilt of the substrate with incremental movements of the coaxial nozzle (predominantly in the +Z direction) allows a continuous spiralling weld track to be deposited or ‘grown’, layer on layer, out of the substrate. This helical multi-layering technique allows a thin-walled 3D contour to form which accurately follows the specification of the original CAD surface profile. To improve the aesthetics of the vase for the purpose of the exhibition, the external surface was lightly shot blasted, primarily to remove excess powder, and the internal surface of the bowl was polished (Figure 11).

These are just some examples of LMD projects undertaken at TWI – to find out more and see how we can help you reduce costs, improve processes and solve your industrial challenges, please email contactus@twi.co.uk.