- Nd:YAG Laser Beam Hardening and Cladding of Steel
Carbon dioxide lasers have been used for industrial surface engineering for years, but applications for the technology were slow to emerge. However, the development of average power Nd:YAG lasers coupled with flexible fibreoptic beam delivery systems offered an alternative laser source with several processing advantages. This 1997 project sought to compare past studies of laser cladding with a 2kW average power CO2 laser with surface engineering applications for transformation hardening, cladding and alloying with a 2kW average power Nd:YAG laser with beam delivery via a 1mm diameter, 10m long fibreoptic cable. Our experts undertook laser transformation hardening of medium carbon steel and the laser cladding of plain carbon steels with nickel alloy 625 using a 2kW Nd:YAG laser with fibreoptic beam delivery. Characteristics for both processes were assessed and compared with those achieved using CO 2 lasers of similar average power.
- Effect of Preheat and Interpass Temperatures on Nickel Alloy Cladding
Although nickel weld alloy overlay claddings had been used to provide corrosion resistance to carbon and low alloy steel components, at the time of this 2013 CRP project there was no clear guidance on the allowable maximum preheat/interpass temperatures for their manufacture, without compromising productivity and quality. If the interpass temperature is too high it can result in excessive dilution and microstructural changes within the weld metal, reducing the corrosion resistance. However, on the other hand, if the interpass temperature is too low it could impact productivity. This project sought a clear understanding of the effect of interpass temperature on alloy 625 weld overlay cladding. Our experts determined that changes in corrosion rate were related to the increased dilution of the overlay. It was also found that a change in the preheat / interpass temperature could affect the corrosion rate, even if the welding parameters were kept the same. Experimental results showed a direct relationship between the corrosion rate and metallurgical changes such as the degree of second phase precipitation associated with an increased preheat/interpass temperature.
- Mechanical Performance of Laser Metal Deposited Alloy 718
This CRP work was created to address the industrial need for performance data for laser metal deposited alloy 718, a well-established material that was widely used in aeroengine designs. The TWI team also sought to optimise process parameters on the basis of performance rather than in relation to metallurgical quality. To achieve this, we deposited rectangular blocks of alloy 718 on 316L stainless steel plates (Figure 1), before subjecting the samples to two-stage heat treatment. Wrought alloy 718 was also used to provide a benchmark for fatigue and tensile testing. Both high energy input (HEI) and low energy input (LEI) were investigated with a series of tests, including tensile tests in air under ambient and elevated temperatures (630°C) and fatigue testing in air under ambient conditions and creep rupture testing at 630°C (Figure 2).
Public Funded Projects
Our expert teams are also called to participate in public funded projects in partnership with other organisations from industry and academia to solve specific challenges, typically for particular industry sectors.
- Remanufacture of Rail Wheels: Aurora Project
This UKRI-funded project aimed to develop a remanufacturing cell for rail wheels including in-process and post-production inspection to ensure accuracy and integrity of the wheels. This project addressed the cost of wheel replacements which, at the time of the project, typically involved either turning all of the wheels on a train to match the diameter of the most worn wheel or simply replacing the worn wheel. This project not only investigated cladding as an alternative repair strategy but also addressed the lack of industry standards for repaired wheels. The manufacturing cell was designed to be reconfigurable so that it could accommodate wheelsets of different diameters and software was written to control the automation of the welding process while also monitoring the weld current, weld speed, volts and wire feed speed (Figures 3-4). In-process inspection was undertaken with laser ultrasonic testing (LUT).
- Refurbishment of Railway Axles (ReLASE Project)
Also concerned with repair solutions for the rail industry, the ReLASE Project investigated the use of laser cladding to increase the service life of railway axles and reduce scrappage rates (Figure 5). Our experts worked alongside representatives from Tata Steel, LASE and Wall Colmonoy to provide a cladding solution that provided increased wear and fatigue resistance for the wheel-seat areas of axles. The project team not only produced laser-engineered coatings for the refurbishment of locomotive axles and other assets but also assessed the mechanical properties of the coated samples and developed a reliable means of inspecting various coatings. Wall Colmonoy produced powders of varying compositions from which LASE were able to produce coupon samples (Figure 6), before TWI carried out X-ray computed tomography (Figures 7-8) to assess the coating quality and defect characterisation and to down-select coupons for fatigue testing. By optimising the coating process of the selected powders, defects such as cracking, voiding, porosity and lack of fusion were minimised. The fatigue testing of the best coupons enabled the comparison of the mechanical performance of cladded coupons with coupons of parent material, showing that the laser cladding process offered a solution for the repair of railway axles.
- ModuLase: Re-Configurable Laser Processing Head
Funded by the European Union’s Horizon 2020 research and innovation programme, the ModuLase project was created to develop a reconfigurable laser processing head that is capable of performing welding, cutting and cladding processes (Figures 9-10) through the use of three modular end-effectors. Intelligent sensor technologies were also incorporated to provide in-process monitoring. The project team had to account for the different laser beam energy distributions, power densities, stand-off distances, Rayleigh lengths, gas, wire/powder feed requirements for each process. The development of the ModuLase system offered reduced capital investment costs, reduced downtimes and lower running costs compared to regular systems.
Dedicated Industrial Member Support and Other Projects
Much of the work undertaken at TWI is conducted confidentially on behalf of individual Industrial Member companies. However, there are some examples of these types of project work that involved laser cladding that we are able to share with you, as follows…
- Powder Metal Repair Process
TWI’s experts worked with a leading aero engine manufacturer to develop laser cladding for the repair of blades and seal segments (Figure 11).
- Laser Direct Metal Deposition for Shaft Refurbishment
An Industrial Member asked TWI to refurbish three worn shafts from industrial rotating equipment. Our experts opted to use laser cladding using direct laser metal deposition for the repair (Figure 12). The shafts were prepared to create a satisfactory surface before material was deposited on the shafts. One of the three shafts was used for experimentation in order to create the process parameters while the other two were due for re-use following successful refurbishment and post deposition machining. This project required the procurement, installation and commissioning of additional equipment. The two shafts were successfully clad according to a drawing supplied by the client and using an approved weld procedure developed by TWI.
Please see here to find out more about laser cladding services and support at TWI:
https://www.twi-global.com/what-we-do/services-and-support/laser-cladding