Technical Insight: Laser Welding

Laser welding is a fusion process that is used to join metals or thermoplastics together using a laser beam. Because the heat source is highly concentrated, thin materials can be welded together at high speeds to produce narrow, deep welds between square-edged parts in thicker materials.

The uptake of laser welding has been driven forward by the high-volume production of high-quality welds with low levels of distortion. Used to join a variety of materials like carbon and stainless steels, aluminium, titanium and nickel alloys, laser welding has found uses in applications ranging from welding car bodies and aircraft fuselage panels to the welding of shipbuilding structures and joining components in medical devices.

TWI has years of experience in the development and qualification of laser welding procedures and technologies for a range of applications across all industry sectors. This work includes core research programme (CRP) projects that are designed to meet the needs of several Industrial Members, joint industry projects that allow interested parties to pool their funding for increased outcomes and exclusive access to the project findings, public-funded projects where our experts work alongside others from industry and academia, and dedicated work on behalf of specific Industrial Members.

Core Research Programme

Our core research programme projects are designed to meet the needs of our Industrial Membership. Industrial Members of TWI have access to the full reports for all of our CRP projects. With regards to laser welding, many of these projects have focused on advancing and developing laser welding processes…

- Advances in Laser Welding

In 1976, we upgraded our 2kW CO₂ gas laser to a 2.5kW routine continuous output power with a maximum power of 2.7kW. This was achieved by adjusting the gas flow nozzles and resonator optics, increasing not just the output power and tube efficiencies but also providing greater reliability, higher power densities at the workpiece and the ability to weld thicker and faster than other lasers of a similar or higher power.

- Laser Welding of Butt and T Joints in Deep Drawing Low Carbon Steel Sheets

This 1982 CRP project focused on laser welding butt and T joints in 2, 3 and 4mm thick deep drawing, low carbon steels has been examined. The steels included fully and semi-killed and rimming materials, with the welds being made at different powers and speeds ranging from 1 to 6kW and 1 to 7 metres per minute. The welded joints were assessed using visual, microsection and radiographic examinations, while the T joints were also examined for post-weld distortion. The results demonstrated that both butt and T joints can be made at a range of laser power and welding speed combinations.

- Plasma Control in Laser Welding Austenitic Stainless Steel

This 1983 CRP project investigated the control of plasma via a jet of helium during laser welding as well as the limitations arising from absorption of the laser beam in the plasma above laser welds. Experiments were carried out to optimise the angle of the control jet to the laser beam, the intersection point of the jet with the laser beam, and the helium flow rate required for laser welding Types 316 and 321 austenitic stainless steel of 6, 9.5 and 13mm thickness with a 5kW fast axial flow laser. The tests showed improvements in welding speed and penetration of up to 30% when the laser beam/plasma interaction was the limiting factor. Plasma control can also be used to control weld bead shape and reduce distortion as well as allowing low welding speeds that can help avoid cracking in certain materials.

- Solidification Cracking of High Speed TIG and Laser Welds

Also in 1983, we investigated the application of high travel speeds for laser and TIG welding of austenitic stainless steel sheets. Attention was paid to solidification cracking behaviour, with welds being made at speeds of 800-1500mm/min and 1000-6000mm/min for the TIG and laser processes respectively. Both processes showed a correlation between increased travel speed and cracking. Ferrite was shown to reduce cracking sensitivity, but its effect was limited by segregation during solidification, which led to local areas solidifying to austenite even in materials of high Cr_eq/Ni_eq ratio.

- Laser Welding T Joints in Low Carbon Steel Sheets

By 1983 our experts were revisiting the topic of laser welding T joints in low carbon steel sheets, with trials conducted on 2, 3, and 4mm thick steels. The trials established practical process application data with respect to laser beam impingement angle, laser beam/workpiece alignment and workpiece fit-up.

- Laser Welding 12.5mm Niobium Microalloyed Structural Steel

Continuing our research into the different welding parameters for various materials, this 1984 project assessed laser welding for six 12.5mm thick C-Mn-Si-Al-Nb structural steels to BS 4360 Grade 50D. Weldability lobes showed that porosity-free welds could not be created at powers less than 7kW given the material and its thickness. However, Charpy and CTOD properties showed good weld metal toughness results, which are associated with a martensite microstructure, could be obtained at welding speeds of 0.9m/min and above.

- Laser Welding of Structural Steel with Wire Feed

We conducted a 1985 CRP project to investigate laser welding trials using a wire feed. This had the potential to improve the tolerance to gaps at the joint line and allow modifications to be made to the weld metal composition to control properties, as well as allowing thicker sections to be joined with multipass welds. Welds were made in 8mm thick C-Mn-Si-Al-Nb structural steels to BS 4360 Grade 50D, using a 5kW laser and a wire feed system to fill a joint gap with standard 1.2mm diameter Cu coated MIG welding wires. The research showed that gaps up to 2mm wide could be welded satisfactorily and the wire feed technique was found to be simple and straightforward to use. Although some welds suffered from porosity, its occurrence was not fully understood. Weld metal microstructures containing acicular ferrite were favoured by low weld metal carbon equivalents, while impact testing of half size Charpy specimens showed that good results could be obtained (13.5J temperatures of below -40°C). In addition to single pass wire feed welds, the possibility of multipass welding was demonstrated, which would allow thicker materials to be welded (up to 25mm in this case).

- Laser Welding Low Carbon/Low Sulphur Structural Steels

Laser welding trials continued with the welding of five 12.5mm thick C-Mn-Si-Al-Nb structural steel batches to BS 4360 Grades 43E and 50D. We used laser powers in the range of 5.2kW-9.1kW on materials with carbon contents of between 0.11% to 0.15% and sulphur from 0.005% to 0.019%. Testing including metal hardness, microstructure and Charpy impact tests were conducted and compared to results obtained on other steel compositions. The outcomes of this research for critical applications added to existing work on laser welding with a wire feed.

- Optimising a Gas Jet Plasma Laser Welding Control System

When laser welding, a plasma cloud can form above the weld pool and interact with the laser beam. When welding with high laser powers and at low welding speeds this plasma cloud can significantly reduce the power reaching the workpiece, reducing weld penetration. Past work at TWI had resulted in the development of gas jet plasma control devices for use of 2 and 5kW lasers, which work by blowing a jet of helium gas through a nozzle to disrupt the plasma formation. This 1988 project advanced this development for use with a 10kW CO₂ laser, while also assessing the effect on welding performance. Varying nozzle bore diameters, gas flow rates and nozzle positions were investigated, with respect to the laser beam/material interaction point, when making partial penetration melt runs in 18mm thick micro-alloyed C-Mn steel to BS 4360 Grade 50D and full penetration melt runs in 12mm thick plate of a similar type.

- Shielding Gases for CO2 Laser Welding

This 1989 CRP project looked into the effectiveness of different commonly available shielding gases as compared to helium for the CO₂ laser welding of lap joints in 0.7mm thick high strength low alloy (HSLA) autobody steel. Where the penetration was shown to be comparable to that created with the helium shield, further comparisons were carried out with regards to fusion zone, HAZ width, hardness strength, and porosity.

- Application of Resistance/Laser Welding to AI-Li Alloy 8090

Resistance and laser welding were both studied as part of a project investigating the joining of Al-Li alloys. The two processes were applied to Al alloy 8090 (Al-2.5Li-1.2Cu-0.7Mg-Zr) and conditions for making resistance spot and seam welds in 1.5mm sheet and laser welds in 2mm sheet were developed. Weld defects and the static strengths of the welds were assessed, the resistance welding performance was compared with the Al-Mg-Si alloy L113, and laser welding (using a Trumpf 5kW fast axial flow CO₂ gas laser) up to 4mm thick was attempted.

- Fabrication Aspects of a Laser Welded Lightweight Panel

In 1992, TWI undertook an examination of laser welding for the creation of sandwich panels with low distortion. These lightweight panels consist of two skins separated by a corrugated core. They are used for structural components in industries ranging from construction to marine, aerospace, automotive and more due to their high stiffness, high strength, low weight, low cost and ready applicability. This work aimed to serve a broad number of industry sectors by assessing laser welding for its various advantages over other methods of fabrication, such as TIG welding, resistance welding, and diffusion/adhesive bonding, due to its ability to produce continuous, single-sided deep penetration welds (stake welds) at high welding speeds (>1m/min)and with low distortion.

- CO2 Laser Welding of 5000 Series Aluminium Alloys

The same year, we investigated the application of laser welding to aluminium alloys in order to deliver advantages of high speed, low distortion welding with these materials. The high reflectivity and thermal conductivity of aluminium alloys had caused difficulties with welding aluminium, causing a tendency towards cracking and high levels of porosity. Laser welding experts at TWI determined that a high-quality parabolic beam focusing element could increase the power density of the laser beam at focus, compared to spherical focusing optics, enough to affect the reflectivity problem. During this project, TWI evaluated a parabolic beam focusing system used in conjunction with a high-power CO₂, laser when welding a number of 5000 series Al alloys between 2 and 8mm thick. The material surfaces were cleaned using petroleum ether prior to welding but were otherwise in the as received condition. The resulting melt runs were assessed in terms of tensile properties, levels of porosity and susceptibility to cracking, hardness and weld metal chemical analysis. Work was performed on both autogenous and wire feed welding techniques, and some butt welds were carried out using the wire feed technique.

- Cold and Hot Wire Feed Laser Welding of Structural Steel

It had been shown that cold, solid wire feed could be used with laser welding to control the weld metal composition and thereby the weld metal properties without significant processing difficulties. TWI conducted an R&D project to assess and develop the process, creating a method for feeding hot wire into the weld. The weld metal properties related to specific elements transferred from metal cored wires of a controlled composition were studied for both hot and cold filler wire feeds. For this project, we used specially manufactured metal cored wires of 1.2mm diameter, containing a range of titanium (0 - 0.06wt%) and oxygen (300 - 1500ppm) contents to fill weld gaps of 1.8mm. A 10kW CO₂ laser was used to weld 12mm thick structural steel (BS4360 Grade 50D) with both cold and heated wire before the welds were evaluated in terms of porosity content, hardness and impact toughness properties.

- High Pressure Inert Assist Gas Laser Welding of Cut Edges

By 1993, laser cutting had become an industrially-accepted production process, but laser cut components required high-quality edge preparation ahead of any welding, especially for high performance joints in materials such as stainless steel, nickel based alloys, titanium alloys and aluminium alloys. We conducted a CRP project to evaluate laser welding of laser cut edges using both low pressure oxygen and high-pressure inert gas for stainless steel AISI 316 (3mm thick), Inconel 600 (6mm thick), aluminium alloy 2024 (2mm thick), aluminium alloy 5754 (1.6mm thick), and titanium 6A14V (3mm thick).

- Laser Welding of Plastics Film and Sheet

Although lasers had been used for drilling, cutting and certain welding procedures for plastics since the 1970s, industrial adoption had been slowed by the cost of lasers at the time. With cost reductions and the mass production of lasers by the mid-1990s the potential of lasers to deliver high speed processing for a range of plastic materials and joint configurations that may be difficult to join using other techniques. As such, this TWI project investigated plastics joining techniques using CO₂ lasers as a localised heat source to provide continuous high-speed processing, as well as the feasibility of using Nd:YAG lasers in the processing of plastics.

- Laser Welding of Aluminium Alloys

Although laser welding had already proven to provide low general heat input, low distortion, high welding speeds, the potential for automation and the inherent flexibility of the laser system when welding steel components, there was a desire to provide these same advantages when using aluminium alloys given the driving force of weight reduction in industries such as aerospace, automotive, off-road transportation, shipbuilding, construction and domestic appliances. This 1995 CRP project investigated CO₂ and Nd:YAG laser welding of butt joints in 2mm and 6mm thick aluminium alloys, representative of a range of industrial interest, in order to determine mechanical properties, assess susceptibility to porosity and cracking, and produce guidelines for the use of lasers for welding of aluminium alloys with regard to process procedures.

- A Review of Joint Tracking Systems for Laser Welding

By 1996, TWI was beginning to take account of advances in online monitoring and control equipment for joint tracking systems that could be applied to laser welding. Laser welding required different joint tracking system specifications to those used for arc welding due to generic differences between the processes. This project reviewed methods for joint tracking in relation to laser welding and defined outline system specifications for a number of laser welding applications. This furthered laser welding by providing improved quality assurance for our Industrial Members in addressing the relatively low tolerance of the process to joint misalignment and fit-up brought about by standard engineering parts tolerances. To achieve this, the joint tracking systems typically need to locate the joint to between 0.1mm for 1mm thick sheet and 0.4mm for 6mm thick plate. In addition, the joint tracking systems needed to be able to operate at welding speeds of between 1-10 m/min for typical plate and sheet applications.

- Autogenous Welding of High Nitrogen Superaustenitic Stainless Steels

Laser and TIG welding were both tested during welding trials undertaken at TWI in 1997 to quantify and optimise the corrosion resistance of autogenous weldments in high nitrogen ‘superaustenitic’ stainless steels. Austenitic stainless steels offer an attractive combination of corrosion resistance, toughness, ductility and ease of fabrication. The highest alloy grades became known as superaustenitic steels, containing 6-7%Mo and up to 0.5%N for excellent pitting corrosion resistance. Older austenitic grades were unable to produce weldments with corrosion resistance matching that of the parent, due to molybdenum segregation in the weld metal and nitrogen loss from the molten weld pool. The conventional approach was to use an overalloyed nickel-based filler, but use of this filler type could cause problems due to a tendency for corrosion at the fusion line unmixed zone. To assess and compare the older and newer, ‘super’ austenitic steel grades, we examined corrosion resistance of autogenous weldments, both in an established grade (S31254) and in two more recently developed 0.5% nitrogen superaustenitic steels (UNS S34565 and S32654).

- CO2 Laser Weld of Steel Tailored Blanks for Automotive Use

By 1997, CO₂ laser welding of tailored blanks had become an established technique to achieve weight and cost savings in automobile body manufacture. TWI worked alongside British Steel, Rover Group and BOC to investigate a range of aspects of CO₂ laser welding for tailored blank technology. This included determining the effect of process gas and welding speed on formability of CO₂ laser butt welds in zinc coated steel sheet, optimising CO₂ laser butt welding of re-phosphorised steels, evaluating CO₂ laser cutting for sheet preparation, establishing fit-up requirements for CO₂ laser butt welds in 0.7 and 0.8mm thick zinc coated steel, and assessing the formability of CO₂ laser butt welds in iron-zinc coated steel with surface mismatch as well as completing the CO₂ laser welding of case study tailored blanks.

- An Initial Study on Laser Welding of Magnesium Alloys

Although magnesium alloys had conventionally been welded using arc methods, including TIG for the repair of castings, interest in magnesium’s lightweight properties and high stiffness-to-weight ratio for the aerospace and automotive sectors created this 1998 CRP project to assess laser welding of these materials for a fast, flexible, and low heat input joining process. TWI’s experts reviewed the literature for data on the laser welding of magnesium alloys, assessed CO ₂ and Nd:YAG laser welding for a range of magnesium alloys, and determined the quality and basic mechanical properties of laser welds produced in a range of magnesium alloys, providing an important body of knowledge for our Industrial Members.

- A Thermal Model for Laser Welding of Thermoplastic Polymers

As a number of research organisations and companies developed the use of transmission laser welding for thermoplastic polymers, TWI addressed an industry need to understand some of the fundamentals of the process to provide more confidence in its use. This included understanding the behaviour and response of materials in a laser beam in respect to material properties on the welding process and the effects of different welding parameters. This 2000 project sought to develop and validate a finite element model of the process of transmission laser welding between two thermoplastic polymer parts.

- The Use of Process Gases for High Power Nd:YAG Laser Welding

Keyhole laser welding was widely used by different industries for joining relatively thin sections, typically with steels up to 6mm. Characterised by high travel speeds and low heat input, resulting in high production rates and low thermal distortion, these thin section welds are relatively undemanding when it comes to controlling any laser induced plasma or plume. However, the increased use of lasers for welding thicker sections at slower speeds called for better understanding of the gas shielding and ways to control the laser induced plasma. This built upon existing research into plasma suppression and control for high power CO2 laser welding.

- ClearWeld™ - TWI's Innovative Joining Process for Textiles

TWI developed the ClearWeld^TM technique for welding thermoplastic fabrics using transmission laser welding and the introduction of a low visibility laser-absorbing coating onto one or both of the fabrics to be joined to achieve selective heating. This allows for control of the melt volume and thereby seam flexibility while sealing the seams in one operation, without the use of tapes and allowing curved seams. Opening up new design opportunities for fabric seams to be used on foul weather or dangerous environments, this development showed excellent potential for high-speed seaming and automation, with the process applied to both pure synthetic fabrics (Figure 1), blends of synthetic and natural fibres, and to waterproof laminates (Figure 2).

- Clearweld Process for Laser Welding of Plastics and Fabrics

This CRP project sought to progress the Clearweld®, high-precision transmission laser welding process, which was originally developed by TWI. The process allows for the seamless joining of clear or coloured plastics and synthetic textiles without leaving a visible dark or black weld line. This 2001 project aimed to source and select suitable absorbers for laser welding using the Clearweld® process and to assess a method of introducing the absorber into the joint region. We also established and evaluated Clearweld® processing methods and assessed the use of the Clearweld® process for a range of material types and industrial applications.

- Welding of Thin Galvanised Sheet to Hydroformed Tube

As car manufacturers struck a balance between luxury, performance, safety and emissions, they began to use hydroformed tubes to lower mass and increase stiffness and integrity as compared to traditional resistance spot-welded stampings. However, spot welding could not be applied to these tubes as the process requires access to both sides of the part to be joined. To solve this problem and allow thin galvanised steel sheet to be joined to hydroformed tube, TWI investigated Nd:YAG laser welding and pulsed alternating current metal active gas welding (AC MAG), as they were both deemed suitable for single-sided welding of thin sheet. In addition to comparing the processes, we also compared the performance of two different types of Nd:YAG laser sources was compared; a lamp and a diode pumped source. These laser sources were compared in terms of travel speed, weld quality and process tolerance when welding thin, galvanised steel sheet.

- Joining Aluminium Alloys - The Twin Spot Way

Returning to laser welding of aluminium alloys for the first CRP project on the topic since 1995, this project compared ‘twin spot’ distribution to a conventional single, circularly symmetric, focused laser spot. With a focus on reducing porosity, this project assessed the effectiveness and practicality of a twin spot focused energy distribution to reduce porosity when laser welding 2024 aluminium alloy.

- Porosity Levels for Laser Welding Al Alloy

As aerospace companies reacted to increased competition a number of UK-based industrial companies and research and technology organisations (RTOs) united to create the CEMWAM (Cost Effective Manufacture: Welding of Aerospace Materials) programme to investigate new design and manufacturing approaches. This project was created as part of the CEMWAM programme to assess Nd:YAG laser welding of 3.2mm thickness 2024 aerospace aluminium alloy, including the effect of parent material and filler wire cleanliness, shielding gas delivery and laser beam energy distribution on the presence of porosity.

- Welding Titanium Alloys - The Laser Way

We conducted further work into laser welding and titanium alloys for the aerospace industry in 2003, developing Nd:YAG laser welding procedures for grade Ti-6Al-4V titanium alloys of 3.25 and 6.35mm thickness range using 3-4kW laser power. In addition, we examined the influence of welding procedure and parent material preparation variables on weld surface appearance and internal porosity.

- Laser Welding of Aluminium Alloys: Principles/Applications

This 2004 research project provided out Industrial Members with an analysis of the current and potential future production applications of laser welding in aluminium alloys across different industry sectors.

- Bridging the Gap

This 2004 project compared CO₂ laser welding (with and without filler wire) against hybrid CO₂ laser MAG welding. The project investigated the processes for making butt joints in 8mm thickness CMn steel as well as obtaining acceptable welding conditions for producing fully penetrating butt joints in 8mm C-Mn steel using the hybrid CO ₂ laser MAG process.

- Performance Assessment of Yb Fibre Laser Technology

This 2005 CRP project assessed the performance of an Yb fibre laser in the power range from 4-7kW for welding structural steel in the thickness range 8-12.7mm.

- Fibre Laser Welding of High Strength Steels for Automotive

As the automotive industry continued to seek reductions in vehicle body weight to improve fuel efficiencies and reduce emissions, attention turned to lighter materials including ultra-high strength (UHS) steels. At the time of this 2007 project, these steels offered material savings and/or improved crashworthiness without significant modifications to the manufacturing process, beating competition from aluminium alloys and composite materials. However, there was little information about the laser weldability and weld performance of UHS steels. TWI created a project to develop welding procedures for joining thin-sheet UHS steels using fibre-delivered solid state lasers, and establish the performance and formability of the welds produced. Our laser welding team examined the effect of similar and dissimilar material/thickness combinations on the weldability of UHS steels, established the static performance and formability of laser welds in UHS steels, while also examining the effect of laser process parameters on the weld and heat affected zone (HAZ) hardening/ softening.

- Precision Laser Welding of Plastic Components

Transmission laser welding of plastics uses sources that pass through most natural polymers, below which an absorber is placed to halt the laser energy and provide heating at the joint. Precise control of the process is vital when welding small or complex parts. This control depends on the amount of energy applied and the location of this energy. While the beam power and part manipulation can be controlled easily, TWI conducted a 2007 project to determine the minimum weld width available as a result of different laser sources and absorbers. These studies allowed accurate delivery of heat (in terms of amount and location), which benefitted industries such as medical and electronics as they sought methods to join smaller and increasingly complex devices.

- Laser Welding of Titanium Alloys with Low Internal Porosity

This 2009 CRP project sought to establish the tolerance for the different processing factors to control weld metal porosity when laser welding titanium alloys using fibre-delivered lasers with a directed argon gas jet. The tests focused on Nd:YAG laser welding of 3.2mm thick titanium alloys, assessing different jet positions, angles and gas flow rates, with the project building on previous studies to provide practical recommendations for robust laser welding of titanium alloys with low internal porosity.

- Clamping/Joint Gaps for Through-Transmission Laser Welding

This 2010 project returned to the topic of through transmission laser welding, seeking to address challenges around clamping pressure and the ability to join more complex geometries. Used for welding plastics used for industry applications such as photographic tank and automotive parts, fuel cells, medical devices and technical textiles, the process was assessed to determine the pressure distribution applied by a sliding clamp. The effect of clamping pressure was studied in terms of weld strength for both a sliding and a fixed clamp system, and the effect of any irregularities in the workpieces were investigated.

- Modulated/Twin Spot/High Beam Titanium Alloy Laser Welding

Continuing to advance laser welding for the benefit of our Industrial Members, this project investigated the challenge of porosity in laser welds, which was of particular concern for machined components that could be subject to high stress levels or cyclic stresses. Pores within the welds can break the surface after machining, creating potential stress concentration sites and shortening fatigue life. Porosity in laser welds is typically caused by unsuitable welding parameters, incorrectly prepared material and inadequate inert gas shielding. Although research found that a directed gas jet can be used to significantly reduce porosity levels when neodymium-doped yttrium aluminium garnet (Nd:YAG) laser welding titanium alloys (to levels within those required by international standards), because the gas jet requires very precise alignment to work effectively, it was questionable if this was an industrially robust approach. Aiming to meet porosity criteria specified in laser welding standards consistently, particularly in aluminium, titanium and nickel alloys, TWI researched two alternative approaches to producing high quality laser welds in titanium alloys; laser power modulation and twin spot welding. The aim was to develop Nd:YAG laser welding routines for titanium alloys, resulting in butt welds to at least quality Class A of AWS D17.1, without having to use a directed gas jet. The tests were monitored with high-speed video imaging to allow us to observe the differences in the keyhole and weld pool behaviour when laser welding with either a twin spot configuration or a modulated laser power. Our experts also undertook simultaneous early titanium alloy welding trials on the, at the time, relatively new, high beam quality Yb-fibre laser.

- Investigating Multi-Pass Fibre Laser Welding of Thick Steel

Although multi-pass, narrow gap arc welding had been used for welding thick section steels and stainless steels, such as with pipe joining or pressure vessel manufacture, there were concerns over the productivity. So, as beam power, power density and stand-off distance increased with new fibre and disk lasers, laser welding became a potential solution for high quality, high productivity, low distortion welding of thick section steels and stainless steels, using a multi-pass welding approach. TWI conducted this 2012 CRP project to develop parameters for high quality, multi-pass, fibre-delivered laser welding of thick section (25mm) steel and determine suitable welding parameters to maximise joint completion rate. This work was built upon through another CRP project (in 2015), that set down the key findings related to the Multi-Pass Fibre Laser Welding of Thick Section Steel.

- Sliding Seal Reduced Pressure Laser Beam Welding Trials

Continuing to address the challenge of thick section laser beam welding, this 2016 project combined TWI’s laser welding knowledge with our expertise in electron beam welding. Electron beam welding had been proven to be able to produce suitable thick section welds, but the capital investment costs and dictates on component size and/or complexity was dissuading potential users. A localised, sliding, sealing chamber had been developed for reduced pressure (0.1-10mbar) electron beam welding, which TWI adapted for laser beam welding. Trials find that penetration depths could be increased by up to 70% in S275 steel and 30% in Ti-6Al-4V by using this technique. Furthermore, we found that reduced pressure laser beam welding could be carried out successfully using a smaller, robot-mounted chamber design, which, when coupled with a 5kW fibre laser, increased penetration depths further.

- In-Bore Multi-Positional Laser Welding

Multi-positional laser keyhole welding was already established in the automotive industry by the time of this 2018 project, but other potential applications for the process existed, including the manufacture and repair of ageing nuclear reactors and the construction of new-build nuclear power plant pipelines. Laser welding offered advantages with regards to its flexibility for remote deployment and operation as well as the speed of joint completion. This project undertook industry-aligned tests on multi-positional in-bore welding of 304L stainless steel, Ti64AlV and nickel alloy 718, using a 5kW fibre laser, with results being assessed against the ‘stringent’ criteria in ISO 13919-1 and ‘Class A’ criteria in AWS D17.1. TWI also demonstrated that the in-bore laser welding head can be successfully integrated with a snake arm robot as used for a number of nuclear decommissioning and repair projects.

- Solidification Cracking Susceptibility of AA6061 and AA2024 Aluminium Alloys during Laser Welding

This CRP project, completed in 2023, combined our expertise in laser welding with our knowledge of finite element analysis (FEA) to solve the challenge of weld zone hot cracking, whereby impurities or solute atoms are segregated to the weld metal and/or heat-affected zone (HAZ) grain boundaries, leading to the formation of low melting point brittle films, which can then crack during the final stages of solidification. Commonly-used materials that are susceptible to hot cracking include heat-treatable aluminium alloys (e.g. 2000, 6000 and 7000 series). Hot cracking can be controlled by influencing the welding parameters, but this can require several trials before the desired laser beam energy distribution is determined for a given application. By using computer-based finite element analysis (FEA), the laser beam welding process and the hot cracking behaviour of the laser weld itself, can be simulated by introducing a moving heat source to a model that contains the full information of the material(s) being joined. TWI brought this all together with modelling and experimental work to investigate

the link between thermal transients, strain transients and internal stresses and susceptibility of laser-welded aluminium specimens to exhibit hot cracking. Experimentally validated FEA models were then established using measured temperature and strain histories, before the validated models were used to identify correlations between thermal transients, strain transients, and the susceptibility to hot cracking. The resulting FEA model forms the basis of a method to predict the type of laser energy distribution needed to reduce or mitigate hot cracking (Figures 2-5).

Joint Industry Projects

While our CRP projects advanced laser welding and increased the levels of knowledge and technical excellence in the process at TWI, there were some projects that we created that were more aligned to specific industry sectors or likely to be of interest to a particular group of Industrial Members. These projects were launched as joint industry projects (JIPs), that allowed interested parties the opportunity to act as sponsors in return for exclusive access to the research outcomes and the ability to have input into the direction of the projects themselves.

Examples of this research include further research into high productivity arc and laser welding of titanium and titanium alloys, completed in 2006, the exploitation of power beam welding of thick section steel for structural applications in 2007, and an investigation into advanced arc and laser fabrication and repair welding of nickel superalloys, which concluded in 2010.

More recent JIP work focuses on the adoption of handheld laser welding technology, with an impartial assessment of its suitability for industrial use, including a comparison with conventional manual welding approaches. By assessing this emerging technology (Figure 6), which promises faster, more versatile, cost effective and consistent welding results than more conventional manual arc welding processes, such as MIG/MAG or TIG welding, this project offers data and information to support decisions on whether the technology is robust, safe, fast, versatile and cost effective for the Sponsors’ industrial applications.

Public-Funded Projects

TWI’s technical excellence in laser welding has contributed to a several public-funded projects over the decades, typically working alongside partners from industry and / or academia to solve specific challenges.

Although the European Commission-funded TailorWeld project aimed to develop and demonstrate an innovative laser welding system, using simple and robust diffractive optical elements to increase the flexibility and simplify the application of laser welding, removing a key barrier to entry for a large number of SME fabricators, many of our public-funded projects worked for specific industries.

Example projects include the European Commission-funded QCOALA project, which aimed to ensure further use of and increased confidence in laser technologies for welding of thin-gauge aluminium and copper, as used in electric car battery interconnections and in thin-film PV assemblies. Also European Commission-funded, the Radicle project worked to develop a laser welding control system capable of integrating process sensor data obtained before, during and after welding, to adjust the laser welding parameters accordingly and deliver welded joints targeting zero defects, helping to strengthen the EU’s position in both laser welding and high value manufacturing. Elsewhere, the ShipTest project developed a fully automated laser guided inspection system for weld defect detection on ship hulls.

The OLIVER project, funded by Innovate UK, developed technologies for laser welding of structural titanium components, and the LaserJacket project, also Innovate UK-funded, investigated the use of thick-section laser welding for the manufacture of jacket support structures for offshore wind turbines, while LaserPipe developed an in-bore laser welding head for use on nuclear pipelines.

The aerospace industry was also the subject of a number of public-funded projects that TWI were invited to join, such as the AFSIAL project, aiming at the development and demonstration of a metallic solution for fuselage and wing structures, combining innovative aluminium alloys of the Al-Cu-Li family and advanced assembling technologies such as laser beam and hybrid welding.

The OASIS project saw TWI work alongside Saab AB, University West (Trollhättan, Sweden), VZLU A.S., Romaero S.A. and Queen’s University (Belfast, U.K.) to successfully develop robotic laser beam welding to help fabricate a new design of aircraft cargo door (Figure 7). This involved a series of detailed design reviews of the proposed door, helping to identify suitable laser beam welding process variants, aluminium alloys and joint configurations to use between the door’s frames, stringers and skin, as well as helping to foresee and resolve weld access issues, before optimal weld parameters were developed. The final approach involved firstly a single-sided full penetration keyhole pass, to fuse the frames and stringers to integral shoulders on the door’s skin, followed by one or two dressing passes, using the same equipment, but defocusing the laser beam (Figure 8). Next, TWI assisted in the design of the welding fixture for the manufacture of full-scale demonstration doors (Figure 9), before successfully joining four 2m long curved frames, as well as three shorter inter-frame stringers to complete the welded construction of a full door (Figures 9-11). The project showed that laser welding-based production could not only reduce the weight of the doors but also manufacturing time and costs.

The Innovate UK-funded e-Tau project was created to develop, test and validate a novel precision laser welding system optimised for use on large aerospace and automotive structures, combining a cutting-edge high precision Tau robot manipulator and advanced laser beam wobbling optics, integrated with intelligent quality assurance and control sensors (Figures 12-13). The aim being to provide an automated, fast and high-quality laser welding system with repeatable results for large automotive and aerospace structures.

Also with funding from Innovate UK, the WeldZero project was created to improve the quality of car bonnet welds, eliminating production welding defects and improving automated welding solutions across industry, through a better understanding of welding processes. This included the development of a low-cost imaging solution with in-production predictions to assist with early defect detection of process set-up problems that could otherwise lead to imperfect welds (Figures 14-16).

Public funding was instrumental in the Toolform programme, which sought to assess the feasibility of using laser welding to add to the arc welding expertise of Sheffield-based pressure vessel fabricator, Portobello Fabrications. As experts in the production of components designed to withstand extreme corrosive environments and elevated temperatures or pressures from 2-20 bar, Portobello Fabrications needed to work to stringent welding standard requirements. Through the introduction of laser welding, Portobello Fabrications were able to unlock considerable savings in set-up times and efficiency by implementing laser welding rather than arc welding.

TWI worked alongside CAV Advanced Technologies, Leonardo Helicopters and TISICS Titanium Composites, supported by the MTC, the NITC at Queen’s University Belfast and IPG Photonics, on an Innovate UK initiative to help the UK aerospace industry supply chain understand and develop near-net-shape titanium alloy and titanium metal matrix composite fabrication possibilities, using advances in laser welding, fixtures, gas shielding and NDT. The project saw our experts advise on suitable welding equipment before the development of specific laser beam welding procedures for the desired applications.

TWI worked with JCB, backed by Tata Steel on an Innovate UK initiative to develop new designs and manufacturing methods for off-highway vehicles. The ELSOHA project aimed to improve efficiencies and productivity while reducing environmental impacts. TWI’s expertise in welding and joining allowed us to assess a range of material candidates for the new designs against a backdrop of where these materials and associated joining processes, are already used in other industries. TWI then developed, through welding trials, suitable processes, parameters and fixtures for laser stake welding and hybrid laser-arc butt welding of demonstrator panels and tailored sections. This helped JCB assemble a suite of design-materials-joining process combinations, which would enable the manufacture of novel, lighter-weight structures going forwards (Figures 17-20).

The Modulase project was created to develop a reconfigurable laser processing head capable of performing welding, cutting and cladding tasks. This was achieved through the use if three modular end-effectors which were aligned with intelligent sensor technologies, allowing for adaptive process control, quality assurance, and semi-automated process parameter configuration (Figures 21-24). This Horizon 2020-funded project delivered benefits for industry including lower capital investment costs, reduced downtimes, and reduced running costs.

TWI joined a project within the framework of the EUROfusion Consortium to advance remote in-bore cutting and welding for nuclear fusion reactors. The project built upon previous work to build and test a snake arm-mounted in-bore orbital laser welding head with the development of miniaturised welding and cutting tools for future in-bore pipe cut-and-replace operations (Figures 25-30).

The InnoSeam project developed and tested a new seam monitoring and tracking system with the aim of reducing post-weld inspection requirements for laser welded structures used in the aerospace industry. Innoseam developed real-time seam detection, inspection and tracking, multi-sensor process monitoring and, based on observed changes in those sensor signals, the automatic alerting of possible set-up, equipment or welding faults. This included the use of a new version of Permanova’s seam finding, inspection and tracking system, which was combined with in-built LED coaxial illumination and imaging of the seam and the welding zone, along with plug-and-play compatibility with sensor-embedded delivery fibres for additional process monitoring. TWI’s team assessed the system and identified fault-detection functions before assisting in the validation of the performance for use on aerospace structures used by GKN Aerospace (Figures 31-32).

Dedicated Industrial Member Support and Other Projects

Much of our work is conducted on behalf of specific Industrial Members to improve processes and solve challenges related to their industry and operations.

As an impartial and independent organisation, TWI typically conducts these in strict confidence with exclusive access to the results being provided to the Member company. However, there are some instances where we are able to provide examples of the type of work undertaken directly on behalf of Industrial Members in different industry sectors, as well as projects undertaken to develop laser welding for specific applications…

- Laser Welding of PEEK for Inflatable Bag Manufacture

Our experts worked on this project to develop a technique for making bags from Victrex® APTIV® polyether ether ketone (PEEK) film that were to be used as novel internal support in the consolidation and forming of a hollow three-dimensional thermoplastic composite structure. The pre-pressurised bag was to be placed inside the pre-preg structure before thermal consolidation and would become an integral part of the internal surface of the composite as thermal processing was completed (Victrex patents pending). The bags needed to be able to arrest the egress of air whilst retaining the flexibility of the joined material, with laser welding being chosen as the most suitable joining method (Figures 33-36).

- Laser Welding Research Improves Quality of Aluminium–Copper Joints

Experts at TWI developed laser welding procedures to greatly improve the welds made between copper and aluminium. This addresses complications around the differing chemical compatibility of the materials which can cause the formation of brittle intermetallic phases and, consequently, inadequate weld properties. To counteract this issue, TWI developed approaches that minimise the formation of these brittle phases for overlap joints of high purity-copper (Cu) and aluminium (Al) thin sheets and plates (with thickness range from 1mm to 6mm) (Figure 37). This development promised benefits for the automotive industry in particular, given the extensive use of Al and Cu in the construction of vehicle batteries.

- Welding of Fuel Tanks

TWI assessed and compared electron beam, laser and conventional fusion welding processes for a new design of storage tank for motor vehicle fuels. The tank had a similar shape and dimensions to a small suitcase and was designed to hold adsorbed natural gas as a fuel.

A series of queries from Industrial Members to help solve technical issues with joining aluminium to copper led to the development of a high-speed laser technology-based solution. This solution was applicable to the welding of high capacity battery cells, which use aluminium and copper as the anode and cathode terminals, improving electric current flow and boosting vehicle performance. Laser welding offers high processing speeds and is highly repeatable and fully automated. The project team demonstrated successful welds in a range of material thicknesses, ranging from 0.2mm up to 1mm, with micro analysis of the welds showing that a high-speed laser welding approach was capable of minimising the formation of the brittle intermetallic phases, and improving the electrical performance of the dissimilar joints.

- Laser Spot Welding

Our experts assisted a razor manufacturer with laser spot welding, using an Nd:YAG laser, to attach platinum coated stainless steel blades to stainless steel sprung support bars. With the need to produce 117,000 spot welds per hour, there was a requirement for high reliability and production rates. Delivering 13 spot welds per blade, the robotically manipulated, fibre delivered laser beam provided welds with a good cosmetic appearance and minimal distortion (Figures 38-39).

- Joining Techniques for Cardiovascular Device

TWI was called to develop novel techniques to join thin nitinol (NiTi) wires for medical applications. NiTi, an equiatomic nickel-titanium alloy, is widely used in the medical industry for its unique properties. It is a shape-memory alloy, whose superelasticity makes it an ideal material for cardiovascular implants, such as heart valves, stents and stent grafts. Although NiTi’s unique properties make it ideal for medical applications, they also present complications in the manufacturing of cardiovascular implants and devices. Most medical devices are currently obtained from laser-cutting of NiTi tubes, or from assemblies of NiTi elements (e.g. wires) joined at specific locations by crimping or soldering. NiTi metal stents are hand-stitched to the fabric (as shown in Figure 40). Tests determined that laser micro welding was the most suitable method for the task, allowing us to optimise the techniques to achieve an improved joint between metal frame and polymer. We also conducted analysis of the laser micro welded NiTi, comparing the mechanical strength of the welded wires against the as-received wires using tensile testing, and examining the micro-structure and microhardness of welded specimens. We used scanning electron microscopy to understand the surface morphology of the welded region, heat-affected zone and parent material, and determined transformation temperatures for the austenitic, martensitic and rhombohedral structure phases using differential scanning calorimetry.

- Development of a Bespoke Laser Site Welding System

Technip FMC approached TWI for help with assessing the feasibility of carrying out laser welding in otherwise inaccessible locations at their site. The pipe welding requirements were mocked up at laboratory scale at TWI with welding trials conducted on representative coupons. This first round of trials helped develop process understanding before a second round of trials investigated the tolerances of the chosen welding procedure to changes in its essential variables, with the emphasis on maximising these tolerances for robust site work, as well as confirming the fitness-for-purpose of the welds made. Following this, a TWI team developed a concept for a Class 1 laser site welding system that was in line with the relevant ISO and IEC laser and machine safety standards. Once engineering and electrical drawings of the bespoke mechanical and control components of the system were approved, the bespoke components were manufactured at our machine shop before integration into the overall system, ready for lab testing. Following successful tests, the system was then transported to TechnipFMC’s site on the Cromarty Firth in Scotland, for the successful follow-up site integration test (Figures 41-44).

- Demonstrating Expertise in Automotive Battery Welding

Building upon decades of supporting the automotive industry, TWI applied our laser welding expertise to the challenge of electric vehicle battery manufacture. Battery welding requires the careful containment, control and management of thermal events. In addition to addressing these challenges, TWI developed knowledge related to the storage of battery cells and optimised the process of battery welding using a structured knowledge transfer in order to allow the client to deliver the technology to market with confidence.

These are just some examples of the many laser welding-related projects undertaken at TWI over the decades, demonstrating our expertise and knowledge as well as an ability to meet the varied challenges of industry. To find out more about laser welding services at TWI, please see here:

https://www.twi-global.com/what-we-do/research-and-technology/technologies/welding-joining-and-cutting/lasers/laser-welding