Laser welding or TIG welding: which process suits your metalworking?

This comparison goes through the points that decide the choice in practice: heat input and distortion, seam appearance, speed, gap size and joint preparation, materials, induction and occupational safety.

This article replaces neither a risk assessment nor legal advice nor a welding engineering assessment of the specific component.

Two heat sources, two ways of working

In TIG welding, the current is supplied via a non-consumable tungsten electrode; welding takes place under shielding gas. The filler material is added separately. EWM emphasises that this decouples the addition of filler metal from the current.

In hand-held laser welding, a fibre laser concentrates its radiation in the near infrared onto a small focal spot. For the hand-held machines it uses itself, the ifw Jena cites focus diameters between 50 and 150 µm. Modern handpieces oscillate the beam across the seam, according to the ifw up to 7 mm wide, and feed wire.

This results in a different working style. In TIG welding, the hand controls heat and filler. With the laser, in the ifw’s assessment, the technology takes over part of this, and the wire feed sets the speed.

Heat input and distortion

Fraunhofer ILT describes laser beam welding of metallic materials as a process characterised “in particular by a low and controlled heat input into the component”. The ifw Jena sums up the practical effect for hand-held machines concisely: weld faster, straighten less.

How much heat enters the component per unit of seam length depends on power and travel speed, as well as on material, sheet thickness and seam shape. No generally valid percentage for “less distortion” can be derived from this.

The difference becomes relevant above all where distortion causes follow-up costs:

• thin sheets that distort easily
• assemblies that must be dimensionally accurate after welding
• parts where straightening accounts for a noticeable share of working time

Seam appearance, penetration and rework

TIG stands for clean seams. Fronius cites as advantages that no weld spatter is produced and that the seams are of particularly high visual quality; EWM describes the process as “clean” and as particularly suitable for root passes.

With the hand-held laser, the strength lies more in penetration. Using a 1.4462 duplex steel, the ifw Jena shows that full penetration is possible from one side. At the same time, it names a need to adapt drawings — full penetration instead of throat thickness (a-dimension) — and double wire as an approach for building up the seam. The ifw also sees a need to adapt standards, so that deep penetration is not limited to automated and mechanised systems.

A uniform seam appearance is not yet proof of quality. Which tests a seam must pass follows from the requirements placed on the component — regardless of the process.

Speed and actual lead time

Fronius lists low welding speeds as a disadvantage of the TIG process, and EWM describes the deposition rate as “not very high”. The ifw Jena names faster welding as an advantage of the hand-held laser.

For cost-effectiveness, however, it is not only the time at the torch that counts. In addition, there are:

• Setting up and securing the laser area
• Putting on the protective equipment
• Positioning the extraction
• Preparing and clamping the parts
• Rework and testing

Only the lead time measured on your own parts is reliable.

Gap size and joint preparation

The focal spot measures only a fraction of a millimetre. Hand-held machines additionally offer beam oscillation and wire feed; according to the ifw Jena, the wire feed serves, among other things, to improve gap bridging.

How large a gap may be depends on the machine, oscillation width, wire, material and sheet thickness. As a point of reference from a different setting: for an automated laser welding cell with wire feed, Trumpf states that gaps up to 1 millimetre wide can be closed. This is expressly not a guide value for hand-held machines.

For joint preparation, this means:

1. Check cutting and edge fit before the seam is planned.
2. Clamp the parts so that the gap does not open during welding.
3. Remove residues, contamination and coatings in the seam area wherever possible. In FBHM-135, the DGUV names the removal of residues and contamination from workpiece surfaces as a measure in TIG welding; welding over organic coatings can produce pyrolysis products.
4. Determine the limits for your own gap through trial welds.

Materials and sheet thicknesses

TIG covers a broad range of materials. EWM puts it this way: if a metallic material is suitable for fusion welding at all, it can be joined with this process. The DGUV lists unalloyed, low-alloy and high-alloy steels as well as aluminium, copper, nickel, titanium and their alloys. According to EWM, the lower limit is around 0.3 mm for steel and 0.5 mm for aluminium and copper. According to Fronius, TIG is not suitable for large workpiece thicknesses.

With the laser, reflection plays a role. Fraunhofer ILT describes copper and aluminium as highly reflective at a wavelength around 1 µm. This affects the process and — via reflected radiation — laser protection.

According to the manufacturer’s specifications, the Beamlux laser welding machine is intended for steel, stainless steel, galvanised sheet and aluminium.

Induction and qualification of welders

TIG is considered demanding. EWM speaks of a skilled “touch” and good training, while Fronius cites the high level of skill required as a disadvantage.

With the hand-held laser, in the assessment of the ifw Jena, the technology compensates for part of the experience, above all wire feed and beam oscillation. In its own tests with students, the institute compares one week of TIG training with half a day on the hand-held laser. It cites acceptable welding results even with little experience as an advantage.

Two restrictions apply:

• According to the ifw, very experienced TIG welders are not always the best laser welders. They have to weld faster, and seeing, hearing and feeling the process are different.
• A shorter induction does not mean no training. The ifw offers a three-day course that ends with a welder qualification test to DIN EN ISO 9606-1 on CrNi steel.

Irrespective of proof of qualification, § 8 OStrV requires instruction based on the risk assessment where there are hazards from artificial optical radiation, namely before employment begins and at least annually thereafter.

Laser protection: what class 4 means in operation

According to the BG ETEM, hand-held laser machines are predominantly class 4 lasers. Hazards arise from the direct or reflected beam; with high-power machines, according to the BG ETEM, even the diffuse reflection from the process area can in the worst case endanger unprotected eyes. Radiation in the near infrared is not visible.

This has organisational consequences that do not arise in this form with TIG welding:

• Laser area: Under TROS Laserstrahlung, this is the area in which the exposure limit values can be exceeded. It does not have to coincide with the working area.
• Laser safety officer: Under § 5 OStrV, before class 3R, 3B and 4 laser equipment is put into operation, the employer must appoint a laser safety officer in writing, unless they themselves have the necessary expertise. As an example of delegated powers, the TROS names switching off the laser system when defects are found. Responsibility for the risk assessment and protective measures remains with the employer.
• Safety devices: On the systems described by the ifw Jena, these include contact monitoring on the workpiece, an indicator on the handpiece, a third element such as a foot switch or plasma sensor, and a key switch.
• Protective equipment: The ifw does not consider laser safety goggles alone to be suitable for longer periods of use, because they do not protect the face. Where arc and laser welding take place in the same area, it recommends a hybrid helmet.

DGUV Information 203-093 serves as practical guidance for the risk assessment. If the employer complies with the TROS, they can assume that the corresponding requirements of the regulation are met; other solutions must achieve at least the same level of safety. This section provides an overview and does not replace the risk assessment for your own workplace.

Fume, gases and secondary radiation

TIG is not emission-free either. In FBHM-135, the DGUV describes how TIG welding releases hazardous substances as particles and gases. Factors to consider include ozone when welding aluminium materials and high-alloy steels, as well as thoriated tungsten electrodes; as a rule, electrodes without added thorium are to be used. According to the BGHM, the welding area must be selected or shielded so that persons in the vicinity are protected from radiation and flying sparks.

Laser welding is not emission-free either. According to the BG ETEM, the interaction of the beam with the material generally releases particulate and gaseous hazardous substances, and UV radiation and visible blue light can also arise as secondary radiation. A DGUV research project identified titanium as the material with the strongest secondary radiation emissions in pulsed laser beam welding. Particularly with titanium, the exposure limit value near the process zone was in some cases reached after less than one minute. Light-tight gloves and clothing are recommended.

The following therefore applies to both processes: extraction at the point of origin, skin protection and shielding of the surroundings belong in the planning.

When TIG remains the better choice

The ifw Jena expressly does not see hand-held laser beam welding as a replacement for arc processes, but as a complement. TIG can remain the better choice if:

• root passes are welded, for which EWM describes the process as particularly suitable
• the geometry, seam section or seam requirement do not suit the hand-held laser — a limitation that the ifw expressly names
• materials are processed that an existing laser machine does not cover according to the manufacturer’s specifications
• drawings and qualifications are designed for TIG and adapting them is not economical
• there is no laser in the company yet and welding is only done occasionally, so that a laser safety officer, laser area and protective equipment would have to be set up for just a few seams
• work is carried out at locations where a laser area cannot be set up safely

When a laser welding machine is worth considering

A laser welding machine can be worthwhile if distortion and straightening work cause noticeable costs, if there are many similar seams that suit the hand-held laser, or if skilled workers for demanding TIG welding are scarce. The ifw expressly names the shortage of skilled workers as one driver.

The BL Welding Machine from Beamlux is mobile, water-cooled and works with a continuous wave fibre laser. It is available with 1,500, 2,000, 3,000 and 6,000 W, has a double-swivelling welding head and is intended for welding, cutting, weld seam cleaning and rust removal. The versions with 1,500 to 3,000 W start from €12,600 plus VAT; the 6,000 W version is available on request.

In addition to the machine price, there are laser protection, extraction, protective equipment and induction. Whether the purchase pays off depends on how many seams actually benefit from the laser.

Conclusion: a complement, not a replacement

Laser welding or TIG welding is not a question of principle but a question of the seam. The comparison shows:

1. The laser can weld with lower heat input, less distortion and higher speed.
2. TIG remains strong for root passes, a broad range of materials and spatter-free seams.
3. The laser requires careful joint preparation and organised class 4 laser protection.
4. Both processes release hazardous substances and require extraction.

Which process suits your own metalworking can be clarified most reliably with trial welds on your own components and a complete calculation that includes occupational safety.

Sources

• Fraunhofer ILT – Joining of metals — Laser beam welding with low and controlled heat input; high reflectivity of copper and aluminium at wavelengths around 1 µm.
• ifw Jena – “Hand-held laser welding – hazards and protective measures: experience report from welder training” — Presentation document published on dguv.de in the section of the Wood and Metal department; advantages, limitations, safety devices, protective equipment and training.
• DGUV – Fachbereich AKTUELL FBHM-135 “Hazards from hazardous substances in tungsten inert gas welding (TIG) – preventive measures” — Hazardous substances, ozone, thoriated electrodes and protective measures in TIG welding.
• BGHM – Arbeitsschutz kompakt 042 “TIG welding” — Shielding against radiation and flying sparks, extraction, fire protection.
• BG ETEM – etem magazine “Underestimated risks” on hand-held laser machines — Laser class, reflection, secondary radiation and hazardous substances with hand-held laser welding machines.
• IFA/DGUV – research project FF-FP 0439 on UV radiation in hand-held laser welding processes — Secondary radiation, exposure limit value for titanium, recommendations on skin and eye protection.
• DGUV Information 203-093 — Practical guidance for the risk assessment when operating open laser equipment for material processing with manual guidance or manual positioning.
• OStrV – German regulation on the protection of workers from artificial optical radiation, § 5 and § 8 — Appointment of the laser safety officer and instruction of employees.
• TROS Laserstrahlung – General part (BAuA) — Definition of the laser area, duties and powers of the laser safety officer, presumption of conformity.
• EWM – Basics of TIG welding — Process principle, materials, minimum sheet thicknesses, root passes and requirements for manual skill.
• Fronius – What is TIG welding? — Advantages and disadvantages of the TIG process.
• Trumpf – press release on the TruLaser Weld 5000 — Gap bridging with wire feed in an automated laser welding cell.

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