Article: Laser Welding Technology in Australia - 2010

Laser Welding Technology in Australia - 2010

1.0 Introduction:

The purpose of this paper is to take an up-to-date look at the laser welding technology currently being utilised in Australia.

During the last decade a number of laser manufacturers in Europe and the USA have started producing laser welders, which are designed solely for a specific industry and application. This has made the technology more affordable and user friendly, and therefore contributed to a wider up take of the technology in Australia.

The focus of this paper is predominantly on laser welding equipment that is affordable and applicable to the majority of manufacturers in Australia. The paper will discuss the types of lasers currently available, laser safety, laser applications and the advantages and disadvantages of lasers.

2.0 Types of Laser Welders Available:

In its basic form a laser produces intense light that can be focused to a precise spot, with enough energy to weld metals. The initial technical factors to consider when selecting a laser source are its Wavelength and Output Power. The wavelength of a laser effects how the beam will react with materials i.e. if the incorrect wavelength is used the laser beam will just reflect off the surface and have no affect on the metal. To better understand wavelengths and where lasers fit in, we need to take a quick look at the Electromagnetic Spectrum:

2.1 Nd:YAG: Refers to the type of crystal used in the laser, which produces a wavelength of 1064nm. This wavelength is just outside the visible range of our eyes (400nm to 700nm) so we are unable to see it. However a laser with a wavelength of 1064nm is effectively absorbed by conductive metals, making it ideal for welding. The output powers available for Nd:YAG lasers range typically from 30W to 800W. Nd:YAG lasers are well established technology, and are currently the most popular for laser welding applications, which require small spot or seam welds with a few millimetres penetration depth.

Due to the wavelength of Nd:YAG lasers being close to our eyes visible range, we can use the same optics to manipulate the laser beam, as for our own eyes. This benefit has resulted in a number of different Nd:YAG laser systems being available, for a range of applications.

These systems can be categorised in the following 3 groups:

1. Manual Laser Welding: These are usually complete systems with a small welding chamber where the operator holds the piece in their bare hands, or uses basic jigging. The operator positions the piece whilst looking through a microscope and then fires the laser via a foot peddle. They are ideal lasers for small volume production, and lower budgets. Most manual welders are classified as Class1 (the same as a DVD player), which means they require no additional safety precautions.

2. Semi-Automatic and Fully Automatic Laser Welding: Semi-automatic and automatic laser welders with built in xyz motion and optional rotation axis are used for controlled seam welds, higher volume production and/or higher precision & repeatability. The piece is moved either by remote joystick or automation software. Often these systems can also be used in manual mode, however in these instances it is important to ensure the system has not compromised the ergonomics. Added features of these systems are the ability to do incline laser welding, and a visible red pointer laser to aid in automation setup.

3. Mobile Laser Welding: These are fairly new to the market, and are used where the item to be welded is not easily moved i.e. for large tool and mould repairs. These systems are on wheels and the laser head is positioned on the end of a free moving or motorised arm, so you can take the laser to the work area. Inclined welding is possible on certain models. Due to the higher power requirements of the intended applications, these systems often require 3 phase power.

2.2 CO2: Instead of a crystal, a CO2 laser cavity uses a sealed glass tube filled with Carbon Dioxide gas. The wavelength produced is 10,600nm, which is a long way from our eyes visibly spectrum. This wavelength is not well absorbed by metals, in fact about 80% of this laser light can be reflected off the surface of metals. However a CO2 laser is capable of producing much higher output powers than Nd:YAG lasers, i.e. 10,000W and higher. Once the laser has passed the melting point of the surface, the high reflectivity becomes less of an issue and more of the power is absorbed for the welding process.

To produce the high output power of a CO2 laser, generally requires large equipment and coolers. These lasers are generally used for larger applications that require brute force.

2.3 Fibre: In a fibre laser the intense light is generated in an erbium doped single mode glass fibre, the wavelength produced is 1090nm. Fibre lasers are the latest technology currently available, and offer another level of control and higher weld repeatability. Fibre lasers have recently become more popular in laser marking, but there are a few manufacturers who have also used this technology in laser welding. Due to the small spot size (0.02mm) and shot repeatability, fibre laser welders are most commonly used by medical device companies that are looking for very small controlled laser welds.

3.0 Laser Safety:

A common concern when considering laser technology is safety, in particular eye safety. Australia’s laser safety regulations are inline with Europe’s and the USA. All lasers brought into Australia must be classified and have the correct classification label clearly placed on its outer housing. The classification classes are mainly (but not wholly) dependent on the lasers wavelength and power.

Laser Safety is easy to handle once you understand the classifications, and the required precautions for a particular class of laser. Below is a list of the classifications, which we have simplified for the purpose of this paper, and should not be used in place of the official Australian Standards.

Class1
A Class1 laser is safe under all conditions of normal use, e.g. DVD Player. This class includes high-power lasers within an enclosure that prevents exposure to the laser beam and includes door interlocks that disable the laser when opened. 

Class1M
A Class1M laser is safe for all conditions of use except when passed through magnifying optics such as microscopes and telescopes. Class1M lasers produce large-diameter beams, or beams that are divergent. 

Class2
A Class2 laser is safe because our eyes blink reflex will limit the exposure to no more than 0.25 seconds. It only applies to visible-light lasers (400–700nm). Class2 lasers are limited to 1mW continuous wave. Many laser pointers are Class2.

Class2M
A Class2M laser is safe because of the blink reflex if not viewed through optical instruments. As with Class1M, this applies to laser beams with a large diameter or large divergence, for which the amount of light passing through the pupil cannot exceed the limits for Class2.

Class3R
A Class3R laser is considered safe if handled carefully, with restricted beam viewing. Visible continuous lasers in Class3R are limited to 5mW. 

Class3B
A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as from paper or other matte surfaces are not harmful. Protective eyewear is typically required where direct viewing of a Class3B laser beam may occur. Class3B lasers must be equipped with a key switch and a safety interlock.

Class4
Class4 lasers include all lasers with beam power greater than Class3B. By definition, a Class4 can cause eye damage as a result of direct or diffuse beam viewing. These lasers may ignite combustible materials, and thus may represent a fire risk. Class4 lasers must be equipped with a key switch and a safety interlock. Most entertainment, industrial, scientific, military, and medical lasers are in this category.

For many industrial applications a Class4 laser is housed in an enclosure with safety interlocks, therefore the overall system is classed as Class1.

4.0 Common Laser Welding Applications:

Laser welding can give you precise control of the energy you deliver to a weld. It is this controllability, speed and localised heating, which allows a laser to successfully weld materials with high melting points or high conductivity.

Most applications of lasers are therefore based around jobs that require: strong welds, repeatable results, non contact, precision, process control, small heat-affected-zone or welding complex alloys e.g. Titanium and Stainless Steel.

Sensor Manufacture:
Sensor manufacture requires delicate but gas tight and mechanically stable welded joints, which often have to be virtually invisible. Laser welding is often a popular choice to meet these demands, especially if the sensor is heat sensitive. Laser welding is used to weld force sensors, pressure sensors, load cells, pyrometers, and thermocouples.

Aerospace
The use of laser welding technology in Aerospace is still in its early stages. Typical repairs jobs currently being done are: camshafts, crankshafts, compressor rotors, turbine rotors, gears, rollers and casing parts.

Materials that can be processed range from GGG 40 up to extremely heat resistant Nickel based alloys. Due to the limited heat-affected-zone (only tenths of millimetre), formation of coarse grain does not take place. The properties of the material remain preserved after welding. It is also possible to laser weld at room temperature without thermal pre-treatment of the material.

Sheet Metal
The use of laser welding for thin sheet metal parts is growing in popularity.

Applications are:
- Seams and corner joints on casings
- Butt-welding of pipes
- Welding of short tubes on smooth sheet metal
- Rotation seams on turning parts
- Welding seams on junctures

Parts manufactured from Steel, Zinc, Titanium, Copper or Nickel Silver can be welded, without edge burning, oxide-free and without visible distortion even on long seams.

Finishing work, such as sanding or straightening, becomes to a large extent unnecessary, since the high quality seams resulting from laser welding alone usually meet the optical requirements without finishing work.

Tool & Mould Repair
A laser can precisely repair tool and mould damage caused by wear and tear, without any loss of form. Only minor finishing is required since the deposit application is similar to the original contour. The laser fusion welding process allows fine energy dosing: Only a small volume of material is melted, thus avoiding tension. Consequently, the welds are free of cracks. In most cases pre-warming of the material is not required.

The tensile strength of the material can be reproduced by using a selection of filler wires. Even copper and aluminium alloys are welded with successful results. And for tool Steels it is possible to obtain hardness of up to 60 HRC.

Medical Devices
Due to their control and precision, laser welding machines have become an indispensable production tool for Medical Devices. They are popular for manufacture of surgical instruments and endoscopes.

Laser welding is typically used to produce:
- Narrow welding seams with high strength
- Hermetic seals
- Corrosion-resistant
- Porous free, suitable for high-temperature-sterilization
- Biocompatibility in accordance with the basis material

Jewellery
In Australia laser welding is often used by small manufacturers, designer jewellers and repair workshops. Common jobs are re-tipping of rings without removing the stone, filling porosity, repairing chains, assembling parts, repairing Titanium glasses frames, and creating new designs.

No solder is needed in the welding process, which reduces cleanup and saves on solder expenses. Finishing work is often limited to a quick polish or cleaning of the jewellery.

Dental
Laser Welding has become very popular in dental. Among other applications, laser welding is used for manufacture and repair of implant constructions, crown and bridge, orthodontics and partial denture.

The laser reduces the working time in dental restorations by up to 80% in comparison to alternative methods of soldering. The laser’s precision and very small heat-affected-zone makes it possible to weld directly on the model or next to ceramic.

Laser welding makes efficient joining possible, without the use of solder, thus retaining the corrosion resistance of the basis material. The result is a stable and biocompatible welding joint.

5.0 Advantages:

There are 3 main advantages most people consider when looking to invest in laser technology, which are as follows:

1. Enabler: Laser technology can allow you to do a process that no other technology can achieve.

For example:

- Welding complex alloys, or dissimilar alloys
- Precise welding of small parts
- Welding in close proximity to heat sensitive components
- Repeatable welds
- Clean hermetic seals
- Solder free welds
- Contact free welding
- Welding complex structures

2. Product Improvements:

- Stronger welds
- More visually appealing welds. Consistent welds with no flux used.
- Smaller heat-affected-zone, resulting in less distortion and less strain on neighbouring components, increasing product life.
- Competitive advantage

3. Process Improvements:

- Reduced preparation time prior to laser welding i.e. no heat treatment
- Faster welding process than alternative technology
- Reduced post welding process i.e. no cleaning of the weld or grinding
- Repeatable results from each operator
- Easy for employees to be trained on and use, no specialised skills required
- Less welding fumes in the process
- Reduced running costs i.e. no expensive solders, non contact and no mechanical wearing parts.

5.1 Disadvantages:

The main disadvantage is the Capital Cost. The cost of a laser welding system can start from just under $30k and range up to $100k’s. This is less of an issue if the above advantages can be realised when manufacturing high value or high volume products.

The other disadvantage is related to mobility. There have been recent developments in making lasers more mobile, however they are still not as mobile as MIG and TIG welders.

Some people cite laser safety as a disadvantage, however for most applications there are now many laser systems that are correctly enclosed to meet Class1 classification (same as a DVD player).

6.0 Conclusions:

Laser welding continues to become more widely used in Australia, and in a growing range of applications.

Nd:YAG lasers are still the most popular choice in areas where small precise laser welds are needed. For applications that require larger welds and more brute force, CO2 lasers are the preferred choice.

There is now a large range of Class1 enclosed laser welders available in Australia designed for a range of specific applications. These lasers are available as manual, semi-automatic and fully automatic systems.

The main advantage of laser welding is that it enables you to produce a product or process that was not previously possible with other technology. Other advantages are centred on improved product quality and reduced process times. The competitive advantages gained from laser welding technology can be balanced against the disadvantages when realised for manufacturing high value or high volume products.

Authors: Neil Penman MSc - Managing Director
& Keith Ormesher BEng - Technical Engineer. M2 Lasers Pty Ltd