Welding by pulsed Nd:Yag Laser is a process that achieves fusing of components without the use of additional materials (fillers). While the laser is not always a substitute for conventional welding methods, its unique characteristics offer the possibility of fabricating components from difficult or previously impossible to weld materials, and give the process several advantages over other joining methods.
These advantages include the ability to join a wide range of similar and dissimilar materials; low and controlled heat input results in small heat affected zones and a minimum of distortion; and no direct contact with the weld area and therefore no mechanical force and tool wear.
Other advantages of laser welding include it:
- is easily automated
- offers high accuracy
- has a high degree of control and repeatability on welding parameters
- is flexible through beam delivery by fibre optic cables
- has a high welding speed
The Process
The laser beam, generated by a light source and a laser rod or laser crystal, is directed to the workpiece using mirrors or fibre optics. Just before reaching the workpiece, the beam is focused using a lens to increase the power density to a value where it is capable of melting the material.
The energy of electromagnetic radiation (light) of the laser beam is absorbed by the material and converted into heat energy, so raising its temperature.
Welding is usually carried out with the material positioned near the focal point, where the energy density of the beam is highest. The position of the focal point greatly influences the weld shape and weld depth.
Often an inert gas is used to prevent reaction of the hot metal with the surrounding atmosphere and to protect the optics from fumes and possible weld spatter. Materials to be welded are placed on a CNC x, y, z table which is moved under the beam to follow the joint line.
For tube welding, a CNC rotary axis is used.
1. Spot Welding
Today's technology requires parts to become smaller and smaller. Pulsed laser spot welding allows spot diameters from 0.1 to 2.5mm in diameter with penetration up to 2mm.
2. Seam Welding
Seam welding is achieved by a series of overlapping spot welds with pulse repetition rates of up to 500 pulses per second. The resulting weld seams are of high integrity and are capable of meeting the most demanding requirements on hermetic sealing. Penetration of up to 4mm and weld diameters of 0.1 to 3mm are achievable.
3. Weld Geometry
Laser welding is applied to many conventional joint designs. Because of the small beam diameter and fusion zone, good joint fit-up is necessary. Low heat input allows welds to be placed near heat-sensitive components such as glass-to-metal seals, gaskets and electrical devices.
Detonators of airbags are welded with explosives already encapsulated. Pacemakers and transmitters have electronic devices built in before welding.
Comparison to Other Welding Processes
| |
Laser |
E-Beam |
Resistance |
TIG |
| Heat Generation |
Low |
Moderate |
Moderate |
Very high |
| Weld Quality |
Excellent |
Excellent |
Good |
Excellent |
| Weld Speed |
High |
High |
Moderate |
Moderate |
| Operating Costs |
Moderate |
Moderate |
Moderate |
Low |
| Tooling Costs |
Low |
High |
High |
Moderate |
| Controllability |
Very Good |
Good |
Low |
Fair |
| Automation |
Excellent |
Good |
Fair |
Fair |
| Range of Dissimilar Materials |
Wide |
Wide |
Narrow |
Narrow |
Application Range
High strength, crack-free welds are achieved in steel with carbon contents below 0.2 per cent, tantalum, nickel, beryllium-nickel and iron-nickel alloys, titanium, copper alloys and high grade aluminium.
The LaserXperts
Mt Warning Industrial Park
29 Quarry Rd
Murwillumbah NSW 2484
Australia
Tel: +61 6672 1777
Fax: +61 6672 1778
Laserxperts@norex.com
www.laser-x-perts.com
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Tailored Blanks?
The laser welding of tailored blanks allows the production of very strong and light car bodies, even with the use of conventional steels. A tailored blank comprises a flat sheet whose shape, metallurgy and thickness are appropriate for the specific stresses it will experience. A number of tailored blanks are butt-welded together using lasers to form a single sheet comprising materials of varying characteristics. The 'patchwork quilt' sheet is then pressed into a final shape. One panel may therefore be formed from a number of tailored blanks, allowing the weight and strength to be placed exactly where it is required. Stronger and lighter panels are the result. Tailored blanks are currently being used in rocker panels, chassis rails, panel skirts, door inners and body side outers. Current tailored blank technology is based on steel materials, although increasing exploration of aluminium tailored blanks is being undertaken. It can be imagined that laser-welded tailored blanks used in conjunction with hydroforming (see "Hydroforming - Part 1" ) could result in extraordinarily light, strong and complex shapes. Julian Edgar
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