Laser welding is used when there is a need to limit the size of heat-affected-zone (HAZ), to avoid distortion and to automate the process. CO2-, solid state, fiber and disk lasers can function as welding source. Pulsed lasers provide higher power density than continuous wave (cw) lasers and are preferred for precision welding of miniature components.
Laser welding is applicable for both, metal welding and plastic welding. Many products and parts in the electronic, medical, aerospace and automobile industry are manufactured by laser welding (both spot and seam welding). Laser precision welding does not require a vacuum system, foreign or filler materials or any mechanical contact. As the heating is highly localized and rapid, laser hermetic welding of electronic devices is widely seen in the electronics industry avoiding the damage of electronic components adjacent to the welds.
Heat conduction welding
At relatively low laser power densities, the laser energy is absorbed at the surface and conducted into the interior of the workpiece by thermal conduction. As the depth, which can be melted is limited, heat conduction welding produces a relatively shallow and wide weld and is used for welding of relatively thin materials.
In heat conduction welding, the energy transfer efficiency is equivalent to the absorption property of the metal. Metals with high thermal diffusivity such as copper will require e.g. five times more laser power density for similar results with iron alloys.
Keyhole (deep) welding
Under high power densities, a keyhole is formed in the metal. The energy transfer efficiency can be much higher than the absorption of the metal because of the multiple reflection effect within the keyhole. Higher aspect ratio (depth/width) can be achieved if the welding mode is shifted from conduction to keyhole mode. Therefore, keyhole mode laser welding is more commonly used in the praxis.
In keyhole mode laser welding, the heat transfer and fluid flow process are very complex. An imperfect collapse as well as instability of the keyhole will entrap gaseous species, including vaporized alloying elements and shielding gas. This can be considered as a possible cause of porosity in the weldment, especially of low viscosity aluminium alloys. Welding parameters and additional techniques have to be properly chosen to avoid the transition region where the keyhole is unstable, so that porosity could be minimized.
The restrained contraction of a weld during the rapid cooling sets up tensile stresses in the joint and may cause hot cracking in the weld fusion zone during solidification of the weld metal (solidification cracking). Optimization of pulsing by selecting proper laser pulse shapes and ramping sequences can reduce the strain rate and avoid hot cracking. In laser welding of alloys, not only properly laser and process parameters, but also the right composition of the alloys have to be selected.
Laser precision welding is typically autogenous. Joint design, edge preparation and manufacturing fitup tolerances are critical as excessive gaps usually cause the lack of fusion or undercut. In general, for both butt and lap welds, the maximum fitup gap should be less than 5% of the thickness of the thinner material being welded. Argon is preferred as inert shielding gas because it is less expensive than helium. It also provides excellent coverage because it is heavier than air.
Transmission Laser Welding
Laser transmission welding has become one of the most preferred approaches for the joining of thermoplastics. The laser beam passes through the laser transparent top part and is absorbed by the bottom part, typically containing carbon black. The absorbed laser energy softens and melts both plastic parts. With externally applied clamping pressure, the parts are bonded upon cooling. Key advantages are low mechanical and thermal load of the joining parts and vibration-free processing.
Nearly all thermoplastics and thermoplastic elastomers can be welded with lasers. The welding seam strength is comparable with that of the base material. Recently, special pigmentations are developed to produce non black color plastics, which absorb laser radiation and hence, open new possibilities in laser welding of plastics.
- Laser spot welding as a more cost-effective alternative to resistant welding
- Laser seam welding with a CNC multi axis motion system
- Laser welding with filler materials to improve weldability and to compensate for imperfect fitup (gap bridging)
- Welding of dissimilar materials
- Laser deposition welding for parts repair or modification (laser cladding)
- Hybrid welding with the combination of arc preheating and laser welding
- Simultaneous and mask transmission welding of plastics with high power diode lasers
- Remote welding with high power lasers and scanner optics
- SHADOW welding (Stepless High speed Accurate and Discrete One pulse Welding) using a single pulse to generate a quasi-continuous weld of several milimeters in length
- Globo welding using an air-supported glass sphere as a dynamic clamping device for 3D and large scale plastic welding applications
Area of expertise
KJ Laser Micromachining is your first place in laser precision and micro welding in North America and Canada. Our expertise covers a wide range of laser joining technologies, including joint design, weldability of materials, inert gas shielding and plasma control. Our experience in materials science and laser-material interaction permits a precise control of laser pulse duration, pulse shape and energy to produce sound seam and spot welds, which are free of distortion, micro cracks and porosities. The laser weld penetration depth is in the range of 0.5 mm to 2 mm (0.020 – 0.080”). Dissimilar materials such as steel to copper or aluminium can be joined without using filler materials.
Our laser welding services also include laser hermetic welding, laser tube welding with rotary chucks, laser welding of dissimilar materials and laser transmission welding of thermo plastics. In the near future, KJ Laser Micromachining will also provide metallographic cross section analysis of weld microstructure and geometry.
Among others, steel, titanium, highly reflective and conductive metals (aluminium, copper and their alloys), high melting point metals (molybdenum, tungsten or tantalum) and thermoplastic materials can be laser welded. Thin metal foils down to 0.002” (50 µm) can be fused to solid parts with no burn through.
Sub-contract micromachining and R&D
Our laser welding services include samples testing, feasibility study, prototyping and contract manufacturing. We can also play a vital role during your product design and development period by conducting welding and metallurgical investigations in laser precision and micro welding.
System development and process automation
KJ Laser Micromachining has the capability to design and develop customized laser welding systems for the high-volume and automated manufacture of parts or components.