Laser Surface Treatment
Lasers are used to modify surfaces by selectively removing coatings or by phase transition of crystalline materials such as metals in order to change the material’s characteristics.
The aim of such operations will be to increase electrical conduction; to surface harden carbon steels for better wear resistance; or to clean surfaces prior to bonding or putting mould tools back into service.
Transformational hardening using a laser has considerable advantages over conventional hardening techniques as it is rapid, selective and restricted to the surface. This means that components may be hardened only at wear points, leaving the bulk of the material unhardened and therefore less brittle.
Carbon Steels are suitable for laser hardening; the first step is for the surface of the metal to be rapidly heated to a level above the austenising point. This temperature will be below the material melting point and so will not damage the part. Lasers are ideal for this operation, possessing sufficient power density to locally raise the temperature of any surface within line-of-sight. Diode lasers are often the laser of choice for this operation as they are attractive in terms of cost per Watt and at a wavelength of just under 1um, are, unlike CO2 lasers, fairly well absorbed by solid metals.
The second step is quenching – the surface must be rapidly cooled during which the Austenite transforms to a Martensite phase. Again, laser processing provides a key advantage over other forms of heating – as the laser is capable of raising the surface temperature so rapidly, the total heat added will be sufficiently small that components or tools will self-quench by internal thermal conduction.
Plastic Injection Mould Cleaning
Moulds and tools can develop deposits which inhibit their efficient operation, particularly those moulding rubber tyres or footwear. Lasers are also suitable for removing other deposits such as soot, oil and silicone.
Such large-scale operations require high average power and also high peak power to cleanly ablate such organic deposits. A Q-switched source such as Rofin’s DQ-Series is suitable.
Removal of Coatings
Paint can be locally stripped using laser from regions where electrical connection or earthing is required. In the production of solar panels, all layers applied need removing from the edge region of the glass substrate so that the panel can be sealed from ingress in all weather conditions.
As with cleaning operations, Rofin’s DQ-Series high power Q-switched YAG can perform the task at commercial throughputs.