Laser Marking :: Material Considerations

Color

• Dark colors absorb more light than lighter colors.
• This is also true with absorption of laser light.
• Although the difference is usually marginal.
• Painted colors have little effect since the laser usually vaporizes away paint.

Surface Finish

• While surface finish is not a big factor in the thermal process, it may be important for readability.
• If the laser does not induce a color change, a rough surface will require deep engraving to achieve a readable contrast with the surrounding material.
• A smooth machined surface will yield excellent readability with very shallow engraving.

Material Hardness

• For all practical purposes, material hardness is not a factor in laser marking.
• The laser can mark a hardened steel part just as readily as an un-tempered material.

Reflectivity

• Laser light must be absorbed to generate heat.
• If target material is highly reflective to the laser wavelength, might have to increase power, decrease pulse rate & beam velocity.

Absorption/Temperature

• Some plastics exhibit steep absorption-to-temperature curves (as temperature increases, absorption increases).
• The material reaction can run away in milliseconds.
• If the laser power is reduced in order to compensate, there is insufficient absorption to achieve the initial temperature increase.
• The plastic will not respond to the laser at all.

Thermal Conductivity

• Highly conductive materials will convey heat away from the point at which the laser is attempting to increase the temperature.
• The laser parameters will have to be adjusted to compensate for the material’s attempt to heat-sink itself.
• Aluminum is a classic example. Aluminum marking will require more power and/or slower marking speed.