Q&A: Laser Marking
By Scott Sabreen
Question: We are marking large alphanumeric characters (1” height and 1/8” stroke width) using an Nd:YAG laser. The marking time is 45 seconds. Can you suggest ways to reduce the cycle time?
Answer: There are several techniques that can decrease marking cycle time while achieving high resolution quality.
- First, adjust the beam expander (telescope) to increase the spot size. By adjusting the beam expander, you will be able to maintain the proper focal distance and laser output beam characteristics. This is preferable to manually adjusting the laser distance beyond its maximum focal point.
- Second, select a larger aperture – 2.0mm versus 1.2mm for example – which will allow broader vector lines to be drawn.
- Third, use vertical bi-directional or serpentine vector line fill to minimize the laser reposition time (sometimes referred to as galvo settling times) vs.unidirectional fill.
- Fourth, you may be able to eliminate the image outline and use “fill-only”. The line separation distance – center point to center point – may need to be adjusted to eliminate voids in the filled character.
Once the suggested changes have been made, you will likely be able to increase your marking speed with optimally filled vector lines.
Question: Can you explain the difference in “Wall Plug Efficiency” between Nd:YAG lasers and fiber lasers?
Answer: A standard arc-lamp Nd:YAG laser, as sold, is rated at 75-100 watts total raw output power. This is different than the power density (watts/cm2) at the focused work site. YAG lasers have poor wall plug efficiency in the range of 1.5 percent. As a result, 985 watts of each available 1,000 watts is converted to wasted heat and not useful laser output power.
Fiber lasers, by design, generate less heat and manage the heat generated much more effectively. Fiber lasers have wall plug efficiency in the range of 35 percent. Since the laser light is always contained in a fiber, there are no additional sources of loss inside the laser cavity. Therefore, a 20-watt fiber laser produces an average of 20 watts of power.
Scott Sabreen is the founder and president of The Sabreen Group, Inc., a plastics engineering consulting firm. He is a board member for the Society of Plastics Engineers Decorating/Assembly Division, technical editor for Plastics Decorating and expert engineer for Omnexus/SpecialChem, Intota-Guideline and Nerac. Sabreen may be reached via email at firstname.lastname@example.org.