BASICS OF LASER MARKING & APPLICATIONS  

Electro-magnetic Spectrum: Nd:YAG and Carbon Dioxide lasers emit radiation at different wavelengths. Fundamentally, the 1.064 micron wavelength of the Nd:YAG is an order of magnitude shorter than the 10.6 micron radiation from a Carbon Dioxide laser. In materials processing, the shorter wavelength of the Nd:YAG couples better to metal while the longer Carbon Dioxide wavelength is more suitable for cutting plastics, ceramics and other organic materials. The electro-magnetic spectrum below shows where the Nd:YAG and CO2 laser emissions are located relative to other lasers and radiation sources.

In general,  Nd:YAG lasers at the fundamental 1.064 wavelength are best suited for marking metals while the CO2 laser is more suited for plastics, painted or organic marking. This is the Global Standard.

Laser markers are used to produce alpha-numeric characters, bar codes, serial numbers, logo's, artwork and other graphic images using a non-contact thermal process. Beam characteristics of Nd:YAG laser markers are classified according to their mode structure. For applications requiring higher average power, the multi-mode output is most desirable. Multi-mode output spot diameters are typically 30 to 60 microns. TEMoo or End Pumped by Diode Array (DPSS) Systems use much substantially lower powers to get comparative Outputs as compared to Lamp Pumped Systems due to superior Beam Characteristics.  Fixed or fiber optic beam delivery may be employed from the resonator to the scanning assembly.

LASER BEAM GENERATION
ND:YAG LASER

Note : This is the system followed by Rita Laser, and all topmost global companies. The flash lamp used is a Krypton Lamp.

ACOUSTO –OPTIC Q SWITCHING (PULSING THE LASER BEAM)
When an RF signal is applied to the transducer an acoustic wave is projected through the quartz which momentarily compresses the material and changes its index of refraction. Some of the light passing through the Q-switch is diffracted to a small angle and misses the rear mirror momentarily, causing the lasing action to cease. During this phase, the atoms in the laser rod gain energy which is stored until the RF signal is removed. The resulting burst of laser energy may be several kilowatts of peak power, significantly more peak power than the laser would emit without the Q-switch. Q-switching is the most common means of producing very short pulse widths and very high peak power from a relatively low power Nd:YAG laser. Q-switches at Rita Laser and globally typically operate at frequencies from 1 to 50 kHz.

LASER POWER – A MACHINE SPECIFICATION
 
Average Power and Power Density: A continuous wave (CW) Nd:YAG laser marker rated at 50 watts produces the same average power as a 50 watt light bulb. The difference is the light bulb projects white light of all wavelengths in all directions. The laser emission is coherent (traveling in one direction), mono-chromatic (of one wavelength) and in phase. The power density, expressed in watts/cm2 tells us how concentrated the laser energy is at the point of focus. A laser producing 50 watts of power in a 0.005" diameter spot will produce considerably higher power density than the same laser with a 0.500" spot diameter. The effective marking power of the laser is the net power density produced at the point of focus or where the best laser mark is achieved. Rita Laser produces Marking Lasers with Powers ranging from 30 to 150 Watts, with the highest Flux Ratings for Longest Possible Machine Life (LPML)
 
 
GALVANOMETER SCANNING (BEAM STEERING) – HOW A MARKING LASER “WRITES”

Galvanometer or XY Scanner: The output of the laser marker is typically directed by moving mirrors operating in both the X and Y planes. The XY mirror sets are each independently connected to highly accurate, repeatable and extremely fast galvanometer drivers (motors). Precision beam steering, and thus the laser mark, in both the X and Y axis is controlled by the software and control electronics.

MARKING FIELD

Flat Field Lens: The most common method to focus the laser beam in a laser marker is after it is positioned by the XY galvanometer mirrors by using a flat field lens. Typical flat field lens sets provide marking areas from 60 mm to over 300 mm in diameter. These flat field lenses provide a relatively large marking area and permit fast, high quality laser marks and distortion free pictures to be made on a broad range of metals and other materials.
 
 

SOME FAQS
 

1.What Materials Can Be Marked?

CO2 :   Suitable materials include: engraving plastic, acrylic, coated metal, wood, glass, stone, leather and rubber. Most organic materials mark well.
 
Nd:YAG   Suitable Materials include :  Hardened and non-hardened Steels; Aluminum; Stainless Steels; Gold, Silver, Copper, Invar;  Coated & Plated Metals; Nylon, ABS, PES, Polycarbonate, PVC, Styrene, Resins. Most metallic materials mark well.

2. How Fast Are The Machines?

Speed varies depending on whether you are engraving or cutting, the detail required and the material. Top Line Speeds are in the region of 5000 mm/second

3. What Else Is Needed To Operate The Machines?

In addition to the machine you need:

Computer (IBM PC or Compatible running Windows™ 95/98.) Rita Laser normally provides this with preloaded Marking Software

Graphics program (CorelDraw and AutoCAD are popular programs)

Exhaust system (to safely evacuate engraving chamber of any smoke or odors generated in the engraving or cutting process and expel it.) This is not normally needed when marking Metals with an Nd: YAG Laser.

Chiller  Laser provides this. De-ionized water is needed as cooling medium for initial Charge and Top-up

Voltage Stabilizer Where Power Fluctuations are common

Air Conditioning   Where ambients exceed 30 o C and/or Dusty Conditions prevail

4. Are The Machines Safe?

All Laser Systems' platforms contain a CO2 laser in a class 1 enclosure (Class I is the safest laser rating) or an Nd:YAG Laser in a safe Housing. Rita Laser voluntarily follows the Safety Recommendations laid out in ANSI Z 316. Safety Glasses are provided as Standard Equipment with the machine, and it is common sense for the Operator not to look continuously at the emitted Laser Beam. During the Laser Marking Process, no effluents or other Pollutants are produced.


5. Are The Machines Easy To Use?

     All  Laser systems are designed for ease of use. Following are the basic setup steps:

1. On your computer, prepare the graphics to mark or engrave - just as you would do for a standard printer
2. Load the material to be engraved or cut into the machine
3. Use the  “mark” command in the graphics software to mark on the work piece.

6. How Much Maintenance Is Required?

Periodic cleaning is the most common general maintenance on a Laser Machine. It is desirable to clean the two exposed mirrors and lens in the same way one would clean a camera lens. The moving parts and engraving table should also be wiped down. Periodic cleaning requires less than 5 minutes.
With periodic cleaning, most potential problems are eliminated. Other maintenance such as part replacements and adjustments have been minimized, but when necessary can be accomplished by the machine operator on site with minimal down time.