The use of laser marking and laser engraving is in demand, mainly as a result of government requirements that call for readable product and part identification. Note as well that the power of the laser beam has been discovered by the community-at-large to help create traditional artisan effects on a broad scale. Is there a difference between laser marking and laser engraving? The answer is yes and it is an important difference. Laser marking is the more generic term, which covers many different techniques, one of which is laser engraving. Engraving will require the use of a technology using inks or bit heads and alter the surface of the item. Excellent of course for permanent marking of parts or for applying a registered trademark or logo to products. Laser marking uses of a low powered beam causing material under the surface to oxidize, or turn black. The result is a high contrast image that is permanent and resistant to wear. It is also known as laser dark marking. This process is used to apply a variety of information, including serial numbers or product codes. It does not corrupt the material’s surface, it cannot be washed off and is not susceptible to abrasion. Every design can be reproduced at the same high quality and lasers provide the level of detail you cannot get with old-fashioned printing or writing.
Laser marking systems use a low-powered beam and are self-contained, and are comprised of a laser, power supply, controller, protective covering and software for a computer that will run it. Since there are several types of lasers, researching the system you need is critical. Laser marking results are impressive when you appreciate that the data presented via a laser marking technique can contain approximately 100 times the amount of information on the grocery store UPC bar codes—while taking about 75% less space. Some parts or materials cannot tolerate the engraving method thus laser marking offers the perfect solution for marking items that cannot have any grooves or holes. This is particularly critical when used for marking medical devices, where any indentations might tend to breed bacteria. For that reason, the FDA must approve the marking method used by the medical industry in the manufacture of instruments or implantable devices. Laser marking is normally performed on metals but also used on plastics.
Engraving on the other hand will create visible grooves that will reveal a desired shape, design or customized information. It is a physical process and should not be confused with etching, for example, which is a chemical process. Laser engraving results in an image but is also noticeable by touch. Laser engraving requires a high heat laser, vaporizing the material surface, and usually applied to metal, plastics, wood, leather, glass and acrylics. This process is widely used in the automotive industry. Laser etching is a more precise form of laser engraving and is the preferred method for working on precious metals.
Basically the machines for both laser marking and laser engraving are the same. Laser engraving is extremely popular in production line manufacturing, and will mark materials such as glass and product while they are moving. When more precise engravings are required, a laser table added to the set-up to allow the controller more command over the design.
Important progress has been made. Early on, today’s traditional engraving were the worst laser-engravable materials. This problem has now been solved using lasers at shorter wavelengths than the traditional 10,640 nm wavelength CO2 laser. Using Yb: Fiber Lasers, Nd:YVO4 or Nd:YAG lasers at 1,064 nm wavelength, or its harmonics at 532 and 355 nm, metals can now easily be engraved using commercial systems.
Sub-surface laser engraving (SSLE)
Sub-surface laser engraving is the process of engraving an image in a transparent solid material by focusing a laser below the surface to create small fractures. Such engraved materials are of high-grade optical quality (suitable for lenses, with low dispersion) to minimize distortion of the beam. BK7 glass is a common material for this application. Plastics are also used, but with far less desirable results when compared to the engraving done in optical crystal.
Since its commercial application in the late 1990s, SSLE has become more cost effective with a number of different sized machines ranging from small (~US$35,000–60,000) to large production scale tables (>US$250,000). Although these machines are becoming more available, it is estimated that only a few hundred are in operation worldwide. Many machines require very expensive cooling, maintenance and calibration for proper use. The more popular SSLE engraving machines use the Diode Pumped Solid State or DPSS laser process. The laser diode, the primary component which excites a pulsed solid state laser, can easily cost one third of the machine itself and functions for a limited number of hours, although a good quality diode can last thousands of hours.
Since 2009, use of SSLE has become more cost effective to produce 3D images in souvenir ‘crystal’ or promotional items with only a few designers concentrating on designs incorporating large or monolithic sized crystal. A number of companies offer custom-made souvenirs by taking 3D pictures or photos and engraving them into the crystal.