Engraving

Engraving is the practice of incising a design onto a hard, usually flat surface, by cutting grooves into it. The result may be a decorated object in itself, as when silver, gold, steel or glass are engraved, or may provide an intaglio printing plate, of copper or another metal, for printing images on paper, which are called engravings. Engraving was a historically important method of producing images on paper, both in artistic printmaking, and also for commercial reproductions and illustrations for books and magazines. It has long been replaced by photography in its commercial applications and, partly because of the difficulty of learning the technique, is much less common in printmaking, where it has been largely replaced by etching and other techniques. Other terms often used for engravings are copper-plate engraving and Line engraving. These should all mean exactly the same, but especially in the past were often used very loosely to cover several printmaking techniques, so that many so-called engravings were in fact produced by totally different techniques, such as etching.

Woods/Natural materials
Directly "burning" images on wood were some of the first uses of engraving lasers. The laser power required here is often less than 10 watts depending on the laser being used as most are different. Hardwoods like walnut, oak, mahogany and maple produce good results. Softwoods can be judiciously engraved but tend to vaporize at less-consistent depths. Burning a softwood with a fan blowing on it requires lowest power, quickest speed of cut, and enough airflow to extinguish what is trying meanwhile to ignite. Hard papers and fiberboard work well; linty papers and newsprint are like softwoods. Fur is not engraveable; finished leathers though can be laser-engraved with a look very similar to hot-branding. Certain latex rubber compounds can be laser engraved; for example these can be used to fabricate inking-stamps.

Paper masking tape is sometimes used as a pre-engraving overcoat on finished and resiny woods so that cleanup is a matter of picking the tape off and out of the unengraved areas, which is easier than removing the sticky and smoky surround "halos" (and requires no varnish-removing chemicals).

Plastics
Standard cast acrylic plastic, acrylic plastic sheet, and other cast resins generally laser very well. A commonly engraved award is a cast acrylic shape designed to be lasered from the back side. Styrene (as in compact disc cases) and many of the thermoforming plastics will tend to melt around the edge of the engraving spot. The result is usually "soft" and has no "etch" contrast. The surface may actually deform or "ripple" at the lip areas. In some applications this is acceptable; for example date markings on 2-litre soda bottles does not need to be sharp.

For signage and faceplates, etc., special laser-engraving plastics were developed. These incorporate silicate or other materials which conduct excess heat away from the material before it can deform. Outer laminates of this material vaporize easily to expose different colored material below.

Other plastics may be successfully engraved, but orderly experimentation on a sample piece is recommended. Bakelite is said to be easily laser-engraved; some hard engineering plastics work well. Expanded plastics, foams and vinyls however are generally candidates for routing rather than laser engraving. Urethane and silicone plastics usually don't work well-- unless it is a formulation filled with cellulose, stone or some other stable insulator material.

Many light switchplates from companies such as Leviton or Lutron can be laser engraved. Again, experimentation may be necessary to develop the correct laser settings to result in engraving the surface rather than melting it. Often times the laser engraving is followed by paint filling the engraved surface to produce more contrast between the engraved surface and the surrounding surface.

Metals
The best traditional engraving materials started out to be the worst laser-engravable materials. This problem has now been solved using lasers at shorter wavelengths than the traditional 10,640nm wavelength CO2 laser. Using Nd:YVO4 or Nd:YAG lasers at 1,064nm wavelength, or its harmonics at 532 and 355nm, metals can now easily be engraved using commercial systems.

Coated metals
However, the same conduction that works against the spot vaporization of metal is an asset if your objective is to vaporize some other coating away from the metal. Laser engraving metal plates are manufactured with a finely-polished metal, coated with an enamel paint made to be "burned off". At levels of 10-30 watts, excellent engravings are made as the enamel is removed quite cleanly. Much laser engraving is sold as exposed brass or silver-coated steel lettering on a black or dark-enamelled background. A wide variety of finishes is now available, including screen-printed marble effects on the enamel.

Stone and glass
Stone and glass do not turn gaseous very easily. As expected, this makes them generally a better candidate for other means of engraving, most notably sandblasting or cutting using diamonds and water. But when a laser hits glass or stone, something else interesting happens: it fractures. Pores in the surface expose natural grains and crystalline "stubs" which, when heated very quickly, can separate a microscopic sized "chip" from the surface because the hot piece is expanding relative to its surroundings. So lasers are indeed used to engrave on glass, and if the power, speed and focus are just right, excellent results can be achieved. One should avoid large "fill" areas in glass engraving because the results across an expanse tend to be uneven; the glass ablation simply cannot be depended on for visual consistency, which may be a disadvantage or an advantage depending on the circumstances and the desired effect.

Jewelry / Jewellery
The demand for personalized jewelry has made jewelers more aware of the benefits of the laser engraving process.

Jewelers found that by using a laser, they could tackle an engraving task with greater precision. In fact, jewelers discovered that laser engraving allowed for more precision than other types of engraving. At the same time, jewelers discovered that laser applied engravings had a number of other desirable features.

At one time jewelers who attempted to do laser engraving did need to use large pieces of equipment. Now the devices that perform laser engraving come in desktop units. Some entrepreneurs have placed such units in mall kiosks. That has made laser engraving jewelry much more accessible. The makers of machines for laser engraving jewelry have developed some very specialized equipment. They have designed machines that can engrave the inside of a ring. They have also created machines that have the ability to engrave the back of a watch.

A laser can cut into both flat and curved surfaces. Jewelry contains both flat and curved surfaces. That points-up the reason why jewelers have welcomed all the adaptations for the creation of laser engraved jewelry.

Fine Art
Laser engraving can also be used to create works of fine art. Generally this involves engraving into planar surfaces, to reveal lower levels of the surface or to create grooves and striations which can be filled with inks, glazes, or other materials. Some laser engravers have rotary attachments which can engrave around an object. Artists may digitize drawings, scan or create images on a computer, and engrave the image onto any of the materials cited in this article.

Industrial applications

Printing
Direct laser engraving of flexo photopolymer plates or sleeves (which fit over a mandrel) is attracting wider interest following some recent technical developments and mergers of vendors. Up to now the process has been associated with wide-web flexo printing of, for example, film or paper packaging (flexible packaging). Here it competes with rotary gravure, although direct laser engraving is also being introduced. For the less expensive flexo process, the technology is being adapted for smaller formats suitable for engraving flexo plates or sleeves mounted on the actual printing cylinders.

This includes narrow and wide (up to 61.5 inches wide), and mid-web flexo presses (up to 20-24 inches wide), which could open up the market for self-adhesive label and packaging converters interested in the digital - that is filmless - route. With this process there is no integral ablation mask as with direct laser imaging (see below). Instead a high-power carbon dioxide laser head burns away, or ablates, unwanted material. The aim is to form sharp, relief images with steep, smooth edges to give a high standard of process color reproduction. A short water wash and dry cycle follows, which is a lot less involved than in the post-processing stages for direct laser imaging or conventional flexo platemaking using photopolymer plates.

Dupont has introduced a new type of finishing for the flexo graphic industry that removes the need for polymer plates to be washed and dried, meaning there is no swell in the plate material. It is called a Fast machine, and can be used for material up to 42" x 60".

Direct laser imaging
Closely related is the direct imaging of a digital flexo plates or sleeves 'in-the-round' on a fast-rotating drum, or cylinder. This is carried out on a platesetter integrated within a digital prepress workflow, that also supports digital proofing. Again, this is a filmless process, which removes one of the variables in obtaining the fine and sharp dots for screened affects, including process color printing.

With this process the electronically-generated image is scanned at speed to a photopolymer plate material that carries a thin black mask layer on the surface. The infrared laser-imaging head, which runs parallel to the drum axis, ablates the integral mask to reveal the uncured polymer underneath. A main ultraviolet exposure follows to form the image through the mask. The remaining black layer absorbs the ultraviolet radiation, which polymerizes the underlying photopolymer where the black layer has been removed. The exposed digital plate still needs to be processed like a conventional flexo plate. That is, using solvent-based washout with the necessary waste recovery techniques, although some water-washable digital plates are in development. This technology has been used since 1995 and is only now becoming more widely used around the world as more affordable equipment becomes available. Trade sources say there are around 650 digital platesetters installed in label, packaging and trade platemaking houses.

In flexo direct laser engraving can be done using a CO2-laser. This makes it possible to direct ablate the non-printing area. This way steps like UV-exposing, chemical washing and drying are not necessary anymore. Before the year 2000 lasers only produced lower quality in rubber-like materials. In these rubber-like materials, which had a rough structure, higher quality was impossible. At the Drupa 2004 the direct engraving of polymer plates was introduced. This had also an effect on the rubber-developers who, in order to stay competitive, came with new high quality rubber-like materials. Since then direct laser engraving of flexo-printingforms is seen by many as the modern way to make printing-forms for it is the first real digital way.

Sub Surface Laser Engraving (SSLE)
Sub-surface laser engraving is the process of engraving an image below the surface of a solid material, usually glass, with an optical clarity to minimize distortion of the laser.

Since its inception in the late 90's, SSLE has become more cost effective with a number of different sized machines ranging from small (~$35,000-60,000US) to large production sized tables (>$250,000US) - still although these machines are becoming more available there is estimated only a few hundred in operation worldwide. Many machines require very expensive cooling, maintenance and calibration for proper use. The primary component being the laser diodes, which excite a pulsed solid state laser, can easily cost 1/3rd of the machine cost itself that have a limited number of hours.

In past 5 years the 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. Quality of the designs and images varies greatly between vendors in the promotional and personal services sector (photo engravers) - the mass producing curio vendors have the habit of reducing resolution of the points and lowering output to maximize their laser diodes lifespan. When properly produced, designs in this medium can be striking and mesmerizing.