Editing Laser engraving (section)

==Laser engraving machines==
[[File:Laser Marking on Stainless Steel.ogv|thumb|Laser marking on stainless steel]]
[[File:Laser Engraving Machine.jpg|thumb|A laser engraving machine]]
[[File:Laser Engraver.jpg|thumb|A laser engraver]]

A laser engraving machine consists of three main parts: a laser, a controller, and a surface.<ref name="Ganeev-2014" /> The laser is a drawing tool: the beam emitted from it allows the controller to trace patterns onto the surface. The controller determines the direction, intensity, speed of movement, and spread of the laser beam aimed at the surface. The surface is chosen to match the type of material the laser can act on.

The point where the laser beam touches the surface should<!-- should? --> be on the focal plane of the laser's [[optical]] system and is usually synonymous<!-- this doesn't seem to be the right word --> with its [[focus (optics)|focal point]]. This point is typically small, perhaps less than a fraction of{{vague|reason="fraction of" gives no useful information here|date=November 2019}} a millimetre (depending on the optical wavelength). Only the area inside this focal point is significantly affected when the laser beam passes over the surface. The energy delivered by the laser changes the surface of the material at the focal point. It may heat up the surface and subsequently [[Wikt:vaporise|vaporise]] the material, or perhaps the material may [[fracture]] (known as "glassing" or "glassing up") and flake off the surface. Cutting through the paint of a metal part is generally how material is laser engraved.

If the surface material is vaporised during laser engraving, ventilation through the use of blowers or a [[vacuum]] pump are almost always required to remove the noxious fumes and smoke arising from this process, and for removal of debris on the surface to allow the laser to continue engraving.

A laser can remove material very efficiently because the laser beam can be designed to deliver energy to the surface in a manner which converts a high percentage of the light energy into heat. The beam is highly focused and [[collimated]]—in most non-reflective materials like [[wood]], [[plastic]]s and [[vitreous enamel|enamel]] surfaces, the conversion of light energy to heat is more than {x%}{{vague|reason=WTF?|date=November 2019}} efficient.<ref>{{Cite web |date=2024-07-05 |title=An In-depth Guide To Laser Cutting & Engraving |url=https://craftetch.com/laser-cutting-engraving/ |access-date=2024-07-28 |language=en-US}}</ref> However, because of this efficiency, the equipment used in laser engraving may heat up rather quickly. Elaborate cooling systems are required for the laser. Alternatively, the laser beam may be [[pulse]]d to decrease the amount of excessive heating.

Different patterns can be engraved by programming the controller to traverse a particular path for the laser beam over time. The trace of the laser beam is carefully regulated to achieve a consistent removal depth of material. For example, criss-crossed paths are avoided to ensure that each [[etching|etched]] surface is exposed to the laser only once, so the same amount of material is removed. The speed at which the beam moves across the material is also considered in creating engraving patterns. Changing the intensity and spread of the beam allows more flexibility in the design. For example, by changing the proportion of time (known as "duty-cycle") the laser is turned on during each pulse, the power delivered to the engraving surface can be controlled appropriately for the material.

Since the position of the laser is known exactly by the controller, it is not necessary to add barriers to the surface to prevent the laser from deviating from the prescribed engraving pattern. As a result, no [[resistive mask]] is needed in laser engraving. This is primarily why this technique is different from older engraving methods.

A good example of where laser engraving technology has been adopted into the industry norm is the [[production line]]. In this particular setup, the laser beam is directed towards a rotating or vibrating mirror. The mirror moves in a manner which may trace out numbers and letters onto the surface being marked. This is particularly useful for printing dates, expiry codes, and lot numbering of products travelling along a production line. Laser marking allows materials made of plastic and glass to be marked "on the move". The location where the marking takes place is called a "marking laser station", an entity often found in packaging and bottling plants. Older, slower technologies such as [[hot stamping]] and [[pad printing]] have largely been phased out and replaced with laser engraving.

[[File:Wikilaser1.png|thumb|Mirrors on both X and Y carriages allow exact positioning.]]
For more precise and visually decorative engravings, a ''laser table'' (also known as an "X–Y" or "XY" table) is used. The laser is usually fixed permanently to the side of the table and emits light towards a pair of movable mirrors so that every point of the table surface can be swept by the laser. At the point of engraving, the laser beam is focused through a [[lens (optics)|lens]] at the engraving surface, allowing very precise and intricate patterns to be traced out.

A typical setup of a laser table involves the fixed laser emitting light [[Parallel (geometry)|parallel]] to one [[Coordinate axis|axis]] of the table aimed at a mirror mounted on the end of an adjustable rail. The beam reflects off the mirror [[angle]]d at 45 [[degree (angle)|degree]]s so that the laser travels a path exactly along the length of the rail. This beam is then reflected by another mirror mounted to a movable [[cart|trolley]] which directs the beam [[perpendicular]] to the original axis. In this scheme, two [[degrees of freedom (physics and chemistry)|degrees of freedom]] (one vertical, and one horizontal) for etching can be represented.

In other laser engraving devices such as flat table or drum engraving, the laser beam is controlled to direct most of its energy a fixed penetration depth into the material to be engraved. In this manner, only a particular depth of material is removed when the engraving takes place. A simple machined stick or [[angle-iron]] can be used as a tool to help trained technologists adjust the engraver to achieve the required focusing. This setup is preferred for surfaces which do not vary in height appreciably.

For surfaces that vary in height, more elaborate focusing mechanisms have been developed. Some are known as dynamic [[auto-focusing|auto focus]] systems. They adjust the lasing parameters in real time to adapt to the changes to the material as it is being etched. Typically, the height and depth of the surface are monitored with devices tracking changes to [[ultrasound]], [[infrared]], or [[visible light]] aimed at the engraving surface. These devices, known as pilot beams or pilot lasers (if a laser is used) help guide the adjustments made to the lens of the laser in determining the optimal spot to focus on the surface and remove material effectively.

"X–Y" laser engraving machines may operate in [[vector (geometric)|vector]] and [[raster graphics|raster]] mode.

Vector engraving follows the line and curve of the pattern to be engraved, much like a pen-based [[plotter]] draws by constructing line segments from a description of the outlines of a pattern. Much early engraving of signs and plaques (laser or otherwise) used pre-stored [[font]] outlines so that letters, numbers or even logos could be scaled to size and reproduced with exactly defined strokes. Unfortunately, "[[fill character|fill]]" areas were problematic, as [[cross-hatch]]ing patterns and dot-fills sometimes exhibited [[moiré effect]]s or [[uber-pattern]]s caused by the imprecise calculation of dot spacings. Moreover, rotations of a font or dynamic scaling often were beyond the capabilities of the font-rendering device. The introduction of the [[PostScript]] page-description language now allows much greater flexibility—now virtually anything that can be described in vectors by PostScript-enabled software like [[CorelDRAW]] or [[Adobe Illustrator]] can be outlined, filled with suitable patterns, and laser-engraved.

Raster engraving traces the laser across the surface in a back-and-forth slowly advancing [[linear]] pattern that will remind one of the [[printhead]] on an [[inkjet printer|inkjet]] or similar printer. The pattern is usually optimized by the controller/computer so that areas to either side of the pattern which are not to be engraved are ignored and the trace across the material is thus shortened for better [[material efficiency|efficiency]]. The amount of advance of each line is normally less than the actual dot-size of the laser; the engraved lines overlap just slightly to create a continuity of engravure. As is true of all rasterized devices, curves and diagonals can sometimes suffer if the length or position of the raster lines varies even slightly in relation to the adjacent raster scan; therefore exact positioning and repeatability are critically important to the design of the machine. The advantage of rasterizing is the near effortless "fill" it produces. Most images to be engraved are bold letters or have large continuously engraved areas, and these are well-rasterized. Photos are [[rasterized]] (as in printing), with dots larger than that of the laser's spot, and these also are best engraved as a raster image. Almost any page-layout software can be used to feed a raster driver for an X–Y or drum laser engraver. While traditional sign and plaque engraving tended to favour the solid strokes of vectors out of necessity, modern shops tend to run their laser engravers mostly in raster mode, reserving vector for a traditional outline "look" or for speedily marking outlines or "[[hatching|hatches]]" where a plate is to be cut.