Laser – Fascination from light

• 1917 – Albert Einstein discovers the physical principles of the laser.
• 1928 – Rudolf Ladenburg establishes experimental proof.
• 1960 – First ruby laser of Theodore Maiman.
• 1970 – Systems are created for processing materials.
• 1980 – Semi-conductor laser diodes make CD and DVD drives possible.
• 1990 – Lamp-pumped lasers are an integral part of industry.
• 2000 – New pump geometries for high laser output levels are implemented.
• 2006 – The fiber laser captures the market.

1. Introduction (marking by laser)

Lasers have already secured a permanent place in the industrial landscape as tools for identification and engraving. The reason for this has certainly been the technological and process-related advantages compared to other identification processes such as pad printing, ink jet printing, embossing or electrochemical identification (etching), which have been in use since the early 1970s. New application areas are constantly opening in the decorative and artistic field as well in which lasers either replace or are combined with conventional processes. Depending on the material and the desired result (appearance, surface texture, processing time etc.), a wide range of different laser systems is available on the market. These processes differ mainly in how the radiation is generated and in the optical output. Although the most suitable laser is the key element of a laser marking or engraving system, it is the control unit, machine housing, additional equipment and especially the performance capabilities of the software that can make working with the laser even more versatile and effective and allow it to become a universal tool, the laser processing machine.

1.1 Physical background

The term "Laser" is an invented word and stands for "Light Amplification by Stimulated Emission of
Radiation". The technology makes use of an effect postulated as early as 1917 by Einstein. At this point
we will take a short excursion into atomic theory.

1.1.1 The electron in the atomic envelope

In their basic state, electrons (negatively charged) move in fixed orbits around the nucleus of the atom (positively charged The distance from the orbits to the nucleus corresponds to the energy states of the electrons. The further away an electron is from the nucleus, the more energy it has in the potential field of the nucleus. If energy is directed at the atom through radiation, the electrons in the atomic envelope can take on energy and thus increase their distance from the nucleus of the atom. The energy states (orbits) always assume discrete values, i.e. there are only certain "permissible" orbits for electrons. There is no evidence
of intermediate states.

1.1.2 Spontaneous emission

In simple terms, each electron actually has its own "fixed place" in the atomic envelope and moves about the nucleus in a specific orbit. As mentioned previously, however, electrons can change orbits if energy is introduced. They assume a higher energy level. However, since there is a natural predisposition to take on the lowest energetic state (apples fall down, not up) the electron leaves the excited state (E2)
after a more or less random time, generally just fractions of a second, and moves back to its original orbit around the nucleus (E1). During this transition, the energy corresponding to the difference between
the two states is emitted in the form of a photon (radiation, light particle, electromagnetic wave).
Since this transition is spontaneous, i.e. it takes place without any external influence, it is referred to as "spontaneous emission".

1.1.3 Stimulated emission

Spontaneous emission is subject only to stochastic constraints, i.e. the transition to the original state occurs at random, not at any specified point in time
that can be precisely determined. However, Einstein postulated stimulated emission, which was later demonstrated experimentally. If an atom or molecule
is in an excited state and is them "hit" by a photon,
the photon "stimulates" the excited electron to return
to its original place. As a pre-condition, the energy of the impacting photon must correspond precisely to
the difference between the excided state (E2) and
the basic state (E1). A photon identical to the
impacting photon is then generated. Thus two
identical photons leave the atom or molecule,
meaning they have the same wave length (light colour), the same direction and are equal in phase. Coherent light is generated.

1.1.4 The resonator (laser source)

To be able to make use of the effect of stimulated emission described above, an active medium is brought into a resonator consisting of two mirrors. The light is able to move back and forth between the two mirrors. The excited atoms or molecules are stimulated on their way through the active medium and additional photons are generated, thus releasing an "avalanche of photons". In the case of solid-state lasers, the active medium in turn is excited by radiation (light). This light can originate either from gas discharge lamps
(lamp pumped lasers) or from laser diodes (diode-pumped systems). In CO2 lasers, electrons are excited by a high-frequency voltage via electrodes.

One of the two mirrors, referred to as the output mirror, does not reflect all the radiation. Instead it allows a certain portion to pass through. This portion is the laser radiation that leaves the laser. If an optical switch (Q-switch) is now added to this resonator, the resonator can be "turned on and off".

1.1.5 Other components of a marking/engraving laser

After leaving the laser source, the laser beam that is generated must still be directed selectively at the places on the workpiece to be processed where a reaction in the material should be induced. Two different techniques are available for this purpose in the area of marking.

In "plotter systems" as they are generally encountered in CO2 lasers, the laser beam is moved by the optics, which in turn are movably positioned on an x/y co-ordinate system. Depending on the size of the plotter system, relatively large marking fields can be implemented. However, there are some restrictions in terms
of the speed at which the workpiece can be moved, since the optics must always be moved as well.

Instead of moving the optics, the laser beam can be deflected by mirrors. This method involves (Galvo) scanners. Two movable, rotating mirrors, one for deflection in the x direction, the other in the y direction, ensure that the laser beam is positioned inside the marking field. Downstream from the mirrors are special lenses called f-theta optics which refocus the expanded beam on one level again. Since the deflection mirrors are relatively low in weight, the laser beam can be deflected at very high speed. The size of the marking field depends on the focal length of the lens that is installed. Common sizes are 110 * 110 mm² or 180 * 180 mm². A shorter focal length results in a smaller lettering field, but also in a more sharply focused laser beam.

Activation of the plotter mechanics or scanner is controlled by computer. Manufacturer-specific programs for control generally have basic functions that are required for identification or marking tasks, but often differ in the details of more special functions. Before deciding on a system from one manufacturer or another, it is therefore advisable to arrange for a presentation demonstrating available options and how user friendly a specific system is.

2. Selection of laser systems depending on materials

2.1 Physical differences between CO2 and Nd:YAG radiation

As mentioned above, two different types of laser are available with the Nd:YAG and CO2 laser. The following table gives an overview of the differences between the two systems:

With a solid-state laser, the active medium, generally Yttrium/Aluminium/Garnet doped with Neodymium (Nd:YAG), absorbs energy with the Q-switch closed. When the Q-switch is opened, a pulse is delivered quasi-instantaneously, similar in effect to releasing a compressed spring. The energy stored in the crystal is released in a very short time of from 10 to 100 nanoseconds. This produces a pulse with a very high peak output of from 30 to 150 kW. This energy is sufficient to melt and evaporate materials. The wave length is 1064 nm (near infrared).

A CO2 laser does not provide this option of increasing the pulse. The peak pulse output is therefore considerably lower than for a Nd:YAG laser, while pulses are significantly longer. The wavelength of the
CO2 laser is 10,600 nm (far infrared), or about ten times that of the Nd:YAG laser. Since the focus diameter depends primarily on the wavelength, a Nd:YAG laser is theoretically capable of focusing 10 times better at the same focal length of the focusing optics and is therefore able to achieve a higher output density in the focus. In addition, the light or radiation energy depends on the wavelength. The shorter the wavelength, the "harder" the laser radiation.

Because of these differences in physical nature there can be no single laser that is best for all applications. Each principle has its strengths and weaknesses.

2.2 Different technologies of solid-state lasers

2.2.1 Lamp-pumped laser

Lamp-pumped laser radiation sources are the most commonly used type in the area of deep laser engraving, as they have been for some time. They provide sufficient laser output at a high pulse energy and ensure outstanding processing results.

The laser crystal receives its energy from an arc discharge lamp. Due to the principle involved, efficiency is relatively poor compared to other technologies. The laser must always be cooled with water. Laser lamps have a limited service life of about 500 - 1000 h, but can be replaced by the user in just a few minutes and are relatively cheap.

Although the technology involved is "old", its continued existence is still justified for certain applications.
If the price for a system is considered in terms of Watts of output power, this option delivers the most output power for the money invested. High output is required when a relatively large amount of material must be removed in a relatively short time.

Illustration: Design of lamp-pumped laser

2.2.2 Diode-pumped laser

The Nd:YAG crystal is excited in this case by special laser diodes that are significantly more efficient compared to lamps. The emission wave length of a laser diode can also be precisely adjusted to the absorption wavelength of the Nd:YAG crystal. This results in significantly improved efficiency in comparison to lamp-pumped systems with reduced cooling overhead.

Diodes also have a much longer expected service life than laser lamps. It is typically in the range from 20,000 - 25,000 hours. Easy on-site replacement is possible for end-pumped systems, similar to disc lasers.

For applications in the area of laser marking, other than fiber lasers, diode end-pumped laser sources are used almost exclusively. These systems are compact, maintenance-free and require no additional water cooling. They are entirely air cooled. Because the pump diodes are located in the control section, the laser head can remain in the system if the diodes are replaced. Only a 19" insert is replaced. This minimises downtimes and cuts cost, since no readjustment of the system is required.

Illustration: Principle of diode-pumped disc lasers

2.2.3 New technology: diode-pumped fiber lasers

A fiber laser is a special form of the solid-state laser. The active medium is the Ytterbium-doped core of a glass fiber. It is therefore a glass laser with optical conductor properties. The laser light, which is guided in through the fiber, is greatly amplified due to the long length. Fiber lasers are optically pumped. This is generally done by coupling radiation from diode lasers in parallel to the fiber core or into it. For this purpose, modern systems use double clad fibers.

The advantages of the fiber laser are in its sturdy design, which consists of relatively few mechanical components. The load on single pump diodes is very low, and compared to previous systems, the diodes have an extremely long service life (> 100,000 hours).

Due to system properties, fiber lasers have outstanding beam quality (a measure of focusing capacity).
This ensures excellent results even for extremely fine marking and engraving.

The compact design and air cooling allow for integration into a laser machining system, an enormous space-saving feature.
The disadvantage of fiber lasers is that the pulse energy or peak pulse output is still limited. Further development is still in progress, however, so that fiber lasers can already be used today for some high-quality engraving tasks.

• Active medium Yb-doped glass fiber
• Power is supplied by many individual diodes

2.2.4 Comparison

Theoretical beam diameter (without additional mode diaphragms):

2.2.5 Which laser technology is the "best"?

There is no clear answer to this question. Each technology has its strengths and weaknesses. The application must determine which laser is the first choice for which task. It is therefore indispensable to review the processing task carefully and weigh the available options. With this approach, the supposedly "old" technology of lamp-pumped lasers is still highly valued by service providers today as an all-round solution. However, with future development, fiber lasers have the potential to challenge this status in the future.

2.3 Which laser for which material?

The most important criterion for selecting a suitable laser system is the material(s) to be processed. The absorption and thus the effect of the laser radiation depend heavily on the material and wavelength. We will see that individual systems each have their own strengths and there is only a very small intersection of materials that can be processed on both systems. The comments below referring to the Nd:YAG laser apply equally (with appropriate adjustments) to the fiber laser.

2.3.1 Metals

Iron-based materials and alloys (steels and stainless steels) as well as non-ferrous metals such as copper, aluminium, brass, etc. and of course precious metals such as silver, gold and platinum. In addition, workpieces made of such metals as lead, tin, zinc, nickel and workpieces with corresponding coatings (chrome and zinc) are found.

The CO2 laser can only be used to a limited extent in machining metals, since metals reflect practically all the long-wave CO2 radiation and only a small amount is absorbed by the metal. Furthermore, the CO2 laser is lacking the peak pulse output needed to be able to melt and evaporate metals. Only anodised aluminium can be directly marked. Additional materials are required to mark other metals and must be applied before marking (by painting or immersion) and then burnt into the surface. Engraving (removal of material)
is not possible.

Thus metals neatly represent the domain of the Nd:YAG laser, which is able to mark and engrave all commonly used metallic materials. Even precious metals can be processed with excellent results using suitable systems. Carbides also present no challenge for solid-state lasers.

2.3.2 Plastics

Some plastic materials can be processed with both systems, some with only one or the other, and some cannot be processed with either system. In addition to the basic material, the colour (pigments) and other admixtures (filling materials, additives, flame retardants, etc.) play an important role in the choosing of the right laser system.

For example, the CO2 laser can be used advantageously for acrylic glass. It is capable of engraving and cutting acrylic glass. Only surface marking is possible with the YAG laser. Special plastics are also available on the market with a two-layer composition that is very well suited for manufacturing signs and similar items with the CO2 laser. The CO2 laser is also frequently used to manufacture stamps, since commonly used laser rubbers have been optimised for processing with that type of laser.

However, good quality marking (i.e. high in contrast) of most technical plastics - for example ABS, PC, PS, PP, PA etc. - is only possible with the Nd:YAG laser. The CO2 laser would simply melt or burn the surface.

2.3.3 Glass, leather, wood, paper

The CO2 laser is extremely well suited for these "organic" materials, while the Nd:YAG laser normally does not produce usable results in this area.

2.3.4 Ceramic

When evaluating whether a system is suitable for identifying ceramic products, the main question is what results should be achieved. The CO2 laser can generally be used to engrave most types of ceramic, but there is no change in the colour of the material. Removing a coloured glaze may result in a colour contrast, however, so that the actual ceramic is revealed.

For identification rich in contrast (change of colour in the material), the only real possibility is the Nd:YAG laser. However, it is not capable of marking all ceramic materials without exception: some can be marked only with great difficulty and others not at all.

The following table shows an overview of which types of laser are suitable for specific materials:

3. There are many variants of marking by laser

As we have already seen, the laser is an extremely flexible tool. It can be used for numerous materials, processes and results. To become more familiar with detailed possibilities, we will categorise applications by processes, processing strategies and desired results.

3.1 Terminology distinctions

When describing work with lasers, terms such as identification, marking and engraving are often used.
In this context, we make a distinction between simple surface processing and removal of material. 

In surface processing and marking, only a very small amount of material on the order of less than 1/100 of a millimetre is removed. The marking is created by producing a colour contrast in places that were processed compared to the surrounding area. This colour contrast can be produced either by changing the material through oxidation or changes in the structure, or by removing a cover layer. Examples are anodised aluminium, special multi-layer materials or painted surfaces. The purpose of the identification is irrelevant.

Engraving describes the process as soon as an appreciable amount of material is removed. Engraving can be used for a technical function, for example in stamping dies or mould and die production, or can be used for decorative purpose.

3.2 Marking

As mentioned in the introduction to this section, marking can be used for different purposes on parts
and workpieces.

3.2.1 Technical marking

Marking may simply serve the purpose of recording information, which is frequently the case for industrial products. Information about the manufacturer (with logo), type and function of parts (circuit diagrams) and other information can be applied according to the customer's needs. The need for identification in this area is steadily increasing in response to customer need for product tracking. To this may be added system-related advantages of lasers compared to other identification processes. Identification by laser is very flexible, since no masks or printing plates are required. Different information can be applied from one workpiece to the next. Furthermore, laser identification is highly durable. Since there is no need to work with ink or other additives, laser marking is resistant to physical or chemical effects such as heat, solvents, lubricants, etc.

3.2.2 Marking with a decorative character

A very simple example of this is marking a pen or key ring with a company logo or name. In addition to the information content, marking can also have a decorative function when marking is intended to enhance the value of an object. The visual appearance plays a great role in this case. This includes engraving engagement rings, the whole range of advertising materials and the area of high-quality gifts.

In addition to these two tasks, laser marking can also be used to safeguard products against forgery. For example, parts of watches, glasses and jewellery can be identified almost invisibly by laser. Depending on the material and the focal length of the focusing optics, cutting heights of as little as 0.1 mm can be achieved!

3.3 Engraving

Engraving may be subdivided into normal engraving and deep engraving. There is no sharp dividing line between these two applications. Indeed, different uses of the same terminology in different industries results in mixing of the two terms. In the area of laser technology, deep engraving begins at 0.05 - 1 mm. A separate section is dedicated to deep engraving. The technological observations in that section also apply in general to normal engraving.

Typical applications in the area of engraving are decorating jewellery and utility items. Thus laser engraving can be used in the area of weapons (knives, swords, hunting weapons, etc.). Unlike conventional mechanical or craft processes, lasers have shorter machining and processing times. They also require significantly less personnel. Once the workpiece has been set up, the operator can devote his or her attention to other tasks, since the laser process does not need to be monitored. No clamping is required, since processing does not involve contact. The fineness of the laser beam can reduced to a focus
diameter of just a few hundredths of a millimetre, thus opening up entirely new possibilities compared to mechanical processes.

3.4 Scope of possibilities

Three main parameters of lasers can be adjusted to a specific processing or marking task: output, pulse repetition frequency and speed. These three parameters largely determine the visual appearance on the workpiece. Laser processing depends essentially on the response of the material with which you are working. Nevertheless, the most commonly used materials do offer a certain range of possibilities.

3.4.1 White marking

A relatively "soft" setting of the laser beam causes the surface to be brightened similarly to sand blasting. This is referred to as "white marking". The surface of the workpiece is just lightly melted, which causes light that strikes it to be diffused. The result is marking with a high quality appearance often associated with the area of jewellery and watches or applications that use polished or chrome-plated surfaces.

3.4.2 Processing coated materials

Marking is performed by removing a cover layer (for example eloxal, paint, chrome layer). The colour contrast is created by "free lasering" of the basic material. This process is used in the area of day and night design, for example, and in the production of all types of tags. Typical materials for this application are eloxated/anodised aluminium, burnished steel, painted plastics or coated laser foil.

3.4.3 Annealing marking

With iron-based alloys/steels and titanium, heat enters the surface locally and produces a thin oxide
layer, resulting in the familiar annealing colours. This process is used especially for parts with narrow dimensional tolerances (for example tools, bearing shells, etc.), since it does not result in any
dimensional changes in the workpiece yet at the same time produces marking that is high in contrast
with excellent legibility.

3.4.4 Marking by removal of material

The thermal energy of the laser is used to melt and evaporate material selectively, resulting in slightly depressed marking (0.001 - 0.05 mm). Practically no heat is absorbed by the workpiece. By choosing suitable laser parameters, light marking (for example on burnished or anodised surfaces) or dark marking rich in contrast can be achieved.

3.4.5 Combination of different processes

If a suitable processing strategy is selected, a combination of different marking principles listed above can be used together. For example, after material is first removed, a second pass could be made to brighten the marking. Certain parameters cause the areas that are being processed to darken when material is removed. By investing a little time in creating programs, highly decorative results can be achieved.

4. Deep laser engraving

Deep laser engraving differs from normal engraving as it is defined above especially in the amount of material that is removed and in the mostly technical background of engraving. While normal engraving is performed only in a two-dimensional or 2 1/2-dimensional area, with deep engraving we enter three-dimensional space. The purpose is not just to remove material on one level, but rather to create free form surfaces in the foreground. Competing processes are mechanical engraving, milling and electrical discharge machining.

4.1 Restrictions

The restrictions in deep engraving are in removal output and the resulting surface quality (Ra ³ 0.4).
In some cases a combination with mechanical processes is therefore useful.

4.2 Advantages of the process

Laser engraving has a large number of advantages:

Wide range of materials:
In addition to metals and their alloys, tempered materials, high-strength steels, carbides, ceramics and graphite can be processed. The hardness of the material plays practically no role.

Fine structures:
Because of the very small focus diameter (15 - 100 µm), extremely fine structures can be produced that would be too fine for engraving pens.

High process reliability:
Because no wearing tools are required, laser engraving has very high process reliability. Tool costs are eliminated.

Environmentally friendly:
Since no cooling lubricant is required and there is no machining tailings or similar waste, the process is very environmentally friendly.

Short set-up times:
Set-up and programming times are considerably shorter compared to mechanical machining.

Low maintenance overhead:
The maintenance overhead of modern laser systems is very low and is limited in air cooled systems
mainly to cleaning optical components.

Lasers thus have advantages for tasks related to relatively fine structure. Process times are considerably shorter compared to mechanical engraving or electrical discharge machining. Before the electrode(s) are completely engraved during electrical discharge machining, the laser has already finished machining the workpiece. The profitability advantage compared to electrical discharge machining may be a factor of
about 5 or 6 times! The following table shows a comparison from actual practice:

5. Process of laser engraving: From template
to finished workpiece

The beginning of laser engraving is an idea or a technical drawing to be implemented. Depending on the task and data material, implementation for the finished workpiece consists of various work operations:

5.1 Data preparation

In an ideal case the (CAD) data is already available. In some situations, however, it must first be created. For simple tasks such as applying text, the software installed on the laser system is generally used to create a program. Operation of the software is based on simple graphics programs. It is better to prepare extensive 2D data in commercially available graphics programs, since these programs generally have better graphical capabilities than programs for laser control. In addition, frequently the data received by the customer is in a variety of formats, while laser control systems can only read in a limited selection of data formats in which the data must first be converted. 2 1/2-D structures can also be created by subdivision in a graphics program. Programs are available on the market for engraving free form surfaces (3D engraving) which are also familiar in the engraving area. The program is completely almost entirely in the additional software and the complete layout is transferred to the laser system using the appropriate import filters of the laser control system or postprocessors. Once this data has been created, it can simply be called up again later in a subsequent order.

3D structures are broken down by the corresponding CAD/CAM software into individual layers which the laser subsequently processes. The amount removed per layer is varies from 0.5 - 5 µm.

5.2 Determining parameters

Before beginning with any machining, the optimum parameters must be determined. Important standards in this regard include dimensional accuracy, surface quality, raised engraving edge and machining time. Surface quality has a great effect on machining time. Roughing and finishing are also used in laser engraving to achieve the smoothest possible surface. However, "finishing" is required from the very beginning because a roughing structure would simply be reproduced during a subsequent attempt at finishing.

Since the laser beam does not have a cutting edge, no exact statement can be made here defining how deep the engraving is. To be able to determine the depth, several initial trials are necessary in which the response of the material is determined. Once a material/parameter combination has been determined, it can be saved and reloaded again when needed. High-quality systems are able to measure engraving depth during lasering and regulate the process according to specifications.

5.3 Setting up the workpiece

A number of different tools are available to help in setting up the workpiece.

5.3.1 Pilot laser

Commonly used laser systems have a pilot or target laser beam consisting of a red rectangle indicating
the limit of engraving. However, this preliminary display meets only very limited requirements in terms of accuracy. The refraction index of the optics in use depends on the wave length. This means that the red preview laser will be deflected differently than the actual laser used for machining. The further one moves
on the edge of the lettering field, the more pronounced this effect becomes. Deviation in that area may amount to more than one millimetre. For high-quality applications, optical systems (see 5.3.4 and
LAS - Live Adjust System from ACSYS) offer the option of exact positioning.

5.3.2 Stops / zero-offset clamping systems

Stops are easier to work with and considerably more precise. In the simplest cases these consist of an angle or prism or zero-offset clamping systems, which are familiar from the area of tool machines. In this case the laser system is generally set up exactly during commissioning. The co-ordinate system of the laser system is used for the dimensional reference.

5.3.3 Workpiece probing

Systems specialised for laser engraving can also be fitted with mechanical systems for workpiece probing in three axes/levels. Position correction is then performed automatically by software.

5.3.4 Optical systems

The process of optical "probing" is similar to mechanical probing. Integrated camera systems ensure fast and accurate aligning of the engraving to the reference edges of workpieces. Systems of this type also provide an option for a convenient preview of marking. A live image of the object being marked appears in the laser control software. Then the operator can decide based on the screen image whether the layout still needs to be changed - for example because some letters would "disappear" in holes that are drilled on the workpiece or the size of the lettering needs to be adjusted to provide a consistent visual impression. The actual alignment can then be performed on screen simply by clicking with the mouse.

5.4 Laser machining

After alignment is complete, the actual machining is performed. (Deep) engraving of workpieces by laser represents a thermal process. Part of the workpiece is melted and evaporated by selectively introducing energy in short, pulses high in energy. The increased pressure causes the melted material to be driven away. Spraying sparks may be seen during this process. As mentioned previously, material is removed in layers down to the desired depth.

5.5 Other processing steps

Powdery residue may form during machining. If so, it can be cleaned off by or removed ultrasonically. Mechanical processes such as brushing, blasting with sand or glass beads, or phosphoric acid are used to remove layers of oxide or tinder.

5.6 Laser engraving applications

Typically applications prominently feature fine textures:

• Engraving dies
• Engraving stamping dies
• Decorative engraving of jewellery and utility items
• Engraving hot stamping dies
• Engraving moulds or moulded inserts

Following are a few typical examples of laser engraving with corresponding explanations of
individual workpieces.

6. Laser marking and engraving systems with different levels of automation

Standard systems are designed to be able to mark and identify as wide a range of products as possible. The only restrictions on the maximum dimensions of the workpiece are the size of the working area and the focal length of the laser. Most providers of laser marking and engraving systems offer their systems in different sizes so that working together with the customer they can select the optimum machine for the expected range of parts. An engraver who works only with jewellery is very unlikely to encounter the difficulty of having to identify a workpiece one metre in length. On the other hand, markers who work for hire need to cover the widest possible range with their machines to be able to respond to as many customer requirements as possible. By contrast, there are also applications that involve working with a clearly defined range of parts with very high numbers of units produced. Order volumes up to several hundred thousand parts a year are possible. Processing orders of this type with standard systems results in a high need for personnel, which in turn may make it impossible to achieve competitive prices in some situations. In this case, automating a system may provide an advantage, for example designing the system so that parts are supplied and removed automatically instead of manually.

Example: Laser machining system (scanner-based):

A laser machining system consists of the following main components:

• Laser radiation source
• Controller/power supply unit
• Beam deflection (scanner – optical axes)
• Focusing optics (f-theta lens)
• Laser protection housing, in some cases with additional mechanical axes

The laser beam is deflected by two motor-driven mirrors in the x and y directions. Then the laser beam is focused on the workpiece by a flat field lens, called an f-theta lens. The marking or engraving layout is created by the AC LASER PC-controlled laser software. This software package has full graphical capabilities and everything needed to mark serial numbers, logos, barcodes, data matrix codes or to create and machine two and three-dimensional engravings.

6.1 Levels of automation

Various means are available for economical processing of large numbers of units. They can be used to increase piece throughput or to reduce handling times. This makes it possible to adjust standard systems to specific tasks by using different building blocks from the array of available modules. The more flexible the system, the more useful the machine is for the user. This approach can lead to highly specialised machine concepts capable of handling workpieces fully or semi-automatically. The greater the level of automation, the more limited the possibilities such a machine can offer. However, intelligent solutions also make it possible to process single pieces or other workpieces in manual mode.

6.1.1 Extension with standard options

The simplest and usually the most economical version is a machine equipped with options that can be provided modularly from the building blocks offered by the system manufacturer. Commonly requested additional equipment includes:

• Cross table. This option extends the marking range of the laser, which is usually 110 mm * 110 mm by means of additional mechanical axes. This makes it possible to implement larger marking or to fit the machine with a larger number of palletized workpieces that can be processed one after the other. Instead of moving workpieces with a cross table, the laser can also be moved by additional mechanical axes. This is generally advantageous, since very large marking fields can be achieved even with compact external dimensions in this manner. Moving the laser is also the better alternative for very heavy workpieces.
• Round (cycle) table. If a system is equipped with a rotary table, the next workpiece can already be inserted at the same time marking is in progress. The rotary table rotates into the machine at the press of a button. The workpiece that has just been processed can be removed while the next one is already being marked.
• Sign magazines. Sign magazines are useful when a large number of signs (or tags) must be marked with the same dimensions. The tags are discharged either via a slide, with the tags falling into a container, or they are stacked up in another magazine.
• Endless conveyor belts. An endless conveyor belt running through the machine that can be fitted with workpiece-specific holders is a useful option wherever the part geometry makes it possible to use a belt of this type. The marking time is also extremely short in comparison to the insertion time. If belts of this type are equipped with prisms for holding workpieces, they are especially suitable for marking cylindrical or other rotation-symmetrical parts.

6.1.2 Customer-specific solutions based
on standard machines

If the standard options are not sufficient, an attempt will be made to adjust a standard machine to the relevant task so as to provide the greatest benefit for the customer. The layout of a standard machine always has the advantage that standard parts can be used and availability of replacement parts is guaranteed at any time. In addition, the extra charge for designing a special solution is lower. In the simplest case, this variation could be changing the machine housing, or it could consist of entire supply and handling systems.

Link to "Customer-specific solutions"

6.1.3 Customer-specific solutions

Complete special solutions usually allow the highest level of specialisation or the best possible adjustment to specific task requirements. When working together with a provider, however, it is especially important to be aware of experience in the relevant area. The devil is in the details of highly specialised solutions and only the necessary experience will help to recognise problems in the early stages and eliminate them through appropriate design measures. Therefore, deciding to go with a cheap provider may turn out in the long run to have been a costly solution paid for with frustration, increased time overhead and possibly unsatisfactory results.

Link to "Custom SHARK"

7. Looking ahead

Modern laser technology already offers a wide range of applications today. However, there is still great potential in the area of laser radiation sources and applications.

For example, there are now already "picosecond" lasers, which generate impulses only 1 picosecond in duration. This results in practically no heating of the material being machined, a feature that will make it possible to machine parts that are very sensitive to heat as well. Using different laser wavelengths will
make it possible to machine materials, especially plastics, for which no other machining could not be achieved in any other way.

In the area of laser radiation sources, ever more efficient systems are being developed with a constantly increasing service life and decreasing operating costs.

It will certainly be interesting to observe how laser ­systems continuously develop into new applications, always with the goal of opening up even more advantages for users and allowing them to gain a
competitive edge.