Frequently asked questions
- Which laser types are there?
- How does laser hardening work?
- How does laser surface cladding work?
- How does laser re-melting work?
- What is a focus shift?
- What is the advantage of special-concrete machine frames?
- Why is it important that a laser machine control is fast?
- What is adaptive processing?
- What is the carbon equivalent?
- What is the shaping of pulses?
- What is a cross jet?
- How is the property “beam quality” defined?
- What is “beam shaping”?
- What does “programmable beam quality” mean?
Finding one's way through the different laser terms
Laser are labelled according to different criteria – a non-professional can easily mix the terms up. Structuring the field serves to facilitate understanding the matter:
Structure according to the state of aggregation of the active medium
The active medium is the substance that generates the laser radiation (photons).
If this substance is a gas (or usually a gas mixture), we call it a gas laser.
For example: The CO2 laser
If this substance is solid (or usually a solid mixture of substances), we call it a solid-state laser.
For example: The Nd:YAG laser
Structure according to the substance of the active medium
The active medium is the substance or the mixture of substances that generates the laser radiation (photons). A laser is therefore called according to the chemical elements that appear in this substance.
Example 1: Nd:YAG laser; neodymium-doped yttrium aluminium garnet laser – the laser radiation is generated in the neodymium
Example 2: CO2 laser; carbon dioxide laser – The carbon dioxide molecules generate the laser radiation. This laser is a gas laser – the gas mixture contains other gases.
Structure according to excitation
Energy must be supplied to the laser to generate the laser radiation. This is also called pumping (“pump in” energy).
Example 1: lamp-pumped – the energy will be supplied by means of strong flash lights or arc lamps
Example 2: HF-pumped – high frequency pumped – the energy will be supplied by means of radio waves
Example 3: diode laser-pumped – diode lasers (semiconductor laser) are applied to supply the required energy to the laser. Yes – lasers can supply other lasers with energy – it is a so-called “two-stage” laser.
Structure according to beam properties – beam profile
Laser generate parallel beams with a certain profile. This allows the laser to illuminate for instance a round or rectangular spot or to form a ring.
Structure according to beam properties – wavelength
Lasers generate beams with exactly one wavelength – if this wavelength is in the range that is visible to human beings, we call it: light of exactly one colour.
Example 1: UV laser; ultraviolet laser – the radiation has shorter waves as light, so we cannot see it
Example 2: IR laser; infrared laser – the radiation has longer waves as light, so we cannot see it
Structure according to beam properties – time axis
Lasers can continuously generate radiation – from switching them on up to switching them off – or operate periodically; that means they can change their output power over the time.
Example 1: cw laser continuous wave – evenly on
Example 2: pw laser pulsed wave – operates in a pulsed way
Example 3: ps laser – the pico-second laser generates very short laser impulses
Structure according to the geometric shape of the active medium
The active medium is in the laser and has a particular geometric shape. A distinction is made between:
Example 1: Rod laser
Example 2: Disk laser
Example 3: Fibre laser
The bundled laser beam impinges the workpiece to be machined, the light is transformed into heat in a depths of less than a micrometer - the workpiece is heated on the surface. The material has melting temperature after about 0.1 seconds and the heat spreads deeper into the material by means of heat conduction. Due to a relative movement of the beam, there is a certain residence time; afterwards the heat that is present in the area close to the surface will be conducted rapidly into deeper areas of the component – this allows realising the rapid cooling that is required for the martensite formation. The result is a hardened track. If a bigger surface must be hardened, it is necessary to realise more tracks.
The process can be carried out as “bare hardening” under inert gas. The advantage is that no scalings occur and the hardening process on the workpiece is not visible to the naked eye. Laser hardening is often also performed without inert gas. Thereby are generated very thin, barely measurable layers of scale. They can be easily removed from the hardened component and provide the advantage of using a higher laser output power during the hardening process (a higher share of the beam is absorbed).
If the process is carried out at higher outputs, the material melts and solidifies afterwards rapidly – this is called laser-remelting.
What are the advantages of the procedure?
The generated hardening tracks have a width of 0.1 up to 10 millimetres depending on the processing parameter; but hardening depths of up to 1 millimetre can be obtained. The surface hardening process provides the following advantages:
very low in distortion,
often applied in machined and ready-processed components,
no quenchant required,
fast and contact-free,
hight hardening values achievable,
partial hardening possible and reasonable,
hardening also on spots difficult to reach,
hardness profile well adaptable to component geometry and
easy to integrate into a continuous production process.
Examples for application:
Laser hardening can be reasonably applied on spots, where only certain areas of the component must be hardened, like e.g.:
hardening of cutting edges,
hardening of bearing seats.
The laser hardening provides a solution in particular when the workpiece must not be distorted by means of the heat treatment, such as e.g.:
hardening of guide rails and
hardening of rotary cams.
Even areas of components that are difficult to reach (e.g. inner contours) can be hardened as only a small visual path must be used:
hardening of abrasively strained parts in channels and
hardening of connecting links.
What does LASERVORM offer you?
During the production preparation, LASERVORM will inform you about the possibilities of the procedure, provides advice about solving your hardening task and develops solution possibilities by means of producing samples. We take care of the contract manufacturing of your components and offer you reliably the best production results thanks to using state-of-the-art laser technology ( Nd:YAG laser and diode laser). By using 4-axis up to 6-axis NC systems and 6-axis industrial robots even the most complex surfaces can be hardened. The martensite formation can also be pre-calculated at very complex geometries by means of a simulation software (WIAS SharP). Upon demand, we will offer a tailor-made hardening machine based on our basic machines LV Midi and LV Maxi or as special machine LV Special.
You require knowledge about how your workpiece has been machined?
When required, we will use a pyrometer-based temperature control and offer different possibilities to document the laser processing, like e.g. the production of cross-section polishes to evaluate the hardness, hardness geometry and crystalline structure.
How does the coating with light work?
The laser coating – or the laser surface cladding – is a single or two-stage process. Technically speaking, the following distinction must be made:
Cladding (coating) Filler material is joined as coat by casting to the basic material, no (intended) dilution of the basic and filler material
Alloyage Basic and filler material form one alloy
Dispersing Filler material is put into the fused basic material, no (intended) change of the filler material
All three above mentioned methods can be carried out with the laser, the usual layer thicknesses are 0.1 mm up to 1 mm.
What are the advantages of the procedure?
Thick layers are produced (very low porosity).
The layers have a metal fused bond with the substrate – this results in a good coating adhesion.
A broad material range can be processed, even thermally sensible hard materials can be put in.
The procedure allows a geometrically exactly dosed application – it is not necessary to cover areas that must not be coated, a minimum rework is required (beside a better use of the high-quality coating materials, this especially saves processing time and tooling costs for hard and wear resistant layers).
Complex workpiece shapes can also be coated as defined.
In spite of the (adjustable) fusing of the substrate, the heat input into the component to be coated is very low.
Examples for application:
Today's known and industrially used laser surface claddings are applied for example:
valves and valve seats of combustion engines,
components of the tool and mould design and construction,
used turbine blades for regeneration.
By continuously developing the procedure further in terms of process safety and processable material, there are more and more fields of application for components
in machine construction,
in precision mechanics,
in medical technology,
in motor and turbine construction, etc.
By applying the laser procedure, the following objectives in
component optimisation according to the respective local load (e.g., hot corrosion, point load),
reduction of the component number that composes the product (integral construction) and
material adaptation (graded layers)
can be obtained.
What does LASERVORM offer?
LASERVORM turns the single-stage laser coating with powdery filler material into a tool to solve construction and production tasks of the industrial application by means of own developments and the use of new technologies. There are 6 different laser systems with powder and wire filler material for the job shop.
We document the processing results by means of an adequate evaluation technology – this allows performing the quality certification according to your requirements. We will inform you and provide you detailed advice, produce samples and series – please contact us and tell us about your tasks, we will work out tailor-made solutions.
Do you wish to insert light structure components of LVAdditiveStructure technology into your products? Please contact us, we will provide advice for the construction dimensioning or take care of the construction revision in order to deliver entire light structure components.
Re-melting by means of the laser?
The principle of the procedure is equal to laser hardening. But the melting point on the component surface is exceeded by applying higher power densities. By means of beam or component movement, part of the workpiece is temporarily melted. A rapid cooling is obtained in this procedure as well by leading the heat into the cold component areas.
The high application of energy at the surface causes big temperature gradients in the melted material. The resulting high melting bath convection results in a homogeneous distribution of the elements within the melted area.
What are the advantages of the procedure?
The strong melting bath convection and the rapid solidification of the melted material of this process has the following advantages for the application of the procedure:
removal of inhomogeneities in the material
generation of fine-grained and thereby solid and viscous solidification joining
low thermal total load of the processed component
It is also possible to re-treat and thereby harden and temper previously applied layers with insufficient substrate adherence or too high porosity by this procedure.
Examples for application:
The application fields of this procedure are especially the treatment of function surfaces on components of cast iron materials and the re-treatment of thermal spray coatings.
Re-melting of camshafts of ductile iron in the highly stressed
surface areas of the cams
Repressing of the plasma sprayed coatings
What does LASERVORM offer?
We offer information about the procedure and provide advice about the possibilities for the application on your products. The production of samples allows you to test and evaluate our procedure offer.
Beside laser processings of individual pieces up to series, we offer testing and documenting treatment results. Our standard machines are also adequate for re-melting applications.
Lasers generate parallel radiation of one wavelength. Such radiation can be bundled easily (e.g. by means of converging lenses) to a small spot – the focus.
This is regularly applied in the laser material processing: the light is bundled in a focus and the lens is positioned so that the focus is on the component surface to be processed. The technologically important parameter is the power per area (power density).
The light bundling of the converging lens is based on the different refractive indexes of the lens material (e.g. glass), the ambient air and the shape of the lens.
If an important amount of energy is transferred through the lens (or other optical components) – the laser system is operated – this will result in heating the optics. The result can be notable focal position changes by means of geometrics modifications of the optics and refractive indexes within the optics. All forms of impurity on the optic surfaces have a strong impact as they result in a notable increase of the absorbed beam share and thereby increase the optic heating significantly.
The technological consequence: The power density distribution changes over the time on the workpiece surface – the focus shift influences the processing result.
The focus shift can be massively influenced by the optics dimensioning. Moreover, it is possible to face the focus shift with active and passive measures for focus shift compensation.
Decreasing focal spots of modern fibre lasers or disk lasers result in increasing power densities on the workpiece and thereby increasing process speeds.
This excellently positive property for the production challenges the machine construction twice:
Higher speed and speeding up at increasing requirements to path accuracy of the movement system.
LV CBase is the answer of Laservorm to this challenge. Special-concrete reinforced machine frames provide
high rigidity and good damping
economical production even at a quantity of 1 (i.e. this technology can even be applied for special machines)
very high design freedom and high integration of function elements
Industrial bus systems
Industrial buses are the control-related backbone of a laser machine or system. Laser processes proceed often in high process speeds. Important quality criteria for good control solutions are:
real-time capability combined with a short
bus cycle, low
jitter and the
aptitude for information relevant to security and
separation of time-critical and not time-critical information for the highest
Excellently solved are the requirements with the real-time ethernet bus EthernetPOWERLINK. Hard real-time requirements for drives, laser power, fast beam formation installations and all safety-related aspects can be fulfilled by means of this system.
We are a manufacturer of special machines and our solutions have to be projected regularly according to the customer request or connections must be established to the control system and bus system of the customer. As a matter of course, we are acquainted with all current bus systems.
Programmable safety engineering
Programmable and bus-based safety engineering is not an end in itself, but benefits the customer in
a higher productivity by staged safety concepts,
highest level of flexibility and guaranteed future of a special machine solution and
reduction of the error probability and therefore of the downtimes
of a laser system.
We are familiar with all well-known product lines of different manufacturers, but we prefer the openSAFETY concept of a manufacturer-independent, bus-based safety solution.
Typical memory-programmable controls and industrial bus systems often cannot cover the requirements of modern laser machines entirely.
Driven by this knowledge, we have designed an extremely efficient analogue and digital interface assembly together with an electronics designer and producer of the region, the IMM Elektronik GmbH. This allows us to process and coordinate signals much more quickly than with the classical CNC and PLC technology.
The product has been designed in the context of the FASKAM linkage. We are grateful for the promotion of this research and development project.
Real components do not have the ideal geometry, it can therefore be important to adapt the respective processing programme separately to each component. The classic way of “manually breaking-in” is today often replaced by automatised measurement and correction processes.
“Determine the actual situation” → “compare with the ideal and use it to calculate the precise processing programme” → “machine the respective component”
The determination of the required parameters (often the position and/or geometry) can be performed prior to the actual processing step or permanently during the machining. The last mentioned procedure allows preventing modifications that occur during the procedure (like e.g. position change by means of welding distortions).
There is a varied complexity of solutions put into practice. A simple way is e.g. the automatic correction of only one coordinate in space (Where should the welding process start along the X axis?). More complex solutions determine for instance a multitude of coordinates in space, lead them back to areas, calculate paths to scan a 3D surface, etc.
Carbon is an element that turns iron into steel. The share of carbon has an effect on various properties of steel like stability, formability, weldability, etc.
Unalloyed steels can usually be welded at carbon content of up to 0.24%. Additional pre- and post-treatments are required at higher values.
But steel can contain further alloy contents that differ considerably in their effect on the welding properties.
The carbon equivalent is a comparative figure that provides information about the welding work. Up to a content of 0.44% an alloyed steel can be welded theoretically. In practice, however, this depends also of other factors (like e.g. the pre- or post-regime).
There are different formulas to determine the value of the carbon equivalent due to a multitude of steels. The following formula is recommended by the International Institute of Welding for a steel with more than 0.18% of carbon:
The shaping of pulses means generally that the laser power can contain a shape that differs from the rectangular shape (a variable laser power over the time) within the shaping of a pulse.
At pulsed lasers for welding (typical pulse lengths of 0.1 ms up to 20 ms), this behaviour can be obtained by means of temporary variable pump energy supply.
In which situation is the shaping of pulses necessary?
By means of shaped pulses, the energy supply and thus the technological result can be optimised.
A typical application of the pulsed laser welding is the following procedure: The welding impulse starts with a very high power and decreases rapidly within a short time (e.g. 1 ms) to a significantly lower level – this value will then be maintained longer (e.g. 10 ms). This system allows heating the material rapidly up but avoids overheating – this facilitates a longer phase of melt formation (time for melt distribution, outgassing) at a reduced sprayer inclination.
Consequences of polluted optics
Always ensure the cleanliness of optical components of laser systems for material machining. The operator is responsible for the light emitting aperture – here the interface to the process requires the full attention of the operator as polluted optics lead to
power loss (and thereby a reduced power on the component),
modifications in the power density distribution on the workpiece surface,
reinforced optics heating and thereby also
These aspects can notably change the processing result.
Safety glasses and monitoring solutions
A typical safety solution for high-quality machining optics consists in mounting a safety glass that has been designed as wear part in front of the process side. In this connection, it is important that the safety glasses are furnished with an anti-reflection coating to avoid considerable power reductions.
Safety glasses can be cleaned in case of slight pollutions or must be replaced in case of heavy impurity (e.g. burned-in weld splatters).
For industrial applications and in particular automatic units is an automatically operating safety glass monitoring useful (machine operator is released from performing the control, the process reliability increases). A typical technical solution is the determination of the stray-light part (increased due to impurity).
In which cases is the cross jet applied?
Rapid gas cross flows (cross jet) have been proven as additives for optics protection in particular in case of heavy impurity levels from the machining process. They are usually applied additionally to the safety glass in order to deflect for instance welding splatter into the direction of the beam outlet aperture so that they do not reach the safety glass.
Cross jet solutions must be operated with clean gases (typically cleaned compressed air) and cause thereby considerable operating costs and sound emission.
The intensity peaks of a laser beam are called modes. An exact definition of this term would lead deeply into wave physics.
The laser radiation can have various numbers of modes or only one mode. In case of one mode – a so-called single mode – the laser beam can be optimally focussed and can be used e.g. for the laser drilling. But is not always advantageous to have only one mode. A beam with an even intensity is thereby generated within the beam radius made of one beam with various modes, the beam is homogenised (multi mode).
But the number of modes is not the only criterion that decides on the focusability of a laser beam. The type of generation for instance is also important. In order to quantify the focusability of a laser beam, the beam parameter product (BPP) has be established. It is the result of the half opening angle and the beam radius in the focus, it is a parameter that stays the same over the entire beam path.
There are different possibilities to measure properties of laser radiation. One of them are photodiodes that convert the incident radiation into an electrical current flow. It is possible to measure the power with it. If many little photodiodes are arranged into a field, a CCD element, it is possible to measure the arriving power respectively on many little areas, which is a measure for the intensity. If the intensity distribution of a laser beam should be determined, CCD elements are a good solution. How this looks like during the evaluation by means of a software display the following images:
To realise the intended processing task, the beam diameter, distribution, and shape must be adapted to the task. There are many possibilities to shape the beam. The focusing lens and mirror are important. They are very important to obtain high intensities because the focussing is only possible with them. But the intensity can be even increased by means of beam expansion systems. Even though the beam radius is first increased, the laser beam can be focussed easier afterwards. By means of two lenses that are positioned like in telescopes or by means of a specific position of two prism to one another, such beam expanders can be put into practice.
A beam mask that lets laser radiation pass within determined contours can be used for labelling or structuring by means of laser beams that are equipped with an homogeneous beam profile. In most cases the laser beam is not homogeneously distributed before its generation so that beam homogenisers must be applied. It is possible to apply them by means of a roughened and thereby dispersive surface of an arced quartz-glass bar. But this effect can be obtained also by a multitude of smaller lenses. A specific component for the beam homogenisation is the kaleidoscope. It is metallised inside and pointed in its extreme. The beam can also be homogenised by means of segment mirrors or Fresnel lenses. But often is it necessary to process more spots at once. Beam splitters are used therefore that are based on the different reflection directions of two sides of a prism or on partially transmitting mirrors.
There are even more options for the beam shaping when the optical components move. The rotation of the components allows realising laser beam drilling, which is called trepanning drilling. The diameter can be increased thereby and possible asymmetries of the beam can be compensated. Rotating optics (lenses, mirrors) allow the processing in pipelines and at spots that are difficult to reach. But it is also possible to apply a vibration of the mirrors instead of the rotation, in order to process for instance short lines. In case of complex shapes, scanning systems are used that are put into practice by means of two rotating mirrors. This procedure allows determining bigger areas, which is also realised using a polygon mirror. This is a prismatically shaped mirror with reflecting lateral areas that have all the same edge length. Another beam shaping element is the acoustoptic modulator. It is important to know that the deflection of a beam can be performed by means of a grid. Fluctuations in density suffice therefore. As sound waves are fluctuations in density, the ultrasound of the beam can be deflected. Optics can not only be moved, but also be deformed. These are then called adaptive optics and are a beam shaping changing during the processing. This technology is applied in particular to adapt the focal position of workpiece shapes. In order to increase the intensity, it is also possible to overlay laser beams.
Programmable beam quality
Strictly speaking, the beam quality cannot be programmed or modified in real time at lasers customary in the market. Due to a rapid, spacial and temporal modulation of the laser beam on the processing spot, it is possible to obtain the actual result of a programmable beam quality.
The programmable beam quality is the combination of the synchronous movement on the feed track (NC axes), the adaptation and modification of the laser power or laser pulsing and rapid deflection of the laser beam in one up to three axes (optical axes). The laser power can be influenced depending on the track, speed and time.
Purposes of application:
broader hardening tracks
variable welding bead width
controlled melting bath movement
influenced temperature fields