Laser Marking Flashcards
What is traditional marking?
Putting a visual feature on a part. E.g. mechanical engraving, chemical etching, ink jet, painting etc
What are the 3 main parts of laser marking?
- Laser
- Optical system and its control
- Surface - materials interaction and marking mechanism
What are the 2 main laser marking methods?
The mask marking
The beam deflected method
Mask vs beam deflection in regard to marking speed, marking area, flexibility and cost of investment.
Marking speed- Mask is the fastest whereas beam deflection scanning can take several seconds per part.
Marking area- Mas is smaller area limited by beam size and energy per pulse whereas beam deflection is limited by lens selection.
Flexibility - mask has unique pattern required for each mark. Time consuming to change each mask. Suited for very high volume making but beam flection is highly flexible.
Cost of investment- is lower for mask but beam is higher due to expensive scanning systems.
What materials does a CO2 marking system mark?
Wood
Polymers
Painted & Anodized Coating
Textiles
What materials does a fiber laser marking system mark?
Metals
Polymers
Coatings
Ceramics
What are the 2 ways of scanning control?
Raster(side to side) and Vector(fast to mark).
What are the 5 laser marking mechanisms?
- Engraving
- Removing layer
- Annealing
- Colour marking
- Bonding
What is laser engraving?
- Engraving is obtained when the material absorbs a high amount of laser
light leading to a relatively deep cut in the surface. - Surface damage is always evident and the contrast is poor. usually for permanent marks.
- can be with or without colour change which could be chemical or caused by surface texture scattering light.
-sustainable as removed need for additional stickers
What is Laser Removing layer?
During the laser irradiation process, a covering layer evaporates/ablates.
* Very thin layers such as colour and/or anodizing layers are especially suited for laser marking by layer removal.
* High contrasts can be achieved with a small amount of laser power since these layers absorb laser radiation
extremely well.
-Fiber laser or CO2 laser is best suited for paint removal for low initial cost, cost of ownership and compact size. ALL YAG/FIBRE can remove anodizing layers.
What is laser marking by annealing/Tempering?
- Marking by Annealing is used with all metals (predominantly steel) containing carbon, which shows a colour change when exposed to heat.
- Process speed is lower compared to other marking, as annealing colour change relies solely on thermal effects effect to bringing carbon in to the surface.
- This surface marking gives excellent contrast without disrupting the surface finish (burr-free process).
YAG/FIBER SUITABLE NOT CO2
What properties determines the colour of the mark?
Colour of the mark is determined by the maximum temperature , interaction time and properties of the metal.
How is there a colour change in steel?
- Creation of oxide layer on the surface
of steel. - Air contains enough oxygen for the
reaction. Marking speed and colour
depth can be increased with pure
oxygen environment - The oxide layer absorbs light and so
increased thickness of oxide controls
colour - Easier to control with modern fiber
lasers as they can control pulse length
and repetition rate independently - Requires uniform heating of area to be coloured
– Gaussian beam profile NOT ideal.
How is there a colour change in titanium?
- Similar process to steel
colour marking. - Producing TiO2 oxide
coating - Used in the production of
jewellery
What is laser marking by colour change?
Some materials can undergo
chemical changes when exposed to
laser radiation of a specific
wavelength.
* The chemical change can be either
light or heat induced.
* The colour change can be due to
changes in chemical composition or
in molecular structures.
What are the two types of colour change?
- Thin film interference - Fibre/DPSS
laser induced surface oxidation
(Stainless steel, Titanium). - Chemical Reaction - Excimer laser /
UV induced photo-chemical colour
change for aircraft cable marking
(white to black).
What is IR laser polymer colour change?
Colour changing additives (0.01%-4%) aremixed into the polymer.
Additives are activated using near-IR lasers (Fiber, YAG etc.)
Suitable for opaque and transparent polymers. Additives consist of a laser absorber and a colour former. eg.TiO2
What is UV laser polymer colour change?
Shorter UV wavelengths (3*Nd:YAG 355nm) give smaller beam size
= greater resolution of mark (2500dpi)
* No engraving, marks can be sterilised.
* Small amount of material degredation in the surface can cause colour
change appearance.
What are the advantages of laser marking by colour change?
Advantages
* No chemicals or tools
* Very fine detail achievable
* Multicolour-not possible
with anodizing
What are the disadvantages of laser marking by colour change?
Disadvantages
* Cost of laser equipment
* Slower than printing
* Unknown long term properties of
surfaces. Corrosion and wear
resistance
What is laser marking by bonding?
- Uses precise lasers and marking materials to permanently high-contrast, high resolution marks over the surface.
- Appropriate for metals, glass, plastics and ceramics.
- The inclusion of pigments enables the creation of high-contrast, high-resolution marks, with the ability of tailoring the colour.
What parameters affect laser marking?
Power density
* Interaction time
* Thermal properties
– Thermal conductivity
– Heat capacity
– Melting point
– Boiling point
* Optical Properties
– Material
– Wavelength
What are the advantages of lasers in production lines?
Advantages
* Very high processing speeds
* Low operation cost (no additional consumables)
* Constant high quality and durability of results
* Process cleanness (no paints, inks or acids are used, which could
contaminate the product)
* Non-contact processing (no tool wear, no workpiece distortion)
* The possibility to mark fragile, soft and hard surfaces
* Very high flexibility and ease of automation (markings are changed
through the changes of input data to the control software)
What are the disadvantages of lasers in production lines?
Disadvantages
* Fume – collection, treatment and disposal. This is often overlooked!
Proper fume treatment can be costly.
* High capital and start up costs
