As product traceability grows in importance, manufacturers are increasingly integrating automated component marking systems into their production lines and systems.
Several component marking options are available, but which is the best?
Modern manufacturers use inventory control and asset tracking to support quality and traceability in production. This, in turn, ensures the right parts are used in the correct places and guarantees the accurate, timely identification of affected parts when quality deviations are identified.
It can also simplify maintenance and management activities throughout the working life of the product, helping operations and maintenance staff track failures and match replacement parts.
But tracking components requires them to be marked in some way. Marking methods include manual hand stamps and engraved dies, but the more common methods in industrial applications are lasers, dot peening, chemical etching and scribing.
Laser technology is generally seen on more advanced systems. For many applications, however, this approach can be overly complex or expensive, in which case manufacturers have three main options available.
Dot Peen marking: Also known as dot marking, stylus pin marking and micro percussion marking, this component marking method employs a stylus that rapidly punches a series of dots onto the surface of a material. The stylus is programmed to move around the surface, resulting in a succession of dots that create digits, text, logos and 2D data matrix barcodes.
Dot peen marking provides fast, accurate, low-stress marking and can mark through coatings or film on the material surface. Dot peen machines can mark a wide range of materials. The angle of the stylus tip may be changed to further reduce the chance of material flaws.
Chemical etching: This works by the electro-chemical dissolution and/or oxidation of metal from the surface being marked through a stencil impression to give the required mark. This is achieved by sandwiching a stencil between the surface being marked (connected to the anodic polarity of the etching unit) and an electrolyte soaked pad (connected to the cathodic polarity), and passing a low voltage current between the two.
Many electrolyte solutions exist, the compositions of which may vary according to component material type. However, they are all designed to produce some form of chemical attack of the material. Once the material has been etched, the electrolyte is neutralized by removing all traces of it from the component.
Scribe marking: A pneumatically-driven pin is driven into the metal surface to be marked. It is then moved through the metal, giving a continuous engraved line to produce the required inscription. Marking machines can mark a wide range of materials, although clearly softer materials will be easier to mark. The harder the material, the shallower the depth of mark will be. The type of material will also influence the life of the stylus.
The angle of the stylus tip may be changed to reduce the chance of chipping. Changing the angle may also increase the readability of the mark. Smooth, well finished work pieces are easier to mark than rough, scaled work pieces. The more complex the finish, the deeper the mark will have to be to remain readable. Painted work pieces may be marked but there is the risk that the marking process can cause the paint to chip.
Shedding light on laser marking
Typical marking lasers come in three types – carbon dioxide (CO2), YAG or fibre.
The most basic form of a CO2 laser consists of a gas discharge with a reflector at one end, and an output coupler (a partially reflecting mirror) at the output end. CO2 lasers have a high wavelength (operating in the infrared) which makes them a poor choice for metal marking applications because the laser radiation is often reflected by the target material.
YAG and fibre lasers have shorter wavelengths which not only provide better marking resolution, but are also easily absorbed by metal.
YAG lasers (also called flash lamp or lamp-pumped lasers) use a bulb lamp as a pumping mechanism and yttrium aluminium garnet (YAG) synthetic crystal as the gain medium. They are becoming less popular because the bulbs have a short life and the lasers are inefficient – they generate a lot of heat and therefore require a liquid coolant.
Solid state fibre lasers have become the industry standard for reliable, high quality marking. The laser source is sealed, preventing dust and particle contamination. This also enables longer distances between the control unit and the marking head, allowing the laser source to be situated remotely from the point of use. Furthermore, it reduces leakage, resulting in greater efficiency.
Overall, the fibre laser is cheaper to run and has fewer replacement parts than the YAG laser. The fibre laser is air-cooled, which makes it more compact and easier to integrate into existing systems and processes.
This article features in the June 2018 edition of industry magazine Automation, read the full article here