Up to the mark: how to keep track of components

In today’s fast-moving manufacturing environment, component marking is critical. Modern marking systems are often fully automated and integrated within production lines and ERP systems to provide complete product traceability – from the point of manufacture all the way through to point of use.

Automation has increased the speed and complexity of manufacturing and this has to be mirrored in component tracking. Individual parts are made at high speed, which must then be assembled quickly and precisely. By marking each component with a unique identity, this can be scanned prior to each operation and tracked efficiently through production.

This is also used beyond the production process: accurate traceability also helps to ensure that replacement parts are speedily replaced, for instance, or that a rogue batch can be recalled quickly.

Components can be marked in various ways, from a simple serial number to a scannable barcode. There are several ways to achieve this including laser marking, chemical etching, scribing, dot peening (also known variously as dot marking, stylus pin marking and micro-percussion marking.

Laser marking has three main variants: CO₂, YAG and fibre. CO₂ lasers have a relatively long wavelength, making them a poor choice for metal marking. YAG and fibre lasers use shorter wavelengths that are easily absorbed by metal – and provide better marking resolution.

The light source of fibre lasers is sealed, to prevent dust and particle contamination. This enables longer distances between the control unit and marking head which is vital in some production line applications. It also reduces leakage, to boost efficiency. YAG systems are usually for specialist applications – especially in the scientific sphere – while fibre lasers are more commonly used in the industrial sector.

Although laser marking has significant benefits, it will be too expensive and complex for many applications – meaning that manufacturers must offer a range of other options to choose from.

Chemical etching (also called electrochemical or electrolytic etching) uses an electric current to mark alphanumeric data or Data Matrix codes onto metal surfaces. It is common for small to medium production runs in the aerospace industry, which has tight tolerances over surface treatment. A stencil of the design to be marked is placed between the electrode and the surface, and a low voltage current passed through an electrolyte to etch the material. It does not deform the material being marked, which is important in applications ranging from small pipes and shims to feeler gauges.

In scribe marking, a pneumatically actuated pin is driven into the metal surface then moved through the metal to engrave an inscription in a continuous line. In this method, the workpiece must be held firmly or there is little chance of making a good quality mark therefore scribe machines need firm fixturing because they generate high lateral forces during operation.

Finally, dot peening uses a stylus to indent a series of dots on a material surface. The stylus is programmed to move across the surface and create characters, logos or a Data Matrix code – a kind of ‘barcode’ that stores large amounts of data.

Dot peen marking is fast and accurate and can mark through coatings or film on a material’s surface. It is particularly useful for permanently marking a Data Matrix code onto metal components.

When using dot peening, the depth of the mark – which is a measure of legibility – depends on factors such as marking force, marking gap (the distance from the stylus tip to the workpiece), material hardness and angle of the stylus tip.

A larger marking gap creates a deeper mark. However, if the gap is too large then the stylus will start to stick and drag the workpiece. This is solved by reducing the gap or increasing the marking force. While the stylus tip angle is usually set at 90°, it can either be reduced or increased. A wider angle (such as 120°) will make a shallower mark but lengthen the life of the stylus. On the other hand, a smaller angle (say 60°) will make a deeper mark while reducing stylus life. Dot peening machines can mark characters from 0.15 to 49.95mm high.

There are many reasons for carrying out product marking – ranging from simple identification (such as adding a company logo) to production line tracking. The wide range of available options ensures that all types of capability – and budget – are catered for.

Pryor Marking Technology www.pryormarking.com