Making its mark

The history of marking products as an indication of origin and quality can seemingly be traced back to Roman times when blacksmiths would indent their swords to distinguish them from their rivals. Since then the process of marking parts has moved on considerably and the practice is as much about identification and traceability as quality.

One company that has pioneered component marking, particularly for aerospace applications, is Pryor Marking Technology. The company's own history is extensive dating back to 1849 when Edward Pryor began engraving maker's marks for the thriving cutlery industry in Sheffield.

The company then became well known as a producer of punches for marking metal parts manually and in fact it still produces these simple products today.

Pryor's involvement with aerospace dates back to the Second World War when the UK production of aircraft was massively increased.

“Things then began to change radically in the late 1970s when we developed a computer controlled marking machine,” states company sales director, Alastair Morris (pictured). “Our then technical director (now MD, Neil Andrew) took apart a home computer and wired it up to a solenoid to drive a pin to make dots in metal. He used a computer to control the X and Y movement and that enabled us to mark our own designs. Effectively it allowed us to write the marking.

“Dot marking is still a very important part of the business, particularly in aerospace. We also have scribe marking, where you engrave the metal, laser marking, chemical etching and other marking technologies such as inkjet printing and RFID tags.

It's a vision thing

Pryor spent many years developing machine readable marking with a major aero-engine manufacturer, especially for its turbine blade manufacturing. These systems have now been adopted across the industry.

“Rather than just having letters and numbers it meant using 2D data matrix codes because they mean a large amount of data can be stored over a small area. That required us to start developing vision systems. At that point it was difficult to read codes marked on metal because there is not much contrast with the mark and the background surrounding it. We bought a vision company in the 1990s and that enabled us to develop this area of expertise in-house.”

Pryor's marking technology is used not only for identification but also to help manage the production processes. In the example of a turbine blade it may need to be marked several times using different methods as it moves through production stages.

“Our marking methods include inkjet marking for the lost wax investment casting of the blade, marks actually cast into the blade, which then get machined off during the next processes. We then need to apply other marks that will last through the next stages, such as surface coatings. Finally we apply a code that will last through the blade's service life. The important thing is you can capture data at every stage of the manufacturing process which can then be stored.”

The development of different marking methods has coincided with a development of software which allows for more traceability.

“Our in-house software development team initially used the software just to drive the marking machines but that has now developed into a suite of software that also records the traceability,” says Morris.

This recording of manufacturing data is a useful in identifying any potential problems that might occur during an engine's operating life.

Morris explains: “This data goes beyond a Manufacturing Execution System because it doesn't just provide manufacturing data it offers manufacturing data for unique components. This traceability means if you have a failure in a part you can access its entire manufacturing history and importantly find all the other components that share that history.

“Engine manufacturers then don't have to ground an entire fleet of engines if they can identify exactly which part may be at risk and replace it.”

Making a gateway

Marking also means costly errors can be avoided during manufacturing.

“You can set up the software to make gate stages during production. The system scans the code at each stage and if some process has not been carried out then the software will not let the part proceed to the next stage. It adds more control to the manufacturing process. A finished turbine blade can be worth many thousands of pounds so you don't want to scrap it because a stage of the manufacturing has been missed along the line.”

Pryor's latest advances have been to introduce automation and robotics into the marking process.

“We have robotic systems for both large and small parts,” notes Morris. “It has allowed us to bring together many of the different aspects of our business to offer turnkey solutions. We use the vision technology to guide the robot, the marking systems on the end effector, and we use our software to control the robotics.

“The benefit is that you can mark any component in any location so you don't have to have a particular fixture or marking station. Another benefit is it enables you to put multiple marks on one component. So if you have to mark a big component in lots of places the robot can move around the part putting different marks in different places that may involve awkward locations or awkward angles. This would take a lot longer if done manually. It can also offer flexibility with simple reprogramming.”

What impact are advanced new alloys and composite materials having on marking technologies?

“This is really why we have all these different methods of marking,” Morris states. “There is a balance between marking a component and damaging it. For example, laser marking is not widely used in aerospace on metals because of the effect it can have on the material's properties. On advanced alloys you may have to use chemical etching. Aerospace specifications are very rigorous with what you can and can't do, so our marking methods have to conform to these and this is where a lot of our specialist knowledge comes into play.

“With composite materials we are working on ways in which you can mark them without causing serious damage. At the moment people tend to put labels on composite parts or paint them on but that would not be acceptable if it was a critical component.”

So what developments in marking could we expect to see in the future?

Morris concludes: “We have to develop our equipment to be flexible to keep up with revised manufacturing flows. We are seeing more requests for in-process marking so instead of having to move the component to a marking station it can be marked while it is on the machine it is being processed on.

“Engine manufacturers have set the standards for traceability, but I see that changing as manufacturers demand more and more data about all their parts.”

www.pryormarking.com