Following the installation of an aqueous-based ultrasonic washing and drying line, manufacturing procedures have been streamlined at the Stonehouse, Gloucestershire, factory of sub-contractor Norman Precision. In addition, there has been a marked improvement in the quality of its machined aluminium and stainless-steel parts — particularly those that are subsequently plated or painted.

Automatic washing machines are increasingly taking over from manual degreasing tanks on shopfloors for the batch cleaning of components. However, Norman Precision’s four-tank ultrasonic system from Alton-based Turbex Ltd (www.turbex.co.uk) differs from customary stand-alone machines in that the operator can start processing the next basket of components while the previous load is being rinsed or dried in another tank.

Operations manager Bob Savory says: “Another way in which our cleaning system differs from those run by most sub-contractors is the way we have adopted it as the hub of our activities, linking the machine shop and dispatch. This has triggered a cultural change in our working practices that has led to a better understanding of our processes and how to improve them. Errors and re-work have consequently been reduced to almost zero.”

About 60% of throughput at the factory is machined aluminium, the remainder being numerous grades of stainless steel including 17-4PH, 303, 304, 316 and 4140. These materials reflect the large amount of work carried out for the aerospace, oil and gas, automotive, medical and defence industries. Many components produced are complex, so swarf tends to become trapped, making it difficult to clean and dry them.

Previously, manual removal of swarf using an air line — sometimes followed by processing in a rotary chemical system — struggled to achieve the required level of cleanliness, so the washing of some components was sub-contracted. Others due for anodising, plating, painting or powder coating were just cleaned superficially, as it was the responsibility of the finishing companies to prepare them for coating.

The effectiveness of the methods used by such third parties was variable; but now that Norman Precision is cleaning all components internally, it can control the quality of the finishing processes to a much higher degree. The result is an overall improvement in the quality of finished components delivered to customers.

Ease of use

All of Norman Precision’s machinists operate the Turbex line. As soon as a batch of components has been produced, it is taken to the cleaning section for washing, the cycle taking less than half an hour.

This avoids the previous situation of having aluminium parts stacked for hours awaiting cleaning, which resulted in the water content of the coolant leaching silicon from the aluminium and pitting the surfaces of components.

The problem was worse during minimally manned night shifts, as machined components were waiting around for longer. Furthermore, even some stainless-steel parts can rust if left for long periods in the presence of water, especially in places where they have been handled, and they were previously vulnerable to extended periods lying around on the shopfloor.

On arrival at the cleaning line, a batch of components is placed in a stainless steel basket, which has its base lined with a plastic mesh to prevent damage to the surfaces of the parts. With the help of an overhead gantry, along which a pneumatic lifting device moves, the operator transfers the load to the four tanks in sequence. All are held at a temperature of 50°C, which accelerates the cleaning and drying while allowing the components to be handled immediately after processing.

Cleaning process

Tank 1 contains tap water with detergent and an ultrasonic oscillator to assist the removal of particulates and other residue. The action is enhanced by short, automatic movements of the basket up and down (this technique is copied at the two subsequent stages).

The water is periodically cleansed by pumping it through a coarse and fine filter into an adjacent recirculation cylinder, from which the tank is replenished. Meanwhile, the ultrasonics are turned off to save energy.

After 10min, the basket passes to the second and third stages for 1min each. The first of these subsequent stages contains tap water agitated by compressed air, while the second is filled with water that is continuously de-ionised.

The last stage is an air-assisted dryer in which components spend 10min, after which the water has usually evaporated. Occasionally, if parts contain particularly awkward areas, they may be returned for a further 10min. There is the option to increase the temperature, but this complicates subsequent handling and is usually avoided.

Mr Savory says: “Before installing the new washing system, we had been looking to upgrade component cleaning for some time and researched several alternatives. We short-listed two but opted for the Turbex solution, partly because it had a smaller footprint; space is limited in our factory.

"More important was the fact that operators could walk away from the cleaning line to do other tasks; the other system we considered was really for large-volume production environments and needed an operator in full-time attendance.”

Mr Savory mentioned two further advantages of the Turbex cleaning line. First, customers are impressed when they visit the production facility at Stonehouse and see that Norman Precision takes this aspect of quality control seriously.

Second, the equipment appears to consume little power; the company does not monitor the cleaning system separately but has noticed little increase in electricity bills since it was installed.