Bearing up… the importance of optical inspection of air bearings

Quality control fundamental to production

Integration of quality control throughout the manufacturing process is fundamental to production, enabling ABL to achieve high levels of performance from their products. With a range of spindles operating between 80,000 and an incredible 350,000 rpm, it’s imperative that critical components are machined with sub micron accuracy. Nearly all components are manufactured in house with only a small amount of work outsourced to sub contractors including specialist processes such as heat treatment, anodising and shaft coppering.

Fig. 1.0 shows a typical spindle manufactured by ABL

A priority for ABL is that all machined components are meticulously inspected for abnormalities which could affect the spindle once it is fully assembled. With such extreme rotational speeds, all components, and especially the air bearings, need to be inspected for accuracy. The rotating shaft, the main component in the spindle, is inspected under the Lynx microscope. Running along the length of the steel shaft are grooves where the copper is inserted. The copper forms one half of the electric motor that drives the shaft and under extreme speeds it is imperative that it adheres to the steel of the shaft. If the copper lifts it leads to instant and catastrophic failure. After the shaft has been milled but before the copper is inlayed it is meticulously inspected under the Lynx. Adrian Farwell, who is responsible for quality at ABL, explains the importance of optical inspection:

“Sometimes it can be difficult to assign meaningful tolerances to components and so assessing the part by optical inspection is essential and a key part of our rigorous quality procedures”

The milling is optically inspected for burrs, eroded edges and scores on the surface of the metal. This is vital in ensuring the copper is easily and precisely deposited onto the shaft. If the surface finish is not clean and precise the copper will not adhere to the shaft. Components manufactured at ABL which are critical to the function of the spindle are subject to 100% inspection. Other components with lower fuction emphasis are batch inspected.

Lynx revolutionary optical inspection provides the solution

Optical inspection procedures are conducted under the optics of the Lynx stereo zoom microscope.

The Lynx is a revolutionary zoom stereo microscope which removes the need for restrictive microscope eyepieces by employing patented eyepieceless technology. The result is an ergonomic microscope delivering optimum operator comfort through fatigue free viewing, increasing productivity and accuracy. Adrian continues to explain the advantage of using a Lynx as a stereo inspection tool.

“Firstly, the eyepieceless viewer is what initially impressed us because it is much less tiring on the eyes than our previous stereo microscope. However, when we saw the performance of the oblique and direct viewer, the decision was made. We find the Lynx with the oblique and direct viewer a superb inspection tool and it has become invaluable to us.”

The oblique and direct viewer is an optical accessory enabling engineers to view components from a 34º angle which can then rotate a full 360º to provide easy inspection all the way around a component, allowing operators to switch between direct and oblique views. The Lynx microscope also has a camera attachment supporting the quality process where questionable differences can be captured digitally, circulated electronically and documented as part of the continuous improvement for quality.

Inspection of air bearing jets

Another critical component within ABL spindles are the air bearings themselves, each containing jets that control the film of air between the shaft and the bearing. Amongst many other components, the fitted jets are crucial to the functionality of the spindle and are inspected 100%. The air passing through the jets provides a cushioning between the shaft and the bearing allowing for free rotation. Although some of the jets are only microns in aperture they are inspected under the Lynx for the quality of the machining and to ensure that the chamfers are clean with no ragged edges.

Also the pocket size, form and depth have to be perfect as any irregularity could cause problems with the air flow resulting in the shaft colliding with other components in the spindle.

“The oblique viewer gives you that extra dimension and there is no other way we can do it. We get so much use out of the Lynx for our applications. It is invaluable and an absolute godsend” says Adrian.

Quality control provides absolute precision and performance

ABL have been manufacturing for many years and the integration of quality control throughout their design, manufacturing, assembly and test processes has enabled ABL to achieve levels of performance that are admired by their customers and the envy of their competitors. ABL’s facility is very well equipped with the very latest equipment. Modern technology combined with tried and tested traditional methods and a skilled workforce ensure that ABL produces components manufactured with absolute precision.

With expansion at a rapid rate, ABL are leading the way in utilising air bearing technology. With the demand for smaller, faster spindles constantly increasing, ABL can develop their business yet continue to provide customers with products skilfully manufactured to high precision.