Dawson Shanahan has invested in a dedicated manufacturing cell comprising four automated high-speed grinding machines; this is playing a crucial role in helping the company to improve the accuracy of finished parts and levels of productivity for components supplied to customers in the medical, automotive and electronics industries. Developed in conjunction with Earlsdon Technology (E-Tech), the grinding machines use specialised tooling to achieve surface finishes with tolerances that the company believes are more accurate than anything achieved previously on high-speed systems of this type.
Dawson Shanahan is one of a small number of independent engineering companies to specialise in both cold forming and precision engineering using a wide range of conventional machine tools. The company has production centres in Potters Bar and Welshpool and designs, produces and supplies finished components to customers throughout industry and around the world, with almost 80 per cent of its sales being exported.
The E-Tech grinding machines include groove, slot and centreless grinders, and have been installed as part of an ongoing development programme to increase manufacturing capacity, especially for precision parts that are often based on high-performance steels or other exotic engineering materials. Jeff Kiernan, Commercial Director at Dawson Shanahan, states: "We have seen a considerable increase in demand in recent years from customers looking for component parts produced to ever tighter tolerances – often to within a few microns – for both small batches and large-volume production runs. As a result, we needed to expand our machining facilities, especially our grinding cells, to increase productivity while enhancing levels of quality and repeatability still further."
Specialist grinding wheels
Dawson Shanahan has worked closely with E-Tech to develop the new grinding machines. Wherever possible, they use common features to simplify operation and maintenance; for example, twin grinding spindles with dressable and demountable Cubic Boron Nitride (CBN) vitrified grinding wheels, plus automatic part feed and orientation systems, using standard bowl feeders and pneumatic air conveyors.
Key to the successful operation of the machines has been the development of special-purpose CBN grinding wheels, carried out by both companies in conjunction with the grinding wheel manufacturer, Asahi Diamond Industrial. These 400mm diameter wheels typically operate at speeds of 4000rpm and are automatically balanced to eliminate vibration, and dressed during operation, with the latter using in-situ diamond dressing wheels to maintain exact outer edge profiles and a long operating life. Machine control is via standard Siemens touchscreen PLCs, with bespoke programming, which also provides the facility for detailed diagnostics, with data being downloaded for review as part of Dawson Shanahan's extensive ISO quality control procedures.
These features are enabling Dawson Shanahan to achieve precise and consistent tolerances, as Kiernan explains: "We believe that we are reaching levels of precision for high-speed grinding that are currently unrivalled by any other company in Europe. For example, we are producing finished components in 2.5 seconds that are machined to within 0.7microns over a surface area of just 3.0mm2; there is no need for further polishing or burr removal. Additionally, many of the parts that we manufacture typically incorporate slots with chamfered profiles ground into shafts measuring several millimetres in diameter; here we can hold tolerances of 20 minutes of a degree, which, over an extremely small area, equates to levels of precision of just a few microns."
The high operating speed of the grinding machines, even with short dwell times, demands that extremely efficient, high-pressure, temperature-controlled cooling systems are used to prevent problems caused by differential expansion of tool parts or burning of components during manufacture. The cooling systems incorporate specially designed, multi-head spray nozzles, with pressure-regulated oil being circulated through the machining spindles to maintain a consistent temperature. The coolant systems also feature sophisticated centrifugal filtration, while extraction units ensure that all oil mist is removed safety from the machining areas.
Kiernan concludes: "The E-Tech machines are enabling us to move our precision grinding operation to a new level, in terms of speed, capacity, flexibility and accuracy. Alongside our overall engineering and cold forming services, this will play a vital role in helping us expand our business in high-technology export markets, especially in North America and the Far East."