Tuesday 2 December 08 - 04:46
 

CNC Machining

'Burr-Free' Standards Need Thermal Process

Companies, using state of the art multi-axis CNC precision machinery, repeatedly produce complex components to extremely tight tolerances, yet still deburr by hand. “Parts now take seconds to produce but minutes to deburr”, complains a client of specialist thermal deburrers, the Deburring Centre Ltd, Dorset.

Deburring by hand introduces variations, surface damage and errors. The ambiguous existing industrial standard of 'deburr all edges' is no longer accepted.

Drawings now often specify a size that is acceptable, for example: Deburr to 10x magnification. Components with safety critical applications, including the hydraulic, medical, and auto industries, set their standard by specifying 'this part must be thermally deburred'.

Thermal deburring is a non selective process which can guarantee the removal of all potentially loose pieces and contaminants. The process surrounds the components with a mixture of natural gas and oxygen in a sealed chamber. The gas permeates every hole, flows over every edge and covers every burr. This mixture is then ignited and the resultant heatwave which lasts for 20 milliseconds is enough to vapourise the burrs but insufficient to affect the component's metallurgy. The burrs because of their relative large surface area to mass ratio are unable to dissipate heat. Their temperature passes their ignition point and they burst into flames, oxidising in the oxygen rich atmosphere. The oxide settles on surfaces as a light powder which can be  easily washed.

The process is fast, with multiple components capable of being fired together with machine cycle times of 30-120 seconds. Computerised controlled conditions mean that every component, run and batch are consistent. No surfaces are touched, scratched, scraped or damaged. And because the process is non selective - every, burr is removed.

www.deburr.co.uk

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Deburring Centre Ltd

Stevens Rowsell is a specialist precision sheet metal engineering company in East Sussex