Patent of the month: Post-synthesis processing of super-hard materials

Materials World magazine
,
1 Mar 2017

Dr Jennifer Unsworth of intellectual property firm Withers & Rogers describes a novel lapping technique. 

With millions of tools produced every year to meet the demands of global engineering and manufacturing, tooling is a giant industry that relies particularly on the hardest materials available. 

Materials classified as super-hard exhibit a Vickers hardness of at least 2000kg/mm2, diamond being a common example. The super-hard nature of these materials makes them particularly suitable for application in tools and tool coatings. 

But although they are incredibly hard, they are far from indestructible. In fact, many super-hard materials can be surprisingly brittle and lack toughness. This poses a number of challenges when performing post-synthesis processing operations, such as cutting, lapping and polishing materials of this type, as any processing techniques for super-hard materials must conform to an extremely narrow set of constraints.

Element Six Technologies Limited is an international player in the field of processing technology and has been processing synthetic diamond for over 50 years. The company has recently patented a novel lapping method for processing super-hard materials. Its UK patent (GB2522982) was granted on 18 October 2016 and can be found at bit.ly/2ll2Ori.

Lapping involves placing an abrasive material (see Figures, A) between two bodies (B and C), before moving the two bodies relative to one another. This causes material to be removed from one of the bodies (100). The key feature of Element Six's innovative method is the use of two discrete processing periods during the lapping process. 

The first processing period involves applying a loading force (D) to a non-central location of the product. Unprocessed materials often exhibit a non-uniform thickness, so the application of the loading force centres on the thickest material region in order to focus material removal at this location.

The second processing period, which occurs during the final stages of the lapping operation, involves centralising and reducing the loading force (E) applied to the product. This reduces damage to the material caused by the lapping process and also prevents edge rounding.

Due to the high-quality finish that its method is able to achieve, Element Six has found that it can eliminate subsequent lapping operations with finer grit sizes. Not only does the removal of this processing step optimise process efficiency, enabling Element Six to increase its product output – it also greatly reduces processing costs, as fewer abrasives are used.