BUE is a common problem in high speed machining and occurs when material from the work piece welds onto the rake face of the tool during the shearing process. It is partly caused by the material’s high affinity to the carbide or by edge crumbling.
Certain types of steels and stainless steels, aluminium, nickel and titanium based materials are more susceptible to BUE. This can result in premature edge failure and poor surface finish.
High spindle speeds can exacerbate the problem, but cutting performance can be controlled by choosing the right cutting tool and strategising cutting parameters. By combining proper cutting data, the right type of cooling media, machining strategy and suitable geometry or coating, BUE can be overcome.
It is also important to achieve a correct temperature in the shearing zone so there is a proper undisturbed chip flow. Temperature can be made consistent by ensuring constant axial and radial engagement and fine tuning the cutting speed/feed.
In terms of cooling media, water with 5 to 10% oil mixture can be used, but mist lubrication with air-oil mixture can offer a better greasing effect to reduce the risk fo thermal shocks on carbide tools. Air blow function removes chips but has no cooling effect.
According to Walter, its Protostar Ti-40 end mill has advanced micro/macro geometries and an CAN coating to increase metal removal rate and secure undisturbed chip flow.
The company’s PVD-Alox coating A12O3 can also be used in indexable tools. This coating is said to have good chemical resistance and low friction behaviour to allow higher cutting data and reduced BUE.