Production Processes Group

- research into manufacturing technology

Bill O'Neill - Current Research

Cold Gas Dynamic Manufacturing

The IFM at Cambridge University has an active research programme for the research and development of free-form-fabricated metal components. The technology relies on the principal of cold gas dynamic spraying (CGDS). In principle CGDS involves high-pressure, high-flow rate gas, heated to relatively low temperatures (150^o-600^oC). By using a converging/diverging nozzle, the gas stream - and any powder entrained into it - is accelerated to velocities in excess of 500-1000m/s. As the particles hit the target surface, they impact and consolidate, producing localised forge bonding. The metallic coatings have a porosity of just 0.5-5%, and are unaffected by high-temperature reactions like oxidation and carburisation. Moreover, the 'cold' deposition process ensures that no potentially detrimental, thermally-induced micro structural transformations occur during deposition.

High Speed Laser Cutting

This programme examines the fluid dynamics of melt ejection and thermodynamics of melt production in an attempt to gain further insight into the performance of conventional laser cutting systems. The overall objective of the project is to increase laser cutting speeds through theoretical and experimental research studies. At present cutting speeds of 40m/min have been achieved on 1mm mild steel plates operating with 2.75kW of CO₂ laser power

Ultrafast Laser Processing

Absorption of ultra-short laser pulses takes place on a timescale much shorter than energy transfer of excited electrons to the lattice atoms (typically a few ps). The result is the creation of a highly ionised surface layer (plasma) at near solid density. Surface melting can virtually be eliminated along with plasma shielding, which takes place in typical nanosecond laser ablation. Hence, femtosecond laser ablation can yield precise materials processing resulting from efficient energy deposition while simultaneously minimising heat conduction and thermal damage to surrounding material. Focussed intensities >10¹³ W/cm² are easily obtained with micro-joule pulses and the processing of, for example, normally transparent dielectrics can be achieved thro' multi-photon absorption. We are studying Femtosecond laser ablation in a range of materials (e.g. metals, ceramics, polymers, glasses) to improve the understanding of ultra short laser materials interactions with a view to applying this new processing regime in a wide range of manufacturing applications

Supersonic Laser Drilling

This programme examines the fluid dynamics of melt ejection during conventional laser drilling whilst operating with sonic and supersonic jet streams. CFD and empirical analysis of high brightness laser drilling has identified a dynamic instability of melt ejection caused by the non-linear interaction of the incoming and outgoing gas fields. Current results have suggested that significant improvements in drilling rates and hole quality can be achieved through the implementation of tailored supersonic jet streams.