In Jet Interferometry for Ultra Precise Electrolyte Jet Machining

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Ultra-precision machining techniques permit the manufacture of the most high value components. Component complexity continues to develop and researchers are challenged to remove smaller volumes of material in a more precise manner while maintaining work piece integrity. Micro-machining, micro electrical discharge/electrochemical machining and high speed laser processes are now commonly used for micro component manufacture for the microelectronics, biomedical and aerospace industries. Electrolyte Jet Machining (EJM) is a newer process which is yet to be embraced in a meaningful way by these industries. The process itself has several attractive capabilities, such as the ability to process difficult to machine materials with no resulting thermal loading of parts and no induced residual stress. A particularly interesting aspect of the technology is that, with simple modifications, the process may also run in reverse as an additive manufacturing technique to precisely deposit materials. The work to be undertaken here will make use of a custom built MkI prototype EJM tool at the University of Nottingham which was recently completed by the Investigators. As well as being able to perform material surface machining, this has unique capabilities and represents a significant advancement in terms of the state-of-the-art. The investigators have demonstrated a new functionality in terms of computer controlled signal generation which is capable of creating so called 'dial-up-surfaces' or surface manufacture against a specification for surface texture/morphology as opposed to surface roughness alone. Surface texture control within a machining process is notoriously difficult to achieve, commanding a premium price for high value components since surface condition often dictates performance. Typically, micro surface textures are of interest to several groups of researchers outside of engineering. These include biomedical researchers who study cell/surface interaction and aerodynamicists who look to enhance the performance of surfaces interacting with fluid flow. To unlock the full potential of EJM, novel on machine instrumentation must be created. This instrumentation must allow fast, accurate, high precision process data to be collected to support real-time adaptive process control. It should also allow for on-machine surface metrology to be undertaken which is increasingly an essential requirement for successful industrial processes. For EJM to be successfully exploited in both a research environment, and critically as a viable production technology this novel set of process instrumentation must be investigated and then developed to allow accurate and timely metrology to be undertaken on the machine while the process is under way. The instrumentation to be investigated here will be split into two key areas. Firstly, a novel form of in-jet laser interferometer will be designed and optimised for use with EJM. The sensor will provide high speed, high precision process control measurement data. This will allow the material removal rate of the process and the form of the material removal area directly in line with the jet to be measured. In addition a fibre optic arrangement will be included to allow beam delivery. Since stand-off distances are short within EJM this will be possible with a high brightness source (laser) to deliver a spot to the work piece. In addition to the in-jet laser two additional sensors will be deployed to the machine head, external to the jet. These will be custom designed single line coherence scanning interferometer devices, configured for single line based detection (to allow increased acquisition rates).These techniques will allow the collection of disparate data sets in real-time which will be manipulated through control algorithms to perform online processing and adaptive machining. This represents a step change in the viability of this process for the production of complex and high value parts.