In Jet Interferometry for Ultra Precise Electrolyte Jet Machining

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.

The impact of this project will be felt in the development of a new manufacturing capability built upon Electrolyte Jet Machining. The development of new instrumentation will unlock new potential in this area. Enhanced capability will be first utilised as part of this project for collaboration with researchers outside of engineering who seek to enhance surface performance in both bioengineering and chemical processing. Furthermore industrial partners who have engaged in this project range from technology users (Precision Micro and Rolls-Royce) through to metrology machine makers (Taylor Hobson). Naturally work undertaken here will also contribute directly to the global research community within non-conventional machining, and optical metrology.

The domestic industrial and research need is significant. Augmentation of the EJM process is likely to have critical impact in industrial sectors of biomedical implants and aeroengine manufacture, stalwarts of the UK economy. Both areas make use of highly resistant engineering materials whose performance in service is safety critical. For this reason many thermal manufacturing processes (laser, EDM etc) cannot be used. Hence alternatives for precision finishing are essential. Furthermore, there are several key areas of interest (stay clean surface, expedited bone ingress) for which structured surfaces may enhance component performance in service. However, all processes used to create these must be validated. With the development of the instrumentation proposed here the way will be paved for EJM to be explored for these applications.

Industrial impact and pathway development will be achieved by a series of seminar sessions for which funding has been requested in this project. These will permit project partners and invitees external to project to receive a demonstration of this machining technique and the underpinning instrumentation. Funding has also been requested to allow the investigators to produce a series of specimens and provide accompanying process and metrology data as part of this activity. By targeting researchers from disciplines outside of engineering it is expected that highly interdisciplinary follow on activity will emerge from the final stages of this project. Between industrial collaboration and research facilitation there are a range of short term through to longer term impact routes associated with this project.

Reach into the academic community will be addressed through tradition routes of journal publication and disseminations at recognised international conferences. Efforts will be made to see that dissemination also takes place beyond traditional manufacturing outlets to ensure that exposure of the outputs from the project is maximised.