Design of a portable device to inspect the shape of taper-lock holes

Drilling is one of the, if not THE most important machining operation within Airbus' assembly machining department. Per year, more than 110 million holes are being produced. A small portion of these holes need to be tapered, so-called taper-lock, in order to realise compressive stresses when fastening the bolts that go through them, thus achieving a beneficial stress distribution inside the workpiece material. The geometry of these tapered holes is very crucial, as it has to provide a perfect-fit seat for the tapered fastener. Any inconsistency in terms of its geometry or size would cause the taper-lock not sitting properly, resulting in unwanted stress concentrations within the material.

In order to avoid this, Airbus places a great deal of importance on the inspection of the tapered holes produced within their assembly machining departments. As the moment this is inspection is carried out using tapered plug gauges that exhibit the shape of the to-be-drilled hole and which are painted with engineering blue ink before the inspection of each hole. When pressed into the taper any irregularity of the hole is identifiable by a non-uniform pick up of the engineering blue ink from the gauge onto the hole. Since this entire inspection routine is carried out manually, i.e. both the engineering blue is applied to the gauge and then the gauge is pressed into the tapered hole by hand, and the assessment of the engineering blue coverage of the hole taper is determined visually by the operator, the entire inspection procedure is subject to variation. Moreover, it is rather time consuming and costly. As a result, Airbus are keen to replace the traditional inspection procedure using painted plug gauges by a more sophisticated means, and are therefore extremely keen on introducing a portable device with which this inspection can be carried out in the futures.

The aim of this project is to design, develop, build and extensively test a portable device with which Airbus can inspect ('reverse engineer') small diameter long depth tapered holes (taper-lock). This will be achieved by addressing the following objectives:
Literature review to establish the current knowledge and state-of-the-art in inspection of hole geometries, in particular tapers.
Creation of the list of specifications for the novel device, i.e. hole sizes-geometries that need to be inspected, handling constraints, accuracy requirements, definition of testing routines.
Collation of design ideas with subsequent evaluation and identification of the most promising one. This will include both hardware, i.e. how the actual hole geometry can be ascertained ("scanned"), and software, i.e. how to process the obtained data in order to acquire information about the quality of
Building of a prototype system, followed by extensive testing of this prototype.
Refinement of the design to incorporate modifications addressing shortcomings revealed during the test phase.
Further testing of refined prototype, and final verification of its capability and overall feasibility.

It is envisaged to produce a fully-working prototype of the portable taper-lock inspection device within the course of this PhD research project in order to demonstrate the feasibility. This can, in collaboration with a suitable manufacturer, then be further developed into a marketable product in a reasonable time frame beyond this research project.