Combined EDM and ultrasonic drilling
AssigneesROLLS-ROYCE plc, Spark Tec Limited
InventorsJames R. Watkins, Mohamed F. El-Menshawy
Life of this patent
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Abstract
To drill small holes in a metal component having a non-conductive, e.g. ceramic, surface layer apparatus is provided capable of carrying out both ultrasonic and EDM drilling operations without dismounting the component. The drilling operation commences with an ultrasonic drilling phase and change over to essentially EDM operation when breakthrough of the ceramic surface layer is detected. Breakthrough is detected by applying a low voltage pulse signal to a drilling electrode and sensing when current starts to flow between the electrode and the workpiece. When a multiplicity of holes are drilled simultaneously the changeover to EDM is triggered by breakthrough of the first electrode but may be delayed to permit the remaining electrodes to breakthrough.
Claims24
An apparatus electro discharge machining a small hole in an electricall conductive workpiece having a substantially non-conductive surface, comprising EDM electrode means the position of which relative to the workpiece is adjustable to form a machining gap, dielectric supply means for supplying dielectric fluid into the region of the machining gap, power supply means connected in use between the electrode means and the workpiece and arranged when operative to produce machining pulses for electro-discharge machining through the conductive workpiece, ultrasonic means for imparting to the electrode means ultrasonic vibrartions in an axial direction for ultrasonically machining through the non-conductive layer, control means for sequencing the ultrasonic and EDM maching operations in separate phases, and detection means responsive to establishment of electrical continuity between the EDM electrode means and the conductive substrate to commence the electro-discharge machining phase of the conductive workpiece after breakthrough of the non-conductive layer is detected in the ultrasonic machining phase.
A method of forming at least one small hole in an electrically conductive workpiece having a substantially electrically non-conductive surface layer, comprising two sequential phases of operation wherein in a first phase an electrode is used to form a hole in the non-conductive surface layer by ultrasonic drilling and in a second phase the electrode is used to extend the hole through the conductive workpiece by EDM machining, commencement of EDM machining in the second phase being dependent upon detection of breakthrough of the non-conductive surface layer during the first phase ultrasonic drilling.
Dependencies are inferred from the claim text.