Polishing of complex internal geometries

Abstract

This invention concerns improvements in the polishing of internal surfaces and structures of components, particularly components with a complex internal geometry. Embodiments of the invention use an alternating current electromagnet ( 48 ) driven by a signal generator ( 50 ) to constantly alter the rheology of the magnetorheological fluid ( 5 ). An improved magnetorheological fluid ( 25,30 ) is also disclosed.

1 . Apparatus for polishing the internal geometry of a component with magnetorheological fluid, the apparatus comprising an electromagnet and a signal generator to drive the electromagnet, wherein the signal generator generates an alternating current such that the electromagnet produces an alternating magnetic field. 
     
     
         2 . Apparatus according to  claim 1 , wherein the signal generator is adjustable to generate different wave shapes in the alternating current. 
     
     
         3 . Apparatus according to  claim 2 , wherein the signal generator is adjustable to generate different frequencies in the alternating current. 
     
     
         4 . Apparatus according to  claim 3 , wherein the signal generator is adjustable to generate different amplitudes in the alternating current. 
     
     
         5 . Apparatus according to  claim 1 , further comprising magnetorheological fluid comprising elongate polishing media units 
     
     
         6 . Apparatus according to  claim 5 , wherein the polishing media units comprise abrasive particles bonded to the outer surface of rod-shaped ferromagnetic components. 
     
     
         7 . Apparatus according to  claim 6 , wherein the abrasive particles comprise a ceramic grinding media. 
     
     
         8 . Apparatus according to  claim 1 , wherein a plurality of electromagnetic coils are formed around the outside of the component, at least two of the coils being arranged at a non-parallel angle to each other. 
     
     
         9 . Apparatus according to any of  claims 1 , wherein a plurality of pairs of electromagnets are provided separate from the component, the electromagnets within each pair being located at opposing sides of the component, and at least two of said pairs of electromagnets being arranged at non-parallel angles to each other. 
     
     
         10 . A magnetorheological fluid comprising a suspension of elongate ferromagnetic polishing media units having abrasive particles bonded to the outer surface of rod-shaped ferromagnetic components. 
     
     
         11 . A magnetorheological fluid according to  claim 10 , wherein the abrasive comprises a ceramic grinding media. 
     
     
         12 . A method of polishing the internal geometry of a component, the method comprising the steps of at least substantially filling an internal cavity of said component with a magnetorheological fluid and activating an electromagnet to apply a magnetic field to the magnetorheological fluid, wherein the electromagnet is powered by an alternating current such that it produces an alternating magnetic field to agitate the magnetorheological fluid. 
     
     
         13 . A method according to  claim 12 , further comprising altering one or more characteristics of the alternating current. 
     
     
         14 . A method according to  claim 13 , wherein the one or more characteristics is altered as an initial setup step before the magnetorheological fluid is agitated. 
     
     
         15 . A method according to  claim 13 , wherein the one or more characteristics is altered while the magnetorheological fluid is agitated. 
     
     
         16 . A method according to  claim 20 , wherein the wave form of the alternating current is varied. 
     
     
         17 . A method according to  claim 20 , wherein the frequency of the alternating current is varied. 
     
     
         18 . A method according to  claim 13 , wherein a plurality of electromagnetic coils are formed around the outside of the component, at least two of the coils being arranged at a non-parallel angle to each other, and wherein said non-parallel coils are powered sequentially. 
     
     
         19 . A method according to  claim 13 , wherein a plurality of pairs of electromagnets are provided separate from the component, the electromagnets within each pair being located at opposing sides of the component, and at least two of said pairs of electromagnets being arranged at non-parallel angles to each other, and wherein said non-parallel pairs of electromagnets are powered sequentially. 
     
     
         20 . A method according to any of  claims 19 , wherein the magnetorheological fluid comprises a suspension of elongate ferromagnetic polishing media units having abrasive particles bonded to the outer surface of rod-shaped ferromagnetic components.