Process for the manufacture of piezoceramic multilayer actuators

Abstract

For the manufacture of multilayer actuators, the laminate is split into several actuators, which are pyrolized and then sintered. Because lamination in the unsintered body often produces non-homogeneity in the density, and the shrinkage during the firing of the ceramic is not of a constant value, the final geometry of the actuators can only be accurately obtained by the hardening of the sintered actuators. But in this case the internal electrode layers deposited in the actuators are thereby also processed, which can cause electrical flashovers and leakage currents during operation. Thus, according to the invention, a procedure is provided in which the block of the stacked green films provided with internal electrodes is laminated, that at least one actuator is separated from the block, that the actuator obtains its shape by means of a machining operation, that it is then sintered, that the sinter skin produced by the sintering is used as an insulating layer and that the sinter skin is abraded at the points where the internal electrodes are connected to the external electrodes.

1 . Process for the manufacture of piezoelectric multilayer actuators, in which thin layers made from a piezoceramic material, termed green films, onto which at least one internal electrode is placed, are stacked one above the other into a block, so that the internal electrodes are led out alternately at opposing faces of the actuator, where they are interconnected by an external electrode, characterised in that the block is laminated, that at least one actuator is separated from this block, that the actuator obtains its shape by means of a machining operation, that it is then sintered, that the sinter skin produced by the sintering is used as an insulating layer and that the sinter skin is abraded at the points where the internal electrodes are connected to the external electrodes.  
     
     
         2 . Process according to  claim 1 , characterised in that the shaping is achieved by machining.  
     
     
         3 . Process according to  claim 1  or  2 , characterised in that multilayer actuators, which have square, polygonal, circular or elliptical cross-sectional areas, are produced by the shaping.  
     
     
         4 . Process according to  claim 1  or  2 , characterised in that rotationally symmetric multilayer actuators are produced by the shaping.  
     
     
         5 . Process according to one of  claims 1  to  4 , characterised in that one or more through-holes or pocket holes are introduced into the laminated block of at least one multilayer actuator.  
     
     
         6 . Process according to one of  claims 1  to  4 , characterised in that prior to lamination, holes of the required size, shape and number are punched in the green films and the green films provided with the internal electrodes are then stacked one on top of the other in the required number and arrangement, so that the boreholes or pocket holes are produced in the desired arrangement and depth.  
     
     
         7 . Process according to one of claims  5  or  6 , characterised in that a thread is machine-cut in the boreholes or in the pocket holes, respectively.  
     
     
         8 . Process according to one of  claims 5  to  7 , characterised in that to increase stability and to maintain dimensional accuracy, the borehole or the pocket holes in the multilayer actuators can be filled prior to lamination with a filler.  
     
     
         9 . Process according to  claim 8 , characterised in that a hard, dimensionally stable and, during lamination, thermally stable material, is used as a filler.  
     
     
         10 . Process according to  claim 8  or  9 , characterised in that a filler made from metal or ceramic or another hard, dimensionally stable and, during lamination, thermally stable, material is used.  
     
     
         11 . Process according to  claim 8 , characterised in that a plastic or thermoplastic material is used as a filler.  
     
     
         12 . Process according to  claim 11 , characterised in that a highly-flexible rubber or a rubber-like plastic is used.  
     
     
         13 . Process according to one of  claims 8  to  12 , characterised in that the filler is used in the form of pins or threaded pins.  
     
     
         14 . Process according to  claim 13 , characterised in that following lamination, the pins or threaded pins are withdrawn or unscrewed from the laminate.  
     
     
         15 . Process according to  claim 8 , characterised in that a filler is used that remains dimensionally stable approximately up to the lamination temperature and is thermally removed.  
     
     
         16 . Process according to  claim 15 , characterised in that a wax or a low-melting-point polymer is used as a filler, and that these fillers smelt during lamination or sintering.  
     
     
         17 . Process according to  claim 15 , characterised in that a suitable organic material that pyrolizes without residues during lamination or sintering is used as a filler.  
     
     
         18 . Process according to  claim 15 , characterised in that the thermal removal is achieved by smelting and/or thermal decomposition in a thermal process preceding sintering, for example an appropriate debonding process.