Manufacture - Capillary drilling

Capillary drilling

Fig. 22-12 Typical automated manufacture of compressor blades.

36. Similar in process to stem drilling but using tubes produced from glass incorporating a core of platinum wire (cathode). A twenty per cent nitric acid solution is passed through the tube onto the workpiece and is capable of producing holes as small as 0.009 in. diameter. Depth of the hole is up to forty times greater than the tube in use and therefore determined by tube diameter.
37. Automation has also been added to the process of electro-chemical machining (E.C.M.) with the intro- duction of 360 degree E.G. machining of small compressor blades, ref. fig. 22-12. For some blades of shorter length airfoil, this technique is more cost effective than the finished shaped airfoil when using precision forging techniques. Blades produced by E.C.M. employ integrated vertical broaching machines which take pre-cut lengths of bar material, produce the blade root feature, such as a fir-tree, and then by using this as the location, fully E.C.M. from both sides to produce the thin airfoil section in one operation.