Patent GB-617607-A (GB)
Abstract: 617,607. Milling impeller wheels. VLIEG, C. B. DE. Dec. 20, 1945, No. 34633. [Class 83 (iii)] [Also in Group XXXVII] In a method and apparatus for forming the vanes on the inducer portion 30, Fig. 1, of a supercharger impeller, a blank, indexably mounted on a workholder 49, Figs. 14 and 15, is rotated about the axis of the work spindle 48 so that it is fed against a rotating cutter 40 whose cutting side is parallel with but offset from the work spindle axis, and the blank is indexed to locate each vane structure in succession at a cutting station. The curve of the vanes is modified by feeding the cutter head 42 transversely by means of a rotating cam 46, and the root surfaces between the vanes are tapered by feeding the work spindle along its axis by means of a face cam 54. The entrance edges of the vanes may be finished to a feather edge by a concave cutter in a machine as described in Specification 590,788. The electrical control and circuits of the driving motors are described, (see Group XXXVII). Cutter head. The cutter head 42, Figs. 15 and 24, carries a motor 44 for the cutter spindle, and is angularly adjustable on a slide 45 mounted on guides 64, 65 for longitudinal and transverse movement on the base 41. The slide 45 is urged transversely by a spring 82 to maintain a roller 76, adjustable by a micrometer screw 81, in contact with the cam 46, which is rotated in synchronism with the feed movement of the work spindle by a shaft 55. Work head. The work head 47, Figs. 15, 16 and 19, is mounted on guides for longitudinal movement on the base and is traversed towards the cutter preparatory to the milling operation by a screw 51 which is rotated either manually by a shaft 89 or a reversible motor 52. At the forward limit of this traverse, the head is looked in position by the engagement of taper blocks 92, 94. A two-speed motor 53, carried by the head drives through worm-type reduction gearing a shaft 119 on which a long pinion 121 meshes with a gear 122 on the work spindle 48 and a gear 123 on the cam-shaft 55. The work spindle is urged towards the cutter by a spring 125 under the control of a face cam 54 acting on a roller 124. The workholder 49 is secured to the spindle by a split clamp 103 and has a face 105 parallel with the spindle axis on which the blank is indexably secured by a centre post 106 and nut 108, the centre post being offset from the axis of the spindle. An indexing stop 111 is provided on the work holder. Operation. For the first operation of rough milling the front face of the vanes, the cutter head is set up so that the cutter 40A, Figs. 3 and 29, is intermediate the plane J through the work centre and the plane K containing the axis of rotation of the work spindle, with its cutting edge in a plane M parallel to planes K and J, the distance between the planes M, J being sufficient to leave stock for the finishing cut. The motor 52 rapidly traverses the work up to the cutter, and a switch LS2A operated by a trip 131, Fig. 15, on the work head energizes the motor 53 to rotate the work spindle so that the blank is rotated clockwise into the cutter about the axis K, and, at the same time, the cutter head is fed transversely by the cam 46 to modify the arcuate shape of the vanes. Owing to the close spacing of the vanes, the cut is terminated short of the opposite end of the blank. Trips 132, 133, Fig. 16, on the cam 54 operate switches to control the forward slow feed and rapid reverse feed and the return traverse of the work to the start position ; at the end of the rapid reverse feed, the kinetic energy of the moving parts carries the work beyond its initial setting but the motor is controlled (see Group XXXVII), to rotate again in the forward direction for sufficient time to return the work exactly to its initial setting. The blank is then indexed to repeat the roughing cut for each vane structure, the stop 111 engaging notches 120 in the blank. For the second operation of rough milling the rear face of the vane, the cutter 40B, Figs. 5 and 30, is set up, preferably in another machine, with its cutting edge parallel to the plane J, but on the opposite side from the first position at a distance corresponding to the distance between the planes M, J. The feed movement is counterclockwise and cuts are made in succession similarly to the first cut. Two finishing cuts are made similarly to the roughing cuts, the cutter edges being spaced from the plane J a distance which will give the desired vane thickness ; a formula for determining this distance is given. For the roughing cuts, the cam 54 has a plain face so that there is no axial feed of the work spindle, but, for the finishing cuts, it has a stepped face to provide this feed and give the taper to the root surfaces 37, Fig. 1, between the blades. In all four operations, the cutter rotates in a direction for climb-milling.