Planet Carrier And A Process And Apparatus To Manufacture It

Abstract

The present invention is directed to an integral planet carrier with no joints, a method of manufacturing it and an apparatus for doing so. Such integrally manufactured components have better strength than a conventionally produced multi-piece jointed planet carriers or integral planet carriers made from casting process. The present invention provides a hot forging process which can be used for the manufacturing of the planet carrier. The manufacturing process comprises of forward extrusion of a billet followed by backward extrusion. This is followed by bending operation, which is in turn followed by a flattening operation. Post-forging heat treatment and other treatments such as shot blasting follow. Finally machining is carried out to arrive at the final integrally formed planet carrier. The forward extrusion, backward extrusion, bending and flattening operations are done on a press or hammer having sufficient energy and load capacity. Preferably these operations are performed on a hydraulic press in order to achieve the required accuracy and precision.

1 . A planet carrier, characterised in that said planet carrier is an integral planet carrier ( 7 D), devoid of joints and is made using hot forging, said planet carrier ( 1 ) comprising a cylindrical part or a head ( 7 B) which has a flattened part ( 7 A), and a shaft ( 5 B), and wherein sections of said planet carrier ( 1 ) are carved out and machined to produce a final integral planet carrier ( 7 D). 
     
     
         2 . A planet carrier as claimed in  claim 1  characterised in that it has continuous grain flow lines. 
     
     
         3 . A process of making an integral planet carrier ( 7 D), characterised in that said process comprises the steps of:
 heating of a billet to produce a heated billet;   forward extruding said heated billet to produce a first preform ( 4 ) having a head ( 4 A) and a shaft ( 4 B);   backward extruding said first preform ( 4 ) to produce a second preform ( 5 ) having a walled hollow part ( 5 A) and a shaft ( 5 B);   ensuring that the temperature of the second preform ( 5 ) is maintained at or above a minimum forging temperature;   bending or deforming walled hollow part ( 5 A) of said second preform ( 5 ) to produce a third preform ( 6 ) having a head with a bent or deformed or a tilted wall portion;   flattening said bent or deformed or tilted wall portion to produce a hot forged integral planet carrier having a head ( 7 B) with a flattened part ( 7 A);   heat treating said hot forged integral planet carrier ( 7 ) having a flattened head ( 7 A) followed by shot blasting it to produce treated integral planet carrier ( 7 C);   machining of said treated integral planet carrier ( 7 C) to produce final integral planet carrier ( 7 D);   said process thus leading to an integrally formed planet carrier ( 7 D).   
     
     
         4 . A process as claimed in  claim 3 , characterised in that in the step of heating, said billet is heated in a furnace to a temperature of 1150 to 1280° C. 
     
     
         5 . A process as claimed in  claim 3 , characterised in that said forward extruding step is carried out at a forward extrusion station using a combination of a forward-extrusion-top-die (FT) and a bottom die (FB), wherein said heated billet is placed on said bottom die (FB) aligned concentrically along the central longitudinal axis of said forward-extrusion-top-die (FT) and said forward extrusion top die (FT) is moved axially and concentrically towards the said heated billet till said first preform ( 4 ) is produced which has a solid upper cylindrical section or a head ( 4 A), and a lower cylindrical section or a shaft ( 4 B), wherein the diameter of the head ( 4  A) portion is larger than that of the shaft ( 4 B). 
     
     
         6 . A process as claimed in  claim 3 , characterised in that said backward extruding step is carried out in an hydraulic press using a combination of a backward-extrusion-top-die (BT) and a backward extrusion bottom die (BB), wherein the side surface of the backward extrusion top die (BT) is recessed circumferentially from its bottom face up to a length (L 1 ) thereby creating a recess or gap (R 1 ) between said side surface and the internal face of the upper cavity of said backward extrusion bottom die (BB), and wherein material of said head ( 4 A) flows into said gap (R 1 ) under the force applied by the movement of said backward-extrusion-top-die (BT) to produce a walled hollow part ( 5 A) having an open end as a part of said second preform ( 5 ). 
     
     
         7 . A process as claimed in  claim 3 , characterised in that in the step of ensuring that said second preform ( 5 ) remains over a minimum forging temperature, second preform ( 5 ) is heated if its temperature falls below said minimum forging temperature, heating being carried out preferably to a temperature between 1150 and 1280° C. 
     
     
         8 . A process as claimed in  claim 3 , characterised in that said bending step to produce said third preform ( 6 ) is carried out on a forging equipment, preferably a hydraulic press using a bending top die (DT) and a bending bottom die (DB), wherein when the second preform ( 5 ) or heated second preform ( 5 ), as the case may be, is placed on said bending bottom die (DB), such that there is a projection of said walled hollow part ( 5  A) that projects above the top surface of said bending bottom die (DB). 
     
     
         9 . A process as claimed in  claim 8 , characterised in that said bending top die (DT) has an internal cavity of conical shape with a surface that is inclined at an angle with respect to the central longitudinal axis of said second preform ( 5 ). 
     
     
         10 . A process as claimed in  claim 8 , characterised in that said angle is less than 90 degrees. 
     
     
         11 . A process as claimed in  claim 8 , characterised in that said angle is between 15 and 55 degrees. 
     
     
         12 . A process as claimed in  claim 8 , characterised in that the length of projection is 20% to 70% of the external length of said walled hollow part ( 5 A). 
     
     
         13 . A process as claimed in  claim 8 , characterised in that said bending-top-die (DT) is pushed towards the second preform ( 5 ) until said projection is substantially within said conical cavity, thereby forming a third preform ( 6 ) that has said bent or tilted wall portion. 
     
     
         14 . A process as claimed in  claim 3 , characterised in that said flattening operation performed on said bent or tilted wall portion of said third preform ( 6 ) is carried out using the same bottom die as used in said bending step, and wherein a flattening top die (FLT) having an annular or ring shaped cavity is used for carrying out the flattening of said tilted wall portion to produce a hot-forged integral planet carrier ( 7 ). 
     
     
         15 . A process as claimed in  claim 3 , characterised in that said hot-forged integral planet carrier ( 7 ) is heat treated and subjected to post-forging treatments such as shot-blasting to produce a treated integral planet carrier ( 7 C). 
     
     
         16 . A process as claimed in  claim 3 , characterised in that said treated integral planet carrier ( 7 C) is machined to produce a final integral planet carrier ( 7 D). 
     
     
         17 . A process as claimed in  claim 3 , characterised in that said minimum forging temperature is 900° C. 
     
     
         18 . A process as claimed in  claim 3 , characterised in that in the step of ensuring that said second preform remains over a minimum forging temperature, the walled hollow part ( 5 A) of said second preform ( 5 ) is heated if the temperature of said second preform ( 5 ) falls below said minimum forging temperature, heating being carried out preferably to a temperature between 1150 and 1280° C. 
     
     
         19 . A hot forging apparatus to make a planet carrier ( 7 D), characterised in that said apparatus comprises the following tools placed sequentially:
 a billet heating station for heating said billet;   a forward extrusion station to forward extrude said billet into said first preform ( 4 );   a backward extrusion station to backward extrude said first preform ( 4 ) into said second preform ( 5 );   a bending station to deform said walled hollow part ( 5  A) of said second preform ( 5 ) to produce a third preform ( 6 ) having a deformed or bent or tilted walled hollow part;   a flattening station for flattening said deformed or bent or tilted walled hollow part to produce said as-forged integral planet carrier ( 7 );   a heat treatment and post-forging treatment station for treating said as-forged integral planet carrier into a treated integral planet carrier ( 7 C); a machining station to machine said treated integral planet carrier ( 7 C) into said final integral planet carrier ( 7 D).   
     
     
         20 . A hot forging apparatus as claimed in  claim 19 , characterised in that said bending station comprises a forging equipment, preferably a hydraulic press, in which are placed a bending top die (DT) and a bending bottom die (DB), both dies placed co-axially, and wherein said bending top die (DT) has a conical cavity that faces said bending bottom die (DB), wherein when said second preform ( 5 ) is placed on said bending bottom die (DB), said bending top die (DT) is capable of moving towards said bending bottom die (DB) so as to accommodate the projection of said second preform ( 5 ). 
     
     
         21 . A hot forging apparatus as claimed in  claim 19 , characterised in that surface of said conical cavity has an angle less than 90 degrees when measured from its central longitudinal axis. 
     
     
         22 . A hot forging apparatus as claimed in  claim 19 , characterised in that said angle is between 15 and 55 degrees. 
     
     
         23 . A hot forging apparatus as claimed in  claim 19 , characterised in that said flattening station has a flattening top die (FLT) having an annular second recess or a ring shaped cavity. 
     
     
         24 . A hot forging apparatus as claimed in  claim 19 , wherein a heating station is provided between said backward extrusion station and said bending station for heating said second preform ( 5 ).