Research On A Flexible Roll Milling Technology Based On Multi-point Adjusting Methodology

Axial roll milling technology is a continuous local bulk forming process, It has a conical top die which moves around the centre of the workpiece(or drives the workpiece to revolve) when pressing it locally, and its lower die is almost the same with the one of conventional forging method. Multi-point adjusting technology is an advanced flexible manufacturing method which is mostly applied in sheet forming process. In this method, the conventional solid die is replaced by a series of discrete elements which can be called"element group", and the desired shape of the product is formed by the envelope surface of the"element group".Flexible roll milling is a new bulk forming method. It is based on axial roll milling and Multi-point adjusting technology, and belongs to a sort of flexible process. In this method, the conical top die of axial roll milling is replaced by continuous flexible roller. During the forming process, the flexible roller revoles in its own axis while pressing the blank, and the blank can be driven to rotate by the friction. The flexible roller is supported by a series of close packing control units on its top, and it can be shaped by adjusting these control units in order to forming various top surface of workpieces. It can be applied in the short or moderate-run production of workpieces which have revolving body, such as automobile jackshaft and bevel gear. FEM model has been established in this article in order to analyses its feasibility. The main content and results are as follows: 1. The finite element analysis for flexible roll millingThe article has finished modeling of flexible roll milling, and the stage model method has been chosen as the top roller's modeling solution., the definition has been given to mesh style of blank, material model, temperature of blank, friction factor, and the movement of the top roller and the bottom die. The article has run a simulation of a workpiece which has revolving paraboloid surface by using 9 and 16 controllers separately. And the results showed that more controllers leads to higher surface quality. The total axial load and each controller's load(including axial load and radial load) has been given. And by comparing the axial load with traditional die forging, the result indicates that the axial load of flexible roll milling is around 30 times smaller than that of traditional die forging, and typical axial roll milling method like rotary forging is only 5-20times smaller. By using the flow net and point tracing method, the flow in the workpiece has been analyzed. And the result shows that the direction of flow is opposite to the direction of the workpiece rotation. The edge of top surface is distorted against centre, the former flow slower than the later. The metal in blank side moves toward the blank edge and gathers during the forming process, And the surface metal moves a little faster than the lower metal.2. The defect analyses of the flexible roll millingSeveral defects are found in the simulation, including the distortion of the workpiece, the centric knob of the workpiece, the deviation of the workpiece, the surface impression, the insufficient filling in bottom die, the crack in edge and the non-uniform deforming of top and bottom(mushroom effect). The former three are mainly caused by unsuitable processing variables, including the problem of center alignment of the roller and the shape of the roller's tip, and can be avoided by suitable processing variables. But the latter four are unavoidable. The surface impression depends mainly on the number of the roller controllers, more controllers leads to slighter impression, and in real production the continuous roller will bring smooth surface; The problem of insufficient filling is very apparent while forming workpieces with complex bottom shape. In order to solve the problem, larger contact area between the roller and the blank and smaller friction factor of bottom die are suggested; the mushroom effect can be diminished by a rational blank shape, and the edge crack is related with the desired surface curve.3. The finite element analysis for improved method of flexible roll millingThe method of two flexible rollers type and cone-shaped flexible roller type has been brought forward. The two new method has some advantages than the normal single roller type, but both lead to higher costs and complexity of the equipment. This article has simulated the process of the two new type, and the result shows that the two rollers type improves the forming of the blank a little and the cone-shaped roller type improves a lot.4. The design of the flexible roll milling equipmentThe design of the top roller structure of corresponding equipment has also been presented in this article, and the preliminary structure of adjusting model, forming model and driving model has been illustrated. A detailed transmission plan has been given, and some critical components have been given the finite element analysis of structure strength and optimized.