Research On Flexible Bending Technology For 3-D Surface

The 3-D surface flexible bending technology is a novel method for sheet metal flexible forming. Its basic principle is that sheet metal can be formed by continue local way through the curve of changeable curvature which is composed of several short rollers with highly adjustable, revolving and asway ability themselves and then through short rollers'press displacement and friction between rollers and sheet metal. Sheet metal can be formed by the curve which is composed of adjustable rollers according to the needed workpiece's shape through this technology which is considered as the combined technology between multi-point forming and traditional bending. Along with the development of industry, many industry domains such as avigation, shipbuilding, chemical industry and boiler industry, whose requirements for 3-D surface part is largeness, diversification and speediness, therefore, a forming technology for 3-D surface part with the characteristics of shortcut, high quality, low cost, flexible ability and intellectualized ability is demanded urgently. The 3-D surface flexible bending technology is brought forward depending on such background, which has the characteristics such as dieless forming ability, low cost, simple equipment, flexible ability, high efficiency, continuous manufacture and automatization.Research of 3-D surface flexible bending technology is focused on two aspects which are design of 3-D surface flexible bending prototype and numerical simulation on 3-D surface flexible bending process. The main contents and results of the research are as follows:1. Discussion for the basic process and form of 3-D surface flexible bending technology.The basic process of 3-D surface flexible bending can be summarized as: firstly, adjusting the positions of the short rollers to form the curve with needed curvature according to the shape of workpiece; secondly, supplying certain press displacement for up short rollers and driving the short rollers; finally, sheet metal is continuous local formed by friction between rollers and sheet metal. The basic form of 3-D surface flexible bending can be summarized as two kinds which are the form of short rollers'equivalent rotate speed and the form of short rollers'different rotate speed. The former form can manufacture sphericity part, saddle part, twisty part and so on. The latter form has certain revolve press ability, which can manufacture dished part. From the basic process and form of 3-D surface flexible bending, the technology is considered as a linear, continuous and local forming technology, therefore, it has the characteristics of high efficiency, continuous and flexible ability.2. Design of 3-D surface flexible bending prototypeThe prototype's whole design project has been brought forward. The thinking of the design is that dividing the prototype into many same working cells. Every working cell is a suit of independent machine. Working cell is composed of short roller, asway machine and adjusting machine. Working cell is the key design content. Short roller is designed by putting the driving equipment into its inner, this design can enhance short roller's flexibility. Asway machine is designed by tailor-made pin, this design is simple, practical and has strong carrying capability. Adjusting machine is designed by slip screw transmission machine, this design has the characteristics of simple structure, convenient manufacture, low cost, running stability, locking itself easily and high adjusting precision. The design principle of working cell is minishing the dimension of parts in the premise of satisfying intensity and space dimension's demand, the purpose of doing this is minishing the working cell's dimension to the greatest extent in order to making the prototype more flexibility.3. Finite element analysis of prototype's key parts and movement imitation of working cellAfter designing the prototype, some key parts are needed to be checked and optimized. These key parts including short roller's rotate shaft, asway machine's pin and adjusting machine's nut are analyzed by finite element method. The analytical results are as follows: Three parts have enough intensity to satisfy the demand of design. The dimension of shaft and pin can be optimized. Working cell is a key component, after its design, its movement state is needed to be observed. Working cell's movement state is imitated by movement analytical module of CATIA. The imitation result is the same as prospective state.4. Establishment of FEA model of 3-D surface flexible bending processUsing LS-DYNA explicit dynamical analysis method, choosing BWCalgorithmic cell-SHELL 163, analyzing non-linear inelastic material model, confirming boundary conditions, short roller's virtual rotate speed and local coordinate according to the principle of 3-D surface flexible bending process, establishing the FEA model for the first time and giving the sphericity part's and saddle part's FEA models.5. Numerical simulation on 3-D surface flexible bending processTaking sphericity part's and saddle part's forming process for example, doing the research of the stress's and strain's distributing of 3-D surface flexible bending process, getting the conclusions as follows: The distributing of equivalent stress is asymmetry, equivalent stress is higher than yield stress in the forming zone and lower than yield stress in the springback zone and formed zone. When forming the 3-D surface part with same formed degree, the forming force of 3-D flexible bending is lower than the one of die forming. Taking sphericity part and saddle part for example, doing some research of the impact of the up short rollers'press displacement, sheet thickness and material to the processing, the result are summarized as follows: The trend of action force is firstly raising, then calm, finally descending. Along with the increasing of press displacement, the action force between short roller and sheet metal is increasing, the curvature of workpiece is also increasing and very sensitivity to the press displacement; along with the increasing of sheet thickness, the action force between short roller and sheet metal is increasing, sheet metal's forming effect is better and better, crinkly phenomena is less and less; when the sheet thickness and formed degree are same, steel sheet metal's forming effect is better than aluminum sheet metal, the action force between steel sheet metal and short roller is larger than the one between aluminum sheet metal and short roller.