2017 2nd International Conference on Electrical and Electronics: Techniques and Applications (EETA 2017) ISBN: 978-1-60595-416-5

Deformation and Defects in Hydroforming of Stainless Steel Ripple Plate with Controllable Corrugated Quantity and Depth

Shao-hua WANG*, Bo WANG, Ai-jun XU, Chao CUI, Xin LIU and Zhuo-xun YI Beijing Spacecraftes, Beijing 100194, China

Keywords: Hydro-forming, Ripple plate, Corrugated quantity and depth, deployable structure.

Abstract. Hydro-forming can effectively solve the forming problem of complicated components. Aiming at the difficulty of stamping problem and poor forming quality for an aerospace deployable structure with ripple characteristics, hydro forming process is designed by analyzing deformation and defects. Combined with numerical simulation, defects of punch round corner region during hydro-forming are studied. Cavity pressure loading path, blank holder gap, corrugated quantity and depth are also optimized. The results show in the process the punch round corner is the weakest region, wrinkles will particular appeared in the blank holder zone. The corrugated quantity is in inverse proportion to the corrugated depth. In this paper, the finite Element Analysis model of corrugated quantity and depth is presented and calculated by the Dynaform program. This work is of directive significance to the optimal design and operation of ripple plate forming.

Introduction Hydro-forming is one kind of flexible forming, illustrated in Fig.I. The geometrical shape of the final product is determined mainly by the design of the punch. The die is just an easy design cavity. There is Fluid medium sealed in a die cavity which will be pressurized to shape the blank. When the punch move close to the die cavity, the blank is forced down and pressured up by the liquid in the die cavity[1-3].

Figure 1. Schematic drawing of hydroforming process. The liquid like oil or water will be high pressurized which will transmit energy to the blank and shaped with the punch. The limit drawing ratio (LDR) value of sheet metal can be greatly improved and there are less worn out of the product’s surface with high dimensional accuracy. hydroforming is one kind of new sheet forming technology which can be used in the field of automotive and aircraft industries since the early 20th century. An increasing great variety of parts are being produced using this technology with the development modern industry. The products manufactured through hydroforming are light but of high intensity. Using hydroforming, some complicated aerospace and aircraft structures with small characters can be easily formed[4-8] with less cost and less step. The stainless steel ripple plate with controllable corrugated quantity and depth is one deployable structure emerged in the field of aerospace industry. Because its complex geometric shape, the distribution of thickness and stress is complicate along the axial line in the forming area. The corrugated quantity is in inverse proportion to the corrugated depth. In order to deploy volume,

214 multiplication the corrugated depth by quantity is the final aim. Because of the big corrugated depth, the ragged side is the easiest place to crack. In this work, there is numerical simulation by Dynaform, strain and stress distribution were analyzed. Moreover, the experiments of different designed corrugated quantity and depth have identical view.

Basics Conditions

Shape and Dimensions of Ripple Section The shape and dimensions of ripple section are shown in Fig.II. It can be seen that the depth is 2mm, the quantity is 6. The diameter is 210mm which is very typical structure in aircraft .The ripple zone is from d 86.2 to d 114.5.

Figure 2. Shape of typical ripple part.

Material of Blank This ripple plate will be shaped by a 0.1mm-thick stainless steel material. The material performance parameters of stain steel can be seen in Table1. The elongation is 40% which means good plastic performance. Table 1. Material performance parameters of sheet stainless. Yield stress/MPa Ultimate tensile Anisotropy Strain hardening Elongation% stress/ MPa factor,r exponent,n

205 520 0.56 0.25 40

Simulation model In the actual forming, the die and punch are always closed as a confined space. We only obtain the final product, meanwhile the processing likes a black box and cannot be observed in time. With the rapidly development of computer technology, numerical simulation can predict the defect and provide various forming information like stress and strain distribution, forming limit, thickness distribution, crack, wrinkle and so on. This is a good way to observe the forming process which optimize the forming parameters to cut down the research times and cost. In this paper we use commercial explicit software Dynaform 5.6.

Figure 3. Simulation model.

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In simulation, punch and die were modeled as a rigid element and meshed. The blank was modeled as shell. The contact between die and punch, binder and blank will be determined by friction coefficient μ. μ=0.1 was used for the interface between the blank and the punch. μ=0.05 for the blank and the die. The gap between die and binder is constant. In this paper it will be 12 times of thickness and is 0.12mm. There has friction between die and blank which will hinder the blank material flow into die. In order to get high quality product, a correct friction force is really important. It is helpful to avoid thinning of the blank with a suitable gap between the binder holder and blank. Due to the small radii of ripple plate, the forming pressure should be increased high to 100MPa.The blank deformation becomes uniform with the counterforce of pressured force. Technology Parameters Considering the forming pressure and the size of model, we choose a 550t double-action sheet hydroforming machine. In experiments, the binder will be move down until the aimed location to hold the blank and then the punch step down to force blank. Meanwhile the pressure will be increased as the curve in Fig. IV. Form the loading curve we can see at the first the pressure increased quickly while the blank will be mostly formed. Then it is the shaping time while the blank will be formed to final shape under the effect of 100MPa pressure.

Figure 4. Loading pressure.

Influence of R on the Blank Forming In order to investigate the hydroforming loading pressure and geometry size of ripple parts, R1 and R 0.5 were both carried out.

Figure 5. Influence of R. The punch corner is the first zone contact with the blank and the forming stress is easily gathered there. So we simulate R1 and R0.5 to optimize the shape of ripple parts. Choosing a big corner radio of ripple part is one promising and effective method to increase the limit drawing ratio and the forming limit of sheet metal and improve the forming performance during sheet hydroforming. R on the deformation of the blank is a significant parameter for forming limit. Small R is not good for blank material flow which means the final corrugated depth is not quality.

216 Experimental Results

Failure Modes In the experiment, the fracture will be happened at the corner of punch nose as shown in fig.VI. The results show in the process the punch round corner is the weakest region, wrinkles will particular appeared in the blank holder zone. The corrugated quantity is in inverse proportion to the corrugated depth. In the simulation, it is same facture zone: the corner of punch nose as shown in fig.VII. This prove the simulation is accuracy which can be used to optimize the modules.

fracture

Figure 6. Fracture at punch nose of the corner.

Figure 7. Wall thickness distribution.

Success Modes We optimize the shape of corrugated quantity and depth, final obtain the success products, as shown in Fig. VIII. The corrugated quantity is six and depth is 2mm. The final product is successful fit the punch’s shape. Surface quality is good without scratch.

Figure 8. Final ripple part.

Conclusion The corrugated quantity is in inverse proportion to the corrugated depth. In this paper, the pressure should be more than 100MPa which will directly force the blank to shape, especially small waves. In order to get large developable volume, the radio should be bigger than 1mm. The blank holder gap is 12 times of blank thickness to ensure the friction between blank and die is reasonable. This work is of directive significance to the optimal design and operation of ripple plate forming.

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Acknowledgment The authors express their great appreciation to National Natural Science Foundation of China (Grant NO. 51405487) and National Science and Technology Major Project of China (Grant NO. 2014ZX04001-171) for supporting this work.

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