Research On The Design And Numerical Simulation For Highly Flexible Stretch-forming Machine

With the development of the national economy and machinery manufacturing industry,sheet metal forming techniques are widely used in many products which including theaircrafts, high-speed trains, ships, buildings and other products. Taking the aircraftindustry as an example, skin panels are the key shape parts of aircrafts. Skin panels havemany varieties and complex shapes and have been produced in small batch orsingle-piece. Currently, stretch-forming (SF) process is the main way to realize the skinforming. SF machine is the main equipment for producing of skin parts. SF machinesused in China are mostly imported from abroad, which have the stable and reliableperformance and high forming precision. However, control systems for these SFmachines are very complex and expensive. Especially, foreign SF machine manufacturersmonopolize their core SF technologies. Therefore, it is very significant to develop SFmachine with independent intellectual property rights. The machine frame is the mainbearing member and the mounting base of the whole SF machine. It requires sufficientstrength and stiffness to ensure safe service. Its mechanical performance directly affectsthe precision of sheet stretching and service life of the SF machine. In the traditionaldesign, its geometrical dimensions are mainly calculated based on designer’s experiencebecause the frame structure is very complex. The lack of accurate strengthcalculation easily leads to material waste or insufficient stiffness. Finite element analysis(FEA) can help to solve these problems effectively while designers use FEA in the framedesign and structure analysis.In this paper, the structure features and state of the art in SF equipment at home andabroad are introduced. The concept of flexible multi-clamp SF (FMCSF) is described and then the progress of FMCSF process and equipment are reviewed as well as. The FMCSFprinciple is to use the flexible discrete clamps instead of a rigid integral clamp. Based onthis review, the idea of how to design the novel FMCSF machine is proposed. The stressdistribution of the machine frame is calculated through using the FEA software ABAQUS.Analysis of the stress and strain of the machine frame under maximum load andimprovement of the frame structure to greatly reduce weight and increase strength andstiffness are carried out.The major contents and conclusions in this paper can be summarized as follows:1. Definition of the design scheme of novel FMCSF machine and analysis of itsworking mechanism. The machine frame of the new FMCSF machine consists of threecomponents, which are the support base, stretching frame and movable gantry hydraulicpress. It adopts a modular structure of small FMCSF machine (for blank with max.1600mm width) and medium FMCSF machine (for blank with max.2400mm width) usedfor large FMCSF machine (for blank with max.4000mm width). There is also anadjustable stretching frame structure adopted in the FMCSF machine for a wide range ofmetal sheets. The hydraulic press is designed to improve the stretched panel quality andreduce the finished panel springback.2. Establishment of the FEA models for highly flexible stretch-forming machine,analyses of the deformation of the stretching frame under maximum loads andimprovement of the frame structure. Two design schemes of the stretching frame areproposed. Although the initial two schemes can satisfy the design specifications, thedeformation and the weight of the stretching frame are not ideal to end-users. Afterthe improvement of stretching frame structure, max. stress in the frame is reduced from99.24MPa to73.56MPa, the max. horizontal deformation is reduced from4.85mm to1.00mm and the weight of the stretching frame is reduced by29.3%.3. Press frame design and numerical simulation with FEA for movable gantryhydraulic press. The press consists of four parts: the beam, platform, column and cylinder.Two design schemes are presented and the press frame has better strength and stiffness while the hydraulic cylinders are placed above the worktable according to the numericalsimulation results.4. Evaluation of the frame strength for highly flexible SF machine and movablegantry hydraulic press under eccentric loads while using either small or mediumFMCSF machines. The simulation results show that the deformation and stress of thehighly flexible SF machine under partial load are in the reasonable range of requirements.5. Worktable design for FMCSF machine and the drawings modeling for the wholemachine. Three design schemes of the worktable are proposed and numerical simulationwith FEA is used to investigate the deformation of each scheme. The optimal scheme isselected through comprehensive comparison the weight and the simulation results of eachscheme. After the improvement of worktable structure, the weight of the worktable isreduced by23.9%.