Based On The Uncertainty In The High-pressure Pipe Forming Load Path Optimization

Tube hydroforming process has got widespread concern in the field of plastic metal processing. Because it can reduce the weight, save materials and provide high quality of surfaces and mechanical properties. In recent years, this technology has been widely used in automotive, aviation, aerospace, defense, chemical, medical and other fields. At present, the design of this process is still based on deterministic theory, which assumed that the material properties and process parameters have determined value. But in real life, the material properties and process parameters have characteristics of dispersion and randomness, which directly led the fluctuations of quality during processing and high rejection rate.In this paper, the tube hydroforming process for the sub-frame of a domestic SUV is studied. First, the structure and quality requirements of the sub-frame have been analysis, after the measurement of the work, quality problems is that, the minimum of thickness is less than the design dimensions. Using finite element simulation software to simulate and analyze the entire forming process, to find reasons which cause quality problems. And based on this, there is a method to increase the minimum thickness:optimizing the load curve.Then, dispersion and regularity of process parameters and random material properties will be studied to identify and classify process parameters in tube hydroforming process. Using experimental design and variance analysis techniques to select key parameters, which have a great impact on the minimum thickness. And establish a surface response equation between the measurement of the quality (minimum thickness) and key parameters.Finally, based on the response surface equation combined with the dispersion and randomness of material properties and process parameters, a model of process reliability will built. By optimizing the loading curve to improve process reliability and achieve the purpose of reducing production costs.The study shows that by setting a reasonable load curve can not only improve the minimum thickness, but can also reduce dispersion of the quality of products produced caused by the volatility and random of material properties and process parameters. This provides a reasonable reference for the design of loading curve in other tube hydroforming processes.