Process Control Modeling and Real-Time Error Compensation in Tube Hydroforming

Tube Hydroforming (THF) is the metal forming process where metal tubes take the shape of a die cavity by being pressurized internally by a fluid in addition to axial material feed applied. This process has applications in automotive fields and household goods, offering benefits such as tight tolerances, lower part weight and fewer secondary operations. However, it is affected by long lead times due to loading path design and by process challenges related to errors such as the variation of tribological conditions that occur during hydroforming. The use of Finite Element Analysis (FEA) has greatly enhanced the THF field with the ability to simulate the process to generate loading paths (material feed versus pressure curve). However due to the nature of THF process being influenced by many variables such as material properties, tube geometry and tribological conditions, FEA leads to a lot of computation time.;This research presents the development of an interactive, real time Database Generated Loading Path Scheme (DGLPS) for various THF families. By classifying most of the asymmetric THF parts into families such as Bulge and Single Y-Shape THF parts; different loading paths are simulated and stored in the DGLPS. Interactivity with DGLPS is made available such that a user can request a loading path by providing input parameters. The DGLPS provides the material feed data by employing interpolation techniques and the pressure curve by multiplying the maximum pressure to a developed pressure profile with unit amplitude. Loading path results from DGLPS for a variety of desired parameters for different THF families matched FEA simulations with minimum variation of less than 5%.;This research reviews errors occurring in THF by broadly categorizing based on association with material feed and with internal pressure. The dominant material feed error is identified as frictional error. This research introduces an error compensation scheme, the Database Back-Step (DBS) method to compensate the loading path due to the effect of the frictional error. In this method the forces at the cylinder-tube interface are monitored and compared to acceptable forces in a database. Variation in this force from the expected force is corrected by stepping back into the database for another loading path that compensates the difference based on the coefficient of friction established from this force. This is accomplished in real time during the forming process via a Data Dynamic Exchange link between the database and the control unit. Based on experimental results the friction tended to vary from 0.01 to 0.15 for a Double T-Shape THF family demonstrating the need for error compensation. This shows that the DBS method provides an assured error compensation effort by obtaining optimized loading paths.;Differences may occur when comparing the loading paths and the position of the press cylinder (stroke) after applying the loading paths. This indicates the possibility of errors associated with the equipment. This research proposes the Real Time Stroke (RTS) Controller method as a solution for improving the cylinder stroke by compensating for equipment errors. This method focuses on developing a plant model of the equipment involved, a closed loop system whereby the reference input is obtained from the DBS method and designing a controller. Simulations of the process control have been done with Think and Do Live software. The results from the RTS method show a close tracking of the reference input with reduced overshoots beyond the reference loading paths. Control with above approaches results in efficient and concerted control merging the loading path design flexibility with process and machinery dynamic response.