Variable Contact Pressure and Variable Drawbead Height Influence on Deep Drawing of Al Alloys Sheets
The process of deep drawing is influenced by many factors. During the forming process, only two of those factors can be controlled. They are blank holding force and drawbead height. Realisation of such control requires relatively complex computerized apparatus. For this experimental research, electro-hydraulic sheet-metal strip sliding device has been constructed. Basic capacity of realized device is obtaining contact pressure and drawbead height as functions of time or stripe displacement. Additional features consist of the ability to measure drawing force, contact pressure, drawbead displacement etc. Presented in the paper are the results of influencing of increasing and decreasing drawbead height functions in combination with increasingdecreasing function of contact pressure. Stripe material is aluminium alloy AlMg4,5Mn0,7 sheet metal. Contact condition are additionally influenced by application of mineral oil or completely dry tool and stripe surfaces. Drawbead geometry, with rounding radii of 2 and 5 mm, is also varied. The accomplished results indicate that simultaneous effects of variable drawbead height, variable contact pressure, tool geometry and appropriate friction conditions can influence the plastic flow process in line with desired change of forming force.
A strip-drawing simulator with computer-controlled drawbead penetration and blankholder pressure
Abstract Failure in the stretch-drawing of sheet metal panels is caused predominantly by either wrinkling or splitting. Wrinkling, which can occur in the flange inside the blankholder or in the unsupported side wall of the stamping part, is due to compressive circumferential stresses that result in buckling of the sheet. Splitting, on the other hand, is caused by excessive tensile stresses. Both modes of failure are influenced by blankholder force (BHF). Material flow is often modified locally by the insertion of drawbeads into the tooling. In industrial practice, drawbeads are a fixed component of the tooling and thus exercise their controlling function with a set penetration. A multiple-action hydraulic sheet-metal strip-drawing test apparatus has been constructed for the purpose of studying the effectiveness of feedback controls in sheet-metal forming. This device simulates the flow of sheet-metal in the blankholder and over the die shoulder in the stamping of sheet-metal panels. Its special features consist of the ability to adjust both the BHF and the drawbead penetration while the strip is being drawn and to measure forces in the sheet on either side of the die shoulder. Feedback control of the strip-drawing process using a proportional plus integral controller is demonstrated and the results are presented in the paper. The controller adjusts the drawbead position to eliminate the deviation of the punch force from the desired force. The results indicate that the addition of feedback control to the process reduces the effects of undesirable input variations as well as of disturbances on the output.
Variable Tribological Conditions on the Blank Holder as Significant Factor in Deep Drawing Process
Friction on the work part flange very significantly influences the deep drawing process. Blank holding force (BHF) is normal force for that friction. Presented in the paper are short review of analysis of for type variable BHF (VBHF) influence during the process. The experimental researches were performed on a special laboratory computer device. Realized are pure deep drawing process (drawing ratio 2) of the Al−alloy sheet metal, with dry surfaces. Influence of VBHF monitored mainly through thinning strain distributions and drawing depth. After performed experiments we can conclude that some type of VBHF are important factor for advancing deep drawing process.