| The goal of any manufacturing industry is to increase productivity while maintaining finished part quality. Sheet press forming is an industry distinguished by a high ratio of material surface area to material thickness. Variations such as those occurring in the properties of the sheet and lubrication can disturb a stable process causing scrap. Conceptually, incorporating real time control into the process will improve production by reducing the effects of random process disturbances.;The present work focuses on developing the ability to characterize sheet flow over the die shoulder. This is part of a global effort developing a die with real time control. To this end, two transducers/sensors were developed, calibrated, and evaluated. The first, called the Roller Shoulder Transducer, is primarily a research tool used in conjunction with a strip test machine. Strip tensions are measured by the transducer which are used to quantify bending effects and calculate an average friction coefficient. Verification of the two units (varying in shoulder radius) is performed with a test series consisting of varying strip thickness, strip speed, and drawbead speed. The design is capable of measuring DBRF within 0.5% and pull force within 2-3% error. From these verification tests it is shown the aforementioned parameters do not significantly affect the friction profile during drawbead penetration.;The second sensor developed is for monitoring sheet tension in an actual forming die. Originally, this sensor concept used commercial manganin gages (piezoresistive) for transduction which required a thorough test series to characterize gage response. Normal and shear loading, creep, strain sensitivity, and temperature induced output are some of the factors studied. Variables included surface texture and relative size of the contact tooling. When loaded by hydrostatic pressure, gage response is linear. When loaded in the manner of the sensor concept (by contact), gage response is non linear. Pronounced hysteresis in the gages was noted and attempts to reduce it or eliminate it were unsuccessful. A prototype sensor was built based on the knowledge gained from the test series.;Concurrent with the latter development stages of the manganin gage based sensor was a design utilizing strain gages. Trials with each design in a strip test machine showed the hysteresis limited the manganin sensor's accuracy to about 15% error. Ultimately, a strain gage based design having six gages in each bridge was used to show axial stress would be the parameter most likely measured in a forming die. In tests establishing a calibration procedure, axial stress was predicted within 3% on the punch side and DBRF. |
