Influence of friction on the prediction of forces, pressure distributions and properties in upset forging

Experiments on the rotary forging of discs are described in which measurements are taken of pressure distribution under the rocking die using a pressure-sensing platen.The results suggest a deformation mechanism for the spread of the disc, involving the development of plastic hinges away from the immediate die contact area. This would explain central tensile failures and related phenomena observed previously.

Pressure-Distribution Measurements in Rotary Forging:

The measurement of tooling-workpiece interface forces is needed for process design, process modeling and analysis and process monitoring for control. One approach to measuring local interface loads with minimal disturbance of the surface and process is to embed sensors in the surface below the surface region of interest. Small piezoelectric sensing elements were cast into surfaces and their ability to measure loads applied normal to the surfaces was assessed. Sensor outputs were analyzed in terms of sensor depth below the surface, distance along the surface from the load location to the sensor location and sensor to sensor spacing. A mechanical model of the sensor-surface system was developed which predicted sensor output. The use of this sensing concept and type of sensor was demonstrated in strip drawing tests. Using temperature compensated sensors, workpiece holddown force was measured in tests during which drawbead penetration was varied.

Force Sensors Embedded in Surfaces for Manufacturing and Other Tribological Process Monitoring

A water jet of 50 mm diameter is used in conjunction with a calibrated split-platen pressure cell to determine how the normal and shear stresses engendered during perpendicular and inclined impact ...

Transient Stress Distribution Caused by Water-Jet Impact

This paper describes and classifies stress measurement techniques used in metal forming to provide research workers with a critical evaluation of usable methods. Eight techniques are considered; pressure transmitting pins, photoelasticity, ridged metallic sheets, paper sheets, split tools, strain gauged tools, orifices in tools and visioplasticity. In addition to these, some new transducer designs using optics and conical pins are presented. These are particularly useful for pressure measurement in hot forming operations.

G.H. Daneshi

Papers

A split-platen pressure cell for the measurement of pressure distribution in upsetting operations