2006 Volume 47 Issue 546 Pages 606-610
Damage to and fracture of dies of cold forward extrusion of a bolt part former was detected by use of a fractal property of acoustic emission (AE) during a practical manufacturing operation. Two conditions of lubrication, with and without vegetable oil, were employed. A fractal dimension m of AE amplitude was used to detect damage to and fracture of the die. The extrusion rate was set to 100 pcs./min. A decrease in m was observed after a certain number of repetitions of extrusion N under both conditions. Under the condition without vegetable oil, the die insert was completely ruptured by N = 2850. The m took a minimum value at N = 2807, and then increased. The progress of the defects on the surface of the workpiece showed good agreement with the change in m. Under the condition with vegetable oil, the die insert was completely ruptured by N = 11000. A decrease in m was observed at N = 9000. A fast overload fracture with a ratchet mark was mainly observed on the fractured surface of the die insert under the condition without vegetable oil. The region of stable crack propagation around the die radius was dominant under the condition of lubrication with vegetable oil.
