Selection of Operating Parameters to Prevent Central Bursting Defects During Cold Extrusion

Abstract

Central bursts, or chevrons, are the internal arrows shaped defects occasionally encountered in cold extrusions or drawn wire (Figure 1). In cold extrusion the defect is usually observed in the final, light step of a multistep extrusion. When central bursting occurs, the load-carrying capacity of the part is drastically reduced. The possibility of central burst occurrence has required manufacturers of critical parts, e.g., axle shafts and steering gear components, to install and maintain ultrasonic equipment for 100% inspection of the formed parts. Although inspection can prevent the use of components containing central bursts, the rejection of extruded items increases production costs because both material and time are consumed in the manufacture of the unacceptable parts. Thus, it is desirable to completely prevent the occurrence of central bursts.