Analysis of cracks generated in the spinning-mandrel teeth

• Detecting three distinct regions on the fracture surface of a splined mandrel as zone “A” arranged lamellas, zone “C” wavy structure, and zone “B” transition region.
• Significantly higher amount of sulfur (S), as being the most detrimental element in the steel, near the crack path than in regions away from the crack path.
• Insufficient tempering temperature to fully reduce the brittleness of the mandrel.
• Combination of fatigue and impact caused by metal (mandrel)-to-metal (work piece) contact.

The spinning process, using a splined mandrel, is always prone to premature failure of the splined mandrels. Such a failure is thought to be related to the magnitude of the forming forces exerted on the mandrel by the forming rollers during the spinning process. In the present paper, the characteristic of corner cracks in the mandrel teeth (made of S7 tool steel) of a spinning process has been investigated. The rotational speed of the mandrel is about 300 rpm during spinning process and the sheet metal (i.e. AISI 1020) is in contact with mandrel teeth to get the mandrel shape at the end of process. During this process, the mandrel teeth eventually break away. Fractography analyses using scanning electron microscopy (SEM) clearly confirm “fatigue” as being the main reason for the failure.