Making the tanking in halves requires a great deal of shrinking on the Pullmax. All of this shrinking causes the material to work harden. If I went any further, I would have had to anneal the halves or I would have run the risk of fracturing the aluminum.
While the Pullmax is a fantastic machine, it really in not meant for excessive shrinking. Unlike the spring loaded die of a Yoder or Pentingell power hammer, the Pullmax is rigid. Thus, it doesn't compensate for the thickness gains associate with the shrinking operation. If you do not compensate manually, the Pullmax essentially pushes the metal causing it to flow. I continually had to trim excess material off of the center on the halves as I was "shrinking". This flow of metal becomes apparent when you run the part though the English wheel and it doesn't require you to change the height of the lower anvil to account for the supposed thickness differences. Also, the extra work associated with the flow of material causes the metal to work harden quicker.
