May 2011 - The blacksmith performs swaging on an anvil with a lower and upper die. The swages, also known as dies, enclose the workpiece, and the process is used to produce a single piece. A unique aspect of swaging is that the grain flow of the forged material is not cut off like it is in machining, and therefore, it tolerates higher loads.

Swages are permanent molds in which the pre-formed workpiece is pressed in. Less-complicated parts can be produced cold stated or after the material has been heated to forging temperature. The workpiece takes the shape of the cavity. Large workpieces or complicated ones may be forged in several stages using swages for making crankshafts or connecting rods. The advantages of this forming process are low production costs, greater accuracy and clean surfaces.

Higher production
Single-piece production is very costly and does not guarantee exact size and repeatability. For a higher production rate using a swage on a workpiece, it has to be heated to forging temperature, a process known as drop forging.

The tools for this process are expensive, and drop forging is economical only for mass production. Materials that can be drop forged are alloyed and unalloyed steels, copper alloys and magnesium alloys.

Materials used for the tools are water-hardening carbon steel with 0.09 percent carbon content for flat swages. Alloyed steels containing chromium, nickel and molybdenum are used when more extensive reshaping is required for the process.

The cavities are milled out of solid steel blocks. The insides of the dies are beveled (inside die 1:5, outside 1:10) so the finished workpiece can be removed easily. Using this process means the working materials are shrinking when cooled, and the swage expands with the heat of the workpiece. Therefore, workers must provide for a shrinkage allowance between 1.2 percent and 1.5 percent.

This type of forging also is named compression molding. It can be explained using the terms free-form forging in the preliminary forging, die-drop forging and stress-relief annealing.

The heaviest phase of shape transformation takes place in the preliminary forging die and in the intermediate die to preserve the exact dimensions and precise shape of the finishing die.

Shaping by upsetting
Another type of process for shaping workpieces in mass production is upsetting. This means the initial cross-section of the workpiece is increased by upsetting.

In the upsetting machine, the metal bar is held in gripping dies, which have jaws that are forced together. The ram mounted on the upsetting sledge is then forced against the end of the metal piece, causing the bulge. The work sequence involves heating the material only once.

The advantages over drop forging are there is no beveling of the swage and it is more economical because material losses because of scaling are low.

Open-frame and closed-frame upsetting are used in production. Open frame is when the ram forces the heated material into a die with a simple guide, and closed die upsetting involves using complete die-halves. FFJ

Udo O.J. Huff is an independent consultant with project experience in machine building, welding engineering, training and development. He holds Master of Education and Bachelor of Science in Technology degrees from Bowling Green State University. Questions or comments? E-mail uhuff@sbcglobal.net.

Interested in purchasing reprints of this article? Click here