The flowchart shown in Fig. 1.1 is a graphic representation of the processing of the raw iron ore material from the time it is put into the blast furnace until the time it is shipped to be processed into castings, sheet, or bar stock. In this book the emphasis is on the tools needed to process these ferrous and nonferrous raw material. Other material, such as plastics, are included to complete the picture.
As shown in Fig. 1.1, the end product of the blast furnace is pig iron. The pig iron may then be processed into either cast iron or steel. In either case the impurities are carefully controlled. Any element added to pure iron is classified as an impurity. The control of the addition of impurities to the base material-in this case iron-is the first step needed to ensure the desired physical properties of the end product at that point of manufacture.
If the pig iron is fed into a cupola and processed, the end product is cast iron. Cast iron is composed of carbon, silicon, manganese, sulfur and phosphorus in combination with iron. The percentages of each of these components are: approximately 2 to 4% carbon, 1 to 3% silicon, 1 to 2.5% manganese, 0.04% sulfur, 0.06 to 3% phosphorus, and about 90% iron. To achieve special properties, other elements may be added.
Cast iron is used in the main sections of jigs and fixtures in many instances because it can be cast into the desired shape and therefore requires a minimum amount of machining. Cast iron is a very stable material and it has suitable compressive strength for use as jig and fixture bodies or for die sets.