Forming Processes Chapter 10

What is Forming? Forming is a second method of giving a part size and shape. Forming processes changes the size and shape, but not the volume of the material. The material will weigh the same before and after a forming process.

Stages of Forming Forming uses pressure. All materials being formed go through two major stages as stress is applied. In the elastic stage, stress will stretch the material. However, when the stress is removed, the material will return to its original size and shape.

Stages of Forming At the end of the elastic range is the yield point. Beyond this point, additional stress will permanently deform the material. In other words it will change the shape of the material. During the plastic stage the material starts to yield (give in) to the stress.

Stages of Forming It will be permanently stretched into a new shape. Added stress will cause more change in the shape. The plastic stage continues up to the fracture point. At this point the material breaks into two or more pieces and is destroyed.

Stages of Forming All forming practices have three major things in common:  A shaping device is used.  A material forming temperature is established.  There is a method for applying force.

Shaping Devices The shaping tool is to forming as the mold is to casting. The tool gives size and shape to the material. Two basic types of shaping devices are used in forming processes: dies and rolls.

Dies Dies are flat pieces of material. They must be harder than the material they are forming. Tool steel is used for metal and mnay plastic-forming dies. The dies generally have a shape cut to them. This may be a cavity or a raised portion.

Dies Three major types of dies can be used:  Open dies  Die Sets  Shaped Dies or molds

Dies Open dies are the simplest type of die. An open die is basically two flat, hard plates. One half of the die does not move. The other half moves to hit (hammer) or put pressure (squeeze) on the material between the dies.

Die Sets Die sets have shapes machined or engraved on their faces. Usually the shape on one half of the die fits the shape on the other half. Two types of dies are closed and mated. These dies either fit together or mate with each other.

Shaped Dies or Molds Shaped or one-piece dies and molds are used when air or liquid pressure forms the part. Pressure or vacuum forces the material against the die. This type of die is called a mold. This process is called thermoforming when it is used to make plastic parts or products.

Shaped Dies or Molds The material is held in a frame and is heated. The hot material is lowered over the die. The air in the mold cavity is drawn out. The atmospheric pressure inside the cavity forces the plastic into the cavity.

Material Temperature Material temperature is an important factor in all forming processes. Forming can occur at room temperature with some materials. Forming is described by its temperature:  Hot forming  Cold forming

Kinds of Force Forming processes use three kinds of force:  Compression  Drawing  Bending Most of the common techniques use four types of machine tools:  Hammers  Presses  Roll formers  Draw benches

In Summary Forming is changing the size and shape, but not the volume of a material. The change is caused by applying force above the yield point and below the fracture point. Material temperature is important in all forming processes.

In Summary Forming processes must have a source of pressure. The most common source is a machine’s metal