A guide to upset forging.

A guide to upset forging

Full understanding of the part is important for economical upset forging. We work with our customers for development of new parts, redesign of existing parts, and conversion from castings and weldments to forged parts. Given the right application, no process has yet been developed to produce a metal product from a ferrous or alloy grade that is superior to a forging in strength-to-weight ratio, shock and fatigue resistance, structural integrity, and cost effectiveness.

Upset forging is the process by which bar stock is gripped between a stationary and a moving die and shaped under considerable pressure as a heading tool moves against the end of the bar, displacing stock to fill the contours of the dies. This is a closed-die process with a minimum of waste material in the form of flash.

Upset forging differs from the impact process typical for hammer forging and has advantages over the conventional press-forging process in that split gripping dies allow the upsetter to forge unusually long shaft lengths.

The cross-sectional area or profile of the resulting upset shape is always changed from that of the original bar stock. Simple parts can be made from one or two workstrokes or passes. But frequently, several additional passes are needed to attain the mass and shape of the final configuration.

Defining processes

The upset forging process can be categorized into four classifications: solids, semipierced, hollow (fully pierced), and tubular. Following is a brief description of these processes.

Solids. Almost any rolled shape can be used as the starting stock. Solid forging offers advantages over bar stock and weldments. It reduces waste, requires less machining, and offers reoriented grain flow to enhance strength and machinability.

Semipierced. A semipierced forged part is produced with an opening parallel to the centerline and has a length of penetration or opening of any shape that exceeds the width or diameter of the cavity. This kind of forging has a high strength-to-weight ratio. In many cases, a semi-pierced upset forging can compete with a steel casting because it offers lighter weight and reduced cost in material, heat treating, and machining.

Tools for semipierced upset forgings are generally more expensive than tools for solid upsets. However, savings in material and subsequent machining often justify the increased tool cost.

Hollow fully pierced upsets. Fully pierced upsets are extensions of semipierced bodies. The skills and technology to make these are different, so we will consider them separately.

Hollow-body forgings can offer maximum economy for finished parts that require or can tolerate an opening for the full length. When the upset is fully pierced for weight savings only, little or no machining may be required inside the opening. It is sometimes possible to pierce the forging to size to eliminate drilling or boring operations altogether.

Tubular upsets. Upsets made from tubing have many advantages. The factors of wall thickness and material must be carefully evaluated before a tubular upset is specified. Wall thickness limits the amount of material that may be gathered or reshaped per pass. with hot-rolled seamless tubing, both concentricity and ovalness can be limiting factors.

Tubing can be upset into a wide variety of shapes, such as internal, external, and flange. Tubular upset forgings offer substantial savings and improved products compared to competitive methods.

Suggestions for efficient upsets

We have highlighted the most common hot upsetting forge processes performed daily by most upset manufacturers. In general, there are two rules.

* It is important to keep parts as simple as possible. All parts require machining to some degree. Therefore, do not complicate forging designs with features that do not provide a benefit either in quality or finished cost.

* Most forging manufacturers use either the standards of the Forging Industry Association (FIA) or have their own commercial tolerances. In cases where forgings are designed to require better than commercial or standard tolerances, the result is added cost.

If a surface is to be machined, allowance for adequate stock removal is usually the less costly approach. It is always good practice to consult one of the producers of commercial upset forgings when a part is in the initial design stage. The experience and guidance of forge shops can result in many benefits for your design, for product reliability, and finished product cost.

A detailed brochure on the upset forge process is available from our firm. For a free copy, Circle 561.