Forging

Forging ProcessesOpen Die Forging

A hot forming process, which uses standard flat, "V" or swage dies.

Impression Die Forging

Utilizes a pair of matched dies with contoured impressions in each die. When the dies close, the impressions form a cavity in the shape of the forging.

Ring Rolling

Forms axisymmetric shapes in a hot forming process. The process begins with a "donut" shaped preform, which is made by upsetting and piercing operations.

Open Die Forging

Impression Die Forging

Ring Rolling

Cold Forging

Common Applications for Forgings

Aerospace  Aircraft Engines  Airframe and auxiliary equipment

Guided missiles and space vehicles Automotive

  Passenger cars  Trucks, busses and trailers  Motorcycles and bicycles

Bearings, ball and roller Electric power generation/transmission Industrial and commercial

  machinery and equipment Hand Tools Industrial tools Internal combustion engines Metalworking and special industry

machinery

Mechanical power transmission  equipment, incl. bearings

Off-highway, equipment (construction,  mining and materials handling

Ordinance and accessories Oil field machinery and equipment Pipeline fittings Plumbing fixtures, valves and fittings Pumps and compressors Railroad equipment and spikes Rolling, drawing and extruding

equipment and  tools for nonferrous metals

Ship and boat building and repairs Special industry machinery Steam Engines and turbines Steel works, rolling and finishing mills

Types of forging dies

Single-impression

Double-impression Interlocking

1 All features should be oriented so that they can be formed in impressions moving in opposite directions.

Features such as undercuts and holes oriented other than in the direction of forging are not typically forged and must be fully machined.

2. Forging cost is minimized and tolerances reduced when forging loads are balanced, eliminating side loads on the machine members that restrain the dies

Design Rules for Parts Made From Impression Die Forgings

3 Sharp exterior corners require high forging pressures to fill the corresponding die features. Sharp interior corners (fillets) cause difficulties in metal flow, and may require one or more preform dies to attain, or may require additional machining operations. Therefore, radii should be as large as possible consistent with functional and assembly constraints. Corner and edge radii should also be uniform to minimize die sinking cost.

4 Draft angles should be the maximum allowable, consistent with functional, assembly and weight constraints. For ferrous forgings, draft angles less than 5° usually prohibit the use of hammers. Dies installed in presses are usually equipped with knock-out pins to eject the forging from the cavity, and can produce forgings with little or no draft. As a general rule, less draft is required on the outside of a feature than on the inside.

5. All datum targets and tooling points should be located on features made in the same die half, as illustrated in Figure. The upper die half is preferred since there is less contact between the die and the forging, and consequently less cooling.

6. Parts that are symmetrical about an axis are the most economical for upset forging. Upsetting generally increases the diameter of the beginning stock. Therefore, the stock size will generally correspond to the smallest as-forged diameter. This is the case for the flanged member shown in Figure.

7. Where material properties are critical, it is important to specify the required properties in all directions. This includes tensile strength, yield strength, ductility and impact toughness. The open die forger will design the forging process to develop grain flow that will optimize the properties. Otherwise the forging will be designed so that the grain flow follows the final contour of the forging.

8. In view of the end use of the product, specify the nondestructive testing methods to be employed and acceptable methods for employing them.

9. Open die forging can be employed for a wide range of shapes. For example, non-symmetrical shapes may be forged.

Design Rules for Parts Made by Cold and Warm Forging

Commercially made cold forgings typically weigh less than 23 kg (50 lb), although larger forgings have been cold forged.

Net shape cold forgings should be considered for products made in high volumes with surfaces that are difficult or expensive to machine due to geometric configurations.

Shapes that can be made by upsetting and bending, such as bicycle pedal cranks, are good candidates for cold forging.

Net or near-net shapes, such as tripot inner races or universal joint crosses, can be manufactured using cold or warm lateral extrusion.

Cold forgings do not require draft angles to release them from the tooling.

Solid or tubular shaped products with either through or blind holes, with net formed splines or other axial features, can be made by cold forging.

When specifying blind holes, keep in mind:     • Holes that are deep in proportion to their diameter are difficult to forge.     • Maintain uniform side wall thicknesses.    • The wall at the bottom of the blind hole should be at least as thick as the side walls.        (See Figure)

The hole on the left can be forged; the one on the right will require a drilling operation

Consult with the forger to determine the net shape capability, and design net shape surfaces within those capabilities. When designing solid shapes, minimize the difference between the largest and smallest diameters of the part (See Figure A.) Avoid undercut diameters in products to be cold forged. They can be forged in some cases if the undercut is wide as illustrated in Figure B.

Figure AFigure B

Avoid extremely thin or thick wall sections when designing tubular parts.

Undercuts can be forged in some cases if they are wide compared with the diameter of the feature.

Avoid sharp corners: use fillets and radii.

13-3 Powder Metallurgy.

Design considerations

Definition: Powder metallurgy

The process of making parts by compressing and sintering powders into shape

Design considerations in powder metallurgy:Ejection from the dieAxial variations

Reverse tapers

Corner reliefs

Design considerations in powder metallurgy: Holes at right

angles to the direction of pressing

Undercuts

Knurls

Design considerations in powder metallurgy: Blind holes

Flanges

Corners

Design considerations in powder metallurgy:Wall thickness

Chamfers

Changes in cross section

13-4 Plastic Molded Parts

Design considerations

Assemblies

Drawings

PhotoDisk

Quick QuizWhat is the term for the process of

compressing and sintering powders into shape to make parts? Powder

metallurgy

Design considerations in molded parts:ShrinkageSection thickness Gates

Design considerations in molded parts: Parting or flash line

Molded holes

Fillets and radii

Design considerations in molded parts: Internal and external draft Threads Ribs and bosses

Undercuts

Assembly considerations for molded partsHoles and threads Inserts

Heat forming and heat sealing

Press and shrink fits

Assembly considerations for molded parts Mechanical fastening

Adhesive bonding

Boss caps

Rivets

Assembly considerations for molded partsUltrasonic bonding

Friction or spin welding

Ultrasonic staking