UNIT III Bulk Deformation Process

Bulk Deformation Processes Characterized by significant deformations and massive shape changes "Bulk" refers to workparts with relatively low surface area ‑ to ‑ volume ratios Starting work shapes include cylindrical billets and rectangular bars

A product is produced by shaping the metal into required shape and size. In this method “no machining process “ is carried out. The deformation is obtained by applying the force, the metal is plastically deformed into required shape.

Advantages of bulk deformation process Reduces the cavities present in the metal. Wastage of material is negligible. Production is high when compared to other manufaturing processes.

Bulk Deformation Processes Rolling : Compressive deformation process in which the thickness of a plate is reduced by squeezing it through two rotating cylindrical rolls.

Forging : The workpiece is compressed between two opposing dies so that the die shapes are imparted to the work.

Drawing : The diameter of a wire or bar is reduced by pulling it through a die opening (bar drawing) or a series of die openings (wire drawing)

Extrusion : The work material is forced to flow through a die opening taking its shape

Swaging Process that reduces/increases the diameter, tapers, rods or points round bars or tubes by external hammering

Cold Forging Process in which slugs of material are squeezed into shaped die cavities to produce finished parts of precise shape and size.

Sizing Process of squeezing all or selected areas of forgings, ductile castings, or powder metallurgy products to achieve a desired thickness or precision

Riveting Process where a head is formed on the shrank end of a fastener to permanently join sheets or plates of material;

Staking Process of permanently joining parts together when one part protrudes through a hole in the other; a shaped punch is driven into the end of the protruding piece where a deformation is formed causing a radial expansion, mechanically locking the two pieces together

Coining Process where metal while it is confined in a closed set of dies; used to produce coins, medals, and other products where exact size and fine details are required, and thickness varies about a well-defined average

Classification Hot working of metal Cold working of metal

Cold working Cold working is metal forming performed at room temperature. Advantages: better accuracy, better surface finish, high strength and hardness of the part, no heating is required. Disadvantages: higher forces and power, limitations to the amount of forming, additional annealing for some material is required, and some material are not capable of cold working.

Warm working Warm working is metal forming at temperatures above the room temperature but bellow the recrystallization one. Advantages: lower forces and power, more complex part shapes, no annealing is required. Disadvantages: some investment in furnaces is needed.

Hot working Hot working involves deformation of preheated material at temperatures above the re crystallization temperature. Advantages: big amount of forming is possible, lower forces and power are required, forming of materials with low ductility, no work hardening and therefore, no additional annealing is required. Disadvantages: lower accuracy and surface finish, higher production cost, and shorter tool life.

Forging

Forging operations Forging is a process in which the workpiece is shaped by compressive forces applied through various dies and tools. It is one of the oldest metalworking operations. Most forgings require a set of dies and a press or a forging hammer. A Forged metal can result in the following: -  Decrease in height, increase in section - open die forging  Increase length, decrease cross-section, called drawing out.  Decrease length, increase in cross-section on a portion of the length - upsetting  Change length, change cross-section, by squeezing in closed impression dies - closed die forging. This results in favorable grain flow for strong parts

Stages in Open-Die Forging (a) forge hot billet to max diameter (b) “fuller: tool to mark step-locations (c) forge right side (d) reverse part, forge left side (e) finish (dimension control) [source:

Stages in Impression-die (Closed-Die) Forging [source:Kalpakjian & Schmid]