Lect-06 -Important Questions with answer PDF

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ME335-MANUFACTURING PROCESSES LECTURE-06 FORGING - IMPORTANT QUESTIONS 01. Define forging process. State its applications. Draw the schematic of stress flow patterns of (a) cast; (b) machined; (c) forged part  Forging is a basic process in which the workpiece is shaped by compressive forces applied through various dies and tooling.  Forged parts now include large rotors for turbines, gears, cutlery, hand tools, components for machinery, aircraft, railroads, and transportation equipment

02. Describe about Cold Forging Vs hot forging:  Forging may be carried out at room temperature (cold forging) or at elevated temperatures (warm or hot forging), depending on the homologous temperature.  Cold forging requires higher forces, because of the higher strength of the workpiece material, which also must possess sufficient ductility at room temperature to be able to undergo the required deformation without cracking.  Cold-forged parts have good surface finish and dimensional accuracy.  Hot forging requires lower forces, but the dimensional accuracy and surface finish of the parts are not as good as those in cold forging 03. Explain the open die forging process with a neat sketch  Open-die forging is the simplest forging operation.  Open-die forging can be simply described by a metal workpiece (blank), placed between two flat dies, and reduced in height by compressing it (Fig. 14.3), a process called upsetting or flat-die forging.  The die surfaces may have shallow cavities or features to produce relatively simple shapes.  The deformation of a workpiece under frictionless conditions is shown in Fig. 14.3b.

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04. Describe about barreling effect occurs in open die forging process with a schematic  Barreling (Fig.13.c) is caused primarily by frictional forces that oppose the outward flow of the workpiece at the die interfaces; thus, it can be minimized by using an effective lubricant.  Barreling also can develop in upsetting hot workpieces between cold dies. Here, the material at the die surfaces cools rapidly, while the rest remains relatively hot; consequently, the material at the top and bottom of the workpiece has higher resistance to deformation than the material at the center. As a result, the central portion of the workpiece expands laterally to a greater extent than do the ends

EXAMPLE 14.1 Calculation of Forging Force in Upsetting A solid cylindrical workpiece made of 304 stainless steel is 150 mm in diameter and 100 mm high. It is reduced in height by 50%, at room temperature, by open-die forging with flat dies. Assume that the coefficient of friction is 0.2. Calculate the forging force at the end of the stroke.

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05. Describe the impression die forging and closed die forging operation with sketches  In impression-die forging, the workpiece takes the shape of the die cavity while being forged between two shaped dies (Figs. 14.6a–c).  This process is usually carried out at elevated temperatures, in order to lower the forging forces and develop enhanced ductility of the workpiece.  Note in Fig. 14.6c that, during deformation, some of the material flows outward and forms a flash.  The flash has an important role in impression-die forging: The high pressure, and the resulting high frictional resistance in the flash, presents a severe constraint on any radially outward flow of the material in the die.

06. Explain briefly about closed die forging and true closed die forging process with a schematic diagram  In true closed die forging, however, a flash does not form (hence the term flashless forging), and the workpiece completely fills the die cavity

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07. Explain briefly the following forging operations with neat sketches: (a) Coining operations: (b) Heading operation; (c) Piercing operation (a) Coining – forging operation:  A closed-die forging process, coining was originally used in the minting of coins, and jewelry (Fig. 14.11), but currently is used to produce a wide range of parts with high accuracy, such as gears, industrial seals, and medical devices.  The blank or slug is coined in a completely closed-die cavity, in order to produce fine details, such as in coins; the pressures required can be as high as five or six times the strength of the material.

(b) Heading forging operation  Also called upset forging, heading is essentially an upsetting operation, performed on the end of a rod or wire in order to increase the cross-section.  Typical products are nails, bolt heads, screws, rivets, and various other fasteners (Fig. 14.12).  Heading can be carried out cold, warm, or hot

(c) Piercing forging operation:

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 This is a process of indenting (but not breaking through) the surface of a workpiece with a punch, in order to produce a cavity or an impression (Fig. 14.13).  The workpiece may be confined in a container, such as a die cavity or may be unconstrained.  A common example of piercing is the indentation of the hexagonal cavity in bolt heads. Piercing may be followed by punching to produce a hole in the part.

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