MACHINING OF METALS.ppt

7/27/2019 MACHINING OF METALS.ppt

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MACHINING OF METALS



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COURSE OUTCOMES(CO):

• To understand the main classifications of

metal machining

• To learn how to identify the problems

occurred during machining process in

metallurgical perspective.

• Able to handle machining precisely and

familiarize with the basic machineries

such as lathe, milling, grinder etc.



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EBT 207 MACHINING OF METALS

• Basic principle of tool shops practice andsafety precautions.

• Introduction to machining.

• Classification of machining operation.

• Fundamentals and technology of operating

the lathes, milling, drilling and grinding

machines.



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INTRODUCTION TO

MACHINING



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• Machining is the most important of themanufacturing processes.

• In the machining of metals the ultimate goal is toproduce the highest quality part within anestablished cost.

• Machining can be defined as the process of removing material from a work piece in the form of chips.

• The term metal cutting is used when the materialis metallic.

•



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• Most machining has very low set-up cost

compared to forming, molding, and casting

processes.

• However, machining is much more expensive for

high volumes.

• Machining is necessary where tight tolerances

on dimensions and finishes are required.

• Machining is not just one process; it is a group of

processes.



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• The common feature is the use of a cutting tool toform a chip that is removed from the workpart,called swarf .

• To perform the operation, relative motion isrequired between the tool and work.

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This relative motion is achieved in most machiningoperation by means of a primary motion, calledcutting speed and a secondary motion called feed.

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The shape of the tool and its penetration into thework surface, combined with these motions,produce the desired shape of the resulting worksurface.



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• Common machining process involve turning,boring, broaching, drilling, sawing, milling,grinding, tapping, threading, reaming and honing.

• Machining is a part of the manufacture of almostall metal products.

• The machinist is involved with making a selectionof such variables as tool bit material, geometry of cutting surface and edge, depth of cut, cuttingspeed, plus the environment surrounding thecutting operation.

• A room, building, or company where machining is

done is called a machine shop.



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A simple explanation of machinability is ameasure of the ease with which aspecified finish may be produced on ametal.

Machinability is the ratio of time andexpense that is required for a certainquality finish.

The two major factors related tomachinability are cutting tool life and rateof metal removal from the workpiece.



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Working temperature during machining

can be source of one of the more serious

problems.

On a workpiece that is turned against a

single-edged cutting tool bit withoutcoolant, an average of 75% of the heat

may be carried away by the chips.

Machinist can reduce this temperature at

the tool bit by;



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1. Increasing the shear plane angle of the

cutting tool.

2. Reducing the cutting speed.

3. Softening the workpiece by heating

treating.

4. Selecting an appropriate cutting fluid.



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The Machining section is divided into the following

categories:

1. Drilling



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• Drilling, is used to create a round hole.

• It is accomplished by a rotating tool that is typically has twocutting edges.

• The tool is fed in a direction parallel to its axis of rotationinto the workpart to form the round hole.

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Drilling operations are operations in which holes areproduced or refined by bringing a rotating cutter withcutting edges at the lower extremity into contact with theworkpiece.

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Drilling operations are done primarily in drill presses butnot uncommonly on lathes or mills.



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2. Turning/Lathe



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• Turning operations are operations that rotate theworkpiece as the primary method of moving metalagainst the cutting tool.

• In turning, a cutting tool with a single cutting edgeis used to remove material from a rotatingworkpiece to generate a cylindrical shape.

• The speed motion in turning is provided by therotating workpart, and the feed motion is achievedby the cutting tool moving slowly in a directionparallel to the axis of rotation of the workpiece.

• Lathes are the principal machine tool used inturning.



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3. Milling



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• Milling machines are the principal machine tool used inmilling.

• In milling, a rotating tool with multiple cutting edges is

moved slowly relative to the material to generate a plane or straight surface.

• Milling operations are operations in which the cutting toolrotates to bring cutting edges to bear against the

workpiece.

• The direction of the feed motion is perpendicular to thetool's axis of rotation.

• The speed motion is provided by the rotating milling cutter.The two basic forms of milling are —

1.Peripheral milling

2.Face milling



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4. Grinding



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• Grinding is a type of machining using an abrasivewheel as the cutting tool.

• Grinding practice is a large and diverse area of manufacturing and tool making.

• It can produce very fine finishes and very accurate

dimensions.

• It is usually better suited to the machining of very hardmaterials than is "regular" machining (that is, cutting larger chips with cutting tools such as tool bits or milling cutters),and until recent decades it was the only practical way tomachine such materials as hardened steels.



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5. Chip Formation

http://en.wikipedia.org/wiki/File:Metal_Cut_diag.jpg



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• Other conventional machining operations include

shaping, planing, broaching and sawing.

• Miscellaneous operations are operations that

strictly speaking may not be machining operations

in that they may not be chip producing operations

but these operations are performed at a typicalmachine tool.

• Burnishing is an example of a miscellaneous

operation. Burnishing produces no chips but can

be performed at a lathe, mill, or drill press.



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• Other operations falling into miscellaneouscategories include shaping , planing ,boring, broaching and sawing.

• An unfinished workpiece requiringmachining will need to have some material

cut away to create a finished product.

• Machining requires attention to many

details for a workpiece to meet thespecifications set out in the engineeringdrawings or blueprints.



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• Beside the obvious problems related to correctdimensions, there is the problem of achieving thecorrect finish or surface smoothness on theworkpiece.

• The inferior finish found on the machined surfaceof a workpiece may be caused by incorrect

clamping, dull tool, or inappropriate presentation of a tool.

• Frequently, this poor surface finish, known as

chatter, is evident by an undulating or irregular finish, and the appearance of waves on themachined surfaces of the workpiece.

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MACHINING OF METALS.ppt