MACHINING OF METALS.ppt
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Transcript of 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.
•
This relative motion is achieved in most machiningoperation by means of a primary motion, calledcutting speed and a secondary motion called feed.
•
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.
•
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.
•
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
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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.