Manufacturing and process

अब Quizwiz के साथ अपने होमवर्क और परीक्षाओं को एस करें!

ability to retain hardness at high temperatures

Hot hardness

To increase shear plane angle

Increase the rake angle - Reduce the friction angle

Performed on internal surface of a hole

Internal Broaching

Other Abrasive Processes

Lapping

Uses fluid suspension of very small abrasive particles between workpiece and lap ( tool ) .

Lapping

fluid with abrasives , general appearance of a chalky paste .

Lapping compound

optical lenses , metallic bearing surfaces gages .

Lapping compour Applications

Cutting Fluid Filtration Advantages : fluid

Longer tool life

Cutting Fluid Filtration Advantages :

Lower machine tool maintenance

Differences with honing :

Lower pressures between tool and surface

designed to reduce chip and tool - work friction

Lubricants

A power - driven machine that performs a machining operation , including grinding

Machine Tools

A material removal process in which a sharp cutting tool is used to mechanically cut away material so that the desired part geometry remains

Machining

Cutting action involves shear deformation of work material to form a chip

Machining

highly automated machine tool capable of performing multiple machining operations under computer numerical control ( CNC ) in one setup with minimal human attention .

Machining Centers

Machining provides the final shape , dimensions finish , and special geometric details that other processes cannot create

Machining in Manufacturing Sequence

Other processes create the general shape of the starting work part

Machining in Manufacturing Sequence

Cutting fluids applications

Manual application by means of a squirt can or paint brush

A family of shaping operations , the common feature of which is removal of material from a starting workpart so the remaining part has the desired geometry .

Material Removal Processes

A family of shaping operations the common feature of which is removal of material from a starting work part so the remaining part has the desired shape

Material Removal Processes

Highly automated machine tool that can perform turning , milling , and drilling operations on a workpart

Mill - Turn Centers

Rotating multiple - cutting - edge tool is moved slowly relative to work to generate plane or straight surface

Milling

Cutting fluids applications

Mist

Drilling and milling use rotating multiple cutting edge tools .

Multiple Cutting Edge Tools

More than one cutting edge

Multiple Cutting Edge Tools

Motion relative to work usually achieved by rotating

Multiple Cutting Edge Tools

Used for drilling , reaming , tapping , milling , broaching , and sawing

Multiple cutting edge tools

Used for nonferrous metals and gray cast iron

Non - steel Cutting Carbide Grades

also called prismatic ) - block or plate

Nonrotational

( NR )

Nose radius

Problems with dry machining :

Operating at lower cutting speeds and production rates to prolong tool life

A simplified 2 - D model of machining that describes the mechanics of machining fairly accurately

Orthogonal Cutting Model

Problems with dry machining :

Overheating of the tool

Cutter axis is parallel to surface being machined

Peripheral milling

Cutting edges on outside periphery of cutter

Peripheral milling

Used for peripheral or slab milling

Plain Milling Cutter

Milling Cutters Principal types :

Plain milling cutter

Another form of end milling used to mill shallow pockets into flat parts

Pocket Milling

Functions in machining :

Positions tool relative to work

Shear strain in machining can be computed from the following equation , based on the preceding parallel plate model

Shear Strain

Differences with honing

Shorter strokes

harder than Al2O3 but not as tough

Silicon carbide ( SIC )

One cutting edge

Single - Point Tools

Point is usually rounded to form a nose radius

Single - Point Tools

Turning uses single point tools

Single - Point Tools

Used for turning , boring , shaping , and planing

Single point tools

Tool Geometry Two categories :

Single point tools - Multiple cutting edge tools

Broaching Advantages

broach Owing to complicated and often custom - shaped geometry , tooling is expensive

In this section , the following cutting tool materials are discussed

cast cobalt alloys

Generally performed after other manufacturing processes , such as

casting and forging and bar drawing

In this section , the following cutting - tool materials are discussed :

cemented carbides , cermets , and coated carbides

In this section , the following cutting - tool materials are discussed :

ceramics

often used to cut long bars , tubes , and similar shapes to specified length

circular sawing

Cutting Fluid Filtration Advantages :

cost Cleaner fluids reduce health hazards

Each machining operation produces a characteristic part geometry due to two factors :

cutting tool Shape of the cutting tool

( ERA )

end relief angle

performed on the outside surface of thework

external broaching

Cutting fluids applications

flooding

Abrasive processes material removal by hard abrasive particles

grinding

In this section , the following cutting - tool materials are discussed :

high - speed steel and its predecessors plain carbon and low alloy steels

( > 600 ipm )

high feed rate drive

( < 0.0001 " accuracy )

high precision

Automatic Screw Machine Applications

high production of screws - and similar small hardware items

( > 40,000 rpm )

high speed spindle

Other abrasive processes :

honing , lapping , superfinishing , polishing , and buffing

Milling Two forms :

peripheral milling and face milling

Most common application

shape metal parts

( SCEA )

side cutting edge angle

( SRA ) .

side relief angle

Best surface finish is achieved by :

speeds Denser wheel structure = more grits per wheel area

In this section , the following cutting - tool materials are discussed

synthetic diamond and cubic boron nitride .

Two types of feed motion in external cylindrical grinding :

traverse feed , and plunge - cut .

Machining material removal by a sharp cutting tool

turning milling drilling

In peripheral milling , the direction of cutter rotation distinguishes two forms of milling :

up milling and - down milling

Two basic types ( AISI )

Tungsten - Molybdenum

A single point cutting tool removes material from a rotating workpiece to generate a cylindrical shape

Turning

Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape

Turning

Most important machining operations :

Turning - Drilling - Milling

Traditional Chip Removal .

Turning - Milling - Drilling - Boring - Reaming - Shaping

Rotation and feeding of drill bit result in relative motion between cutting edges and workpiece to form the chips

Twist Drill Operation

By far the most common cutting tools for hole - making

Twist Drills

Usually made of high speed steel

Twist Drills

Nontraditional Machining

Ultrasonic - Electrical Discharge - Electro - arc - Optical Lasers - Electrochemical

Stands on the floor

Upright Drill

Broaching Advantages

Variety of work shapes possible

Chips generated in machining are wasted material , at least in the unit operation

Wasteful of material

hardness is the most important property to resist abrasive wear

Wear resistance

Variety of part shapes and special

Why Machining is Important

Variety of work materials can be machined

Why Machining is Important

Very straight edges and surfaces

Why Machining is Important

Use filtration system to continuously or periodically clean the fluid

Dealing with Cutting Fluid Contamination

Friability

Abrasive Material Properties

High hardness

Abrasive Material Properties

Toughness

Abrasive Material Properties

Wear resistance

Abrasive Material Properties

filtration Problems with dry machining :

Absence of chip removal benefits of cutting fluids in grinding and milling

Variety of part shapes and special geometry features possible such as :

Accurate round holes

most common abrasive

Aluminum oxide ( Al₂O3 )

Other Abrasive Processes

Honing

Same as automatic bar machine but smaller

Automatic Screw Machine

linear continuous motion of bandsaw blade which is in the form of an flexible loop with teeth on one edge

Bandsawing

Continuous chip

Basic Types of Chip in Machining

Continuous chip with Built - up Edge ( BUE )

Basic Types of Chip in Machining

Discontinuous chip

Basic Types of Chip in Machining

Serrated chip

Basic Types of Chip in Machining

Similar but smaller and mounted on a table or bench

Bench Drill

drill does not exit work on opposite side

Blind - holes

Moves a multiple tooth cutting tool linearly relative to work in direction of tool axis

Broaching

High cutting temperatures result in the following :

Can cause inaccuracies in part dimensions due to thermal expansion of work material

Primarily fine - grained Al₂O3 ,

Ceramics

high speed turning of cast iron and steel

Ceramics Applications

Combinations of TiC , TiN , and titanium carbonitride ( TiCN ) , with nickel and / or molybdenum as binders

Cermets

high speed finishing and semifinishing of steels , stainless steels , and cast irons

Cermets Applications

Cutting edge cuts an angle on the corner of the cylinder

Chamfering

Nontraditional Machining

Chem - milling - Abrasive Jet Cutting - Electron Beam Machining- Plasma Arc Machining

R= to/tc

Chip Thickness Ratio

Flutes must provide sufficient clearance to allow chips to be extracted from bottom of hole

Chip removal

Methods of Holding the Work in a Lathe

Chuck

The chuck is available in several designs , with three or four jaws .

Chuck

Rotational - cylindrical or disk - like shape

Classification of Machined Parts

Broaching Advantages

Close tolerances

cast irons and steels in turning and milling operations

Coated Carbides Applications

Methods of Holding the Work in a Lathe

Collet

consists of a tubular bushing with longitudinal slits running over half its length and equally spaced around its circumference

Collet

Ductile work materials ( e.g. , low carbon steel )

Continuous Chip

High cutting speeds

Continuous Chip

Low tool - chip friction

Continuous Chip

Sharp cutting edge on the tool

Continuous Chip

Small feeds and depths

Continuous Chip

BUE forms , then breaks off , cyclically

Continuous with BUE

Ductile materials

Continuous with BUE

Low - to - medium cutting speeds

Continuous with BUE

Tool - chip friction causes portions of chip to adhere to rake face

Continuous with BUE

Instead of feeding the tool parallel to the axis of rotation , tool follows a contour that is other than straight , thus creating a contoured form

Contour Turning

Cutter overhangs work on both sides

Conventional Face Milling

designed to reduce effects of heat in machining

Coolants

Cutting fluids can be classified according to function :

Coolants - Lubricants

Provides a stepped hole , in which a larger diameter follows a smaller diameter partially into the hole

Counterboring

occurs on top rake face

Crater wear

Gradual wear occurs at two locations on a tool :

Crater wear - Flank wear

Applications : machining steel and nickel - based alloys

Cubic Boron Nitride

Sawing Typical functions

Cut off unwanted portions of part

Tool is fed radially into rotating work at some location to cut off end of part

Cutoff

Garbage ( cigarette butts , food , etc. )

Cutting Fluid Contamination

Molds , fungi , and bacteria

Cutting Fluid Contamination

Small chips

Cutting Fluid Contamination

Tramp oil ( machine oil , hydraulic fluid , etc. )

Cutting Fluid Contamination

Any liquid or gas applied directly to machining operation to improve cutting performance

Cutting Fluids

Approximately 98 % of the energy in machining is converted into heat

Cutting Temperature

The remaining energy ( about 2 % ) is retained as elastic energy in the chip

Cutting Temperature

1. Single - Point Tools 2. Multiple Cutting Edge Tools

Cutting Tool Classification

End Milling Cutter Applications :

Cutting slots

The three dimensions of a machining process :

Cutting speed v- Feed f - Depth of cut d

main categories of grinding :

Cylindrical grinding

Dry machining

Dealing with Cutting Fluid Contamination

Replace cutting fluid at regular and frequent intervals

Dealing with Cutting Fluid Contamination

-wasteful of material -time-consuming

Disadvantages Machining

Used to create a round hole , usually by means of a rotating tool ( drill bit ) that has two cutting edges

Drilling

Avoids problems of cutting fluid

Dry Machining

No cutting fluid is used

Dry Machining

Cutter diameter is less than work width , so a slot is cut into part

End Milling

Looks like a drill bit but designed for primary cutting with its peripheral teeth

End Milling Cutter

( ECEA )

End cutting edge angle

Milling Cutters Principal types :

End milling cutter

Teeth cut on side and periphery of the cutter

Face Milling Cutter

is a workholding device that fastens to the lathe spindle and is used to grasp parts with irregular shapes .

Face Plate

Cutter axis is perpendicular to surface being milled

Face milling

Cutting edges on both the end and outside periphery of the cutter

Face milling

End Milling Cutter Applications :

Face milling

Milling Cutters Principal types :

Face milling cutter

Methods of Holding the Work in a Lathe

Face plate

The tool is fed radially into the rotating work on one end to create a flat surface on the end .

Facing

Variations of turning that are performed on a lathe :

Facing - Contour turning - Chamfering - Cutoff - Threading

occurs on flank ( side of tool )

Flank wear

Peripheral milling cutter in which cutting edges have special profile to be imparted to work

Form Milling Cutter

Milling Cutters Principal types :

Form milling cutter

Cutting force becomes excessive , leading to brittle fracture

Fracture failure

Three Modes of Tool Failure

Fracture failure - Temperature failure - Gradual wear

capacity to fracture when cutting edge dulls , so a new sharp edge is exposed

Friability

Delivery of cutting fluid to drill point to reduce friction and heat is difficult because chips are flowing in the opposite direction

Friction makes matters worse

Form Milling Cutter Important application

Gear - making

Broaching Advantages

Good surface finish

Gradual wearing of the cutting tool . reduction in cutting efficiency

Gradual wear

Material removal process in which abrasive particles are contained in a wheel that operates at very high surface speeds .

Grinding

is most important abrasive process

Grinding

Differences with honing :

Higher frequencies

Best surface finish is achieved by :

Higher wheel speeds

one in the headstock and the other in the tailstock

Holding the Work Between Centers

Methods of Holding the Work in a Lathe

Holding the work between centers

Functions in machining :

Holds work part

Abrasive process performed by a set of bonded abrasive sticks using a combination of rotational and oscillatory motions .

Honing

Common application is to finish the bores of internal combustion engines .

Honing

High cutting temperatures result in the following :

Produce hot chips that pose safety hazards to the machine operator

Form of end milling in which the outside periphery of a flat part is cut

Profile Milling

End Milling Cutter Applications :

Profile milling and pocketing

Cutting Fluid Filtration Advantages : fluid

Prolong cutting fluid life between changes

Functions in machining :

Provides power at speed , feed , and depth that have been set

material removal rate can be found as :

RMR = vfd

Large drill press designed for large parts

Radial Drill

Used to slightly enlarge a hole , provide better tolerance on diameter , and improve surface finish

Reaming

Cutting Fluid Filtration Advantages :

Reduce fluid disposal cost

High cutting temperatures result in the following :

Reduce tool life

Each machining operation produces a characteristic part geometry due to two factors :

Relative motions

between the tool and the workpart

Relative motions

Classification of Machined Parts

Rotational - Nonrotational

Cuts narrow slit in work by a tool consisting of a series of narrowly spaced teeth

Sawing

Traditional Chip Removal

Sawing - Broaching - Planing - Grinding Honing - Lapping

Variety of part shapes and special geometry features possible such as :

Screw threads

Brittle work materials ( e.g. , cast irons )

Segmented Chip

High tool - chip friction

Segmented Chip

Large feed and depth of cut

Segmented Chip

Low cutting speeds

Segmented Chip

Cyclical chip formation of alternating high shear strain then low shear strain

Serrated Chip

Most closely associated with difficult - to - machine metals at high cutting speeds

Serrated Chip

Semi continuous - saw - tooth appearance

Serrated Chip

Forming - part geometry is created by the shape of the cutting tool

Shape of the cutting tool

Both use a single point cutting tool moved linearly relative to the workpart

Shaping and Planing

Similar operations

Shaping and Planing

Other machining operations :

Shaping and planning - Broaching - Sawing

The basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides

Slab Milling

Width of cutter is less than workpiece width creating a slot in the work

Slotting

Best surface finish is achieved by :

Small grain sizes

Differences with honing :

Smaller grit sizes

Used for low carbon , stainless , and other alloy steels

Steel Cutting Carbide Grades

Other Abrasive Processes

Superfinishing

Similar to honing - uses bonded abrasive stick pressed against surface and reciprocating motion

Superfinishing

Ball - nose cutter is fed back and forth across the work to create a three dimensional surface form

Surface Contouring

Most grinding is performed to achieve good

Surface Finish

Two main categories of grinding :

Surface grinding

high speed machining of nonferrous metals and abrasive nonmetals such as fiberglass , graphite , and wood

Synthetic Diamonds Applications

Used to provide internal screw threads on an existing hole Tool called a tap

Tapping

Cutting temperature is too high for the tool material , causing the material at the tool point to soften

Temperature failure

Pointed form tool is fed linearly across surface of rotating workpart parallel to axis of rotation at a large feed rate , thus creating threads

Threading

drill exits the opposite side of work

Through - holes

A machining operation generally takes more time to shape a given part than alternative shaping processes

Time consuming

Complete failure of cutting edge