Nota Final Pembuatan.docx

8/10/2019 Nota Final Pembuatan.docx

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CHIP TYPE

1.

Discontinuous chip

Brittle work materials

Low cutting speeds

Large feed and depth of cut

High tool-chip friction

2.

Continuous chip

Ductile work materials

High cutting speeds

Small feeds and depths

Sharp cutting edge

Low tool-chip friction

3.

Continuous chip with Built-up Edge (BUE)

Ductile materials

Low-to-medium cutting speeds

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

BUE forms, then breaks off, cyclically


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4.

Serrated chip

Semi continuous - saw-tooth appearance

Cyclical chip forms with alternating high shear strain then low shear strain

Associated with difficult-to-machine metals at high cutting speeds

TURNING

Single point cutting tool removes material from a rotating workpiece to generate a cylinder

Facing

Tool is feed radially inward

Contour turning

Instead of feeding tool parallel to axis of rotation, tool follows a contour that is other than

straight, thus creating a contoured shape


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Chamfering

Cutting edge cuts an angle on the corner of the cylinder, forming a "chamfer"

Cutoff

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

Threading

Pointed form tool is fed linearly across surface of rotating workpart parallel to axis of rotation at

a large feed rate, thus creating threads

IMPORTANT FORMULA

DoDf = 2d

fr = Nf Tm = L/fr

MRR = vfd

MRR = material removal rate, mm3/min, f = feed, mm


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MILLING

Machining operation in which work is fed past a rotating tool with multiple cutting edges.Axis of tool

rotation is perpendicular to feed

Peripheral Milling . Face Milling

Cutter axis parallel to surface being machined Cutter axis perpendicular to surface being milled

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

periphery of the cutter

Method Of Milling

Up Milling Down Milling

Up milling is also referred to as conventional

milling. The direction of the cutter rotation

opposes the feed motion. For example, if the

cutter rotates clockwise , the work piece is fed to

the right in up milling.

Down milling is also referred to as climb milling.

The direction of cutter rotation is same as the feed

motion. For example, if the cutter rotates

counterclockwise , the work piece is fed to the

right in down milling

Type Of Milling Process

Slab Milling Basic form of peripheral milling in which the cutterwidth extends beyond the work piece on both

sides

Slotting Width of cutter is less than workpiece width,

creating a slot in the work


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Conventional Face Milling Cutter overhangs work on both sides

Profile Milling Form of end milling in which the outside periphery

of a flat part is cut

Pocket Milling Another form of end milling used to mill shallow

pockets into flat parts

Surface Contouring Ball-nose cutter fed back and forth across work

along a curvilinear path at close intervals to create

a three dimensional surface form

End Milling Cutter diameter is less than work width, so a slot is

cut into part


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IMPORTANT FORMULA

fr = Nntf

MRR = wdfr

)( dDdA

r

mf

ALT

A = O = D/2

)( wDwOA

INVESTMENT CASTING

Process

(1) Wax patterns are produced,

(2) Several patterns are attached to a sprue to

form a pattern tree

(3) The pattern tree is coated with a thin layer of

refractory material,

(4) The full mold is formed by covering the coated

tree with sufficient refractory material to make

it rigid


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(5) The mold is held in an inverted position and

heated to melt the wax and permit it to drip

out of the cavity

(6) The mold is preheated to a high temperature,

the molten metal is poured, and it solidifies

(7) The mold is broken away from the finished

casting and the parts are separated from the

sprue

Advantages Disadvantaged

Complex shapes which are difficult to

produce by any other method are possible

Size is limited to weight of the casting

Very fine details and thin sections can be

produced

More expensive process because manual

labor is required

Very close tolerance and better finish can

be produced

Very little or no machining required

Since no parting line, dimensions across it

would not affect


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DIE CASTING

A permanent mold casting process in which molten metal is injected into mold cavity under high

pressure .

Pressure is maintained during solidification, then mold is opened and part is removed

COLD WORKING

Performed at room temperature or slightly above

Many cold forming processes are important mass production operations

Minimum or no machining usually required

(These operations are near net shapeor net shapeprocesses)

Advantages Disadvantages

Better accuracy, closer tolerances

Higher forces and power required in the

deformation operation

Better surface finish Surfaces of starting workpiece must be

free of scale and dirt

Strain hardening increases strength and

hardness

Ductility and strain hardening limit the

amount of forming that can be done

HOT WORKING

Deformation at temperatures abovetherecrystallization temperature

Recrystallization temperature = about one-half of melting point on absolute scale

In practice, hot working usually performed somewhat above 0.5Tm

Metal continues to soften as temperature increases above 0.5Tm, enhancing advantage of hot

working above this level

Why Hot Working?

Capability for substantial plastic deformation of the metal - far more than possible with cold

working or warm working

Why?

Strength coefficient (K) is substantially less than at room temperature

Strain hardening exponent (n) is zero (theoretically)

Ductility is significantly increased


Workpart shape can be significantly

altered

Lower dimensional accuracy

Lower forces and power required

Shorter tool life

Metals that usually fracture in cold

working can be hot formed

Higher total energy required (due to the

thermal energy to heat the workpiece)


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Types of Forging Dies

Open-die forging- work is compressed between two flat dies, allowing metal to flow laterally

with minimum constraint

Impression-die forging- die contains cavity or impression that is imparted to workpart

Metal flow is constrained so that flash is created

Flashless forging- workpart is completely constrained in die

No excess flash is created


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IMPRESSION-DIE FORGING

Several forming steps often required, with separate die cavities for each step

Beginning steps redistribute metal for more uniform deformation and desired metallurgical

structure in subsequent steps

Final steps bring the part to final geometry Impression-die forging is often performed manually by skilled operator under adverse

conditions

Sequence in impression-die forging:

(1) Just prior to initial contact with raw workpiece,

(2) Partial compression

(3) Final die closure, causing flash to form in gap between die plates.

Advantages Limitation

Higher production rates Not capable of close tolerances

Less waste of metal Machining often required to achieve

accuracies and features needed

High strength


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Sheet and Film Production Processes

Most widely used processes are continuous, high production operations

Processes include:

Slit-Die Extrusion of Sheet and Film

Blown-Film Extrusion Process

Calendering

BLOWN-FILM EXTRUSION PROCESS

Combines extrusion and blowing to produce a tube of thin film

Process sequence:

Extrusion of tube

Tube is drawn upward while still molten and simultaneously expanded by air inflated into it

through die

Air is blown into tube to maintain uniform film thickness and tube diameter


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CALENDERING

A typical roll configuration in calendering

Feedstock is passed through a series of rolls to reduce thickness to desired gage

Expensive equipment, high production rates Process is noted for good surface finish and high gage accuracy

Typical materials: rubber or rubbery thermoplastics such as plasticized PVC

Products: PVC floor covering, shower curtains, vinyl table cloths, pool liners, and inflatable boats

and toy

Criteria

Cost of the equipment is high

Production rate is high

Close control is required over all temperatures and rotational speed.

Good surface finish and high accuracy in film making process.

Eg. PVC flooring, shower curtains, table cloths, inflatable boats and toys.


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Others Type of Molding

COMPRESSION MOLDING

Molding materials:

Phenolics, melamine, urea-formaldehyde, epoxies, urethanes, and elastomers

Typical compression-molded products:

Electric plugs, sockets, and housings; pot handles, and dinnerware plates

Simpler than injection molds

No sprue and runner system in a compression mold

Process itself generally limited to simpler part geometries due to lower flow capabilities of TS

materials

Mold must be heated, usually by electric resistance, steam, or hot oil circulation

Compression molding for thermosetting plastics:

(1) Charge is loaded

(2) And (3) charge is compressed and cured

(4) Part is ejected and removed.


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BLOW MOLDING

Molding process in which air pressure is used to inflate soft plastic into a mold cavity

Important for making one-piece hollow plastic parts with thin walls, such as bottles

Because these items are used for consumer beverages in mass markets, production is typically

organized for very high quantities

Blow Molding Process

Injection blow molding: (1) parison is injected molded around a blowing rod; (2) injection mold is

opened and parison is transferred to a blow mold; (3) soft polymer is inflated to conform to the blow

mold; and (4) blow mold is opened and blown product is removed.

Accomplished in two steps:

Fabrication of a starting tube, called aparison

Inflation of the tube to desired final shape

Forming the parison is accomplished by either

Extrusion or Injection molding


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POWDER METALLURGY

Metal processing technology in which parts are produced from metallic powders

Usual PM production sequence:

1.

Pressing - powders are compressed into desired shape to produce green compact

Accomplished in press using punch-and-die tooling designed for the part

2.

Sintering green compacts are heated to bond the particles into a hard, rigid mass

Performed at temperatures below the melting point of the metal

Powder metallurgy products

Iron and steel

Copper and alloys Aluminum

Molybdenum

Tungsten

Tungsten carbide

Nickel

Tin

Why Powder Metallurgy is Important ?

PM parts can be mass produced to net shape or near net shape, eliminating or reducing the

need for subsequent machining

PM process wastes very little material - ~ 97% of starting powders are converted to product

PM parts can be made with a specified level of porosity, to produce porous metal parts

o Examples: filters, oil-impregnated bearings and gears

Certain metals that are difficult to fabricate by other methods can be shaped by powder

metallurgy


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Reduction in the production time. Pure metal powders are very expensive to

produce.

Dies required are very expensive and

needed large quantities of products.

Volume must be justified. Close dimensional tolerances can be

maintained

Size of the products to be produced is

limited because of the large presses are

required.

Composition of product can be controlled.

No risk of contamination.

Lack of metals powder like steels, bronzes,

brasses etc.

Although the cost of metal powder is high,

there is no loss of material. The parts can

be produced clean & bright, ready for use

Strength properties are lower than those

of similar article produced by conventional

methods.

Useful for magnetic core having special

desirable properties

Poor plastic properties impact strength

and elongation. Composition, structure and properties can

be controlled more easily and closely than

any other fabricating process.

Die design limit the size of products.


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FUSION WELDINGARC WELDING

Arc Welding

A fusion welding process in which coalescence of the metals is achieved by the heat from an

electric arc between an electrode and the work

Electric energy from the arc produces temperatures ~ 10,000 F (5500 C), hot enough to melt any

metal

Most AW processes add filler metal to increase volume and strength of weld joint

An electric arc is a discharge of electric current across a gap in a circuit

It is sustained by an ionized column of gas (plasma) through which the current flows

To initiate the arc in AW, electrode is brought into contact with work and then quickly separated

from it by a short distance

A pool of molten metal is formed near electrode tip, and as electrode is moved along joint,

molten weld pool solidifies in its wake

Two Basic Types of AW Electrodes

Consumable consumed during welding process (Source of filler metal in arc welding)

No consumable not consumed during welding process(Filler metal must be added separately)

Arc Shielding

At high temperatures in AW, metals are chemically reactive to oxygen, nitrogen, and hydrogen

in air

Mechanical properties of joint can be seriously degraded by these reactions

To protect operation, arc must be shielded from surrounding air in AW processes

Arc shielding is accomplished by:


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Shielding gases, e.g., argon, helium, CO2

Flux

Power Source in Arc Welding

Direct current (DC) vs. Alternating current (AC)

AC machines less expensive to purchase and operate, but generally restricted to ferrous metals

DC equipment can be used on all metals and is generally noted for better arc control

SOLID STATE WELDING (SSW)

Coalescence of part surfaces is achieved by:

Pressure alone, or

Heat and pressure

If both heat and pressure are used, heat is not enough to melt work surfaces

For some SSW processes, time is also a factor

No filler metal is added

Each SSW process has its own way of creating a bond at the faying surfaces

Essential factors for a successful solid state weld are that the two faying surfaces must be:

Very clean

In very close physical contact with each other to permit atomic bonding

Processes under SSW group

Forge welding

Cold welding

Roll welding

Hot pressure welding

Diffusion welding

Explosion welding

Friction welding

Ultrasonic welding


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FRICTION WELDING

SSW process in which coalescence is achieved by frictional heat combined with pressure

When properly carried out, no melting occurs at faying surfaces

No filler metal, flux, or shielding gases normally used

Process yields a narrow HAZ Can be used to join dissimilar metals

Widely used commercial process, amenable to automation and mass production

Friction welding (FRW): (1) rotating part, no contact; (2) parts brought into contact to generate friction

heat; (3) rotation stopped and axial pressure applied; and (4) weld created.

Applications:

Shafts and tubular parts

Industries: automotive, aircraft, farm equipment, petroleum and natural gas

Limitations:

At least one of the parts must be rotational

Flash must usually be removed

Upsetting reduces the part lengths (which must be taken into consideration in product design)

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