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Gandhinagar Institute of Technology
Subject : Production Technology
(2161909)
Topic : Machinability of Metals
Mechanical : 6th : B
Prepared By :
Darshit Panchal (130120119114)
Guided By :
Prof. Sajan Chourasia

Machinability:
 Ease or difficulty with which metal can be machines
 Materials with good machinability require little power to cut, can be cut
quickly, easily obtain a good finish, and do not wear the tooling much; such
materials are said to be free machining.

Results of (Free Machining) Modifications:
 Three main machining characteristics become evident
- Tool life is increased
- Better surface finish produced
- Lower power consumption required for machining

Grain Structure:
 Machinability of metal affected by its microstructure
 Ductility and shear strength modified greatly by operations
such as annealing, normalizing and stress relieving
 Certain chemical and physical modifications of steel improve
machinability
- Addition of sulfur, lead, or sodium sulfite
- Cold working, which modifies ductility

Low Carbon Steel:
 Large areas of ferrite interspersed with small areas of pearlite
- Ferrite: soft, high ductility and low strength
- Pearlite: low ductility and high strength
• Combination of ferrite and iron carbide
 More desirable microstructure in steel is when pearlite well distributed
instead of in layers

High Carbon Steel:
 Greater amount of pearlite because of higher carbon content
- More difficult to machine steel efficiently
 Desirable to anneal these steels to alter microstructures
- Improves machining qualities

Alloy Steel:
 Combinations of two or more metals
 Generally slightly more difficult to machine than low-or high-carbon
steels
 To improve machining qualities
- Combinations of sulfur and lead or sulfur and manganese in proper
proportions added
- Combination of normalizing and annealing
 Machining of stainless steel greatly eased by addition of selenium

Cast Iron:
 Consists generally of ferrite, iron carbide, and free carbon
 Microstructure controlled by addition of alloys, method of casting, rate
of cooling, and heat treating
 White cast iron cooled rapidly after casting
- hard and brittle (formation of hard iron carbide)
 Gray cast iron cooled gradually
- composed by compound pearlite, fine ferrite, iron carbide and flakes
of graphite (softer)

Cast Iron:
 Machining slightly difficult due to iron carbide and presence of sand on
outer surface of casting
 Microstructure altered through annealing
- Iron carbide broken down into graphitic carbon and ferrite
• Easier to machine
 Addition of silicon, sulfur and manganese gives cast iron different
qualities

Aluminum:
 Pure aluminum generally more difficult to machine than aluminum
alloys
- Produces long stringy chips and harder on cutting tool
 Aluminum alloys
- Cut at high speeds, yield good surface finish
- Hardened and tempered alloys easier to machine
- Silicon in alloy makes it difficult to machine
• Chips tear from work (poor surface)

Copper:
 Heavy, soft, reddish-colored metal refined from copper ore (copper sulfide)
- High electrical and thermal conductivity
- Good corrosion resistance and strength
- Easily welded, brazed or soldered
- Very ductile
 Anneal: heat at 1200º F and quench in water
 Does not machine well: long chips clog flutes of cutting tool
- Coolant should be used to minimize heat

Effects of Temperature & Friction:
 Heat created
- Plastic deformation occurring in metal during process of forming chip
- Friction created by chips sliding along cutting-tool face
 Cutting temperature varies with each metal and increases with cutting speed and rate of
metal removal
 Greatest heat generated when ductile material of high tensile strength cut
 Lowest heat generated when soft material of low tensile strength cut
 Maximum temperature attained during cutting action
- affects cutting-tool life, quality of surface finish, rate of production and accuracy of
workpiece

Factors affecting surface Finish:
 Feed rate
 Nose radius of tool
 Cutting speed
 Temperature generated during machining process

Surface Finish:
 Direct relationship between temperature of workpiece and quality of surface
finish
- High temperature yields rough surface finish
- Metal particles tend to adhere to cutting tool and form built-up edge
 Cooling work material reduces temperature of cutting-tool edge
- Result in better surface finish

Effects of Cutting Fluids:
 Perform three important functions
- Reduce temperature of cutting action
- Reduce friction of chips sliding along tool face
- Decrease tool wear and increase tool life
 Three types of cutting fluids
- Cutting oils
- Emulsifiable (soluble) oils
- Chemical (synthetic) cutting fluids

Cutting Fluids:
 Generally used for machining steel, alloy steel, brass and bronze with high-
speed steel cutting tools
 Not used with cemented-carbide tools
• If used, great quantities of cutting fluid are applied to ensure uniform
temperatures to prevent carbide inserts from cracking
 Not generally used with cast iron, aluminum, and magnesium alloys
• Good results have been found in some cases

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2161909 130120119114

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