Machining and Heat Treatment

Question 1

What is Machining

Answer 1

Where a part is shaped into its desired geometry by material removal using a sharp cutting tool

Question 2

Explain Machining

What is the Difference Between a Positive and Negative Rake Angled cutting tool?

Answer 2

Cutting Action Causes Shear Deformation of part
This causes the formation of a chip
As the Chip is removed a new surface is exposed

Positive Rake Angles reduces the cutting forces required to shear the part
Negative Rake Angle Increase Tool Stability and Strength , but require higher cutting forces to shear the part

Question 3

What is this Process

Answer 3

Turning
A Machining process that uses a single-point cutting tool
Material removal from a rotating workpiece to form a revolved geometry

Question 4

What is this process

Answer 4

Drilling
A Machining Proces that uses a Drill Press - multi-edge cutting tool.
To Create a Round hole

Question 5

What are these Two Dilling Holes Called

Answer 5

a) Through Hole
b) Blind Hole

Question 6

What is this Process

Answer 6

C) Peripheral Milling
d) Face Milling
A Machining process that uses a rotating multi-edge cutting tool
moves across workpiece to remove material

Question 7

What are the 3 Parameters of a Machining Process?

What is the formula for the Material Removal Rate?

What is the Difference Between Roughing and Finishing

Answer 7

Roughing Removes large amounts of material at low accuracy (High Feeds & Depths, Low Cutting Speed)
Finishing removes Small amount of material at high Accuracy ( Low Feeds and Depths, High Cutting Speeds)

Question 8

What are the Benefits to Machining

Answer 8

Close Tolerances
Good Surface Finishes
Special Geometric Features (Threads, Holes etc.)

Question 9

What Machined Features Should be Avoided

Explain why

Answer 9

Sharp Corners
Internal Corners
Edges
Points

Internal Corners require pointed cutting tools which are fragile
Sharp Corners and Edges create Burrs, and are dangerous to handle

Question 10

What are the 3 Modes of Tool Failure

Which is preferred

What are the two types of gradual wear for a tool

Answer 10

Fracture Failure - Excessive and Dynamic Cutting Forces, leads to brittle fracture
Temperature Failure - Cutting Temperature is to High for the tool material
Gradual Wear

Gradual wear is preferred, (Long tool life)

Crater wear - Occurs on top Rake Face
Flank Wear - Occurs on Flank (Side of tool)

Question 11

Draw a Labeled graph for Tool Flank wear against cutting time
On the Graph draw Multiple Cutting Speeds

What is a tool Life Criterion

Answer 11

Point where tool doesnt exhibit uniform wear, boundary to failure region

Question 12

What is the Taylor Tool Life Equation
What do the parameters depend on

Answer 12

Question 13

Name 3 Important properties a tool should possess

Answer 13

Toughness - to avoid Fracture
Hot Hardness - to retain hardness at high temperatures
Wear Resistance- ability to resist abrasive wear

Question 14

What is Heat Treatment

Answer 14

Heating and Cooling processes that affect the microstructure of the material, affecting its mechanical properties

Question 15

What is Annealing

Why is annealing done

Answer 15

(Heat treatment) Heating and Soaking Metal at a suitable temperature for a certain time, then slowly cooling it down.

Reduces Hardness and Brittleness
relieves internal stresses and alters microstructure
Obtains More Desirable mechanical properties
Softebs metals for forming or machining

Question 16

Explain the difference between Full Annealing and Normalising

What does this difference cause

Answer 16

Full Annealing and Noramlising both Heat and Soak Metal at a suitable temperature for a certain time

Normalising involves a fast cooling, full annealing involves a slow cooling

Normalising Results in higher strength, higher hardness but lower ductility then full annealing.

Question 17

Define Hardenability

Descibe the behavior of steels with a Good Hardenability

How is the Hardenability of a steel increased

Answer 17

Relative Capacity of a steel to be hardened by a transformation to the martensite phase from austenite under rapid cooling.
Depth below the surface of the steel which is hardened

Steels with a good Hardenability can be hardened more deeply below the surface and don’t require high cooling rates.

Alloying of steel
Alloying certain elements extend the time before the transition into pearlite, more uniform distribution of phases and finer microstructures result in higher hardenability

Question 18

What is structure is formed when Autenite is cooled Moderateltly, Slowly and Quenced

Answer 18

Question 19

What is Precipitation Hardening

What is it used for

Answer 19

Fine particles are precipitated , hardening the metal by blocking the movement of dislocations

Strengthing alloys of aluminium copper and magnesium

Question 20

What is a Solvus Line

What does it indicate

Answer 20

Boundary (Temperaute) which a solid Solution becomes unstable and separates into multiple phases

When the alloy is cooled Below the solvus line,
solute atoms precipitate out of the solution (Solubility decrease)

Question 21

Explain the Process of Precipitation Hardening

Answer 21

Question 22

What is Nitriding and Carbursing

Answer 22

Thermochemical treatments that alter the composition of only the parts surface

Carbursing: Heating a part of Low carbon steel in a Carbon Rich environment, Cabron diffuses into the surface.

Nitriding: Nitrogen is diffused into the surface of an alloy, produces a thin hard casing without the need to quench.