Final Exam Review

Material-Process-Geometry Relationships

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Function

Process

Material Geometry

Role of Prod Engr

Role of Mfg Engr

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Materials in Manufacturing

Most engineering materials can be classified into one of four basic categories: 1. Metals

2. Ceramics

3. Polymers

4. Composites

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Processing Operations

Three categories of processing operations:

1. Shaping operations - alter the geometry of the starting work material

2. Property‑enhancing operations - improve physical properties of the material without changing its shape

3. Surface processing operations - clean, treat, coat, or deposit material onto the exterior surface of the work

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Shaping – Four Main Categories

Solidification Processes - starting material is a heated liquid that solidifies to form part geometry

Deformation Processes - starting material is a ductile solid that is deformed

Material Removal Processes - starting material is a ductile/brittle solid, from which material is removed

Assembly Processes - two or more separate parts are joined to form a new entity

Comparing Processes

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Stress-Strain Relationships

Figure 3.3 Typical engineering stress‑strain plot in a tensile test of a metal.

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True Stress-Strain Curve

Figure 3.4 ‑ True stress‑strain curve for the previous engineering stress‑strain plot in Figure 3.3.

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Strain Hardening

Figure 3.5 True stress‑strain curve plotted on log‑log scale.

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Recrystallization and Grain Growth

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Scanning electron micrograph taken using backscattered electrons, of a partly recrystallized Al-Zr alloy. The large defect-free recrystallized grains can be seen consuming the deformed cellular microstructure.

--------50µm-------

Phase Dispersion – speed of quenching

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Allotropic Transformation and Tempering

Figure 6.4 Phase diagram for iron‑carbon system, up to about 6% carbon.

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Tempered Martensite

Austenizing

Quenching

Figure 27.5 Precipitation hardening: (a) phase diagram of an alloy system consisting of metals A and B that can be precipitation hardened; and (b) heat treatment: (1) solution treatment, (2) quenching, and (3) precipitation treatment.

Precipitation Hardening - Al 6022 (Mg-Si)

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Machining Relationships

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Machine Tool

Workpiece

Workholding Tool Cutting Tool

Higher shear plane angle means smaller shear plane which means lower shear force, cutting forces, power, and temperature

Figure 21.12 Effect of shear plane angle : (a) higher with a resulting lower shear plane area; (b) smaller with a corresponding larger shear plane area. Note that the rake angle is larger in (a), which tends to increase shear angle according to the Merchant equation

Effect of Higher Shear Plane Angle

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Turning Parameters Illustrated

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Machining Calculations: Turning

Spindle Speed - N (rpm) v = cutting speed Do = outer diameter

Feed Rate - fr (mm/min -or- in/min) f = feed per rev

Depth of Cut - d (mm -or- in) Do = outer diameter

Df = final diameter

Machining Time - Tm (min) L = length of cut

Mat’l Removal Rate - MRR (mm3/min -or- in3/min)

oDπ

vN

2fo DD

d

rm f

LT

fNfr

dfvMRR

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Unit Power in Machining

Useful to convert power into power per unit volume rate of metal cut Called the unit power, Pu or unit horsepower, HPu

or

Tool sharpness is taken into account multiply by 1.00 – 1.25 Feed is taken into account by multiplying by factor in Figure 21.14where MRR = material removal rate

MRRP

P cu

MRRHP

HP cu

What if feed changes?

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Unit Horsepower

The significance of HPu is that it can be used: 1) to determine the size of the machine tool required to perform a particular cutting operation; and 2) the size of the cutting force on the workholding and cutting tools.

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E

MRRCHP

E

HPHP

v

MRRCHP

v

HPF

MRRCHPHP

fucg

fucc

fuc

000,33000,33

HPu ~ hp/in3/min

Cf ~ correction factor

MRR ~ in3/min

Fc ~ lb

V ~ ft/min

E ~ machine tool efficiency

33,000 ~ conversion between ft-lb & hp

Example

In a turning operation on stainless steel with hardness = 200 HB, the cutting speed = 200 m/min, feed = 0.25 mm/rev, and depth of cut = 7.5 mm. How much power will the lathe draw in performing this operation if its mechanical efficiency = 90%.

From Table 21.2, U = 2.8 N-m/mm3 = 2.8 J/mm3

Since feed is 0.25 mm/rev, the correction factor is 1

21

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Example: Solution

MRR = vfd

= (200 m/min)(103 mm/m)(0.25 mm)(7.5 mm)

= 375,000 mm3/min = 6250 mm3/s

Pc = (6250 mm3/s)(2.8 J/mm3)(1.0) = 17,500 J/s

= 17,500 W = 17.5 kW

Accounting for mechanical efficiency, Pg

= 17.5/0.90 = 19.44 kW

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Flow of Molten Liquid Requires Heating

Heat Transfer of Liquid in Mold Cavity During and After Pouring

Solidification into Component

Casting

Common process attributes:

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Gating System

Channel through which molten metal flows into cavity from outside of mold

Consists of a downsprue, through which metal enters a runner leading to the main cavity

At top of downsprue, a pouring cup is often used to minimize splash and turbulence as the metal flows into downsprue

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Pouring Calculations

Minimum mold filling time, MFT

MFT =V/Q

Q: volumetric flow rate, cm3/s

V: mold cavity volume, cm3

Chvorinov's Rule

where TST = total solidification time; V = volume of the casting; A = surface area of casting; n = exponent usually taken to have a value = 2; and Cm is mold constant

n

m A

VCTST

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Amount and Composition

Figure 6.2 Phase diagram for the copper‑nickel alloy system.

Shrinkage in Solidification and Cooling

Figure 10.8 Shrinkage of a cylindrical casting during solidification and cooling: (0) starting level of molten metal immediately after pouring; (1) reduction in level caused by liquid contraction during cooling (dimensional reductions are exaggerated for clarity).

Shrinkage in Solidification and Cooling

Figure 10.8 (2) reduction in height and formation of shrinkage cavity caused by solidification shrinkage; (3) further reduction in height and diameter due to thermal contraction during cooling of solid metal (dimensional reductions are exaggerated for clarity).