Final Exam Review

Material-Process-Geometry Relationships Function Role of Prod Engr Material Geometry Role of Mfg Engr Process

Materials in Manufacturing Most engineering materials can be classified into one of four basic categories: Metals Ceramics Polymers Composites

Processing Operations Three categories of processing operations: Shaping operations - alter the geometry of the starting work material Property‑enhancing operations - improve physical properties of the material without changing its shape Surface processing operations - clean, treat, coat, or deposit material onto the exterior surface of the work

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

Stress-Strain Relationships Figure 3.3 Typical engineering stress‑strain plot in a tensile test of a metal.

True Stress-Strain Curve Figure 3.4 ‑ True stress‑strain curve for the previous engineering stress‑strain plot in Figure 3.3.

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

Recrystallization and Grain Growth 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

Allotropic Transformation and Tempering Austenizing Quenching Figure 6.4 Phase diagram for iron‑carbon system, up to about 6% carbon. Tempered Martensite 12

Precipitation Hardening - Al 6022 (Mg-Si) 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. 13

Machining Relationships Machine Tool Workholding Tool Cutting Tool Workpiece

Effect of Higher Shear Plane Angle 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 15

Turning Parameters Illustrated

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) Df = final diameter Machining Time - Tm (min) L = length of cut Mat’l Removal Rate - MRR (mm3/min -or- in3/min)

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 21.14 where MRR = material removal rate

What if feed changes? As feed decreases, we are cutting material that is progressively harder due to strain hardening from prior pass.

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. 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

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

Common process attributes: Casting Common process attributes: Flow of Molten Liquid Requires Heating Heat Transfer of Liquid in Mold Cavity During and After Pouring Solidification into Component

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

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

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).