Chapter 15

Question 1

Name the three material removal processes

Answer 1

Machining - sharp cutting tool

Abrasive process - Hard abrasive particles like grinding

Nontraditional process - Energy forms

Question 2

Benefits of Machining (3)

Answer 2

Screw threads

Accurate round holes

Very straight edges and surfaces

Question 3

Disadvantages of machining (2)

Answer 3

Wasteful of material

Time consuming relative to another shaping process

Question 4

Explain turning. What moves what does it form

Answer 4

Single point cutting tool

rotate workpiece to form a cylindrical shape. Move tool.

Question 5

Explain drilling. What moves what does it form

Answer 5

Rotate toolpiece. Move tool.

Creates round holes with two cutting edges

Question 6

Explain milling. What moves what does it form

Answer 6

Rotate multiple-cutting-edge tool. Move piece.

Cut a plane or straight face.

Question 7

Explain single-point tools vs multiple cutting edge tools.

Answer 7

One dominant edge. Point rounded to form a nose.

More than one cutting edge.

Question 8

Describe the three dimensions of machining.

State the Material removal rate formula Rmr

Answer 8

Cutting speed v - Primary motion

Feed f - secondary motion

Depth of cut d - penetration of tool below work surface

Rmr = v f d

Question 9

Roughing vs finishing

Answer 9

Roughing - High feeds and depths; low speed

Finishing - Low feeds and depths; high cutting speed

Question 10

State the three functions in machining

Answer 10

Holds workpart
Positions tool relative to work
Provides power at determined speed, feed, and depth

Question 11

State the Chip thickness ration r

Answer 11

r = to / tc

to - depth of cut
tc - chip thickness
Ratio always less than 1

Question 12

State the four basic types of chips (3)

Answer 12

Discontinuous - Brittle work. Low cutting speed. Large feed and depth of cut. High tool-chip friction

Continuous - Ductile. High cutting speed. Small f and d. Low tool-chip friction

Continuous with Built-up edge - Ductile. Low to med v. Tool-chip friction causes portions of chip to adhere to rake face. Built-up edge forms and breaks off cyclically

Serrated - Difficult-to-machine metals. High cutting speed. Cyclical chip forms with alternating high shear strain then low shear strain.

Question 13

State the merchant equation for minimizing the energy thru shear plane angle phi. What does it say? (3)

Answer 13

phi = 45 + alpha/2 - beta/2

Phi is angle from surface to chip shear plane.
Alpha is orthogonal angle to tool face.
Beta is orthogonal angle b/w resultant force of tool to face of chip.

In order to increase shear plane angle increase rake angle and/or reduce the friction angle (reduce coefficient of friction).

Larger shear angle, smaller shear plane which lowers shear force, cutting forces, power, and temp

Question 14

State the Power to perform machining formula

Answer 14

Pc = Fc v
HPc = Fc v / 33,000

Pc - cutting power
Fc - cutting force
v - cutting speed

Question 15

Problems with high cutting temp (3)

Answer 15

Reduce tool life

Produce hot chips = safety hazard

Cause inaccuracies from thermal expansion of work material

Question 16

Cutting temp formula

Answer 16

T = (0.4 U)/ (p C) (v to/K)^0.333

T = temp rise
U = spec energy
v = cutting speed
to = depth of cut
pC = volumetric specific heat of work material
K = thermal diffusivity of work material