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Manufacturing Processes
Attributes of Manufactured Products
Type of Industries
Industry – produces or supply goods and services
Types Primary – cultivate and exploit natural resources
Examples – mining, agriculture, etc. Secondary – takes outputs of primary industries
and convert them into consumer and capital goods.
Tertiary – service sector
Types of Industries
Secondary Industries
Type of Products
Consumer Goods – purchased directly by consumers. Examples: cars, personal
computers, TVs, etc.
Capital Goods – purchased by other industries to produce goods and supply services. Examples: aircrafts, railroad
equipment, construction equipment, etc.
Product Variety and Production Quantity Quantity
Low 1 to 100 units/year
Medium 101 to 10,000 units/year
High 10,001 to millions of units/year
Variety Soft - small difference between products Hard – products differ substantially
Quantity vs Variety
Manufacturing Capability
Planta de manufactura Interdependencia entre materiales, procesos y
sistemas. Capability
Technical and physical limitations of a manufacturing industry. Manufacturing processes Product size and weight Production capacity
Materials
Metals (usually used as alloys) Ferrous – steel, cast iron, etc. Non-ferrous – aluminum, copper, gold, etc.
Ceramics Compound that includes metallic and non-metallic
(O, N,etc.) elements. Clay - hydrous aluminum silicates Silica - basis of all glass products Alumina and Silicon Carbide – abrasive
Crystalline and glasses
1/2
Materials
Polymers – compound formed of repeating structural units called mers. Carbon + one or more of H, N, O, Cl, etc.
Plastic Types Thermoplastic Thermosetting Elastomers
2/2
In addition to the three basic categories, there are: 4. Composites ‑ nonhomogeneous mixtures of the
other three basic types rather than a unique category
Figure 1.3 – Venn diagramof three basicMaterial types plus composites
Geometric Attributes
Shape Classification
Machine Tool Movement and Control
Limitations
Axial symmetry Two dimensional axes
Nonrotational symmetry Min of two dim axes
Surface Min 1 axes
Surface Limitations
Dimension
ANSI (American National Standards Institute) Numerical value expressed in appropriate units of
measure and indicated on a drawing and in other documents along with lines, symbols and notes to define the size or geometric characteristic, or both, of a part feature.
Length, width, height, diameter, angles, etc.
12’’3’’
4’’
Dimensioning Systems
U.S. Customary System (USCS) Inch (in)
International System (SI) Meter (m)
Tolerance
ANSI The total amount by which a specific dimension is
permitted to vary. Tolerance = Max Limit – Min Limit Types
Bilateral Unilateral Limit dimension
Bilateral Tolerance
Variation is permitted in both positive and negative directions from the nominal dimension
It is possible for a bilateral tolerance to be unbalanced; for example, 2.500 +0.010, -0.005
Figure 5.1 ‑ Ways to specify tolerance limits for
a nominal dimension of 2.500: (a) bilateral
Unilateral Tolerance
Variation from the specified dimension is permitted in only one direction, either positive or negative, but not both
Figure 5.1 ‑ Ways to specify tolerance limits for a nominal
dimension of 2.500:
(b) unilateral
Limit Dimensions
Permissible variation in a part feature size, consisting of the maximum and minimum dimensions allowed
Figure 5.1 ‑ Ways to specify tolerance limits for a nominal dimension of 2.500:
(c) limit dimensions
Tolerance must be…
close enough to allow functioning of the assembled parts.
as wide as functionally possible.
Tolerance
Tolerances and Manufacturing Processes Some manufacturing processes are
inherently more accurate than others Examples:
Most machining processes are quite accurate, capable of tolerances = 0.05 mm ( 0.002 in.) or better
Sand castings are generally inaccurate, and tolerances of 10 to 20 times those used for machined parts must be specified
Other Attributes
Angularity – a part feature is at specified angle relative to a reference surface.
See table 5.1
http://www.delvest.com/angularity.htm
Other Attributes
Circularity/Roundness – the degree to which all points on the intersection of the surface and a plane perpendicular to the axis of revolution are equidistant from the axis.
See table 5.1
Other Attributes
Concentricity – the degree to which any two (or more) part features have a common axis.
See table 5.1
http://www.delvest.com/concentricity.htm
5" OD x 2" ID x 2" long. 5' OD and 2' ID will be concentric within .020' TIR (5" OD - 2" = 3" separation).
Other Attributes
Cylindricity – the degree to which all points on a surface of revolution are equidistant from the axis of revolution.
See table 5.1
Other Attributes
Flatness – The extent to which all points on a surface lie in a single plane.
See table 5.1
http://www.delvest.com/flatness.htm
Other Attributes
Parallelism – the degree to which all points on a part feature are equidistant from a reference plane, line or axis.
See table 5.1
http://www.delvest.com/parallelism.htm
Other Attributes
Perpendicularity/ Squareness – the degree to which all points on a part feature are 90° from the reference plane, line or axis.
See table 5.1
http://www.delvest.com/perpendicularity.htm
Other Attributes
Straightness – the degree to which a part feature is a straight line.
See table 5.1
http://www.delvest.com/straightness.htm
Surfaces
What we touch when holding a manufactured part. Nominal surfaces – intended surface contour. Actual surfaces of a part are determined by the
manufacturing processes used to make it Importance
Aesthetic Affect safety Friction and wear Affect mechanical properties Affect assembly Smooth surfaces make better electrical contacts
Surface Components
Figure 5.2 ‑ A magnified cross‑section of a typical metallic part surface
Surface Attributes
Four Elements of Surface Texture 1. Roughness - small, finely‑spaced deviations
from nominal surface determined by material characteristics and process that formed the surface
2. Waviness - deviations of much larger spacing; they occur due to work deflection, vibration, heat treatment, and similar factors
Roughness is superimposed on waviness
3. Lay: predominant direction
or pattern of the surface texture
4.Flaws - irregularities that occur occasionally on the surface Includes cracks, scratches, inclusions, and
similar defects in the surface Although some flaws relate to surface texture,
they also affect surface integrity
Surface Attributes
Surface Roughness and Surface Finish Surface roughness - a measurable
characteristic based on roughness deviations Surface finish - a more subjective term
denoting smoothness and general quality of a surface
In popular usage, surface finish is often used as a synonym for surface roughness
Both terms are within the scope of surface texture
Surface RoughnessAverage of vertical deviations from nominal
surface over a specified surface length
Figure 5.5 ‑ Deviations from nominal surface used in the two definitions of surface roughness
Surface Roughness Equation
Arithmetic average (AA) is generally used, based on absolute values of deviations, and is referred to as average roughness
where Ra = average roughness; y = vertical deviation from nominal surface (absolute value); and Lm = specified distance over which the surface deviations are measured
dxL
yR
m
a
L
m0
An Alternative Surface Roughness Equation Approximation of previous equation is
perhaps easier to comprehend:
where Ra has the same meaning as above; yi = vertical deviations (absolute value) identified by subscript i; and n = number of deviations included in Lm
n
i
ia n
yR
1
Cutoff Length
A problem with the Ra computation is that waviness may get included
To deal with this problem, a parameter called the cutoff length is used as a filter to separate waviness from roughness deviations
Cutoff length is a sampling distance along the surface. A sampling distance shorter than the waviness width eliminates waviness deviations and only includes roughness deviations
Figure 5.6 ‑ Surface texture symbols in engineering drawings:
the symbol, and (b) symbol with identification labels
Values of Ra are given in microinches; units for other measures are given in inches
Designers do not always specify all of the parameters on engineering drawings
Material Properties
Mechanical – strength, toughness, ductility, hardness, elasticity, fatigue, creep, ratios
Physical – density, specific heat, thermal expansion, thermal conductivity, melting point, magnetic and electrical qualities
Chemical – oxidation, corrosion, degradation, toxicity, flammability
Manufacturing – manufacturability, effects on product properties, service life, cost