manufacturing processes attributes of manufactured products

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