COMPUTER CONTROL IN PROCESS PLANNING Unit 2 (ME CAD/CAM)

COMPUTER CONTROL
PROCESS PLANING
UNIT 2
PART DESIGN PREPARATION

CCPP


1

Design Drafting
Computer-Aided Drafting and Design (CADD)is
the process where a drafter/designer/engineer
creates drawings or models that define a given
product before it is ready to be manufactured.
The drafter is the key link in the design
engineering process and manufacturing steps,
and must possess a working knowledge of
design principles, material properties, and
manufacturing processes.
CCPP


2

Basic Dimension
A theoretically exact size, profile, orientation, or
location of a feature or datum target, therefore, a
basic dimension is untoleranced.

Most often used with position, angularity, and
profile)
Basic dimensions have a rectangle surrounding it.

1.000

GEOMETRIC CHARACTERISTIC CONTROLS
14 characteristics that may be controlled

TYPE OF
FEATURE

TYPE OF
TOLERANCE

CHARACTERISTIC
FLATNESS

INDIVIDUAL (No
Datum
Reference)

FORM

STRAIGHTNESS
CIRCULARITY
CYLINDRICITY

INDIVIDUAL or
RELATED
FEATURES

PROFILE

LINE PROFILE
SURFACE PROFILE
PERPENDICULARITY

ORIENTATION

RELATED
FEATURES
(Datum
Reference
Required)

RUNOUT

ANGULARITY
PARALLELISM
CIRCULAR RUNOUT
TOTAL RUNOUT
CONCENTRICITY

LOCATION

POSITION
SYMMETRY

SYMBOL

Characteristics & Symbols

cont’d.

Maximum Material Condition MMC

Regardless of Feature Size RFS
Least Material Condition LMC
Projected Tolerance Zone

Diametrical (Cylindrical) Tolerance Zone or Feature
Basic, or Exact, Dimension
Datum Feature Symbol

Feature Control Frame

CAD-input / output devices
II. Input Devices
a. Keyboard,mouse,joystick,scanners,digital camera, bar code
reader, touch Sreeen,Speech input device (microphone)

III. Output Devices
a. Monitor , Speaker, Printers ( different types)

CCPP


7

TOPOLOGY
 Topologydescribes how elements are bounded and connected.

 Geometry describes the shape of each individual element.

CCPP


8

Topological entities
Topological entities comprise all the entities that are used to
construct the structure or skeleton of a model

January 26, 2014


9

Geometric
transformation
Graziadei/Leone
2O & 2A

October 29, 2012

Geometrical transformations
Transformations are a
turn, flip, or slide of any
figure.

Geometrical transformations
If a figure is represented by ABC, the image of this
figure will be represented by A’B’C’ (ABC PRIME)

Image

A
B
C
’

A
’

Preimage

C

B
A figure and its image will be congruent to each other.
’

They will have the same shape and the same size.

Transformations: Translations
(slides)
A translation is a transformation whose points are
all the same relative distance from the pre-image
and which is pointing in the same direction.

Transformations: Reflections
(flips)
A reflection is an isometry in which a figure and its image have
opposite orientations

3
3

3
7
2
0

3
3

3
7

2
0

An isometry is when the distance between any two points in
the pre-image must be the same as the distance between
the images of the two points.

Doing reflections: easy tricks
Y-Axis

Tricks

If the mirror line is the yaxis, just change each (x,
y) into (-x, y)
X-Axis
If the mirror line is the xaxis, just change each (x,
y) into (x, -y)

Symmetry
If a line is drawn down the middle of an object,
both sides would be identical.

Axial Symmetry
The points on the left side of the Y-axis will be
at the negative coordinates of the points on the
right side: a perfect mirror image.
Example:

4

4

1
0

1
0
5

5

Transformations: Rotations
(turns)
A rotation turns all of the points in a figure
around a given point, called the center of
rotation. The center of rotation is the only point
that does not change during the rotation.

A’ =
r(A)

A’B’ =
r(AB)

A
B
A’

B’

Transformations: Rotation
180-degree turn = half turn

A positive angle rotation is when one figure is
rotated counter-clockwise

A negative angle rotation is when the figure is
rotated clockwise.

Transformations: Identity
If the point of the pre-image and of the image is
exactly the same, this point is united.

If ALL of the points of the pre-image and image are the
same, the entire figure is united.

Transformations: Expansions &
Contractions
Produces an image that is the same shape as the
original, but it is a different size.
Expansion if the scale factor is greater than 1
Contraction is the scale factor is between 0 and 1

Inverse translations
If a transformation maps the pre-image onto its
image, then the inverse transformation maps the
image back onto the pre-image.

Basically, it is the same process, but backwards.
A
’
A

t1

B
’
B

C

C
’

DATA STRUCTURES
Each geometric model of an object in a CAD system is represented by a
set of data. The data consist of numerical values, names, codes and
symbols. This data are stored in computer memory in an organized
manner. This organization represents the relationship of each data
element to other elements; included in this relationship is the
topological relationship of surface geometry. There are also other
relationship, such as names and their associated geometries. A more
complete survey on the different types of data structure for computer
graphics can be found in two technical papers by Williams (1971) and
Grays (1967). In this section only a general data structure of CAD will be
described.

The first item in the edge list, therefore, represents the number of
edges. In the fig, edge 1 is represented by the data “ 3,3,4,5,” where the
first 3 indicates that there are three edges; 3,4 & 5. Each edge has two
vertices (edge 3 has V1 & V3). Finally, a vertex may store all the
coordinates of vertices.
22.10.2013


24

For holes, circles, and other curves and curved surfaces, a code is
necessary to distinguish them for polyhedron surfaces.
For manufacturing purposes technological information’s, such as
dimensions, tolerances, and geometric tolerances, are essential. They
must also be included in constructing the CAD data structure. Most
current systems explicitly (or more approximately externally) define
such information in a manner similar to the way in which a draftsman
would. Dimensioning and tolerancing information is not implicit
defined within the model. For a explicit dimensioning another list is
added to store the dimensioning information.

CCPP


25

Data Exchange Between CAD/CAM
Systems (Data structures)
Why do we need Data Exchange?
Why do we need Data Exchange
Design projects require data to be shared between suppliers
Different companies often used different CAD systems

All CAD systems have their own database formats
They are mostly proprietary and often confidential
Data is stored in different ways e.g. 1.0,2.0,3.0 or X1.0,Y2.0,Z3.0,
etc.

Data conversion between systems becomes necessary
CCPP


27

Data Exchange Formats
IGES (Initial Graphics Exchange Specification) 1980 US NIST,
National Institute of Standards and Technology

DXF
VDA – German Automotive Industry
SET – Airbus
PDES – American fore-runner of STEP

STEP
STL
VRML
CCPP


28

GEOMENTRIC MODELING FOR
PROCESS PLANNING
In the preceding section, the fundamentals of CAD were discussed. In this
section a discussion 3-D representation schemes and their applications to
process planning is presented.
There are seven different types of graphics representation schemes:
Wire frame
Primitive instancing

Spatial occupancy enumeration
Cell decomposition
Constructive solid geometry (CSG)

Boundary representation
Sweeping
CCPP


29

GT coding
Introduction

It is true that classification helps to bring like things together, but
with out having a proper coding system which reflecting the
classification is introduced, handling, processing families of similar
data or retrieving relevant information is more cumbersome and
inefficient. Most of the time, coding is thought of in its
cryptological sense, meaning to restrict and suppress the
dissemination of intelligence and/or information during
communication. However, when we describe it in the business
and industrial context, quite the reverse is true. In industries
properly designed codes are used as a shorthand, as a means to
compress information and improve its communication
effectiveness through the business and the outside environment.

CCPP


30

Types of Coding
Industrial codes can take several forms. Those, which use the
alphabet and/or numerals, are called alpha or numeric codes or as
combinations of the two as alphanumeric codes. But there are also
special symbol codes which are not derived from either alphabetic or
numeric sources. Here we can see the different types of codes as
follows.
Attribute code structure
Hierarchical Type

Hybrid Type
Special Symbol codes

Sample footer

31

Attribute code structure
In this type of structure, the interpretation of each symbol in the
sequence is fixed and represents one feature. Thus, the value of any
given digits (or position) within the code does not depend on the
preceding digits. Another name of this type of symbol is poly-code. The
problem associated with poly-code is that the code tends to be relatively
long. On the other hand, the use of poly-code allows for convenient
identification of specific part attribute. This can be helpful in
recognizing parts with similar processing requirements. A typical
attribute code is illustrated in the table below.

Sample footer

32

Hierarchical Type
In this type of code structure, each code number is qualified by the preceding
digits (characters). Thus if the first digits define the type of material used,
such as steel, the second digits will define a feature related to steel (like
carbon constraint), and the next digit will define a feature related to the
feature defined in the second digit and so on. A typical hierarchical code
structure is shown in Figure below. As it was shown in the diagram, each digit is
directly related to the preceding digits. Thus the second digits “2” may define
a power unit of the work part, the digit in the third position may then define
the type of power system (i.e. weather it is mechanical, hydraulic, or electric).
In the fourth position if a digit “1” is preceded by “1”, then it may define the
sub unit of the driving system that is a rotational part, or if it is proceeded by
“3” it might have totally different meaning.

Sample footer

33

Hybrid Type:
Most of the commercial parts coding system in industries are a
combination of the two pure structure (i.e. poly codes and mono codes).
The hybrid is an attempt to achieve the best feature of both poly-codes
and mono-codes. Hybrid codes are typically constructed as a series of
short poly codes. Within each of these shorter chains, the digits are
independent, but one or more of symbols in the complete code number
are used to classify the part population into groups, as in the hierarchical
structure. This hybrid coding seems to best serve the need of both design
and production.

Sample footer

34

Special Symbol codes:
This is a type of code that used picture or symbols of an object other than
numbers or alphabets to represent an activity, event, words, etc. This
special symbol codes can be hieroglyphical, which can best characterized
by the symbolic therbligs, created by Frank and Lillian Gilbreths or of more
recent vintage, the flow chart codes for tracking the handling of data
within a system. During their study of work and time-and motion, they used
an epitomized hieroglyphic code symbols to represent a fundamental
motions such as reach, grasp, think, etc. The hieroglyphic code symbols
described by the therbligs codes pictorially represent the action they
describe.

Sample footer

35

Principles of Coding
As in the case of classification, an industrial coding has also its own
principles.

These includes:
1. No code should exceed five characters without a break in the
string. That means when the code number becomes shorter it
becomes easy to handle and, fewer errors committed.
2. Identity codes should of fixed length and pattern. If we use
varying-length codes within a given class of materials it will
proliferate error rates and require justification in handling (right or
left) to the longest code in use.
3. All-numeric codes produce fewest errors.

4. Alphanumeric combination codes are acceptable if the alpha
field is fixed and used to break a string of numbers.
CCPP


36

The optiz system
The Opitz coding system uses the following digit sequence:
12345 6789 ABCD
The basic code consists of nine digits, which can be extended by
adding four more digits. The first nine digits are intended to
convey both design and manufacturing data. The general
interpretation of the nine digits is indicated in Fig in next slide
The first five digits, 12345, are called the “form code” and
describe the primary design attributes of the part. The next four
digits, 6789, constitute the “supplementary code”. It indicates
some of the attributes that would be of use to manufacturing
(work material, raw work piece shape, and accuracy). The extra
four digits, “ABCD”, are referred to as the “secondary code” and
are intended to identify the production operation type and
sequence. The secondary code can be designed by the firm to
serve its own particular needs.
CCPP


37

CCPP


38

CCPP


39

EXAMPLE
Given the part design of Fig. 9.7, the form code for this part is discussed below.

The overall length/diameter ratio, L/D = 1.6, so the first code = 1. The part is
stepped on both ends with a screw thread on one end, so the second digit code
would be 5 the third digit code is 1 because of the through hole. The fourth and
fifth digits are both 0, since no surface machining is required and there are no
auxiliary holes or gear teeth on the part. The complete form code in the Opitz
system is “15100”. To add the supplementary code, we would have to properly
code the sixth through ninth digits with data on dimensions, material, starting
work piece shape, and accuracy.
CCPP


40

The MICLASS system
The MICLASS classification number can range from 12 to 30 digits The first 12
digits are universal code that can be applied to any part. Up to 18 additional
digits can be used to code data that are specific to the particular company or
industry. For example, lot size, piece time, cost data, and operation sequence
might be included in the 18 supplementary digits.
The component attributes coded in the first 12 digits of the MICLASS number
are as follows:
1st digit

Main shape

2nd and 3rd digits

Shape elements

4th digit

Position of shape elements

5th and 6th digits

Main dimensions

7th digit

Dimension ratio

8th digit

Auxiliary dimension

9th and 10th digits

Tolerance codes

11th and 12th digits

Material codes

CCPP


41

THANK YOU

January 26, 2014


42

COMPUTER CONTROL IN PROCESS PLANNING Unit 2 (ME CAD/CAM)

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (14)

Similaire à COMPUTER CONTROL IN PROCESS PLANNING Unit 2 (ME CAD/CAM)

Similaire à COMPUTER CONTROL IN PROCESS PLANNING Unit 2 (ME CAD/CAM) (20)

Dernier

Dernier (20)

COMPUTER CONTROL IN PROCESS PLANNING Unit 2 (ME CAD/CAM)