manufacturing technology (me461) lecture7

8/12/2019 Manufacturing Technology (ME461) Lecture7

1/25

Manufacturing Technology

(ME461)

Instructor: Shantanu Bhattacharya


2/25

Review of previous lecture

Bezier Curves.

End conditions of Bezier curves.

Plotting of a Bezier curve.

Surface modeling.

Surface entities.

Surface representations (parametric, non

parametric, implicit, explicit forms).

Hermitian, Bezier and B-spline surface patches.


3/25

CAD/ CAM data exchange

It is common knowledge that the primary cause of data sharing

problems between two or more systems is software

incompatibility.

This is due to the fact that vendors of computer applications

design different proprietary formats to store the data required

and produced by their systems.

There are two solutions one of which is to develop the systems in away that they are compatible with each other, in which case the

two commercial products are integrated and the second is to have

a neutral data exchange format for the purposes of data sharing.

By neutral file, we mean that the file has a format that can be

utilized by various systems.


4/25

Translation Strategies

In a direct translation strategy, one translator is capableonly of translating the information of one pair ofsystems.

If we have N systems, every system has to have N-1translators installed in order to input the database ofany other system created.

The total no. of translators needed would then be N(N-1).

Moreover, the strategy is so complicated that it is almostimpossible for a system to transfer data to all other

systems.


5/25

Translation Strategies In the indirect strategy, a neutral database structure is created. Neutral means

that the file format is independent of different formats utilized by the various

CAD/CAM system vendors.

With this strategy, each system needs only to have a preprocessor and a post

processor to transfer the database universally. The function of a preprocessor is

to translate the neutral file format database to the systems own database format

when the system is reading the database .

The function of a post processor is to translate the given database format to

neutral file format when output is made. In this strategy, N CAD/CAM systems will

need only 2N translators. However, indirect translating is usually slower than

direct translating.

A successful data exchange format or standard or neutral file must meet a

minimum set of requirements. The standard must cover the common entities,

such as wireframe and surface entities, used in various modeling systems.

The standard format has to be compact, which may help achieve faster storage

and retrieval; i.e., higher speed in converting data to and from the neutral format

and smaller size resulting neutral file.

Among many standards available today, the IGES and PDES standards are the most

widely used.


6/25

IGES (Initial graphics exchange

specification) This was first published in 1980 and later updated in 1983, 86, 88 and 1990. It

is the first widely accepted standard exchange format used to communicate amodeling database among dissimilar CAD/CAM systems.

In fact IGES has been used for supplying data between suppliers andcustomers, as a means to create model of objects etc.

The basic elements of IGES are entities we have discussed in previoussections. Therefore, the format of the data is basically a description of

entities. In IGES, each entity is assigned a number. Numbers 1 through 599 and 700 through 5000 are allotted for specific

assignments, and 600 through 699 and 10,000 through 99,999 are for userdefined entities.

Entities are classified as geometric entities (such as shape, curve, surface)and non geometric entities (such as relation between various entities).

The geometric entities are described via two distinct but related Cartesiancoordinate systems, namely, the model space coordinate system (MCS) or localcoordinate system (W-workingCS).


7/25

PDES (Product data exchange

standard)

The international organization for standardization (ISO) is currentlyinvolved in developing an international standard called STEP (Standard fortransfer and exchange of product model data).

STEP is a step for global standardization of exchange of informationrelated to automated manufacturing and results in the PDES.

The fundamental differences between IGES and PDES is that the IGESutilizes the basic entities as elements of the design whereas PDES dataexchange is done in terms of applications.

This philosophy is also called mental models and is reflected in the PDESthree layer architecture: Application layer-Interface between user andPDES in which the application model is explicitly expressed and thedescription and information are expressed, Logical layer which is used toprovide a consistent and computer independent description, Physicallayer which takes care of the structure of the data and its format of theexchange file.


8/25

Drawing Exchange File format

DXF has been developed by Auto desk inc. to assist ininterchange of drawings between AutoCAD and otherprograms.

The overall organization of DXF is as follows:

1. Header section: general information about the drawing.2. Tables section: Definitions of named items.

3. Blocks section: Describe the entities constituting each blockin the drawing.

4. Entities section: The drawing entities, including any blockreferences.

5. END OF FILE


9/25

Computer Aided Process Planning

Process planning serves as an integration link

between design and manufacturing and is

very important for designing a process.

In this topic we will be looking at steps to

develop a process plan, computer aided

process planning (both variant and generative

approaches), Knowledge based processplanning and feature recognition approaches.


10/25

Overview of manufacturing processes

Here we review some basic manufacturing processes like turning, drilling,

milling, and grinding. Some other manufacturing processes can be otherthan cutting processes like forming, production of electronic circuit

boards, soldering etc.

Turning operations:

1. Turning is a common and a versatile machining process for producing

cylindrical, conical, or irregularly shaped internal or external surfaces ona rotating work piece.

2. The machine tool used is the lathe.

3. Typical parts include pins, shafts, spindles, handles, and various other

components having O-ring grooves, holes, threads (both external and

internal), and many other shapes.4. Cutting operations can b performed on a lathe include straight turning,

taper turning, profiling, turning and external grooving, facing, face

grooving, drilling, boring and internal grooving, cutting off, threading and

knurling as shown in the next figure.


11/25

Various cutting operations performed on Lathe machines


12/25

Overview of manufacturing processes Drilling operations:

1. Drilling is another common machining operation for producing through holes or blind

holes.

2. For example assembly processes involving fasteners such as rivets, screws, and bolts

require holes.

3. To perform the drilling operations, a cylindrical rotary end cutting tool called a drill is

employed.

4. Different types of drills and drilling operations are used as shown below.


13/25

Overview of manufacturing processes Other operations that involve hole making include boring,

counter-boring, spot facing, countersinking, reaming, and

tapping.1. Boring: Involves enlarging an already drilled hole.

2. Counter-boring: Only one end of the drilled hole is enlarged.

3. Spot facing: Finishing off a small surface area around the

opening of a hole.4. Countersinking: It is similar to counter-boring except that

the hole enlarged at one end is conical (tapered). The idea is

to accommodate the conical seat of a flathead screw inside.

5. Reaming: Reaming is a sizing process used to make analready drilled hole dimensionally more accurate and to

provide a very smooth surface.

6. Tapping: It is the process of producing internal threads in

work-pieces by using a threaded tool with multiple cuttingteeth; the tool is called a tap.


14/25

Milling operations:

1. Milling is used to produce a variety of shapes such as flat, contoured,and helical surfaces.

2. It is used for thread and gear cutting operations, among others.

3. The milling process involves simultaneous rotary motion of milling cutter

and linear motion of work piece.

4. Based on the direction of cutter rotation and work piece feed the millingprocess is classified into upmilling and down milling based on different

or similar direction of the cutter rotation with respect to the work-piece

motion.

5. A large variety of milling cutters are used to produce different shapes for

example, plain milling cutters are used to produce flat surfaces; sidemilling cutters for cutting slots, grooves and spines; T-slot cutter for

milling T-slots; and form milling cutters for milling gears and other

concave and convex shapes.


h d f f


15/25

Methods of estimating parameters for

various milling operations

f f


16/25

Grinding Operations:

1. In grinding, material removal is achieved by

employing a rotating abrasive wheel. In fact,grinding is quire similar to milling except that

abrasive wheels are used in place of milling cutters.

2. Grinding is generally used to obtain the finest

dimensional accuracy and surface finish in

manufactured products.

3. Common grinding operations include surface

grinding, cylindrical grinding, internal grinding, andcenterless grinding.

4. For estimating the various parameters of surface

grinding for both horizontal and vertical grinding

cases are given in the next figure



17/25

Parameter estimation of horizontal

and vertical surface grinding

S f h bt i d f diff t


18/25

Surface roughness obtained from different

manufacturing processes

h l ?


19/25

What is process planning?

Products and their components are designed to perform certain functions.

The design specifications ensure the functionality aspects.

In manufacturing the task is to produce components that meet design

specifications.

The components are then assembled into final products.

Process planning acts as a bridge between the design and manufacturing bytranslating design specifications into manufacturing process details.

Process planning therefore refers to a set of instructions that are used to make a

component or a part that meets up with the design specifications.

The question is what information is required and what activities are involved in

transforming a raw part into a finished component, starting with the selection ofraw material and ending with the completion of the part.

The following basic steps are involved in developing a process plan.

B i t i d l i


20/25

Basic steps in developing a process

plan

This involves a no. of activities like:

1. Analysis of part requirements.

2. Selection of raw work piece.

3. Determining manufacturing operations and their sequences.

4. Selection of machine tools.

5. Selection of tools, work holding devices, and inspection

equipments.

6. Determining machining conditions (cutting speed, feed and

depth of cut) and manufacturing times (setup time,

processing time, and lead time).


21/25

Analysis of part requirement The primary purpose of process planning is to translate the design

requirements for parts into manufacturing process details.

At the engineering design level, the part requirements can be defined asthe part features, dimensions, and tolerance specifications which in turn

determine the processing requirements.

For example consider the part given in figure (a) with plain geometric

feature.

The part is successively

modified by a step (b).

A slot (c).

A side step (d).A blind cylindrical hole (e)


22/25

f d


23/25

Determining Manufacturing Operations and

their sequences.

The next logical step in process planning is to determine the appropriate types of

processing operations and their sequence to transform the features, dimensions,and tolerances of a part from the raw to finished state.

There may be several ways to produce a given design. Sometimes constraints such

as accessibility and setup may require that some features be machined before or

after others.

Furthermore, the types of machines and tools avialable as well as the batch sizesinfluence the process sequence.

For-example, a process plan that is optimal on a three or four axis machine may

not be optimal on a five axis machine because of the greater flexibility of higher

axis machines.

Surface roughness and tolerance requirements also influence the operation

sequence. For example, a part requiring a hole with low tolerance and surfaceroughness specifications would require a simple drilling operation. The same part

with much finer surface finish and closer tolerance requirements would require

first a drilling operation and then a boring operation to obtain the desired surface

roughness and the tolerance on the hole feature of the part.


24/25

Sometimes operations are dependent on one another. For example,

consider figure (a), in which the operations on the part show the following

dependence:

1. The holes must be drilled before milling the inclined surface because the

holes cannot be drilled accurately on an inclined surface.

2. However, if the inclined surface has to be finished before drilling, an endmill should be used to obtain a flat surface perpendicular to the axis of

the drill before drilling the hole.

Determining Manufacturing Operations and

their sequences.

3. Cutting forces and rigidity of the

workpiece may also influence

the operation sequence.

4. In (b) hole H2 must be produced

before machining the slot . If the

hole is machined after finishing

the slot, it may bend.

S l ti f hi t l


25/25

Selection of machine tools The next step in process planning after the selection of

manufacturing operations and their sequence is to select the

machine tools on which these operations can be performed.

A large number of factors influence the selection of machine

tools.

1. Work piece related attributes such as the kinds of features

desired, the dimensions of the work piece, its dimensionaltolerance, and the raw material form.

2. Machine tool related attributes such as process capability,

size, mode of operation (e.g., manual, semiautomatic,

automatic, numerically controlled etc.), tooling capabilities(e.g., size and type of tool magazine), and automatic tool

changing capabilities.

3. Production volume related information such as the

production quantity and order frequency

manufacturing technology (me461) lecture7

Documents