7/29/2019 MPii (S) Lecture 10

1/15

Straightness and flatness testing

The features such as straightness, flatness , roundness and profile areimportant aspect of engineering design and manufacturing. For example

piston rods, instrument components and machine tool sideways shouldall meet certain requirement to function properly, so their accuratemeasurement is essential.

Straightness testing.

Straightness is extending continuously in the same direction withoutcurving. Straightness can be checked with straight edges or with dialindicators. Autocollimetors is used for measuring straightness.

7/29/2019 MPii (S) Lecture 10

2/15

Autocollimetor Autocollimetor resumbles a telescope with a light beam which bounces

back from the object, are used for acurately measuring small angulardeviations on the flat.

7/29/2019 MPii (S) Lecture 10

3/15

Flatness. In the manufacture of precision parts and assemblies, flatness is a

critical quality of the manufactured surfaces. Flatness is a horizontal surface without a slope, tilt, or curvature.

Flatness can be measured by mechanical means using a surface plate

and a dial indicator. Another method for measuring flatness is by

interferometry. The device, a glass or fused quartz disk with parallel flatsurface, is placed on the surface of the workpiece. When amonochromatic (i.e. of only one wavelength) light beam is aimed at thesurface at an angle, the optical flat splits it into two beams, appearing aslight and dark bands to the naked eye. However, a truely flat workpiece

surface will not split the light beam and thus the fringes will not appear.

7/29/2019 MPii (S) Lecture 10

4/15

Process Planning

7/29/2019 MPii (S) Lecture 10

5/15

Introduction to process planning

Process planning involves the sequence of individual manufacturingoperations for each component, sub-assembly and final assembly of allsub-assemblies.

It determines the most approperiate manufacturing process and the orderin which they should be performed to produce a given part or product. Itincludes:

1) what processes and methods should be used and in what sequence.

2) determining tooling and gauging requirement. 3) selecting production equipment and systems and 4) estimating production time and cost of production for the selected processes,toolings and equipment.

The process planning starts with the selection of raw material and endswith the completion of part and usually begins after the basic process hasprovided initial part shape.

It is also called as operation sheet, route sheet, operation planning. It requires a through knowledge of machining processes, and assembly

processes and exhaustive knowledge of the plant capabilities and the skill

7/29/2019 MPii (S) Lecture 10

6/15

Processing Sequence to manufacture a part.

The process needed to manufacture a given part determined by thematerial out of which the part is made. A typical processing sequence to

fabricate a discrete part consists of:

1. A basic process--- it establishes the initial geometry of the part.e.g. Metal casting, forging, rolling, extrusion etc.

2. One or more secondary processes----. these processes transformthe basic shape into the final geometry.

3. Operations to enhance physical properties---- include heattreatment

4. Finishing operations---- include coating on the workpart surfacesuch as electroplating, painting etc.

7/29/2019 MPii (S) Lecture 10

7/15

Process planning classification

Process Planning is classified into the following two processes:-

1. Manual or traditional process planning.2. Computer-aided Process Planning (CAPP)

It is divided into two partsi) Retrival or Variant CAPP systemsii) Generative CAPP systems

7/29/2019 MPii (S) Lecture 10

8/15

The manual experience-based planning

method The manual experience-based process planning is most widely used.

Traditionally, process planning is accomplished by manufacturingengineers who are knowledgeable in the particular processes used in thefactory and are able to read engineering drawings

It is mainly based on a manufacturing engineer's experience and

knowledge of production facilities, equipment, their capabilities,processes, and tooling.

Based on their knowledge, skill, and experience, they develop theprocessing steps in the most logical sequence required to make each part.

There is much deviations in the level of details among differetcompanies and industries.

The major problem with this approach is that it is time consuming anddeveloped plans may not be consistent and optimum.

7/29/2019 MPii (S) Lecture 10

9/15

2. Computer Aided Process Planning (CAPP)

Computer aided process planning is developed to overcome theproblems experienced while using the manual experience-based processplanning .

Computer aided process planning is nothing but automating the processplanning function by means of computer system.

CAPP integrates and optimizes system performance in best possibleway. For example, when one changes the design, it must be able to fallback on CAPP module to generate manufacturing process and costestimates for these design changes.

Similarly, in case of machine breakdown on the shop floor, CAPP mustgenerate the alternative actions so that most economical solution can beadopted in the given situation.

7/29/2019 MPii (S) Lecture 10

10/15

Methods in Computer Aided Process

Planning (CAPP). Two major methods are used in computer aided process planning; the

variant/ retrival CAPP method and the generative CAPP method.

1) The variant or retrival CAPP method

In variant CAPP approach, a process plan for a new part is createdby recalling, identifying and retrieving an existing plan for a similar partand making necessary modifications for the new part.

Sometimes, the process plans are developed for parts representing a

family of parts called master parts. The similiarities in design attributesand manufacturing methods are exploited for the purpose of formationof part families.

Ad d di d f

7/29/2019 MPii (S) Lecture 10

11/15

Advatages and dis-advantages of

varient methodAdvantages.

1. Once a standard plan has been written, a variety of components canbe planned.

2. Comparatively simple programming and installation (compared withgenerative systems) is required to implement a planning system.

3. The system is understandable, and the planner has control over thefinal plan.

4. It is easy to learn, and easy to use.Dis- Advantages.

1. The components to be planned are limited to similar componentspreviously planned.2. Experienced process planners are still required to modify the

standard plan for the specific component.3. It cannot be used in an entirely automated manufacturing system,

without additional process planning.

7/29/2019 MPii (S) Lecture 10

12/15

2) The generative CAPP methodIt is a system which automatically synthesizes a process plan for a

new component. In the generative CAPP, process plans are generated bymeans of decision logic, formulas, technology algorithms and geometrybased data for converting part from raw material to finished state. Thelevel of detail is much greater in a generative system than a variant system.

There are two major components of generative CAPP. Geometry based coding scheme defines all geometric features for

process related surfaces together with feature dimensions, locations,tolerances and the surface finish desired on the features.

Process knowledge in form of decision logic. Development ofmanufacturing knowledge base is backbone of generative CAPP. It

includes selection of processes, machine tools, jigs or fixtures, tools,inspection equipment and sequencing operations.

7/29/2019 MPii (S) Lecture 10

13/15

Advantages and Dis-advantages of thegenerative approach

Advantages:-1. Generate consistent process plans rapidly;2. New components can be planned as easily as existing components;3. It has potential for integrating with an automated manufacturing

facility to provide detailed control information.

Dis-advantages:-1. It is time consumig process.2. Require thorough knowledge of the processes and related intricacies3. Cost effective.

7/29/2019 MPii (S) Lecture 10

14/15

Advantages of CAPPCAPP has some important advantages over manual process planning

which includes;

Reduced process planning and production lead-times

Faster response to engineering changes in the product

Greater process plan accuracy and consistent process plans thanwhen traditional process planning is used.

It can increase productivity of process planners.

It can reduce the skill required of a planner.

Inclusion of up-to-date information in a central database

Improved cost estimating procedures and fewer calculation errors More complete and detailed process plans.

Improved production scheduling and capacity utilization..

Improved ability to introduce new manufacturing technology and

rapidly update process plans to utilize the improved technology.

7/29/2019 MPii (S) Lecture 10

15/15

It can reduce both process planning and manufacturing cost.

Improved legibility over manually written route sheets.

CAPP programs can be interfaced with other application

programs, such as cost estimating, work standards, and others.