SCALE RATIOS

Engineering and architectural drawing scales The recommended scales for use in engineering drawing practice and in architectural and building drawings are specified in Table 5.1.

NOTE: If, for special applications, there is need for a larger enlargement scale or a smaller reduction scale than those shown in the table, the recommended range of scales may be extended in either direction, provided that the required scale is derived from a recommended scale by multiplying by integral powers of 10. In exceptional cases where for functional reasons the recommended scales cannot be applied, intermediate scales may be chosen.

Australian Standard

Technical drawing

Part 101: General principles

For history before 1992, see Preface.

Second edition AS 1100.101—1992.

PUBLISHED BY STANDARDS AUSTRALIA

(STANDARDS ASSOCIATION OF AUSTRALIA)

1 THE CRESCENT, HOMEBUSH, NSW 2140

ISBN 0 7262 7806 8

Accessed by WOODSIDE ENERGY LTD on 21 Nov 2001

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Concurrent Engineering Design

The production process executes the final results of the design process to produce a product or system. In the pas\. the creative design process was separated from the production process. With the advent of computer modeling. this separation is no longer necessary. and the modern engineering design approach brings both proc'CSses together.

Concurrent engineering is a nonlinear team approach to design that brings together the input. processes. and output elements necessary to produce a product. The people and processes are brought together at the very beginning. which is not normally done in the linear approach. nte team consists of design and production engineers. technicians. marketing and finance personnel. planners. and managers. who work together [0 solve a problem and produce a product.

Many companies are finding that concurrent engineering pmcticcs result in a belter. higher-quality product. morc satisfied customers. fewer manufacturing problems. and a shorter cycle time between design initiation ,md final production.

Figures 2.7 and 2.8 represent the concurrent approach to engineering design. based on 3-D modeling. The three intersecting circles represent the concurrent nature of this design approach. For example. in the ideation phase. design engineers interact with service technicians to ensure that the product willlJe easily serviceable by theconsumer or technician. This type of interaction results in a better prodllct for the consumer. The three intersecting circles also represent the three activities that are a major part of the conCllrrent engineering design process: ideation. refinement. and implementation. These three activities are further divided into smaller segments, as shown by the items surrounding the three circles.

Design for manufacturabiJity (DFM) and design for assembly (OFA) practices developed out of concurrent

engineering as an elTon to capture manufacturing and assembly knowledge up front in the imitial design

process. This allowed engineering and manufacturing professionals 10 speak a common language that results in an optimilcd product design. OFM and OFA cvcntually cxpanded to include other practices. such as design for serviceability and design for reliability. This led to the realization that it is important to include others in the design process. such as marketing, sales. field service, finance, purchasing. and quality control.

The center area in Figure 2.8 represenL~ the 3-D computer model and rellects the central importance of 3-D

modeling and graphics knowledge in engineering design and production. With the use of a modeling approach. everyone on the team can have access to the current design through a computer terminal. This data sharing is critically important to the success of the design process.

The Engineering Design Process

Bertoline--Wiebe--Miller:

Fundamentals of Graphics

Communication,3/e

The McGraw-Hill

Companies,2001

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Design Ability

What Designers Say The wish to design things is inherent in human beings, and design is not something that has always been regarded as needing special abilities. It is only with the emergence and growth of industrial societies that the ability to design has become regarded as a specialised talent. Although there is so much design activity going on in the world, the ways in which people design are actually rather poorly understood. It has been thought that perhaps many people possess design ability to some degree, but that only a few people have a particular design 'talent'. However, there is now a growing body of knowledge about the nature of designing, about design ability and how to develop it, and about the design process and how to improve it. When designers are asked to discuss their abilities, and to explain how they work, a few common themes emerge. One theme is the importance of creativity and intuition in design, even in engineering design. For example, the architect and engineering designer Jack Howe has said: I believe in intuition. I think that's the difference between a designer and an engineer... I make a distinction between engineers and engineering designers... An engineering designer is just as creative as any other sort of designer. Some rather similar comments have been made by the industrial designer Richard Stevens: A lot of engineering design is intuitive, based on subjective thinking. But an engineer is unhappy doing this. An engineer wants to test; test and measure. He's been brought up this way and he's unhappy if he can't prove something. Whereas an industrial designer.., is entirely happy making judgements which are intuitive. Engineering Design Methods Strategies for Product Design THIRD EDITION Nigel Cross The Open University, Mi/ton Keynes, UK JOHN WILEY & SONS, LTD Chichester- New York. Weinheim • Brisbane. Singapore. Toronto

Computer-Aided Design and Manufacture of Injection Forging

The design activity is responsible not only for the performance and appearance of the product but also for the cost of the component. Design, therefore, cannot be an isolated activity but must address all available manufacturing routes, with a view to optimizing the quality and cost of the component. With reference to nett-forming, the design exercise is conducted not only to specify the component-form but also to address all manufacturing constraints—machine, material, tooling, and processing conditions. Computer-aided “design for manufacture” is currently the main form of implementing of the “concurrent engineering.” To enable this, CAD/CAM is popularly used as a design approach. Using CAD/CAM approaches, simultaneous design would be effected efficiently by supporting the designer with information on all possible resources required for the design and manufacture of components. Some CAD/CAM systems [42] have demonstrated the potential for the development into decision-support systems for component/tool design. Computer-aided design and manufacture for nett-forming by injection forging is being developed as an aspect of research associated with the development of a decision-support system [64]. Methodology In order to develop a decision-support system for component/tool design using a CAD/CAM approach, several design/evaluation methods have been developed [58, 60, 64–68]. These are described briefly in the following texts. Geometric Modeling The popular strategy used for the development of the design-support systems for forging was to evolve a 2D-CAD system for component and tool design. The system was linked to a knowledge-based system to enable the evaluation of manufacturability. Subsequent to the evaluation of the geometry, the component was transferred to a CAD software to enable detailed design. This approach required the design to operate in several software environments. An integrated system, supported by solid modeling, would enable design and assessment of a component more efficiently. A solid modeling-approach—principal feature modeling—was used to enable component-design for forging within a solid modeling environment [65, 66]; the approach enables integration of currently available 2D-based knowledge-based systems. Design for manufacture requires that the component form is specified in a modular form in order to enable the evaluation of the design. The component may be defined as a combination of primitive forms as is the case in “design by features;” alternatively, the primitive forms which constitute the component may be extracted and identified automatically. Unfortunately, both these approaches are currently at a stage of refinement which only allows their applications to a limited range of component forms. Principal feature modeling [67] combines the strategies of both “design by feature” and “feature recognition” to enable efficient modeling and feature manipulation; the approach was proven to be particularly efficient for the modeling of forging/machining components [65]. Designing is attended to with reference to a prescribed set of performance requirements rather than to prescribed form features. The principal features, which represent the principal geometric profiles of a component, may be defined by the designer using arbitrary geometry—a group of curves on a plane or a curved surface. The principal features which have been generated are linked, exclusively, to a set of prescribed attributes which are catalogued in a database. COMPUTER-AIDED DESIGN, ENGINEERING, AND MANUFACTURING Systems Techniques And Applications VOLUME V I Editor CORNELIUS LEONDES Boca Raton London New York Washington, D.C. CRC Press MANUFACTURING SYSTEMS PROCESSE.

Roughness and waviness

A trace across a surface provides a profile of that surface which will  contain short and long wavelengths (see Figure 4.11). In order for a surface to be correctly inspected, the short and long wavelength  components need to be separated so they can be individually analysed. The long waves are to do with dimensions and the short waves are to do with the SE Both can be relevant to function but in different ways. Consider the block in Figure 6.1. This has been produced on a shaping machine. The block surface undulates in a variety of ways. There is a basic roughness, created by the tool feed marks, which is superimposed on the general plane of the surface.

Thus, one can identify two different wavelengths, one of a small scale and one of a large scale. These are referred to as the roughness and waviness components.

Roughness and waviness have different influences on functional performance. A good example illustrating the differences concerns automotive bodies. Considering the small-scale amplitudes and wavelengths called 'roughness', it is the roughness, not waviness, which influences friction, lubrication, wear and galling, etc. The

next scale up from roughness is 'waviness' and it is known that the visual appearance of painted car bodies correlates more with waviness than roughness. The reason for this is the paint depth is about 100um and it has a significant filtering effect on roughness but not waviness.

Engineering Drawing for Manufacture

by Brian Griffiths

Publisher: Elsevier Science & Technology Books

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DESIGNATION AND RELATIVE POSITIONS OF VIEWS

An object positioned in space may be imagined as surrounded by six mutually perpendicular planes. So, for any object, six different views may be obtained by viewing at it along the six directions, normal to these planes. Figure 3.5 shows an object with six possible directions to obtain the different views which are designated as follows: 1. View in the direction a = view from the front 2. View in the direction b = view from above 3. View in the direction c = view from the left 4. View in the direction d = view from the right 5. View in the direction e = view from below 6. View in the direction f = view from the rear Figure 3.6a shows the relative positions of the above six views in the first angle projection and Fig.3.6b, the distinguishing symbol of this method of projection. Figure 3.7 a shows the relative position of the views in the third angle projection and Fig. 3.7b, the distinguishing symbol of this method of projection. NOTE A comparison of Figs. 3.6 and 3.7 reveals that in both the methods of projection, the views are identical in shape and detail. Only their location with respect to the view from the front is different. MACHINE DRAWING Third Edition Dr.K.I. Narayana Dr.P. Kannalah K. Venkata Reddy NEW AGE INTERNATIONAL (P) LIMITED, PUBLISHERS

Extrusion Blow Molding Machine Parts and Functions

Extrusion Blow Molding Machine Parts and Functions

• Extruder Motor—Drives the screw in the barrel to rotate and push the

melted material into the die head.

• Gearbox—Reduces the speed of the extruder motor into a required speed enough to push the material into the die head.

• Hopper—A feed reservoir into which the material is loaded.

• Extruder—A part of the machine that accepts solid resin material, conveys it in a surrounding barrel by means of a rotating screw, melts the

material by means of heaters, and pumps it under pressure into the die

head.

• Cooling Fans—Cools down the barrel during machine shut down to prevent the material from degradation.

• Heating Bands—Device attached on the barrel and the die head used to melt the solid material at a required set temperature.

• Die Head—Used to form the melted resin into a parison and also used for adjusting the characteristics of molten resin to create a stable parison.

• Die & Pin—Used to align the flow of parison to get a good and centered parison.

• Hot Cutter—Cuts the parison after the mold is closed for the blowing process.

• Blow Pin—Used to blow compressed air into the parison to inflate it after the mold has been closed and form the desired design of the mold.

• Mold—A hollow form or a cavity into which a molten plastic material, called parison, is introduced to give the shape of the required component.

• Deflasher—Used to cut the excess material on the bottle which is called a flash material (top and bottom).

• Post Cooling—A part of the machine that is used to cool down the inside of the bottle, to lessen the cooling time required inside the mold.

• Article Discharge—A part of the machine used to take the bottle out.

Higher Institute for Plastics Fabrication
WORKBOOK
for
Extrusion Blow Molding
Practical Course
Prepared by
Extrusion Blow Molding Department
1st Edition 2009

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What Is Computer-Aided Process Planning (CAPP)?

In this section we introduce the topic of CAPP, and review important components of this technology. Chang and Wysk (1985) define process planning as “machining processes and parameters that are to be used to convert (machine) a workpiece from its initial form to a final form predetermined from an engineering drawing.” Implicit in their definition is the selection of machining resources (machine and cutting tools), the specification of setups and fixturing, and the generation of operation

sequences and numerical control (NC) code. Traditionally, the task of process planning is performed by a human process planner with acquired expertise in machining practices who determines from a part’s engineering drawings what the machining requirements are.

Manual process planning has many drawbacks. In particular, it is a slow, repetitive task that is  prone to error. With industry’s emphasis on automation for improved productivity and quality, computerized CAD and computer-aided manufacturing (CAM) systems which generate the data for driving computer numerical control (CNC) machine tools, are the state-of-the-art. Manual process planning in this context is a bottleneck to the information flow between design and manufacturing.

CAPP is the use of computerized software and hardware systems for automating the process planning task. The objective is to increase productivity and quality by improving the speed and accuracy of process planning through automation of as many manual tasks as possible. CAPP will increase automation and promote integration among the following tasks:

1. Recognition of machining features and the construction of their associated machining volumes from a geometric CAD model of the part and workpiece

2. Mapping machining volumes to machining operations

3. Assigning operations to cutting tools

4. Determining setups and fixturing

5. Selecting suitable machine tools

6. Generating cost-effective machining sequences

7. Determining the machining parameters for each operation

8. Generating cutter location data and finally NC machine code

Traditionally, CAPP has been approached in two ways. These two approaches are variant process planning and generative process planning. In the following section we discuss these and other issues in a review of work in this field.

THE

MECHANICAL

SYSTEMS

DESIGN

HANDBOOK

Modeling, Measurement,

and Control

OSITA D. I. NWOKAH

YILDIRIM HURMUZLU

Southern Methodist University

Dallas, Texas

CRC PRESS

Boca Raton London New York Washington, D.C.

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Polymer molding

Thermoplastics are molded as viscous liquids. Injection molding and extrusion dominate, but all molding processes impose flow that can orientate the molecules; if the molding is cooled fast enough the alignment is frozen in (Figure 19.5).

If not, polymers mostly prefer to form an amorphous structure. In some polymers crystallinity may develop on slow cooling. All polymers shrink as the mold cools from the molding temperature to room temperature because of thermal contraction and the loss of free volume caused by crystallization. Allowance must be made for this when the mold is designed.

Materials

Engineering, Science,

Processing and Design

Michael Ashby, Hugh Shercliff and David Cebon

University of Cambridge,

UK

AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD

PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

Butterworth-Heinemann is an imprint of Elsevier

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Design Process

Before any discussion of CAD, it is necessary to understand the design process in general (Fig. 3). What are the series of events that lead to the beginning of a design project? How does the engineer go about the process of designing something? How does one arrive at the conclusion that the design has been completed? We address these questions by defining the process in terms of six distinct stages: 1. Customer input and perception of need 2. Problem definition 3. Synthesis 4. Analysis and optimization 5. Evaluation 6. Final design and specification A need is usually perceived in one of two ways. Someone must recognize either a problem in an existing design or a customer-driven opportunity in the marketplace for a new product. In either case, a need exists which can be addressed by modifying an existing design or developing an entirely new design. Because the need for change may only be indicated by subtle circumstances—such as noise, marginal performance characteristics, or deviations from quality standards—the design engineer who identifies the need has taken a first step in correcting the problem. That step sets in motion processes that may allow others to see the need more readily and possibly enroll them in the solution process. Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition. Edited by Myer Kutz by John Wiley & Sons, Inc.

Variations and Extension to the Injection-Molding Process

Injection Blow Molding.

A preform (this looks like a test tube with bottle cap threads) is injection molded in one cavity, removed and then placed into another where it is pressurized with gas to stretch the hot preform into a thinnerwalled

seamless bottle or container such as a milk bottle or gas tank. This is depicted in Figure 7. This is an extension of injection molding more than a variation.

Injection Compression/Coining.

With this technique the mold is only partially closed during injection. At the appropriate time and with the right amount of plastic in the mold, the clamp is then completely closed, forcing (compressing) the plastic to the shape of the mold cavity. A variation on this is coining.

The clamp is closed but the mold has components that compress the plastic in the cavity as the plastic cools. Coining is where the cavity volume is changing during the solidification of the plastic. Plastic is injected into the cavity and then the movable platen closes completely, or a mold component moves to compress the plastic to compensate for shrinkage or densification.

Gas-Assist Injection Molding.

Here, plastic is injected into the cavity until it is 50–85% full, then high pressure gas, usually nitrogen, is  injected to finish filling the cavity by pushing the plastic flow front to the end of the cavity. This leaves a gas bubble or channel inside the part. This saves plastic, reduces cost, and often improves part strength especially in thick sections. Gas can be injected at the nozzle of the machine or directly into the mold as depicted in Figure 8. Gas-assist molding can be considered as a variation of co-injection molding where the outer layer or skin of the part is plastic and the core is a gas channel rather than another type of plastic.

“Injection Molding” in EPSE 2nd ed., Vol. 8, pp. 102–138, by I. I. Rubin,Robinson Plastic Corp.

JOHN W. BOZZELLI

Midland, Michigan

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Extrusion

General Features of Single Screw Extrusion

One of the most common methods of processing plastics is Extrusion using a screw inside a barrel as illustrated in Fig. 4.1. The plastic, usually in the form of granules or powder, is fed from a hopper on to the screw. It is then conveyed along the barrel where it is heated by conduction from the barrel heaters and shear due to its movement along the screw flights. The depth of the screw channel is reduced along the length of the screw so as to compact the material. At the end of the extruder the melt passes through a die to produce an extrudate of the desired shape. As will be seen later, the use of different dies means that the extruder screwharrel can be used as the basic unit of several processing techniques.

PLASTICS

ENGINEERING

Third Edition

R.J. Crawford, BSc, PhD, DSc, FEng, FIMechE, FIM

Department of Mechanical, Aeronautical

and Manufacturing Engineering

The Queen’s University of Belfast

l E I N E M A N N

OXFORD AMSTERDAM BOSTON LONDON NEW YORK PARIS

SAN DlEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO

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Drawing Number

The drawing number is used for part identification and to ease storage and retrieval of the drawing and the produced parts. While there is no set way to assign part numbers, common systems are nonsignificant, significant, or some combination of the two previous systems.

Nonsignificant numbering systems are most preferred because no prior knowledge of significance is required.

Significant numbering systems could be used for commonly purchased items like fasteners. For example, the part number for a washer could include the inside diameter, outside diameters, thickness, material, and plating.

A combination of nonsignificant and significant numbering systems may use sections of the numbers in a hierarchical manner. For example, the last three digits could be the number assigned to the part (001, 002, 003, etc.). This would be nonsignificant. The remaining numbers could be significant: two numbers could be the model variation, the next two numbers could be the model number, and the next two could be the series number while the last two could be the project number. Many other possibilities exist.

Dimensioning and Tolerancing

Handbook

Paul J. Drake, Jr.

McGraw-Hill

New York San Francisco Washington , D.C. Auckland Bogata

Caracas Lisbon London Madrid Mexico City Milan

Montreal New Delhi San Juan Singapore

Sydney Tokyo Toronto

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DEFINING PLASTIC PART REQUIREMENTS -2

Weather Resistance Temperature, moisture, and UV sun exposure affect plastic parts’ properties and appearance. The end-use of a product determines the type of weather resistance required. For instance, external automotive parts such as mirror housings must withstand continuous outdoor exposure and perform in the full range of weather conditions. Additionally, heat gain from sun on dark surfaces may raise the upper temperature requirement considerably higher than maximum expected temperatures. Conversely, your requirements may be less severe if your part is exposed to weather elements only occasionally. For example, outdoor Christmas decorations and other seasonal products may only have to satisfy the requirements for their specific, limited exposure. Radiation A variety of artificial sources — such as fluorescent lights, high-intensity discharge lamps, and gamma sterilization units — emit radiation that can yellow and/or degrade many plastics. If your part will be exposed to a radiation source, consider painting it, or specifying a UV-stabilized resin. Appearance Aesthetic requirements can entail many material and part-design issues. For example, a need for transparency greatly reduces the number of potential plastics, especially if the part needs high clarity. Color may also play an important role. Plastics must often match the color of other materials used in parts of an assembly. Some applications require the plastic part to weather at the same rate as other materials in an assembly. Engineering Polymers Part and Mold Design THERMOPLASTICS A Design Guide Bayer Corporation • 100 Bayer Road • Pittsburgh http://www.bayer.com/polymers-usa

Oblique projection

In oblique projection, the object is aligned such that one face (the front face) is parallel to the picture plane. The projection lines are still parallel but they are not perpendicular to the picture plane.

This produces a view of the object that is 3D. The front face is a true view (see Figure 2.7). It has the advantage that features of the front face can be drawn exactly as they are, with no distortion. The receding faces can be drawn at any angle that is convenient for illustrating the shape of the object and its features. The front face will be a true view, and it is best to make this one the most complicated of the faces. This makes life easier! Most oblique projections are drawn at an angle of 45 ~ and at this angle the foreshortening is 50%. This is called a Cabinet projection. This is because of its use in the furniture industry. If the 45 ~ angle is used and there is no foreshortening it is called a Cavalier projection. The problem with Cavalier projection is that, because there is no foreshortening, it looks peculiar and distorted. Thus, Cabinet projection is the preferred method for constructing an oblique projection.

An oblique drawing of the bearing bracket in Cabinet projection is shown in Figure 2.8. For convenience, the front view with circles was chosen as the true front view. This means that the circles are true circles and therefore easy to draw. The method of construction for oblique projection is similar to the method described above for isometric projection except that the angles are not 30 ~ but 45 ~ .

Enclosing rectangles are again used and transposed onto the 45 ~ oblique planes using 50% foreshortening.

Engineering Drawing for Manufacture

by Brian Griffiths

Publisher: Elsevier Science & Technology Books

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Critical Role of Computers in Modern Manufacturing

A number of steps are involved in manufacturing a part from its conceptualization to production. They include product design, process planning, production system design, and process control. Computers are used extensively in all these stages to make the entire process easier and faster. Potential benefits of using computers in manufacturing include reduced costs and lead times in all engineering design stages, improved quality and accuracy, minimization of errors and their duplication, more efficient analysis tool, and accurate control and monitoring of the machines/processes, etc. Some of the applications of computers in manufacturing are shown in Figure 1.5. In computeraided design (CAD), computers are used in the design and analysis of the products and processes. They play a critical role in reducing lead time and cost at the design stages of the products/process. Also, computers may be utilized to plan, manage, and control the operations of a manufacturing system: computer-aided manufacturing (CAM) (Bedworth, Handerson, and Wolfe, 1991). In CAM, computers are either used directly to control and monitor the machines/processes (in real-time) or used off-line to support manufacturing operations such as computer-aided process planning (CAPP) or planning of required materials. At higher levels, computers are utilized in support of management. They play a critical role in all stages of decision making and control of financial operations by processing and analyzing data and reporting the results (management information systems, MIS) (Hollingam, 1987). Computers facilitate integration of CAD, CAM, and MIS (computer-integrated manufacturing, CIM) (Vajpayee, 1995) (see Figure 1.5). They provide an effective communication interface among engineers, design, management, production workers, and project groups to improve efficiency and productivity of the entire system. THE MECHANICAL SYSTEMS DESIGN HANDBOOK Modeling, Measurement, and Control OSITA D. I. NWOKAH YILDIRIM HURMUZLU Southern Methodist University Dallas, Texas CRC PRESS Boca Raton London New York Washington, D.C.

FORMING - DRILLING - REAMING - BORING

FORMING

Forming is the process of turning convex, or concave or of any irregular shape. Form turning may be accomplished by the following methods:

1.using a forming tool

2.combining cross-land longitudinal feed.

3.tracing or coping a template.

DRILLING

Drilling is the operation of producing a cylindrical hole in a work piece by the rotating cutting edge of a cutter known as drill.

REAMING

Reaming is a process of finishing and sizing a hole, which has been drilled or bored. The tool used is called reamer, which has multiple cutting edges. The reamer is held on tailstock spindle, either direct or through a drill chucks and is held stationary while the work is revolved at a very low speed. The feed varies from 0.5 to 2mm per revolution.

BORING

Boring is the operation of enlarging and truing a hole produced by drilling, punching, casting or forging.

1.The work is revolved in a chuck or a faceplate and the tool, which is fitted to the tool post, is fed in to the work.

2.The work is clamped on the carriage and a boring bar holding the tool is supported between the centers and made to revolve.

fr. NTTF ( NETTUR TECHNICAL TRAINING FOUNDATION)

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Torsion

A bar is under torsional stress when it is held fast at one end, and a force acts at the other end to twist the bar. In a round bar (Fig. 4.9) with a constant force acting, the straight-line ab becomes the helix ad, and a radial line in the cross-section, ob, moves to the position ad. The angle bad remains constant while the angle bod increases with the length of the bar. Each cross section of the bar tends to shear off the one adjacent to it, and in any cross section the shearing stress at any point is normal to a radial line drawn through the point. Within the shearing proportional limit, a radial line of the cross section remains straight after the twisting force has been applied, and the unit shearing stress at any point is proportional to its distance from the axis.

The twisting moment, T, is equal to the product of the resultant, P, of the twisting forces, multiplied by its distance from the axis, p. Resisting moment, T,, in torsion, is equal to the sum of the moments of the unit

shearing stresses acting along a cross section with respect to the axis of the bar. If d A is an elementary area of the section at a distance of z units from the axis of a circular shaft [Fig. 4.9 (b)], and c is the distance from

the axis to the outside of the cross section where the unit shearing stress is Z, then the unit shearing stress acting on dA is (ZZ/C) dA, its moment with respect to the axis is (zz2/c) dA, and the sum of all the moments

of the unit shearing stresses on the cross section is f (rz2/c) dA. In this expression the factor fz2 dA is the polar moment of inertia of the section with respect to the axis. Denoting this by J the resisting moment may be written zJ/c.

The polar moment of inertia of a surface about an axis through its center of gravity and perpendicular to the surface is the sum of the products obtained by multiplying each elementary area by the square of its distance from the center of gravity of its surface; it is equal to the sum of the moments of inertia taken with respect to two axes in the plane of the surface at right angles to each other passing through the center of gravity section of a round shaft.

The analysis of torsional shearing stress distribution along noncircular cross sections of bars under torsion is complex. By drawing two lines at right angles through the center of gravity of a section before twisting,

and observing the angular distortion after twisting, it has been found from many experiments that in noncircular sections the shearing unit stresses are not proportional to their distances from the axis. Thus in a rectangular bar there is no shearing stress at the comers of the sections, and the stress at the middle of the wide side is greater than at the middle of the narrow side. In an elliptical bar the shearing stress is greater along the flat side than at the round side.

Plastics

Engineered

Product

Design

Dominick Rosato and

Donald Rosato

ELSEVIER

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Insulated Runners

The insulated runner system (Figure 41) allows the molten polymer to flow into the runner, and then cool to form an insulating layer of solid plastic along the walls of the runner. The insulating layer reduces the diameter of the runner and helps maintain the temperature of the molten portion of the melt as it awaits the next shot. The insulated runner system should be designed so that, while the runner volume does not exceed the cavity volume, all of the molten polymer in the runners is injected into the mold during each shot. This full consumption is necessary to prevent excess build-up of the insulating skin and to minimize any drop in melt temperature. The many advantages of insulated runner systems, compared with conventional runner systems, include: • Less sensitivity to the requirements for balanced runners. • Reduction in material shear. • More consistent volume of polymer per part. • Faster molding cycles. • Elimination of runner scrap – less regrind. • Improved part finish. • Decreased tool wear. However, the insulated runner system also has disadvantages. The increased level of technology required to manufacture and operate the mold results in: • Generally more complicated mold design. • Generally higher mold costs. • More difficult start-up procedures until running correctly. • Possible thermal degradation of the polymer melt. • More difficult color changes. • Higher maintenance costs. Product and Mold Design d9b604f1c18a4896b020a210866ec775.

Standards ANSI ISO

Standards If a machinist in a machine shop in a remote location is required to make a part for a US-built commercial aircraft, he or she must understand the drawings. This requires worldwide, standardized drafting practices. Many countries support a national standards development effort in addition to international participation. In the United States, the two groups of standards that are most influential are developed by the standards development bodies administered by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). See Chapter 6 for a comparison of US and ISO standards. ANSI The ANSI administers the guidelines for standards creation in the United States. The American Society of Mechanical Engineers sponsors the development of the Y14 series of standards. The 26 standards in the series cover most facets of engineering drawings and related documents. Many of the concepts about how to read an engineering drawing presented in this chapter come from these standards. In addition to the Y14 series of standards, the complete library should also possess the B89 Dimensional Measurement standards series and the B46 Surface Texture standard. ISO The ISO, created in 1946, helped provide a structure to rebuild the world economy (primarily Europe) after World War II. Even though the United States has only one vote in international standards development, the US continues to propose many of the concepts presented in the ISO drafting standards. Dimensioning and Tolerancing Handbook Paul J. Drake, Jr. McGraw-Hill New York San Francisco Washington , D.C. Auckland Bogata Caracas Lisbon London Madrid Mexico City Milan Montreal New Delhi San Juan Singapore Sydney Tokyo Toronto

Linear and angular dimensioning

The latest ISO standard concerned with dimensioning is ISO 129"1985. However, it is known that a new one is soon to be published which is ISO 129 Part 1 (the author sits on BSI/ISO committees and has seen the draft new standard). It has been through all the committee approval stages and has been passed for publication. However, it is being held back, awaiting the approval of a Part 2 so that they can be published together. The BSI estimates the publication date will be 2003, hence it will be ISO 129-1:2003.

There have been versions prior to 1985 and each has defined slightly different dimensioning conventions. Needless to say, the 2003 convention gives a slightly different convention to the 1985 one! Throughout this section, the 2003 convention will be presented so that readers are prepared for the latest version. Figure 4.3 shows a hypothetical spool valve that is defined by 14 dimensions in which 12 are linear and two angular. The valve is shown using the ISO principles of line thickness described in

Chapter 3. Note that the valve outline uses the ISO type 'A' thickness whereas the other lines (including the dimension lines) are the ISO type 'B' thin lines. The outline thus has more prominence than the other lines and hence the valve tends to jump out of the drawing page and into the eye of the reader. The valve dimensions

follow the dimensioning convention laid down in the future ISO 129-1:2003 standard. Tolerances have been left off the figure for convenience. In this case there are two datum features. The first is the left-hand annular face of the largest cylindrical diameter, i.e. the face with the 30 ~ chamfer. Horizontal dimensions associated

with this datum face use a terminator in the form of a small circle.

The other datum feature is the centre rotational axis of the spool valve represented by the chain dotted line. All the extension lines touch the outline of the spool valve. The dimension values are normally placed parallel to their dimension line, near the middle, above and clear of it. Dimension values should be placed in such a

way that they are not crossed or separated by any other line.

Engineering Drawing for Manufacture

by Brian Griffiths

Publisher: Elsevier Science & Technology Books

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Cold Slug Wells

At all runner intersections, the primary runner should overrun the  secondary runner by a minimum distance equal to one diameter, as shown in Figure 39. This produces a feature known as a melt trap or cold slug well. Cold slug wells improve the flow of the polymer by catching the colder, higher-viscosity polymer moving at the forefront of the molten mass and allowing the following, hot, lower-viscosity polymer to flow more readily into the mold-cavity.

The cold slug well thus prevents a mass of cold material from entering the cavity and adversely affecting the final properties of the finished part.

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The "shaft basis" and the "hole basis' system of fits

In all the examples given above, the discussion has been concerning 'shafts' and 'holes'. It should be remembered that this does not necessarily apply to shafts and holes. These are just generic termsthat mean anything that fits inside anything else. However, whatever the case, it is often the case that either the shaft or the hole is the easier to produce. For  example, if they are cylindrical, the shaft will be the more easily produced in that one turning tool can produce an infinite number of shaft diameters. This is not the case with the cylindrical hole in that each hole size will be dependent on a single drill or reamer.

The right-hand diagram in Figure 5.10 shows the situation in which the shaft is the more difficult of the two to produce and this is referred to as the 'shaft basis' system of fits. In this case the system of fits is used in which the required clearances or interferences are obtained by associating holes of various tolerance classes with shafts of a single tolerance class. Alternatively if the shaft is the easier part to produce then the hole basis system of fits is used. This is a system of fits in which the required clearances and interferences are obtained by associating shafts of various tolerance classes with holes of a single tolerance class. In the case of the shaft basis system the shaft is kept constant and the interference or clearance functional situation is achieved by manipulating the hole. If the hole-based system is used, the opposite is the case. The appropriate use of each

system for functional performance situation is thus made easier for the manufacturer.

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Engineering Drawing for Manufacture

by Brian Griffiths

Publisher: Elsevier Science & Technology Books

Forging Simulation

According to the difficulties which have just been presented, the design problem often results in trial and error. It is both time and money  consuming, as the shapes of the dies are complex, difficult, and expensive to produce. In order to lower these costs, several simulation strategies have been developed to replace the actual trials. Easy to form model materials such as lead, plasticine [52], and wax [64] can be substituted to the current metal, making it possible to reduce the forming force. These materials, and more particularly plasticine and wax which are more widely used today, exhibit nearly the same behavior as the metal under hot isothermal conditions. One of the main restriction of this approach is the temperature dependency of the model materials, which is quite different from the behavior of the metal.

However, for most of the processes, the forging is so fast that the heat exchanges with the dies is small and that the heat generated by the material deformation is not enough to significantly modify the material flow. Thus, this technique provides an easy way to study the material flow, to predict the major defects such as folds [42] and insufficient pressure in the die details, and to estimate the forging force. Moreover, it is possible to study the material deformation and the fibering by mixing model materials of several colors. With some mechanical models, the total strain can be computed out of these pieces of information [52]. By mixing model materials with different properties, or by adding some other components, the behavior of the model material can be slightly adjusted to the behavior of the studied metal. As often for metal forming processes, the friction phenomenon is difficult to simulate. However, some kind of model materials for the lubricants can be proposed.

The main shortcoming of this simulation approach is that although the dies can be produced into a less expensive material and without heat treatment, they are as complex as the actual process, which requires significant time and energy to produce them. Moreover, as has been mentioned earlier, the thermal effects cannot be taken into account.

Nowadays, the numerical simulation provides much faster results as the toolings are only virtually designed. Moreover, these results are more accurate and more varied, such as the flow at different times of the process, the velocity field, the strain, the strain rates, the stresses, the temperature, the tool wear, and the tool deformation. Several softwares have been marketed, such as the well spread FORGE2 and DEFORM2D (initially called ALPID), [47] for axisymmetrical and plane strain problems.

They are actual tools for designers and their industrial use is ever increasing. Indeed, they make it easy to quickly find the main shortcomings of the studied design, and then to test several modifications to improve it. For expensive safety parts, or for very large single parts, they also provide a quality insurance as they give an estimation of the mechanical characteristics of the part which should otherwise be obtained by destructive testing. Regarding the true three-dimensional problems, automatic remeshing difficulties, as well as  computational time and memory requirements, have long hindered the industrial use of these softwares. 

Nowadays, both the software and hardware progresses have made these computations possible. They are used in forging companies, for instance to understand the development of a fold and test whether a new preform design can remove it [22]. The tool shape discretization required for the numerical simulation, often a finite element mesh of the tool surface by triangles, can almost directly be obtained from the CAD design. It reduces to rather insignificant times the specific numerical design required by the finite element simulation. FORGE3 and DEFORM3D [66] are such available softwares

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COMPUTER-AIDED DESIGN,

ENGINEERING, AND MANUFACTURING

Systems Techniques And Applications

VOLUME V I

Editor

CORNELIUS LEONDES

Boca Raton London New York Washington, D.C.

CRC Press

MANUFACTURING

SYSTEMS PROCESSES

Facing, KNURLING, FILING

Facing

Facing is the operation of machining the ends of a piece of work to produce a flat surface square with the axis. This is also used to cut the work to the required length. The operation involves feeding the tool perpendicular to the axis of rotation of the work piece.

KNURLING

Knurling is the process of embossing a diamond shaped pattern on the surface of a work piece. The purpose of knurling is to provide an effective gripping surface on a work piece to prevent it from slipping when operated by hand. The tool is held rigidly on the tool post and the rollers are pressed against the revolving work piece to squeeze the metal against the multiple cutting edges, producing depressions in a regular pattern on the surface of the work piece.

FILING

Filing is the finishing operation performed after turning. This is done in a lathe to remove burrs, shape corners, and feed marks on a work piece and also to bring it to the size by removing very small amount of metal. The speed is usually twice that of turning. The file should b slowly moved forward so that the work may pass 2 to 3 revolutions during the cutting stroke. During the return stroke the pressure is relived but an end wise feeding movement is given, overlapping the previous cut.

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ISO tolerance ranges

Tolerance bands need to be defined which can be related to functional

performance and manufacturing processes. The ISO has published tolerance ranges to help designers. Examples of these tolerance ranges are shown in Figure 5.4. This table is only a selection from the full table given in ISO 286-2:1988. The full range goes up to IT18 and 3m nominal size. The tolerance ranges are defined by 'IT' ranges as shown in the  diagram from IT1 to IT11. The range given in the ISO standard is significantly more complicated than the extract in Figure 5.4. It should be noted that the range increases as the IT number gets larger and the range increases as the nominal size increases. The latter is fairly logical in

that one would expect the tolerance range to be larger as the diameter increases because the precision that can be achieved must be relative. The ranges were not chosen out of the blue but empirically derived and based on the fact that the relationship between manufacturing errors and basic size can be approximated by a parabolic function.

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Engineering Drawing for Manufacture

by Brian Griffiths

· ISBN: 185718033X

· Publisher: Elsevier Science & Technology Books

State of the Art of Design Techniques for Non-Steady-State Metal Forming Processes

Basic Design Techniques

The forging problem can be summarized as to find the best process design, which makes it possible to form the required part. We do not consider the preliminary problem of dressing. We assume that the

forged part has already been designed out of the shape of the final part, which will often be obtained after machining. The problem is just to design a deformation path for the material in order to obtain a prescribed shape with satisfactory properties and for the lower cost. Of course, the deformation paths are not unique, and that can include several forging  operations. So the problem is to find the best shapes of the preforming tools, the best forming temperatures (both the initial temperature of the billet and the temperature of the dies), the best forging velocities, the best lubricant and lubrication conditions, etc.

The optimality conditions regard several parameters which may depend on the process itself. However,

most of the time, the optimal forging design has to obtain the right final part without major defects such as folds, to minimize the number of operations, to minimize the size of the initial billet, to reduce the maximum forging force during the operations, and so on.

This is a complex design problem as often the material flow is three-dimensional and difficult to foresee. It is not possible to simplify it into a less complex problem which could be more easily studied. In fact, in this area, there is a deep lack of simple mathematical models. Just a few problems can be analytically solved, such as the upsetting of a cylinder (or a bar) between flat dies without friction. Although it provides some interesting tendencies, it is far too simple to be useful for the design of a close-die forging process. So, the industrial practice was mainly based on thumb rules and empirical knowledge which have been obtained either by actual experiences, by reduced scale or simulation experiments, or by more complex mathematical models [51, 2].

Some approximated models and methods have been developed, for instance by Chamouard [11], in order to predict the filling of the forging dies and the forging force. Unfortunately, they are not easy to use. In order to bring them within the reach of these persons, recently, the Chamouard’s approach has been incorporated into computer software [56]. However, according to the present computer performances and the restricting hypothesis of such models, this is probably not the most efficient and modern way to simulate the process, as we shall see.

As a matter of fact, all the proposed methods are restricted to two-dimensional (axisymmetrical or plane strain approximation) problems. For complex three-dimensional flows, the 3D problem has first to be decomposed into several 2D plane strain problems (see Fig. 5.1), which is both not easy and not always possible.

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COMPUTER-AIDED DESIGN,

ENGINEERING, AND MANUFACTURING

Systems Techniques And Applications

VOLUME

V I

Editor

CORNELIUS LEONDES

Boca Raton London New York Washington, D.C.

CRC Press

MANUFACTURING

SYSTEMS PROCESSES

Step formation and release of products in blow Blow Molding

Mold is opened, after a long-parison which flows through the side pieces, mold will close, followed by movement of the blades are cut off above the parison mold. After the parison mold stuck on the move, which was originally under the tip of the die head is now under blowpin, Then blowpin down to blow the parison to expand the shape of the cavity.

At the top of the mold are part of a hardened steel, serves as the foundation adjacent to the cutting of the parison excess of the mold.

The foundation is called the striker plate cutting, cutter was called the outing blowpin end of the sleeve is attached.

Product formation steps and expenditures.

1.Mold catch parison, the knife cut off the excess parison upper mold, then mold moves downward move the position of blowpin.

2.Blowpin move down to blow the parison into a product, which is then followed by cooling the product in the mold.

3.The process of cooling, the mold opens and moves towards the bottom to catch the parison die head again. It is equivalent blowpin move, which goes along with the product because the mouth(which is due to shrinkage after cooling) blowpin gripping end.

4.Blowpin rose steadily up to the mouth blowpin held back by the nest, regardless of the end blowpin and fall. Meanwhile parison mold was arrested and will move down blowpin next to the blowing process.

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Thread Cutting operation

In a thread cutting operation the first step is to remove the excess material from the work piece to make its diameter equal to the major diameter of the screw thread. Change gears of correct size are then fitted to the end of the bed between the spindle and the lead screw. The shape or form of the thread depend s on the shape of the cutting tool to be used. In a metric thread, the included angle of the cutting edge should be ground exactly 60o. The top of the tool nose should be set at the same height as the centre of the work piece. A thread tool gauge is usually used against the turned surface to check the cutting tool so that each face of the tool may be equally inclined to the center line of the work piece.

The speed of the spindle is reduced by one half to one-fourth of the speed required for turning according to the type of the material being machined, and the half-nut is then engaged. The depth of cut which usually varies from 0.05 to 0.2 mm is applied by advancing the tool perpendicular at to the axis of the work or at an angle equal to one-half of the angle of the thread, and 30o in the case of metric thread, by swiveling the compound rest.

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Recommended Design for Molded-in Threads

Molded-in threads can be designed into parts made of engineering thermoplastic

resins. Threads always should have radiused roots and should not have feather

edges – to avoid stress concentrations.

Figure 35 shows examples of good design for molded-in external and internal threads. For additional information on molded-in threads, see page 105. Threads also form undercuts and should be treated as such when the part is being removed from the mold i.e., by provision of unscrewing mechanisms, collapsible cores, etc. Every effort should be made to locate external

threads on the parting line of the mold where economics and mold reliability are

most favorable.

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Product and Mold Design