Fabrication & Welding - Basic Principles

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Fa brica t ion a nd WeldingBasic Principles of Fabricated

Component Design:Manufacture and Test Methods

(Higher)

5794


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September 1999

Fa brica t ion a ndWelding

B a sic P rinciples of Fa brica t ed

Component Design :Ma nufa ct ure a nd Test Met hods

(Higher)

S upport Ma t eria ls

HIGHER STILL


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Fabrication and Welding: Basic Principles of Fabricated Component Design,

Manufacture and Test Methods (Higher) - Teacher/Lecturer Information1

CONTENTS

LECTURERS / TEACHERS INFORMATION AND SUPPORT MATERIAL

Section Content

Section 1 The learning outcomes to be covered in the unit

Section 2 Teaching and learning advice

Section 3 Assessment procedures detailing what is to be assessed, when it

is to be assessed and method of recording results

Section 4 Resource Requirements including course notes book lists and

audio-visual list.

Section 5 Health and Safety

Section 6 Acknowledgements

STUDENTS INFORMATION AND SUPPORT MATERIAL

Section Contents

Section 1 The outcomes to be covered in the unit

Section 2 The assessment instruments for the outcome

Section 3 Students guide to working on this unit

Section 4 Course notes, technical information sheets and tutorials.


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SECTION 1 : OUTCOMES

The outcomes to be covered in the unit

Outcome 1

Interpret fabrication drawings, identify and interpret welding symbols.

Performance criteria

a. Interpretation of welding symbols is correct in terms of manufacturersinstructions and relevant standards.

b. Interpretation of fabrication drawings is correct in terms of manufacturersinstructions.

Range statement

Welding symbols: butt welds, filler welds, resistance welds, welding process, weld

location, weld details (contour, dimension, pitch, site instructions).

Fabrication drawings: assembly instructions, forming instructions, dimensions,

conventions, general information.

Evidence requirements

Graphic and written/oral evidence to demonstrate that the student can identify and

interpret common welding symbols.

Graphic and written exercises to demonstrate that the student can interpret simple

fabrication drawings according to manufacturers instructions, including details

identified in the range statement.

Outcome 2

Illustrate the factors affecting the design of fabricated components.


a. Explanation of the factors affecting the structural integrity of design is accurate interms of the component.

b. Explanation of the factors affecting the functional aspect of design is correct interms of the component.

c. Illustration of the interrelationship among structural, functional and manufacturingaspects of the fabricated component design are clear and accurate.


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Fabrication and Welding: Basic Principles of Fabricated Component Design,Manufacture and Test Methods (Higher) - Teacher/Lecturer Information

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Range statement

Components: tanks, drums, pressure vessels

Structural integrity: structural stiffening, shape, change of shape, added stiffness.

Functional: external service environment, internal service environment.


Written and/or pictorial evidence that the student clearly understands the difference

between the structural and the functional aspects of design and of the methods used toadd rigidity and/or stiffness to the container.

Written and/or pictorial evidence that the student can select a container that

incorporates the structural, functional and manufacturing aspects of design and

annotates the pictorial evidence accordingly.

Supplementary oral evidence to ensure that the student can cover the range.

Outcome 3

Describe the manufacturing methods used for a fabricated component.


a. Description of the advantages and limitations of the methods used for componentmanufacture is comprehensive, clear and accurate.

b. Identification of the equipment and the sequence of manufacturing methods usedfor a component are correct.

c. Completion of a flowchart is correct in terms of the given specification.d. Explanation of the reasons why continuous testing is carried out on fabricated

components as they are being manufactured is clear, comprehensive and accurate.

Range statement

Components: tanks, drums, pressure vessels, structures.

Manufacturing methods: cutting, forming, jointing, handling, finishing.

Continuous testing: stage inspection, material checking.


Written and/or pictorial evidence that the student clearly understands the

manufacturing methods in use for container construction together with their relativeadvantages and disadvantages.

Performance evidence that the student can produce a flow-chart and specify the

appropriate methods in the correct sequence.

Written and/or pictorial evidence that the student can explain testing and the reasons

for choice of methods.


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Outcome 4

Describe inspection and test procedures used during and after manufacture of

fabricated components.


a. Description of pressure tests and associated safety regulations is comprehensive,clear and accurate.

b. Specification of functional dimensions used in a dimensional test is correct.Range statement

Tests: pneumatic, hydraulic,

Functional dimensions: tolerances, component size.




Performance evidence that the student can mark from given drawings the functional

dimensions of the component.


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SECTION 2 : TEACHING AND LEARNING ADVICE

Teaching Methods

Outcome 1 Main Topic

Interpretation of fabrication drawings and welding symbols.

Industrial drawings should be used as source for identification of symbols and

drawing interpretation, with constant reference to BSEN 22553 Welded, brazed and

soldered joints-Symbolic representation on drawings: 1995 (BS 499 part 2 ) The

coverage of welding symbols should concentrate on the identification and

interpretation of the weld symbol and not focus on the actual drawing of the symbol

Outcome 2 Main Topic

Design principlesElements of fabricated component design and their interrelationship. Use should be

made of good examples of functional design such as a pressed steel car wheel, fuel

containers, car radiator, liquid food containers with radiused corners. The design ofbridges and gantries should be discussed. Sheets of paper, or cardboard can be

utilised to show the effects of poor design. Holes, both round and square in card, can

be used to demonstrate material failure by simple tearing and observing where the

tearing starts.

The context in which the design is taught should be limited to functional aspects such

as size shape strength etc and interrelationships between the design of the component

and the manufacturing methods.

Outcome 3Main Topic

Manufacturing methods

Support sheets giving cutting, forming, jointing and finishing processes together with

worksheets on handling costs comparisons between the various processes should be

used. Flowcharts based on the use of scale models to show the operation layouts. A

selection of exemplar layouts can be used to help with teaching operation sequences

and process choice.

Works visits should be arranged to enhance student experience.

Hands on student activities and support materials can and should be used where

possible.

It should be the lecturer / teachers aim to constantly apply the outcomes to practical

situations to enable students to constantly apply underpinning knowledge themselves.


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Outcome 4Main Topic

Quality assurance

Awareness of the variety of tests that a component may be subjected to during and

after manufacture. Workshop activities to demonstrate simple leak tests and low

pressure testing of containers.

Teaching Plan

The teaching plan below gives guidance on suggested teaching order and guidance on

the timing of assessment.

LEARNING

ACTIVITY

UNIT CONTENT

Interpret fabrication drawings, identify and interpret welding symbols

(O 1)

Lecturer input Drawing interpretation: drawing principles projection methods,identification of welding symbols, use of BSEN 22553: 1995

Formative assessment (O 1)

Practical

exercise/tutorial

Interpret industrial drawings and manufacturer instructions, identify weld

symbols on industrial type drawings

Assessment Assessment (O 1)

Illustrate the factors affecting the design of fabricated components (O2)

Lecturer input Design principles: structural integrity, functional aspects, and environmental

requirements.

Practical activities Show the effects of poor design by the use of card or paper. Demonstratematerial failure by simple tearing and observing where the tearing starts

around square and round holes.

Assessment (O 2)

Describe the manufacturing methods used for a fabricated component

(O3)

Lecturer input Manufacturing operations: operational sequences, manufacturing methods,

flowcharts, equipment, continuous testing, inspection methods and materialchecking

Formative assessment (O3)

Practical activity Produce operational sequence sheets, design flowcharts for manufacture.

Assessment (O3)

Describe inspection and test procedures used during and after

manufacture of fabricated components (Lo4)

Lecturer input Quality assurance: inspection and testing methods, dimensional checks, leak

testing.

Workshop activity Conduct simple leak test, carry out dimensional checks.

Assessment (O4)


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SECTION 3: ASSESSMENT PROCEDURES

Assessment procedures detailing what is to be assessed, when it is to be assessed

and method of recording results

Outcome 1

The assessment should ensure that students can identify weld symbols and interpret

drawings and manufacturers instructions. This section can be integrated with thesection on planning and manufacturing sequences and an integrated assessment is

possible.

A combined identification and interpretation exercise should be used to cover the

range and performance criteria (a). For example, the assessment could be in the form

of a table that contains welding symbols. Students should complete the table

alternating between identifying a symbol from a sketch to sketching a symbol from a

description. All items in the range should be covered.

Alternatively, students can also sketch the weld joint as identified by the symbol.

Drawing interpretation should be based on a series of questions relating to features

found on fabrication drawings.

Outcome 2

The assessment should be mainly a combination of written and graphical exercises.

The student should be able to understand functional and manufacturing aspects ofdesign. This could be assessed by the use of a written exercise based on the factors

affecting the design of a fabricated component, combined with structured questions,formulated around a sketch/drawing of a fabricated structure.

Outcome 3

The assessment of this outcome could be organised so that an assignment or project

forms the backbone where the design parameters of a container are assessed.

Manufacturing processes, process flowcharts and manufacturing instructions are

required for the manufacture of a fabricated component and finally the integration of

testing methods are considered to ensure that the design criteria have been complied

with during manufacture. Hands-on student activities and support material should beused wherever possible. It should be the teacher or lecturers aim to constantly relate

the outcomes to practical situations.

Outcome 4

Written exercises in the form of inspection reports could be used to evidence that the

student can explain testing methods produce sequence of testing operations and

justifying their use. The identification of functional dimensions of a component can

be achieved by the annotation of sketches or integrated with outcomes 2 and 3.


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Assessment Timing

Assessments should be carried out under closed bookconditions. It is difficult to

allocate a time scale to each outcome assessment, as it is possible to carry out the

assessment as teaching and learning progresses. A notional timescale for the average

student to complete the assessment is given in the table below.

Assessment Procedures

OUTCOME NUMBER APPROXIMATE TIME ALLOCATION

1 60 minutes

2 60 minutes

3 70 minutes

4 40 minutes

Retention of evidence

All written work should be retained for verification purposes.

Reassessment

Time is allowed within units for the assessment and reassessment of outcomes.Where a student has not attained the standard necessary to pass a particular outcome

or outcomes, there should be an opportunity to be reassessed. It is not necessary toreassess the students on all questions provided the lecturer / teacher is

satisfied that the students overall performance is satisfactory. Reassessmentinstruments should be designed to ensure the same degree of rigor. Alternative

fabricated components, weld symbols and sketches can be used for the purposes of

reassessment.

Recording Procedures

Student achievement can be recorded using the sample sheets that follow. As anoutcome is achieved it can be ticked and any relevant comments entered if required on

the Record of Assessment Checklist.

The Record of Performance sheet can be used to record information on assessment

schedules and deadlines including reassessment dates if applicable.


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RECORD OF ASSESSMENT

AND

OBSERVATION CHECKLIST

BASIC PRINCIPLES OF FABRICATED COMPONENT DESIGN,MANUFACTURE AND TEST METHODS

Class: _____________________________

Date: _____________________________


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RECORD OF ASSESSMENT / CHECKLIST

NAME LO 1 LO 2 LO 3 LO 4 COMMENTS

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20


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STUDENTS RECORD OF

PERFORMANCE


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RECORD OF STUDENT NAME

PERFORMANCE CLASS:

Topic Date Due/

Week Number

Achieved/

Not Achieved

Comments Date Completed

Lecturer / Teacher Name:

Lecturer / Teacher Signature:

Date:


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SECTION 4 : RESOURCES

Resource Requirements including course notes, book list and audio-visual list.

Course notesCourse notes are included as examples of the type of information that should be given

to students.

Recommended Book List

TITLE PUBLISHER AUTHOR

Which Process? Abington ISBN 1855730081 Houldcroft, P.

Welding Processes and

Technology

Pitman ISBN 0273411551 Romans, D. and Simons, E.N.

Welding Processes Cambridge ISBN 05021215307 Houldcroft, P.

Technician Fabrication &Welding 1

Cassell Ltd ISBN 0304300276 Cooper, K. J. and Greenwood,T. P.

Welding and Fabrication

Technology

Pitman ISBN 0273015060 Kenyon, W.

Basic Welding and Fabrication Pitman ISBN 0273013211 Kenyon, W.

Blueprint Reading for Welders Delmar ISBN 0827329970 Bennett, A. E. and Siy, L. J.

Basic Engineering Drawing Longman Scientific &

Technical ISBN 0582988551

Rhodes, R. S. and Cook, L. B.

Welding and Metal Fabrication

Journals

The Welding Institute The Welding Institute

Engineering Design forTechnicians

Pitman Hawkes, B and Abinett, R

The Engineering Design Process Pitman ISBN 0 273 01895 7 Hawkes, B and Abinett, R


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Recommended Video list

TITLE SOURCE

Aluminium Gas Metal Arc Welding Murex

Aluminium Gas Tungsten Arc Welding Murex

Basic Skills Gas Metal Arc Welding Murex

Basic Skills - Gas Metal Arc Welding Murex

Conducting Welder Approval Tests The Welding Institute

Cores for Satisfaction Murex

Facts of NDT The Welding Institute

Process and Practice Gas Tungsten Arc Welding Murex

Process and Practice Gas Metal Arc Welding Murex

Safe Electric Arc Cutting and Welding Murex

Safe Oxy Acetylene Cutting and Welding Murex

Stainless Steel - Gas Metal Arc Welding Murex

Stainless Steel - Gas Tungsten Arc Welding Murex

Thermal Joining BBC Education

College Teaching/Learning pack

UNIT NUMBER TITLE SOURCE

2570012 Manufacture of Containers Anniesland College

2570012 Manufacture of Containers Motherwell College

Key Resources and workshop facilities

industrial drawings assignment sheets, planning sheets a selection of components highlighting design features low pressure leak testing equipment (small pump) industrial visits. access to fabrication and welding workshops current British/European standards (details in the table below)


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British/European standards

NUMBER TITLE

BSEN 22553 : 1995 (BS 499 part 2 ) Welded, brazed and soldered joints-Symbolic representation

on drawings

Current Standards

The use of current British and European standards is required throughout the course.

It is recommended that users contact the British Standards office for information on

current standards in use. the contact address is listed below.

British Standards OfficeQuality House

2000 Academy ParkGower Street

Glasgow

G51 1PP

TEL: 0141 427 2825 (Customer service 01819967000)

Technical information sources

The journal Connectfrom the Welding Institute includes a series entitledJob

Knowledge for Welders which will provide information on materials used in the

fabrication and welding industry.

The journal is published by TWI Abington Hall, Cambridge CB1 6AL, Telephone

0223 891162, FAX 0223 892588.

The articles contained in the journal can be freely reproduced as long asacknowledgement is made to The Welding Institute.


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SECTION 5: HEALTH AND SAFETY

The safety of teaching / lecturing staff and students working in the fabrication and

welding workshops must be the primary concern of everyone involved.

This has to take precedence over all other activities and be sustained against allother pressures.

There are many aspects to safety as follows:

Statutory requirements Centre procedures Centre structure Staff training and behaviour Workshop/laboratory features Student training and behaviourIt is beyond the scope of this document to provide details of all of these items, which

should be embraced as part of centre safety policy. Lecturers / Teachers must,however, be satisfied that all appropriate safety measures are in place before

embarking on work within the fabrication and welding workshops.

Student training is a recurrent activity which is likely to be the direct responsibility of

the Lecturer / Teacher. While this has to take place on a continuous basis as work in

the workshop/laboratory proceeds, it is helpful to perform specific safety training at

course commencement. Such training might form part of the course induction as its

relevance extends across all course units. This is particularly important for fabricationand welding students, as they should be encouraged to develop their own safety

culture, which should become a lifelong asset.

There is a rich diversity of material available on the subject but as a minimumstudents should have access to the bookletBe Safe available from the local LEC as

part of the skillseekers programme. The large welding companies such as Murex and

The Welding Institute provide excellent Health and Safety materials.


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SECTION 6: ACKNOWLEDGEMENTS

We gratefully acknowledge the support and assistance provided by colleagues at

Motherwell College, Kilmarnock College, Falkirk College, Perth College and

Anniesland College who have contributed material and helpful advice for this pack.


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Fabrication and Welding: Basic Principles of Fabricated Component Design,Manufacture and Test Methods (Higher) Student Materials

1

STUDENT INFORMATION AND SUPPORT MATERIAL


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SECTION 1: OUTCOMES

The outcomes to be covered in the unit

Outcome 1

Interpret fabrication drawings, identify and interpret welding symbols.


a. Interpretation of welding symbols is correct in terms of manufacturersinstructions and relevant standards.

b. Interpretation of fabrication drawings is correct in terms of manufacturersinstructions.

Range statement

Welding symbols: butt welds, filler welds, resistance welds, welding process, weld

location, weld details (contour, dimension, pitch, site instructions).Fabrication drawings: assembly instructions, forming instructions, dimensions,

conventions, general information.


Graphic and written/oral evidence to demonstrate that the student can identify and

interpret common welding symbols.

Graphic and written exercises to demonstrate that the student can interpret simple

fabrication drawings according to manufacturers instructions, including details

identified in the range statement.

Outcome 2

Illustrate the factors affecting the design of fabricated components.


a. Explanation of the factors affecting the structural integrity of design is accurate interms of the component.

b. Explanation of the factors affecting the functional aspect of design is correct interms of the component.

c. Illustration of the interrelationship among structural, functional and manufacturingaspects of the fabricated component design are clear and accurate.


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Range statement

Components: tanks, drums, pressure vessels

Structural integrity: structural stiffening, shape, change of shape, added stiffness.

Functional: external service environment, internal service environment.


Written and/or pictorial evidence that the student clearly understands the difference

between the structural and the functional aspects of design and of the methods used toadd rigidity and/or stiffness to the container.

Written and/or pictorial evidence that the student can select a container, which

incorporates the structural, functional, and manufacturing aspects of design and

annotates the pictorial evidence accordingly.

Supplementary oral evidence to ensure that the student can cover the range.

Outcome 3

Describe the manufacturing methods used for a fabricated component.


a. Description of the advantages and limitations of the methods used for componentmanufacture is comprehensive, clear and accurate.

b. Identification of the equipment and the sequence of manufacturing methods usedfor a component are correct.

c. Completion of a flowchart is correct in terms of the given specification.d. Explanation of the reasons why continuous testing is carried out on fabricated

components as they are being manufactured is clear, comprehensive and accurate.

Range statement

Components: tanks, drums, pressure vessels, structures.

Manufacturing methods: cutting, forming, jointing, handling, and finishing.

Continuous testing: stage inspection, material checking.


Written and/or pictorial evidence that the student clearly understands the

manufacturing methods in use for container construction together with their relativeadvantages and disadvantages.

Performance evidence that the student can produce a flow-chart and specify the

appropriate methods in the correct sequence.


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Outcome 4




a. Description of pressure tests and associated safety regulations is comprehensive,clear and accurate.

b. Specification of functional dimensions used in a dimensional test is correct.Range statement

Tests: pneumatic, hydraulic.

Functional dimensions: tolerances, component size.


Performance evidence that the student can mark from given drawings the functional

dimensions of the component.

Written and/or pictorial evidence that the student can explain testing and the reasons

for choice of methods.


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SECTION 2: ASSESSMENT

The assessment instruments for the outcome

This unit covers:

interpretation of fabrication drawings and the identification of weld symbols factors affecting the design of fabricated components manufacturing methods used for the fabrication of components quality assurance methodsOutcome 1

Outcome 1 will be assessed by the use of written questions.

You will be required to identify a welding symbol from a given sketch or sketch a

weld joint from a given symbol.

You will be required to identify the weld symbols as given on a drawing of afabricated component.

Drawing interpretation question where you are required to identify various aspects

from a fabricated component drawing.

Outcome 2


You will be required to state examples for each of the following aspects of fabricated

design:1. Structural2. Functional3. ManufacturingYou will be required to answer questions relating to the design aspects of for a given

fabricated component.

Outcome 3


You will be required to complete a planning operations sheet for the manufacture of afabricated component or, to include details of the processes and equipment required.

You will be required to give written details related to the inspection and testing of acomponent detailed in a previous question.

Outcome 4


You will be required to explain the processes and procedures required in the testing of

the fabricated component detailed in the assessment for Outcome 2.


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SECTION 3: STUDENT GUIDE

In this unit you will be introduced to Basic Principles of Fabricated Component

Design, Manufacture and Test Methods. This will include the principles associated

with the manufacture of pressure vessels and simple structures together with the

associated quality assurance processes and techniques.

An essential part of the unit will be the topic on interpretation of drawings and

identification of weld symbols in accordance with the new British and Europeanstandards (BSEN).

As far as possible practical exercises based on design and manufacture will be used as

the teaching method. The quality assurance topic will include you being involved in

the testing of a fabricated component and reporting on subsequent defects.

You will also have the opportunity to plan a sequence of operations for the

manufacture of a fabricated component.

Prior knowledge

You will not require any prior knowledge of fabricated component design in order to

undertake this unit.


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SECTION 4: COURSE NOTES AND TUTORIALS

Welding Symbols

Details of symbols

Details of symbols used in fabrication and welding drawings can be found in BSEN

22553: 1995 Welded, brazed and soldered joints Symbolicrepresentation on

drawings.

Position of symbol on drawing

The welding symbol consists of the following components (see Figure 1):

Arrow line (a) Reference line (b) Identification line (c) Welding symbol

(b) (d)

(a)

(c)

Joint

Figure 1

Position of the reference line

The reference line shall preferably be drawn parallel to the bottom edge of the

drawing. If this is not possible it should be drawn perpendicular (see figure 2).


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Position of the arrow line

The position of the arrow line with respect to the weld is of no special significance

(see figure 2). The arrow line shall:

Join one end of the continuous reference line such that it forms an anglewith it

Be completed by an arrow head.

Figure 2

Position of symbol with regard to the reference line

The symbol is placed either above or beneath the reference line, in accordance with

the following regulation:

The symbol is placed on the continuous side of the reference line if the weld(weld face) is on the arrow side (see figure 3a)

The symbol is placed on the dashed line side if the weld (weld face) is onthe other side of the joint (see figure 3c)


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Figures 3a, b and c

The distinction between arrow side and other side is detailed in Figure 3b.

For symmetrical welds only

To be welded on the arrow side

Figure 3a

Other Arrow Arrow Other

Side side side side

Weld on arrow side Weld on other side

Figure 3b

To be welded on the other side

Figure 3b

Note:

More detailed information is available from the standard including elementary

symbols, combined symbols, supplementary symbols, dimensioning of welds and

indication of welding process (in accordance with ISO 4063).


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Fabrication Processes

The main processes used in the manufacture of fabricated components are as follows:

Design Marking out Cutting Forming Joining Assembly and Inspection

Marking out

Where small quantities only are required or one-off jobs, it is usual to usual to use the

method of direct marking from the drawing. This entails working from set datum

points which may be squared lines on plates or square edges.

TemplatesIf set shapes, rolling diameters or angles have to be formed then use is made of set

templates. The use of a set template is shown in figure 1a.

If a large number of items have to be produced then a template is used (see figure 1b).

Templates are made from wood, special card like paper or metal depending on the

number and type of object. The cost of making the template is justified if large

batches have to be produced. It is important that, after marking out, critical

dimensions are checked by a competent person before drilling, etc., to avoid any delay

and expense which would occur due to mistakes. Care should be taken in planning

the marking out of a number of components from a single sheet, to achieve economy

of material.

The position of holes can be pre marked through the template but these should then be

marked using a centre punch or nipple punch. To help with identification, dab marks

can be circled with white paint.


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Figure 1a Figure 1b

Marking-off large plates

Large plates have to be marked off in the flat position or on the floor. A datum line

is used and this is scribed adjacent to one edge with the aid of a straight edge and

scriber. An alternative method of marking out a straight line on a large plate is by theuse of a chalkline (see figure 2). The procedure for using a chalkline is as follows:

1. The line is located on the plate2. The chalked line is stretched and flicked on to the plate3. The line is then marked (chalked) on the plateNote:

An engineers square can be used to ensure the line is pulled up in a straight line from

the plate.

T E M P L A T E

SET TEMPLATE

51m

m

T E M P L A T E

USE OF TEMPLATE


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The use of a chalkline

S T E E L P L A T E

C H A L K L I N E

M A G N E T T R Y - S Q U A R E

Figure 2

Metal cutting

The two main methods used to cut plate material are as follows: Thermal cutting ShearingThermal cutting

Thermal cutting can be by the oxy-fuel method or plasma. In oxy-fuel cutting the fuel

gas can be propane or acetylene. Propane is cheaper than acetylene and requires a

special cutting nozzle.

The process works by the principle of rapid oxidation. When carbon steel is heated to

a temperature of approximately 850C the iron in the steel burns in the presence ofthe oxygen and oxides are formed. At this stage a chemical reaction takes place. This

is called an exothermic reaction, which in turn produces more heat, which melts the

oxides that have been formed and the molten oxide is blown away. The equipment

consists of gas supply and accessories, cutting torch and suitable cutting nozzle.

Cutting nozzle

A cutting nozzle consisting of an outer nozzle, which supplies a mixture of gasses inthe form of a pre-heating flame and an inner nozzle that supplies the blast of cutting

oxygen. A selection of nozzle types is shown in figure 3a.


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Hand cutting torch

The most common type is a high pressure torch which is made up of a mixing

chamber containing the combined gasses and a tube section carrying the cutting

oxygen to the nozzle (figure 3b). The cutting oxygen is released on to the workpiece

by a lever on the top of the torch. Accurate cutting of standard shapes can made by

the use of a selection of cutting aids (figure 4 ).

Factors influencing the quality of cut

A good quality cut depends on the following:

Correct nozzle size for plate thickness Correct gas pressures Correct cutting speed Correct nozzle distance from plate Good operator techniqueIf all these factors are present then a smooth cut edge is produced. This cut edge iscalled the Kerf.

The effects of variation in flame cutting procedures can be seen in figure 5.


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Figure 3

Cutting Nozzles

A B C D E

A O N E - P I E C E C U T T I N G N O Z Z L E - P A R A L L E L B O R E , 3 - 9 P R E - H E A T H O L E S , N O S K I R T.

B T W O - P IE C E C U T T I N G N O Z Z L E - V E N T U R I B O R E , P R E - H E A T A N N U L U S , N O S K I R T.

C T W O - P I E C E N O Z Z L E - V E N T U R I B O R E , P R E - H E A T F L U T E S , L O N G S K I R T.

D T W O - P I E C E N O Z Z L E - P A R A L L E L B O R E , P R E - H E A T S L O T S , L O N G S K I R T.

E T W O - P I E C E N O Z Z L E - P - A R A L L E L B O R E , P R E - H E A T F L U T E S , O X Y G E N C U R T A IN .

ACETYLENE

ACETYLENE

NATURAL GAS

PROPANE

PROPANE

NOZZLE DESIGN FEATURES

Figure 3a

Cutting Torch

90O

E N S U R E E D G E O F P L A T E

R E M O V E R U S T & S C A L EB E F O R E C O M M E N C I N G

F U E L G A S

F U E L G A SVALVE

H E A T IN G O X Y G E NVALVE

C U T T I N G O X Y G E NC O N T R O L L E V E R

HEATINGO X Y G E N

CUTTINGO X Y G E N

MAINTAINC O R R E C TDISTANCE

MIXER IN

H E A DA D J U S T P R E S S U R E S

CORRE CTLY ATR E G U L A R S

Figure 3b

Figure 4


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Cutting aids and attachments

CUTTING BEVEL

60O

S E L E C T N O Z Z L E & P R E S S U R E S

F O R I N C R E A S E D T H I C K N E S S

O F B E V E L

B L O W P I P E S T E A D I E D A N D

C U T T I N G A N G L E M A I N T A IN E D

U S I N G T W O S U I TA B L E

S T R A I G H T B A R S

BEVAL ATTACHMENT

A D J U S T A B L E R A D I U S B A R

P O I N T F I TS P U N C H M A R K

A T C I R C L E C E N T R E

R O L L E R C A R R I E S B L O W P I P E

R A D I U S B A R F I T S O N

B L O W P I P E H E A D

LARGE CIRCLE CUTTING

30O

CUTTING BEVELLED EDGE ON INCLINE

RADIUS BAR

SMALL CIRCLE GUIDE


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Figure 5

Types of Edge Produced Flame cutting faults

Description Edge condition

Good cut, all settings correct

Rounded top edge due to melting, scale

forming, gouging and drag lines at

pronounced bottom edge, brittle bottomedge, scale difficult to remove.

Cause:

Travel speed too slowUndercut edge, drag lines excessive, topand bottom edge rounded.

Cause:

Travel speed too fast

Melted and rounded top edge, undercuton edge caused by oxygen strumming out

of nozzle, bottom edge square.

Cause:

Nozzle distance from workpiece toogreat.

Rounded top edge, heavy beading

evident, appearance of cut edge otherwise

good.

Cause:

Nozzle height incorrectEdge has a regular bead, wide kerf at thetop of edge with undercut beneath.

Cause:

Cutting oxygen pressure too great.


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Rounded and melted top edge, slag

adhering to edge, taper face.

Cause:

Pre-heat flame too large.

Shearing

The most common form of shearing is by the use of a guillotine. There are four main

types of guillotine:

Hand operated lever - bench type shear Foot operated - treadle type Electric power driven Hydraulic power

Hand operated lever type guillotines and treadle guillotines are used to cut sheet metal

up to 1.6mm thick. Power operated guillotines are used in thick plate work usually up

to 12mm thick.

Treadle and power guillotines are fitted with front guides and back gauge/stops, on

some machines these are set electrically (figure 6).

Safety

Safety guards are fitted to guillotines to protect the operator from the cutting blade,these can be adjusted mechanically.


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Figure 6

Cutting set up adjustable back stop

STARTING

LEVER

EMERGENCYSTOP

FIXED S ID ES T O P

CUTTING LINE

TOP BLADE

LOWER BLADE

CLAMPING RAM

PLATE

TOP BLADE

LOWER BLADE

ADJUSTABLE

BACK STOP

CLAMP

Rolling and bending

Bending rolls are used to produce cylindrical forms. Bending rolls can be hand

operated for sheet metal use or power operated for thick plate work. In the main rolls

are horizontal but in some cases they can be vertical when forming of large plate is

required. As a rule of thumb the minimum diameter that can be rolled is twice the rolldiameter.

Roll types

The most common roll types arepinch andpyramid(figure 7). Pinch type rolls are

used for forming sheet metal

Pyramid type rolls are used for heavy plate forming and as the name suggests the rolls

are arranged in the form of a pyramid. The top roll is adjusted up and down and can

be partly detached to allow the work to be removed.


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Pre-forming

The design of rolling machines does not allow the leading and trailing edges to be

formed therefore it is necessary to pre-form the plate prior to rolling to ensure the

leading and trailing plate edges are curved. This can be achieved by bending on a

press, using the rolls themselves or in the case of sheet metal hand formed with a

mallet. The curve can be checked using a set template.

Figure 7

Roll types

Pyramid type Pinch type

Bending

Sheet metal is bent using folding machines. The three main steps in folding are asfollows:

1. Clamping in clamping, the material is pressed between a lever-operated topclamping blade and the folding beam.

2. Folding in folding, the bottom folding beam is pulled up causing the work tobend

3. Removal of the work care must be taken when folding to ensure that the workcan be removed from the machine. Planning should be carried out prior to

folding and a folding sequence should be established.

These steps are detailed in figure 8.


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Figure 8

Folding stages

FO L D IN G - S TA N D A R D B E D B A R

B E N D IN G - S M A L L R A D IU S

R E V E R S E B E N D S

25 .4mm

M A X R A D I U S

U S E O F R A D IU S F IN G E R S

Bending Thick Plate

Thick plate is bent by using a press brake. Press brakes come in two forms,mechanical and electro-hydraulic. A press brake is really a wide ram press, and can

be used for various types of work. It consists of a top tool and a bottom dye. Press

brakes can be up-stroking and down-stroking. In up-stroking a ram pushes the bottom

tool up to meet the top fixed tool. Hydraulic press brakes are usually up-stroking

types. In down-stroking the ram brings the top tool down to meet the bottom fixed

tool. Examples of tooling can be seen in figure 9.


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Figure 9

Press brake tooling

MAXDEPTHOFBO

X

1 2 3 1 2 3


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Joining

The most common joining method used in fabrication is welding. Details of common

welding processes can be found in the tables below.

PROCESS DESCRIPTION APPLICATION

Manual

Metal Arc

An arc is formed between a flux-coated

electrode and the joint to welded,causing the joint edges and theelectrode end to melt. Molten filler is

transferred across the arc into themolten weld pool where both fusetogether to form a welded joint

protected during cooling by a layer ofslag. Very high quality welds may beproduced.

Welding of structural steelwork. New and

repair work

Hard-facing applications

Boilers, ships, pressure vessels, bridges,

container tanks.

Metal ArcGasShielded

The power source is normally a d.c.Rectifier with the torch connected tothe positive pole. A filler wire iscontinuously fed through the torch

from a wire reel. The welding arc isself-adjusted by the machine. Ashielding gas is also passed through the

torch to the workpiece. The current isadjusted by varying the wire feedspeed. The most common forms of

MAGS welding are Dip transfer, usedon thin sheet and Spray transfer usedon heavy plate.

Widely used in the fabrication industry.

Structural steel work, shipbuilding, car bodyrepair, stainless steel fabrications,aluminium work, pipe work

TungstenArc GasShield

The arc is struck between a non-consumable tungsten electrode bymeans of an H.F. spark and theworkpiece.

A suitable gas shield is introduced into

the weld pool protecting the weld poolfrom atmospheric contamination.

The current can be AC or DC

depending on the material to be weldedor the welding operation. AC is

preferred for the welding of aluminiumand magnesium alloys.

High quality welding of ferrous and non-ferrous metals Thin sheet materials.

Root runs in pipes used in oil productionwork.

Food processing equipment.

Car industry.

High precision production work.

Repair work on non-ferrous materials.

Aircraft industry.


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Fabrication Design

Stiffening of fabricated components:

A thin sheet metal plate will not support a heavy load, however a thick metal plate of

the same cross sectional area will. It may be part of the design process that the

component has to be light in weight but strong enough to support a load. In this casethe thin sheet must be stiffened to make it rigid and strong. An example of stiffening

can be demonstrated by using simple card (figure 10a).

Figure 10a

Principle of stiffening

P A P E R TH I C K N E S S

P A P E R

TH I C K N E S S

A R E A O F H I G H S TR E S S

A R E A O F H I G H S TR E S S

N E U TR A L A X I S

N E U TR A L A X I S

TU M B LE R O F W A TE R

E M P T Y T U M B L E R S

N O TE P A P E R

O R I G I N A L P A P E R

C O R R U G A TE D

B Y FO LD I N G

Building in rigidity

A simple method of imparting rigidity to a structure is by forming a flange on the

ends of the plate or by forming a safe edge (figure 10 b). In cylindrical work the

introduction of dome shapes or curves help with stiffening. The swaging of a

cylindrical shape container can add rigidity and it also adds to the aestheticappearance of the object. (Figure 10 c).


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Bolted, welded or riveted stiffeners

Large panel sections can be made more rigid by the use of applied stiffeners such as

top hat sections, angle sections, heavy plate flat barandD shapedbar. These

stiffeners can be spot welded, tack welded, bolted or riveted to the panels (figure 10d).

Angle frames can also be used to support fabricated structures.

It is also possible to impart rigidity to a sheet metal structure such as ducting, by

introducing a diamond break fold to the component. This also helps minimise

drumming in sections of sheet metal ducting, due to vibration from extractor fanmotors. (figure 10 e)

Figure 10 b

Edge Flanging and Safe Edges

Figure 10c

Curved surfaces and swaging


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Figure 10 (continued)

Figure 10d

Applied stiffeners

TOP HAT SECTIONE D G E S F O L D E D

F L A T B A R

S T I F F E N E R

D - S H A P E D B A R

S T I F F E N E R

A N G L E I R O N

S T I F F E N E R

R I V E T

Figure 10e

Angle Frames and Diamond Folding

ANGL E IRON

ST IF F ENER

RIVET


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Assembly and Inspection

Figure 11 gives details of the inspection methods used to check a pressure vessel for,

alignment (plumb line), squareness (set square), dimensional accuracy (straight edge

and tape measure) and straightness (tensioned wire).

Figure 11

Inspection methods

=

=

T O P V E S S E L

B O T T O M V E S S E L

T O P S U P P O R T

B O T T O M S U P P O R T

T I M B E R S U P P O R T F O R P L U M B L I N E

PIPE

F L A N G E S

P U L L E Y

W E I G H T

P L A T FO R M B R A C K E T S A L I G N E D

U S I N G T E N S I O N E D W I R EP L A T F O R M

S U P P O R T

B R A C K E T S

BULK LIQUID

VESSEL


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Fabrication & Welding - Basic Principles

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