Fabrication and Welding

Fabrication and WeldingBasic Principles of Fabricated

Component Design:Manufacture and Test Methods

(Higher)

5794

September 1999

Fabrication andWelding

Basic Principles of FabricatedComponent Design:

Manufacture and Test Methods(Higher)

Support Materials

HIGHER STILL

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

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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 itis to be assessed and method of recording results

Section 4 Resource Requirements including course notes book lists andaudio-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 1Interpret fabrication drawings, identify and interpret welding symbols.

Performance criteriaa. Interpretation of welding symbols is correct in terms of manufacturers’

instructions and relevant standards.b. Interpretation of fabrication drawings is correct in terms of manufacturers’

instructions.

Range statement

Welding symbols: butt welds, filler welds, resistance welds, welding process, weldlocation, weld details (contour, dimension, pitch, site instructions).Fabrication drawings: assembly instructions, forming instructions, dimensions,conventions, general information.

Evidence requirementsGraphic and written/oral evidence to demonstrate that the student can identify andinterpret common welding symbols.

Graphic and written exercises to demonstrate that the student can interpret simplefabrication drawings according to manufacturers’ instructions, including detailsidentified in the range statement.

Outcome 2Illustrate the factors affecting the design of fabricated components.

Performance criteriaa. Explanation of the factors affecting the structural integrity of design is accurate in

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

terms of the component.c. Illustration of the interrelationship among structural, functional and manufacturing

aspects of the fabricated component design are clear and accurate.


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Range statementComponents: tanks, drums, pressure vesselsStructural integrity: structural stiffening, shape, change of shape, added stiffness.Functional: external service environment, internal service environment.

Evidence requirementsWritten and/or pictorial evidence that the student clearly understands the differencebetween 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 thatincorporates the structural, functional and manufacturing aspects of design andannotates the pictorial evidence accordingly.

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

Outcome 3Describe the manufacturing methods used for a fabricated component.

Performance criteria

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.

Evidence requirements

Written and/or pictorial evidence that the student clearly understands themanufacturing methods in use for container construction together with their relativeadvantages and disadvantages.

Performance evidence that the student can produce a flow-chart and specify theappropriate methods in the correct sequence.

Written and/or pictorial evidence that the student can explain testing and the reasonsfor choice of methods.


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Outcome 4Describe inspection and test procedures used during and after manufacture offabricated 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.

Evidence requirementsDescribe inspection and test procedures used during and after manufacture offabricated components.

Performance evidence that the student can mark from given drawings the functionaldimensions of the component.


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SECTION 2 : TEACHING AND LEARNING ADVICETeaching Methods

Outcome 1 Main Topic

Interpretation of fabrication drawings and welding symbols.Industrial drawings should be used as source for identification of symbols anddrawing interpretation, with constant reference to BSEN 22553 Welded, brazed andsoldered joints-Symbolic representation on drawings: 1995 (BS 499 part 2 ) Thecoverage of welding symbols should concentrate on the identification andinterpretation of the weld symbol and not focus on the actual drawing of the symbol


Design principlesElements of fabricated component design and their interrelationship. Use should bemade of good examples of functional design such as a pressed steel car wheel, fuelcontainers, car radiator, liquid food containers with radiused corners. The design ofbridges and gantries should be discussed. Sheets of paper, or cardboard can beutilised to show the effects of poor design. Holes, both round and square in card, canbe used to demonstrate material failure by simple tearing and observing where thetearing starts.

The context in which the design is taught should be limited to functional aspects suchas size shape strength etc and interrelationships between the design of the componentand the manufacturing methods.


Manufacturing methodsSupport sheets giving cutting, forming, jointing and finishing processes together withworksheets on handling costs comparisons between the various processes should beused. Flowcharts based on the use of scale models to show the operation layouts. Aselection of exemplar layouts can be used to help with teaching operation sequencesand process choice.

Works visits should be arranged to enhance student experience.Hands on student activities and support materials can and should be used wherepossible.

It should be the lecturer / teachers aim to constantly apply the outcomes to practicalsituations to enable students to constantly apply underpinning knowledge themselves.


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Quality assuranceAwareness of the variety of tests that a component may be subjected to during andafter manufacture. Workshop activities to demonstrate simple leak tests and lowpressure testing of containers.

Teaching PlanThe teaching plan below gives guidance on suggested teaching order and guidance onthe timing of assessment.

LEARNINGACTIVITY

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)

Practicalexercise/tutorial

Interpret industrial drawings and manufacturer instructions, identify weldsymbols 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 environmentalrequirements.

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 startsaround 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 aftermanufacture of fabricated components (Lo4)

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

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 assessedand method of recording results

Outcome 1The assessment should ensure that students can identify weld symbols and interpretdrawings and manufacturers instructions. This section can be integrated with thesection on planning and manufacturing sequences and an integrated assessment ispossible.

A combined identification and interpretation exercise should be used to cover therange and performance criteria (a). For example, the assessment could be in the formof a table that contains welding symbols. Students should complete the tablealternating between identifying a symbol from a sketch to sketching a symbol from adescription. 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 featuresfound on fabrication drawings.

Outcome 2The 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 factorsaffecting the design of a fabricated component, combined with structured questions,formulated around a sketch/drawing of a fabricated structure.

Outcome 3The assessment of this outcome could be organised so that an assignment or projectforms the backbone where the design parameters of a container are assessed.

Manufacturing processes, process flowcharts and manufacturing instructions arerequired for the manufacture of a fabricated component and finally the integration oftesting methods are considered to ensure that the design criteria have been compliedwith during manufacture. Hands-on student activities and support material should beused wherever possible. It should be the teacher or lecturer’s aim to constantly relatethe outcomes to practical situations.

Outcome 4Written exercises in the form of inspection reports could be used to evidence that thestudent can explain testing methods produce sequence of testing operations andjustifying their use. The identification of functional dimensions of a component canbe achieved by the annotation of sketches or integrated with outcomes 2 and 3.


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Assessment TimingAssessments should be carried out under closed book conditions. It is difficult toallocate a time scale to each outcome assessment, as it is possible to carry out theassessment as teaching and learning progresses. A notional timescale for the averagestudent 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 evidenceAll 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 outcomeor 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. Alternativefabricated components, weld symbols and sketches can be used for the purposes ofreassessment.

Recording ProceduresStudent 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 onthe Record of Assessment Checklist.

The Record of Performance sheet can be used to record information on assessmentschedules and deadlines including reassessment dates if applicable.


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RECORD OF ASSESSMENTAND

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

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12

13

14

15

16

17

18

19

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STUDENTS RECORD OFPERFORMANCE


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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 givento students.

Recommended Book List

TITLE PUBLISHER AUTHOR

Which Process? Abington ISBN 1855730081 Houldcroft, P.

Welding Processes andTechnology

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 FabricationTechnology

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 FabricationJournals

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 representationon drawings

Current StandardsThe use of current British and European standards is required throughout the course.It is recommended that users contact the British Standards office for information oncurrent standards in use. the contact address is listed below.

British Standards OfficeQuality House2000 Academy ParkGower StreetGlasgowG51 1PPTEL: 0141 427 2825 (Customer service 01819967000)

Technical information sourcesThe journal Connect from the Welding Institute includes a series entitled JobKnowledge for Welders which will provide information on materials used in thefabrication and welding industry.

The journal is published by TWI Abington Hall, Cambridge CB1 6AL, Telephone0223 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 andwelding 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 behaviour

It is beyond the scope of this document to provide details of all of these items, whichshould be embraced as part of centre safety policy. Lecturers / Teachers must,however, be satisfied that all appropriate safety measures are in place beforeembarking on work within the fabrication and welding workshops.

Student training is a recurrent activity which is likely to be the direct responsibility ofthe Lecturer / Teacher. While this has to take place on a continuous basis as work inthe workshop/laboratory proceeds, it is helpful to perform specific safety training atcourse commencement. Such training might form part of the course induction as itsrelevance extends across all course units. This is particularly important for fabricationand welding students, as they should be encouraged to develop their own safetyculture, 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 booklet Be Safe available from the local LEC aspart of the skillseekers programme. The large welding companies such as Murex andThe 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 atMotherwell College, Kilmarnock College, Falkirk College, Perth College andAnniesland College who have contributed material and helpful advice for this pack.

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 1Interpret fabrication drawings, identify and interpret welding symbols.

Performance criteriaa. Interpretation of welding symbols is correct in terms of manufacturers’

instructions and relevant standards.b. Interpretation of fabrication drawings is correct in terms of manufacturers’

instructions.

Range statement

Welding symbols: butt welds, filler welds, resistance welds, welding process, weldlocation, weld details (contour, dimension, pitch, site instructions).Fabrication drawings: assembly instructions, forming instructions, dimensions,conventions, general information.

Evidence requirementsGraphic and written/oral evidence to demonstrate that the student can identify andinterpret common welding symbols.

Graphic and written exercises to demonstrate that the student can interpret simplefabrication drawings according to manufacturers’ instructions, including detailsidentified in the range statement.

Outcome 2Illustrate the factors affecting the design of fabricated components.

Performance criteriaa. Explanation of the factors affecting the structural integrity of design is accurate in

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

terms of the component.c. Illustration of the interrelationship among structural, functional and manufacturing

aspects of the fabricated component design are clear and accurate.


4

Range statementComponents: tanks, drums, pressure vesselsStructural integrity: structural stiffening, shape, change of shape, added stiffness.Functional: external service environment, internal service environment.

Evidence requirementsWritten and/or pictorial evidence that the student clearly understands the differencebetween 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, whichincorporates the structural, functional, and manufacturing aspects of design andannotates the pictorial evidence accordingly.

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

Outcome 3Describe 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.

Evidence requirements

Written and/or pictorial evidence that the student clearly understands themanufacturing methods in use for container construction together with their relativeadvantages and disadvantages.

Performance evidence that the student can produce a flow-chart and specify theappropriate methods in the correct sequence.


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Outcome 4Describe inspection and test procedures used during and after manufacture offabricated 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.

Evidence requirementsPerformance evidence that the student can mark from given drawings the functionaldimensions of the component.

Written and/or pictorial evidence that the student can explain testing and the reasonsfor choice of methods.


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SECTION 2: ASSESSMENT

The assessment instruments for the outcomeThis 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 methods

Outcome 1Outcome 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 aweld 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 aspectsfrom a fabricated component drawing.


You will be required to state examples for each of the following aspects of fabricateddesign:1. Structural2. Functional3. Manufacturing

You will be required to answer questions relating to the design aspects of for a givenfabricated component.


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.


You will be required to explain the processes and procedures required in the testing ofthe 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 ComponentDesign, Manufacture and Test Methods. This will include the principles associatedwith the manufacture of pressure vessels and simple structures together with theassociated quality assurance processes and techniques.

An essential part of the unit will be the topic on interpretation of drawings andidentification 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 asthe teaching method. The quality assurance topic will include you being involved inthe testing of a fabricated component and reporting on subsequent defects.

You will also have the opportunity to plan a sequence of operations for themanufacture of a fabricated component.

Prior knowledgeYou will not require any prior knowledge of fabricated component design in order toundertake this unit.


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SECTION 4: COURSE NOTES AND TUTORIALS

Welding Symbols

Details of symbolsDetails of symbols used in fabrication and welding drawings can be found in BSEN22553: 1995 Welded, brazed and soldered joints – Symbolic representation ondrawings.

Position of symbol on drawingThe 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 thedrawing. If this is not possible it should be drawn perpendicular (see figure 2).


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Position of the arrow lineThe 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 withthe 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 OtherSide 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 elementarysymbols, combined symbols, supplementary symbols, dimensioning of welds andindication of welding process (in accordance with ISO 4063).


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

• Design• Marking out• Cutting• Forming• Joining• Assembly and Inspection

Marking outWhere small quantities only are required or one-off jobs, it is usual to usual to use themethod of direct marking from the drawing. This entails working from set datumpoints 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 ‘settemplates’. 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 thenumber and type of object. The cost of making the template is justified if largebatches have to be produced. It is important that, after marking out, criticaldimensions are checked by a competent person before drilling, etc., to avoid any delayand expense which would occur due to mistakes. Care should be taken in planningthe marking out of a number of components from a single sheet, to achieve economyof material.

The position of holes can be pre marked through the template but these should then bemarked using a centre punch or nipple punch. To help with identification, dab markscan 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 lineis used and this is scribed adjacent to one edge with the aid of a straight edge andscriber. 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 plate

Note:An engineers square can be used to ensure the line is pulled up in a straight line fromthe plate.

TE M P LATE

SET TEM PLATE

51m

m

TE M P LATE

USE OF TEMPLA TE


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The use of a chalkline

S T E E L P L AT E

C HA LK L INE

M A G N E T T RY -S Q U A RE

Figure 2

Metal cuttingThe two main methods used to cut plate material are as follows:• Thermal cutting• Shearing

Thermal cutting

Thermal cutting can be by the oxy-fuel method or plasma. In oxy-fuel cutting the fuelgas can be propane or acetylene. Propane is cheaper than acetylene and requires aspecial cutting nozzle.

The process works by the principle of rapid oxidation. When carbon steel is heated toa temperature of approximately 850°C the iron in the steel ‘burns’ in the presence ofthe oxygen and oxides are formed. At this stage a chemical reaction takes place. Thisis called an exothermic reaction, which in turn produces more heat, which melts theoxides that have been formed and the molten oxide is blown away. The equipmentconsists 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 cuttingoxygen. A selection of nozzle types is shown in figure 3a.


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Hand cutting torchThe most common type is a high pressure torch which is made up of a mixingchamber containing the combined gasses and a tube section carrying the cuttingoxygen to the nozzle (figure 3b). The cutting oxygen is released on to the workpieceby a lever on the top of the torch. Accurate cutting of standard shapes can made bythe 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 technique

If 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 IE C E C U TT ING N O Z Z LE - PA R A LL E L B O R E , 3 - 9 P RE -HE AT H O LE S , N O S K IRT.

B T W O -P IE C E C UT T IN G N O Z ZL E - V E NT U R I B O R E , P RE -HE AT A N N U LU S , N O S K IRT.

C TW O -P IE CE NO ZZ LE - V E N TU R I B O RE , P R E -H E AT FL UT E S , LO N G S K IRT.

D TW O -P IE CE N O Z ZL E - PA RA LLE L B O RE , P R E -H E AT S LO T S , L O N G S K IRT.

E T W O -P IE C E N O Z Z LE - P -A R A LL E L B O R E , P RE -HE AT F LU T E S , O X Y G E N C UR TA IN .

ACETYLENE

ACETYLENE

NATURAL GAS

PROPANE

PROPANE

NOZZLE DESIGN FEATURES

Figure 3a

Cutting Torch

90O

EN SU RE ED GE O F PLATE

R EM O VE RU ST & SC ALEBE FO R E C O M M EN CING

FU EL G AS

FU EL G ASVALVE

H EATING O X YG ENVALVE

C UTTIN G O XYG E NC ON TRO L LEV ER

H EATINGO XYG EN

C UTTIN GO XYG EN

M AINTA INC OR RE CTD ISTA NC E

M IX ER INH EAD AD JU ST P RES SU RES

C OR RE CTLY ATR EG ULAR 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 LE & P R E S S U R E SF O R IN C R E A S E D TH IC K N E S S

O F B E V E L

B LO W P IP E S T E A D IE D A N DC U TT IN G A N G LE M A IN TA IN E D

U S IN G T W O S U ITA B LES T R A IG H T B A R S

BEVAL ATTACHMENT

A D JU S TA B LE R A D IU S B A R

P O IN T F ITS P U N C H M A R KAT C IR C L E C E N T R E

R O LL E R C A R R IE S B L O W P IP E

R A D IU S B A R F IT S O NB LO W P IP E H E A D

LARGE CIRCLE CUTTING

30O

CUTTING BEVELLED EDG E O N INCLINE

RADIUS BAR

SMALL CIRCLE GUIDE


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Figure 5

Types of Edge Produced – Flame cutting faults

Description Edge conditionGood cut, all settings correct

Rounded top edge due to melting, scaleforming, gouging and drag lines atpronounced bottom edge, brittle bottomedge, scale difficult to remove.

Cause:• Travel speed too slow

Undercut edge, drag lines excessive, topand bottom edge rounded.

Cause:• Travel speed too fast

Melted and rounded top edge, undercuton edge caused by oxygen strumming outof nozzle, bottom edge square.

Cause:• Nozzle distance from workpiece too

great.

Rounded top edge, heavy beadingevident, appearance of cut edge otherwisegood.

Cause:• Nozzle height incorrect

Edge 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, slagadhering 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 maintypes 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 metalup to 1.6mm thick. Power operated guillotines are used in thick plate work usually upto 12mm thick.

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

STARTINGLEVER

EMERGENCYSTOP

FIX ED SIDES TOP

CUTTING LINE

TOP BLADE

LOWER BLADE

CLAMPING RAM

PLATE

TOP BLADE

LOWER BLADE

ADJUSTABLEBACK STOP

CLAMP

Rolling and bending

Bending rolls are used to produce cylindrical forms. Bending rolls can be handoperated for sheet metal use or power operated for thick plate work. In the main rollsare horizontal but in some cases they can be vertical when forming of large plate isrequired. As a rule of thumb the minimum diameter that can be rolled is twice the rolldiameter.

Roll types

The most common roll types are pinch and pyramid (figure 7). Pinch type rolls areused for forming sheet metal

Pyramid type rolls are used for heavy plate forming and as the name suggests the rollsare arranged in the form of a pyramid. The top roll is adjusted up and down and canbe partly detached to allow the work to be removed.


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Pre-formingThe design of rolling machines does not allow the leading and trailing edges to beformed therefore it is necessary to pre-form the plate prior to rolling to ensure theleading and trailing plate edges are curved. This can be achieved by bending on apress, using the rolls themselves or in the case of sheet metal hand formed with amallet. 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 tofolding and a folding sequence should be established.

These steps are detailed in figure 8.


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Figure 8

Folding stages

F O LD IN G - S TA N D A R D B E D BA R

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

R E VE R S E B E N D S

25 .4m mM A X R A D IU 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 canbe used for various types of work. It consists of a top tool and a bottom dye. Pressbrakes can be up-stroking and down-stroking. In up-stroking a ram pushes the bottomtool up to meet the top fixed tool. Hydraulic press brakes are usually up-strokingtypes. In down-stroking the ram brings the top tool down to meet the bottom fixedtool. Examples of tooling can be seen in figure 9.


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Figure 9

Press brake tooling

MAX DEPTH OF BOX

1 2 3 1 2 3


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JoiningThe most common joining method used in fabrication is welding. Details of commonwelding processes can be found in the tables below.

PROCESS DESCRIPTION APPLICATION

ManualMetal Arc

An arc is formed between a flux-coatedelectrode and the joint to welded,causing the joint edges and theelectrode end to melt. Molten filler istransferred across the arc into themolten weld pool where both fusetogether to form a welded jointprotected during cooling by a layer ofslag. Very high quality welds may beproduced.

Welding of structural steelwork. New andrepair 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 torchfrom a wire reel. The welding arc isself-adjusted by the machine. Ashielding gas is also passed through thetorch to the workpiece. The current isadjusted by varying the wire feedspeed. The most common forms ofMAGS 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 intothe weld pool protecting the weld poolfrom atmospheric contamination.

The current can be AC or DCdepending on the material to be weldedor the welding operation. AC ispreferred 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 ofthe same cross sectional area will. It may be part of the design process that thecomponent 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 stiffeningcan be demonstrated by using simple card (figure 10a).

Figure 10a

Principle of stiffening

PA PE R TH IC KN E SS

PA PE RTH IC KN E SS

A R EA O F H IG H S TR E SS

A R EA O F H IG H S TR E SS

N E UT R AL AX IS

N E UT R AL AX IS

TU M BLE R O F W AT ER

E M P TY TU M BLE R S

N O TE PA P ER

O R IG IN A L PA PE RC O R R U G ATE DB Y FO LD ING

Building in rigidityA simple method of imparting rigidity to a structure is by forming a flange on theends of the plate or by forming a safe edge (figure 10 b). In cylindrical work theintroduction of dome shapes or curves help with stiffening. The swaging of acylindrical 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 stiffenersLarge panel sections can be made more rigid by the use of applied stiffeners such astop hat sections, angle sections, heavy plate flat bar and D shaped bar. Thesestiffeners 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, byintroducing 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

TO P H AT SEC TIO NED G ES FOLDE D

F LAT B A RS T IFF E N E R

D -S H A P E D B A RS T IFF E N E R

A N G LE IRO NS T IFF E N E R

R IV E T

Figure 10e

Angle Frames and Diamond Folding

A N G LE IR O NS TIF FE N E R

R IV E T


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Assembly and InspectionFigure 11 gives details of the inspection methods used to check a pressure vessel for,alignment (plumb line), squareness (set square), dimensional accuracy (straight edgeand tape measure) and straightness (tensioned wire).

Figure 11

Inspection methods

=

=

TOP V ES SE L

B OTTOM VE S SE L

TOP S UPP O RT

B OTTOM SUP P ORT

TIM B E R S UPP ORT F OR P LUM B LINE

P IP EFLANG E S

P ULLE Y

W EIGHT

P LATFO RM B RACK E TS ALIG NEDUS ING TE NSIONE D W IRE

P LATFO RMS UPP ORT

B RACK E TS

BULK LIQU IDVESSEL


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Fabrication and Welding

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