Fabrication & Welding - Basic Principles

Fa brica brica t ion ion a nd Wel Welding ding Basic Prin Pr incipl ciple es of Fab F abr ri cate cated d C om ompone ponent nt De D esign: Manufacture and Test Methods (Higher) 5794

September 1999 HIGHER STILL

F a b r ic i ca t i on a n d Welding B a sic si c P rinci rinci p l e s of of Fa brica brica t e d C om p onent D esign esi gn : Ma nufa ct ure a nd Te Te st Met Met ho hods ds (Higher)

S upp up p ort Ma t e ria ls

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.

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

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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 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, 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.

Performance criteria a. 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 statement Components: tanks, drums, pressure vessels Structural integrity: structural stiffening, shape, change of shape, added stiffness. Functional: external service environment, internal service environment. Evidence requirements 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 to add 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. Performance criteria a. Description of the advantages and limitations of the methods used for component manufacture is comprehensive, clear and accurate. b. Identification of the equipment and the sequence of manufacturing methods used for 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 the manufacturing methods in use for container construction together with their relative advantages 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 t he reasons for choice of methods.


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Outcome 4

Describe inspection and test procedures used during and after manufacture of fabricated components. Performance criteria a. Description of pressure t ests 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 requirements Describe inspection and test procedures used during and after manufacture of fabricated components. 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 principles

Elements 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 of bridges 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 3 Main 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 4 Main 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. Demonstrate material 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 material checking 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 the section 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 of design. 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 be used wherever possible. It should be the teacher or lecturer ’s 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 book conditions. 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 to reassess the students on all questions provided the lecturer / teacher is satisfied that the students overall performance is satisfactory. Reassessment instruments 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 an outcome 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 notes

Course 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 I SBN 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


Engineering Design for Technicians

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


Cores for Satisfaction

Murex

Facts of NDT


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

BSEN 22553 : 1995 (BS 499 part 2 )

TITLE

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 Office Quality House 2000 Academy Park Gower Street Glasgow G51 1PP TEL: 0141 427 2825 (Customer service 01819967000)

Technical information sources

The journal Connect from the Welding Institute includes a series entitled Job 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 as acknowledgement 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 all other 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, 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 t o 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 fabrication and 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 minimum students should have access to the booklet Be 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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STUDENT INFORMATION AND SUPPORT MATERIAL

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

1


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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 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, 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. Performance criteria a. 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.


3

Range statement Components: tanks, drums, pressure vessels Structural integrity: structural stiffening, shape, change of shape, added stiffness. Functional: external service environment, internal service environment. Evidence requirements 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 to add 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. Performance criteria a. Description of the advantages and limitations of the methods used for component manufacture is comprehensive, clear and accurate. b. Identification of the equipment and the sequence of manufacturing methods used for 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 the manufacturing methods in use for container construction together with their relative advantages 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

Describe inspection and test procedures used during and after manufacture of fabricated components. Performance criteria a. Description of pressure t ests 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 requirements 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 t he 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 methods Outcome 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 a fabricated component. Drawing interpretation question where you are required to identify various aspects from a fabricated component drawing. Outcome 2

Outcome 2 will be assessed by the use of written questions. You will be required to state examples for each of the following aspects of fabricated design: 1. Structural 2. Functional 3. Manufacturing You will be required to answer questions relating to the design aspects of for a given fabricated component. Outcome 3

Outcome 3 will be assessed by the use of written questions. You will be required to complete a planning operations sheet for the manufacture of a fabricated 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 a component detailed in a previous question. Outcome 4

Outcome 4 will be assessed by the use of written questions. 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 European standards (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 – Symbolic representation 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 angle with 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 on the 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. Other Side

For symmetrical welds only

Arrow side

Weld on arrow side

Arrow side

Other side

Weld on other side

Figure 3b

To be welded on the arrow side

Figure 3a

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 fro m set datum points which may be squared lines on plates or square edges. Templates If 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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TEMPLATE

m m 1 5

TEMPLATE

SET TEMPLATE

Figure 1a

USE OF TEMPLATE

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 the use of a chalkline (see figure 2). The procedure for using a chalkline is as follows: 1. The line is located on the plate 2. The chalked line is stretched and ‘flicked’ on to the plate 3. 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 from the plate.


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The use of a chalkline TRY-SQUARE

MAGNET

CHALK LINE

STEEL PLATE

Figure 2

Metal cutting The 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 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 850°C the iron in the steel ‘burns’ in the presence of the 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 in the 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 technique

If all these factors are present then a smooth cut edge is produced. This cut edge is called 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

NOZZLE DESIGN FEATURES

A O N E - P I E C E A C E T Y L E N 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 ACETYLENE 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 A T U R A L G A S 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 P R O P A N 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 P R O P A N 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 .

Figure 3a

Cutting Torch CUTTING OXYGEN

HEATING OXYGEN

CUTTING OXYGEN CONTROL LEVER

H E A T IN G O X Y G E N VALVE

MIXER IN HEAD

ADJUST PRESSURES CORRE CTLY AT REGULARS FUEL GAS

MAINTAIN CORRECT DISTANCE

90

O

REMOVE RUST & SCALE BEFORE COMMENCING

FUEL GAS VALVE

ENSURE EDGE OF PLATE

Figure 3b Figure 4 Fabrication and Welding: Basic Principles of Fabricated Component Design, Manufacture and Test Methods (Higher) – Student Materials

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Cutting aids and attachments

RADIUS BAR

SMALL CIRCLE GUIDE

RADIUS BAR FITS ON BLOWPIPE HEAD

P O I N T F I TS P U N C H M A R K AT CIRCLE CENTRE ADJUSTABLE RADIUS BAR ROLLER CARRIES BLOWPIPE

LARGE CIRCLE CUTTING

BEVAL ATTACHMENT

BLOWPIPE STEADIED AND 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 STRAIGHT BARS

O

30 O

60

SELECT NOZZLE & PRESSURES FOR INCREASED THICKNESS OF BEVEL

CUTTING BEVELLED EDGE ON INCLINE CUTTING BEVEL


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Figure 5 Types of Edge Produced – Flame cutting faults Description Good cut, all settings correct

Edge condition

Rounded top edge due to melting, scale forming, gouging and drag lines at pronounced bottom edge, brittle bottom edge, scale difficult to remove. Cause: • Travel speed too slow Undercut edge, drag lines excessive, top and bottom edge rounded. Cause: • Travel speed too fast

Melted and rounded top edge, undercut on edge caused by oxygen strumming out of nozzle, bottom edge square. Cause: • Nozzle distance from workpiece too great. Rounded top edge, heavy beading evident, appearance of cut edge otherwise good. Cause: • Nozzle height incorrect Edge has a regular bead, wide kerf at the top 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

FIXED SIDE STOP

STARTING LEVER EMERGENCY STOP

CLAMP

CLAMPING RAM TOP BLADE

CUTTING LINE

ADJUSTABLE BACK STOP

PLATE

LOWER BLADE

TOP BLADE LOWER BLADE

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 roll diameter. Roll types The most common roll types are pinch and pyramid (figure 7). Pinch type rolls are used for forming sheet metal Pyramid type rolls are used for heavy plate forming and as t he 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 as follows: 1. Clamping – in clamping, the material is pressed between a lever-operated top clamping blade and the folding beam. 2. Folding – in folding, the bottom folding beam is pulled up causing the work to bend 3. Removal of the work – care must be taken when folding to ensure that the work can 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

25.4mm MAX RADIUS

F O L D I N G - S TA N D A R D B E D B A R

BENDING - SMALL RADIUS

USE OF ‘RADIUS FINGERS’

REVERSE BENDS

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

M A X D E P T H O F B O 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

Manual Metal Arc

DESCRIPTION

APPLICATION

An arc is formed between a flux-coated electrode and the joint to welded, causing the joint edges and the electrode end to melt. Molten filler is transferred across the arc into the molten weld pool where both fuse together to form a welded joint protected during cooling by a layer of slag. Very high quality welds may be produced.

Welding of structural steelwork. New and repair work

Metal Arc Gas Shielded

The power source is normally a d.c. Rectifier with the torch connected to the positive pole. A filler wire is continuously fed through the torch from a wire reel. The welding arc is self-adjusted by the machine. A shielding gas is also passed through the torch to the workpiece. The current is adjusted by varying the wire feed speed. The most common forms of MAGS welding are Dip transfer, used on thin sheet and Spray transfer used on heavy plate.

Widely used in the fabrication industry.

Tungsten Arc Gas Shield

The arc is struck between a nonconsumable tungsten electrode by means of an H.F. spark and the workpiece.

High quality welding of ferrous and nonferrous metals Thin sheet materials.

A suitable gas shield is introduced into the weld pool protecting the weld pool from atmospheric contamination.

Hard-facing applications Boilers, ships, pressure vessels, bridges, container tanks.

Structural steel work, shipbuilding, car body repair, stainless steel fabrications, aluminium work, pipe work

Root runs in pipes used in oil production work. Food processing equipment. Car industry.

The current can be AC or DC depending on the material to be welded or the welding operation. AC is preferred for the welding of aluminium and magnesium alloys.

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 case the 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 TUMBLER OF WATER

NOTE PAPER

EMPTY TUMBLERS

ORIGINAL PAPER CORRUGATED BY FOLDING

PAPER THICKNESS NEUTRAL AXIS

PAPER THICKNESS

AREA OF HIGH STRESS

NEUTRAL AXIS

AREA OF HIGH STRESS

Building in ri gidity 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 aesthetic appearance 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 bar and D shaped bar. These stiffeners can be spot welded, tack welded, bolted or riveted to t he 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 fan motors. (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 ANGLE IRON STIFFENER

RIVET

EDGES FOLDED

FLAT BAR STIFFENER

TOP HAT SECTION

D-SHAPED BAR STIFFENER

Figure 10e Angle Frames and Diamond Folding

ANGLE IRON STIFFENER

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 TIMBER SUPPORT FOR PLUMB LINE

TOP VESSEL

=

TOP SUPPORT

=

BOTTOM VESSEL PIPE FLANGES

BOTTOM SUPPORT

P L A T FO R M B R A C K E T S A L I G N E D USING TENSIONED WIRE PLATFORM SUPPORT BRACKETS

PULLEY

BULK LIQUID VESSEL

WEIGHT


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Fabrication & Welding - Basic Principles

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