-SQA-SCOTTISH QUALIFICATIONS AUTHORITY
HIGHER NATIONAL UNIT SPECIFICATION
GENERAL INFORMATION
-Unit Number-
2570257
-Superclass-
XE
-Title-
TUNGSTEN ARC GAS SHIELDED WELDING PROCESS
-----------------------------------------DESCRIPTIONGENERAL COMPETENCE FOR UNIT: Developing an understanding of the
principles and applications of the T.A.G.S. welding process.
OUTCOMES
1.
explain the operating principles and equipment functions of the TAGS
welding process;
2.
select the process parameters for a specified application;
3.
produce an inspection report for a TAGS welded component.
CREDIT VALUE:
1 HN Credit
ACCESS STATEMENT: Access to this unit is at the discretion of the centre.
However, it would be beneficial if the candidate had competence in welding and
fabrication. This may be evidenced by possession of N.C. Module:
2270754 Introduction to Gas Shielded Welding Skills
or similar qualifications or experience.
`
----------------------------------------For further information contact: Committee and Administration Unit, SQA,
Hanover House, 24 Douglas Street, Glasgow G2 7NQ.
Additional copies of this unit may be purchased from SQA (Sales and Despatch
section). At the time of publication, the cost is £1.50 (minimum order £5.00).
Unit No. 2570257
Continuation
HIGHER NATIONAL UNIT SPECIFICATION
STATEMENT OF STANDARDS
UNIT NUMBER:
2570257
UNIT TITLE:
TUNGSTEN ARC GAS SHIELDED WELDING PROCESS
Acceptable performance in this unit will be the satisfactory achievement of the
standards set out in this part of the specification. All sections of the statement of
standards are mandatory and cannot be altered without reference to SQA.
OUTCOME
1.
EXPLAIN THE OPERATING PRINCIPLES AND EQUIPMENT
FUNCTIONS OF THE TAGS WELDING PROCESS
PERFORMANCE CRITERIA
(a)
(b)
(c)
(d)
The identification of variables affecting the arc conditions is
correct.
The identification of equipment components and connections is
correct.
The description of functions of equipment components is correct.
The principles of the tags welding process is correctly described.
RANGE STATEMENT
Variables: heat source; voltage; current and polarity; power sources.
Equipment components: suppressors; torch types; gas pressure and flow
control; all inter-connecting cables and hoses; high frequency unit; surge
injectors.
Equipment: composite, non composite.
Operating principles:
limitations
arc
initiation,
atmospheric
protection;
advantages;
EVIDENCE REQUIREMENTS
Written evidence is required to show that the candidate can outline the principles
and equipment functions of the TAGS Welding Process, as specified in PCs (a)
to (d).
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Unit No. 2570257
Continuation
OUTCOME
2.
SELECT THE PROCESS PARAMETERS FOR A SPECIFIED
APPLICATION
PERFORMANCE CRITERIA
(a)
(b)
(c)
(d)
The identification of the applications of the TAGS welding process
is correct.
The preparation of the TAGS welding equipment for use is in
accordance with manufacturer’s instructions.
The selection of the process variables is correct for a specified
application.
The selection of welding techniques is correct and appropriate for
the application.
RANGE STATEMENT
Variables: shielding gases; electrode type; voltage; polarity; current; flow rates;
material and thickness range.
EVIDENCE REQUIREMENTS
Performance evidence is required to show that the candidate can select process
parameters as specified in PCs (a) to (d). A minimum of 2 materials must be
used in the process with thickness within a 1mm to 25mm range.
OUTCOME
3.
PRODUCE AN INSPECTION REPORT FOR A TAGS WELDED
COMPONENT
PERFORMANCE CRITERIA
(a)
(b)
(c)
(d)
The application of visual inspection methods to the welded joint is
correct.
The identification of faults and their effects on welded structure is
correct.
The selection of method of fault rectification is correct.
The production of an inspection report is correct.
RANGE STATEMENT
The range for this outcome is fully expressed in the performance criteria.
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Unit No. 2570257
Continuation
EVIDENCE REQUIREMENTS
Written evidence in the form of an inspection report for a TAGS welded
component is required, detailing visual inspection methods, faults identified, the
probable cause of these defects, the effect on the welded structure and the
proposed rectification as specified in PCs (a) to (d).
MERIT To gain a pass in this unit, a candidate must meet the standards set out
in the outcomes, performance criteria, range statements and evidence
requirements.
To achieve a merit in this unit, a candidate must demonstrate a superior or more
sophisticated level of performance. This may be demonstrated by:
(i)
showing a wide knowledge and understanding of the subject by justifying
the answers to the assessments using reasoned discussion for or against
a given decision.
-----------------------------------------
ASSESSMENT
In order to achieve this unit, candidates are required to present sufficient
evidence that they have met all the performance criteria for each outcome within
the range specified. Details of these requirements are given for each outcome.
The assessment instruments used should follow the general guidance offered by
the SQA assessment model and an integrative approach to assessment is
encouraged. (See references at the end of support notes).
Accurate records should be made of the assessment instruments used showing
how evidence is generated for each outcome and giving marking schemes
and/or checklists, etc. Records of candidates’ achievements should be kept.
These records will be available for external verification.
SPECIAL NEEDS
Proposals to modify outcomes, range statements or agreed assessment
arrangements should be discussed in the first place with the external verifier.
 Copyright SQA 1997
Please note that this publication may be reproduced in whole or in part for
educational purposes provided that:
(i)
(ii)
no profit is derived from the reproduction;
if reproduced in part, the source is acknowledged.
4
Unit No. 2570257
Continuation
HIGHER NATIONAL UNIT SPECIFICATION
SUPPORT NOTES
UNIT NUMBER:
2570257
UNIT TITLE:
TAGS ARC GAS SHIELDED PROCESS
SUPPORT NOTES: This part of the unit specification is offered as guidance.
None of the sections of the support notes is mandatory.
NOTIONAL DESIGN LENGTH: SQA allocates a notional design length to a unit
on the basis of time estimated for achievement of the stated standards by a
candidate whose starting point is as described in the access statement. The
notional design length for this unit is 40 hours. The use of notional design length
for programme design and timetabling is advisory only.
PURPOSE This unit will familiarise candidates with the principles, equipment
functions and parameters of the T.A.G.S. welding process. On completion of
this unit candidates will be able to identify and describe all the equipment
components, set up the equipment ready for use and complete a welded artefact
in a given time. Candidates will also be able to visually inspect the welded joint
for defects and write a report on this inspection.
CONTENT/CONTEXT
The following information gives further clarification
regarding the context in which the outcomes are to be achieved.
Corresponding to outcomes 1-3:
Outcome 1
All variables associated with TAGS welding processes should be identified and
an explanation of the effect they have on the weld quality explained. Variables
such as voltage, current, electrode extension, gases used and their properties,
etc.
Types of power sources used should be fully explained.
All equipment components used and inter-connecting cables and hoses should
be fully explained and their function within the system.
Outcome 2
This outcome should be undertaken in a workshop environment with the
candidate having hands on experience of the process. A practical demonstration
of setting up the equipment should be given followed by the candidate being
given the opportunity to do the same. Typical applications of the TAGS process
should be explained along with the appropriate welding techniques which would
be employed for each application. The candidate should be allowed to prepare
his/her own materials before completing at least two test pieces from material
and thickness stated below:
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Unit No. 2570257
Continuation
low carbon steel, low alloy steel, stainless steel, aluminium and aluminium
alloys, nickel and nickel alloys, copper and copper alloys.
Thickness: 1mm to 25mm range.
Outcome 3
Using the test pieces obtained from previous outcome the candidate would
visually inspect the welds for defects. Prior to this an explanation of the types of
defect which might be found in the weld, the probable cause, the effect on the
welded component and an explanation of the method of rectifying the fault would
be given. The inspection report would be written up using the criteria stated in
the evidence requirements.
APPROACHES TO GENERATING EVIDENCE As contained in content/context
corresponding to outcomes.
ASSESSMENT PROCEDURES
Centres may use the Instruments of
Assessment which are considered to be the most appropriate.
Examples of Instruments of Assessment that could be used as follows:
Outcome 1 PC(a) Written questions asking for an explanation of variables
affecting arc conditions and the reasons for these effects.
PC(b) Possibly a line drawing of T.A.G.S. set up asking for equipment and
connections to be identified.
PC(c) Written questions asking for a description and use of three named
components.
PC(d) Written question asking for a description and use of three named
components.
Outcome 2 Practical exercise to suit requirements of local employers.
Checklist may be used to evidence the candidate knowledge of setting up
equipment.
Outcome 3 A written inspection report on a visual examination for weld defects is
produced.
PROGRESSION
Successful completion of this unit would lead to a fuller
understanding of unit number 2570277 Advanced Gas Shielded Welding
Processes.
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Unit No. 2570257
Continuation
REFERENCES
1.
2.
Guide to unit writing.
For a fuller discussion on assessment issues, please refer to SQA’s
Guide to Assessment.
3.
Information for centres on SQA’s operating procedures is contained in
SQA’s Guide to Procedures.
For details of other SQA publications, please consult SQA’s publications
list.
4.
 Copyright SQA 1997
Please note that this publication may be reproduced in whole or in part for
educational purposes provided that:
(i)
(ii)
no profit is derived from the reproduction;
if reproduced in part, the source is acknowledged.
7