The welding of aluminium and its alloys

Welder approval

While the procedure approval test is performed to demonstrate acceptable mechanical properties, the welder approval test is carried out to demon­strate that the welder has a sufficient level of skill to deposit weld metal of an acceptable quality. A similar philosophy to that for procedure approval is adopted - a number of standard tests are called up in the standards, suc­cessful completion of which gives a range of approval for a number of essen­tial variables. Since the purpose of the test is to assess the skill of the welder the essential variables are different from those of the procedure approval test. The specifications most frequently encountered are BS EN 287 Part 2 and ASME IX.

10.3.1 BS EN 287 Part 2

BS EN 287 Part 2 complements the procedure approval specification BS EN 288 Part 4. The specification regards the welding process as an essen­tial variable and restricts the processes covered by the specification to MIG, TIG and plasma-arc welding although other processes may be approved by agreement (Table 10.8).

Materials are grouped for the purposes of approval as follows:

• Group W21,pure aluminium and aluminium-manganese alloys with less than 1.55Mn;

• Group W22 non-heat-treatable alloys;

• Group W23 heat-treatable alloys.

Dissimilar metal joints are treated in a similar manner with a test piece made in one group conferring approval to weld a number of combinations as shown in Table 10.9.

An approval test on wrought material gives approval to weld both cast and wrought alloys within the same group and combinations of wrought and cast material. Any alloys not contained within the grouping system must be approved individually.

The approval range for the filler metal and the shield gas is not perhaps as clear as that with the parent metal groups. A test made with a specific filler metal and shielding gas gives approval to weld with any other filler metal compatible with the parent metal group provided that there is no change in the process or shield gas and that this does not require a change in the welder’s technique. This last variable is unfortunately not quantified.

Thickness and pipe diameter are both essential variables; the ranges of approval are given in Tables 10.10 and 10.11.

Joint type is an essential variable. An approval test on a pipe also approves the welder for welding plate; a plate approval for welding pipe of over 500 mm; a plate butt weld made in the flat (PA) or horizontal-vertical position (PC) position approves for butt joints in pipes of 150 mm or more in diameter welded in similar positions. A butt weld approves a fillet weld. Welding a backed test piece approves a double sided joint with a back - gouge but not for unbacked joints.

An approval test with a specific filler metal and gas combination approves the welder to weld with any filler metal and gas that are compatible with

For structural hollow sections ‘D' is the dimension of the smaller side.

the parent metal, provided that this does not require a change in the welder’s technique.

The last and perhaps the most important variable from the welder’s point of view is the welding position as shown in Table 10.12, the principle being that a test carried out in a more difficult position approves for welding in the easier positions. The specification requires that the test is carried out with conditions similar to those to be used in production such as edge preparation, position, welding time, preheat and heat input. The test piece must have at least one stop and start in both the root run and in the capping pass.

The test regimes for the various types of joint are given in Table 10.13.

The acceptance standard is specified in EN 30042 ‘Guidance on Quality Levels for Imperfections’ and is specified as defect level ‘C’ for excess weld metal, excess convexity, excess throat thickness and penetration and level ‘B’ for the remaining defects.

The welder may submit a second test piece if the first fails to achieve the required standard. If this test piece also fails and the failure can be attrib­uted to a lack of skill then the welder is required to be re-trained before being permitted to attempt the test once more. Successful completion of a test approves the welder for a period of two years although the approval certificate must be endorsed at six monthly intervals by the employer. This can be done provided that the welder is engaged on work within the range of approval and that the work is of an acceptable quality. The period of approval can be extended beyond two years by the examining body pro­vided that the employer can produce documentary evidence such as six monthly radiographic, ultrasonic or fracture test reports.

10.3.2 ASME IX welder approval

The ASME code covers both procedure approval (qualification) and welder approval. Welders are divided into two categories, those who perform manual or semi-automatic (MIG) welding and those who operate machine or automatic welding equipment. As with EN 287 Part 2 the welder must

1 Radiography or fracture test, not both.

2 A tensile test may be used instead of a bend test for alloys with low ductility. A bend or tensile test must be carried out if the MIG welding process (131) is used.

3 The examining body may request additional macro-testing and penetrant examination.

4 The fracture test may be replaced by at least 4 macro-sections.

be provided with a written welding procedure. There are a number of essen­tial variables for three of the processes relevant to aluminium as shown in Table 10.14. For information on the range of approval of the essential vari­ables reference should be made to the clause listed in Table 10.14, to be found in ASME IX.

Approval testing for a butt (groove) weld is by bend testing although this may be replaced by radiography - it is permitted to use the first production weld made by the welder for this approval. Qualification for a fillet weld is by macro-examination and fracture testing.

The approval is valid for a period of six months. Provided that the welder welds with the relevant process within this six month period the approval can be extended indefinitely unless there is any reason to question the welder’s competence.

10.3.3 BS EN 1418 welding personnel - approval testing

BS EN 287 Part 2 covers the approval of manual welders - BS EN 1418 has been produced to specify how operators of mechanised or automated equipment should be approved. The full title of the specification is ‘Welding Personnel - Approval testing of welding operators for fusion welding and resistance weld setters for fully mechanized and automatic welding of metallic materials’. The specification makes it clear that only those opera­tors responsible for setting up and adjusting operating parameters during welding need to be approved. Programmers of equipment who do not actually operate the equipment in production are not required to be approved, nor are resistance welding operators.

Definitions are given in clause 3 where:

• Automatic welding is defined as welding operations where all parame­ters are pre-set and cannot be adjusted during welding.

• Mechanised welding is where all of the activities are performed auto­matically but the welding variables can be changed during welding.

• Robotic welding is defined as automatic welding using a pre­programmed manipulator.

The welding operators or resistance weld setters may be approved by one of four methods:

• By performing the welding procedure test specified in EN 288 Part 3 or 4.

• By performing a pre-production or production welding test. This test may be carried out on non-standard test pieces, on test pieces simulat­ing production or on actual production items that have been identified as test pieces prior to welding. Testing is to the requirements of EN 288 Part 8.

• By taking actual production items for testing. As in the point above testing is to the requirements of EN 288 Part 8.

• By performing a function test. In this the operator/resistance weld setter is required to know the relationship between parameter deviations and welding results, to set and control the parameters in accordance with an approved welding procedure, to test the operation of the welding unit and to be capable of recognising and reporting any malfunctions. Annex B of the specification gives information of what knowledge the opera­tor/resistance weld setter would typically be expected to have.

Provided that the operator/resistance weld setter successfully completes one of the above tests then there is no limit to their range of approval. This is provided that they continue to work with the same type of welding unit, the welding process is not changed and they work in accordance with an approved procedure. Automatic and robotic welding approval using a multi­run technique gives approval for welding with a single run but not vice versa; approval to weld without a sensor gives approval for welding with a sensor but not vice versa; changing the robot type, system or control unit requires re-approval as does any change to the other essential variables.

Provided that the operator/resistance weld setter works with reasonable continuity, i. e. no break is longer than six months, and there is no reason to question their competence then the approval is valid for a period of two years. The employer must endorse on the approval certificate at six monthly intervals that this is so. If the employer keeps records of non-destructive or mechanical tests carried out at a maximum of six month periods and these confirm that the required quality is being maintained then the examining body can endorse the approval certificate at the end of the two year valid­ity period for further periods of two years.