aluminium in commercial vehicles - European Aluminium Association

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160 EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER XIII 4. MIG and TIG weld repairs A road vehicle can sustain damage and will need to be repaired. Repairing a commercial vehicle made from aluminium alloys is no more difficult than repairing a steel vehicle, but should be done according to a strict procedure in a properly equipped workshop by skilled operatives under the supervision of an official body and/or classification society if the vehicle's duty calls for this. No repair work should commence without knowing the type of freight (liquid, powder etc.) which the vehicle has been used to carry and before taking the appropriate safety precautions: cleaning, degassing, with explosimeter checks, dust removal etc. as necessary. 4.1. Choice of alloy The alloy of the semi-finished products used for the repair work must be the same as (or compatible with) the original alloys as indicated in the manufacturer's manual. Welding of silo body (Feldbinder) 4.2. Preparations This is the most important phase as it will determine the quality and strength of the repair: • for cutting out, preference should be given to the plasma torch or a carbide cutting wheel rather than a high speed steel (HSS) wheel or abrasive wheels that might introduce inclusions into the weld seam, • very carefully grind the area to be welded to remove all traces of paint and various residues, • carefully degrease with suitable agent
EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER XIII 161 4.3. Welding The rules for repairing are basically as described in Chapter VII for forming and as described in this chapter for welding. When carrying out repairs it is essential to: • hold the components, e.g. tank, chassis etc., securely in their relative positions. Clamps should be adjusted to allow expansion however, as too much restriction could aggravate the adverse effects of contraction. It is also useful to mark areas of the structure likely to suffer maximum stress, referring to the manufacturer's design calculations if these are available, • support built-up parts to control clearances, • pay particular attention to the weld direction. The purpose of this is to limit deformation and minimize the risk of hot cracking. Volume contraction in the weld bead is approximately 6 % between the fluid state and the solid state at ambient temperature. It is this phenomenon which causes the risk of cracking, • change the path of welds in order to avoid going back over an original weld (Figure XIII.1), • perform any necessary tests, e.g. radiography, dye penetration etc., • chose the right welding process (TIG or MIG). TIG welding is preferable for minor repairs where access from behind is not possible as it is easier to use and allows better penetration control than MIG welding. FIGURE XIII.1 WELD REPAIR Compact TIG welding machines weighing less than 20 kg are now available on the market capable of delivering a welding current of around 160 A. These machines are easy to carry and are ideal for small, localized repairs. For minor repairs such as a breach in the skin of a tank, the patch must be perfectly matched to the shape of the breach but should be slightly enlarged by hammering to compensate for contraction following welding. Without this precaution the residual stress might well cause systematic cracking. This phenomenon is more pronounced the smaller the patch. ‰ New weld
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ALUMINIUM IN COMMERCIAL VEHICLES
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Aluminium in Commercial Vehicles ha
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VII. FABRICATION . . . . . . . . .
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CHAPTER II ALUMINIUM IN TRANSPORT 1
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EUROPEAN ALUMINIUM ASSOCIATION ALUM
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CHAPTER III WHY USING ALUMINIUM 1.
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CHAPTER IV FREQUENTLY ASKED QUESTIO
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CHAPTER V ALUMINIUM ALLOYS FOR COMM
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CHAPTER VI DESIGN AND CALCULATION 1
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CHAPTER VII FABRICATION 1. INTRODUC
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CHAPTER VIII WELDING 1. FOREWORD .
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