Preliminary Requirements

Safety Requirements

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURERS MATERIAL SAFETY DATA SHEETS FOR CONSUMABLE MATERIALS INFORMATION SUCH AS, HAZARDOUS INGREDIENTS, PHYSICAL/CHEMICAL CHARACTERISTICS, FIRE, EXPLOSION, REACTIVITY, HEALTH HAZARD DATA, PRECAUTIONS FOR SAFE HANDLING, USE AND CONTROL MEASURES AND ALSO TO TAKE LOCAL REGULATIONS INTO CONSIDERATION.

Procedure

1. SUBTASK 70-31-10-310-060 Technical Data

   1. Strength and dimensions.

      1. The strengths of the different spot welds must not be less than the values specified on the illustration. Strength tests are not necessary for the usual approval. The melted area diameters of the different spot and projection welds (as measured at each interface in the joint) must not be smaller than the values specified on the illustration.

      2. When the melted area width of seam and stitch welds is specified, it must (where measured at each interface in the joint) not be lower than that specified in the illustration at the start of an assembly run. At the end of the run, the melted area width must not be less than 90 percent of that specified for seam welds or less than 70 percent of that specified for stitch welds.

   2. Constant quality.

      1. The difference in shear strength, in a subsequent group of welded aluminum and magnesium alloy test pieces, must be plus or minus 12.5 percent (of the average value, in at least 90 percent of the test pieces) and plus or minus 25 percent (of the average value, in the remaining test pieces). The shear strength of annealed and stress relieved test pieces, of materials other than aluminum and magnesium alloys, must not change by more than 10 percent (of the average value, in at least 86 percent of the test pieces) or plus or minus 20 percent (of the average value, in the remaining test pieces).

      2. Shear strength tests are not necessary for the usual approval procedures. The results of tests made for the approval of welding machines, will be used to show that the machine can make welds of a constant strength.

   3. Position - (Refer to Figure).

      1. Unless specified differently in the text or illustration, resistance welds must be in the center of overlap-A.

      2. For spot welds, edge distance B must not be less than 50 percent of the minimum overlap.

      3. For stitch and seam welds, edge distance B will not apply if the edge of the piece is not too thin, pushed in or out too much, cracked or damaged.

      4. For spot welds, edge distance B will not apply when completed parts are cut from rings, which were spot welded all around.

   4. Length (Or quantity) of seam and stitch welds.

      1. The length of seam and stitch welds must not be less than that specified, in the text or illustration.

   5. Indentation.

      1. For parts other than foil backed, porous sheet, abradable materials:

         1. Unless specified differently, the maximum permitted indentation for welds (made on formed or stamped parts and not of the deep drawn type) is 10 percent of the sum of the basic or nominal thickness of the two outer parts.

         2. If the deep drawing of parts causes the weld area to become thin, the thickness of each such part in the joint (where the permitted indentation is calculated) will be used as the correct thickness at the welded joint or 82 percent of the nominal thickness of the initial material, or that which is larger.

      2. For foil backed, porous sheet, abradable materials:

         1. Unless specified differently, the indentation of the assembly (which does include the porous sheet) will not be more than 10 percent of the mating part index.

      3. For screens or strainer elements:

         1. The indentation data does not apply to parts made from wire mesh or sheets with holes.

   6. Penetration.

      1. For parts other than foil backed, porous sheet, abradable materials:

         NOTE

         The penetration can be as high as 90 percent of the indentation thickness of the related pieces in titanium and titanium alloy welds.

         1. Unless specified differently in the text or illustration, the weld penetration (into each outer piece), at the centerline of the weld nugget, must not be less than 20 percent of the indentation thickness of the thinnest piece to be attached and not larger than 80 percent of the indentation thickness of the related pieces.

         2. For overlapping welds in seam and stitch welds, penetration in the overlap areas must not be less than 15 percent of the indented thickness of the thinner piece.

         3. For a distance equal to one half the individual spot diameter, both at the start and at the end of seam and stitch welds, which do not form a closed circuit, minimum penetration is waived, but fusion is necessary.

      2. For foil backed, porous sheet, abradable materials:

         1. Unless specified differently, the weld penetration must be 100 percent through the porous sheet and backing foil. It must show signs of fusion, to 50 percent penetration, of the mating part thickness.

      3. For screens or strainer elements:

         1. The penetration data does not apply to parts made from wire mesh or sheets with holes.

   7. Tack welds.

      1. Tack welds used to hold the parts must not cause damage to the base metal or cause deterioration of the last quality weld.

      2. Unless specified differently in the text or illustration, tack welds mu st be fully contained in the last quality weld.

   8. Sheet separation.

      1. Unless specified differently in the text or illustration, the sheet separation between adjacent welds must not be more than 10 percent of the thickness of the thinnest sheet to be attached or 0.015 in. (0.38 mm), or that which is less.

   9. Tolerances.

      1. Unless specified differently in the text or repair illustration, the tolerances that follow are permitted:

         1. The distance between the different spot welds in a row (also that between the rows of spot welds) must not be more than plus or minus 0.060 in. (1.52 mm) of the distance necessary on the repair illustration.

         2. The distance between the seam welds must not be more than plus or minus 0.060 in. (1.52 mm) of the distance necessary on the repair illustration.

         3. The number of spots to the inch (or millimeter), for a length of stitch welds on a group of parts (as measured along a 1.000 in. (25.4 mm) length of weld), must not be less than that on the control test piece with the least number of spots to the inch (or millimeter). Only the control tests, related to that group of parts, can be used to find the permitted limit.

         4. Distance A/2 - (Refer to Figure), from the center of the weld to the edges of the piece, must be less than plus or minus 0.060 in. (1.52 mm) of the distance necessary - (Refer to step 5.B. and the repair illustration).

         5. Edge distance B, of the spot welds - (Refer to Figure), must be less than plus or minus 0.060 in. (1.52 mm) of the distance necessary - (Refer to step 5.B. and the repair illustration).

2. SUBTASK 70-31-10-310-061 Resistance Welding Procedures

   1. Cleaning.

      1. The surfaces of the parts to be welded must be cleaned, with no unwanted coatings (such as, oxides, scale, plasma spray, flame plate or plating), to cause damage to the welding procedure.

      2. 

         CAUTION

         WIRE BRUSHES USED TO CLEAN THE CORROSION FROM HEAT-RESISTANT STEELS AND ALLOYS, MUST HAVE BRISTLES MADE OF AUSTENITIC CORROSION-RESISTANT STEEL. WHEN WIRE BRUSHES ARE USED, ALWAYS MAKE SURE THAT THE UNWANTED MATERIALS ARE FULLY REMOVED AND NOT ONLY POLISHED.

         Wire brushes or silicon carbide abrasives can be used for the rough removal of protective coatings, unwanted materials and surface scale. Silicon carbide abrasives are to be used for the last surface cleaning procedure and the removal of oxides; then, clean by the solvent wipe method. Refer to the SPM TASK 70-11-26-300-503.

      3. It is recommended that the last step to remove oxides, from aluminum and aluminum alloys, is a chemical procedure. This last step must be done as soon as possible before the assembly and welding procedures.

      4. No unwanted coating, remaining from the cleaning procedure, must stay on the surfaces to be welded.

      5. Approved marking dyes can be used to find the weld locations but do not use on aluminum or titanium parts.

   2. Assembly.

      1. Parts to be welded must be assembled with the necessary clamps, fixtures, or jigs so that, after welding, the parts will be correctly aligned.

      2. Unless specified differently, in the text or repair illustration, tack welds, used to hold the parts, must be in the center of the structural (quality) welds to be made.

   3. Welding.

      1. Set-up the welding machine, as specified in the Welding Schedules. If no schedules are available, obey the instructions given in step 4 - Welding Schedules.

      2. Weld the necessary test-pieces. Make sure that the destructive and mechanical tests agree with the instructions, given in Step, step 5 - Technical Data.

      3. Weld the parts. During the usual operations, the electrode points can be cleaned. To do this, apply a light rotational pressure to the surface of the point with 240 aluminum oxide cloth, attached to a soft lead or wooden bar.

      4. 

         CAUTION

         DO NOT CLEAN OR DRESS THE WELDS TOO MUCH, SO THAT LOCAL PARTS OF THE BASE MATERIAL WILL BECOME THIN.

         After welding, remove all unwanted weld flash and pick-up material by filing, light grinding and/or wire brushing.

   4. Inspection.

      1. Visually examine the welds for flash removal, quality of overlap data, indentation and sheet separation.

Figure: Positions of seam, spot and stitch welds

Positions of seam, spot and stitch welds