Instructions for Weld Finish of the "K" Series Adapters Installed on Large Wheel Loader Buckets{0679, 6101, 6102, 6104, 6805} Caterpillar

Wheel Loader: All

Introduction

While buckets are being loaded, stresses are developed in the adapter welds. The most severe stresses are concentrated at the start of the welds on the two strap adapters. The points of stress are at the front of the base edge under the nose of the abrasion and flush mount adapters. Applications of the welds in these areas must be of the highest quality.

Two methods for repairing adapter welds have been identified that offer improved weld quality and enhance resistance to fatigue cracking. The preferred method is a Tungsten Inert Gas (TIG) welding process. Another method is toe grinding (Burr Grinding) and does not require an experienced welder or specialized equipment.

This special instruction outlines the recommended procedure for repairing welds on K Series adapters for large wheel loader buckets with early hour fatigue cracks. Repairing the welds on K Series adapters for LWL's with early hour fatigue cracks will increase service life.

TIG Dressing of Fillet Welds for Improved Fatigue Life

Welding Material

The suggested welding equipment is as follows.

• GTAW (TIG) Power Source (with variable amperage adjustment recommended) and a torch with a 200 Amp or greater capacity.

• Tungsten electrodes (2.4 mm (0.094 inch) or 3.2 mm (0.125 inch) diameter preferred).

• Tungsten grinder for safely and effectively sharpening the tungsten electrodes.

• A gas flow meter with variable flow adjustment and a flow rate scale applicable to the scale referenced in the required Weld Procedure Specification.

• 100% Argon shielding gas of a suitable purity for GTAW (TIG) welding.

• Radius gages capable of measuring the engineering required toe radius.

• Fillet weld gages capable of measuring fillet leg length and throat size.

• Undercut gages capable of measuring to at least a minimum of 0.5 mm (0.020 inch) weld undercut.

• A grinder or a needle peening tool suitable for removing scale and silicates.

• Degreaser suitable for cleaning prior to welding. Degreaser is required if oil or grease is present on or near the metal in the affected weld area.

Preparation for Welding

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Illustration 1	g02178773
(A) Electrode point should be two to three times the diameter of the electrode (1A) Example of a properly dressed electrode with striations, or marks, parallel to the axis of the rod (1B) Example of a contaminated electrode

1. Cleanliness and tungsten electrode preparation are the first steps to ensuring a proper TIG dressing. The fillet weld and surrounding base metal must have all contaminants thoroughly removed. Rust, dirt, oil, scale, silicate islands, and so on, must not exist. This cleanliness can be accomplished quickly via a grinder with a carbon steel wire attachment. Next, prepare a 2.4 mm (0.094 inch) tungsten electrode to the dimensions shown in Illustration 1. Grinding striations should run parallel not transverse.

   Dress the tungsten electrode with the grinding striations parallel to the axis of the electrode as indicated by the red lines on electrode (1A). Refer to Illustration 1. The length of the electrode point should be approximately two to three times the diameter of the electrode.

   If the electrode becomes contaminated after use, the electrode will produce an unstable arc. A sound weld is difficult to produce with an unstable arc. The tungsten should be redressed when the electrode shows signs of contamination. Refer to electrode (1B) in Illustration 1.

2. Adjust shielding gas flow rate to 15 CFH and current control to approx. 225 amps. If a ramp down control is present on the power source, utilize to ensure proper crater fill control.

3. If filler wire is needed, the filler must be compatible with the base materials within the welded joint.

4. All mill scale, rust, silicates, and so on, be properly removed from the weld face, weld toes, and adjacent weld areas. If grease or oil is present, the area must be cleaned with a suitable solvent compatible with welding. The solvent must be safe for the welder or weld operator.

5. Layout of the TTD location and lengths shall be to the engineering requirements. The layout marks shall be visible to the welder prior to and during welding.

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Illustration 2	g02178775
(a) Initial start and stop points for TTD welds (b through f) Restart options for TTD welding

6. The initial start and stop of the TTD weld shall be to Illustration 2 (a). The starts and stops shall extend at least 3 mm (0.12 inch) beyond the prescribed TTD weld length. The welds must begin and end in the center of the weld face.

7. If a restart in the middle of TTD weld is needed, then one of the restart options in Illustration 2 must be used. Restart options are shown by Illustrations 2 (b through f) .

8. Verify fillet weld leg and throat size to the drawing requirements prior to TTD with a suitable fillet weld gage. Examples of the gages are shown below in Illustration 8.

9. Eliminate all sources of potential air drafts from the weld area to minimize the disruption of the shielding gas.

Weld Process

A number of different techniques exist for TIG dressing due to the variability of the contour of the fillet weld toe that must be reshaped. A stringer or weave manipulation of the torch can be employed so long as a smooth, contoured minimum radius of 5 mm (0.20 inch) exists between the base material and weld metal

1. The weld progression must not be performed in the uphill direction.

2. Maintain approximately a 3 mm (0.12 inch) arc length between the electrode and the molten weld puddle during the welding process. A slight weave motion of approximately 1 mm to 3 mm (0.04 inch to 0.12 inch) may be used to provide a desirable bead profile.

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Illustration 3	g02178870
(B) 60 to 90 degree torch angle

3. The torch angle should be approximately 60 to 90 degrees from the base plate as shown in Illustration 3.The torch angle may vary as needed to allow for weld puddle manipulation for the different weld positions.

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Illustration 4	g02178871
Push angle, arrows show the direction of travel (C) 15 to 25 degree torch angle

4. Use a push angle of approximately 15 to 25 degrees to prevent undercut and provide an acceptable toe radius to the weld. Refer to Illustration 4.

5. Once welding is initiated, starts and stops in the TTD should be minimized, or if possible eliminated from the weld.

Note: Maintain a 10 to 25 deg push angle for both stringer and weave

Note: Poorly shaped fillet welds with 70 to 90 degree transition angles to the base material will probably require several overlapping TIG dressing runs to smooth out the weld toe transition region properly.

Note: TIG dressing can be conducted in the vertical position as long as the TIG dressing is performed in a DOWNHILL progression.

Note: If undercut or other circumstances require the addition of filler metal, hand feed "ER70S-2" (1/16 inch dia.) into the weld pool. Then repeat the TIG dressing to achieve desired toe radius/profile.

Once TIG dressing is completed and the area is allowed to cool, the area needs to be cleaned and painted to prevent pitting due to corrosion.

TIG Toe Dress Weld Inspection

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Illustration 5	g02178877
Optimum shape, smooth transition from TTD to base metal (1) Base metal (2) TTD weld bead radius (3) Fillet weld

1. The TTD weld bead profile must have a toe radius, and have a smooth transition from the TTD weld bead to the base metal. Refer to Illustration 5.

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Illustration 6	g02178878

2. After TTD, measure the toe radius of the fillet weld with suitable gauge capable of accurately measuring the toe radius. Refer to Illustration 6.

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Illustration 7	g02178879

3. Verify that the throat size of the fillet weld was not adversely affected after the TTD process as shown in Illustration 7.

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Illustration 8	g02178880
Example of an undercut gage

4. Use an undercut gage to determine the amount of weld undercut. Maximum Depth Measured from plate surface not to exceed 5 mm (0.2 inch). Refer to Illustration 8

5. Visually inspect for any types of weld discontinuities. Any visible discontinuities found in the TTD weld should be removed completely and the weld repaired.

Typical TIG Toe Weld Defects and Repairs

1. Radius Less Than Design Requirements: Redress the weld toe using a slight weave technique as previously described.

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Illustration 9	g02178883
Example where transition to the base metal is not smooth (1) Base metal (2) TTD weld bead radius (3) Fillet weld (4) This area may be ground before TTD is applied

2. Transition of TTD Weld to the Base Plate Is Not Smooth, Refer to Illustration 9: Redress the weld bead without filler metal. Grinding some of the TTD may be necessary to remove the excess weld metal.

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Illustration 10	g02178884
Example of undersized weld throat after TTD (D) Normal weld throat (5) Throat undersized after TTD

3. Transition of the TTD to the Weld Face Causes the Throat of the Fillet to Be Undersized, Refer to Illustration 10: Reweld the undersize area with the TTD process adding filler wire if needed, or weld with the original welding process.

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Illustration 11	g02178885
Example of a weld undercut (6) Undercut

4. A TTD Weld with an Excessive Undercut, Refer to Illustration 11: Reweld the undercut with the TTD process adding filler wire, or weld with the original process.

5. Porosity and/or Other Discontinuities Visible in the TTD Weld: Porosity and any other visible defects must be removed and the weld repaired.

Toe Grinding of Fillet Welds for Improved Fatigue Life

Illustration 12	g02178888
(7) Carbide tipped burr, the preferred burr shape

Note: The profile or geometry of the weld toe controls the fatigue performance of fabricated structures. These fabricated structures have attachments that are fillet welded to highly stressed members. Fatigue performance improvement can be achieved through alteration of the original toe profile by several post weld treatment options. This procedure describes a method of using a mechanical means in order to remove adverse profiles and adverse stress risers. This method creates a smooth transition from one component to the next component.

Equipment

Illustration 13	g02178890
(E) 45 degrees (F) 45 degrees (G) Minimum depth of 0.8 mm (0.03 inch) and a maximum depth of 1 mm (0.04 inch) (8) Burr tool (9) Direction of travel (10) Weld (11) Plate

The burr tip should be located over the weld toe. The axis of the tool should be maintained at 45 degrees to the parent plate and inclined at 45 degrees to the direction of travel. Grinding should extend to a depth of 0.5 mm (0.02 inch) below the last visible traces of the weld toe. The minimum grinding depth is 0.8 mm (0.03 inch) and the maximum grinding depth is 1 mm (0.04 inch). The resulting ground surface should be smooth with no grinding marks running parallel to the weld, but transverse (90 degrees) to the weld. All traces of the original weld toe should not be visible via the use of a lower powered magnifying glass.

Illustration 14	g02178891

Illustration 15	g02178892
Example showing the finished appearance