Description

Technical Field

The present development is related with Military Aviation Industry more particular to structural assembly of Aircraft.

Background of invention

When thick slender components are machined out, it is natural that the warpage will occur. Such warpage needs to be removed by appropriate process in order to remove residual stresses and to reduce fit-up stresses during assembly. The present invention is to remove the warpage without adverse effect on other properties

Summary of invention

A maximum of 9 mm warpage was measured on the typical spar after machining as shown in fig. 2. This is due to slenderness of the part (Length 4900 mm). This invention / process give the procedure to remove warpage.

Drawings

Fig-1: Spar view
Fig-2: Warpage measurements on the spar
Fig-3: Positioning of Tools (Hylam Block)
Fig-4: Test specimen location

Process details description
Following warpage removal procedure to be carried out on the spar after complete machining.

i. Inspect the part and identify the bow (in the plane of web) and warpage zone and mark on the part, for carrying out warpage removal on the 4-point bending machine.

ii. If bow is observed carry out checking and straightening operation to remove the bow on the part using the 4-point bending machine.

iii. Heat the part to temperature 155° ± 15 °C for 20 ±5 min.

iv. Before starting the warpage removal, position the Hylam blocks in the inner surface (pockets) of the spar. (Fig. 3).

v. Position the part on the 4-point bending machine such that the load is applied along Z-direction.

vi. Apply the load of 5 - 10 ton over the span of 20 - 30 cm on the marked area to remove the warpage as shown in Fig. 4.

vii. Carry out the straightening operation immediately after heating the part as referred in (iii).

viii. Check the contour of the base of the web using appropriate template along Z-direction.

ix. The profile of the part on bending template should be within a permissible clearance of +/- 0.2 mm at the length not less than 200 mm..

x. Repeat the straightening operation (warpage removal) jjntil warpage is removed. (If required reheat the part to temperature of 155° ±15° C for 20 ±5 min.)
The above procedure s to be carried out by ensuring the following

1) The cumulative time of heating the part should not exceed 10 hrs.
2) Ensure that the temperature does not exceed 170 °C.
3) Straightening operation should be carried out in hot condition only.

After completion of above procedure the mechanical properties is to be checked on the test pieces, which include ultimate tensile test, 0.2% proof test, % elongation, micro structure and hardness test.

CLAIMS We claim that the>

1. The process is useful to remove warpage of the range of 8 to 12 mm in a length of 4.9 meters of spar made of 2014 Al-alloy bar.

2. There is no significant change in the mechanical properties after removal of warpage.

3. There is no adverse effect on the geometry and hence in subsequent assembly process.