DESCRIPTION

TECHNICAL FIELD

The invention describes a process for the problems incurred during shrink fitting of Steel bushes in to structural frames / mating bracket (Aluminium alloy) of an aircraft.

BACKGROUND OF INVENTION

For making Shrink fit assembly, the bush is deep feezeed in liquid nitrogen (at = -1702 c) for sufficient time to get optimal shrinkage of material, it is then pressed immediately into the structural frame/ mating bracket. After bush pressing, the bushes are allowed to reach to room temperature, bushes due to material property needs restore its original dimension. However, due to the factor called material shrinkage and due to interference fit between bush outer diameter (OD) and structural bracket internal diameter (ID), the bush ID may not come back to its original dimension leading to under size of Bush ID which is the final fitment point with the corresponding assembly mating part.

SUMMARY OF INVENTION

Bushes are to be designed by considering the shrinkage allowance to accommodate the shrinkage on ID so that final fitment will be achieved. Tolerance of OD also may be controlled to the lower band to achieve better results. (Fig.3)

DRAWINGS

Fig.l: Setup for trails of shrinkage allowances. Fig.2: Wing attachment bracket Fig.3: Experiment analysis
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PROCESS DETAIL DESCRIPTION

Test block and bushes were prepared as per the aircraft requirements. This trial caters to allkind of bushes like, plain bush, collar bush, high thickness and low thickness etc. Test block and Bushes were made as per the drawings to achieve low, medium and maximum interference as per the design requirements. The bushes were deep freezed in liquid nitrogen (at = -1702 c) for 30 minutes to get an optimal shrinkage then pressed immediately { with 30 seconds) into the structural frame/ mating bracket. After bush pressing, the bushes are allowed to reach to room temperature for 30 minutes.

Measurements were taken for ID of the bushes to cross check the designed value. Also, a check with go and no go gauge is made. The test results are plotted in the table for reference. The experiment has been repeated until the desired shrink factor of internal diameter of the bush is arrived. The design experiment data has been fed into software to get the shrink pattern of the bushes. (Fig. 3)

Table-1
Shrinkage allowance on bushes used in wing root fittings

Table-2
Shrinkage allowance is to be considered on all other bushes.
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CLAIMS

1. The process for shrinkage allowance for pressing steel bush into Aluminium housing.

2. Elimination of Assembly Rework
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