Extraction Tool for bushes from Deep and Blind Holes

2 Field of the Invention

The Invention relates to a tailor made tool to extract bushes, rigidly held due to interference fit, from deep and blind bores of assemblies without causing stress on subjected parts.

3 Background of the Invention

Bushes made of steel alloys are used in assemblies located in many critical zones of aircraft. Highest strength to weight ratio is achieved by use of wear resistant bush on wear prone structural materials like aluminium alloys. These bushes are assembled to the main structural component using shrink fit technology. The outer diameter of bush is maintained more than the receiving inner diameter of the bore of structural part. These bushes are cooled by immersing in liquid nitrogen to achieve sufficient contraction. They are taken out of liquid nitrogen and immediately assembled into the bore of structural item. Once the room temperature is reached, the bushes will tend to expand to their natural size there by providing sufficient holding on structural part.

However, after assembly of bushes, due to quality reasons related to diametrical dimension, surface finish etc, these bush may need removal from the structural items. Significant force is required to liberate the bush from the structural item.

Extraction of bush from through bores where accessibility is available is possible by use of suitably made pullers. Difficulty arises when the requirement is to extract bush from bores which are blind and positioned deep inside the structural item.

Brief Description of Wing Spar Assembly:

The Wing Spar assembly (Ref Fig No. 1) consist of an Aluminium alloy structural item (Item No. 1) where two steel alloy bushes are assembled. While
one of the bush (Item No. 2) is positioned at the top surface, the other bush (Item No. 3), which is a collar bush, is located at a depth of 150 mm from the surface. The bore where the bush is pressed is a blind one. The bushes are assembled using shrink fit method by immersing them in Liquid Nitrogen which is at -80 Degree Celsius to ease the assembly.

Details of the Problem and Its Significance

After assembly of bush, following issues may necessitate removal of bush.

A. The bush on assembly need to expand to a specific dimensional range after achieving normal temperature. Due to minor variations in extend of expansion towards each direction, there are chances of dimensions (inner diameter in particular) falling beyond the acceptable limits.

B. During next assembly stage, there are chances of misalignment of the mating part that may create scoring marks on the mating surfaces.

C. Reworking of Bush in in-situ condition is not practical due to poor accessibility and visibility once tools are inserted. There are chances of structural part to get scoring marks during the repair activity.

D. Bush need to be replaced for cases of oversize and scoring marks.

E. Normal tools cannot provide sufficient locking and force to extract the bush from the deep and blind bore.

F. Existing method to remove the bush involves loading of assembly in Boring .machine, trueing the inner diameter which is a time consuming and pain staking effort, opening out the bush inner diameter till wall thickness is weak enough to pull out the bush using

ft

a nose plier. This method possess a risk of bush rotating inside the bore while machining, there by damaging the closely controlled Bore Dimensions leading to rejection of part.
3.1 Prior Art

Document CN203471680U with title “Blind hole bush extractor", is a bush extractor applied to airplane tools. The blind hole bush extractor is characterized in that the extractor is composed of a grabbing sleeve and a push-out bolt and the grabbing sleeve is formed by connecting a spindle sleeve with elastic grabbing bars. This technique is limited only shorter depth holes and cannot be used for deep holes where hole diameter to hole depth aspect ratio is more.

Document CN207139689U with title “Case bush extractor", discloses case bush extractor, it includes application of force clamps, application of force are by first and second pincers handles. The force is applied from first end of first pincers handle to the first end of second pincers handle, first pincers handle with second pincers handle is articulated, the second end of first pincers handle is provided with first blade, the second end of second pincers handle is provided with the second blade, first blade with the second blade is used for respectively cutting into case bottom. This technique not suitable for the deeper holes from where bush needs to be removed.

Document JPH09117874A with title “BUSH EXTRACTION DEVICE”, discloses bush extraction technique using spring and cam mechanism. This device involves large number of parts and complicated. This devices sufficient space around the hole from which bush to be extracted. This device not suitable where space is a constraint and not suitable for the deeper holes.

4 Brief Summary of the Invention

The purpose of present invention is to solve above mentioned problems by facilitating removal of bush from deep and blind bores without subjecting structural part to any undue stress and damages.
To achieve the above objective, the present invention involves a design of Tailor Made Extractor Tool set (Figure 2) for carrying out removal of bush safely.

5 Detail Description of the Drawings

Figure 1 shows Schematic Diagram of Wing Spar Assembly of fighter and Trainer Aircraft which consists of Structural Item (Item No. 1) made of aluminum alloy and Two Bushes (Item No. 2 and 3 ) made of steel alloy. Figure 2 shows the Toot in dismantled condition. The tool consists of two numbers of Stepped and trimmed half bushes (Item 5), one Shaft (Item 4), one Clamping and supporting pin (Item 8 ), one Supporting Base (Item 6 ) and one Tightening Nut (item 7). All the items are made of Steel Alloy. Figure 3 shows the Tool inserted inside the assembly in contracted condition

Figure 4 shows the Tool inserted inside the assembly and expanded by inserting the shaft.

Figure 5 shows the tool with bush in extracted condition.

6 Detail Description of the Invention

The design of the Extraction Tool is made in such a way to achieve sufficient locking of the bush for extraction, by utilizing the minute gap of 2 mm available at the bottom of the bush surface.

i) The design of Stepped and trimmed half bushes (Item 5 in Figure 2) is made in such a way that once both the halves are butting to each other, the diameter will be less than the inner diameter of the bush intended to be removed. The collar of the trimmed bush is limited to the available clearance between the bush bottom face and the bottom surface of the Bore in structural part.

ii) Shaft (Item no. 4) is designed such that, once inserted in between the two halves of Item No. 5, Item 5 expands into the gap below the bush bottom face.
iii) Both item No.4 and 5 need to be clamped together using Clamping and supporting pin (Item No. 8). The Bolt is designed with extra length to enable holding to prevent the tool from rotation during the extraction.

iv) Supporting base (Item No. 6) is designed to provide sufficient grip on the Structural item to achieve sufficient support for the extraction operation.

Sequence of Operations (Refer Figure 2, 3, 4 and 5):

Butt two halves Item No.5 (Stepped half Bushes) together and insert into the Structural Part Bush Inner Diameter till it reaches the bottom.

Insert Item No. 4 Shaft in between the Item No. 5 bushes till it reaches the bottom face.

Ensure the expansion of half bushes to move into the gap below the bush’surface.

Align and insert the Item No. 8 (Clamping and Supporting Pin). Tighten to lock the assembly.

Insert Item No. 6 (Supporting Plate) and insert Item No. 7(Tightening nut).

Start tightening Item No. 7. Support Item No. 8 (Clamping and Supporting pin) to prevent rotation of entire tool. Ensure the bush is smoothly getting extracted from the bore.