BACK GROUND OF INVENTION

Bubble assembly were procured for the initial phase of the Hawk production. To produce the canopy assembly and to be self Reliant in the long Run, developing the technology and process . for inhouse manufacturing of bubbles was felt necessary.

The Hawk front and rear bubbles are bigger in size and has complex curved surfaces. Conventional method of. heating the acrylic sheet and wrapping over the forming tool would not be possible. The vision requirement for front bubble from the rear pilot DEP is very critical. The contour of the front and rear bubble is also one of the critical dimension to ensure the pilots comfort seating.

To achieve the above stated technical requirements a Technology and process for forming of bubbles were developed.

OBJECT OF INVENTION

The main objective is to develop the Technique and process for in-house manufacture of front and rear bubble with superior optical and technical performance and to be self reliant in bubble manufacturing.

DETAILED DESCRIPTION OF THE INVENTION

The plastic department of HAL has designed and developed, fabricated and installed a bubble forming machine for the Hawk front and rear canopy bubbles.

As the vision, clarity and sectional contour dimensions is a paramount requirement of canopy bubbles, attempts to make the bubble by vacuum forming was not successful. Though it was possible to obtain reasonably acceptable optical characteristics it was difficult to get the correct contour required for the bubble by vacuum forming Technique.

As vacuum forming of the bubble is taking place in a tool where except in the sealed area the bubble is free to expand on application of vacuum, due to the fact that there is no perfect contour control media. Hence getting the required contour profile at the top and at the side sections is not possible

So as an alternate to vacuum forming contact forming was tried and during trial it was found that the tool marks , impressions were appearing on the formed bubble which was giving distorted image.

Further as a part of improvement in the development process drape forming with grease as an intermediate layer between the tool surface and heated plastic sheet was tried. The tool surface was covered by felt cloth and simplex cloth at the top to avoid the tool impression on the bubble

The grease layer was acting as an intermediate layer which protected the surface of the bubble from any kind of surface imperfections. There by facilitating glossiness on the inside surface and optical clarity.

The bubbles formed by the drape forming Technique using grease were found to have better optical characteristics and dimensions.

Brief desclption of Machine.

The Automatic HAWK bubble forming machine was designed and fabricated for forming of Cast Acrylic sheets into bubbles for canopy assembly. The machine could be operated manual, semi Automatic and Automatic mode. Bubble forming machine shown in figure 1.

The Machine consists of the following stations.

1. Sheet loading station.

It consists of Loading trolley sheet carriage for carrying the sheet to heating station and forming station.

2. sheet Heating station

It consists of air circulate oven for heating the sheet up to 165 deg C.+/-3 deg c.

3. Forming station.

It consists of warming hood to heat the die , Die and Die loading platform with upward and downward movements as shown in figure 2.

Sequence of operations for forming of bubble

Mark and cut Acrylic sheet to size to suit template.fpre mould shape.) cut strips of scrap acrylics 28 x 155 mm (9.5 mm thick) = 6 nos.

Abrade strips on one surface of Acrylic sheet at attachment points. Bond 3 strips on the straight edges of Acrylic sheet using tensol no.3 cement and allow to cure.

Mix the grease properly and keep ready to use for moulding.

Set the oven temp to 160 deg.c.

Apply the grease over the mould

Remove the protection over the sheet and wash in warm water. Wipe sheet dry

Inspect the optical qualities of the sheet.

Load the sheet on trolley and clamp acrylic sheet in the gripper of the carriage moulding bars and push it inside the oven.

Heat the sheet inside the oven at 160 deg c.

Heat grease over the mould under infrared heating shroud to temp 110 - 140 deg.c until grease changes colour.

When Acrylic and grease on mould block are at correct temp raise shroud, open oven door, take the heated sheet to the forming station and wrapped over the mould to take the shape by lifting the mould to the normal height. Allow to cool. The formed bubble over the die is shown in figure 3.

Remove the shell from mould block. Clean with high pressure water jet using teepol and warm water. Dry with Kim wipe. Note: Clean the die after removing the shell.

Place in profile jig. Mark off profile using china graph crayon. Carryout profile check and record. Keep 1 inch extra from trim while marking.

Position shell on photo rig. Assist inspection to carryout vision test. Inspect optical qualities as per MP140032. Record thickness. Take photograph at pilot position.

Rough trim to marking and protect with protex paper.

CLAIMS

1. The bubble with superior optical clarity and acceptable contour dimensions were achieved.

2. Rejections were gradually brought down

3. Self Reliance on bubble production was achieved

4. Quality parameters which are paramount for pilot safety were achieved.