1 Title of the Invention
Forming of CAST ACRYLIC panels of helicopter using Velvet cloth.
2 Field’ofthelnvention
The invention relates to forming of panels (Cast Aci’ylic sheet) of
Helicopters, and in particular, facilitating forming of Helicopter panels
without using grease and pre-heating and heating of forming tool.
3 Background of the Invention
Helicopter panels which are having contour are formed by using Grease.
l'n this process heated acrylic sheet comes ~in confact with the forming tool
which is made up of Composite or Wooden material.'The tool is cdvered
with thick felt and Cloth. Grease is applied on the felt, the tool is heated
under infra-fed lamp hood to.a high temperathre (approximately 100° C)
and allowed to_ soak, so that the felt beComes soft.
The aérylic sheet is cut to suit the moulding jig. The acrylic sheet is heated
in the oven at 155° to 165° centigrade approXimately for 45 minutés. The
forming tool is also pre-heated in the infra-red lamp hood at 100°C for a
predefined time duratign. The grease is applied uniformly on moulding jig.
The heated acrylic sheet is removed from the oven quickly and positioned
on the moulding jig and stretched to get formed. The shéet is clamped and
allowed to cool. The panel is removed from jig after cooling. _The formed
panel' IS cleaned with soap water to remove the grease. Panel IS inspected
.for visibility. Further operations are trimming and polishing.
However. distortion is observed in penel randomly because_of inconsistency
in melting of grease, variation of heating due to multiple
contours of panel and variable parameters like manual stretching and
clamping etc.
If the grease melts fast and flows off the tool; then cloth impression is
noticed on the panel, if grease is not melted properly; then. vision distortion
occurs on panel which is undesirable.
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Panels average acceptance raté in g'rease forming method is 60%, panels
with vision distortion a're reformed again in the oven to achieve vision.
Cost of grease, manpower and electricity is increased due to this. Work
involved like heating the tool, grease application and cleaning of panel to
remove grease is tedious.
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3.1 P.rior-Art
US4550047A describes the forming of panel by using_a lubricant as a
medium beMeen Acrylic and the tool to avoid tool marks on the panel.
However. no mention is made to use velvet cloth in the process.
.EPO 352466A1 describes canopy forming using vacuum fdrniing, but this
method can‘t be used for Helicopter panels which are having multiple
contour and also maintaining the required final vision with uniform
thickness and achieving repeatability of shape is also very important.
4 Brief Summary of the Invention
The invention addresses the above problems. The Method of forming
Acrylic panels by placing Velvet cloth (3) on the forming tool (1) is to use
some medium in place of grease to avoid impression of tool (1) arid vision
distortion.
The invention provides a method'of forming panels (5) (cast acry'lic
sheets) which diminishes or eliminates impression of tool and
distortion in vision.
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Detail Description of the Drawings
Figure-1 describes the forming togl (1) made of Composite material
,covered with two layers of soft cloth-'(Z) and outer layer with Velvet
cloth (3).
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Figure-2 describes the Velvet cloth (3) is spread on the .forming tool;
Weight (4) is hung on the Velvet cloth (3) all around to ensure there is
no wrinkle. The Velvet cloth (3) is placed in such a way that the.
smooth surface comes’ top. The heated acrylic sheet (5) is formed on
Velvet cloth (3) and held in position with retainer (6) without applying
much ”pressure.
Detail Descriptibn ofthe Invention ~
The following specification particularly describes the invention and the
manner in which it is to be petformegj, "should be noted that while
specification and appendices describe’the method of forming panels (5)
(using velvet cloth (3) on the forming tool (1), other embodiments of
present invention may be used for othei' Helicopters and Aircrafts canopy,
bubble and panelé as well. It may be used in forming of other acrylic
panels requirements.
,The invention provides an improved method for the forming of acrylic
panels. In this method as shown in Figure-2 forming tool (1) (wood dr
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composite or metal) surface should be smootH and there should not-be ..
army undulation. The tool ‘should be covered with soft cloth (2) (two layers)
and then it should be covered with Velvet cloth (3), weight (4) is required ,
to be applied all around to ensure there is no wrinkle on the velvet cloth
(3). The Velvet cloth (3) is to be placed in such a way that (the smooth
surface comes‘ top which is coming into contact with heated sheet. It is ensured that velvet cloth (3) is smooth, uniform and free from dust and
other objects.
The Acrylic sheet (5) is héated in the oven at 168° C for 20 minutes,
heated sheet (5) is removed and placed on the ~forming tool (1) covered
with Velvet cloih (3). The sheet is held on tool with pliers; with the retainer
(6) ‘in position for a_ minute to ensure no wrinkle. The pane| is left on the
tool, allowed to cool down under a fan
The panel (5) is removed from jig (1) after cooling; Visibility inspection is
carried out.l(Funner operations are trimming and polishing).
A method of forming cast acrylic panels (5) by using Velvet cloth (3)Vcomprising:
a forming tool (1) covered with two layers of soft cloth (2)_further comprising:
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5 a plural of dead weights (4) hung around the forming Tool (1); to make wrinkle
free cloth (3) ; a retainer (6) holding the heated acrylic panels (5)
23A method acrylic panel forming, as said ih claim 1, that ensures grease
application is not required, pre-heating 'and heating of forming tool (1) is' not
required