Mould Making

Manufacture!of!a!wing!mould! ! !

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In!the!previous!pictorial!a!method!was!described!for!moulding!a!solid!foam!core!wing.!A!CNC!milled!upper!mould!was!used!in!the!process.!The!following!pictorial!gives!a!step!by!step!process!for!making!a!!mould!from!epoxy!resin.!

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First!a!master!model!!must!be!made!to!represent!the!exact!shape!of!the!top!surface!of!the!wing!to!be!made.!For!this!purpose,!a!hot!wire!foam!cutting!technique!is!used.!The!core!will!be!covered!with!0.4!mm!PVC!sheet,!so!the!cutting!templates!must!be!compensated!take!this!into!account.!

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Here!a!model!of!a!tip!panel!is!shown.!The!green!pieces!are!foam!strips!which!will!create!surfaces!in!front!of!the!leading!edge!and!behind!the!trailing!edge!to!place!sealant!for!vacuum!bagging.!The!trailing!edge!strip!(under!the!sanding!block)!is!tapering!in!thickness!as!the!model!has!a!negative!warp.!

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All!the!parts!are!assembled!using!UHU!Por.!On!the!background!plastiboard!strips!are!ready!for!encasing!the!master!model.!

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The!bottom!of!the!model!is!covered!with!0.4!mm!PVC!sheet.!Also!the!top!surface!is!covered!with!this!material.!This!top!sheet!is!cut!with!a!knife!to!make!a!fold!line!where!the!model!meets!the!leading!

edge!strip.!Same!is!done!where!the!model!meets!the!trailing!edge!strip.!The!model!is!sanded!and!cleaned!from!dust.!Then!a!layer!of!epoxy!resin!is!rolled!on!the!model.!At!the!leading!edge!strip!a!few!spots!are!left!dry.!Here!some!cyano!acrylate!glue!is!applied!and!the!PVC!sheeting!is!fixed!in!place!using!a!sharp!edged!pressing!block.!

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The!top!foam!negative!is!used!as!a!pressing!member.!The!whole!package!is!vacuumed.!

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Typical!cross!section!of!the!master!model.!!

After!curing!the!ends!are!cut!at!a!slight!angle!on!the!table!saw!and!the!whole!set!up!is!placed!in!an!enclosure!of!plastiboard.!

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Plastiboard!edges!and!bottom!plate.!Treat!with!release!agent!before!assembly!!The!master!model!is!fixed!to!the!bottom!plate!using!cyano!acrylate!glue.!The!ends!of!the!master!model!is!covered!with!plastic!self!adhesive!packaging!tape.!

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After!having!treated!all!surfaces!with!release!agent,!a!first!gel!coat!layer!can!be!applied.!

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After!the!first!layer!has!gelled,!a!second!layer!is!applied.!

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Immediately!after,!chopped!glass!fibres!are!applied.!

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….and!spread!over!the!entire!surface.!The!second!gelcoat!is!left!to!cure.!

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Then!two!layers!of!glass!fibre!cloth!are!applied….!

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And!impregnated!with!resin!

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A!layer!of!carbon!fibre!fabric!(45!degree!bias)!is!applied!and!impregnated.!

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Try!to!remove!air!pockets!as!much!as!possible.!

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A!generous!amount!of!epoxy!and!filler!material!(sand!or!‘Polyfill’)!is!applied!along!the!leading!and!trailing!edges.!Into!this!mixture!two!aluminium!square!tube!profiles!are!pressed.!Make!sure!that!excess!filler!resin!is!squeezed!out!between!the!profiles!and!plastiboard!edges.!The!top!of!the!profiles!are!also!coated!with!this!filler!material!and!glass!fibre!fabric!cloth!is!folded!over!the!profiles!.!

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A!mixture!of!hollow!spheres!(Blähglaslkugeln,!http://www.weberschock"development.de/fmb/material.html)!and!epoxy!is!mixed.!The!epoxy!is!colored!with!pigment!powder.!This!helps!in!detecting!any!unmixed!material.!

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The!mixture!is!dumped!in!the!mould!and!stamped!with!a!wooden!block.!

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After!the!entire!mould!is!filled!the!whole!set!up!is!left!to!cure.!The!stamping!mass!is!some!3!mm!below!the!top!edges!of!the!plastiboard!enclosure.!

At!one!end!of!the!mould!a!shim!can!be!applied!to!introduce!a!warp.!The!shim!must!stay!in!place!for!the!remainder!of!the!process.!

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After!curing,!the!surface!is!sanded!down!and!!filled!with!a!mixture!of!epoxy!and!milled!cellulose!fibres.!

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A!layer!of!carbon!fibre!fabric!with!resin!is!applied.!

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After!curing,!the!top!surface!is!filled!with!a!mixture!of!epoxy!and!milled!cellulose!fibres.!

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The!mould!after!release.!

After!a!thorough!cure,!the!mould!can!be!released.!The!master!model!will!be!destroyed!in!the!process.!

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The!edges!are!rounded!with!a!file,!the!bottom!surface!sanded!and!given!a!final!coat!of!unfilled!resin.!

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