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Motorcycle News (UK) - - CONTENTS - By Jon Urry MCN CON­TRIB­U­TOR

Last April we high­lighted BMW’S car­bon-fi­bre re­in­forced plas­tic swingarm. Pri­mar­ily con­structed out of in­jec­tion­moulded plas­tic with car­bon at the high-stress parts it is a pos­si­ble pro­duc­tion item on cheaper bikes. But BMW have al­ready pi­o­neered cost-ef­fec­tive car­bon pro­duc­tion.

BMW have made huge steps in mass-pro­duc­ing struc­tural com­po­nents from car­bon, so it’s been get­ting ex­ten­sive use in their cars. Now this tech is fil­ter­ing its way down to two wheels, most no­tice­ably on the re­cent Con­cept 9cento which has struc­tural car­bon com­po­nents and the HP4 Race which has car­bon-fi­bre wheels and body­work. Here’s how they do it.

The process

“We pro­duce car­bon through an in­jec­tion mould­ing process called Resin Trans­fer Mould­ing (or RTM),” ex­plains Karl Vik­tor Schaller, Head of BMW Mo­tor­rad Devel­op­ment. “The key to our process is that you don’t just look at the moulds but also the tools used to cre­ate the shapes.”

Dur­ing a nor­mal RTM process, car­bon sheets are laid into a mould and resin in­jected. The whole mould is pres­surised and heated, giv­ing a shape when the resin cures. BMW, how­ever, have taken this a stage fur­ther.

“For struc­tural com­po­nents you need hol­low spa­ces within the mould, which we achieve through ei­ther sev­eral bal­loon­type blad­ders or a hard ex­pand­able foam,” says Schaller. “This struc­ture pro­vides pres­sure on both sides of the car­bon sheet, cre­at­ing a hol­low area once the resin is in­jected. On the HP4 Race’s wheels, there is light­weight foam within the spokes, which re­mains in­side once the wheels are cre­ated. A ‘sock’ of car­bon is knit­ted us­ing a ma­chine and slipped over a foam shape. This is then put into a mould and more car­bon added be­fore the resin to cre­ate the fi­nal wheel. Should metal in­serts be re­quired, such as in the frame’s steer­ing head, these are also added to the mould be­fore the resin is in­jected.”

Re­peata­bil­ity is key

The fact this process is eas­ily re­peat­able and the com­po­nents pro­duced iden­ti­cal in their struc­ture means it is suit­able for mass pro­duc­tion as BMW are con­fi­dent that each item is the same and there­fore passes safety in­spec­tions. “Un­der­stand­ing the struc­ture is the trick to us­ing car­bon,” ex­plains Schaller.

‘Un­der­stand­ing the struc­ture is key to us­ing car­bon’ BMW’S KARL SCHALLER

9cento Con­cept bike has car­bon fi­bre body­work

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