3D-printed bike made from Ti­ta­nium al­loy

DEMM Engineering & Manufacturing - - NEWS -

Ren­ishaw, the UK's only man­u­fac­turer of a metal-based ad­di­tive man­u­fac­tur­ing ma­chine, has worked with a Bri­tish bi­cy­cle de­sign and man­u­fac­tur­ing com­pany to cre­ate the world's first 3D printed metal bike frame.

Em­pire Cy­cles de­signed a moun­tain bike to take ad­van­tage of Ren­ishaw's ad­di­tive man­u­fac­tur­ing tech­nol­ogy, al­low­ing them to cre­ate a ti­ta­nium frame that would be both strong and light – us­ing topo­log­i­cal op­ti­miza­tion – the new frame is 33 per­cent lighter than the orig­i­nal.

The frame has been ad­di­tively man­u­fac­tured in ti­ta­nium al­loy in sec­tions and bonded to­gether, and it's strong – hav­ing been tested to EN 14766.

Ren­ishaw and Em­pire Cy­cles epit­o­mized the bi­cy­cle de­sign for ad­di­tive man­u­fac­ture, elim­i­nat­ing many of the down­ward fac­ing sur­faces that would other­wise have needed waste­ful sup­port struc­tures.

Ti­ta­nium al­loys have a high ul­ti­mate ten­sile strength (UTS) of more than 900MPa when pro­cessed us­ing ad­di­tive man­u­fac­tur­ing, and near per­fect den­si­ties of greater than 99.7 per­cent are achieved; this is bet­ter than cast­ing and, as any poros­ity is both small and spher­i­cal, it has lit­tle ef­fect on strength.

The project's aim is to pro­duce a fully func­tion­ing bi­cy­cle, so the seat post bracket was tested us­ing the moun­tain bike stan­dard EN 14766; it with­stood 50,000 cy­cles of 1,200 N. Test­ing con­tin­ued to six times the stan­dard with­out fail­ure.

Test­ing of the com­pleted bi­cy­cle frame will con­tinue, both in the lab­o­ra­tory us­ing Bureau Ver­i­tas UK, and on the moun­tain­side us­ing por­ta­ble sen­sors in part­ner­ship with Swansea Univer­sity.

From the Greek word for place, “topo”, topo­log­i­cal op­ti­miza­tion soft­ware is the term given to pro­grams that are used to de­ter­mine the “log­i­cal place” for ma­te­rial – nor­mally us­ing it­er­a­tive steps and fi­nite el­e­ment anal­y­sis.

Ma­te­rial is re­moved from ar­eas of low stress un­til a de­sign epit­o­mized for load bear­ing is evolved. The re­sult­ing model is both light (due to the low vol­ume) and strong. The his­tor­i­cal chal­lenge in man­u­fac­tur­ing these shapes can now be over­come with ad­di­tive man­u­fac­tur­ing, en­abling phys­i­cal 3D mod­els to be re­alised.

Ti­ta­nium al­loys are more dense than alu­minium al­loys, with rel­a­tive den­si­ties of around 4 g/cm3 and 3 g/ cm3 re­spec­tively. There­fore, the only way to make a ti­ta­nium al­loy ver­sion of a part lighter than its alu­minium al­loy coun­ter­part is to al­ter the de­sign to re­move any ma­te­rial not con­tribut­ing to the over­all strength of the part.

The orig­i­nal alu­minium al­loy seat post bracket is 360g and the hol­low ti­ta­nium ver­sion is 200g, a weight sav­ing of 44 per­cent. This is just the first it­er­a­tion; with fur­ther anal­y­sis and test­ing it could be re­duced fur­ther.

The orig­i­nal bike frame weighs in at 2100g. Re­designed to make use of ad­di­tive man­u­fac­tur­ing, the weight drops to 1400g, a 33 per­cent weight sav­ing.

There are lighter car­bon fi­bre bikes avail­able, but Chris Wil­liams, man­ag­ing di­rec­tor at Em­pire Cy­cles, says: “The dura­bil­ity of car­bon fi­bre can't com­pare to a metal bike, they are great for road bikes, but when you start chuck­ing yourself down a moun­tain you risk dam­ag­ing the frame.”

The key ben­e­fit for Em­pire Cy­cles is the per­for­mance ad­van­tages that this con­struc­tion method of­fers. The de­sign has all of the ad­van­tages of a pressed steel ‘mono­coque' con­struc­tion used in mo­tor­bikes and cars, with­out the in­vest­ment in tool­ing that would be pro­hib­i­tive for a small man­u­fac­turer.

Re­search into bond­ing meth­ods re­sulted in Mouldlife pro­vid­ing the ad­he­sive, and 3M pro­vid­ing test fa­cil­i­ties. Ren­ishaw will de­velop this fur­ther in part­ner­ship to look at it­er­a­tive im­prove­ments in bond­ing meth­ods, such as spe­cific sur­face fin­ishes.

A 3D printed moun­tain bike made by Ren­nishaw in the UK is given a tough work­out on rough ter­rain.

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