Two Companies Team Up to Create First 3D-Printed Metal Bike

It began with collaborating to manufacture a bike seat post

Published: Tuesday, March 25, 2014 - 16:21

Bicycle design company Empire Cycles, and Renishaw, the United Kingdom’s only manufacturer of metal-based additive manufacturing machines, have collaborated to create a 3D-printed titanium bike frame. It’s based on the Empire MX-6 mountain bike design but is stronger and about 33-percent lighter. 

A process called topological optimization determined the most efficient use of the titanium throughout the frame’s hollow structure. The most logical placement of material optimizes its design for being lightweight yet able to bear the load.

Employing Renishaw’s AM250 additive manufacturing system, the frame was manufactured in sections and bonded together. The additive manufacturing process, better known as 3D printing, allows for customized construction with the flexibility to make design improvements right up to the start of production.

The two companies originally agreed to optimize and manufacture only the bike’s seat post bracket, but after the part’s successful production, improvement of the whole frame became the new goal. Empire started with a full-size 3D-printed replica of the MX-6. The frame was sectioned into parts that could all be formed in one build using the AM250’s 12-in. (300-mm) build height. The design was updated with guidance from Renishaw’s applications team and an optimized design—one that eliminates many of the downward-facing surfaces that require wasteful support structures—was created using topological optimization.

All parts of the frame can be built at once within the build volume of the AM250

Topological optimization

Topological optimization is a mathematical approach that optimizes material layout given load and design space requirements. Topological optimization software programs use iterative steps and finite element analysis to determine the “logical” material placement. Material is removed from areas of low stress until a design optimized for load bearing is created, resulting in a model that is light and strong. Historical challenges in manufacturing these computer-generated shapes are overcome through the additive manufacturing process. Shapes that are either physically or cost prohibitive for traditional manufacturing processes are not a problem for 3D printing.

The AM250 uses a high-powered fiber laser to produce fully dense metal parts direct from 3D CAD data. Parts are built layer by layer, in thicknesses ranging from 20 to 100 microns, using a range of fine metal powders melted in a tightly controlled atmosphere. A fully welded vacuum chamber and ultra-low oxygen content in the build atmosphere allow processing of reactive materials, including titanium and aluminum.

The AM250 can print 3D objects using a variety of metals, including 316L and 17-4PH stainless steel; H13 tool steel; aluminum Al-Si-12; titanium CP, Ti-6Al-4V, and 7Nb; cobalt-chrome (ASTM75), and Inconel 718 and 625. The AM250 uses a 200 or 400 W laser and an XYZ build volume of 250 x 250 x 300 mm with a Z axis extendable to 360 mm. It can build at rates of 5 to 20 cm³ per hour, depending on the material, part density, and geometry.

The key benefit to Empire Cycles is the performance advantages derived from the additive process. 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. “As no tooling is required, continual design improvements can be made easily, and as the component cost is based on volume and not complexity, some very light parts will be possible at minimal costs,” says Dave Bozich, business manager at Renishaw.

Making it light

The original aluminum alloy seat post bracket is 12 oz (360 g) and the first iteration of the hollow titanium version is 7 oz (200 g), a weight savings of 44 percent. Comparison of the entire frame has the original bike frame weighing in at 4.6 lb (2,100 g), with the redesigned additive-made frame at only 3.1 lb (1,400 g), a 33-percent weight savings.

“There are lighter carbon-fiber bikes available, but the durability of carbon fiber can’t compare to a metal bike,” says Chris Williams, managing director at Empire Cycles. “They are great for road bikes, but when you start chucking yourself down a mountain you risk damaging the frame. We over-engineer our bikes to ensure there are no warranty claims.”

Titanium alloys have more density than aluminum alloys, with relative densities of around .14 lb/in.³ (4 g/cm³) and 11 lb/in.³ (3 g/cm³), respectively. Therefore, the only way to make a titanium alloy part lighter than its aluminum alloy counterpart is to significantly alter the design and remove any material not contributing to the overall strength of the part. The companies believe further analysis and tests could result in further weight reduction.

Making it strong

In addition to durability and corrosion-resistance, titanium alloys have a high ultimate tensile strength (UTS) of more than 900 MPa, when processed using additive manufacturing. With near-perfect densities—greater than 99.7 percent—the process is better than casting, and the small, spherical nature of additive-part porosity has little negative effect on strength. The seat post bracket was tested using the mountain bike standard EN 14766, and it withstood 50,000 cycles of 270 lb ft (1,200 N). Testing continued to six times the standard without failure.

Continued improvement through collaboration

Empire is passionate about partnering with top British engineering companies to create elite products. Research into bonding methods resulted in Mouldlife providing the adhesive, which was tested by technical specialists at 3M test facilities. The wheels, drivetrain, and components required to finish the bike were provided by Hope Technology Ltd.

Empire and Renishaw plan to continue testing the completed bicycle frame in the laboratory, using Bureau Veritas UK, and in the field, using portable sensors in partnership with Swansea University. “We plan to develop this further, in partnership, to look at iterative improvements in bonding methods, such as specific surface finishes,” explains Bozich. “This project demonstrates that excellent results can be achieved through close customer collaboration.”

For further information, visit www.renishaw.com/empire.

About The Author

Renishaw

Renishaw is a global company with core skills in precision measurement, motion control, healthcare, spectroscopy, and manufacturing. The company supplies products and services used in applications as diverse as jet engine and wind turbine manufacturing to dentistry and brain surgery. Also a world leader in additive manufacturing, Renishaw designs and makes industrial 3D printers. Between 13 and 18-percent of annual sales are invested in R&D and engineering. The Renishaw Group has more than 80 offices in 36 countries, with 5,000+ employees.