Do you ever wonder how smaller companies ensure they are making safe bikes and/or implementing quality control?? In traditional custom frame shops we have historically relied on the craftsman’s attention to detail, and the use of quality materials to ensure a safe product.
At Pursuit we work to close the loop between design and manufacturing which accomplishes two things; it allows us to make better bikes, and assures safety. Unlike many smaller companies, we have engineering and testing resources that allow this analysis.. We use both our own in-house engineering and test facilities, as well as off-property testing facilities we have partnered with to provide us greater confidence in our process..
Why it’s More Important with Carbon Fiber
Metal comes with defined tubular shapes and isotropic mechanical properties that are easily confirmed by the builder. Unlike metal, carbon fiber is purchased in sheet form and the mechanical properties are a result of the builders design and production of the bike frame. What this means is that the builder is not only constructing the frame but also creating each raw subcomponent of the frames structure. In many cases, smaller builders do not have the engineering expertise, or the testing equipment needed to truly understand and confirm frame design and manufacturing outcomes.
Design Requirements
When designing a carbon fiber bike frame – once performance goals are determined – the first thing that needs to be done, is to identify the material and material usage requirements to meet those performance goals. The designer can’t rely completely on the carbon fiber manufacturers performance claims, because the frame makers laminate design and manufacturing have a huge impact on the material performance results. This is where a robust system of testing and quality control are important.
Material Testing
The first thing the designers/engineers should do, is test the carbon fiber they are considering. This is a step that many skip. One needs to truly understand how a fiber performs when processed in the same ways that the frame will be manufactured to have accurate data when applying the material to design requirements. The tests that we use at Pursuit™ are a tensile test, which gives us the modulus (stiffness) and ultimate strength of the material. We are able confirm that our manufacturing methods realize the best performance characteristics for that material that we can achieve. We may also perform a burn-off test which indicates the ratio of carbon fibers to epoxy resin which is optimized for the strength to weight ratio of the final part.
Frame Design
Once material is tested and mechanical characteristics of the material and processing parameters are confirmed, we can apply those data to the frame design. Knowing what to expect from the material processed in our own way, we are able to go through the frame and assess how each tube should perform. We rely on both hard-core engineering analysis, and good-old intuition based on Carl’s years of building, and Bill’s centuries of riding. The outcome is the general laminate of each portion of the frame. In some cases it is based on stiffness, such as making the downtube torsionally rigid, while in other cases it is based on strength, such as at the junction of the head and down tubes. However, never is one sacrificed for the other. .
This gets a bit tricky when we take these global ideas for the frame and try to begin to manufacture the frame. Remember, the raw materials of these composite frames are anisotropic sheet goods meaning they are flat and can be difficult to drape over 3-dimensional surfaces. Bicycle frames are a unique challenge as they are an amalgam of complex 3-dimensional shapes, and thus significant work goes into developing ply patterns that realize the frame design goals while also being manufacturable. The hundreds of individual pieces of carbon fiber material that go into making a frame are what defines the ply pattern. An ideal ply pattern is repeatable, easy to work with, and results in a strong frame with an optimal ride. Like the laminate, the ply pattern also requires significant analysis and a keen understanding of the specific manufacturing process.
Manufacturing Development
While we are using some tried and true composite manufacturing methods, we are working to develop the Pursuit™ process that ensures each frame meets the design goals. We focus on the typical quality measures, but have also emphasized measures to ensure sufficient tracking of key manufacturing metrics of each frame.
Serialization – Information related to each individual bike identified by its serial number is recorded. Travelers follow every frame part through the manufacturing process. The traveler includes ALL vital information for each part, such as material, layup, cure profile, and environmental conditions.
Cure Profiles – Curing the carbon fiber is an important part of ensuring that its fatigue life is optimized. In order ensure the part is meeting the temperature and time necessary to properly cure, all tools are fitted with multiple thermocouples and tested for hot and cold spots. Once we know how each tool responds to heat we can program a custom cure profile for that tool. We review and record all cures before logging each record with the appropriate serial number of the frame.
Bond Assurance – All the parts are bonded together and each joint is wrapped with carbon fiber and then cured. If done correctly the bonded joint will be stronger than the surrounding material. To ensure the bonds meet our requirements, we weigh and record after curing to check that all bond-lines are in spec.
Prototype Testing – We test during both process development, and on randomized samples during production. We also do non-destructive tests on all parts as a matter of routine during the manufacturing process. All designs undergo ISO 4210-6 and EN 14781 testing during the design phase, process development phase, prototype evaluation, and with randomized samples. These standards specify both fatigue and impact tests for bicycle frames. Fatigue testing is centered around applying cyclic loads akin to hitting bumps and/or pedaling whereas impact testing is centered on a single front-end collision. Both tests are meaningful to ensure we are building safe, reliable frames, but also provide important information that we can trace back through the design and manufacturing processes.
Riding – The fun part! While we do collect data when we are testing bikes, most of what we evaluate is seat-of-the-pants qualitative feedback. How do we like the feel; is it smooth enough, and stiff enough. How does it feel when we hit bumps, and expansion joints. How does it turn and sprint. Data that we collect includes the use of accelerometers, strain gauges and the basic stuff you get from your Garmin such as power, mileage, time and elevation. All of which is laid on top of the other data in order to give us a complete picture of what is going on.
