YISHUN Knowhow

KNOWHOW

What can we do that the others can’t? What distinguishes our components from others? The answer lies in our origins. We at YISHUN aren’t just bike nerds; we’re experts in lightweight construction. Our know-how means that we can get the absolute best out of carbon.

CARBON SKILLS

Carbon is our passion. We often wonder where the bad image of carbon components for bikes comes from. The only way we can explain it is that it results from bad carbon components. This image saddens us, because carbon has a huge range of fascinating properties.

Carbon is a fibre composite material that is used in countless industries. Its use is also booming in the bike industry. A composite material combines two materials to unite the positive properties of both. In the case of carbon, these two materials consist of the carbon fibres and the corresponding epoxy resin as an “adhesive”. This combination becomes extremely sturdy, while remaining incredibly light.

There are several advantages to carbon. It has a high fatigue strength, is super-sturdy, stiff, does not corrode and offers an enormous design freedom. However, carbon is anisotropic. This means that it is capable of absorbing loads primarily in the fibre direction and less in cross direction. It also absorbs tensile forces in fibre direction much better than it does compressive loads. It is therefore necessary to orientate the fibres in the component in accordance with the load direction. Experience in design, construction and manufacturing is essential, as well as type and quality of the materials used. Thanks to the cooperation with our development supplier TG Engineering (specialized in aerospace) as well as various research projects with the Institute for Lightweight Engineering and Polymer Technology at the XMU and companies in the aviation industry, we have expert knowledge and are familiar with the current state of the art to an extent beyond anyone else in the bike industry.

There are an unbelievable variety of carbon fibres available. There are different fabrics, non-crimp fabrics and many mixed forms. Each has its own characteristics, so it is important to use them correctly. In the bike industry, there are mainly three different carbon bindings: twill weave, plain weave and uni-directional non-crimp fabric (UD-NCF).

Plain weave and twill are fabrics in which the carbon fibres are not ideally stretched, but have regular, short-wave curvatures. This waviness is known as “crimp”. Increased curvatures reduce the mechanical properties, since complex stress conditions prevail where the threads cross one another.

In plain weave, a single weft thread runs alternately over and under a single warp thread. Due to the harsh fibre curvature, plain weave has the worst compression and fatigue strength values among the fabrics mentioned above.

In twill 2/2 weave, one weft thread runs alternately over and under two warp threads. The carbon fibres are therefore stretched to a greater extent than in plain weave. Twill weave is therefore more resistant to slipping and is also easier to drape.

However, maximum stiffness and strength can only be achieved using stretched fibres. This is where the strength of non-crimp fabrics (uni-directional – UD) comes from. The special feature of UD is that the individual fibres are aligned in a single direction only (uni-directional). The carbon fibres are therefore stretched, which in turn leads to significant higher stiffness and strength. However, the fabric is much more complicated to work with and requires a lot of care during when laying up.

We have decided to produce our components in two different looks: the UD finish and the SQ finish. We use UD fabrics almost exclusively. This is due to their high level of stiffness. For the SQ finish we use an additional cover layer with plain weave (spread tow). We ensure that the stiffness of the top layer is adapted to the UD laminate underneath.

We accept the fact that production is more laborious because UD non-crimp fabric does not drape as easily. What counts for us first and foremost is the significantly higher strength.

PRECISE PRODUCTION

We work using the best-known lightweight engineering process for complex components: the prepreg autoclave process. First, every layer of the pre-impregnated semi-finished fiber, the so-called “prepregs”, is mechanically cut to the correct fit.

The next step is laminating, i.e. laying up the individual carbon layers in the moulds. This requires considerable skill, accuracy and experience. Every single component is created layer by layer. We use a lot of thin carbon layers, which makes production more laborious. The following will give you a better idea of how the lamination process works: Depending on the handlebar, up to 84 prepreg plies must be positioned by hand according to a specific plan.

After our technicians have very carefully placed the prepregs in the mould by hand and in the appropriate sequence, everything is vacuum-sealed for curing in our autoclave. The components cure under pressure, a constant vacuum in the tool and temperatures of between 110°C and 150°C. This prevents from inclusions (pores) and fluctuations in quality.

The parts are demoulded by hand and meticulously checked. Each of our handlebars is examined from the inside for defects or unevenness using an endoscope. Only components that are perfect in terms of construction are then subjected to visual quality control.

During the visual inspection, components with defects such as bubbles, dents or folds are separated. The tiniest visual defects, unrecognizable to the untrained eye, are repaired, prepared and finished. We do this because our customers expect, and we want to supply, absolutely perfect components.