Carbon fiber control arm fabrication

[Hardingfv32]

Wondering how they make carbon fiber control arms. This is a statement from Honda F1:

The composite component is laid up in two half moulds which are
bolted together prior to the curing operation. Two thin strips of woven composite (oriented at ±45o to the axis of the tube), known as joining plies, are used to form a “strapped butt joint” in order to bond the two halves together. The tube and joint are consolidated in a single operation by the insertion of a pressure bag (@7bar) and heat in an autoclave.

Question: When is the “strapped butt joint” applied, before or after the two halves are cured?

I have an actual carbon fiber F1 control arm and there is no sign of any strips on the leading or trailing edges. The weave on the part is one piece starting and ending at the trailing edge.

Brian

[Daryl DeArman]

Is your F1 control arm from a recent Honda? Obviously, their components and processes are being improved all the time.

[Dave Welsh]

I recall seeing a vendor that makes the "pressure bags" at a composites trade show in Tampa many years ago. They can make a bag that has a shape and is firm at room temp, and then becomes pliable at elevated temps, and then return to the original shape upon cooling.

It would seem feasible that this could be a method in the manufacturing the control arm you have. Lay up the fabric on the shaped pressure bag, place it in a mold, apply heat and pressure to the bag. The bag would then conform to the shape of the mold. Upon cooling the bag would return to its original shape for removal.

[Stan Clayton]

Brian, the method you describe is essentially the same as we use to make our sports racer wing flap. The primary laminates are placed in each mold half (and wetted out in our case), then the joining strap placed along each long edge of one of the mold halves, with half of the strap extending out over the mold flange. A sacrificial inflation tube is then laid in the mold on top of the strap, and the joining strap's outboard portion is folded back over the tube.

The two mold halves are then bolted together and enclosed within a vacuum bag with a sealed tube feeding atmospheric pressure to the inflation bag. Vacuum is then applied at about 14 psid, which inflates the tube, pressing the primary laminates and the joining strap OUT against the mold halves. Think of it as the inverse of a conventional mold where atmospheric pressure forces the laminates IN against the mold.

Honda are doing the same thing as we are, it's just that they're using higher pressures. It can get rather complex to do, but the basic principle is quite simple.

[ghickman]

There are several methods that can be used to get a one piece hollow tube like you described. At our shop we manufacture carbon fiber golf club heads, bicycle race forks and other sports related items made of carbon fiber.

For some we use dedicated silicone mandrels that the carbon fiber is wrapped around using unidirectional in different orientations and a final wrap of 2x2 twill. The mandrel is stiff enough to wrap the prepreg by hand then is placed in single cavity molds and bolted together. Under heat the silicone expands and forces the carbon fiber outward against the mold and consolidates the layers. When the final tube or shape is cured and cooled the silicone mandrel is pulled out. The final product looks so good its almost a shame to put clear coat on it.

Another method we us are inflatable latex mandrels. They are rigid engough to wrap around and then placed in single cavity molds much the same as above. The mandrel is inflated during cure then deflated and removed afterwards. This is how golf club heads are done.

[Stan Clayton]

Sounds like you're building some really nice stuff, Gary!

[ghickman]

You make some super nice stuff as well Stan. I can appreciate the work you do, the parts are top notch.

I had the bennefit on several of my trips to Taiwan over the past 15 years going to shops that did composite work to pick up techniques that you otherwise can not get out of books (of course they didn't realize all the time I was spying on them). They use this stuff that looks like Silly Puddy, under heat it expands. I've tried to find it in the U.S. but came up with zip. They use it for making bike handle bars where the inflated bag can't go.

Gary