Sunday, 25 May 2014

Con rod machining

The con rod has been machined!! it looks quite good, prior polishing and final work on the bearings. On the sequence below you can see the different machining stages.

The material used on the con rod is 7075 T-6. The bearings are LM-7 Zn bronze, with the top one pressed in and the main one being split. Bolts are M2.

At 14000 RPM the con rod sees a maximum compression load of 820 N and a maximum tension load of 391N. Coefficient of safety is n = 4,4 static and n = 1,1 fatigue (infinite life). I expect fatigue wise it will be safe as 14000 RPM seems quite optimistic for the first test engine for both speed and life time.






After polishing the part will look even better. I will polish it to remove all the tiny notches and sharp edges which will make it look better and improve fatigue resistance.

I will make the split bearings with a tang on each one, and a dowel pin for the real engine. This will improve fitting quality and repeatability of the tolerances.

Next part is the piston, which is one of the most exciting parts of the project.

Wednesday, 21 May 2014

Renault F1 monocoque manufacturing

Just a little insight on how to make composites. This post is related to the Renault R26, already finished some years ago, to show what can be done in composited by the model engineer.

I have to say, this process is very similar to the real thing, and I can assure you I know what I am talking about.

The process is usually the same for every part: design component - design tooling - patterns - moulds - laminating - trimming/assy. The first two are down to you, so we will focus on the actual making-bit. Just a brief note on design. CAD is very powerful to assist production engineering with templates, 1:1 plots, etc. it is not just the 2D drawings, not to mention CAM, so worth considering for any project.


As an example, see below the engine cover and monocoque. Both made in a similar way: basically, the pattern is the actual shape of the part, but made form a solid block of material that we can shape easily, in this case MDF (wood). The better the pattern quality, the better the mould quality and therefore the part. Patterns usually last only one pull, but enough to get a mould, from which several parts can be made. The mould is the negative shape of the part, if you see what I mean.

Paper templates (1:1 plots) are made which are the cross sections of the part to make at certain heights. Each section correspond to a MDF board level that will be stacked to create the rough volume.
After cutting the boards, they are bonded using glue. You might want to pin them to guarantee alignment.


Rough cuts are made using chisels, files, saws, etc. This is quite an elaborate process. Use templates in all the directions required to ensure the shape is within tolerance. Make as many templates as you need, e.g. cross sections every 20 mm. 



Finishing touches using a Dremel. Use also sanding paper to shape by hand the form. Remember that after this all the little holes and gaps will be filled with body filler, which makes things easier at this stage.

Body filler and paint are applied after the finishing touches. At this stage, the surface has to be spotless as this is exactly how the part will look like.  Use good quality paints to prevent reaction with the epoxy resin and release agent. I recommend car body panel paint.


 Apply the release agent and start laminating. In order to draft the part, a several mould pieces mould might be required. See below how to make the splits using panel board to create the bolting flanges. Use plasticine or other paste on the corners to seal the edge of the board to the part. As cure occurs at room temperature, you can use almost anything. Do one mould piece, cure it, and remove the board from the next section to make another mould piece. This has to be repeated as many times as required until all the mould pieces are completed. Do not remove mould pieces during the sequences so the flanges match perfectly from one mould piece to the other. Drill the mould flanges for bolting the mould pieces together during laminating.




When the mould is ready, make the part with the required material and layup thickness. For most of body work, only 2-6 layers are required. Use more material on corners and bolting sections to reinforce high stress areas. The winglets and other elements of the engine cover where manufactured separately, even with different materials/processes, and bonded afterwards. This applies to chassis, floor, gearbox, etc. where many elements of the car are mounted too. Fit inserts and other bits inside during layup to create hard pads for tapping or bolting later on.

Use again body filler for finishing the part and achieving a nice surface. Prep the surface for paint and go for it!




Based on this process, all the other parts of the body work can be made. However, other processes like thermoforming, 3D printing, sheet metal fabricating are also required for particular parts, like end plates, brake ducts, etc. In real F1 world, the process is based on the same steps, but enhanced with the use of better equipment and materials. You might want to take a look at the pattern post  for a more advanced way to make components (http://bernimodels.blogspot.co.uk/2012/11/tooling-wing-test.html). For the Red Bull 1/3 I am planning to use CNCed patterns, although for big body work pieces, I might stick to the process on this post due to size/cost restrictions of my equipment.



Tuesday, 20 May 2014

Con Rod manufacturing IT3

Work has begun on the con rod. I will be extending the post as I work along this part and the next parts untill the engine is finished.

I have started with the blank and the machining fixture. All this will come together as what you see below.
More to come :)

The bearings are already finished for it, but will not be mounted until the body and head are machined. After that, the bearings will be reamed to achieve the final bore tolerance for the crankshaft journal and piston pin.