3D Modeling & CAD for Motorsport: Step 1-A : Planning - Problem Definition
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Step 1-A : Planning - Problem Definition
07.11
| 00:00 | - In this worked example, we're going to go through the design and construction process of a billet valve cover. |
| 00:06 | This is going to give you a real world look at creating a relatively complex and detailed CNC machined part using Fusion 360. |
| 00:14 | This will be an expensive part to produce so we need to be sure we've got it right before we move to the manufacturing stage. |
| 00:21 | Therefore to aid in the design process, we'll use 2D images, also known as canvases in CAD as well as 3D scans taken from our smart phones as reference to model around. |
| 00:33 | If you don't have a 3D scanner or a phone capable of scanning, it's still possible to model this part, you'll just need to spend some more time measuring your vehicle to make sure it'll fit and you won't have the visual reference on your screen. |
| 00:46 | To be transparent, while most modelling jobs tend to take a few hours, this took days if not weeks so in the interest of keeping things digestible, we're going to show you a more general overview rather than detail every single feature down to each mouse click. |
| 01:02 | The time intensive process of fleshing out the idea and determining a suitable modelling process will not be shown but rather an overview of how the final model was achieved and then brought to life while still covering some key details and considerations specific to this design. |
| 01:19 | This section of the course isn't about teaching you anything new. |
| 01:22 | These examples are all about seeing what you've already learned put into action. |
| 01:26 | So if anything you see here has you scratching your head, it's best to stop, go back to the relevant course module and give it another watch to get a better understanding before continuing on with the worked example. |
| 01:38 | So let's get started. |
| 01:39 | For this worked example, we'll be designing a new valve cover for the SR20VET engine in the HPA Toyota 86 racecar. |
| 01:48 | Although the same ideas and principles can be applied to help you design a similar part for your own application. |
| 01:55 | The process for every good design starts with a definition of the problem and in our case, the current valve cover was a factory option that'd had been cut and welded extensively to mount the 4 IGN1A coils and 2 aftermarket breathers to a catch can. |
| 02:11 | Due to vibrations, heat, and a compromised design, the valve cover cracked and opened around the bottom of one of the coil mounts during an endurance race and the car had to be retired from the event. |
| 02:23 | To make sure we have a good understanding of the problem we're trying to solve, let's get the specific requirements and considerations for the valve cover clarified. |
| 02:31 | The main function of the valve cover is clearly to cover the valve train and protect it from the elements while preventing oil from leaking out. |
| 02:39 | In saying that, breathers are required to prevent excessive pressure build up, allowing gasses to escape from the valve cover while minimising the amount of oil that comes with it. |
| 02:49 | For this change, we'll be moving back to a coil on plug arrangement as opposed to the current coil near plug setup, eliminating the need for coil leads which can also be a reliability issue if not installed correctly or damaged. |
| 03:03 | We'll be using the Hitachi coils from the VR38DETT engine in the R35 GTR. |
| 03:10 | These are a proven coil that has been used before on this engine with good results. |
| 03:16 | However, with a factory valve cover, most of the aftermarket kits for this application use shortened coil stalks to tuck the coils inside the valley of the valve cover keeping things tidy. |
| 03:27 | Unfortunately in a higher power endurance racing application, this results in a lot of excess heat around the coils, causing reliability issues and also making them more difficult to be changed if required. |
| 03:41 | The valve cover needs to hold the coils in place over the spark plugs and utilise standard length coils, positioning them out of any valley that could cause excess heat and also allowing these coils to be changed quickly and easily if required with standard parts. |
| 03:56 | Naturally the valve cover will also need to clear all the other components in the engine bay and fit well with the mating flange of the head. |
| 04:04 | At the interface, a high temperature o ring will be used with a groove machined into the flange of the valve cover as opposed to the factory style gasket to help with sealing capability at high pressures. |
| 04:17 | This way we can also match the o ring size of the outer flange to the inner flanges around the spark plug holes to ensure they compress by the same amount. |
| 04:26 | The SR20 head casting has semi circular cut outs in line with the camshaft on the front of the head to allow for access to the large front camshaft bolts as well as on the rear of the head for the distributor drive and a breather. |
| 04:40 | The factory valve cover and moulded rubber gasket protrude down to fill these holes but we're going to change the design slightly to simplify the valve cover machining process and keep the o ring groove in a single plane. |
| 04:53 | We'll have plugs made by a machinist to fill these cut outs which would then create a flat mating surface for the valve cover and o ring. |
| 05:01 | Also in our case the SR20 uses a dry sump system and this means an oil filler cap on the valve cover is no longer required as the oil will be filled through the oil tank. |
| 05:12 | The current valve cover no longer has an oil cap and we'll be leaving it off this design as well as it's just an extra failure point, added machine time and it'll look cleaner without it and again it's just not needed. |
| 05:24 | Considering the previous issues, the valve cover needs to be stiff enough that it doesn't vibrate or move excessively and isn't going to fatigue and crack from vibration. |
| 05:34 | This shouldn't be as much of an issue with how the coils will be mounted and the valve cover being under relatively little load but we still want to make sure we're rounding sharp edges as much as possible to prevent stress concentrations. |
| 05:47 | As with most things we design for motorsport, we also want it to be lightweight and as the valve cover is the central display piece for the engine today, ideally we want it to look good. |
| 05:58 | With these requirements and considerations in mind for a custom machined part, the logical material choice is billet aluminum since it's lightweight, strong, has good heat and corrosion resistance and can look great. |
| 06:11 | Factory valve covers are often stamped steel parts or cast aluminium parts where the manufacturing value justifies the tooling cost and more recently, 3D printed compression moulded and machined polymer based valve covers are becoming more common. |
| 06:27 | However, these are generally not as robust for more demanding applications and the 3D printing technology for this scale of part and material requirement isn't particular accessible just yet. |
| 06:40 | For our manufacturing process we're going to be sending our design to a shop to be machined on a 5 axis CNC mill. |
| 06:46 | It's very important to keep the limitations of this process in mind during our design and there could also be some back and forth between the manufacturer when it comes time to make the part. |
| 06:57 | Now that we have a solid understanding of what we're going to be working on, in the next module, we'll start on the practical work by taking measurements and getting our canvases and 3D scans set up. |
