It’s one thing to design a satellite or rover, but without manufacturing you’re dead in the water. Over the years at BLUEsat the problem, or more specifically the cost, of manufacturing has been recurring issue for our mechanical engineering teams. It’s not unusual for the bill for manufacturing our designs to come in at several times our material costs, not to mention long lead times, lack of quality control and no second chances once the part comes in.
Late last year the society decided that enough was enough and purchased a CNC router. A CNC is a simple machine at its core. It consists of a rapidly spinning tool that cuts away at material, which is then mounted on driven guide rails, controlling its position in space. Using this system in combination with computer controls, a CNC router can cut out almost any geometry that we choose.
The process for making a part on the CNC has three stages:
- Model the part in CAD, we use Autodesk Inventor.
- Create a tool path using CAM software, we use HSM
- Secure your material to the CNC router, load the tool path, and begin cutting.
One of the parts that we made recently was an aluminium work holding jig. The model is shown below. This part has some complex features such as bottom rails, notched sides, counterbored holes and raised supports. To make this part by hand would take days and a very competent machinist, and we don’t have access to either.
Using this model, a tool path was developed with CAM software. The program does most of the heavy lifting, but the user must define the positions of each feature, the speed the machine moves at and how fast it will spin. These speeds are very important to the quality of the final piece and must be tailored to each feature. Below is an example of what the tool path looks like on the computer, red lines indicate that the machine is moving, blue lines show it is cutting.
Finally, with our tool path created, we were ready to set up the CNC itself. The material needs to be secured to the surface of the bed to prevent any movement during the cutting operation. This can be done in a number of ways, such as using a machine vice or work holding clamps. For this piece, we started with work holding clamps and then secured it using holes drilled into the material itself.
Now onto the fun part, the cutting. The tool path is loaded onto the CNC and the machine is set to run. Generally, we do a single operation at a time. This gives us time to clean up after each cut and inspect if it was successful. Here are a few videos of cutting.
Using our CNC has allowed for rapid prototyping of parts, drastically reduced lead times and most importantly, cut manufacturing costs by an order of magnitude.