2022 Wheel Flange & Package Manufacture
This was perhaps one of the most complicated parts that I had to machine this year. The wheel flanges are an integral component of the wheel package assembly, connecting the upright, brake rotor, and bearing. This year they were manufactured from 4340 steel. The flanges were manufactured on a Tormach Mill, Tormach Lathe and Okuma Lathe (manual).
Tormach Lathe and Mill CAM
Using Fusion 360, under 'MANUFACTURE', I configured the following operations using their CAM (computer-aided manufacture) feature. On the Tormach lathe, these operations consist of facing, turning, and boring. On the CNC mill, adaptive clearing and a contour selection to cut the brake rotor spline.
Okuma Lathe
Unfortunately, a large portion of the flanges had to be manufactured on the Okuma lathe as the Tormach Lathe did not have the horsepower to allow for some of the critical turning and grooving operations. The setup on the Okuma is pictured below. It includes a 6 jaw chuck, a live center and liquid coolant. The main operations that were completed on the Okuma were boring the hole through the stock (to 875 thou with a precision of 4 tenths) and grooving/turning the mid-section of the flange (pictured below).
CNC Operations
On the Tormach Lathe, it was quite a process to turn down the 4.5 inch 4340 stock to the required diameters, the smallest being 1.54 in (200 thou off 1.34 in, a critical diameter). Many of these operations exceeded 6 hours of run time. This was compounded by the lower hp provided by our CNC Lathe which meant reducing pass sizes to 10 - 20 thou.
Other issues included ensuring a good surface finish. This was a balance of pass sizing and figuring out the best RPM (or whether to go with a constant SFM instead). Smaller adjustments which still had a significant impact on the surface finish included coolant flow and the state of the carbide inserts I used. Below, the the boring operation on the CNC lathe is displayed (the CAM simulation can be found above).
On the Tormach Mill, in order to mill the spline contour, I had to machine a pair of soft jaws that specially fit the base of the flange. This was because we didn't have a pair of v-blocks that were large enough for the 4.13 in diameter base. Additionally, in order to reach the spline without making contact with the rest of the flange, I borrowed an extended tool holder from the JEPIS shop (at Brown) that perfectly held the 3/16 endmill.
Below, the spline contour is machined with the extended tool holder and custom soft jaws. The other Tormach Mill operation (pictured below) involves machining the 'nubs' at the base of the flange. The nubs are critical as they ensure a fit tight enough so that the wheels are secure, but also a fit lose enough in order for the wheels to be easily removed and replaced. The setup involves the use of two v-blocks and parallel bars to secure the flange in place. The center was found by dial indicating the part into position.
Finished Flanges
Unfortunately, after the heat treatment process, we realized that the 'nubs' had expanded by 2 thou in diameter (which was more than we had anticipated). This meant that the flanges no longer fit properly into the wheel rims. As a result, the four flanges pictured above were scrapped as there was not enough time to remake the parts in time for competition. Instead, we re-used the wheel flanges from the previous year.
Looking back, in the future, the flanges do need to be made earlier in the year. The CAD files will also be adjusted to reflect a more realistic expectation of the heat expansion. It is important to note that I did not design these components, I machined them. Next year, however, there are definitely more areas for improvement. A primary one is the material we use: 7075 aluminum (aircraft grade) is a viable option instead of the less expensive but much heavier 4340 steel. This would also make the machining process much easier and quicker.
If the parts had come back from heat treatment as expected, the final two operations would have included: turning the end of the flange to its critical diameter (at a very slow pace, 1 - 2 thou passes) and creating the inner spline on the EDM (electrical discharge machining).
