View this second part of our two-part video and learn how part configuration considerations affect the forging process. In this short video, Queen City Forging President Rob Mayer answers the following questions:
- What is draft and why is it important?
- What is flash and why is it important?
- How do forging tolerance considerations affect the process?
- How do downstream machining operations impact the forging process?
One of the things about forged tooling that you have to understand is that, in impression dyes, we always need some draft in order to have the part come back out of the dye. You've got two dyes that are coming together, you've got half the cavity in a sense in each dye, and we're forcing that material into that dye. We can't have undercuts. We can't have voids. We can't have ways that trap the metal so that the part won't come back out of the dye. So that's why we need some draft to allow that part to release from the dye. Well, in some limited circumstances, we can produce parts with very little draft, or almost zero draft. What we're counting on there is that the material will chill a little bit, will cool off a little bit, in the dye, and shrink back away from those walls so it releases.
As those two dyes come together, the other thing that will happen is there will be material that will flow out between the dyes, in what we call “flash.” Especially if you have fine details in a cavity, you need to achieve pressures inside the dye to make that material flow into those fine details. And trapping the material in the flash means that you're going to increase the pressure inside the dye until it's filled, and then the excess will flow out into the flash. Now we trim that off in a secondary operation.
Now the other thing that happens with forging machines is with all these moving parts, well the dyes may not exactly register. And that's called mismatch. So you may see some mismatch in dyes as well from the process. So we've got mismatch, we've got dye closure, we've got the tolerances of actually making the dyes, and then we've got the change in dimension that is a result of the dyes wearing from making part after part in that dye cavity.
Most forgings that are used as component parts end up getting machined. So one of the things that is very important is that we understand where the fixturing is on those parts. That is where we're going to grab on to them, or where a customer is going to grab onto them, in order to do the machine operations. Then we take extra efforts to control those surfaces so that that machining process is consistent, so that every part is going to be machined the same way and provide the same results.
These are the kinds of parts you want to use in very severe applications or in very specialized applications, where you need to kind of microstructure that you only get from forging. That's why we make forges.