Detailed forged wheel information from HRE
This is from the COO of HRE in response to information discussed on this thread:
"Everyone uses Closed Die Forging. Open Die or Hand Forging isn't accurate enough and is sort of the modern hammer and anvil. In terms of forging from a circle blank, I don't know anyone that does that as you would in fact not get much benefit from the forging process. The material has to flow and a lot of energy needs to be imparted into the material in order to change the crystalline structure. If you just pressed on something that was already near the final shape, you wouldn't gain much, but I don't really know of anyone that does this.
In terms of 1-pc, the forgings start from bar stock as well and they are close die forged into a blank and then the barrel part is spun. The is the where the forged/spun term comes from. This method of spinning the rim from a forging is actually called flow-forming. In comparison, on 3-pc rims the barrels are spun from 5 mm thick sheet, not a solid. It is almost the same process and uses the same type of machine w/ a similar end result, but w/ 1pc, you have to go back and do a final machining pass. This does allow the 1pc to be extremely precise though if done properly.
Crimsone90's post about these methods is accurate. His earlier post about HRE was not. He assumed we didn't do it the right way. I really don't know many that don't do it like this, maybe some of the cheaper guys, but not anyone that sources from APP or Japan.
There is another source where people use "rotary" forging. Basically the die isn't completely closed and it is tilted at an angle and the 2 die halves are spun relative to one another so the material is squeezed as it is compressed. Some say this is superior to APP's method in orienting the grain better which is actually incorrect because it puts a twist in the grain relative to the spokes but in all honesty, the grain direction in aluminum is not critical. The strength difference is not that high going transverse to the grain direction, but it is nice to have it aligned properly. This is why aluminum in theory is usually treated as isotropic. Once again, this method is much faster and cheaper so a lot of wheel guys use these types of forgings, but we've found the quality to be inferior so we've never found a supplier capable of meeting our minimum requirements. More marketing than practical benefit from our experience and the savings weren't worth taking a quality hit. This could simply be the quality of the company and not the process so we aren't opposed to the process as much as to the companies that supply this type of forging in the U.S. I think Rays Engineering (Volk) uses this method to good effect, but their quotes to us were actually higher than APP so not worth it as APP is already expensive compared to everyone else.
Basically the focus on manufacturing methodology shouldn't be the main concern. In the U.S. there are so few regulations that it is simply too easy to be in the wheel business. You don't have to properly engineer your wheels or meet any minimum requirements like TUV or JWL. We design our wheels to these specifications and the U.S. equivalent RECOMMENDED by SAE, but just looking at our "competitors" at SEMA makes it horrifyingly clear that most don't know what they're doing.
I told my engineer that with time he'd be able to walk through SEMA and see which wheel companies had proper engineering resources and which didn't just by looking at the product. It takes a little bit of experience, but after a while it is easy to see. Companies like BBS an Volk clearly know what they're doing and we can see it in the subtle proportions of their wheels but there are too many out there that from a distance look like an HRE, but up close it is clear they have no clue what they're doing. It is really scary for us but once again, we're in this for the long-haul so we're going to do it the right way and the hard way.
I could make all of our wheels weigh under 20 lbs, but they wouldn't hold up an M5 for more than a few months or a year or so. This isn't a big deal if you're going racing and you're going to continually inspect your wheels and throw them away after a season and you've run the life out of them, but for road wheels, they need to last the lifetime of the vehicle. A rear 1pc forged Porsche 997 TT wheel weighs 31 lbs. It isn't because the Porsche engineers don't know what they're doing!! It is because they're being safe and conservative.
In the U.S. I, too, am wary of most wheel guys, especially all the new 3pc guys, but not because of the manufacturing methodology, but by the lack of proper engineering and testing. Basically there is a company here in SoCal that will cut, box, and ship a wheel for you based on your design without an engineer ever taking a peek at the design. A lot of people are jumping into the wheel business trying to be the next HRE. We call it draw and cut. I know the designers and they're either artists or machinists. Smart guys, but not properly educated to be doing something that is such a critical item when it comes to the safety of your customers.
This is why HRE now has open house events. We want to show people that we're not like everyone else and we welcome everyone to go visit our competitors to see the difference.
Anyway, I actually agree w/ Crimsone90 on his info... just not on his HRE info."
Lake Oswego, Oregon, USA
2015 M4 Coupe