DGR Homework: parting line height and relative stabilities

[jubuttib]

^^^^This is what the guys at MVP told me when I showed them my big D cfr PD and the Z NukeOS...They said both discs looked like they cooled in the mold.

Evidence is mounting.

[keltik]

...If you have access to SolidWorks you can do a mold flow analysis on the tooling itself.

I don't have access to the mold. I would only model a generic putter, a generic mid-range, and a generic driver. I would make up the shape, based on typical forms of each variety. Maybe I would pick a few from the Discraft profiles posted on their website.

I think you would have to know the exact chemistry of the plastic to do a thermal expansion analysis. and for that you would probably need a mass spectrometer. and then you'd still need to know the molecular structure of the compound in both its fluid and solid states. Then you could possibly say how the atoms/molecules reorganize themselves after a thermal event.

The point isn't to simulate the process, rather, the idea is to model the process. There's a difference. In modeling, I would vary 3 parameters: the total thermal expansion/contraction (expansivity times temperature change, a dimensionless parameter), and a suitable pair of elastic parameters (e.g., the bulk and shear moduli). I would step through combinations of these parameters over the range of variation exhibited by all plastic types, and I would use the results to find out how PLH, dome, etc., varies systematically as these physical parameters are varied. The results could later be applied to any particular plastic, by simply looking at the portion of parameter space that is relevant to that plastic.

well you could take a guess at the tooling. You would first have to model the disc itself. Using the Discraft pictures is a good start but you'd still have to do your own measuring to make sure the scale is right. You could always cut some discs in half and then trace the profiles, scan, then cut and paste into ProE, SW, or Inventor. There is a thread somewhere on here where ZAM explained the mold pieces and made a drawing/sketch of how they mate together. you could do a three piece mold. or if I have time at work I could mock up what I think the mold pieces could look like and send you a STEP file. if you want.

I'm still doing the Wolowitz on your thermal warping (for lack of a better term) model. I'm only an engineer. we have to mull things over and then hit with a bigger hammer.

still PM me if you want some 3D CAD models.

[JR]

No need to dice and slice a disc because you can measure the height of a disc with calipers and relate that to the diagrams on the Discraft site.

[JHern]

...The point isn't to simulate the process, rather, the idea is to model the process...

...you'd still have to do your own measuring to make sure the scale is right...or if I have time at work I could mock up what I think the mold pieces could look like and send you a STEP file. if you want...

Thanks for offering, I need to emphasize that I'm not simulating any given disc (at least right now). I'm going to do a "driver-like" profile, a "mid-range-like" profile, and a "putter-like" profile, using the most generic possible mold shapes. Then I'm going to see how much the shape changes out of the mold, and how it varies with plastic properties. I can tweak things around, flatten the dome to different degrees, etc.. Right now, I don't care if I get everything exactly correct in every dimension, I'm not trying to replicate any disc, just trying to get a sense how disc shape differences affect the shrinkage, this is for the purpose of understanding.

The model will be 2D axi-symmetric. I think I can find some open source modeling tools that should work just fine.

[JHern]

I talked to some guys who used to mold discs for Innova...

.... Iiiiiiinteresting... This could actually be a plausible explanation to why so many of Innova's CFR runs are A) more consistent and B) more overstable (not all, but many), and production runs are A) all over the place and B) on average less stable. If they're pushing them out for a big production run they don't have any extra time to let the discs cool in the mold, whereas when doing a smaller run for CFR they can be more careful and let the discs sit a bit longer...

Just a thought, purely hypothetical.

Makes perfect sense to me. I'll see these guys again tomorrow, I'll ask them...

So I asked about this (over a friendly game of poker), and the answer was that they were almost always trying to run the discs at the highest possible production rate, and at least during their tenure they don't recall taking more time to let the disc cool in the mold for CFR or any other discs, at least that's not what the boss wanted. They didn't want to let the disc cool too long in the mold because it comes out way more over-stable than anyone would really like, and the cost of production per disc grows dramatically.

The answer we came up with for why CFR runs are "A) more consistent and B) more overstable" is because of the plastic, it is usually better blend that shrinks less than crappier plastic, thus its shape more closely reflects the shape of the mold.

It's interesting, because in designing the mold itself, you have to plan for shrinkage as part of your regular production (and you have to plan for a given production rate and cost). The Firebird mold itself has an extremely flat top and absurdly high PLH, not because that's the way they want the disc to be after molding, but because if they want to make a disc every 30-40 seconds, then shrinkage will occur and it has to be taken into account. And the shrinkage is plastic-dependent. It seems like the typical behavior is that DX and Pro shrink more than Star, which shrinks slightly more than Champion. This is why molds designed in the DX era make better discs in DX plastic, and why those molds run with more modern poly-urethane rich blends tend to be over-stable in comparison to those run in DX plastic. And this is also why Champion tends to be the most over-stable (relatively), then Star, then the DX and Pro are the most under-stable.

Does this make sense to everybody? Let me know if any part of this isn't clear...I think this is a good thing to understand about the molding process.