A brief primer on how the injection molding process affects flight characteristics

[lyleoross]

Why do different polymers have different flight stability? Is it that they have different warpage?

 

[Beener]

Great post! Spent a decade in the mold design and manufacturing field; brings back some good memories...

 

[jakebake91]

I love getting the real-deal info on how things work. This is really interesting.

One question about metal flake: It's not really metal, right? I think I saw someone get an answer directly from a manufacturer confirming that.

I build and repair injection molds for a living. I can guarantee nobody is putting real metal flakes into the plastics. That would be disastrous for the mold.

 

[AdenoidHynkel]

Why do different polymers have different flight stability? Is it that they have different warpage?

They have different shrink rates which results in different warpage.

 

[lyleoross]

They have different shrink rates which results in different warpage.

And is there a pattern to the warpage? For example, is it always that the wing falls, or is it always that the dome rises or a combination of the two? Or is it more complex with other factors weighing in. Or do the factors balance? If the wing drops the top is less domey.

 

[Putt for D'oh]

My question relates to mold size and item weight. When companies make a mold (i.e. disc) a certain weight, I assume they control density of the injected material (cuz aren't the Star, Champ, Blizzard, Pro, and DX often from the same dye or cast?). So if I want a max weight Firebird, or Nuke, or Aviar, I'm designing that before I inject the plastic, right?

Now my question. If that disc was designed to be 175 grams but weighs 172g or 177g on a scale, then what happened? Was some of the mold underfilled? Or was the density just off?

Trilogy for a little bit now has the disc weight (and name) molded on the underside of the flight plate. Innova has finally started following suit, (just name and still penning weight?)
So that makes me believe they are shooting for a weight when setting up the mold before they start the run, and not an after the fact stamp. I'm sure the mixtures that are being used to change the density and weight for these runs are difficult to make exact and maybe the first discs in the batch run a little heavier or lighter. Some discs have more or less left over scrap of plastic at the injection site as well. I usually ignore it but i've had discs that were 2 grams (my scale) more than their weight on the disc, well cutting off all of that material at the bottom center of the flight plate was 2 grams. I think most discs it is less than a gram of material there but could explain when it is heavier than intended.

 

[wims]

Its not in the mold, its stamped on the disc. It's actually a relief, not an emboss

 

[Flick Maniac]

I really dont think they have a mold piece that says 167g, 168g, 169g for each weigth, and swap it as needed. I think it is some kind of post process. Now the mold name I could see since that ought not change. Didnt they say that the guys weigh a stack of 10 and then divide by 10 and pen them all the same. Thats how you end up with "penned 172 scaled 173.4" posts

 

[Countchunkula]

OP here. You're right that most of the cooling occurs in the mold. Climate does have an effect on the final shape of the disc since it will continue to shrink for a few hours after it leaves the tool, but it's not as major of an effect as some of the other things I listed. I'd reckon that how they store the discs immediately after they cut the sprues off has a larger effect. If they stack them, the ones on the bottom are going to have a different shape than the ones on top.

Welcome to dgcr and thanks for the knowledge!:thmbup:

 

[Putt for D'oh]

Its not in the mold, its stamped on the disc. It's actually a relief, not an emboss

Wow... I had never really inspected close enough to see that it is stamped and not raised up like the brand and disc. hmmm... their scales are probably a bit higher end and better calibrated than mine, maybe thats why I got different weights... but I have cut 2 grams off a disc at the injection site, I normally leave that stuff alone now.

 

[uncle pennybags]

Newer discs from Discraft have the names embossed on the inside of the rim.

 

[Countchunkula]

Newer discs from Discraft have the names embossed on the inside of the rim.

It's been that way for quite some time. At least 5 years, probably 10.

 

[Discette]

I really dont think they have a mold piece that says 167g, 168g, 169g for each weigth, and swap it as needed. I think it is some kind of post process. Now the mold name I could see since that ought not change. Didnt they say that the guys weigh a stack of 10 and then divide by 10 and pen them all the same. Thats how you end up with "penned 172 scaled 173.4" posts

Each disc is individually weighed and marked as it is produced. Discs are not weighed in groups of ten and then averaged.


Since pictures are worth a thousand words, please watch the Gateway video posted above. Note that Dave Mac takes the disc from the machine, clips the sprue and places the disc on a triple beam balance scale. Dave then adjusts the scale and writes the weight on the back of the disc and places the disc on the table to finish cooling. Dave doesn't stack 10 discs on the scale and weigh them together - he weighs each disc individually as it is produced.


Over 10 years ago some poster theorized on the PDGA message board that 10 discs are weighed at a time to explain why weights could be different than marked. Posters continue to spread the "10 discs are weighed together" myth/theory even though the weighing process is clearly visible in the Gateway video.

 

[jakebake91]

Each disc is individually weighed and marked as it is produced. Discs are not weighed in groups of ten and then averaged.


Since pictures are worth a thousand words, please watch the Gateway video posted above. Note that Dave Mac takes the disc from the machine, clips the sprue and places the disc on a triple beam balance scale. Dave then adjusts the scale and writes the weight on the back of the disc and places the disc on the table to finish cooling. Dave doesn't stack 10 discs on the scale and weigh them together - he weighs each disc individually as it is produced.


Over 10 years ago some poster theorized on the PDGA message board that 10 discs are weighed at a time to explain why weights could be different than marked. Posters continue to spread the "10 discs are weighed together" myth/theory even though the weighing process is clearly visible in the Gateway video.

Gateways operation above is probably different than say innovas though.

 

[Halcón]

It's not Dave who's weighing the discs in the video. (Unless by some freak coincidence that dude is also named Dave Mac)

 

[Halcón]

Gateways operation above is probably different than say innovas though.

Yea, but Discette has no clue how Innova's operation is. :|

 

[Discette]

It's not Dave who's weighing the discs in the video. (Unless by some freak coincidence that dude is also named Dave Mac)

The video features David McCormack, the owner of Gateway discs.... aka DaveMac. However, I see that Dave isn't actually the one weighing the discs, Dave was making the mix at the beginning.

 

[Halcón]

The video features David McCormack, the owner of Gateway discs.... aka DaveMac.

I know, just giving you a hard time.

 

[Putt for D'oh]

Each disc is individually weighed and marked as it is produced. Discs are not weighed in groups of ten and then averaged.

*SNIP*
Since pictures are worth a thousand words, please watch the Gateway video posted above.

*SNIP*
even though the weighing process is clearly visible in the Gateway video.

Not really get obtuse on this one, but why the hell are they using a triple beam balance and not a digital top loader?

Also... picture worth a 1000 words (funny was thinking about that comment earlier totally unrelated and how it is so beyond relevant anymore)
The video makes it seem like they weight the discs and then remove the flashing... I'm sure that isn't the case but... if we are supposed to watch and learn from the video...

 

[zontar]

i guess the triple beam goes with the general stereotype of disc golf????