“Dirt Road -Fremont-CA”by Benefactor 123
We all cringe when we see a rough road sign in our path. The jagged accelerations chatter our teeth and shake us to the very bone. Immediately we want to get the road crews out there smooth the rough edges. A die casting machine reacts much the same way when abrupt changes of speed are commanded. We have all seen the “chatterbumps” in the shot traces as the control struggles to obey our commands.
I can remember making barbecue lids on a machine that effectively had a one speed shot. It was necessary to trigger the fast shot almost immediately to have any chance of accelerating to the 120 inches / second needed to fill the casting. I suspect that there are still some Lesters still working out there with a two speed shot.
Having experienced lots of “chatterbumps” it is refreshing to have the capabilities of a modern control. The Visi-Trak control
http://www.visi-trak.com/Media/Vann_Proof_withAd.pdf
running the rebuilt Prince at Cana-datum has up to 6 settable speeds and 6 settable accelerations. I was an old fashioned 3 speed shot proponent until I experienced a full speed launch of a transmission case. Applying targeted smoothing of the speed transitions made it possible to move the porosity out of the seal bores.
Acceleration control solved porosity issue
Having been trained to improve porosity issues by tuning gate and runner shape, I was excited to discover that tweaking of the fill profile actually was helpful and a whole lot easier and quicker to implement.
Shot profile for a transmission case
Since I published this post, my contacts at Visi-Track have given me this link because it is related.
Following is a link to where you can download the Ohio State University paper called “Experimental Determination of Slow Shot Velocity Position Profile to Minimize Air Entrapment”: