Injection Molding Fill Only Procedure
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- Опубліковано 12 кві 2020
- One of the critical principles of plastic injection molding process development and troubleshooting is the fill only part. Known by many terms like fill only, first stage, and 95 - 98% full shot, RJG® Inc. has created this short video to demonstrate a procedure for developing a fill only shot.
- Наука та технологія
The weighing scale is my #1 instrument. I also recommend it as an in process control, independent of cooling time. Tracking variation in part weight is an early indicator of process drift
do not forget to mentioned about the cushion condition
A very useful video for me, thank you, and wish your more videos about the injection molding!
We're so glad you enjoyed it! Thank you!
Hello, I like your video, I'm still learning even after 17 years injection molding.
I contribute that any adjustments made per die design need shot stabilization.
Actual results depend on repeatability.
Hi John. Thanks for watching and contributing!
Gate freeze off analysis will put you on good shape mate
Thank you and lot of love from India
Thanks for watching!
We run validated processes, and I lock down fill time within a range (very tight range ~.08 sec delta from min/max. Very small parts 2-8 grams) This keeps techs from changing transfer/shot size or injection speed outside of a tight window that the process was built off of. The fill time is tied to a visual fill only picture in process sheet. I agree weight would be better, but the reality of a tech bringing a scale to every press for every process change or startup is not as high as I'd like it to be. I should also note, we run 100% virgin material. My question is do you see variance from lot to lot of material or with regrind percent changes where they would need to stroke the screw more and would affect fill times?
Thank you for this. I went through the RJG Master Molder I course and had this situation happen at work today. For some reason I was trying for 95-98% full of a CAD Model weight... yeah
haha, it happens to the best of us! We're so happy this was helpful. Will we see you soon for Master Molder II??
Has this been updated since this video was published? I’ve been trained by RJG to always have a small amount of a short shot at the end of fill, and that sinks are not good enough as this could lead to dieseling, flash, etc.
This seems more like establishing a Decoupled 3 process with cavity pressure sensors to me.
It seams like a more repeatable process than just visual. However you would have to do this at the beginning of every restart and batch change. Not to mention regrind percentage adjustment. But, it also seams that you should be doing a “fill only” procedure at regular periods anyway. So it’s not that much more work. I will definitely play around with this while we wait for the corona to pass.
Reestablishing the first stage at regular intervals is always a good approach. It should be one of the first approaches to troubleshooting. Any of the scenarios you described would cause a viscosity shift. Verifying the fill only part can ensure a more repeatable, robust process.
@@rjg What range would you set for something like this. If the viscosity does change than the density of the part will shift as well. That is the benefit of a visual standard is that no mater the viscosity and shear of the plastic going into the mold the part should look the same. If weight is your standard in a process to verify changes in viscosity or machine repeatability(check ring, load cells, etc) AKA Weight, it would seam that there has to be an allowed range.
Also, If you are going by "most full" cavity doesn't that allow for velocity/viscosity changes for the less full cavities. The goal is always to have a mold with less than 6 percent cavity imbalance. This would work fine in that scenario, but if the mold is a leftover from the 90's with 20 or more percent imbalance that this wouldn't work as well. At our facility we perform our fill only till 98% of the last part to fill. This way the parts all fill at the same speed and "compensate"(Big quote fingers) for cavity imbalance( as long as venting is appropriate). This method is of course not a solution for pure scientific molding. However it is a real world scenario that is all to common.
@@LockSmithNinja The fill only part would typically be used as a reference and not as any quality standard or metric. If you choose to use this method, then you could take a photo of the part and still use that as a visual fill only. The important thing is that we can institute a consistent method for how you got to that visual part.
You bring up a good point in regards to cavity balance. That's the exact scenario that Marty was eluding to in the video. There are always going to be circumstances where we might have to deviate from the norm as you have pointed out. There are also materials and geometries where you cannot short the fill only because the material will freeze.
Full disclosure I work for RJG in the consulting and training department.
@@LockSmithNinja Yes that sounds about right for real world applications a lot of company's run the molds to the ground and only repair when they have to.
Variables are key. Nothing is perfect in this world
I want to ask. Parameter Set N-Fill On is used for parts whose criteria are like what?
Are there exceptions for this rule? Does it work for every part?
Great question! This process will cover about 98% of what's out there, but there is one special exception: parts with a hinge. Because of the pressure losses across the hinge, we get a big difference in density upstream (high) and downstream (low) the hinge. That means the part will be very short, even if the weight is at 99%.
My question what you need to do for the first trial shot ? What are the steps in adjusting parameters
The first shot into the mold can be a bit stressful. There a few options:
1. Use solid model to get the volume and then calculate the shot volume required
2. If you have an existing part , weigh it and use the specific gravity of the resin to calculate the shot volume
3. If you don’t have either of the above , the last resort is to use your experience and guess on the low side. This carries the most risk. Be sure to set safeties on your machine in case you guess too far from what is needed.
In our training we cover these techniques in more detail. Hope this helps!
When you set up the holding presure at half of the max injection presure, how long in secs do you hold it for?
So far I've been using the rule of fillig 95% and then playing with the holding time to get the full shot.
Thanks for these videos, they are well explained and very helpful!
We use a hold time study to determine the correct amount of hold time.
Gate Freeze
run a gate freeze study, ideally should be abt 1-2 seconds above your gate freeze time
The way i was taught was to just gradually increase pack/hold time until the part is packed out.
How to do a short shot method is it useful to prevent damage on mold?
Mold damage usually occurs when the mold closes up on something. Establishing the fill only correctly helps with not overfilling or underfilling the cavity. It also helps you fill it the same every time.
Hi! Do you select content based on upload? And what is this V-P CHG function, is it loading? Sorry not ponel...thank you in advance!
The V-P change function is the setting that changes the machine from the Velocity filling phase to the pressurization phase of the process. This has different names on different brands of machines , ie. V-P , Transfer , Cutoff , Switchover ...
@@rjg switching from injection to holding under pressure?
I have one question, is the facility you guys shoot your videos in climate controlled?
Hi Joseph, no it is not. 🙂
Should lead up to a gate freeze off then you know your
Pack and hold time willl give you your optimization of part weight. Without gate freeze of you don't have control of your stability of weight and optimisation
Yes, a gate freeze study is another part of the process development. Gate freeze would typically be done after fill speed selection and after establishing the correct fill only. After gate freeze then you may do a tonnage optimization, cooling study etc.
So why 99%? Isn't the "rule of thumb" 95-98% full?
We have changed how we teach to a more defined way of establishing a fill only. Previously is was 95-98% visually full. That method was highly subjective. 99% by weight when the fullest part becomes full without hold is much less subjective.
I notice you didn’t adjust the injection time our nissie presses are old and you have to drop pack as low as you can changeover speed to zero and make your fill time your injection time. Is there an easier way, if their was that would be extremely helpful, because my teacher Tim Weston has said if you go past transfer in your 95 you have not decoupled successfully. Which I get setting your pack to zero and changeover speed to zero you won’t travel far past transfer but as far as d2 you didn’t do it right
There are a few different ways to make a fill only part. A few things to keep in mind is how your machine works and another thing is to do it consistently the same way. My preference is to only turn the hold pressure off and leave the time on. Now if the machine’s idle pressure when set at zero still fills the mold then I may turn off the time also being careful that the screw recovery is not extruding material into the mold.
@@rjg good point I never thought about it like that, thank you for the explanation
This looks like the Gibsonville NC training facility
It sure is! :)
Best machine nizzeljapan
My question is how to rid off high gate and hair flash in centre? THANKS
High gates might be over packed or valve gate not shutting off correctly. The flash in the center could be filling to fast at in/s.
Is it material dependent? Whether 99% or 98% fill
It has more to do with the part geometry, mold construction, and machine response. The further you can fill the mold and repeatably make an acceptable part... the better.
Sir I like urs video.sir my question is how to calculate shot size and it's formula.
Well the universal method is pick a shot size drop pressure as low as you possibly can take a shot and find out where it ends up and adjust down from there. Another solution is to get the parts weight from a blue sheet, lookup the extension values on your material and guestimate it.
Hello, Marty, I just wonder what's the meaning of "transfer" in1:03 time, could you give me a cue，thank you in advance!
Hello! The term transfer refers to the stage in injection where the filling of the part or screw forward movement switches from speed control to pressure control. Machines give the option of transferring off time, pressure, position, or cavity pressure. Decoupled II molding separates the process into a fill portion and a pack and hold portion. The point at which we stop filling with speed and start using pressure is known as transfer and is done with position in Decoupled II molding.
@@rjg Thank you for your kind reply, i have understood the transfer meaning. There is only two other things i can't undertand, one is "place our pack and hold pressure on here" in 4:40 time, what's the meaning of "pack"? One is "I have already removed the packed hold" in 00:56 time, what's the meaning of "packed". Thank you in advance.
Would a difference in part temperature have a difference in weight?
The melt/mold temperature could influence the fill only weight and is why it is important to match all of the plastics variables.
In larger cavity molds specifically in HDPE sometimes shot size plus the mold temperature has to be increased,
Can you also give training for PET Sipa machines ??
1. I believe SIPA machines are blow molding. We do not do any training for blow molding, only injection molding.
2. Can you clarify, the shot size and mold temp need to be raised compared to what? In injecting molding the mold temp is dictated by the material and the shot size is determined by the volume of the part being molded.