Why is SolidWorks clamp tonnage so far off from the actual tonnage at the molding machine ?
I have tried finner mesh, different materials, I have entered the process settings from existing plastic parts but the software is always way off. Does anyone know why?
Thanks
Bill Sardini
Design Engineer
Caplugs
Yes
I see, just found it.
could you give a bit more information?
it sounds like you have results from experience/physical test what is the clamping force required?
and what are you getting out of SolidWorks plastics?
i'm not a plastics expert but is there a way to estimate the clamping force? how close is it to physical and the simulation?
it sounds like you're going about things correctly, just trying to understand more about the problem.
I am running a SolidWorks Plastics flow simulation on a 36" pipe cap. I am going to let it run overnight. It takes a while. I have the actual values from the molding machine. I will post both tomorrow along with a manual rule of thumb method of calculating.
Thank You.
Bill
Hello again Jared. The flow sim finally finished. Here are the results from SolidWorks Plastics. I entered the same plastic material process settings
Y-dir. Clamping Force= 1894.3430 Tonne (2090.0000 Ton U.S)
Requiring injection pressure= 97.5948 Mpa (14200.0000 psi)
The common practice rule of thumb calculations
(area x 2.5 ton + (10% per inch over 1") = 2738.00 ton.
The actual plastic part (36" pipe cap) runs in a 950 ton Toshiba at 931 tons.
I am missing somthing or some of the information is incorrect.
Thank You
Bill
so rule of thumb predicts 2738?
software predicts 2090?
and the machine requires 950?
Yes that is correct
Thanks
Bill
any ideas why rule of thumb is so far off from what's required on the machine? probably should figure that out before we try troubleshooting the software.
These rules of thub have been around sence the beginning. Long before software. I believe both have a large safety factor. Which is a good thing. The other major factor is the plastic material Viscosity and wall thickness. MFI Melt flow index. Solidworks Plastics is limited in material option selection. For LLDPE there is two. I tried both. So all I can do is select closest material in the database that I can find. I need to create a custom material that is closer to what we use or find the software settings so that the flow analysis comes out closer to the actual process. This is time consuming. Some of these take 8 hours or more. It is not easy. There is about ten pages. I am not a chemist. I tried to get material (from Matweb) information but it was not enough. Typically it is not a big Issue. They can make spacer plates and put it in a larger molding machine. I am working on a 42" pipe cap that is going to run in a 1500 ton press. There are no other press options with-in a couple hundred miles from here. There is no fix. The estmate needs to be accurate the first time. Based on the 36" I made wall thickness adjusments to accomidate the larger diameter flow distance. I believe it will be close but it will be fine. It would be nice to show the 20,000.00 dollar SolidWorks Plastics softare is worth it. I would love to be able to print a Mold Flow report and have the confidance to show the company it will work. Thats why I was hoping maybe someone else had been down this road and could show some insight on creating custom material's or software settings.
Thank You
Bill
a couple of things
1. from a software perspective. let's say the discrepancy of 1140 is just the "difference" that exists between real and software. do you think it would be safe to say that if you keep everything else constant and only change the geometry that as long as you don't go above 2640 in the software, you'll be able to compare "relative" performance?
2. in #1, i'm not condoning that because the delta is so great but sometimes there are calibrations between physical and simulation that are needed. but what you're seeing is far too much. there are few settings inside the software that would eliminate numerical inaccuracies so my guess would be setup. a couple of ways that i'd go about this problem if it was a tech support or consulting project that i was involved on:
A. what other models do you have that you can try? to see if this "calibration" stays constant?
B. are there are any known good solutions that we can compare the software to. IE, you have calculated a value, you've seen that in physical (2 data points) and now we'll check it in the software.
C. you mentioned the materials aren't different. what else may be different from a process perspective? this is probably going to be the most important part of the investigation. this is what is going to have the biggest effect on the results.
as for getting materials into the software, I believe there are a couple of manufacturers that let you import directly. have you checked with them?
As far as number (1.) I understand what you are saying but I can't make that assumption. Let me put it this way, I can't make a presentation endorcing a 5' x 5' injection mold for 150,000.00 that show's I am making this assumption based on the 20,000.00 software that I recommended to save time and money and to improve accuracy. To take the guess work out of it. Personally I love the software. I think it is great. The software is usually close to the industries rule of thumb. However the company needs to see it was worth it. This would be a good project for the software to shine.
As far as (2.) A, B, and C. Been there done that. I have contacted the manufacturer, I have sent several models to solidworks, I have gave them all the material information I could get. The results as I said are close to manual calculations in general. Probably within an acceptable percentage. Usually within 5%. On this 42" pipe cap project the manual calculatons are showing 2738 tonnage required. The software shows 2778 tons required. Which is fine. Very close. But nowhere near 1500 tons. No complaints from me. Some how we run the 36" pipe cap at 931 ton's. So if I make a basic calculaton based on the diameter the 36" diameter the 42" should run at 1086 Ton's. The parts are Identical except for the Diameter. Based on experience I believe it will run in a 1500 ton press no problem. I have entered the information from the press setup sheet on the 36" cap for the 42" simulation. The conclusion is I am obviously missing somthing in the software that is not consistant with what is actually being done at the molding machine. I was hoping someone would have more experience with SolidWorks Plastics could help with this. Trial and error (changing settings and re-running simulation's) at approx 8 hours each takes forever. I start them before I leave, and they are usually done when I come in in the morning. But not always. Depending on how fine you setup the mesh. I will keep trying. I will eventually figure it out.
Thanks Jared
Bill
bill on 1, i agree with you, but to get to the bottom, if you see the same trends it might help you understand what is going on.
2 it might be worth posting your setup to see if anyone has insight on what might be affecting it. if your settings are exactly the same as they are in the physical case, i'd be confused too. you said you took this to your resller/solidworks, what did they say?
They are working with me. Doing a good job. They have recommended materials in the database and they are more accurate. Comparitively SolidWorks plastics results are more accurate than the number 1 compettors plastic flow analysis. I have had the same parts run on both softwares. So I am really not complaining I just dont understand why such a big difference from the software to the actual. This is an extream case where I need it to be extreamly accurate. It may not be obtainable or reasonable for me to expect that. It seems however if I could find the setting I could dial the software in. The other thing that may be confusing me is the terminollagy at the press and the software are not exactally the same. So Its quite possible I am missunderstanding settings and where they should be entered. I am not a process engineer so I don't setup molding machines and run plastic parts. I believe it is a setting I am missing. There is a setting called aspect ratio at the press. Do you know where this is in the software? I think this multiplies the injection psi pressure by a factor of up to 10 times. This would change the results considerably. The software for the 36" is telling me 2100 tons and we run it in a 950 ton press at 931 tons. The software is very close to the manual way of calculating. So I don't know. I have seen with my own eyes the 36" cap running in this press otherwise I would suspect I was given incorrect information. I am going to run some more simulations. There is obviously a condition at the press which enables them to run this part that I am not simulating correctly. I am going to send some more parts to the VAR. I will post any information I find out. I did have the SolidWorks Plastics training. I have done much research. There is allot to learn.
Thanks Again Jared
Bill
sounds good bill.
just thinking if you post your settings, someone might pick something out that is obvious. but let us know how things go with yoru var and solidworks. i'm curious myself.
I don't have the answer, but what part of SW gives you clamp tonnage for plastic parts? Is this an add on program?