What Actually Causes Flash in Injection Molded Parts?
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- čas přidán 12. 07. 2024
- Flash is one of the most common defects in the injection molding industry. There is a lot of misinformation on the cause of the flash. This video from RJG® addresses one of the leading reasons for flash and discusses ways to troubleshoot and identify the causes.
Learn more, view upcoming courses, and register on our website: rjginc.com/training/courses-o... - Věda a technologie
I'm recently retired from the injection molding industry after nearly a 40yr career, sure have indeed witnessed the industry evolve over the years from when I first started in the business, good to see students of the trade being taught these simple straightforward fixes, keep up the good work RJG!
I can't begin to number weird things I've discovered over the years as to the root causes of flash, from broken tie bars to molds being hung incorrectly some are just merely simple water cooling issues other tougher problems with fill and flash can be rather difficult to solve, especially on very complex parts :)
40 years is amazing! I am sure you are wealth of information. Thanks for the comment and thanks for watching!
@@rjg thx, most of the newer techs at my old company, Mikros Engineering, have been students of yours.
what advice would you give someon who have 0 experience and want to start on the sillicone injection venture ? what do you suggest ?
@@mohammed_marh RJG has good courses plus look into Paulson training as well
I'd like to give everybody an update, I came out of retirement in late 2022 to again be a teammate @ Mikros Engineering they needed some tech help, only for a few more years.
Remember flash from early toy models that come attached to the sprue? As kids, we kind of accepted flash as a fact of life. But it's nice to see how technology and quality has improved.
Absolutely! It is so fun to look back and see how far we have come since then. Technology is a wonderful thing!
Thanks for the presentation. Nicely done. Flash is also caused by tool defects at the parting line of the cavity.
It works both ways. You make a mold flash by improper setup, wrong parameters (like temperatures of the mold halves, too much or not enough clamping force, overfilling/overpacking the cavities) and the flash actually damages the metal.
It's not always clear what was first - the flash or the damage.
@@abcdefghijk6704what works both ways?
How does water temp cause flash?
Your defects will be on the core side when we spot the tool the cavity is considered "bible" you don't grind it you master it. The only way your getting cavity damage would be closing the tool with a part still inside
@@joehart103 Temperature differences (incompetent "process engineers" and/or low quality mold, like chinese) between mold halves or parts (like mold is hot, but slides are run at cold water) can cause a flash.
Browse through comments, like "Darryl Anton", experienced guy claims the same thing as me.
There are many causes of flash, you can't just simplify it to silly statements like "there is a damage".
In this tutorial I learned a little about pac pressure, and you ask how else flash happens. Shot size, dirty tool, wrong die height, wrong material, or wet material, to name just a few. Love what you guys are doing keep it up.
So all those things you listed all come back to tool damage or the plastic pressure exceeding the clamp tonnage. So yes your correct!
Thank you for taking the time to make these videos.
Thank you for watching.
Great presentation! Keep up the great content!
I worked in this field back in the late 1970's and early 1980's. There were no electronic controllers then. Everything had to be set by turning knobs and setting limit switches by hand. The majority of the machines I worked with were toggle clamped, not directly hydraulic. As time passed, the company bought more and larger hydraulic clamp machines. Still, no electronics. It was an interesting time in my life.
Hey Norman, thanks for watching! It's crazy how far the industry has come in such a short period of time, isn't it? That lack of control is exactly where Rod Groleau found his inspiration for in-mold sensors back in the 60's. It's so fun to look at how much injection molding has grown since then.
me too 350 ton toggle IMPCO some Husky in the 80's
FCS IM Machine getting certified by RJG, Excellent!
thanks..very informative ..
Good videos Marty!
Great video Marty! Been trying to explain this to our process technicians since I took a course with you in January. Now I can just show them! Thanks! Looking forward to getting back to RJG for more training!
Fantastic! Looking forward to it!
Look at the cushion before he raised the transfer. The screw was bottoming out, terrible set up. That’s all he did was put less plastic into the mold wearing a lab coat. You companies pay for this bullshit, good for rjg I guess.
Good explanation
Another cause I've seen with is silly is flakes of plastic build up in the mold caused it to flash and the tech kept upping pressure which caused it to really flash.
Incompetent staff at molding plants.
When there is any problem they always increase the clamping force (if possible, most molds are run incorrectly at max. press setting), increase the hot runner temps (problems with injection, cavity filling) and so on. Pushing harder, faster, hotter.
thank you so much for this explanation, will try these adjustments!
Our pleasure! We hope it helps!
Description is very clear, the scenario to use the car is easy to understand, switchover point is the key point but not the injection speed to cause the flash, thanks!
We're so glad it was helpful! Thanks, Rolin!
Love good old decouple molding great experience learned how to process various materials using this method nice JSW all electric machine.
I have been working in plastic for over 10 years and started from zero knowledge to working up to supervisor and now learning process more and more each day. I can say everything in this video is well explained and true in every way. These are the exact steps I take to prevent flash in almost every case when you can tell you are overpacking pressure and blowing the tool open. Obviously sometimes it can be from clogged venting and in "some" cases even injection speed can play a huge factor. But at the root of it all, you have to see how much material you are truly trying to push into a tool and where your cut off point needs to be. Your machines are a lot different than mine but also a great point to make is your shot cushion should not be your exact transfer point. There should always be a little "room for pressure" between the sprue break and the injection nozzle as to not cause a bonnet
Thank you so much for your input! We're so happy you enjoyed the video!! ☺
A great demo. would be nice to show the machine graphs
Thank you
You are welcome! Thanks for tuning in.
Need to show a closer up of mold screen
Decent analogy.
It is appreciated if you make video explaining warpage, reasons and remedies
Great ideas! Thanks for sharing! :)
Thank you RJG and marty for the wonderful explanation. Flash can be a result of any setting parameter in some sense. One of them that interests me is the cavity imbalance. I was able to eliminate flash by changing runner design. The root cause was nothing but one cavity being filled way earlier then the other.
Having good cavity balance is extremely important. We teach students how to do a cavity imbalance study in our classes. To learn more, view upcoming courses, or register on our website: rjginc.com/training/courses-overview/
so what is solution for filled one cavity faster than other ?plz
@@farooqalhamdany5832 redesign the runner like sandeep said
Yall need to come to my factory!! Teach us a thing or to
I hope if you can provide us more videos for injection molding machine processing and how improve part quality.
Thanks for watching, Mahmoud! We certainly will-keep an eye out!
Nice video.
Was the clamp force calculated for the resin used initially?
Are the mould shut off faces ok?
Is the mould cooling ok?
High melt temperature could reduce the viscosity of the material.
Assuming the gate size is correct then a rheology curve should be generated. This could then find the ideal injection speed and a process window .
Applying full injection speed is not going to always give the best results.
As you mentioned a second speed would reduce flash and also allow venting and a better transfer from injection pressure to holding pressure.
Once the injection speed, holding time and pressure have been optimised I would then move on to checking the clamp force by using a DTI and weighing the parts.
Hi Gilly. To answer your questions in this example yes, clamp force was calculated for the mold and specific resin used, the shutoff and cooling were all in proper working order. Your questions and comments show a great approach to developing a process based off of scientific molding principles. The video was developed to dispel the myth that speed causes flash. You bring up great topics that we will use to develop future videos. Thanks again.
nice presentation, please do a video to how to calculate tonnage of a mold
Stay tuned!
2.5 tons per square inch of the projected area of the part is a good place to start. I'm about to graduate and most of my Moldflow fill/pack/hold simulations over the years have suggested clamping forces quite close to this general rule. For a more exact calculation you need to identify the cavity pressure (Psprue + Prunners + Pgate + Ppart) and include a safety factor. Hope this helps.
I've been a Tech for a long time basically call it what you want to { I agree } I do call it decoupling { you have 1 / 2 / 3 } there is so much that goes into it people will say { basics } I also agree as far as flash so many ways // rolled parting line / like you said blow mold open / dirty mold { clean it before you become that dreaded button pusher } / psi / on n on I love being a tech I work with 2 shot molding al diff types of material Was a good vid Id like to see more
Thanks for the comment and tuning in. We will continue to produce more content. Let us know if there is something specific you would like to see.
@@rjg I work at USF Port Huron MI I would love to Talk with you I got Many problems here TY very much /// and I have been threw RJG training too I have a ton of Questions for you
Former QC for here. As long as the flash wasn't too bad, we could take an exacto knife and trim it. But usually on the machines we had (the plant I worked at sold to China in 2004) it was too hot or too cold.
It wasn't the speed. Also, dirty molds and molds that didn't like to release
Trimming off the flash is what we would call “inspecting in the quality”. That is a huge time and $ drain. I have been in that situation before and sometimes it is the only option left but if doing those things don't become normal or accepted and you're always try to improve the situation then you are on the right track. Generally there is something to be done to not have to trim parts.
Where I work, flash is a bad problem. We have to do slot of trimming daily.
You're not alone! We actually hear that a lot. Flash is a huge issue for a lot of molders. We'd love to chat with you about your challenges and help you find a solution that actually works long-term. Feel free to give us a call to discuss: 231-947-3111. Or send us your contact information and location, and we will have your local account coordinator reach out to you.
@@rjg I work at a small plastic facility. The flash on parts is bad. The trimming always gets you backed up because certain cavities you are trimming hundreds of parts. I'm glad you responded.
Video is very helpful, thanks. I have a question though, Duponts nylon guide says to use the maximum pressure for the holding stage. This bottoms out the screw though. Or if I increase the shot size too far I get flash. Should I not use such a high pressure?
Nice presentation. At my plant, flash is usually caused by insufficient mold clamp pressure, 2nd stage pressure being too high, or the nozzle driving too deep into the bushing.
Nozzles don’t dive too deep, they meet and a certain point. You have to already lost your process job
@@downbelowu1928 I worded that incorrectly. I meant screw, not nozzle. As in the stroke being set too high.
Man one of y’all help me then I got flash on one end of a two cavity lip bumper, one end flashes and the other side doesn’t
@@michaelburks7928 registration, check your part thickness on both sides. If not equal shim the side with flash on the cavity side wedge block. Could use labels to test, could be other things but that’s my first assumption.
@@downbelowu1928 you close to Alabama?
Nice video , do you prefer single point injection speed ? Thanks for sharing the knowledge 🙏
One injection speed is preferred whenever possible. There are times when 2-3 speeds are necessary, but you should always ask if the additional speeds are creating a better outcome or adding complexity with no benefit. Simple is always better if it works.
@@rjg thanks 🙏
Would using a pre-loading hydraulic cylinder help eliminate issues with over pressurizing the tool? While also utilizing a smaller sized cylinder and also requiring less pressure? Like ones used on cores?
Hi Jack,
The scenario described is not recommended, because the “smaller sized cylinders” being used, for pre-load purposes, would overload and become inoperable. This situation could also result in other mold damage, such as coining.
Taking the high pressure to screw stop may be causing your flash too.
What about flashing the gate? Everything you said makes sense for flash on the part.
You raised the transfer, god damn scientific shit right there. Could have just said hey dummy, don’t put that much plastic where it can’t fit.
It is also possible to have fluctuations in the clamp force and dosing with worn machines. The mould temperature may also rise during the production run (tempering devices don't work well, cooling inside the mould is inadequate) and cause increasing flash.
You can also have an explosive fill caused by a cold plug. Which may result in a flash or burned part.
It may also be that the mould has flashed once after a fault and filled with a less viscous material than normally. In that case you have plastic stuck inside the mould not making it close well and requiring manual removal (knife and gas burner).
Fluctuating tonnage or material dosing will definitely make keeping the mold closed difficult. All of the examples you listed lead to the same thing: plastic pressure in the mold overcoming the clamp force of the machine. When this happens the clamp will open slightly and cause flash.
@Kinetic I agree. But life is life. If you have a bolt far away from the cavity and use a red hot knife to remove plastic there aren't that many risks if you take into account.the potential slipping direction. Of course working in the part forming area of the mould requires special care and tools & technique.
The other causes of flash other than a to low change - over position are: 1, tool damage. 2, imbalance fill on multi cavity tools. 3, Clamp pressure to low. 4, broken tie bar. Jimbo🏴🇬🇧
I did read someone sayin a dirty tool cause flash, but that would be admitting that you don't set the mould safety pressure and lock-over/high pressure position correctly. 😇🤭🤣🏴🇬🇧
Do you do any thermoset injection?
Hi David,
Unfortunately, we do not. Thanks for watching.
Common processing without doing 98%fill. Slowing down on inject but not watching hold speed. So it slows down on last stage of inject, then goes in fast and hard on pack/hold. So hold speed is critical to watch as well.
God all these clean factories make me realize how shitty of s factory I worked in
Flash could be caused by a lot. Over venting the mold, big shot size, barrel heates too high, or mold damage/tool damage. Shorts are usually just not a big enough shot but usually if you are short on one side and flasing on the other there is a problem with the mold or how the press is leveled.
Clamp tonnage not set right and mold cooling working correctly will cause flash....now is the die-height set correctly is your lockup position correct. Do you have a broken tie-bar and is the mold there damage causing the flash?
Can speed cause flash in some other cases? The runner is being filled faster than the material can pass through the gate. In this case, the runner actually flashes when overcoming the clamp pressure. it is like your garage wall has a window in it and you have to pass through it at 70 miles an hour and your car cannot get skinny enough to pass through the window. Can this be the result when pushing very low MFI material? Isn't it possible to go from a thick area of the part to a thinner area and material is pushed in faster than it can pass through the thin area?
Hi Keith,
Great question. The speed itself is probably not causing the flash but you are on the right track. There is less resistance when flowing through the sprue and runner but in order for there to be flash the plastic has to hit the cavity wall to build pressure. The reason a lot of runners and sprues develop flash is because they are located close to the locating ring in the A half. This are has no support compared to the rest of the mold which rests on platens. What usually happens is the lack of support allows for the mold to slightly open, or deflect, in this area. The common term is known as mold deflection and generally occurs around the center of the mold because the locating ring offers no support. Sometimes mold builders can assist with this by adding support columns to the back of mold, generally in the ejector box.
What are common cause of dosing alarm?is it connected to material temp .?
It could be related to the rear barrel temperatures.
Also mold temperature can cause flashing.
If the temperature is too high, plastic don't freeze in time.
Lower heat profile, reduce first stage injection speed , inadequate vents. Wear and tear maintenance, increase tonnage, reduce speed time, reduce injection pressure and timers.
Are you just naming term you have heard ? Explain how increasing tonnage can cause flash please ..
Closed vents would cause a short or a burn never flash
Not enough clamping pressure. Mold to hot or possibly over hesting of the nold. There are so mwny variables eheb it comes to plastics that's why i love it. Actual mold damahe cojld cause flashing too
Blocked parts in other cavities caused by buttons, the left over material over fills the closest cavities causing hella flash and a list of other problems
If a cavity is blocked off like you said, then the extra plastic will cause a spike in cavity pressure. This is what we mean by injection pressure overcomes the set clamp force.
Tonage tranfer pos and shot size also water temps Vacuum seal parting line gas build up and all be cause. Of flash u can shot a press as fast as u want if u have a good cushion and.Tranfer i been. A mold tech for years and years. This is childs play.
Only two things I know of that cause flash - Overcoming clamp pressure (This could be mechanical problems, wrong cut off, etc.) and mold damage. Also I like to use hydraulic pressure at cut off to set the hold pressure.
Too much hold pressure or hold time will cause flash also incorrect shot size and not enough tonnage
A worn mold.
Clogged or restricted vents can cause flash.
The most common result of clogged vents is burning or short shots.
@@rjg Never heard of short shots causing flash, maybe oversized shots. That will also tend to clog vents. To high of injection rate and or restricted vents will cause burning also. Also check clamp pressure in case of excessive flash.
Most of my experiences with clogged vents have been due to using additives like UV blockers, colorant, and mold release agents for blow molding. It causes a defect called sinks.
Sir u mean we should fill the part by using two profiles?
Thank you for sharing. Is it also possible for a unreasonable product design to cause flash during injection molding process?
Hi Emily, absolutely! Poor part design can lead to a whole slew of problems, one of them being flash.
Clamping pressure too low or high causing the mold to bow in the centre, barrel/ nozzle temperature too high, too much back pressure on screw during filling.
Melt temperatures, filling and excessive back pressure all contribute to having higher pressures in the cavity and if the tonnage is not high enough then flash can occur. Good point on the mold deflection causing flash in the center of the mold.
Other main cause of flash is mold damage. And also, in some particular cases, mold deflection.
Yep, mold damage and deflection can definitely have a big impact on quality.
Flash can be introduced first (improper mold handling, incompetent setters or wanna-be "process engineers"), then it makes the damage in the mold...
been in processing about 14 years there are so many things and variations that can cause flash.i work with machines from 120 tons to 1100 tons.if youre process is where it is supposed to be to the original than obviously something changed.
What do you mean by the process should be the original and something changed? Can you explain?
Original process meaning it was making good parts and something would have to change weather material,heats,mechanical or something else that would make you alter your process from the master setup
In regards to tonnage, we normally run max allowable by the machine, the exception is when your mold is, for example, a 1/3rd the size of the platen. Running too high of tonnage on a smaller mold will cause it to wear outwards.
That's bad. Many molding facilities damage the molds like that. Incompetent staff. Most molds in the world is run with excessive clamping force, twice as much is not uncommon.
Decoupled molding
Good video. I would like to see some videos of profiling speeds and holding pressure, and reasons why you may have to to profile/ use two stages.
Thanks so much for the suggestions, Jason!
Great request !
Other cause too much back pressure?
Worn shut off plates, mold design, low mfi could cause flash
Mold cooling question. How much temperature difference between the halves of the mold is acceptable?
In my workplace they set temps. up to 30 degrees celcius! Way too much in my opinion.
Of course there is a lot of flashing due to thermal expansion/contraction of the mold parts/halves. Plus ejectors or slides seizing.
Pseudo "process engineers" claim that they have to do this due to parts bending or being not spot-on on size, dimensions.
How do you run your molds folks?
I know, in theory whole mold should be run on the same temperature, both halves.
Hello! Mold temperatures should be set according to the resin being molded. The type of material will dictate where mold temperatures should be set. The material should have a material data sheet or processing guide. The mold temperatures recommended by the material manufacturer will be found there. You are correct, starting with both mold halves at the same temperature is recommended. Often 2 different temperatures are used to mitigate a mold or part design issue.
@@rjg Thanks, but still not answered the question - how much is "acceptable" and most common in practice.
A few degrees maybe? Let's say 5 deg.C?
And 10 C (or more) is a clear incompetence in the crew ("engineers", mold design, way the molds are maintained)?
Rjg answers your question the best he could not a good question to be honest..example a door panel with a speaker grille ..speaker grilles are usually pourus running hotter then the rest of the tool. It always falls back on material unless you have features in the part that require higher temperature
@@joehart103 Still no straight answer, no number (or range, for example 5-10 C is "OK", more is very risky).
This is important practical problem.
As far as I know, molds are designed and made and "spotted" at equal temperatures (room temperatures). If you start introducing difference (especially at mating parts) there will be a problem.
Mold technicians are blamed for this. I can't repair flashing, it pops at the same spot after proper repair - because "process wanna-be engineers" set different temps. ruining the mold! And everyone thinks that's "OK".
Hold/pack pressure too high could cause flash
Yeah it's a common issue where I work as well. We had parts shorting out the other night so the tech increased pressure when he really needed to increase shot size and reduce pressure a bit. Ended up causing a large rib to break off in a parting line which took me a good half hour or so to remove.
Chilled water temperature to high
Part should I'll with 95% without holding time
Bad spot. #1
Mechanical problems, slides and lifter timing, wear plate alignment, manifold stack height issues just to name a few... alot of variables cause flash outside of the process
Over packing, shot size, tonnage
So speed doesn't cause flash... but speed causes flash. Got it.
Anyone else remember when RJG used to preach "Its not the tool or the machine, its always the process that causes issues". Pepperidge farms remembers.
Another thing i have seen is guys increase the shot size when the shit goes short and i have to fix the fucking nozzle leak plastic everywhere!
Tool damage is the only other cause of flash.
We are professional supplier for injection machine spare parts.
Let me see u. Use a krussh With thremaset bmc Material. And get rid of the flash. Lol
Why is it called 'flash'?
Flash, also known as flashing, is excess material attached to a molded, forged, or cast product, which must usually be removed. This is typically caused by leakage of the material between the two surfaces of a mold (beginning along the parting line).
I never was a big fan of flash… kind of a wimp, only power he had was speed, but Superman was just as fast if not even faster
Hahaha! And this is why we want to keep him AWAY from our plastic parts! 🤣
Flash is natural die venting lol
What about the weld line at the underfilled frame shaped part? Visual appearance was obviously acceptable but what about dimension and function/durability?
That's a great question! We have a couple articles that might be helpful about weld lines:
rjginc.com/what-is-the-difference-between-weld-knit-and-meld-lines-and-why-does-it-matter/
rjginc.com/what-are-knit-lines-in-injection-molding-and-how-do-you-prevent-them/
@@rjg I know guys. Had the pleasure of a RJG training in China, several years ago. 👍🏻
If youre shot size is too big