injection molding part should avoid gate placement on the fuctional/stress apply area

[samsangsam]

i have a plastic part which have a gate location at the functional area, it seem inproper location as it is the area with force apply. at the field , also found wear at this area.i feel it is unstable at this area and easily have material degradation. but my molder says as long as they can achieve the dimension stability, this is no issue with gate placement at this force apply area. Is it correct?

 

[Nereth1]

There are general issues at the injection points, there are moulded in stresses, stress raisers from surface incontinuities, poor surface finish and dimensional issues - but they may not be issues in your application - sometimes you don't need the full strength of a part or the optimum surface finish, so it doesn't matter.

If the part is failing to perform because of these issues, then you have a problem.

 

[MintJulep]

You are the engineer and you are the purchaser. So if you indicate "no gate in this area" on your drawing then the molder needs to respect that and deliver accordingly.

However, that decision should be made for quantifiable reasons. Not "it seems improper" or "I feel it is unstable".

 

[samsangsam]

very sad to sad, we are in engineering side, we receive drawing in back end of the development and perform support for production, just alway in my mind that this part (gate area) is problem. field can see issue. i don't have evidence to proof to support that this gate area is the root cause. i only have indirect report from field this area seeing problem. that alway why seem improper work use.

anyone here can help to provide more infor about gate should avoid the fuctional area?

 

[MikeHalloran]

So, you haven't seen the actual failures, you are just spreading rumors?

You need to go, wherever, and get some actual broken/unsatisfactory parts, and photograph, destructive test, and otherwise document exactly how they are unsatisfactory.

If you can't get any because they're being used/shipped, then they're not _that_ unsatisfactory, and you have to revise your specifications to not waste resources on whatever inspection you're doing.

If you're jawboning because of something you just learned in an introductory course or a book, you need to break some parts and/or talk to the actual designers so you can understand what compromises were made in order to arrive at a usable design.




Mike Halloran
Pembroke Pines, FL, USA

 

[samsangsam]

i am not spreadng rumos, from design , is it alway compromise to accept the gate in functional area? if you are designer, is it compromise things will do?

or somethings irresposible things ?

 

[MikeHalloran]

Every line of every design represents a compromise.

I can imagine circumstances where I might wish to place a gate within what you might call a 'functional area', whatever that means to you. It may not mean the same to me, and I might be intentionally trying to use the special properties associated with gate flows in order to make a part do something that it wouldn't do if conventionally gated.

If you don't talk to the person who actually designed the part, or at least to some cranky old bastard who can reverse engineer it in his head, you will never know why the part looks like it does.

Do not start the conversation with a word like 'irresponsible'; the conversation may turn out badly for you.





Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

So your field guys are reporting that this part fails. Is that correct?

And you suspect that it is because the gate coincides with force application. Is that correct?

And you want want to solve the problem. That's good.

So get some failed parts from the field guys.

Get some new parts from the molder.

Ask the designer what the forces are.

Do some calcs. Do some tests. Confirm your theory. Or not.

Then you'll have some evidence. Or you'll know that the root cause of the failure is something else.

 

[samsangsam]

Hi,

I am just asking the opinion as understanding that the Gate should avoid the functional/force apply area,is it true or practise for part design.

 

[Nereth1]

As I said in post number 1, it's only true when it needs to be true. If you design with rules of thumb you get a thumb so it's dangerous to have a rule like that.

For example we have 5 gates on a part and every one of them is on the one surface that actually takes a load - and we actually get failures there on occasion when other issues crop up - why don't we move them? Because we want them there so that the mould flows well and we get precise tolerances where we need them. We solve the breakage problem in other ways.

Best practice is to make parts that work optimally. It's not to avoid putting gates in places because of rules of thumb.