ABS Moulded part, Help requested.

It needs the injection point moving, or mutiple injection points, it's a wonder the plastic gets to the far end.

If you try and visualise the flow the problems should be apparent...there are fancy computer programs for it, but hardly necessary in this case.

I'd think an injection point in the centre of the face (so it can flow outwards) or one at each end (or each corner, but there will likely be weld lines where the flows meet) would be better?
Presumably its a simple open and shut tool, so changes should be feasible.

Del

Of course, play with the molding conditions first, pressure temperature of the plastic and the mold, cycle time etc.
As it's much cheaper to try this first.

Del

Thank you Del.

You supported what we are planning to do. But at the same time I have some doubts about its working.and the reason is-

If you look at each weld line they are more or less of same length and intensity.which do not support our logic, if these lines are at all related to the ease of material flow then the nearest weld line to the feed point should be smaller and less intense than distent weld line.

What I am doubting about is feeding at four point will just change the direction of weld lines and even some of holes may get two and four lines.central feed will make lines like directions of sun-rays coming from sun.

Yes, there will always be places where the flows meets, but it depends on the state of the plastic when it meets wether it joins properly or incompletely.

As Nickname poinst out the venting may be critical too in aiding a faster hotter flow with no dead areas.

It's not my field of expertise, I just happen to have picked up a fair bit along the way...
Mold tools are a bit like software... never work right first time

I'd suggest having radii where the holes meet the face, but this can't be doe easilly retrospectively as it's 'metal on'.

Del

1- Del is right you should use the service of a consultant able to use a GOOD soft for simulation.

2- I think that you have several problems to correct:

- position of feed which has to be as central as possible in order to have all over as much as possible same temperature. Is your temperature high enough for this form? The side contact surfaces are big so that the injected material will cool rapidly and on short distances.

- the design of the part itself leads to problems since the flow follows to the least resistance path. It will flow at the rear of holes when the form is filled and pressure goes up, at this moment the material is already cooler so that it has a higher viscosity. It could be better to adapt the wall thickness (if possible) so that the path to the rear has a lower or equivalent resistance as the other.

- where are the vents ? It could be possible that the compressed air has as well an effect.

Filling a form is a complex viscous flow problem and cannot be solved only with qualitative opinions.

Thank you for your good comments,

We are taking all points in consideration,

regards.

Your problem is not unique. You will always get flow (weld lines) around openings. You can totally eliminate these weld lines by heating the mold above the glass-transition stage of the ABS then rapidly cooling the mold. This is called heat/cold molding. If you don't want to go to the expense of purchasing this equipment then you will never entirely rid the part of these weld lines.

http://www.ptonline.com/articles/200805fa4.html

If you want to try and process the weld lines to a minimum you probably do not want to raise melt temperatures. You want to fill fast, thus shorten your injection time and consequently increase your shear rate. Have you developed your rheology curve? Packing the part out can increase the weld line strength but you have to be careful since this will also affect sizing. In addition, ABS needs to be well vented to rid of the volatiles that will be created with a fast injection rate.

You can also install valve gates but the cost would be very high on a part that you have shown.

You can always mold a solid substrate that will not have any weld lines and then punch/drill the holes out post molding. This kind of defeats the reason for injection molding but it would solve your problem.

Good luck

Hi,

Thank you for your valuable comments,

We are working on mould with considering all point, Drilling solid plate can be last option,

Thanks and regards,

I would try to raise the material temp, mold temp, injection pressure and cycle time bit by bit and hope they less noticeable.

even with multi point injection you will get flow lines.

downside being fewer parts per hour and increased mfg cost.

Hi,

Thank you,

Raising too much temp make shrink marks prominent, we are considering all other points, and will get to foroum once we complete job.

Regards.

hello mr. rakesh

I had a few question to you which I think can help.

1. What is the use of this molded part?Functional/Asthetic..etc?

2. Did you try breaking test for this weld lines?Is it your customer dont want to accept it?

3. If breaking test will surpass the required standard..and you or your customer do not want a weld line on the holes...I would suggest you paint with darker color the molded part so weld line would not be visible..since this is an ABS it is very good for painting job.

As you knowweld line can not be eliminated in this kind of situation..if my suggestion in not feasible..stick to the suggestion on Plasteek..

cheers..

R. Zamora

Philippines

Hello Zamora,

Aesthetic is as important as functionality, these hair lines or not acceptable at all,

We are considering all other points suggestes and hope that problem will go.

Thank you very much for you time.

Paint it.