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Learn how to identify common defects, understand why they form, and what to do to minimize them.
Type:
Tutorial
Length:
8 min.
Transcript
00:04
Visual defects are blemishes on the
00:05
part that detract from its aesthetic appearance
00:09
depending on the defect in its location.
00:11
Some visual defects can also affect structural integrity of the part.
00:15
Sync marks are typically small depressions on the surface of a
00:18
molded part that develop above thicker structures on the underside.
00:22
The visibility is a function of the color of the part as well as its surface texture.
00:26
So the depth of the depression is only one criterion.
00:29
Sync marks do not affect the part strength or
00:32
function but are considered to be severe quality defects
00:37
as plastic cools, it shrinks a little
00:39
to compensate during this cooling period.
00:41
Extra material is forced into the mold to fill the gaps.
00:45
Sick marks develop when the plastic material in
00:47
thicker section shrinks without sufficient packing compensation.
00:51
After the surface material has solidified,
00:53
the hotter core material continues to cool.
00:56
A shrinkage pulls the surface of the main wall inward causing a sink mark.
01:01
If your part experiences unbalanced heat removal, it is likely to have sink marks.
01:06
Uneven heat removal is caused by design features such as ribs, legs,
01:10
bosses or anything that creates changes in wall thickness.
01:14
Other causes include high melt temperature
01:16
and insufficient packing due to time or pressure.
01:20
Let's see how to identify visual defects in in an injection molding simulation.
01:25
With injection molding simulation. The visual defects guided results
01:29
show you the location of both saint marks and
01:31
mud lines superimposed on the same model outline.
01:35
If you have defined aesthetic faces,
01:37
the guided results show which of the aesthetic
01:39
faces are impacted by these visual defects.
01:42
Lets turn off the we line result and focus first on the saint
01:45
marks.
01:47
As you can see when sink marks develop,
01:49
they appear above thicker structures such as ribs and bosses,
01:52
the thicker and underlying structure, the deeper the sink mark is likely to be,
01:58
you can move the tolerance slider to show how
02:00
the sync marks compare with your parts tolerant specifications
02:06
to see how the saint marks might appear on the surface of the part.
02:09
Switch to the Saint Marks visualization result,
02:12
use the magnification tool to exaggerate the marks to see them more clearly
02:18
and the surface finish tool to see how
02:20
they might appear with different surface finishes.
02:23
What can you do about these visual defects?
02:26
The guided results provide suggestions for how to reduce
02:29
the appearance of Saint Marks and Wild lines.
02:32
The first suggestion is to edit the model in
02:34
injection molding.
02:35
A good rule of thumb is to keep part thicknesses
02:38
as thin and uniform as possible to reduce surface defects.
02:42
You can edit the simulation model to see the effect
02:44
of various design changes without affecting the original model design.
02:50
Another option is to relocate the gate to or near a thicker section.
02:55
This allows more material to be packed into the
02:57
thicker sections before thinner sections freeze and prevent further flow
03:02
or you could decrease the melt temperature.
03:04
This reduces the volumetric shrinkage experienced by the plastic melt as it cools
03:09
since it doesn't have to cool and shrink so much before it freezes.
03:14
Wild lines are both a weakness and a visible flaw that are often unavoidable.
03:19
They can make the part visually unacceptable and also
03:22
cause structural problems depending on where they occur.
03:24
On the part.
03:25
Sometimes the best you can do with wild lines is to move them.
03:29
We lines are caused by a flow front that
03:31
splits and comes together around a hole or other feature
03:35
or if the part has multiple gates,
03:38
if the different flow fronts cool too much before meeting,
03:40
they may not recombine well causing a weakness in the molded part,
03:45
a line notch and or color change can also appear
03:49
if there are multiple flow paths for the plastic to fill the mold,
03:52
your part is likely to have wild lines.
03:55
There are several causes of multiple
03:57
flow paths including multiple injection locations,
03:59
design features that split the flow
04:02
and variable wall thicknesses that cause the flow front speed to change.
04:06
Let's turn off the saint mark results and look instead at the we line result,
04:10
you'll notice there are a great many potential wild lines and they
04:13
appear around holes and or around structures like ribs and bosses.
04:18
While we lines are unavoidable,
04:20
you can try to improve the quality or strength of the wild line
04:23
and move it to where it will have less of an impact.
04:26
The guided results suggest moving the injection location or editing
04:30
the model to move the location of wild lines.
04:34
This wild line result shows the different wild
04:36
line pattern resulting from changing the injection location.
04:41
Another option is to improve the quality of the wild line
04:43
by increasing the melt temperature or increasing the injection speed.
04:47
So they recombine better when they meet.
04:50
This wild line results show there are fewer
04:52
wild lines when the melt is injected faster.
04:55
Similarly, if you move the injection location,
04:57
so the wild lines form closer to the gates,
04:60
they will be formed at a higher flow front temperature and will be stronger.
05:06
A short shot is a term used when the part is not completely filled,
05:11
the flow front freezes off before all the flow paths are filled.
05:15
An air trap is an air or gas bubble that is
05:17
caught inside the mold cavity by converging polymer melt fronts.
05:22
They can both be visual and structural problems and
05:24
could be eliminated with appropriate part and mold design.
05:28
Air traps usually occur in areas that fill last.
05:31
The trapped air can cause incomplete filling and packing and
05:34
will often cause its surface blemish in the final part,
05:38
if there are multiple variable length flow paths or insufficient venting,
05:42
then your part is likely to have air traps
05:45
as far as possible. Minimize variable wall thickness for more balanced flow paths.
05:50
The air trap result shows the location of potential air traps.
05:54
By moving or adding injection locations,
05:56
you can position the air traps where they can be more readily vented.
06:00
You can compare the various injection locations
06:02
to see which one locates the air traps most effectively
06:07
an injection mark is a visual defect that appears
06:10
on the part where the plastic enters the part.
06:13
Every injection molding part has an injection mark for every gate
06:17
that shows where the plastic was injected,
06:20
injection marks cannot be avoided,
06:22
but you can place the gates where the marks are not very visible.
06:26
This quality prediction result shows that the location of
06:29
the injection location impacts the quality at that location.
06:34
Placing the injection location in the middle of the
06:36
flat face is very visible to the consumer.
06:39
Placing it around the side still leaves a mark
06:41
but the mark is less obtrusive
06:44
solving.
06:45
One problem can often introduce other problems to the injection molding process.
06:49
Each potential solution therefore requires consideration of all
06:53
relevant aspects of the mold design specification.
Video transcript
00:04
Visual defects are blemishes on the
00:05
part that detract from its aesthetic appearance
00:09
depending on the defect in its location.
00:11
Some visual defects can also affect structural integrity of the part.
00:15
Sync marks are typically small depressions on the surface of a
00:18
molded part that develop above thicker structures on the underside.
00:22
The visibility is a function of the color of the part as well as its surface texture.
00:26
So the depth of the depression is only one criterion.
00:29
Sync marks do not affect the part strength or
00:32
function but are considered to be severe quality defects
00:37
as plastic cools, it shrinks a little
00:39
to compensate during this cooling period.
00:41
Extra material is forced into the mold to fill the gaps.
00:45
Sick marks develop when the plastic material in
00:47
thicker section shrinks without sufficient packing compensation.
00:51
After the surface material has solidified,
00:53
the hotter core material continues to cool.
00:56
A shrinkage pulls the surface of the main wall inward causing a sink mark.
01:01
If your part experiences unbalanced heat removal, it is likely to have sink marks.
01:06
Uneven heat removal is caused by design features such as ribs, legs,
01:10
bosses or anything that creates changes in wall thickness.
01:14
Other causes include high melt temperature
01:16
and insufficient packing due to time or pressure.
01:20
Let's see how to identify visual defects in in an injection molding simulation.
01:25
With injection molding simulation. The visual defects guided results
01:29
show you the location of both saint marks and
01:31
mud lines superimposed on the same model outline.
01:35
If you have defined aesthetic faces,
01:37
the guided results show which of the aesthetic
01:39
faces are impacted by these visual defects.
01:42
Lets turn off the we line result and focus first on the saint
01:45
marks.
01:47
As you can see when sink marks develop,
01:49
they appear above thicker structures such as ribs and bosses,
01:52
the thicker and underlying structure, the deeper the sink mark is likely to be,
01:58
you can move the tolerance slider to show how
02:00
the sync marks compare with your parts tolerant specifications
02:06
to see how the saint marks might appear on the surface of the part.
02:09
Switch to the Saint Marks visualization result,
02:12
use the magnification tool to exaggerate the marks to see them more clearly
02:18
and the surface finish tool to see how
02:20
they might appear with different surface finishes.
02:23
What can you do about these visual defects?
02:26
The guided results provide suggestions for how to reduce
02:29
the appearance of Saint Marks and Wild lines.
02:32
The first suggestion is to edit the model in
02:34
injection molding.
02:35
A good rule of thumb is to keep part thicknesses
02:38
as thin and uniform as possible to reduce surface defects.
02:42
You can edit the simulation model to see the effect
02:44
of various design changes without affecting the original model design.
02:50
Another option is to relocate the gate to or near a thicker section.
02:55
This allows more material to be packed into the
02:57
thicker sections before thinner sections freeze and prevent further flow
03:02
or you could decrease the melt temperature.
03:04
This reduces the volumetric shrinkage experienced by the plastic melt as it cools
03:09
since it doesn't have to cool and shrink so much before it freezes.
03:14
Wild lines are both a weakness and a visible flaw that are often unavoidable.
03:19
They can make the part visually unacceptable and also
03:22
cause structural problems depending on where they occur.
03:24
On the part.
03:25
Sometimes the best you can do with wild lines is to move them.
03:29
We lines are caused by a flow front that
03:31
splits and comes together around a hole or other feature
03:35
or if the part has multiple gates,
03:38
if the different flow fronts cool too much before meeting,
03:40
they may not recombine well causing a weakness in the molded part,
03:45
a line notch and or color change can also appear
03:49
if there are multiple flow paths for the plastic to fill the mold,
03:52
your part is likely to have wild lines.
03:55
There are several causes of multiple
03:57
flow paths including multiple injection locations,
03:59
design features that split the flow
04:02
and variable wall thicknesses that cause the flow front speed to change.
04:06
Let's turn off the saint mark results and look instead at the we line result,
04:10
you'll notice there are a great many potential wild lines and they
04:13
appear around holes and or around structures like ribs and bosses.
04:18
While we lines are unavoidable,
04:20
you can try to improve the quality or strength of the wild line
04:23
and move it to where it will have less of an impact.
04:26
The guided results suggest moving the injection location or editing
04:30
the model to move the location of wild lines.
04:34
This wild line result shows the different wild
04:36
line pattern resulting from changing the injection location.
04:41
Another option is to improve the quality of the wild line
04:43
by increasing the melt temperature or increasing the injection speed.
04:47
So they recombine better when they meet.
04:50
This wild line results show there are fewer
04:52
wild lines when the melt is injected faster.
04:55
Similarly, if you move the injection location,
04:57
so the wild lines form closer to the gates,
04:60
they will be formed at a higher flow front temperature and will be stronger.
05:06
A short shot is a term used when the part is not completely filled,
05:11
the flow front freezes off before all the flow paths are filled.
05:15
An air trap is an air or gas bubble that is
05:17
caught inside the mold cavity by converging polymer melt fronts.
05:22
They can both be visual and structural problems and
05:24
could be eliminated with appropriate part and mold design.
05:28
Air traps usually occur in areas that fill last.
05:31
The trapped air can cause incomplete filling and packing and
05:34
will often cause its surface blemish in the final part,
05:38
if there are multiple variable length flow paths or insufficient venting,
05:42
then your part is likely to have air traps
05:45
as far as possible. Minimize variable wall thickness for more balanced flow paths.
05:50
The air trap result shows the location of potential air traps.
05:54
By moving or adding injection locations,
05:56
you can position the air traps where they can be more readily vented.
06:00
You can compare the various injection locations
06:02
to see which one locates the air traps most effectively
06:07
an injection mark is a visual defect that appears
06:10
on the part where the plastic enters the part.
06:13
Every injection molding part has an injection mark for every gate
06:17
that shows where the plastic was injected,
06:20
injection marks cannot be avoided,
06:22
but you can place the gates where the marks are not very visible.
06:26
This quality prediction result shows that the location of
06:29
the injection location impacts the quality at that location.
06:34
Placing the injection location in the middle of the
06:36
flat face is very visible to the consumer.
06:39
Placing it around the side still leaves a mark
06:41
but the mark is less obtrusive
06:44
solving.
06:45
One problem can often introduce other problems to the injection molding process.
06:49
Each potential solution therefore requires consideration of all
06:53
relevant aspects of the mold design specification.
For more, see: Will my part have visual defects?. Airtraps. Sink marks. Weld lines.
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