At Jaycon Systems, we have chosen to use injection molding as the main manufacturing process to bring plastic products to life. However, injection molding is not simple. Engaging in such process requires an extensive knowledge about its machinery and process. In this presentation, we will show you some of the aspects we take into consideration when designing plastic parts for injection molding so we can save our customers time and money in the long run.

1. Engineering guidelines to
Designing
Plastic Parts
for injection molding

2. Hello!
We are
Jaycon Systems
Where a bunch of geeks got together to
bring people’s product ideas to life.
We are passionate about making things, but we
also love the technologies that enable us to make
these things.
We are here to share with you a bit of our
knowledge and give you a glimpse into our
world... The world of making!
2/22

3. In the world of making things, there are
many ways to manufacture products. If these
products are made out of plastic, there are
numerous ways we can mass produce them:
◈ blow molding
◈ casting
◈ compression molding
◈ extrusion
◈ fabrication
◈ foaming
◈ injection molding
◈ rotational molding
◈ thermoforming
Introduction
At Jaycon Systems, we have chosen to use
injection molding as the main manufacturing
process to bring plastic products to life.
However, injection molding is not simple.
Engaging in such process requires an
extensive knowledge about its machinery and
process.
In this presentation, we will show you some
of the aspects we take into consideration
when designing plastic parts for injection
molding so we can save our customers time
and money in the long run.
3/22

4. “
Let’s get started…
What is injection
molding?

5. Injection Molding
Injection molding is the
technique where molten
plastic is injected into a
metal mold. The mold is
composed of two halves,
the “A” side and “B” side.
The halves are separated
and allow the plastic
component to be removed
once it has solidified, thus
creating plastic parts.
5/22

6. “
Now let’s get to it:
What should we keep in
mind when designing
for injection molding?

7. Draft Angles
Draft angles allow for removal of the
plastic from the mold. Without draft
angles, the part would offer significant
resistance due to friction during removal.
Draft angles should be present on the
inside and the outside of the part.
The deeper the part, the larger the draft
angle. A simple rule of thumb is to have a 1
degree draft angle per inch. Not having
enough draft angle may result in scrapes
along the sides of the part and/or large
ejector pin marks (more on this later).
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8. Radiused Edges
Having radiused edges and corners (both
inside and outside) of a part is a multipurpose
feature. This allows for better removal during
part ejection, — in conjunction with drafted
sides — and better material flow (more on this
later). Most importantly, however, is that it
will not only prevent excessive expenses
when creating the mold, but it will prevent
cracks from forming due to stress
concentration. Keep in mind that radiused
corners should maintain same wall thickness,
which means that if inner r=½ thickness then
outer R=3*½ thickness.
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9. Undercuts
Undercuts are items that interfere with the
removal of either half of the mold. Undercuts
can appear just about anywhere in the
design. These are just as unacceptable — if
not worse — as the lack of a draft angle on the
part. However, some undercuts are
necessary and/or unavoidable. In those
instances, necessary undercuts are produced
by sliding/moving parts in the mold.
Keep in mind that creating undercuts is more
costly when producing the mold and should
be kept to a minimum.
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10. Solid vs Shell
As the plastic cools in the mold, it also shrinks, which is
a common characteristic for most materials.
Making a component a shell versus a solid helps reduce
the amount of shrinkage or warpage that happens
during the cooling process. It also helps lowers the cost
of material needed to be used in that part. There are
numerous ways to shell a design, one example is shown
on the sphere (top right of the slide vs bottom left).
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11. Sink Marks
Sink marks are as they sound, a spot
or segment of the plastic surface
that appears and/or feels as if it has
sank into the part.
These marks are caused by a number
of items:
◈ inconsistent wall thickness
(may also lead to voids);
◈ bad radius in corners;
◈ thick support ribs (to be
discussed later);
◈ sharp corners;
◈ not shelling parts out.
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12. Support Ribs/Gussets
Support ribs/gussets are used to give a
product’s walls additional support. They are
used mainly in two situations: (1) where the
part has 90-degree angled walls that meet,
and (2) where a part may be too long or large
and the wall thickness leaves the part flimsy
or weak. Support ribs tend to work best in
the direction in which they are needed, such
as running the length of a long section.
When designing support ribs, it is important
to consider draft angles and base thickness at
no more than ⅔ the thickness of the wall it is
attached to.
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13. Connecting parts together
Products are generally composed of two or more parts
connected together. These parts can be connected with
mounting bosses, snap hooks, screws, etc. A common
way of uniting two parts is using screws through
mounting bosses. Having lips/grooves where the parts
touch is a common way to align parts together.
When planning on how parts will connect, keep in mind
all the previous tips throughout this presentation, such
as draft angles, shelled parts, support ribs/gussets, etc.
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14. Part Lines
Part lines are where the two halves of the mold meet. This generally creates a physical
line on a part that is both visible and noticeable to the touch. These lines, however,
can be hidden or minimized when placed along edges of the part. When designing a
part, always keep in mind its part lines.
Part line
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15. Ejector Pin Locations
Ejector pins are what allow the part to be removed from the mold. These pins literally push
the part out after the material has been injected into the mold and set. However, while
pushing parts out, these pins leave marks on the part. These marks are generally not
removable, so location is key to keep in mind when designing the part.
Ejector Pin
Marks
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16. Gate Locations and Material Flow
Along with ejector pin locations and part lines, it
is also important to know where to have the
gate locations. Gates are where the molten
plastic enters the cavity of the part in the mold.
These gates, once the part cools, leave a mark/
indication of where the gate was, even when
attempted to be removed by a post process.
Gate location is sometimes determined by:
◈ where it will be less noticeable;
◈ where it will not interfere with the rest of
the part;
◈ how the plastic material will flow evenly
through the part;
◈ or a combination of all these.
Gate
marks
16/22

17. Material and Thickness
Depending on (1) how the product works,
(2) the environment it will be in and (3)
the preference of the designer, a
material should be selected. These
materials change how the part feels,
looks and operates. Some are flexible,
some are rigid, some are strong, some
are brittle. The type of material chosen
will often have a significant effect on the
design of the part. Some support ribs
may need to be removed or added, walls
may need to be thicker or thinner, etc.
Example of support ribs
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18. Recommended Wall Thickness
Resin Inches Millimeters
ABS 0.045 – 0.140 1.143 - 3.556
Acetal 0.030 – 0.120 0.762 - 3.048
Acrylic 0.025 – 0.150 0.635 - 3.81
Liquid crystal polymer 0.030 – 0.120 0.762 - 3.048
Long-fiber reinforced plastics 0.075 – 1.000 1.905 - 25.4
Nylon 0.030 – 0.115 0.762 - 2.921
Polycarbonate 0.040 – 0.150 1.016 - 3.81
Polyester 0.025 – 0.125 0.635 - 3.175
Polyethylene 0.030 – 0.200 0.762 - 5.08
Polyphenylene sulfide 0.020 – 0.180 0.508 - 4.572
Polypropylene 0.025 – 0.150 0.635 - 3.81
Polystyrene 0.035 – 0.150 0.889 - 3.81
General rule of thumb 0.040–0.140 1.016 - 3.556
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19. All the concepts presented in
the previous slides make up just
some of the good practices an
engineer has to keep in mind
when designing parts to be
mass manufactured by means
of injection molding.
Conclusion
These practices are also known
as DFM (Design For
Manufacturability) and should
be used as a checklist
constantly throughout the
design and redesign of
products.
Remember, keeping these
practices in mind will ensure
long-term savings in
manufacturing costs and time
for customers.
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20. Think we missed
something?
If you would like to add to our slides,
send us a message and we will do
our best to include it to this
presentation.
Got questions?
We can help because what you just
saw is what we love to do.
Product Design | Engineering | Manufacturing
Get in touch
www.jayconsystems.com
info@jayconsystems.com
+1 (888) 226-4711

21. We love sharing
AND SO SHOULD YOU
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& don’t forget to hashtag us #JayconSystems
21/22

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