Guideline for designing mold tools for parts with planer parting lines such as for encapsulating electronics.

1. Overmold Design Guide
Using
SolidWorks
• Solidify part and manufacturing requirements
• Iterate part to enable faster mold design
• Design Mold tool using “indent method”.
2009 Rob Robinson, CSWP 1

2. Requirements checklist
• Understand Cavist and Henkel products.
• Cover all exposed metal.
• Flow around and through PCB.
• Balance coverage with short cycle time.
• Minimize flow over snapped PCB edges.
• Good appearance builds customer
confidence.
2009 Rob Robinson, CSWP 2

3. Interesting design requirement:
reduce “thermal traffic” at neck.
Snapped edges vary in Guide
precision width, invite Pin
flash
PCB surface is
good for shut off
Long set back reduces material
leak along snapped edges.
2009 Rob Robinson, CSWP 3

4. Cavist Mold-Man 8000
• Metric dimensioned
• Small molds 4x4”
• Large molds 8x6”
• ~4” total shut height.
• Injects polyamide at 425F
• Low pressure
• Adjustable shot size
• Cooling by conduction
into frame. (Option to have
water flow thru frame.)
2009 Rob Robinson, CSWP 4

5. Cover metal – promote flow
SolidWorks hint: Import IGS file from
Small holes allow material to Altium then simplify. Create single
flow through and bind. feature PCB. Selectively suppress
Altium features for assembly speed.
COMPONENT
Collaborate with SIDE
Electrical Engineer
2009 Rob Robinson, CSWP 5

6. Good Appearance plus
great functionality keeps
customer confidence for
Davis Instruments.
2009 Rob Robinson, CSWP 6

7. Part impact on mold checklist
• Mold layout.
• Pull direction.
• Design “Standards”
• Which side down?
• Cable shutoff.
• Sensor protection?
• L.E.D.s or other
components?
2009 Rob Robinson, CSWP 7

8. Mold layout sketch with evolving part overlaid.
Fill
Eject on overmold
material!
Eject pins on pcb
at 3 or more
locations.
Cable location
Symmetrical pattern for
balance because ejector
plate is spring return.
Is this tool center same as Ejector cavity
Mold-Man eject piston?
2009 Rob Robinson, CSWP 8

9. Design dimensional “defaults”
• Consider the coated PCB to be exactly 0.062” thick.
• Design for a nominal 0.063” thickness of Chem 860
over the flat surfaces.
• Less thickness for corners and edges OK.
• Temp-Hum sensor is 0.095” from surface; RTV rubber
should be 0.085” from surface and have a pocket
depth of 0.080” for resilience and reliable shut off.
• Ribbon cable grooves 0.030-.031” deep seems to
work well for shutting off without damage to cable.
• Medical grade rubber tubing from McMaster-Carr is
working well enough to protect L.E.D. from mold
material.
2009 Rob Robinson, CSWP 9

10. Assembly saved as part with all
components and tested with ”Draft
Analysis”.
This particular assembly to be
molded “component side up”
2009 Rob Robinson, CSWP 10

11. Which mold design sequence shall I choose?
• Brute force (tool cuts
calculated and placed
directly in block.)
• SolidWorks “tutorial
method” as typically taught
in a SW instructional course?
(See following “pink” examples.)
• Or the “indent method”
better suited for parts with a
planar parting surface such as
these Davis parts. (Go
“green”.)
2009 Rob Robinson, CSWP 11

12. Requirements
driven
New Overmolded 2D Tool Layout.
Electrical and
Assembly LFV&E
Mechanical
Engineering
Save Assy as Part,
Combine Bodies
Clearances,
Shutoffs, etc
SolidWorks Mold Subroutines SolidWorks
Tutorial
Draft Analysis
Parting Line Method (mold worthiness)
Simpler SolidWorks functions
Cut (split), name
Indent Method and save bodies
Shutoff surfaces
Clearances,
Shutoffs, etc
Parting Surface,
Tooling Split
Insert into Mold
Parts
Unpredicatability
Tool may be
may require
compromised Returning Indent (cut) split
to design part from Mold
Works best for
Rename, save
mold bodies planar parting surface
Detail Mold fill,
vent & eject
features
Insert mold bodies
into new parts
Shop Drawings Great Tool
Required for
curved parting surfaces
2009 Rob Robinson, CSWP 12

13. Successfully generated (whew!) parting surface would
extend to cover only one half of the mold!
….Which led to several frustrations. Considerable training in SolidWorks surfaces
would be advised.
2009 Rob Robinson, CSWP 13

14. Two “half molds”
combined to make
a whole mold is
“awkward”.
Long feature tree
due to incomplete
“part design”.
Powerful features
employed from
designing by
“better method”.
2009 Rob Robinson, CSWP 14

15. Requirements
driven
New Overmolded 2D Tool Layout.
Assembly
Electrical and
Mechanical
LFV&E Take home message:
Engineering
More time spent in part
Save Assy as Part,
Combine Bodies design means less time
in tool design.
Clearances,
Shutoffs, etc
SolidWorks Mold Subroutines SolidWorks
Tutorial
Draft Analysis
Parting Line Method (mold worthiness)
Simpler SolidWorks functions
Cut (split), name
Indent Method and save bodies
Shutoff surfaces
Clearances,
Shutoffs, etc
Parting Surface,
Tooling Split
Insert into Mold
Parts
Unpredicatability
Tool may be
may require
compromised Returning Indent (cut) split
to design part from Mold
Works best for
Rename, save
mold bodies planar parting surface
Detail Mold fill,
vent & eject
features
Insert mold bodies
into new parts
Shop Drawings Great Tool
Required for
curved parting surfaces
2009 Rob Robinson, CSWP 15

16. Take home message #2, insert a
well designed split part into the
tool block with “move dialog” on.
1st insertion of part has already
been “indented” as a “cut”.
2nd insertion of
identical part
2009 Rob Robinson, CSWP 16

17. These are the hidden “cutting bodies”.
Here is the first indent “cut”.
2009 Rob Robinson, CSWP 17

18. Multi-body parts can be inserted
so all cavities are cut at once.
2009 Rob Robinson, CSWP 18

19. Summary
• Spend a lot of time designing and
reviewing the part.
• Don’t hesitate to iterate! Ask why!
• Use layouts, planes and draft analysis.
• Use the flow chart and follow the green.
2009 Rob Robinson, CSWP 19