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Guideline for designing mold tools for parts with planer parting lines such as for encapsulating electronics.
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2009 Rob Robinson, CSWP 1
Overmold Design Guide
• Solidify part and manufacturing requirements
• Iterate part to enable faster mold design
• Design Mold tool using “indent method”.
Using SolidWorks
2009 Rob Robinson, CSWP 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 3
Guide Pin
PCB surface is good for shut off
Snapped edges vary in
precision width, invite
flash
Long set back reduces material leak along snapped edges.
Interesting design requirement: reduce “thermal traffic” at neck.
2009 Rob Robinson, CSWP 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 5
Cover metal – promote flow
COMPONENT
SIDE
Small holes allow material to
flow through and bind.
Collaborate with
Electrical Engineer
SolidWorks hint: Import IGS file from
Altium then simplify. Create single
feature PCB. Selectively suppress Altium features for assembly speed.
2009 Rob Robinson, CSWP 6
Good Appearance plus
great functionality keeps
customer confidence for
Davis Instruments.
2009 Rob Robinson, CSWP 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 8
Mold layout sketch with evolving part overlaid.
Eject pins on pcb at 3 or more
locations.
Eject on overmold
material!
Symmetrical pattern for balance because ejector
plate is spring return.F
ill
Cable location
Is this tool center same as
Mold-Man eject piston?
Ejector cavity
2009 Rob Robinson, CSWP 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 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 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 12
Simpler SolidWorks functions
SolidWorks Mold Subroutines
New Overmolded
Assembly
2D Tool Layout.
L F V & E
Requirements
driven
Electrical and
Mechanical Engineering
Save Assy as Part,
Combine Bodies
Draft Analysis
(mold worthiness)Parting Line
Shutoff surfaces
Parting Surface,
Tooling Split
Rename, save
mold bodies
Insert mold bodies
into new parts
Detail Mold fill,
vent & eject features
Shop Drawings
Cut (split), name
and save bodies
Tool may be
compromised
Unpredicatabilitymay requireReturning
to design
Clearances,
Shutoffs, etc
Clearances,
Shutoffs, etc
Insert into Mold
Parts
Indent (cut) split part from Mold
SolidWorks
TutorialMethod
Indent Method
Great ToolRequired for
curved parting surfaces
Works best for
planar parting surface
2009 Rob Robinson, CSWP 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 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 15
Simpler SolidWorks functions
SolidWorks Mold Subroutines
New Overmolded
Assembly
2D Tool Layout.
L F V & E
Requirements
driven
Electrical and
Mechanical Engineering
Save Assy as Part,
Combine Bodies
Draft Analysis
(mold worthiness)Parting Line
Shutoff surfaces
Parting Surface,
Tooling Split
Rename, save
mold bodies
Insert mold bodies
into new parts
Detail Mold fill,
vent & eject features
Shop Drawings
Cut (split), name
and save bodies
Tool may be
compromised
Unpredicatabilitymay requireReturning
to design
Clearances,
Shutoffs, etc
Clearances,
Shutoffs, etc
Insert into Mold
Parts
Indent (cut) split part from Mold
SolidWorks
TutorialMethod
Indent Method
Great ToolRequired for
curved parting surfaces
Works best for
planar parting surface
Take home message:
More time spent in part
design means less time
in tool design.
2009 Rob Robinson, CSWP 16
Take home message #2, insert a
well designed split part into the
tool block with “move dialog” on.
2nd insertion of identical part
1st insertion of part has already been “indented” as a “cut”.
2009 Rob Robinson, CSWP 17
These are the hidden “cutting bodies”.
Here is the first indent “cut”.
2009 Rob Robinson, CSWP 18
Multi-body parts can be inserted
so all cavities are cut at once.
2009 Rob Robinson, CSWP 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.