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.