Electronics Enclosure
Injection Molding. Snapfits. Master Modeling.
Overview
Key Challenges
U-shape Snap Design
Design for Injection Molding
1 Week Time Constraint
Skills Applied
Master Modeling (SolidWorks)
Injection Molding
Snapfit Design
Electronics Packaging
3D Printing
My Role
Mechanical Engineer - Team of 1
Synapse Product Development
San Francisco, CA
Year
June 2020
About
The purpose of this exercise was to learn the process of designing packaging for electronics. This enclosure was designed using a master modeling approach, incorporates a snapfit design, and can be injection molded. It houses a raspberry pi, LiPo battery and connectors.
System Overview
Requirements
1. Must house a PCB, battery, USB connector
2. Must be possible to injection mold the box and lid
3. Must incorporate a snapfit joint connecting lid to box
4. Must design components using a master modeling approach on SolidWorks
Component Selection
Option 1: RPi 4, Power Bank, USB C, Micro USB connectors
Side View
Front View
Option 2: RPi 4, LiPo battery, LiPo Shim, USB connector
Side View
Front View
Option 3: RPi 4, Li-ion battery, Battery hat, USB connectors
Side View
Front View
Decision: Lipo Battery is the most appropriate power source for this application. It will also be accessible if it needs to be replaced.
Snapfit Design
Selecting Type of Snap
Separable vs Inseparable
Decision: Designing a U-shape snap will teach me the fundamentals of snapfit design with an interesting challenge. It is appropriate for this application and will be easy for a user to assemble and disassemble.
Lid to Box Interface
Cross Section
Top View
U-Shape snap and tabs or cantilever snap
U-Shape snap on both sides of lid
Decision: Including two small tabs on the lid and two slots in the side of the box wall will make it easy for a user to locate the lid and secure it in place. It will also give me practice designing two different interfaces (snap and tabs).
Benchmark Design
I used the battery door of a TV Remote to get an idea of thicknesses, size ratios, and gaps. I used the dimensions as a reference for a CAD model and made iterations as needed.
Gaps, Thicknesses, Tolerances
Version 1 Dimensions
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Box Wall Thickness: 2.0mm - 2.5mm
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Snap Thickness: 1.5mm
3D Printing Tolerance Reference
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0mm - Press fit
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0.1mm - Line to line
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0.2mm - Will slide freely
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0.3mm - Will rattle
I planned to 3D print 3 lids with varying snap engagements and gaps to test out the difference. This exercise would help me understand how slight changes in dimensions can make an impact on a 3D printed part.
Injection Molding
Concept Sketching
Top View
Bosses
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PCB can be screwed to box using screw bosses
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M2.5 Screws
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Either use threaded inserts or tap holes
Ribs
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Ribs can be connected to side wall to support bosses
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Can be used to prevent battery from shifting
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May use adhesive for battery as well
Tooling and Parting Lines
To make the parts possible to injection mold, I had to think about what the tooling would look like and where the parting lines would be. I sketched a cross section of the lid and enclosure and drew the core and cavity. I made sure to consider how the undercuts would be formed using lifters or slides.
I ran a draft analysis in SolidWorks using parting lines as a reference. This helped me see which walls needed drafting. The green indicates that the draft was added.
Master Modeling
Approach
Master modeling was not an essential method for designing this enclosure. I used it solely for the purpose of learning. The diagram above shows an approach that two people could take if they were working on different components (electronics and lid).
