In the structural design of electronic products, snap-fit structures are undoubtedly the most common form of housing fixation. They utilize the elastic deformation of plastic materials to achieve connection and snapping. Here are some design details and characteristics of snap-fits.
1. Snap-Fit Layout
Snap-fits should be evenly distributed around the perimeter of the part as much as possible. For areas prone to deformation (such as the corners of a part), consider placing snap-fits closer to these locations. The design and layout of snap-fits typically need to cooperate with lips and counter-lips to achieve optimal positioning and fixation of the housing.
Description of the image: Table with the following content:
Number Definition Recommended Value Note
A Clearance between female snap and housing 0.20 ≥0.20, for future design changes
B Fitting clearance 0.1
C Engagement Plastic 0.50 / Metal 0.3 0.30~1.00
D Reinforcing wall of female snap 0.50 ≥0.4~0.6
E Clearance between snaps 0.30 ≥0.30, for future design changes
F Length of male snap 4.00 2.50~6.00
G Clearance between snaps 0.30 ≥0.30
H Thickness of male snap 1.00 1.00~1.20
I Thickness of female snap 1.00 1.00~1.20
2. Snap-Fit for Forced Ejection (Undercut)
It is advisable to use a segmented design, generally applied to parts with minimal engagement or designed on soft rubber. Molds use forced ejection for demolding. The undercut amount typically should not exceed 0.25mm. Harder products require less undercut, such as common bottle caps for daily chemical products, pen caps, etc.
Description of the image: Female undercut, using mold forced ejection, undercut amount generally not exceeding 0.25mm.
3. For wider snap-fits, to improve the strength of the female snap, two smaller snap-fits can be designed within a large one. Ribs can be added to the back of the snap-fit to enhance its strength.
Description of the image: A fixed-lock form, which is harder to disassemble than snap-fits made on the inner wall of the housing.
4. The design of snap-fits should facilitate mold demolding. Pay attention to avoid interference with the movement path of lifters in the internal structure of the product. If possible, prefer a "shut-off" design over using lifters.
Description of the image: Using shut-off to avoid mold complexity.
5. For connections between plastic and metal materials using snap-fits, generally, plastic serves as the male snap, and metal as the female snap. The features are often formed using a T-slot cutter on a CNC machine.
Description of the image: Undercut form on a metal shell, shaped with a T-slot cutter on a CNC machine.
6. The engagement of a snap-fit is generally designed according to actual needs. Engagement below 0.5mm is considered a "live lock" (removable), while above 0.5mm is considered a "fixed lock" (permanent or hard to remove). For forms like battery covers, engagement can be designed to 1mm or more.
