Waterproof Switch Assembly for Slim Metal Toothbrush Handles
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Solution Overview
Problem
Metal housings for electrically operated personal care implements, such as toothbrushes, face challenges in creating a waterproof switch area due to thin wall thickness and limited design freedom, leading to insufficient bonding force and potential water ingress.
Innovation Solution
A method involving a metal tube housing with a hard switch component and a soft switch component, where the soft switch component is over-molded into an undercut of the hard switch component, providing a secure and waterproof seal by locking the soft switch component from three sides, preventing peel stress and ensuring a durable bonding connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a metal housing with thin wall thickness is used, then the housing durability and stability are improved while enabling a slimmer product design, but the bonding area between components is limited and sufficient bonding force cannot be achieved
Solution Approach 1:
The patent transitions from a single-dimension bonding approach (flat surface bonding) to a multi-dimensional bonding solution by creating an undercut geometry. The undercut forms a recess that extends into the housing wall, allowing the soft component to be bonded not only to the outer surface but also to the inner surface and side walls of the recess, effectively utilizing three-dimensional bonding area to compensate for the limited outer surface area available on thin-walled metal housings.
Solution Approach 2:
The soft switch component is nested within the undercut recess of the hard switch component, which itself is attached to the metal housing. This nested arrangement allows the soft component to be securely held within the recess, with bonding occurring on multiple surfaces (outer surface, inner surface, and side walls), creating a layered, nested bonding structure that maximizes bonding strength within the limited wall thickness.
2Length of moving object
If a metal housing with thin wall thickness is used, then the overall product design can be slimmer, but the bonding area is limited and let-in flush switch area cannot be overmolded onto the housing
Solution Approach 1:
The switch assembly is segmented into multiple components: a hard switch component (frame) and a soft switch component. The hard component is first attached to the housing to create an undercut recess, and then the soft component is overmolded into this recess. This segmentation allows each component to be manufactured and assembled separately, making the overall manufacturing process feasible despite the constraints of thin-walled metal housing.
Solution Approach 2:
The hard switch component frame is attached to the housing in advance, creating the undercut recess structure before the soft switch component is added. This preliminary action prepares the bonding geometry in advance, allowing the subsequent overmolding process to proceed successfully by providing the necessary recess into which the soft component can be bonded, thereby enabling manufacturing on thin-walled housings.
3Strength
If a simple metal tube housing is used, then the design freedom is reduced and bonding area is limited, but the housing maintains high durability and stability
Solution Approach 1:
While the overall housing maintains a simple metal tube geometry for durability, the local area around the switch opening is modified to include an undercut recess. This localized geometric modification provides the necessary bonding complexity only where needed (at the switch assembly location) without changing the overall simple tube structure, thereby maintaining both durability and the required adaptability for waterproof switch assembly.
Data Source
AI summary
A method for manufacturing a handle for an electrically operated personal care implement comprises the following steps: providing a metal tube housing having a metal wall with an opening therein and an inner surface defining an inner cavity for accommodating an energy source; providing a hard switch component comprising a frame with a recess; attaching the frame of the hard switch component to the inner surface of the metal wall, the frame surrounding the opening and providing an undercut between the recess and the inner surface, the undercut being open towards the opening; and at least partially over-molding the opening to form a soft switch component in the undercut, thereby forming with the hard switch component a switch assembly for activating the energy source, the switch assembly sealing the opening from the inner surface of the metal wall.