Overmolded Stator Lamination Stack for Power Tool Motors
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Solution Overview
Problem
The existing methods for assembling stator laminations in electric motors, particularly in power tools, are costly and burdensome due to the need for welding loose laminations together to form a solid flux ring, and they suffer from inefficiencies in magnetic flux due to air gaps and adhesive/resin use.
Innovation Solution
The stator lamination stack incorporates magnet pockets for embedding permanent magnets, reducing the magnetic air gap with magnetically-conductive spacers and eliminating the need for adhesives or overmold resins, while using an overmold resin layer with magnetically-conductive material in end caps to enhance flux density and structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If loose laminations are used for the stator assembly, then flexibility in assembly is improved, but welding is required which increases cost and manufacturing complexity
Solution Approach 1:
The stator assembly is segmented into multiple loose laminations that can be individually handled and assembled. Each lamination is a separate component that can be positioned independently, providing assembly flexibility while avoiding the need to weld a solid flux ring.
Solution Approach 2:
An adhesive layer is introduced as an intermediary substance between the loose laminations to bond them together. This adhesive mediator replaces the need for welding, eliminating the associated high costs and manufacturing complexity while maintaining the flexibility benefits of loose laminations.
2Loss of energy
If adhesive or resin is used to retain magnets, then magnetic flux is blocked creating air gaps, but eliminating adhesive requires alternative retention methods
Solution Approach 1:
The adhesive layer that was previously used to retain magnets is completely removed from the design. By extracting this harmful element, magnetic flux continuity is restored and air gaps are eliminated, improving magnetic flux efficiency while the magnets are retained through mechanical embedding in magnet pockets.
Solution Approach 2:
Magnets are nested within magnet pockets formed in the stator lamination stack. This nested arrangement provides mechanical retention for the magnets without requiring adhesive, eliminating the magnetic flux blocking effect while maintaining secure magnet positioning.
3Ease of manufacture
If pre-stacked laminations are used, then assembly is simplified, but it is difficult to add or remove laminations
Solution Approach 1:
The lamination stack transitions from a fixed pre-stacked configuration to a dynamic, adjustable assembly. Loose laminations can be individually added or removed based on specific application requirements, providing adaptability while the adhesive layer ensures stable assembly once configured.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly reduces the magnetic air gap, increases flux density by up to 56%, allows for smaller magnets and reduced material usage, and lowers production costs by eliminating adhesive and overmold barriers, while providing dimensional flexibility and improved demagnetization resistance.
Implementation Method 1
reducing the magnetic air gap with magnetically-conductive spacers and eliminating the need for adhesives or overmold resins
Implementation Method 2
overmold resin layer with magnetically-conductive material in end caps to enhance flux density
Data Source
Figure 1
Figure 2~3
Figure 4A
AI summary
A power tool is provided, including a housing, a permanent magnet electric motor in the housing, and an output member coupled to the electric motor. The electric motor includes a rotor and a stator with at least a North pole and a South pole. The stator includes a lamination stack having loose laminations held together via an overmolded resin. The overmolded resin include a longitudinal overmold layer covering at least a portion of at least one of an inner or outer surfaces of the lamination stack, and two end cap portions extending laterally from the ends of the longitudinal overmold layer to firmly cover ends of the lamination stack.