Magnetic Design
By providing magnetic design assistance, Encap enables customers to make step change improvements in performance and cost. The move to encapsulation can often be combined with a redesign of stator geometry or magnetization scheme.

The spindle motor shown below demonstrates the benefits obtainable. The right-hand side shows the original design, while the improved design is shown on the left. Encap redesigned the stator to significantly reduce vibrations, costs, and thermal rise. The stator was reconfigured to reduce vibration, with the plastic unitizing the wound stator, baseplate, and hub.

Thermal Design
The intimate contact of encapsulated plastic over wire-wound devices allows significant removal of thermal energy. Encap performs ANSYS-based thermal design analyses to evaluate and optimize the potential encapsulants and system design. Plastic acts as a thermal pathway, not a heat sink, and as such it is critical to design the component with this consideration in mind. When designs are optimized, relatively low heat rises can be created, as evidenced by the image below, showing a small, encapsulated high-speed spindle motor for the hard drive industry.

Mechanical Design
Encap evaluates the entire insert/encapsulant system to determine new possibilities that can be created in the encapsulated design. Using advanced filler technologies including carbon fiber and ceramics, components are created to take the place of and eliminate current steel and die-cast aluminum load-bearing components. FEA is used to determine the ability of the encapsulated structure to withstand fatigue, stress, and impact loadings. Encap has enabled peak vibration reductions of up to 5 decibels in motor redesign.

An example of Encap’s holistic approach to encapsulation design is shown at right, where a new approach was created to address the challenge of economic and efficient winding of small motor stators. Encap developed a process to produce strip laminations, wind the lams using fly winders, roll form, and then encapsulate the lams in plastic. The plastic acts as a cement to lock lamination ends in contact with each other. An encapsulant with coefficient of thermal expansion (CTE) similar to that of steel was developed in order to maintain the contact between the lamination ends over a range of temperatures. Added benefits are reduced stator steel scrap and improved magnetic properties due to the uniform grain orientation in the poles.

Another example of this holistic approach to encapsulation design is Encap’s work with segmented stator designs. As with roll-formed stators, a segmented stator allows higher slot fill (more power) than is obtainable with conventional stators. Segments are encapsulated with a thin layer of plastic to provide ground insulation. A continuous chain of segments is formed which resolves numerous manufacturing issues. Fly winding is used so that multiple poles can be wound simultaneously. Sufficient wire is left between arc segments, such that the segments can be removed from the winding fixture and oriented into the final geometry. These segments are then placed into an injection mold for encapsulation. Side actions are used to align the segments in their final position. Thermoplastic is injected into the mold, locking the segments together and simultaneously forming mounting and connection features. A low CTE material insures that steel positioning is maintained over a range of time and temperatures.

Tooling Design
Encapsulated designs require specialized injection mold tooling expertise. It is standard for Encap to design tools that handle a variety of the termination methods and which can handle shot-to-shot variations in motor lamination stack thickness. The same tool can be designed to produce motors of multiple stack heights. Many ceramic-filled resins are abrasive to molds and machinery, however, Encap has developed proprietary tooling techniques to mitigate these issues.

The image below shows a tool designed for encapsulation of a 21" diameter stator for a BLDC motor for a remote submersible vehicle (RSV). The part had to be completely and hermetically sealed from the outside atmosphere — in this case, water at a depth of 20,000 feet and a static pressure of 10,000 psi. A series of pins was used to position the stator; the pins were then retracted during the molding process to enable a complete encapsulation. (See Case Studies for additional details.)