Rotor Lamination Stacking

We need stacks of insulated thin sheets. But how do you hold them all together tightly, perfectly aligned, and ready to become the heart of a high-performing motor? This is where the specific technique of rotor lamination stacking becomes critical, and where Sino’s expertise really shines. There are several ways to skin this particular cat, each with its own playbook.

1. Welding: The Quick Bond (When Handled with Care)
   
   You’ll often see lamination stacks with neat weld beads running along their outer diameter. TIG (Tungsten Inert Gas) or laser welding are common choices here. It can be a fast and cost-effective way to achieve a mechanically robust stack.

• The Upside: It’s relatively quick, lends itself well to automation, and can provide good axial strength. For many general-purpose motors, it’s a solid, economical choice.
• The Catch: Here’s where you need a skilled hand. Welding, by its very nature, involves heat. If not controlled precisely, this heat can locally damage the crucial interlaminar insulation. This can create short-circuits between laminations right at the weld zone, leading to increased localized eddy current losses and unwanted hotspots – exactly what we’re trying to avoid! It can also subtly alter the magnetic properties of the steel near the weld.
• Sino’s Approach: At Sino, when welding is the chosen route for a rotor lamination stacking project, we employ advanced, controlled welding processes. This includes precise parameter settings, often utilizing laser welding for its minimal heat-affected zone, and rigorous post-weld inspection. We understand the metallurgy of the electrical steels we work with, ensuring we minimize any negative impact.
  • Real-World Scenario: A client producing robust industrial pump motors needed a cost-effective stacking solution for medium-volume production. Our optimized TIG welding process, combined with strategic weld placement and quality checks, delivered the mechanical integrity they needed without significantly compromising the core loss performance, keeping their unit costs competitive.

2. Interlocking (Stitching/Stamped Features): The Mechanical Lock-In
   
   Think of this like tiny metal Lego™ bricks. During the stamping process where each lamination is cut to shape, small protrusions (bumps or “dimples”) and corresponding recesses are formed directly into the steel. As you stack them, these features interlock, creating a mechanically joined core.

• The Upside: A huge plus is that there’s no heat involved in the joining process itself, so the interlaminar insulation remains pristine across the entire lamination surface. This is fantastic for preserving electrical performance. It’s also a very automation-friendly technique, great for high-volume production.
• The Catch: Those little interlocking features, while clever, do take up a tiny bit of space that could otherwise be magnetic steel. This slightly reduces what’s called the “stacking factor” – the ratio of actual magnetic material to the total stack volume. Also, the stamping process for these features needs precise tooling and can sometimes introduce minor stresses into the laminations.
• Sino’s Approach: We’ve invested heavily in precision tooling and stamping technology. For interlocking rotor lamination stacking, our dies are engineered to create clean, consistent interlocks that maximize holding power while minimizing material displacement. We also advise clients on how the interlocking pattern might influence magnetic flux paths.
  • Real-World Scenario: A manufacturer of servo motors for automated packaging lines required extremely consistent rotor geometry and minimal core losses. Our interlocking solution provided the tight tolerances and excellent electrical insulation they needed for high-speed, precision movements, and our high-speed stamping lines met their volume demands.

3. Bonding (Adhesives/Backlack): The Ultimate Insulated Union

    

   This is where things get really sophisticated. An adhesive coating, often called “backlack” or “bondable insulation,” is applied to one or both sides of the lamination sheet before it’s stamped. After stacking, the entire assembly is subjected to heat and pressure in a curing process. This activates the adhesive, bonding the laminations into an incredibly solid, yet still perfectly electrically insulated, unit.

• The Upside: This method is often considered the gold standard for electrical insulation integrity between laminations. It results in a very rigid, dimensionally stable stack, which is great for reducing noise and vibration. The adhesive can also help to dampen mechanical resonances.
• The Catch: It’s generally a more involved process. The application of the adhesive, the careful handling of coated material, and the curing cycle (time, temperature, pressure) add complexity and can increase the per-unit cost compared to simpler methods.
• Sino’s Approach: Sino has dedicated clean-room facilities and specialized curing ovens for adhesive bonding. We work with various grades of backlack, matching the adhesive properties to the motor’s operating temperature and environmental conditions. Our precise control over the curing process ensures a complete and uniform bond, leading to superior performance in demanding scenarios like high-efficiency EV motors or quiet appliance motors. This advanced rotor lamination stacking is a cornerstone of our offering for premium applications.
  • Real-World Scenario: A high-end electric vehicle manufacturer approached us to produce rotor cores for their next-gen powertrain. Their key requirements were maximum efficiency, minimal noise (NVH), and high rotational speed capability. Our adhesive bonding process using a specialized high-temperature backlack delivered exceptional results, contributing to their vehicle’s impressive range and quiet operation.

4. Cleating or Riveting: The Old Guard (Still Kicking for Some)

    

   These are more traditional mechanical fastening methods. Cleating involves forcing strips of metal into axial grooves punched or machined into the stack’s periphery. Riveting, as the name suggests, uses rivets passed through holes in the laminations to clamp them together.

• The Upside: For certain designs, especially older ones or very large, low-speed industrial motors, these can be straightforward and robust solutions.
• The Catch: Both methods inherently reduce the active magnetic material (lowering the stacking factor) because of the space taken by the cleats/rivets and their associated holes. They can also be more labor-intensive and might not be the best choice for high-speed motors where balance and minimizing windage losses are critical. Over time and under thermal cycling, there’s also a slight potential for looseness to develop.
• Sino’s Approach: While we see these methods less frequently for new, high-performance designs, Sino maintains the capability to produce cleated or riveted stacks for legacy applications or specific customer requirements. We ensure precise alignment and secure fastening to maximize the performance achievable with these techniques.

Here’s how these common rotor lamination stacking methods stack up, if you’ll pardon the pun: