Motor Weight Reduction Via Powder Metallurgy Materials.

Posted by Horizon Technology - September 09, 2020

Weight is a concern in just about every metal-based product today. Notably, cars have been on a strict diet for years now, and powder metallurgy materials have had an important role to play in it.

As sports car owners know, weight loss means better performance. For the rest of us it means improved gas mileage, and that translates to cost savings.

Here's a look at how various powder metal materials influence finished component weight, in automobiles and other industries. You’ll see that in many cases, powder metal (PM) is a key ingredient in reducing weight. And remember, weight costs money.

(Related Article: Choosing Powder Metallurgy Materials Part 1: Durability)

Choosing Powder Metallurgy Materials Part 2: Weight

What Motivates Companies to Lose Weight?

The U.S. Department of Energy's fueleconomy.gov website tells us every extra 100 lbs. a car weighs reduces miles per gallon by 1%. That adds up to a lot of fuel inefficiency:

  • For a vehicle that gets 20 mpg …
  • Driven 12,000 miles per year ...
  • It consumes 600 gallons of gas per year …
  • And if you lose 1% of that, it comes to 6 gallons lost annually per vehicle.

Sound far from exciting? When you multiply that by 80 million vehicles produced annually in the world, that’s 480 million gallons per year

Of course, that’s not the only reason lightweight materials for cars are highly coveted. For some designers, the primary concern is to reduce tailpipe emissions by burning less fuel -- especially outside the U.S. The extra gas bucks in your pocket are a bonus.

A typical conversion from a wrought metal part to a powder metal part provides a significant reduction in weight. If you think about the density of a wrought material, that’s 7.8 g/cc, versus a typical powder metal part, at 7.0 g/cc. That's a 10% reduction in weight!

Automotive isn't the only industry interested in weight saving. But what about other applications? Think about:

  • Electric motors
  • Motion control systems
  • Any application where less weight means less inertia and lower energy consumption

Powder metal materials help you get there in two ways:

  • They can be formed to net shape. Rather than being constrained by cutter paths or the need to let metal flow, designers can put material only where it's needed.
  • Powder metal parts are less dense than solid metals. Spaces left between the sintered metal grains reduce density, so a powder metal component will inherently weigh less than an equivalent cast, forged, or machined part.


Powder Metallurgy for Electric Motors

Perhaps one of the most exciting PM applications for weight reduction is with electric motors. Opportunity is rampant in traditional automobiles, but also with other forms of transportation, like e-bikes and e-scooters. 

Soft magnetic composite materials (SMCs) are an advanced material designed to expand the 3D shape-making capabilities of powder metallurgy while also offering heightened magnetic properties. SMCs, when used in electric motors:

  • Lower total core losses
  • Allow for higher frequencies
  • Lower energy consumption

That’s the appetizer, but here’s the main course: The increased density and shaping flexibility of SMCs can reduce the size of a motor up to 30%.

Think about small electric motors used in e-bikes and e-scooters -- that weight reduction really makes a difference. You don’t want to lug around an excessively heavy bicycle on a long ride. 

SMCs can greatly improve performance for non-traditional styles of electric motors used in small e-transportation. Use of SMCs -- from both a material and shape-making standpoint -- can improve your motor design’s performance: 

  • 20% higher peak torque
  • 40% higher constant torque
  • 20% greater battery range
  • 20% smaller motor diameter

Electric motor efficiency might be the coolest application for lightweight PM materials, but there are other benefits to explore …

Side Benefits of Porous PM Materials

Another reason powder-based parts interest auto industry engineers is their impact on “NVH” (noise, vibration, harshness). The porous nature of a powder metal part dampens sound and vibration -- a perfect design for gears. (For evidence, tap your fingernail on a PM part and notice how it doesn't “ring” like one that's solid.)

The porosity can retain oil for lubrication or filter fluids -- just two more reasons to consider powder metallurgy materials.

PM Meets Design Goals … But Which One?

Weight reduction is a priority for any engineer working on systems with movement. This includes motors and drives as well as cars and aircraft. 

Powder metallurgy materials can help achieve weight-loss goals, and improve performance in the process. Automakers and their suppliers are switching parts to PM wherever it makes sense, and the list of applications will keep growing.

In the end, material choice is a balance of performance and cost. Taking advantage of the net-shaping capabilities of PM can give you the best of both worlds. PM offers advantages, but under its current iteration it’s somewhat limited. What do we need to do to move past those limitations? The following can further reduce the core losses:

To learn more about how new advances in powder metallurgy -- and SMCs -- can improve electric motor performance, check out our Engineers’ Hub for Electric Motor Design!

View the Engineering Hub >

Topics: Powdered Metallurgy, Materials, Design, Properties, automotive

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