Powder Metallurgy Vs. Machining: Advantages & Disadvantages.

Posted by Horizon Technology - June 17, 2020

All manufacturing processes and technologies have their share of pros and cons. Yet, when it comes to powder metallurgy, few processes have changed for the better in a relatively short period of time. 

Today, the advantages of powder metallurgy rival many conventional manufacturing technologies -- even machining -- when it comes to the production of high quantities. There are many angles to look at when comparing powder metallurgy vs. machining -- here are the seven most important:

Advantages of Powder Metallurgy Vs. Conventional Machining

What are the advantages and disadvantages of machining processes compared to powder metallurgy (PM)? While your project’s specific needs will play some role in that answer, we can still break things down across seven categories. Each will help you better determine which manufacturing process is best for your application:

  1. Dimensional precision
  2. Quality
  3. Design flexibility
  4. Affordability (both per part and tooling)
  5. Strength
  6. Speed
  7. Scrap efficiency

1. Precision

Powder metallurgy creates parts with little -- if any -- room for error. Your manufacturer has full microstructural control and can customize the microstructure to meet the specific needs of your application. Done correctly, it’s a net-shape part fabrication process that reduces or even eliminates the need for secondary machining. That saves time, energy, and costs throughout the manufacturing stage of product development. 

Note that, on a part-to-part basis, PM can not provide the same dimensional precision of modern CNC machining.

Powder metallurgy does offer reliable part-to-part repeatability, which in part explains its popularity for large orders. The typical tolerances PM can hold are subject to the material being used to produce the part and process required. We have an overview of capability for some of the more common materials and processes in the e-book.

That said, your manufacturer will have to deal with a bit of distortion inherent to the thermal process every PM part undergoes. Since machining doesn’t involve sintering, it avoids this nagging issue.

2. Quality

Machining’s quality is dependent on the level of technology you’re using. CNC quality is nearly unmatched; manual machining not so much. If you have access to advanced CNC machining software, you can easily match specifications of complex parts. 

Not only is the quality of powder metal parts high, you can also take your part’s properties a step further with advanced materials. While most powder metal parts are made from a traditional iron-carbon-copper mix, there’s an abundant array of alternatives available that offer enhanced properties.

Potential additives include:

  • Nickel
  • Molybdenum
  • Chromium (a staple of stainless steels)
  • Niobium
  • Vanadium

Typically these metals add:

  • Corrosion resistance
  • Magnetic performance
  • Hardness
  • Strength (more on that below)

Unfortunately, harder materials are more difficult to machine (i.e. stainless steel vs., say, aluminum).

3. Design Flexibility

Powder metallurgy is an “additive” process, which means that design starts from scratch instead of from a slab of material. With the ability to create from the ground up, you can achieve advanced part designs in an instant. Powder metal gives you the ability to use geometries that would be difficult or wasteful in machining.

Even so, there’s a limit to net-shape forming with metal powder. The axial compression delivered by a punch moving into the die means your power metallurgy manufacturer can’t form some features. Either the powder won’t be moved into die, or if it does, release of the part afterward becomes difficult or even impossible. These features include:

  • Cross holes (although these can be formed with some newer compaction presses)
  • Undercuts
  • Threads
  • Reverse tapers

However, those features can be added later by machining.

One of the unique aspects of powder metallurgy is the ability to form helical gears. Most helical gears are in the 20° angle range. PM can mold helical shapes up to 35° -- with zero waste. And, in some of the most advanced powder metallurgy processes, you can even form cross-holes.

Powder Metallurgy Vs. Machining Advantages & Disadvantages - tooling4. Affordability (Per Part and Tooling)

Cost-effectiveness is the predominant reason OEMs request powder metallurgy services. PM wins the cost competition vs. machining thanks to:

  • Elimination of process steps
  • More efficient material use (more on that below)
  • Potential lower energy consumption per component produced vs. starting material, when you factor in material losses due to machining
  • Ability to make complex shapes that conserve material

One of the disadvantages of powder metallurgy is that short product runs are a poor fit thanks to per-part costs and tooling costs. For tiny production runs, CNC machining remains a more affordable option. CNC machining requires no tooling costs.

5. Strength

A machining operation can take on any steel you throw at it and slice and dice it. Today’s machine shops work with some amazingly high-strength materials that give great performance.

Powder metal parts by nature aren't as strong as machined parts. Why? They have tiny holes, aka porosity. 

Keep in mind that powder metal parts can be stronger than you think thanks to advanced sintering technology. Sintering may give you the level of strength you need while allowing you to take advantage of powder metallurgy’s many other advantages over machining.

6. Speed

Powder metal, like cupcakes, is better when the batch is large. 

For short-run orders, you may be better off with conventional machining. A machined part only takes a few weeks total. It doesn’t take much effort to put a piece of bar stock in the CNC mill and start whittling away.

But once you have a tool in place, that's when powder metallurgy suppliers begin to shine. It’s infinitely better than machining at producing a 10,000-part job, especially compared with a 10-part job.

7. Scrap Efficiency

Powder metallurgy makes far more efficient use of its raw materials -- we’re talking 3% scrap rates vs. up to 50% in machining. Because the powder metallurgy process is an additive one, your manufacturer only needs as much material as your design requires. 

This is why the world now recognizes powder metallurgy as one of the most sustainable of all metal manufacturing processes.

While scrap materials from machining processes can be recycled, these operations still account for significant material costs, much of which is discarded.

The Winner Is … (and More Debate)

There’s no need to start your project with that depressing thought of, “How much material am I paying for that’s going to get thrown away?” Instead, with the right powder metal process, you can dream of the endless design and cost-cutting possibilities you’ve opened up.

Our free e-book below reveals more about the pros and cons of powder metallurgy vs. machining, stamping, casting, forging, MIM, and more. Don’t miss the chance to discover a cost-cutting or performance-boosting trick you never knew existed!

Powder Metallurgy vs. Competing Methods

Topics: Powdered Metallurgy, Tooling, Materials, Costs, Design, Properties, Processes, machining

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