If you’re new to the powder metallurgy process, you’re not alone.
Powder metal parts have been around for thousands of years in some shape or form. They can be found in numerous industries and offer distinct advantages over parts made through other manufacturing processes, such as forging.
Yet much of the greatest advances in powder metallurgy have come in the 21st century and are confined to a select few manufacturers. Furthermore, many industries that are a great fit for powder metal have been slow in realizing the potential that exists.
So, even though powder metallurgy is an old process that’s a staple in the auto industry, few people understand exactly how the process works. So, how are powder metal parts made? The following is a basic run-through of what powder metallurgy is and what it offers.
Here are the steps in the powder metallurgy process that turn sand-like grains into powder metal parts:
Creating metal powder in the first place is a challenge all on its own. Maybe this explains why there is a very limited number of high-volume ferrous powder producers in North America.
A metal parts manufacturer only purchases powder after it has all the design specs it needs from the client. The manufacturer needs to know exactly what you need the part to do and what properties matter most. Once that happens, the supplier reaches out to its own certified supplier and buys powder based on your performance criteria.
The greatest majority of powder is purchased premixed with additives and lubricants based on product specs. In certain cases the part producers will prepare their own premixes for custom applications.
With the perfect mix complete, the powder heads through a hopper system, which then goes into what’s called a “feed shoe.” The “shoe” then feeds the powder into the die cavity. The die determines the basic shape of the part.
The design of the feed shoe is crucial; poor design will cause issues in the next stage. You can’t just dump powder straight into the die, either, so your manufacturer will need to put its best shoe forward.
The press puts a massive amount of force onto the powder in the die, which causes the particles to mechanically interlock. Imagine your children reaching into a bag of popcorn and squeezing. Popped popcorn has a similar shape to metal powder -- you can see how the pieces interlock.
Think that’s the end of the line? Wrong. At this point the component only has what is known as “green strength.” It’ll maintain its shape, but it’s still not strong enough to stand up to real-world demands.
With forged and machined components, deburring is an important process. It removes any leftover metal protrusions that can cut the hands of anyone touching it and making assembly more difficult.
Deburring is important to powder metal manufacturing even though the process creates a net shape part (or near-net shape part) right off the bat. Burrs are inherent in the powder metallurgy process, and removing it is a must.
Sintering is the process of heating up the part to just below the material’s melting point. This makes the part significantly more durable.
The first step in the sintering stage is lubricant removal. This is followed by …
… with the end goal being improved strength.
The cooling process isn’t just so you don’t need oven mitts to touch the components. It’s actually very important in determining mechanical properties.
While heating fuses metal particles, the way the part is cooled determines its hardness or softness. It’s like letting your homemade chocolate chip cookies sit in the fridge vs. eating them while they’re still gooey.
Most parts are ready for final assembly after sintering -- approximately 60-70% of them. This is arguably the greatest strength of powder metal.
However, some parts may require secondary processes like steam treating or heat treating. These processes may be handled in-house by the powder metallurgy company or outsourced to a partner.
And that’s how a powdered metal part is born! You probably noticed that there are very specific things powder metal manufacturers do that differentiate the end result from competing processes.
That’s why it’s important for engineers and purchasers to research before assuming a certain manufacturing process is the ideal one for their project. Powder metallurgy can produce high volumes of parts quickly, consistently, and with unique properties. But while PM parts are amazing for numerous applications, there other situations it’s not viable.
The quickest way to verify if powder metal is right for you is to go straight to a manufacturer. Another way to compare the advantages and disadvantages of powder metallurgy vs. other processes is check out the links below!