As more metal parts producers learn about the advantages of powder metallurgy, they search for new and improved ways to use this process. At the same time, they’re familiar and comfortable with the capabilities of their current go-to -- forging process.
But what if you could combine the two technologies to make forged metal parts with properties in excess of conventional powder metal (PM)? It’s actually possible, and actually has a name: powder metal forging.
Let’s learn about the uses of PM forging vs. conventional powder metallurgy and traditional forging. As a bonus, we’ll reveal a new alternative that exceeds even PM forging in efficiency …
What Is Powder Metal Forging?
Powder metal forging is the marriage of PM and forging. Also simply called powder forging, this type of metal forging uses powdered materials because of their advantages in:
- Shape-making capability
- Reducing the number of process steps to produce the final component with some potentially unique advantages, such as fracture splitting of the end cap of connecting rods
- Minimal scrap waste
Forging takes care of the rest, producing a high-strength part that will outlast a conventional powder metal component.
The process of creating forged powdered metal starts when the raw powder is compacted and then sintered. Immediately after sintering, but while the part is still hot (above 1800°F), a robot grabs it and transfers it to a forging die.
If real estate is about “location, location, location,” then the powder metal forging process is about “density, density, density.” The objective is to densify the PM part to as close as full density as possible. This gives you higher performance and higher mechanical properties. If done properly, you can eliminate 99%+ of the part’s porosity.
The Good: Conventional Powdered Metal Vs. Forged Vs. Combo Parts
Determining whether to use powder forging involves an understanding of what metals can be forged and which qualities matter most for your project. Powder metallurgy can produce even complex parts at a higher rate of production than forging.
Powder metal materials can undergo conventional sintering treatments that improve tensile strength and bending fatigue strength. Forming is easier vs. stamping and machining because of the net-shaping capabilities innate to PM.
Still, the metal forging process may be the better option when strength is an absolute must and PM is just not enough. Shape complexity is good via powder forging, but PM is still much better.
But there are still many instances when PM forging achieves impressive results. Take the connecting rod as an example. It has a unique shape where the pin end goes inside the piston, and the crank end is the big hole on the bottom that’s molded onto the high shaft. With PM forging, you can actually make those holes during the forging operation, with less material waste and no excessive “flashing” needed to fill the blocking or finishing forging impression.
You might forge 1.2 pounds of raw material for that rod with traditional forging, but with PM forging it might only be 1.02 pounds of a low-cost iron-copper-carbon powder. This means less secondary machining -- putting you ahead of the game.
Even Better: Ultra-High-Temperature as an Alternative to Powder Forging
Combining powder metallurgy with forging sure sounds like a win-win, right? That’s very true .. if your budget is not an issue.
To make forged metal products, the manufacturer needs:
- A compaction press
- A specially designed sintering furnace
- A forging press
- Other equipment
It’s very expensive to keep all these machines running, and that cost will fall directly in your lap.
Conventional PM might not give you the level of properties you want, but traditional forging can be super expensive. So what can be done with those in-between, in-limbo parts?
Ultra-high-temperature sintering can increase a powder metal part’s strength, along with other properties, to get you close to where you’d be with PM forging. We define ultra-high-temperature sintering as heating ferrous powder at temperatures approaching 2500° F.
This is where a compromise might actually give you more than the sum of its parts. Traditional powder metallurgy gives you 50-70% of what PM forging does properties-wise. Ultra-high-temp sintering gives you 80-90% of what PM forging can.
By using ultra-high-temp sintering, you can retain more of the inherent dimensional precision that metal powder offers, but also provide mechanical properties that approach PM forging’s capabilities.
An always-welcome side benefit is that material use may be a bit more efficient with a strictly PM process. When forging a connecting rod, the manufacturer must remove the “flashing” generated. Ultra-high-temperature sintering can produce a connecting rod that gives you the strength requirements without requiring the hand finishing that will make it ready for live action.
Sometimes, custom metal fabrication demands a custom solution. Suppliers of standard powder metal or forging solutions may not be capable of improving your component’s performance.
Ask a powder metallurgy expert about the best approach to cutting costs and improve the efficiency of producing your parts. Powdered metal forging was once great (and in some cases still is), but your goals may require you to think bigger with ultra-high-temp sintering!