Today most metal powder products are produced through compaction and sintering. That hasn't always been the case, though -- just look at the ancient Egyptians.
Arguably, the process we know today only emerged around a century ago. Before that, metal powder products were made through a process more like forging.
The technological improvements in powder metallurgy have come in waves. Are we in for another one soon?
Let’s first look at the history of powder metallurgy to this point. Then we can sort out how the future is shaping up for both supplier and customer.
Ancient people made use of many different metals, but they lacked a way to melt most of them.
While lead and tin have low melting points, the technology to melt materials like tungsten and platinum only emerged in the late 19th and early 20th centuries. As a result, jewelry, swords, and other metal pieces were produced by hammering powders into solid shapes.
There's evidence of this in Central and South America, where, long before the Spanish conquest, natives formed platinum and gold powders into jewelry. Earlier still, Indian craftsmen used the same method to make a 23' tall, 6-ton column of iron, the “Delhi Pillar.” Historians believe the Egyptians used similar processes. In Europe, records show powder forging occurring in Spain in the 18th century, and in England and Russia in the 19th. Russia even produced platinum coins using a powder forging method.
Modern powder sintering emerged in the late 19th century, alongside use of electricity. As fine wire filaments replaced electric arcs, the need for durable tungsten wire increased. Tungsten has a high melting point, and sintering became the accepted production method.
By the 1920s, manufacturers were using metal powders to make cutting tools and self-lubricating bearings. The 1930s saw the arrival of powdered metal oil pump gears along with sintered magnetic materials. Ten years later, German engineers had added firearms components to the growing list of metal powder products.
After World War II, demand for automobiles grew dramatically, and so too did production of sintered metal parts. This was also driven by the availability of higher-performance materials and improvement in compaction technology.
Two related powder metal processes to emerge were metal injection molding (MIM) in the 1980s and additive manufacturing from 2000 on. While conventional powder metal (PM) processing yields shapes compacted in a single axis, MIM has similarities with injection molding and enables creation of more complex geometries.
Metal Additive Manufacturing (AM), which includes 3D printing, takes one of two forms. Either there's a binder added to the powder, holding it together until after sintering, or the powder is sintered as it's deposited. Major differences in Metal Additive Manufacturing from convention powder metallurgy are
Less tooling required
Only suitable for very low-volume production
No compaction occurs
MIM and AM have a neat ability to form complex shapes. It complements what the sintering and compaction side of powder metallurgy can do. But the vast majority of the time, those two methods are cost-prohibitive.
The powder metal industry has continuously reinvented itself in the modern era. and those advances continue:
With the development of advanced materials such as soft magnetic composites and low-alloy materials.
With advanced compaction processes to produce part densities > 7.4g/cc.
With high-temperature sintering to further enhance the performance of PM parts that’ll allow even greater penetration into new and existing industries.
More and more new materials are being materially investigated and commercially implemented. Stay tuned!
New challenges will arrive in the form of emissions standards, further “electrification” of the automobile, and getting customers in hand tool and lawn & garden industries to realize untapped potential -- to name a few. The powder metal industry has been able to make customers’ products cheaper, but the next step is improving performance.
The industry's trade organization, MPIF, periodically publishes a road map prioritizing future technical challenges. Leaving aside additive manufacturing, the 2017 PM Industry Roadmap IDs the major areas of powder metallurgy’s development as:
Increased density
Using materials with higher melting points
Using soft magnetic composites
A small degree of porosity is normal in metal powder products. In some applications this is useful for lubrication or noise deadening. In others, it can limit both structural and magnetic performance.
Progress on increasing density has been slow for some companies. New-and-improved materials are helping, as are improved lubricants and tooling, and warm compaction and high-tonnage presses.
It’s clear that some powder metal parts suppliers are farther ahead than others in this challenge.
Industries using powder metal parts are looking for increased strength. PM components have a reputation of being brittle.
One way of achieving this goal is incorporating:
Vanadium
Tungsten
Molybdenum
Such alloys require sintering at higher temperatures. Ultra-high-temperature sintering is another capability that is unfortunately still limited to a handful of powder metal component suppliers.
We’re seeing increased interest in soft magnetic composite materials, From a variety of industry sectors.
This is because they can be formed into complex, 3D shapes, which in turn helps reduce the size of motors and actuators.
Humans have been making things from metal powders for a very, very long time. Only in the last century, though, has a powder metal manufacturing industry really emerged. And in the last 30 years, the rate of change has dramatically increased -- just like the world outside PM.
This has facilitated advances in industries from automotive and firearms to appliances and medical devices. It’s time for both customer and supplier to dig into the next wave of solutions for density, shape-making, and magnetic performance. And, yes, cost.
The solutions are out there! Trust advanced powder metallurgy to help you clear a path toward innovation.