Powder Metal Materials for Beginners
Powder metal materials free design engineers from the chains of typical metal forming technologies. While most metal forming technologies are best suited for round cylindrical shapes, powder metal can open a wide range of shape options to the designer without risk of high cost due to multiple machining operations.
While this benefit may be well understood, many designers have also recognized powder metals’ limited material properties. Today, instead of compromising the design to suit material properties or limited space, powder metal materials can be formulated and manipulated to suit your application’s needs.
The key is to understand how each possible metal additive influences performance and behavior.
Powder Metal Materials 101
By some estimates, 60%-70% of all parts made by powder metal are formed from an iron-carbon-copper (ICC) blend. During sintering, the iron and carbon combine to form ferrite, basically a form of steel.
The copper contributes in two ways. It melts to fill pores (though at the same time it leaves some voids), and it hardens the ferrite.
What's especially interesting is that in many cases, a very small quantity of alloying material can bring about a substantial change in finished part properties. That's important because while some of these metals are expensive, you’re paying for far less than you’d think.
In addition to “traditional” ICC, other common ferrous powder metal materials include:
- Stainless steel -- corrosion-resistant; sturdy at elevated temperatures
- Low-alloy materials -- higher strength for more demanding operations requiring heat treatment
- Sinter-hardening materials -- can be sintered and hardened in the same operation, eliminating secondary heat treating with improved dimensional precision
- Sintered soft magnetic materials -- for DC applications (speed sensors, solenoids, etc.)
- Soft magnetic composite -- for AC applications (motors, high-frequency transformers, etc.)
Thinking beyond the standard ICC powder metal material offers many benefits.
Increased strength can let a design engineer reduce part dimensions or reduce assembly size altogether, saving weight and space. Greater hardness can mean less wear and longer part life. It might even reduce the need for special coatings or lubrication. Better machinability can open up additional finishing options. Improved weldability might eliminate the need for fasteners.
If you’re not going to use iron-copper-carbon, then now what?
Designers and buyers often look suspicious when their manufacturer suggests powder metal materials more exotic than ICC. Naturally, they are concerned about higher piece costs, but there are two ways to look at this.
First, when adding a more expensive material, the gains in performance and design compactness may reduce the total amount of material needed. This might be important for those trying to reduce weight in automobiles, or any application for that matter. In addition, improving downstream “manufacturability” could reduce the cost of secondary operations. And don't overlook that the quantities of additives needed are often very, very small.
Secondly, dropping ICC altogether in favor of a material like the five categories above can radically change how the part is designed. The result could be a superior product at equivalent or even lower cost.
No More Trade-Offs
There's more to powder metal materials than just iron-carbon-copper. In fact, it's possible to blend powders to provide a very specific set of properties.
Design engineers working with powdered metal can use this to their advantage. Rather than accept the compromises required by a “standard” material -- as when working with castings, forgings, or billet stock -- get a material formulated to deliver exactly what you need!