What Makes an Ideal Component for Powder Metallurgy?

Contents:

Introduction

Material

Size / Shape (Limit)

Mechanical Properties

Closing

Introduction

As powder metallurgy manufacturers, one of the most common questions we get is “What makes a good candidate for the powder metallurgy manufacturing process?”  Although powder metallurgy has a wide range of capabilities, there are certainly some qualities that will allow a component to achieve the best possible results in both cost and performance when utilizing this process.

If your design includes features such as complex geometries, tight tolerances and high-volume production, it is often a strong candidate for powder metallurgy.

Let’s look at a few key factors that help us determine if powder metallurgy is the right process for a given component.

Material

First, we must state the obvious, powder metallurgy components are made with various metals.  The key here is in the word various.  This is one of the features that make powder metallurgy unique.  Components can be made from different types of metal.  The most common metals used are iron, copper and nickel, but these are often blended with other metals to create unique combinations that are not achievable through other processes.

A great example of a unique powder blend is the soft magnetic composite (SMC) powder blend.  This is an iron powder that is coated with an insulating layer.  When utilized in an electric motor this insulating layer reduces eddy current losses.  This technology is emerging as a key player in the electric vehicle industry as automakers look increasingly for ways to increase power output while simultaneously decreasing the size of the motor.  In fact, we previously dedicated an entire blog post to this subject.

One of the ways Porite utilizes the unique material combinations of powder metallurgy is in the manufacture of sintered oil-impregnated bearings.  Our R&D department performs rigorous testing on a variety of materials and has a recommended powder for a variety of uses.  Check out our sintered oil-impregnated bearing material chart here.

Powder as a material is also important for cost-conscious buyers.  Unlike other processes, like machining, where there is significant material waste, powder metallurgy results in very little waste.  The powder needed for a given component is pressed into that component and scrap rates are usually below 5%.  Higher material utilization means a lower final cost.

Size / Shape (Limit)

Size is another important consideration when determining feasibility for powder metallurgy.  Miniaturization is something that powder metallurgy excels at, so a component being too small is rarely a concern.  Components with a diameter of less than 1 cm can be created.

On the other hand, components that are too large can suffer from inconsistent and/or low density.  For this reason, it is important to consider the size of the component along with the chosen material and the press size.

We will use an example to illustrate how this works.  Each type of metal powder has differing pressure requirements.  Bronze, for example, has a lower required pressure than iron.  In this example, we will use iron powder as it is very commonly used.  Iron powder requires between 4 and 6 tons of pressure per square centimeter.  For this example, let’s use the middle of the range and assume a required pressure of 5 tons/cm².

Now that we know the required pressure for our component, we turn our attention to the surface area.  Assume the surface area is 100 cm². The required pressure can be calculated as 5 tons/cm² × 100 cm² = 500 tons. This makes the component suitable for our 500‑ton presses, which are among the larger (though not the largest) presses at Porite Group.

The above example is a good rule of thumb. At Porite Group, our presses reach up to 1,600 tons, though the largest machines are typically reserved for powders requiring higher compaction pressures. In this context, a surface area of 100 cm² represents a component on the larger end of what can be efficiently produced using this process.

Mechanical Properties

An ideal powder metallurgy component usually requires certain specifications that align with the advantages offered by powder metallurgy.  These specifications often fall into one of three categories: geometry, precision and/or performance.

The geometry of a powder metallurgy component often involves intricate designs that are difficult or expensive to achieve via other manufacturing methods.  Splines, grooves and teeth are examples of design features that are ideal for powder metallurgy.  Conversely, it is generally best to avoid designs that have extreme thin-to-thick transitions as these can create density issues.

Powder metallurgy offers a high level of precision and can achieve tight tolerances.  At the same time, the press and sinter manufacturing process is very repeatable with minimal variation.  This allows us, as the manufacturer, to create a high volume of components relatively quickly and still maintain a high standard for quality.

The performance capabilities of powder metallurgy probably deserve their own blog post.  However, we touched on some of this previously in the material section (see the discussion about soft magnetic composites).  One performance feature not yet mentioned, is controlled porosity.  This controllable porosity allows components with higher pore volume to be vacuum‑impregnated with oil.  The result is a bearing that self-lubricates, resulting in little to no maintenance and a longer life.  Read more about this feature in our blog post here.

A couple of other performance factors that buyers usually consider are tensile strength and elongation.  Most common tensile strength ratings for powder metallurgy range from 240 MPa to 380 MPa.  Elongation is generally not a strong point for PM with ratings in the range of 2-10%.  If a component requires a high degree of elongation, it may not be a great fit for powder metallurgy.

There are many post-processing steps that we can take to increase mechanical properties such as surface hardness, strength and dimensional accuracy.  Processes like plating, heat treatment, sizing and machining are all common steps that we, as powder metallurgy manufacturers, take to improve existing mechanical properties.

Let Porite Bring Your Design to Life

Now that you know what powder metallurgy excels at, perhaps you have your own powder metallurgy project in mind.  Reach out to the team at Porite and let’s get that design off the ground!  Contact us here.

If you’re unsure whether your component is a good fit, our engineering team can review your design and provide quick feedback!