Q&A: Powder Metal and Powder Materials Parts

 

List of Questions

How does magnetic pressing work with powder materials?
What part shapes can be made?
What materials can be used?
What densities can be achieved?
How much pressure does magnetic pressing deliver?
Why use Magnepress instead of a mechanical or hydraulic pressing?
Why use Magnepress instead of HIP (Hot Isostatic Pressing) or CIP (Cold Isostatic Pressing)?
Why use Magnepress instead of forging?
Why use Magnepress instead of casting?

For answers to more general questions, click here.

Answers

P/M press animationHow does magnetic pressing work with powder materials?

It works great! The powder is loaded into an electrically conductive tube (such as copper, aluminum, or steel.)  The tube is placed at the center of the electromagnetic (EM) coil.  A current pulse is put through the coil, creating high magnetic pressure radially around the tube. The kinetic energy of the tube wall presses the powder into a high-density, near net-shape part.

For parts like rings or gears, the powder is loaded around a die centered in the tube to form part features such as gear teeth.  A round die can be used to form rings or tubes. Other part shapes are possible.

The pressure pulse lasts less than a millisecond, allowing production rates of many parts per minute. The magnetic pressing can be done either at room or elevated temperature, and in air or controlled atmospheres.

After the part is pressed, it can be sintered, or "baked," to improve its strength.  For some applications, however, the parts are strong enough that the sintering step can be omitted.

 

powder metal partsWhat part shapes can be made?

Lots of shapes. The photo shows several examples, including:

For more examples and details, click here.

 

What materials can be used?

Anything you can load into a tube can be magnetically pressed.  Some examples are:

wpe2D.gif (8554 bytes)What densities can be achieved?

For any given material, Magnepress usually delivers higher density than die pressing. For example, the graph shows densities for a particular steel powder that was warm die pressed at 30 to 60 tons per square inch. The same powder was then magnetically pressed at room temperature (22C) and warm (150C). The magnetically pressed powders were higher density.

We have pressed iron, stainless steel, tool steel, aluminum, ceramics, various nano-powders, and other materials. While some powders are more compressible than others, Magnepress almost always delivers higher density than die pressing.

How much pressure does magnetic pressing deliver?

Magnetic pressing delivers a dynamic pressure, not a static pressure like die pressing. Because of this, it is not very meaningful to report pressures in familiar static units like "tons per square inch" (tsi).  Therefore, the points on the graph above representing magnetic pressing should not be taken literally as indicating 30 tsi of pressure.  Only the % Density axis should be read literally.

The powder is pressed by the kinetic energy of the wall of the tube the powder is in.  The tube wall gets its kinetic energy from the magnetic forces between the coil and the tube.  These forces rise to a peak and fall back to zero within a millisecond.

The best analogy for magnetic pressing is explosive compaction.   The scaling factor in both processes is the amount of energy deposited per unit mass of powder.  The more energy per unit mass of powder, the more dense the powder becomes.

What is the upper limit for pressure? This is usually determined by the strength of the tooling such as the dies or the coil containment structure. If you make the tooling stronger, you can probably increase the pressure.

Why use Magnepress instead of mechanical or hydraulic pressing?

Why use Magnepress instead of HIP (Hot Isostatic Pressing) or CIP (Cold Isostatic Pressing)?

Why use Magnepress instead of forging?

Magnetic pressing offers the performance of a forged part at the lower cost of a P/M part. Here's why:

Why use Magnepress instead of casting?