Cost or Performance… or Both? Why the Compressibility of Powder Metals Matters

Improvements in powder compressibility is a key industry objective of Powder Metallurgy (PM), because it plays a significant role in the economical and effective production of powder metal components, benefiting both the Cost and Performance of your sintered metal parts. To help improve the cost and performance outcomes to our customers, the Atlas Pressed Metal’s Innovation and Technology team investigated the use of warm tool compaction, and lubricant selection to improve the compressibility within certain metal powders to achieve increased density resulting in improved overall performance to meet customer needs.

Compressibility is the ability of a solid or fluid to be reduced in size or volume under pressure. In PM, powder compressibility is quantified as the amount of compaction pressure that is required to achieve a given green density of a part. Typically, the higher the compaction pressure that can be achieved, the higher the resultant green density that can be formed. There are, however, limits to the amount the metal powders can be forced into the resultant shape. The compressibility of the metal powder particles controls how easily they can be compacted and how well they can be fused together during the thermal or sintering process. Highly compressible powder particles will pack together tightly and create a stronger denser component, while less compressible particles will not press together well and may require additional processes to reach a desired density. 

Compressibility is impacted by several factors that may be adjusted to reach optimal process conditions, including:

• Metal particle size and shape
• Chemistry of the metal powders
• Hardness characteristics of the metal particles
• The solid lubricant used in the compaction process
• Compaction and sintering strategy

The solid lubricant is used to help with the green strength of the compact, movement of the particles during the compaction process and facilitate the ejection of the component from the compaction die. Additionally, the solid lubricant protects the compaction tools from excessive wear, particularly at higher compaction pressures.

Warm tool compaction is a technique where the compaction tools are heated to assist in achieving  the desired density and mechanical properties. Warm compaction reduces the yield strength of the metal particles allowing for a more deformable metal particle. Warm compaction is a single action compaction step versus using more costly techniques such as double press/double sinter or cold forging to achieve a similar increase in density.

Following are several examples of studies completed for specific customer applications. The first chart (at right, Copper Steel) summarizes taking advantage of lubricant selection or warm compaction, or both to increase the compaction density as a function of compaction pressure with the same metal powder and chemistry.  The resultant increase of roughly 0.2-0.3 g/cm3 in compaction density led to an increase of ~20-40% in strength in the component for the customer application with respect to compaction force. 

Going beyond solid lubricant selection and warm tool compaction, the Innovation and Technology Team also looked at the type and chemistry of the base metal particles, changes in compaction temperatures of the warm tools and the addition of other elements to further improve compressibility to achieve specific densities for another customer application. 

This additional investigation, illustrated in the chart below, shows that with management of these various factors impacting compressibility, improvements in both green density and sintered density may be achieved.

Our Innovation and Technology Team's research can help you improve both the Cost and Performance of your finished components!

We look forward to working with your team to take our innovations and make them production ready.  Contact us today!