Today the manufacturing world understands the compactibility and compressibility of powdered metals much better than the “old days” (~20 years ago). This growth in knowledge has expanded the industry’s opportunities to produce complex, structural-grade components.
Understanding powder compaction is crucial to controlling properties such as component density, shape, size, porosity, and hardness. To help modernize your part's performance and cost-efficiency, let's review the powder compaction process in powder metallurgy:
Each step of the powder metallurgy process involves many variables that impact the performance and longevity of your final component. A familiarity with the overall process will help you better understand how compaction’s role is pivotal to consistency and precision.
The conventional die pressing and sintering process includes four steps:
Read more about the PM process here.
In powder metallurgy, the compaction process is the shaping, deformation, and densification of a material via pressure from a tooling set. Die compaction, the most common means for shaping and densifying a powder, applies pressure through upper and lower punches to press a powder into a “green,” pre-sintered compact.
A compaction tooling set is designed for each custom component. A basic set of compaction tooling includes a die cavity, upper and lower punches, and a core rod. Tool designers create sets around powder specifications, press designations, and a part’s shape. As you can see above, there are sets for both single-level and multilevel tooling.
In the die pressing process, compaction is a continuous cycle. Tooling motions start in the fill position and then move through the compaction and ejection stages.
The end result is a compacted “green” part. The component's density and strength during this stage are referred to as green density and green strength. For reference, these compacts have similar green strengths to Life Savers candy and Aspirin tablets.
A key to understanding the aspects that influence compaction is knowing about compressibility. Compressibility is the capacity of a metal powder to undergo densification during applied pressure in a closed die. A material's compressibility is impacted by several factors the manufacturer can adjust to reach optimal conditions.
By definition, a particle’s size is less than 1 mm. Even at the microscopic level, size matters.
Particle size influences how well materials can be packed together. Particle shape influences flow, packing, and overall compressibility of the material blend during compaction. Irregularly shaped particles tend to pack together better than other shapes during the conventional pressing process.
Different alloys and elemental compositions tend to show varying compressibility behaviors. For example, elemental powder blends made with iron, nickel, or copper materials compact more easily than prealloyed materials.
The hardness of your chosen material can impact compressibility. Harder materials are more challenging to deform, meaning they’re less compressible. Softer, more ductile particles can deform more easily during compaction.
The presence and amount of lubricants affects how well particles “slide” past each other during compaction (instead of stubbornly staying in place). The proper lubricant and processing can:
Compressibility plays a significant role in the economical and effective production of powder metal components. Specific requirements for improving compactibility may vary based upon your part’s material or application.
Particle size and shape, chemical composition, hardness, and lubrication are all customizable for a smoother pressing process. Your best strategy may include:
Can small changes increase the density – and strength – of your part?
A powder metallurgy expert can look at your application to determine if there are opportunities to improve the performance and life span of your component.
To take full advantage of the powder metal process, visit our blog library and keep learning:
(This article was recently updated with new insights)