What are the advantages of sintered steel?
Sintered Metal Products - PSM Industries
Powder metallurgy is the term for an array of processes used to create structural metal parts and components. The metal powders themselves are derived from raw metal materials. The material is converted to powder form through the atomization process.
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The powder metallurgy process used to create metal products includes the sintering process. Sintering is the thermal process applied to the formed component. Once completed, the metal particles fuse and the part achieves structural integrity.
First, the manufacturer fills a mold or die with the desired powdered metal material at room temperature, or in some cases the die is heated. The powder is compacted at high pressure until it forms the desired shape. The pressure amount varies depending on the metal material and the required density of the final part.
Once this step is complete, the formed metal is removed from the mold or die and placed into a sintering furnace. The furnace temperature depends on the material and density required. As a continuous thermal process, sintering is typically done in a belt conveyor, push, or batch furnace within a controlled atmospheric environment.
The furnace heats the metal form to a specific temperature. The time required varies depending on the application and materials used. As sintering occurs, the metal particles bond together to create a stronger and more rigid form. Some slight shrinkage may occur, which designers must account for when creating the initial design.
Advantages & Disadvantages of Sintered Metal: Strength & ...
Powder metallurgy can make small, complex parts for a variety of industries, including:
- Electric motors
- HVAC
- Automotive
- Firearms
- Lawn and garden
Several decisions must be made when considering the most effective metal forming technology. Engineers must evaluate performance needs, tolerances, budget limitations, and production quantities.
Sintering is a crucial PM process step to improve a part's strength. A compacted PM part is heated in a furnace up to about 2100°F, after which it might move on to various secondary operations.
While most PM parts are sintered, not all materials are suitable for sintering. SMC materials lose their magnetic performance when sintered. But this is only one of many variables when it comes to sintering:
Sintering Advantages and Disadvantages: The Variables
All powder metal parts need to be sintered unless they require the magnetic qualities of SMC materials. Sintering is a customizable process that varies depending on the materials, required properties, and desired tolerances.
Sintering processes vary from part to part, including changes in:
- Time at temperature
- Temperature itself
- Atmospheric conditions
Key elements of sintering are the creation of metallurgical bonds between materials, reduction of variability, and minimization of part waste. Advances in sintering furnace technology now offer the ability to control the furnace in real-time, improving these fundamental elements of the sintering process.
New, advanced systems help manufacturers streamline their processes and collect better data about the end quality of the part.
Sintering Considerations: The Material
What material system would you use to create a new design PM application?
Let's begin with a clear understanding of different part application needs.
High strength structural applications often require high:
- Tensile strength
- Fatigue strength
- Particle hardness
These core requirements necessitate higher alloy and carbon contents and strength-inducing heat treatments. Unfortunately, these requirements also significantly reduce DC magnetic performance.
Improving Performance With Sintered Soft Magnetics
Not all parts have specific strength requirements. Parts that need good magnetic performance often require:
- Very low carbon content
- High-purity materials
- Heat treatments to optimize magnetic properties
Certain alloying elements such as phosphorus and silicon in iron can improve magnetic performance and slightly enhance structural strength, but not to the level possible with higher-strength structural materials.
This type of material might be appropriate for applications like armature housing or fuel injection systems with magnetic solenoids.
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Improving Performance With Sintered Soft Magnetics
Sometimes the right magnetic performance can be achieved with various materials. In many instances, iron-phosphorus suffices. However, higher performance or faster responding solenoids may require the properties of iron-silicon material sintered at ultra-high temperatures for superior magnetic performance.
One of the primary allures of powder metal is its ability for unique material formulations and shape-making capabilities. Powder mixtures can be tailored to meet specific needs, and with proper sintering, can greatly improve overall performance for a better, longer-lasting part.
Standard Sintering vs. Sinter Hardening
With standard sintering, we focus on creating metallurgical bonds between materials. Sinter hardening takes that process a step further, providing heat-treated properties to a sintered part.
Sinter hardening is an accelerated cooling process that increases metal hardness, improving resistance to deformation under stress. It takes advantage of the intrinsic heat in the part during sintering, combining this with accelerated cooling to effectively heat treat the part, achieving high hardness and strength.
Conventionally, you'd form, sinter, and heat treat a part. But with sinter hardening, we can eliminate a thermal cycle and rely on PM's inherent net shaping capabilities to eliminate machining after sinter hardening.
Plus, part-to-part variation is much lower with sinter hardening compared to traditional sinter-heat treat-quench processes.
A caveat of sinter-hardened parts is that traditional machining operations can be challenging due to the hardness of the part.
High-Temp Sintering vs. Ultra-High-Temp Sintering (UHTS)
Traditionally, high-temp sintering utilizes temperatures of 2100-2300°F. Engineers have realized high-temp sintering enhances mechanical qualities compared to ordinary sintering, but often still falls short of other metal-forming technologies like forging.
Technological improvements in powder metallurgy have led to the development of ultra-high-temperature sintering (UHTS). This involves sintering compacted ferrous powder at temperatures approaching 2500°F, far above normal sintering temperatures. Higher sintering temperatures increase costs, but this is often offset by the dramatic improvement in part performance.
It also allows the PM process to use non-traditional alloying elements for unique combinations of strength, ductility, hardness, and heat treat response.
If the current part works with conventional sintering, you likely can't justify the upgrade cost to UHTS. But potential DC magnetic applications and high-strength components could benefit from new materials only achievable with UHTS.
Other Uses of Sintering for Powder Metallurgy
Sintering is also suited for unique parts requiring low-density, high-porosity gas flows.
Using a protective mask analogy, this is akin to breathing through an n95 mask versus a conventional mask. The looser the weave, the easier it is to breathe and let particles through. The tighter the weave, the harder it is to breathe and for particles to pass through.
With a filter, you want certain things trapped outside, so a high-porosity material is essential. Proper sintering can create a tighter, more compact shape while tailoring the necessary open porosity to optimize the often conflicting properties of good flow and filtration.
Improving Part Tolerances and Efficiency with Sintering
When decoding the benefits of sintering, work with an expert powder metallurgy consultant who can recommend the best approach for cutting costs and fulfilling your needs. Note that only Horizon's furnace technology has the unique capability to both sinter-harden and sinter at ultra-high temperatures.
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