All manufacturing processes and technologies have their share of pros and cons. Yet, when it comes to powder metallurgy, few processes have changed for the better in a relatively short period of time.
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Today, the advantages of powder metallurgy rival many conventional manufacturing technologies -- even machining -- when it comes to the production of high quantities. There are many angles to look at when comparing powder metallurgy vs. machining -- here are the seven most important:
7 Advantages & Disadvantages of Machining vs. Powder Metal
What are the advantages and disadvantages of CNC machining processes compared to powder metallurgy (PM)? While your project’s specific needs will play some role in that answer, we can still break things down across seven categories. Each will help you better determine which manufacturing process is best for your application:
Dimensional precision
Quality
Design flexibility
Affordability (tooling and per part)
Strength
Speed
Scrap efficiency
1. Precision
Powder metallurgy creates parts with little -- if any -- error. Your manufacturer has full microstructural control and can customize that microstructure to meet the specific needs of your application. Done correctly, it’s a net-shape part fabrication process that reduces or even eliminates the need for secondary machining. That saves time, energy, and costs throughout the manufacturing stage of product development.
Note that, on a part-to-part basis, PM can not provide the same dimensional precision of modern CNC machining.
Powder metallurgy does offer reliable part-to-part repeatability, which in part explains its popularity for large orders. Powder metallurgy tolerances depend on the material and processing your part requires.
Your small-component manufacturer will have to deal with a bit of distortion inherent to the thermal process every PM part undergoes. Since machining doesn’t involve sintering, it avoids this nagging issue.
A common axial flux stator made via soft magnetic composite (powder metallurgy), manufactured without machining.
2. Quality
Machining’s quality is dependent on the level of technology you’re using. CNC quality is nearly unmatched; manual machining not so much. If you have access to advanced software and understand CNC machining design guidelines, you can easily match specifications of complex parts.
Not only is the quality of powder metal parts high, you can also take your part’s properties a step further with advanced materials. While most powder metal parts are made from a traditional iron-carbon-copper mix, there’s an abundant array of alternatives available that offer enhanced properties.
Potential additives include:
These metals, along with processing steps exclusive to powder metallurgy, can add:
One limitation of the conventional machining process is you can't just throw multiple materials in a blender and get the best properties of both worlds.
Furthermore, machining of hard materials can prove difficult (i.e. stainless steel). What about the machinability of powder metallurgy steel parts, as part of secondary finishing? It's generally a non-issue,. although soft magnetic composites (a material group dedicated to magnetic performance) are usually too brittle to machine.
3. Design Flexibility
Powder metallurgy is an “additive” process, which means that design starts from scratch instead of from a slab of material. With the ability to create from the ground up, you can achieve advanced part designs in an instant. Powder metal gives you the ability to use geometries that would be difficult or wasteful in design for CNC machining.
Even so, there’s a limit to net-shape forming with metal powder. The axial compression delivered by a punch moving into the die means your power metallurgy manufacturer can’t form some features. Either the powder won’t be moved into die, or if it does, release of the part afterward becomes difficult or even impossible. These features include:
However, those features can be added later with machining services.
One of the unique aspects of powder metallurgy is the ability to form helical gears. Most helical gears are in the 20° angle range. PM can mold helical shapes up to 35° -- with zero waste. And, in some of the most advanced powder metallurgy processes, you can even form cross-holes.
4. Affordability (Tooling & Per Part)
Cost-effectiveness is the predominant reason OEMs request powder metallurgy services. PM wins the cost competition vs. machining thanks to:
Elimination of process steps
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More efficient material use (more on that below)
Potential lower energy consumption per component produced vs. starting material, when you factor in material losses due to machining
Ability to make complex shapes that conserve material
One of the disadvantages of powder metallurgy is that short product runs are a poor fit thanks to per-part costs and tooling costs. For tiny production runs, CNC machining remains a more affordable option. CNC machining requires no tooling costs.
5. Strength
Machining operations can produce parts from materials that take on high tensile forces and impact loads. Today’s machine shops work with some amazingly high-performing materials.
Powder metal parts by nature aren't as strong as machined parts. Why? They have tiny holes, aka porosity.
Keep in mind that powder metal parts can be stronger than you think thanks to advanced sintering technology. Sintering may give your part an acceptable level of strength while allowing you to take advantage of powder metallurgy’s many other advantages over machining.
6. Speed
Powder metal, like cupcakes, is better when the batch is large.
For short-run orders, you may be better off with conventional machining. A machined part only takes a few weeks total. It doesn’t take much effort to put a piece of bar stock in the CNC milling machine and start whittling away.
But once you have a tool in place, that's when powder metallurgy suppliers begin to shine. It’s infinitely better than high-volume-production CNC machining, which requires a lot of:
Reprogramming
Retooling
Labor hours
One of the benefits of prototyping with powder metallurgy over prototype CNC machining is that tooling costs are a one-time investment. If prototype tooling is successful, it carries the added value of being usable throughout final production.
(Related Resource: Prototyping Motor Components With SMC Powder - Benefits vs. CNC Machining Prototype Manufacturers)
7. Scrap Efficiency
Engineers have wondered for years how to best reduce scrap in machining operations.
Powder metallurgy makes far more efficient use of its raw materials -- we’re talking 3% scrap rates. Meanwhile, machining parts can result in 50% material waste. Because the powder metallurgy process is an additive one, your manufacturer only needs as much material as your design requires.
The world now recognizes powder metallurgy as maybe the most sustainable metal manufacturing process, and a model of how to reduce material waste in manufacturing.
While machining scrap can be recycled, these operations still account for significant material costs, much of which is discarded.
The Winner Is … (and More Debate)
There’s no need to start your project with that depressing thought of, “How much material am I paying for that’s going to get thrown away?” Instead, with the right powder metal process, you can dream of the endless design and cost-cutting possibilities you’ve opened up.
The free e-book below reveals more about the pros and cons of powder metallurgy vs.:
CNC machining
Stamping
Casting
Forging
MIM -- and more
Don’t miss the chance to discover a cost-cutting or performance-boosting trick you never knew existed!
(This article was originally published in June 2022 and was recently updated)
Metal matrix composites (MMCs) are composite materials containing at least two constituent parts – a metal part and a material or a different metal part. The metal matrix is reinforced with the other material to improve strength and wear. Most metals and alloys make good matrices.
In structural applications, the matrix is usually composed of a lighter metal such as magnesium, titanium, or aluminum. In high-temperature applications, cobalt and cobalt-nickel alloy matrices are common. Continuous carbon, silicon carbide, or ceramic fibers are some of the materials that can be embedded in a metallic matrix material.
For example, MMCs are increasingly found in the automotive industry. These materials use a metal such as aluminum as the matrix, and reinforce it with fibers such as silicon carbide. The space era has increased the demand for MMCs that possess high specific stiffness and near-zero coefficient of thermal expansion (CTE).
Material Properties and Characteristics
Metal matrices posses the advantage of being suitable for use in applications requiring a long-term resistance to severe environments over polymeric matrices. It is a fact that the yield strength and modulus of most metals are higher than those for polymers. Another advantage of using metals is that they can be plastically deformed and strengthened by many thermal and mechanical treatments.
The characteristics of MMCs can be designed into the material based on specific applications.
The following are some key material properties benefits of MMCs:
- Fire resistant
- Operate in wider range of temperatures
- Do not absorb moisture
- Better electrical and thermal conductivity
- Resistant to radiation damage
- Do not display outgassing
- Low CTE and light weight
- Good damping and high compression strength
- High specific stiffness and strength.
Manufacturing Process
The following are the key composite metal matrix material manufacturing processes:
- High-pressure diffusion bonding process - is used for producing continuous- fiber reinforced MMCs. Here, layers of metal foil are sandwiched with long fibers, and then pressed through to form a matrix.
- Casting process - Used for producing continuous - fiber reinforced MMCs. In this process, molten metal is injected into a form with fibers pre-placed inside it.
- Powder-metallurgy process – Used for producing discontinuously reinforced MMCs. Powdered metal and discontinuous reinforcement are mixed together and bonded via a process of compaction, degassing, and thermo-mechanical treatment.
- Physical vapor deposition: In this process, the fiber is passed through a thick cloud of vaporized metal, thereby coating it.
The process for producing discontinuous, particle reinforced or continuous fiber reinforced part begins with a preform that is shaped as the final part. The preform is infiltrated with a molten metal, e.g. aluminum, to produce a metal matrix composite component.
Care should be taken while manufacturing MMCs to maintain the reinforcing fibers strength, to ensure a strong bond of fibers with matrices and between the matrix layers, to provide the correct fiber length, which is greater than the critical length, to ensure uniform distribution of fibers in the matrix, to ensure orientation of fibers in the direction of the applied load, and to achieve the required shape and dimensions of the MMC.
Applications
The following are some of the most common application areas of composite metal matrix materials:
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- Pushrods for racing engines
- Carbide drills
- Tank armors
- Automotive industry - disc brakes, driveshaft, engines
- Aircraft components - structural component of the jet's landing gear
- Bicycle frames
- Space systems
- High density multi-chip modules in electronics
- Parts in particle accelerators
- Attach plates for high-speed robots
Sources and Further Reading