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A Look Into Metal Sintering And How It Works

One of the many reasons why metal is such a powerful tool in manufacturing is the fact that it can easily be shaped in different ways and made to fit various forms. 

For this to happen, the metal material will need to be processed appropriately. And, one of the most prominent ways to get this done is through sintering. Whether it’s the basic format or the more popular direct laser metal sintering, this process has a lot of benefits for manufacturers and metallurgists across the board. 

In this article, we’ll look at the metal sintering process, as well as what you can expect from using a piece of sintered metals in your manufacturing project. 

Understanding Metal Sintering

To kick off, let’s take a look at the process of creating sintered metals and how it is done.

What is Metal Sintering?

In a nutshell, the process of sintering involves fusing together small metal particles by heating them to a temperature below their official melting point. The metal sintering process doesn’t necessarily heat the metal part completely, instead using a sinter press or some other tool to manipulate the shape of the material and bring out what you’re looking out for. 

Metal sintering is used in sintered stainless  steel manufacturing, with the focus being to form complex shapes and develop eastern sintered alloys. Just as well, you can use this process to create sintered aluminum or other metals with high melting points. 

The major force in a traditional sintering process is the decreasing surface energy. As the process goes on, adjacent particles partially coalesce, thanks to the viscous flow or the diffusion process of the material. Eventually, the total surface area will decrease, ending in optimal physical and mechanical properties of the material itself

The Fundamental Components Of Metal Sintering

For the sintering metal process to work, several components need to be in place to ensure a smooth workflow across the board. Some of the things needed when considering how to press powder into solid for metals include:

  • Metal Powders: Of course, you need the powder for the direct metal laser sintering process to work. They are the raw materials, and they can even come with different metals or alloys being finely divided in order to optimize bonding as the sintering process goes along.
    At the end of the day, the properties you get with the final sintered metal product will be based on the powder’s composition, shape, size, and distribution.
  • Binders and Lubricants: While these aren’t always a necessity, they can come in handy. Basically, they’re mixed with the powders to improve flowability and compaction.
    The presence of binders also helps to hold the powder particles together – especially in the starting phase of compaction. On the flip side, lubricants cut out friction and ensure that the die walls easily move during the process.
  • Compaction Tools: A sinter press or hydraulic press is used to compact the metal powders into the shape you’re looking for. These tools apply pressure to the powders, forming a greed compact. However, remember to also be careful with the press and tooling parameters as they will affect the compact’s uniformity and density.
  • Sintering Furnace: This provides a controlled heating environment where the compact is heated for a specific time. All furnace parameters need to be accurate and detailed if you hope to achieve the right density and bonding levels for the metal particles.
  • Cooling System: Once the sintering process is done, you can cool the material to prevent any distortions or stress buildup. The cooling rates will need to be controlled as well, so you can ensure that the final product has optimal dimensional stability. 
  • Heat Treatment: In some cases, you might need to incorporate different heat treatments following the sintering process to modify the sintered part’s microstructure and mechanical properties. This could be annealing, tempering, quenching, etc. 
  • Quality Control and Inspection Tools: All through the process, you want to implement different inspection and quality control tools to monitor the properties of the sintered parts
  • Post-Sintering Processes: Depending on the intended application, you might also need to incorporate additional processes such as machining, surface finishing, and coating to help achieve the desired final properties of the sintered part. 

What Metals Are Perfect For Sintering?

The term “metal sintering” pretty much covers different materials that can handle this process. And, when we consider the ideal metal for a sintering application, different factors can easily influence your decision. However, some of the most popular options available include: 

  • Iron and Steel: Easily the most popular materials used in sintering are steel and metal. They can be alloyed with other elements as well if you need to get the proper properties. With sintered steel, you have a material that works in multiple industries – from power generation to industrial machinery and more.
  • Stainless Steel: If you need optimal corrosion resistance, then stainless steel powders will most likely be your top choice. 
  • Bronze and Brass: These alloys are based on the traditional copper material, and they are usually sintered to create products with optimal electrical and thermal conductivity. 
  • Tungsten and Tungsten Alloys: Tungsten and its related alloys are primarily popi;ar thanks to their impressive density. They also do well to resist wear, making them great for long-term use.
  • Copper: Powders made from this material will provide great thermal and electrical conductivity. With sintered copper, you’re able to get application in electrical contacts, heat sinks, and much more. .
  • Nickel and Nickel Alloys: Nickel powders do well to resist high temperatures and continue working. They also don’t corrode easily, making them perfect for making electrical and aerospace products.
  • Aluminum and Aluminum Alloys: Traditional aluminum offers corrosion resistance and a lightweight build. Applying sintered metal filters to the material makes it useful in manufacturing consumer electronics and other products. 
  • Titanium and Titanium Alloys: Strength is where this material shines. Its impressive strength-to-weight ratio and biocompatibility make it perfect for medical applications, as well as use in the aerospace industry.
  • Cobalt and Cobalt Alloys: With high-temperature strength and impressive wear resistance, cobalt-based powders find application in medicine and industrial services.
  • Precious Metals: Whether it’s platinum, gold, or solver, previous metals offer varying degrees of unique properties. As such, their functionalities vary as well.

Metal Sintering: Which Variant Should You Attempt?

Like many manufacturing processes, metallurgists are usually spoilt for choice when it comes to choosing how to sinter metal. Different techniques and processes are available, each coming with its own characteristics. 

  • Conventional Sintering: This is the most prominent sintering form there is. Metal powders here are heated and compacted, with parameters being controlled to achieve the  proper characteristics. Just as well, the powders are bonded through atomic movement and diffusion.  
  • Vacuum Sintering: In vacuum sintering, you get a controlled vacuum environment to conduct the sintering process. The process reduces oxidation and can also create parts with better mechanical properties and density ratings.
  • Partial Pressure Sintering: For this process, you can tweak the sintering atmosphere by introducing specific gases that help control the partial pressure of specific elements. All in all, you can tailor the microstructure and properties of the sintered material – especially in the case of alloyed powders. 
  • Sinter-HIP (Hot Isostatic Pressing): This process combines both sintering and hot isostatic pressing. Following the initial sintering process, the sintered metal is subjected to high pressure and temperature  in an inert gas environment. This causes additional densification and can reduce porosity and optimize the material’s mechanical properties even more. 
  • Spark Plasma Sintering (SPS): The SPS method is known for its speed, with pulsed direct current and pressure being used to achieve impressive rates of heating. The process generally reduces sintering time and optimizes the material’s microstructure across the board – thus leading to better mechanical properties. 
  • Field-Assisted Sintering Techniques: These techniques make use of external fields, such as magnetic and electrical fields, to improve the traditional sintering process. At the end of the day, you’re left with reduced sintering temperatures and quick turnaround time. 
  • Liquid Phase Sintering: In this method, you get a finite amount of low melting-point metal – or an alloy – and add it to the initial powder mix. In the sintering process, the liquid phase improves particle densification and bonding, thus improving the mechanical properties of the materials.
  • Sintering Under High Pressure: You can use techniques such as High-Pressure Spark Plasma Sintering (HPSPS) to conduct high-pressure metal sintering. With high pressures, you can improve densification and reduce porosity in the material.
  • Microwave Sintering: Here, you essentially get microwaves and use them to heat the metal powders in a selective manner. You get to enjoy a swift and consistent sintering process across the board, and this also doesn’t consume so much energy in the first place.
  • Plasma Sintering: For this option you get a plasma arc and apply it to the powders. They are combined and consolidated, enjoying high heating and impressive levels of temperature  control. 

The Metal Sintering Process

For the overall metal sintering process to work, you need to be careful and follow a step-by-step workflow. As you would expect, different manufacturers and metallurgists tend to have their specific processes. However, we at KDM Fabrications prefer to follow this process: 

Powder Production

In the very first step, you create the metal powders that will be used in the sintering operation. Here, you can make use of methods such as mechanical grinding, atomization, or chemical reduction. 

Whatever you choose, we recommend that you give a lot of thought to the desired properties of the powder as they will play a crucial role in determining what you get in the final product.

Powder Mixing

This step isn’t a necessity, but it also doesn’t hurt to incorporate. Essentially, you have the option of adding components like lubricants and binders to mix the powders and help them optimize the physical properties available. Just as well, the mixing process ensures optimal consistency and homogeneity in the sintered material.

Compaction

Next, you place the mixed powders into a die and apply the sinter press – or hydraulic press, if you will. With the press applying additional pressure, the powders are compacted into the shape of a die, forming the green compact.

Remember that the compact’s density will play a role in determining the final porosity and other properties of the sintered metal. 

Binder Removal

If you’re adding lubricants or binders to the powder mix, you’d need to take them out before the actual sintering begins. This process is usually done through furnace or oven heating, so you can control the parameters properly. 

Metal Sintering

Now, we get into the direct metal laser sintering process itself. Place the green compact in the sintering furnace, then control all sintering parameters across the board. 

As part of the process, you’d find that the metal particles will begin binding together through atomic movement and diffusion. However, they are heated just enough to stop them from completely melting. The temperature is still below the melting point of the material, but just high enough to encourage bonding. 

Densification and Bonding

While the sintering process goes on, you’ll notice a bonding in the metal particles – and an increase in the density of the compact. Adjacent particles wil bond as well, causing neck formation. 

Cooling

Now that your material has reached the ideal sintering state, you can cool the furnace down to room temperature. Remember to ensure that this step is gradual – when cooling is too rapid, you end up causing cracks and thermal stress. To maintain the parts’ integrity, ensure that cooling is as controlled and as gradual as possible. 

Post-Sintering Processes

Depending on what you’re looking to use the sintered parts for, you can perform post-sintering processes on the material. These can be surface finishing, heat treatments, and more. The goal is to ensure that you achieve the right material properties across the board. 

Quality Control and Inspection

Before the final rollout, you want to subject the sintered parts to different quality control measures to ensure that their properties are optimized – from hardness to porosity and density and more. 

Final Product

Once the entire product has gone through quality control, you can use it for your intended application.

Metal Sintering Applications: Where This Process Is Useful

Over the years, the process of metal sintering has become especially popular among many product manufacturers and metallurgists. At the moment, you can find the process being used in some of the following applications: 

Automotive Industry

Metal sintering helps in manufacturing several automotive components – transmission tools, engine parts, vehicle bearings, and ore. They offer cost-efficient solutions with higher dimensional accuracy and wear resistance across the board.

Aerospace and Defense

From heat shields to plane nozzles and more, sintering helps in the development of several aerospace components that need high temperature resistance and a lightweight build.

Electronics and Electrical

You can use sintering to create connectors, electrical contacts, heat sinks, and other components that need improved electrical and thermal conductivity. You can also get sintered materials with bespoke porosity in creating sintered metal filter elements.

Medical and Dental

Materials that act as the products of sintering can be used to make medical implants, surgical instruments, and more. Considering that several ideal metals for sintering are biocompatible, this functionality is especially prominent. 

Consumer Goods

We also see the use of sintered metals in developing some of the prominent consumer goods we use everyday – from writing tools to kitchen appliances and more. 

Industrial Machinery: Sintering is employed in producing industrial machinery components like gears, cams, bearings, and bushings. Sintered parts are known for their durability, wear resistance, and ability to withstand heavy loads.

Oil and Gas Industry

Components like drilling tools and valves that are used in the oil and gas selector can be made through the use of sintering. As long as they’re corrosion-resistant and can handle application in harsh environments, you shouldn’t have an issue here.

Tooling and Cutting Tools

Cutting tools need to be sharp, but lightweight. And, with sintered carbide, you get a tool that operates perfectly in metalworking functionalities for shaping, cutting, and material forming. It is hard and wear-resistant, making it perfect for use. 

Jewelry and Fashion Accessories

The sintering of precious metals also makes them quite ideal for manufacturing jewelry. With their fine details and intricate looks, these materials pair well with sintering to create complex designs that might not be possible with the use of other methods.

Energy Industry

Components that are used in functions like renewable energy and power generation can benefit from sintering. The process helps in making tools with high temperature resistance and mechanical stability, all of which are ideal in different energy environments.

Sports and Recreation

Manufacturers of sports equipment use metal sintering to refine their raw materials, improving their weight distribution and incorporating precise manufacturing across the board.

Firearms and Ammunition

Defense contractors use sintering to produce ammunition casings and firearm components, capitalizing on the process and its ability to create high-strength and intricate materials.

Metal Sintering: Is It All Perfect?

The use of innovative sintered parts has seen a lot of application across the board. And, this itself goes to show just how metal sintered filters are so advantageous. Very quickly, let’s examine the advantage sintered metals provide, as well as some areas where they might not be so strong.

Metal Sintering Advantages

  • Complex Geometries: Thanks to sintering, you can create materials that come with intricate and complicated shapes. This process dares to handle production tasks that several traditional manufacturing methods won’t be able to, making it more versatile for product manufacturers. 
  • Near Net Shape: Sintering also makes it easy to produce parts that are very identical to the final desired shape. This means that you might not need any additional machining or additional processing of metal steps once the sintering itself is done. 
  • Material Efficiency: One of the major benefits of sintering is that it  helps you to optimize material use. Just as well, any excess material by-product can be reused and recycled, thus contributing to a more sustainable manufacturing process.
  • Versatility: You can use different ideal metals in the sintering process. This enables the creation of different parts with a broad range of properties – from the dense and strong to the porous and light.
  • Cost-Effectiveness: Sintering offers a cost-effective alternative for many high-volume production methods. Material waste is cut out, and the process is considerably simpler. 
  • Controlled Porosity: The sintering process helps in developing components with controlled porosity, which is beneficial in applications such as filters and heat exchangers. 
  • Tailored Properties: Manufacturers will be able to easily engineer sintered materials to conform to different thermal, mechanical, and electrical properties. All you have to do is adjust the sintering temperature, material composition, and other parameters.
  • Vibration Dampening: Even in the development of materials with shock absorption and vibration dampening, sintering can come in handy. This leads to the development of components that are easier and more seamless to use. 

Possible Challenges With The Process

  • Limited Strength: Compared to other manufacturing methods, sintered parts might come with lower density and strength levels. 
  • Dimensional Changes: It is also possible for you to find dimensional distortions and changes in sintering due to the shrinkage that comes during densification – something which necessitates careful consideration during overall design.
  • Porosity: We mentioned that controlled porosity is a net positive. However, in situations where it gets excessive, you can end up with sub-optimal mechanical properties.
  • Process Complexity: The sintering process involves different complex steps that need to be accurately controlled in order for you to get the desired results. In some cases, this easily leads to increased complexity.  

Metal Sintering vs Melting: Which Option Serves Your Purpose? 

As you would imagine, sintering isn’t the only metal processing step available to metallurgists and product manufacturers. And if you’re really looking to optimize functionality, you need to also know about an important possible alternative – melting. 

So, what is melting and how does it compare with the traditional sintering process?

A Look Into Metal Melting

When it comes to metal melting, you’re essentially heating a solid metal or alloy to its direct melting point. This is one of the major differences in the metal sintering vs melting debate – while sintering doesn’t heat the metal to its melting point, melting absolutely does. 

With melting, the product is eventually transitioned from solid to liquid, with its atoms moving freely and the translation taking hold. 

During melting, the metal soaks in a considerable amount of heat energy, causing the atoms within it to gain enough kinetic energy to overcome any intermolecular forces that keep them bound. This leads to a phase transition and the transformation of the material into a molten liquid with optimal mobility and very little by way of structural integrity. 

Like sintering, melting has become a critical part of different manufacturing processes that work in different industries. A melted metal can easily be cast indo different molds, leading to the creation of intricate shapes that can be further processed to produce specific products. The addition of cooling and solidification also means that you can form an entirely new structure with different characteristics from the original one.

Comparing Metal Sintering vs Melting 

Now that we understand how metal melting works, let’s look into the comparisons between both and what you should expect to see.

Process Principle:

For metal sintering, you’re heating and compacting metal powders to a temperature that’s hot enough to get it to fuse, but not hot enough to get it to melt. This promotes particle bonding through atomic movement and diffusion without total melting. 

Melting, on the other hand, involves raising the temperature of the material right to its melting point. This causes a transformation that leaves the material in its liquid state and alters it permanently. 

Starting Material:

In sintering, you’re working with a metal powder as the starting material – meaning that you need to consider the powder’s shape, size, and composition. 

On the other hand, melting works on a bulk, solid metal or a metal alloy instead. This helps if you’re asking, “What is solid state sintering,” 

Equipment Required:

Both processes tend to use the same tools – molds, furnaces, and more. However, the difference is that the crucibles and furnaces in melting will need to be able to heat the material to its melting point. 

Final Product Properties:

In sintering, you’re looking to produce materials with controlled porosity and the right mechanical properties. Intricate shapes are also encouraged, with the entire process being as controlled as possible. As for mechanical properties, sintered products can come with lower strength and density compared to others.

For melting, you usually make products that are homogeneous and dense, with the properties being uniform across the board. In terms of mechanical properties, products made from melting usually come with higher strength and density since they don’t have any voids. 

Shape Complexity:

Metal sintering is perfect for producing complex shapes as its products can easily fill molds with fine powders. Melting is more limited to simpler, more straightforward shapes, especially since the molten metal needs to flow and fill its molde themselves.

Material Selection:

With sintering, you’re more than free to choose the powders you want to work with. As long as they’re compatible with the process, you don’t have a problem. 

Melting is a bit more limited in terms of materials that can be properly cast and melted. So, you want to keep a close eye on that.

Material Porosity:

Thanks to the fact that you can control sintering, the process can help to create porous structures for specific applications – such as self-lubricating bearings and filters. For melting, you tend to end up with overly dense materials that don’t have much in terms of inherent porosity. 

Post-Processing:

There’s a high likelihood that you’ll need some additional post-processing when it comes to sintering before you’re able to achieve the right finish and tolerance. For melting, this might not be necessary since you can make near-net shapes immediately.

Cost Considerations

Metal sintering is seen by many as a more cost-effective production process across the board. While the cost of melting can be higher, you should also note that the presence of economies of scale can help to reduce the overhead considerably, thus leading to cost savings. 

Conclusion 

Metal sintering has proven to be one of the most pivotal metal manipulation forms in the market. The process is a tad complex., but having the right company handle it for you can prove to be all the difference. 

This is why you need us at KDM Fabrication. Our metallurgists and technicians will be able to help deliver the right sintering process, ensuring that you can easily fashion metal powders into the form you desire. 

Give us a call today, and we’ll be able to help you out! 

Frequently Asked Questions (FAQs)

What is a sintered metal part?

As the name suggests, a sintered metal part is a component that has been created through the metal sintering process. Metal powders have been compacted into the required shape and have been heated and cooled, bonding together without fully melting. 

In most cases, a sintered metal part is solid and cohesive, maintaining the shape of the initial compact while optimizing density and strength across the board. 

What is the purpose of sintering? 

The overall objective of metal sintering is to create a material that fits into a predetermined shape, while also optimizing its mechanical properties. This will depend considerably on the properties of the powder and the presence of components such as additives and fillers, so it is important to keep an eye on those as well. 

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