Sep. 08, 2025
Metal additive manufacturing has a long, historical arc. Needless to say, the idea of using a laser to melt beds of metal powder was beyond our ancestors in the ancient world. Humans first used metal powders to make parts 5,000 years ago in Egypt. The process they used, which is still used today, is called powder metallurgy. It starts with pouring metal powder into a mold, packing it down to form the net shape and get the powder to stick together. With enough heat and/or pressure, particles want to reduce the amount of surface area they take up which causes them to meld together, resulting in sintering.
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Now, let’s explore how the powders are made today using gas atomization. In this process, a stream of liquid metal is directed into a high-pressure blast of gas which breaks the metal up into small droplets. Basically, you end up with a metal mist that solidifies quickly into round particles of powder.
The process is similar to how Dippin’ Dots are made. To get the nice spheres of ice cream, the mix drips into a chamber full of liquid nitrogen to make the spheres. The biggest benefit of using gas atomization to create the raw material for additive manufacturing is that it offers the highest consistency of sphericity and particle size. That enhances flowability and creates a nice, level bed of powder to draw on with a laser.
Knowing how the powder is made is just the first step in the process. The actual printing method has changed over the years. In the earliest days of experimentation with 3D-printed metals, engineers used selective laser sintering (SLS) which worked with a similar principle to powder metallurgy. However, instead of needing to make a mold, operators used computers to control a laser to sinter the powder.
The downside to this process, as well as for powder metallurgy, is that it leaves micro-gaps, or pores, in the parts, making them less robust and less mechanically sound. These parts frequently require post-processing to reduce the size of those micro-gaps and enhance part performance.
Today, manufacturers create metal 3D-printed parts using direct metal laser sintering (DMLS), although you’ll also hear the phrase direct metal laser melting (DMLM). The metal 3D printer melts each layer—first the support structures to the base plate, then the part itself—with a laser aimed onto a bed of metallic powder. But in this case, the laser is completely melting the powder into a liquid, as opposed to sintering during which no melting occurs. Once a single layer of powder is micro-welded, the build platform shifts down and a re-coater blade moves across the platform to deposit the next layer of powder into the build chamber. The process is repeated layer-by-layer until the build is complete.
Once the print is completed, finished parts undergo the following:
Final metal 3D-printed parts are nearly 100% dense—that’s a substantial improvement over the SLS metal parts of the s. Other specialized treatment options are available—more details on those later.
Still, there are quality considerations when your parts are removed from the printer, and a few solutions to help improve the mechanical and aesthetic properties of the final product.
Often, parts come out of the printer feeling slightly rough. That’s caused by the process itself. When a layer of powder is sintered to a part, you get a sort of gradient from totally melted near the part itself to an area where not everything in the new layer sinters.
Machining, polishing, or bead-blasting can take care of these issues, though. While DMLS achieves nearly 100% density, using hot isostatic pressing (HIP) further reduces any remaining porosity. More about HIP later. That said, if the slightly lower tensile strength on the Z-axis is a concern, you can “thicken up” areas in that plane.
Your materials choice fundamentally affects the outcome of your parts, so it helps to have a general understanding of the advantages of each material available for your project. Here’s a description of each:
Aluminum (AlSi10Mg) is comparable to the series alloy that is used in casting and die casting processes. It has good strength-to-weight ratio, high temperature and corrosion resistance, and good fatigue, creep and rupture strength. AlSi10Mg also exhibits thermal and electrical conductivity properties. Final parts built in AlSi10Mg receive stress relief application. Suitable industries: Aerospace and automotive, consumer goods, manufacturing, and construction.
Cobalt Chrome (Co28Cr6Mo) is a superalloy known for its high strength-to-weight ratio. It has high-performance tensile and creep characteristics and strong corrosion resistance. Suitable industries: Medical and dental, aerospace, industrial manufacturing, and jewelry.
Inconel 718 is a high strength, corrosion resistant nickel-chromium superalloy ideal for parts that will experience extreme temperatures and mechanical loading. Final parts built in Inconel 718 receive a stress relief application. Solution and aging per AMS are also available to increase tensile strength and hardness. Suitable industries: Aerospace, energy, chemical processing, marine.
Stainless Steel 17-4 PH is a precipitation-hardened stainless steel that is known for its hardness and corrosion resistance. If you need to use stainless steel, select 17-4 PH for its significantly higher tensile strength and yield strength, but recognize that it has far less elongation at break than 316L. Final parts built using 17-4 PH receive vacuum solution heat treatment as well as H900 aging. Suitable industries: Aerospace, automotive, medical and dental, oil and gas, chemical processing, marine.
Stainless Steel 316L is a workhorse material used for manufacturing acid- and corrosion-resistant parts. Select 316L when stainless steel flexibility is needed as it is a more malleable material compared to 17-4 PH. Final parts built in 316L receive a stress relief application. Suitable industries: Medical and dental, food and beverage, chemical processing and pharmaceuticals, marine, oil and gas, jewelry, consumer goods.
Titanium (Ti6Al4V) is a workhorse alloy. Compared to Ti grade 23 annealed, the mechanical properties of Ti6Al4V are comparable to wrought titanium for tensile strength, elongation, and hardness. Final parts built in Ti6Al4V receive a vacuum stress relief application. Suitable industries: Aerospace and defense, medical and dental, automotive, consumer goods, bioprinting.
The rapid heating and cooling of the metal material during the DMLS process results in a buildup of internal stresses. While every build undergoes a stress relief treatment per the ASTM standard, additional heat treatments can further improve mechanical properties like hardness, elongation, fatigue strength, and more.
This process combines high pressure and temperature to eliminate any potential porosity within the part and reduce anisotropy. It also increases resistance to impact, wear, and abrasion, and improves fatigue characteristics. Typically, HIP is used for aerospace components that will be under heavy loads. HIP reduces much of the remaining internal micro-porosity by exposing the part to 2,000° F (° C) heat and very high pressure of 15,000psi (103.42 MPa) on all sides to fully solidify the part.
The workpiece is heated above its recrystallization temperature and then cooled rapidly to relieve stresses and remove small imperfections in the microstructure. This is often used for stainless steel parts as it reduces hardness and increases ductility.
This is a secondary heat treatment process applied to certain metal alloys. Part temperature is elevated and held for a designated time, causing precipitate formation. Our standard process is to age 17-4 stainless steel to the H900 condition. By request, Inconel 718 may be aged to boost temperature resistance, strength, and hardness properties.
While these heat-based processes address the mechanical properties of the part, another important concern with 3D printing is surface roughness. The most widely used measure of surface roughness is Ra, or the average roughness between a roughness profile and the mean line. Ra is the deviation from the ideal surface plane measured in microinches or micrometers. A larger Ra unit equates to a rougher surface.
Protolabs DMLS parts have a 200-400 microinch (5.08-10.16µm) Ra with standard finishing and 400-600 (10.16-15.24µm) as-printed. The difference in finish between our normal and high resolution is small. Polishing and machining are available to improve on the as-printed values noted above.
There are two ways to think about density. The first is the mass of the material compared to the volume it occupies. Many times, material density is expressed in grams per cubic centimeter (g/cc).
The density of a metal will determine how much a part of a particular size weighs, and of course weight is an important consideration, especially in aerospace and automotive applications. Engineers and designers in those industries are always looking for ways to reduce component weight to meet emission standards, cut fuel consumption, consolidate many parts into fewer parts, and streamline overall product design.
Dense materials make strong parts—the higher the density, the greater the strength—which is why the percentage of density of a part’s material is so crucial. Density is essentially the concentration of a given material in a given space.
Engineers and designers looking for lower-weight parts might turn to materials or alloys that are less dense. You should be cautious, though, because then you must consider the strength-to-weight ratio, too.
Topology optimization is a critical tool for removing weight while making sure that the part still has the required strength. It works by identifying which areas of the part see the highest loads, and which see little to no load and can therefore be removed. Often, this leads to organically shaped parts that would be hard to make with traditional methods like machining. Thankfully 3D printing makes these shapes possible.
Topology optimization is used today across many industries and at varying levels of scale. For example, the University of North Carolina Formula BAJA team used topology optimization to remove precious ounces from the team’s car by carefully light-weighting the sway bar responsible for preventing rollover during a race. Of course, strength was critical in the part, but removing unnecessary weight could help the team reach top speeds. On a larger scale, aerospace companies are reducing weight in components as small as brackets to save millions of gallons in fuel annually.
The other way to think about density is in terms of porosity, or lack thereof. This is typically expressed as % density or % porosity. The DMLS process generally produces parts that are nearly 100% dense, although a small amount of porosity is typically present. We expect our DMLS parts to meet or exceed 99.5% density through our standard process. For applications that require the highest mechanical performance and fatigue resistance, the small amount of porosity present in a printed component can be reduced even further through hot isostatic pressing (HIP).
All metal additive parts, including those made using DMLS, can undergo radiographic testing to ensure porosity is minimal. X-ray scanning is a common choice for both metal additive parts and cast parts. The key benefit is that you can inspect the inside of the part for porosity without destroying it. Non-destructive radiographic inspection ensures that metal additive parts are free from the pores that could cause cracking while the part is in use.
Sometimes your designs give you the option to choose between 3D printing and CNC machining. Each has its own advantages, but we’re here to focus on materials and how the manufacturing process affects them, if both can handle the geometries of your design:
Key material properties can also vary slightly between the two processes. A few comparisons of popular metals include:
Comparing materials that are available via both our 3D printing and CNC machining services (both stainless steels and titanium), you’ll find that, in general, the printed parts have somewhat better elongation, hardness, and tensile strength.
The process you choose also affects the surface finish of your parts. Parts produced by both of these manufacturing processes can initially come out a bit rough. Those parts built by machining can come out, as some in the industry call it, “as-machined” or “as-milled.” That means you’re going to see some surface roughness and blemishes. Those parts produced by 3D printing will have more surface roughness or graininess, resembling the texture of a cast iron frying pan.
Fortunately, you can improve functionality and aesthetics of manufactured parts with a variety of post-process finishing options.
Several post-process options for machining can help protect parts and improve overall finish. Common processes include plating, anodizing, powder coating or painting, and more. Many of these processes can also be applied to metal additive parts.
For 3D printing, depending on the additive manufacturing technology, build direction, resolution, and materials chosen, you might see issues with part aesthetics. Here’s a quick look at the 3D printing finishing options commonly offer and what you can expect as a result:
Here’s something you may want to consider: Post-processing machining on 3D-printed parts lets you get the complexity that machining alone can’t achieve while ensuring critical features are to spec. It could be your ideal equation for metal manufacturing.
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All in all, if you were to compare 3D metal-printed parts to any manufacturing process, casting would be the most appropriate. Both are based on a liquid turning into a solid and require designers to consider things like uniform wall thickness, avoiding sharp corners and more. The tensile strength of DMLS parts is generally as good or better than cast, but fatigue is worse. Using HIP, however, can address this issue.
DMLS 3D printing is a revolutionary technology that can create complex and functional metal parts from digital models. However, metal 3D printing is not as simple as plastic 3D printing. There are many factors that you need to consider before you start your metal 3D printing project.
In this post, we will share with you some important tips and precautions for metal 3D printing based on our experience and expertise.
We could not guarantee that walls thinner than 0.5 mm can be printed successfully. Thin walls may collapse or deform during sintering due to thermal stress and shrinkage.
Additionally, if you want additional finishing like polishing, brushing, mirror polishing, or other advanced finishing effects on your parts, you should design your parts with even thicker walls. This is because these finishing processes may remove some material from the surface of the parts and reduce their thickness further.
The recommend minimum wall thickness for different finishing options is as follows:
You can also refer to this illustration of DMLS design rules. The blue/teal color represents micron resolution (MR), green is high resolution (HR), and orange is normal resolution (NR). Also, the minimum channel and minimum Z dimensions apply to both NR and HR.
Additionally, if you want your assembly parts to fit together smoothly and accurately, you should design them with enough clearance between them. The minimum clearance for DMLS 3D printed assembly parts is 0.15 mm on each side.
Clearance is the gap or space between two mating surfaces of the parts. It allows for some tolerance and flexibility during assembly.
This means that if you have two parts that need to be inserted into each other (such as a pin and a hole), the diameter of the pin should be 0.3 mm smaller than the diameter of the hole (0.15 mm on each side).
Similarly, if you have two parts that need to slide along each other (such as a rail and a groove), the width of the rail should be 0.3 mm smaller than the width of the groove (0.15 mm on each side).
For parts that require high precision for local assembly, please leave some machining allowance in advance and then use CNC machining to achieve a better fit.
The local assembly is a type of assembly where two or more parts are joined together at a specific location or feature on the part. Local assembly requires high precision and accuracy to ensure that the parts fit together perfectly and function properly.
Therefore, we recommend that you leave some machining allowance in advance and then use secondary machining to achieve a better fit. Machining allowance is the extra material that you add to the part during design or printing to allow for some removal or adjustment later on. We can use tools such as drills, mills, lathes, etc. to refine or modify the part after printing.
For example, if you need a bearing hole with a diameter of 10 mm and a tolerance of +/- 0.01 mm on your part, you can design and print the hole with a diameter of 10.1 mm (0.1 mm machining allowance) and then use a drill to reduce it to 10 mm (+/- 0.01 mm tolerance) after printing.
By leaving some machining allowance in advance and using secondary machining later on, you can achieve higher precision and accuracy for local assembly than by relying solely on DMLS 3D printing.
The average surface roughness (Ra) of DMLS 3D printed parts is about 3.2-6.3 microns, which is much higher than the typical Ra of machined parts (0.4-1.6 microns).
If you need a smoother surface finish for your parts, you may need additional post processes such as machining, polishing, sandblasting or coating. These post processes can improve the surface quality and appearance of your parts, as well as reduce the friction and wear between moving parts. However, they may also increase the cost and lead time of your order.
The sintering process may cause some elongated, thin-walled, shell-like structures to deform due to thermal stresses and shrinkage.
DMLS 3D printed parts require high-temperature sintering after printing to increase their strength and density. Therefore, if your design has such features, you may want to consider modifying them or choosing a different manufacturing method.
Metal 3D printing has an advantage in creating complex structures, but its accuracy and surface quality are inferior to machining.
The laser beam diameter and the metal powder size affect the resolution and surface roughness of the printed parts. Moreover, DMLS 3D printed parts may have internal porosity and residual stresses that affect their mechanical properties.
The accuracy of metal 3D printed parts is not as high as CNC machining. The accuracy of metal 3D printed parts is about +/-0.1 mm or +/-0.2%, whichever is larger. This means that the actual dimensions of your parts may deviate from the design dimensions by up to 0.1 mm or 0.2% in any direction.
Therefore, if your design requires high precision and a smooth finish, you may need additional post-processing steps such as CNC machining or polishing. To know more, please read this post: FacFox CNC Machining vs 3D Printing Services: Compare and Choose the Better One for You.
We recommend using tapping instead of direct 3D printing for creating threads on your metal parts. This is because direct 3D printing may result in poor quality or inaccurate threads due to the nature of the metal powder and the sintering process.
Metal powder is the raw material used for 3D printing metal parts. It consists of tiny particles of metal that are fused together by heat and pressure. Sintering is the final step of 3D printing where the metal powder is heated to a high temperature below its melting point to bond the particles together.
During sintering, some shrinkage and distortion may occur due to thermal expansion and contraction. This may affect the shape and size of the threads and make them uneven or misaligned. Additionally, some residual powder may remain inside or outside the threads and make them rough or clogged.
Therefore, tapping through CNC milling is a more reliable and precise method for creating threads on your metal parts. It ensures that the threads have smooth surfaces and accurate dimensions that match the standard specifications.
Metal 3D printed parts can be further processed by conventional methods such as machining, welding, heat treatment, etc.
DMLS 3D printed parts may not meet all your requirements in terms of surface quality, accuracy, strength, or functionality. Therefore, you may want to further process your parts by conventional methods such as machining, welding, heat treatment, etc.
CNC Machining can improve the surface quality and accuracy of your parts by removing excess material and unwanted features such as support structures or burrs. Machining can also create additional features such as threads, holes or slots that are difficult or impossible to print.
Welding can join multiple DMLS 3D-printed parts together to form larger or more complex assemblies. Welding can also repair any defects or cracks in your parts that may occur during printing or sintering.
Heat treatment can modify the microstructure and mechanical properties of your parts by applying controlled heating and cooling cycles. Heat treatment can increase the strength, hardness, or ductility of your parts depending on the type and duration of the treatment.
These conventional methods can enhance the performance and functionality of your DMLS 3D printed parts and make them suitable for various applications. However, they may also increase the cost and lead time of your order and require additional design considerations.
If you want us to assemble the parts for you, you need to send us an assembly drawing before shipping.
If you do not send us an assembly drawing before shipping, we are not responsible for assembling the parts. You will receive the parts as they are printed and you will have to assemble them yourself.
An assembly drawing is a diagram that shows how the parts should be arranged and connected together. It should include dimensions, labels, annotations and instructions for the assembly process.
We hope this post has given you some useful information about metal 3D printing.
If you have any questions or want to start your own metal 3D printing project with us,
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