Can You Metal 3D Print Threaded Holes?

Metal 3D printing is a highly versatile additive manufacturing process capable of producing fully functional parts with complex and intricate features. This process can create end-use parts, functional assemblies, and components for post-printing assembly. Builds often require threaded features to fasten, join/attach, align, or assemble parts or components. Parts may also require these features to translate motion. Threaded holes are particularly critical threaded features as these features are typically integrated into the parts. These requirements and the criticality of threaded holes give rise to the question, ‘Can you metal 3D print threaded holes?’

This article aims to answer the question by comprehensively exploring the practicality of 3D printing threaded holes. In this article, we will delve into factors to consider, design tips, and printing techniques for threaded holes. We will also discuss alternative methods for creating threaded holes and their pros and cons compared to 3D printing.

Overview of Metal 3D Printing

Metal 3D printing is an additive manufacturing process that creates three-dimensional objects from metals by printing consecutive layers of the material until the object forms. To create the required geometry, printers rely on 3D CAD models that have been designed and horizontally sliced into numerous cross-sectional 2D layers using specialized CAD & CAM software. Metal 3D printing is unique because of the physical characteristics of the raw material, metal. The rules of regular thermoplastic or resin 3D printing rules don't always apply. However, this process retains the advanced capabilities of the 3D printing technology and is capable of 3D printing threads.

There are various types of metal 3D printers and printing techniques. However, they all fall under the following technologies.

• Powder bed fusion
• Direct energy deposit
• Binder jetting
• Material extrusion

These technologies primarily vary by feedstock delivery system - how the printer feeds material to the system; consolidation technology - how the printer fuses consecutive layers to form the desired shape; and the state of the feedstock - powder, wire, foil, or slurry. They are also best suited to different use cases and have different characteristics, such as build size, tolerance, cost, and printing capabilities. Learn more about the types, processes, applications, and benefits of 3D printing in our comprehensive 3D printing guide.

Powder bed fusion

In this technology, a high-energy precision laser selectively traces out a slice of the desired object on a bed of atomised metal powder particles, causing the particles to fuse and form the shape. The build platform drops by a minuscule layer and a horizontal moving arm in the printer sweeps across the powder bed, depositing another thin layer of fresh powder on the previous layer. The laser traces out another slice directly on top of the preceding layer. These processes repeat in consecutive layers of 30 to 60 microns until the printer builds the object from bottom to top.

Direct metal laser sintering (DMLS) is an example of a powder bed fusion technology and is the most common metal 3D printing process. Due to the popularity of this process, a significant number of metal 3D printing projects are carried out using advanced DMLS 3D printing services.

Direct energy deposition

In this process, a high energy source and a feedstock delivery nozzle move in precise uniformity along the X and Y axis. Starting from a bottom layer, they selectively trace out the first cross-section of the object on the build plate. As the nozzle delivers the feedstock (in wire or powder form), the laser heats and fuses the material to form the first layer. The printer then lowers the build plate by the size of a layer, typically in microns. The processes alternate in consecutive layers/slices until the entire object forms.

Binder jetting

Like powder bed fusion, binder jetting uses a power bed of feedstock and prints layer by layer. However, in this method, instead of a laser tracing out the geometry, a print head selectively deposits a binder liquid on the powder bed that binds the powder in the shape of the first layer. The machine lowers the build plate and deposits a fresh layer of powder. Next, the print head deposits the binder to create a subsequent layer. These processes repeat until the complete geometry forms. Parts created via this process require post-processing curing and sintering.

Material extrusion

This process involves feeding the feedstock, typically a heated mixture of a polymer and metal powder, through a controlled nozzle. The nozzle deposits this mixture in consecutive layers until it forms the entire object. The final print requires sintering in a furnace to burn off the thermoplastic and strengthen the part. Material extrusion is the least common metal 3D printing technique as it poses several challenges.

Factors That Influence Metal 3D Printing Threaded Holes

While metal 3D printing is highly versatile, threaded holes are particularly complex features, as their accuracy is critical to their functionality. Can you 3D print threads? Yes, but it depends on several factors, such as thread size, print orientation, and technology used. The threads need to be the right size, shape, angle, and depth to serve their intended purpose. Significant errors can severely impact the functionality of the threaded hole. The feasibility of printing threaded holes from metal depends on several factors. These factors are often interrelated, with multiple factors influencing a print. 

Thread and hole size

Size plays the most crucial role in threaded hole 3D printing. Both the thickness of individual threads and the diameter of the hole are vital considerations. Holes smaller than 0.5 mm are highly susceptible to distortion and closure during printing, irrespective of the overall part size. Small threaded holes are even more prone to closure, especially if the threads extend beyond the required diameter. Additionally, printing threaded holes with thicker threads is generally more straightforward. To ensure successful printing, it's advisable to only print threaded holes of size M2 and above, with sufficient thread thickness.

Printing technology

The tolerances of different printing technologies vary, directly impacting their ability to print threaded holes. Our 3D printing services leverage advanced techniques like DMLS, which print in minuscule layers of less than 100 microns, enabling the creation of accurate, functional threads. Direct energy deposit and jetting technologies also print in layers. However, the end products of these processes require extensive post-processing that can impact threaded holes, especially small ones. Lastly, extrusion technologies are less suitable for metal 3D printing holes, as they can only deposit layers as thin as the extruding nozzle. In addition, the nozzle shape restricts the shapes the threads can take. Again, sufficiently large threads mitigate these concerns. 

Print orientation

Vertical orientation is optimal for printing holes in metal 3D printing, as the printers treat holes as blank spaces, depositing material around them layer by layer until the hole forms. As long as the surrounding walls are thick enough to withstand stress during use, the vertical orientation is ideal for printing functional threaded holes.

In contrast, the horizontal orientation requires the printer to create curves and overhanging arches to form the hole structure. This process necessitates support structures to prevent sagging and flattening at the top and bottom of the hole, respectively.

Thread design

Threaded holes can have a variety of thread thickness, depth, crest shape, angles, and pitch. Some of these characteristics can impact the printability of a threaded hole, albeit slightly. Modern CAD software applications allow you to assign various thread specifications.  DMLS 3D printing can produce complex custom threads. However, it is recommended that you use standard thread specifications.

Design and Printing Tips for Metal 3D Printed Threaded Holes

The following are some design and printing tips that make the process more practical and seamless.

• Incorporate support structures into your design when designing large holes with prominently overhanging threads. Also, include support structures in horizontally oriented thread holes. 
• Threaded holes do not need full thread circumferences to function. In a horizontal print, you can design the roof and floor of the hole to be threadless (smooth), leaving threads only on the sides. This technique makes printing easier and eliminates sagging and flattening concerns.
• Use standard hole sizes. CAD software applications allow users to specify custom hole sizes. However, we recommend using standard hole sizes. This makes it easier to apply tolerancing and account for distortion during printing and post-processing.
• 3D printers have specifiable printing parameters that control and impact various aspects of the print. The layer height and print speed parameters are especially important when printing threaded holes. Higher layer resolution ensures that fine thread details form correctly, while lower print speed allows more time for preceding layers to solidify, thus minimising sagging in overhanging features.
• Always account for post-processing when designing and printing threaded holes. For example, holes may shrink in size during jetting and direct energy deposit post-printing sintering. Similarly, support structure removal may affect the edges of the threads.
• Whether you are 3D printing screw threads or threaded holes, proper design is critical to fully utilising the capabilities of metal 3D printing. Learn more about optimising your design in our 3D printing design guide.

Alternatives to 3D Printing Threaded Holes

In manufacturing, there are situations where it's simply not feasible to print threaded holes. This could be due to factors like specific material requirements, thread type, or the need for very small holes that can't be accurately printed. Additionally, there are cases where printing threaded holes isn't necessary or practical, given the effort involved. For such cases, there are viable alternatives for creating threaded holes.

• Threaded inserts: Threaded inserts are prefabricated fixtures you can insert into an existing hole to make it threaded. These inserts come in standard sizes and types and are cylindrical, featuring threaded interiors. The existing hole’s diameter and depth must correspond with the external diameter and depth of the insert.

Installation methods include snap fitting, adhesive bonding, and welding. While threaded inserts are more straightforward than printing, they require additional parts, tools, and post-processing.

• Tapping: Tapping involves using a specialised drill bit to physically carve out threads in an existing hole. The bit, known as the tap drill, is inserted into the hole, and downward rotating torque is applied.

To use this threading technique, it is essential to use correctly dimensioned standard features. The dimensions of the tap drill and the hole to be threaded, whether printed or drilled out post-printing, are critical. Consult a Tap drill chart to obtain the correct dimensions to use. Tap drill charts show standard hole sizes and their corresponding tap drills needed to create specific thread hole sizes. The image below is an example of a tap drill chart.

Similar to threaded inserts, tapping requires additional tools and post-processing.

Metal 3D printing, tapping, and using threaded inserts have distinct benefits and drawbacks. The table below compares these threading techniques based on different parameters.

There are also several other joining techniques for metal 3D printed parts, such as welding, snap fit, rivets, and brazing, that do not involve threads

Conclusion

In conclusion, can you metal 3D print threaded holes? The most accurate answer is “it depends.” The feasibility of metal 3D printing threaded holes depends on various factors. With the right sizes, printing processes, design techniques, and materials, metal 3D printing can successfully produce accurate and functional threaded holes. However, for certain small sizes, designs, and printing processes, metal 3D-printed holes may not be practical. In such cases, use alternative techniques to create threaded holes.