<p>It's not hollow <em>or</em> enclosed structures that are a problem. It's structures that are hollow <em>and</em> enclosed. Think about it. The machine lays down a thin layer of powder, and then a laser fuses some of that powder together to make a shape. Then, it repeats the process for the next layer. If you try to build, for example, a hollow ball, the ball gets created in the middle of the powder, meaning that there will be powder around the outside of the ball and in the <em>inside</em> of the ball, and with the ball completely enclosed, there is no way for the powder that ends up inside the ball to get out. That's why hollow objects printed in this manner must have a hole somewhere to let out the powder contained in the object.</p>

<p>This is not only true of metal powder, but any 3D printing process that uses a bed of powder or a volume of resin and fuses some of it into a shape. Fused deposition modelling (FDM), the process used by most consumer-level 3D printers, build models in thin air, so only air is trapped inside the printed objects, making the printing of hollow, enclosed objects less of a problem. Of course, one has to deal with gravity. A hollow object might collapse before the filament hardens enough to support its weight.</p>

CC BY-SA 3.0
2016-08-22T17:25:19.007Z
This is true for all powder bed based printers, not just those using metal powder.
the third dimension
CC BY-SA 3.0
2016-08-22T17:36:42.817Z
That is true. My answer comes from my experience modifying my FDM models to work with Shapeways, which uses laser sintering, as described in the question.
John Sensebe
CC BY-SA 3.0
2016-08-23T14:59:18.610Z
Hmmmm.. so how does one make a hollow ball with any other manufacturing method?  Glass-blowing, e.g. seals a viscous fluid just before cooling the object.  Can you produce a hollow steel ball w/o an exit hole that gets sealed post-production?
Carl Witthoft
CC BY-SA 3.0
2016-08-23T15:14:20.527Z
One could print two halves and fuse them together. The seam might be nearly invisible after polishing. With an FDM printer, a hollow ball is less of a problem because the arcs of the sides and closed circular layers would tend to hold things together. A hollow box, however, would be difficult. You'd have a large, flat area with nothing to support the middle. I'd probably print such a box at a 45° angle if I had to, so that nothing is horizontal.
John Sensebe
CC BY-SA 3.0
2017-02-07T23:30:06.457Z
This is exactly what I was going to say.
MakerModder
CC BY-SA 3.0
2016-08-22T14:03:31.830Z
2016-08-22T17:49:35.243Z
2016-08-22T17:49:35.243Z
John Sensebe
<p>Metal powders are the fastest-growing segment within the 3D printing materials market, and 3D printing with metal offers a range of highly-sought out characteristics, including immense strength, reduced weight, biocompatibility and corrosion or thermal resistance, making it ideal for high-demand industries such as aerospace, medical, etc.</p>

<p>Conventional methods require focusing a very intense energy source, such as a laser or electron beam, across a bed of metal powder, fusing the powder particles together in a pre-determined pattern to create the final 3D structure. </p>

<p>While this method does allow for incredibly strong metal 3D structures to be produced, it has its drawbacks, mainly: </p>

<ul>
<li>it is prohibitively expensive and time consuming; </li>
<li>it does not allow for certain types of architectures, such as those that are hollow and enclosed, and;</li>
<li>it is limited by the types of compatible metals and alloys that can be used.</li>
</ul>

<p>If we ignore the cost, why can't we do hollow or enclosed architectures to be printed with this technique?</p>

<p><strong>Source:</strong> <a href="http://www.3ders.org/articles/20160817-a-closer-look-at-the-12-biggest-3d-printing-tech-innovations-of-the-first-half-of-2016.html" rel="nofollow noreferrer">A closer look at the 12 biggest 3D printing tech innovations of the first half of 2016</a>.</p>

CC BY-SA 3.0
2016-08-22T14:20:35.260Z
You should edit the question to include a reference to where you presumably read that this should be impossible.
Tom van der Zanden
CC BY-SA 3.0
2016-08-22T17:53:47.590Z
Thanks for adding the reference but I don't really see where it says that metal printing can't do this. Generally, when you ask a question like "Why is it that X?" it is always a good idea to specify how you got the idea that "X" (which is usually due to reading the claim somewhere) to avoid confusion.
Tom van der Zanden
<print-material><printing-powder><metal-printing>
Why can't powder-based 3D printing techniques create enclosed or hollow structures?
Josip Ivic
# Why can't powder-based 3D printing techniques create enclosed or hollow structures?

(Asked by: username_0 on 2016-08-22)

Metal powders are the fastest-growing segment within the 3D printing materials market, and 3D printing with metal offers a range of highly-sought out characteristics, including immense strength, reduced weight, biocompatibility and corrosion or thermal resistance, making it ideal for high-demand industries such as aerospace, medical, etc.

Conventional methods require focusing a very intense energy source, such as a laser or electron beam, across a bed of metal powder, fusing the powder particles together in a pre-determined pattern to create the final 3D structure.

While this method does allow for incredibly strong metal 3D structures to be produced, it has its drawbacks, mainly:

* it is prohibitively expensive and time consuming;
* it does not allow for certain types of architectures, such as those that are hollow and enclosed, and;
* it is limited by the types of compatible metals and alloys that can be used.

If we ignore the cost, why can't we do hollow or enclosed architectures to be printed with this technique?

**Source:** [A closer look at the 12 biggest 3D printing tech innovations of the first half of 2016](http://www.3ders.org/articles/20160817-a-closer-look-at-the-12-biggest-3d-printing-tech-innovations-of-the-first-half-of-2016.html).

**Tags:** print-material, printing-powder, metal-printing
> **Comments:**
> **username_1**: You should edit the question to include a reference to where you presumably read that this should be impossible.  
> **username_1**: Thanks for adding the reference but I don't really see where it says that metal printing can't do this. Generally, when you ask a question like "Why is it that X?" it is always a good idea to specify how you got the idea that "X" (which is usually due to reading the claim somewhere) to avoid confusion.  

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## 1 answers

### Answer by username_2 on 2016-08-22. Score: 11 | Accepted answer

It's not hollow *or* enclosed structures that are a problem. It's structures that are hollow *and* enclosed. Think about it. The machine lays down a thin layer of powder, and then a laser fuses some of that powder together to make a shape. Then, it repeats the process for the next layer. If you try to build, for example, a hollow ball, the ball gets created in the middle of the powder, meaning that there will be powder around the outside of the ball and in the *inside* of the ball, and with the ball completely enclosed, there is no way for the powder that ends up inside the ball to get out. That's why hollow objects printed in this manner must have a hole somewhere to let out the powder contained in the object.

This is not only true of metal powder, but any 3D printing process that uses a bed of powder or a volume of resin and fuses some of it into a shape. Fused deposition modelling (FDM), the process used by most consumer-level 3D printers, build models in thin air, so only air is trapped inside the printed objects, making the printing of hollow, enclosed objects less of a problem. Of course, one has to deal with gravity. A hollow object might collapse before the filament hardens enough to support its weight.

> **Comments:**
> **username_3**: This is true for all powder bed based printers, not just those using metal powder.  
> **username_2**: That is true. My answer comes from my experience modifying my FDM models to work with Shapeways, which uses laser sintering, as described in the question.  
> **username_4**: Hmmmm.. so how does one make a hollow ball with any other manufacturing method?  Glass-blowing, e.g. seals a viscous fluid just before cooling the object.  Can you produce a hollow steel ball w/o an exit hole that gets sealed post-production?  
> **username_2**: One could print two halves and fuse them together. The seam might be nearly invisible after polishing. With an FDM printer, a hollow ball is less of a problem because the arcs of the sides and closed circular layers would tend to hold things together. A hollow box, however, would be difficult. You'd have a large, flat area with nothing to support the middle. I'd probably print such a box at a 45° angle if I had to, so that nothing is horizontal.  
> **username_5**: This is exactly what I was going to say.  

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