In addition to downloading the print files from the content platforms and creating 3D models yourself, 3D scanning offers another way of obtaining the necessary 3D print model.
The 3D scanner measures the width, height and depth of a real object. Depending on the scanning process, the corresponding color information is also recorded.
As with 3D printing, there are also a wide variety of processes for 3D scanning that can be used depending on the application.
For some applications, 3D scanning is often the only way to create the required 3D data.
Examples are:
- Archaeological Objects
- sculptures
- Listed objects
- Measurement of building structures
- organs and illustrative models
- 3D portraits of people
- Target/actual comparison of manufactured components
- wear test
- dental scans
With this wide range of applications, the requirements for quality, accuracy and possible scan size of the 3D scanner are very diverse.
In most cases, 3D data is acquired with light. “Only” the outer contours are recorded. 3D data of any cavities or channels in the component are not taken into account in most scanning processes.
In order to record the internal structures, we have to use the scanning methods known primarily in medicine, such as CT (computed tomography) and MRT (magnetic resonance imaging).
Before we explain the individual 3D scanning methods in more detail, let’s first look at the process flow of a 3D scan.
What do we have to pay attention to? Which individual steps are necessary to obtain an error-free 3D model.
Contents
Process flow: From 3D scan to 3D model
The idea that a finished 3D model could be delivered immediately from a simple 3D scan would just be too good to be true.
Depending on the scanning system, more or less extensive post-processing is required after the scan.
With a 3D scan, the object is usually scanned or scanned with a laser.
During this scanning, a large amount of data and contour points is created, which is then combined in a common coordinate system to form a point cloud.
A reverse engineering is then generated using the appropriate software.
What started out as one point becomes two, three or more points. Lines or curves are generated from these. These curves and lines then create surfaces (polygons). From this, in turn, a polygon mesh develops.
The surface of the object is then covered with a triangular network, the so-called triangularization.
The entire model must have one closed surface feature.
This surface model that has now been created can now be exported as a printable file (-.stl,-.3mf, -.obj).
“Theoretically” this file could now be printed.
But…
This is usually not sufficient for a good and usable print result.
The following steps should therefore still be carried out:
In order to achieve high scan accuracy, countless points are measured with the 3D scanner. This large amount of data is the basis for a high scan quality, but also makes any necessary post-processing of the files very complex and time-consuming.
With very precise scans, several 100,000 polygons (areas) can be generated. One or the other PC could reach its performance limit as a result.
It is also advisable to reduce the details for the subsequent 3D printing of these scans, since some 3D printers also have limitations in the print resolution for many details.
Our motto here is: Less is more!
This reduction of the areas can often be carried out in the scan programs themselves.
2.Manual or automatic positioning of images
Depending on the scanning process, individual images are created from different positions.
So that the software knows what the scanned component should look like in the end, some of the images have to be positioned manually.
However, the latest types of software and 3D scanners do this work step automatically.
Various scanning errors can occur during 3D scanning due to incorrect lighting conditions, movements of the scan object or reflections on the surface.
In this way surfaces and shapes are created that do not exist in reality.
Such scan errors should definitely be fixed and removed.
Every 3D model must have a closed surface, otherwise the model cannot be printed. No polygon may be missing. The model must therefore be “waterproof”.
Closing these holes can be done automatically or manually.
The final step that may need to be performed is smoothing.
Depending on the quality of the raw scan data, some surfaces of the component are uneven. These can be smoothed out again using the “Smooth” option, or “Smooth” in some programs.
However, the level of detail is reduced and a certain blurriness is created on the 3D model.
Small and fine details may then no longer be displayed correctly.
6. Reverse Engineering – Optional
Depending on the application and the possible purpose of the 3D scan, reverse engineering may make sense.
This is called reverse engineering.
The scan data is processed and exported in the appropriate format (e.g. -.Step) so that the 3D model can be further processed using CAD software.
What should be generally considered with the 3D scan?
- Developing a scanning strategy – How must the component be scanned in order to also reach hidden edges and undercuts?
- Size of the scan object – Which scanning system should be used?
- Application of the scan – 3D printing, animation or virtual reality?
- Type of 3D scanners – resolution, accuracy and scan time?
- Appropriate software – will this achieve the desired end result?
- Reflective or deep black surface – is a pre-treatment with a special spray (e.g. chalk spray) necessary?
What are the 5 major 3D scanning techniques available to us?
1.Photogrammetry
Photogrammetry is a non-contact scanning process that generates a 3D model from 2D images. These images can be photographed with standard cameras or smartphones. Care should be taken to ensure good lighting conditions.
The more photos there are, the better the quality of the 3D model. Of course, processing the data also takes more time.
The software then generates the 3D model. Some programs create this calculation within a cloud.
This scanning method is well suited for getting started with 3D scanning, as the investment costs are low.
Photogrammetry is used, for example, when surveying buildings and generating 3D data of landscape reliefs. Today, drones give us the opportunity to create photos from all angles.
The level of detail is rather low in comparison to the other scanning processes, but is perfectly adequate for many applications. The good cost factor plays a decisive role here.
2.Line light scan
A significantly more extensive and significantly more expensive scanning method is the structured light scan, also known as a projector scan.
As with photogrammetry, camera images are also used here, but a projector is also used.
With the help of the projector, a coded stripe pattern is projected onto the component. An offset camera takes numerous pictures of it. These distorted striped patterns are then converted into a 3D model in the software. The resolution and accuracy are very high.
This method is often used in the industrial sector, for example when scanning machine components or cultural assets.
Areas of application: Mechanical engineering, archeology, dental industry
3.laser scanning
With laser scanning, the object is scanned by a laser beam. The wavelength of the laser and its deflection are precisely measured.
This scanning method is very precise, but the scanning process can take a long time because the laser has to scan the entire object.
Areas of application:
Architecture and interior design, accident reconstruction, automotive, aircraft and mechanical engineering, monument protection and museums
Manufacturer: Faro, Leica, Trimble
4. Computed tomography
In computed tomography, the object is irradiated using X-rays.
Cross-sectional images are generated, which are combined again to form a 3D model.
This procedure only works with materials that can also absorb these rays, such as plastics, ceramics or bones.
Particularly thick metals made of iron or steel, on the other hand, are difficult to X-ray.
Due to the penetration of these rays, internal structures or cavities can also be recorded and displayed three-dimensionally (e.g. art objects).
Computed tomography is the only scanning method that can capture internal structures.
5.Infrared scan
The infrared scan also works similar to the laser scanners. The small but subtle difference in this scanning process is the fact that the illuminated object surface is heated by a few tenths of a degree.
The absorbed thermal energy is captured using an infrared detector and converted into a 3D point cloud.
With the infrared scan, reflective surfaces (e.g. automotive industry) can also be scanned without any problems. This is a key advantage over the other scanning methods.
External factors such as ambient temperature or changing lighting conditions also have no influence on the scan quality.
One of the leading manufacturers is Aimess GmbH from Saxony-Anhalt.