ThinKing February 2018 – Guarantee reproducibility and quality of additive manufactured parts

08.02.2018

 

CT scan of 3D printed parts reveals variations from the “digital plan” in the CAD model and allows the manufacturing process or component shape to be improved.

Engineers often face the challenge of addressing defects in additively manufactured components such as tolerance violations and production delays. The company Hachtel can help with these issues. By using computer tomography, 3D scans of the components are made and compared with the CAD design files. Variations from the digital CAD models can be easily identified – it is then possible to not only evaluate the quality of the parts, but also improve the manufacturing process as well. Hachtel offers the full range of these services from the scan and evaluation of the results to the improvement of the component and the production process.

The State Agency for Lightweighting Baden-Württemberg presents this innovation as its ThinKing for February 2018. Leichtbau BW awards this label every month to innovative products and services from the lightweighting sector in Baden-Württemberg.

Hachtel based in Aalen has over 10 years of experience in using 3D computer tomography as a certification tool to evaluate its own injection molded products as well as for quality testing  and optimizing components for customers. “It is sometimes difficult to precisely evaluate the quality of a component using classical coordinate measuring technology. Even the form and number of measuring points leave a lot of room for interpreting the results,” notes managing director Steffen Hachtel. He introduced industrial computer tomography to the company in 2007. “The CT scan offers transparency and allows us to very quickly and efficiently evaluate the parts in respect of their shape and geometric properties. We can analyze the actual state of the part without destroying it,” explains Hachtel.

Identify variations from the “digital plan”
As the company began to implement additive manufacturing in earnest in 2013, Steffen Hachtel asked what lessons additive manufacturing could learn from injection molding. “CT scans are standard for injection molding and many optimization steps are made in advance thanks to digital simulation. Additive manufacturing still has a deficit in simulation tools and the range of materials and processes is quite large with each one offering very specific properties. This is the gap we are helping to fill with CT scans,” says Hachtel. When the scan is finished, the measurement results are compared with the CAD files. Does the manufactured component vary from its “digital blueprint” and if so, how large is the variation? Are there defects inside the part that cannot be seen from the outside? Comparisons of CT measurements in combination with CAD construction can provide answers to these questions. Close adherence to specified forms is a key factor in 3D printing. Parts can warp or fuse improperly, and particles that do not fully melt during the process can compromise the stability and functionality of the part.

Rescan after reworking can show the effects of adjustments
After the results of the comparison are obtained, it must be determined if the component is suitable for its intended use or if improvements are necessary – including improvements to the production process. Depending on the spatial positioning of the component in the 3D printer or the form and selection of the support elements, the component may shift and warp during the production process. This requires the process itself to be modified and may require adaptation of the shape of the component as well.

When the reworked component is reprinted and subjected to another CT scan, it is very interesting and exciting moment during the optimization process. “This scan gives us a very precise view of how the component has changed in comparison to the previous part and of the actual changes with regard to the optimization. This means that there is an additional engineering and production step, but the second printing produces a much higher quality component,” according to Hachtel.

Process reliability and exact reproduction in preparation for series production
Computer tomography can offer valuable results in the evaluation of the production process for parts produced by additive manufacturing. For these tests, several samples of a part are produced from the same CAD data. Once finished, each component is scanned and the results are compared. “This gives us an idea of the reproducibility within the production process of the parts through 3D printing,” explains Hachtel. “Precise and uniform production is a difficult topic in additive manufacturing. To ensure and optimize a uniform production, it is important to closely inspect the processes and procedures in order to better understand them and to find ways to make them cheaper and eventually make serial production possible,” says Dr. Wolfgang Seeliger, managing director of Leichtbau BW GmbH.

“It is often said that the additive manufacturing offers a lot of room for versatility, but particularly in the case of functional components, it is important that the part that actually comes out of the printer is really the part that should come out according to the specifications,” notes Steffen Hachtel. In Hachtel’s opinion, an additively manufactured component should never be sold without passing a CT quality inspection. “That is the reason why all the parts we produce through additive manufacturing undergo a quality test and analysis through CT scan,” says Steffen Hachtel. “Unlike with prototype parts, this is absolutely essential for functional parts.” Hachtel also offers their expertise to others as a service. “We cover the entire process from the CT scan and analysis all the way to finding the right improvement strategy and corrective processing for the component or production process – all from a single source,” notes Hachtel.

Competitive advantage through reduced time-to-market
The digital measurements from computer tomography have the advantage that they can be recalled at any time, rendering printed reports unnecessary. This allows a better comparison of a new component with a previously produced component to identify the exact effects of a change in the process parameters. Steffen Hachtel explains that the long-term goal is to use the collected volume of previous test results and appropriate simulation tools to someday be able to predict the results of a production so precisely that the first part that comes off the printer already meets the design specifications. “For me, this means that additive manufacturing engineering will become much more dominant in the future – and that will in turn make the procedure more complex,” says Hachtel. “And that is the reason why we need digitalization”, notes Dr. Wolfgang Seeliger. “If development cycles and optimization loops can be accelerated through precise calculations with simulation tools, the reduction in time-to-market results in an enormous competitive advantage and benefits from high process reliability in manufacturing,” says Seeliger.

About Hachtel
Hachtel specializes in mold production and tool construction as well as the production of injection mold plastic components. Since 2007, the company based in Aalen has been a service provider in the area of industrial computer tomography and offers scans and analyses of components and part groups for every type of production. Internet: www.fg-hachtel.de