Additive Quality

Additive manufacturing (AM), or 3D printing is a production method that has been around for some time, but is rapidly gaining traction and increasing its presence in the manufacturing world as time goes on. With this increase also comes a higher need for the quality and inspection of 3D-printed parts. When 3D printing processes are used for prototyping, small deviations may not be critical, although still undesirable. However, when these parts are intended for an end use function, accuracy in quality control, consistency in quality assurance and repeatability in production are vital.

3DPRINTUK’s Quality and Compliance Manager, Alessandro Catania, gives an insight into the quality and validation of an AM-focused company, highlighting the importance of ensuring optimal manufacturing outcomes by full scrutiny from start to finish.

Key highlights

• High volumes require fast and accurate measurements
• End-to-end approach ensures positive outcomes
• Specialised solutions for specialised problems
• Quality control/assurance methods are essential to keep up with the expanding industry

Quality across high numbers of production

Across a large number of printers producing components, the large volume of production creates challenges in terms of maintaining accuracy and consistency in inspection without creating a bottleneck. Catania says that 3DPRINTUK has full confidence in their Quality Management System (QMS): “The in-depth non-conformance side is able to monitor stats generated from failed parts and identify trends in said non-conformances at lightning speed. This allows us to evaluate, identify and eliminate any machine issues at a much faster rate than we used to, massively reducing the impact of any potential manufacturing problems from almost any machine.”

Surface finish, strength and dimensional accuracy are the three main factors that 3DPRINTUK focuses on for determining conformance of a part. Inspection starts with a visual assessment after the build, after each post-processing stage, with one final inspection before shipment. Printing between 80,000 and 90,000 parts every month, a small blemish has the potential to be easily missed, which is the reason for so many separate inspections of the parts. “Each build also features a printed quality control sample that is measured to give us assurance on the general dimensional accuracy of the parts. If any of the dimensions of the sample are outside specific tolerances, then we measure all the parts in the build prior to shipment,” says Catania.

Accuracy and tolerance

3DPRINTUK’s maximum tolerance is ±0.3 mm for anything up to 100 mm, and 0.3 mm for bigger parts. Catania adds that most of the parts they print are well within ±0.15 mm, and they also have a minimum guaranteed thickness of 1 mm for any printed parts, increasing to 2 mm if there are any post-processing requirements.

The yield is monitored by tracking the Right First Time (RFT) KPI, which shows that Multi Jet Fusion (MJF) is their most reliable technology with an RFT score in the high 90s. Selective Laser Sintering (SLS) is a close second, being a “slightly more temperamental process.” A major contributing factor of part failures that was brought to light through the constant part failure data monitoring is a lack of Design for Additive Manufacture (DfAM) knowledge. Catania says “We often receive designs that aren’t quite suitable for our processes and this results in part failures, and the rebuilds ultimately affect our RFT score. Lack of DfAM knowledge is unfortunately a common issue in our industry but we are certain that by raising awareness of a few DfAM principles, our yield would be significantly higher.” 3DPRINTUK has published a short 3-part DfAM guide on their blog with the aim of spreading this knowledge and will continue to share more useful information and design guides with an upcoming website update.

On DfAM Catania adds that “New flexibilities in design are a key benefit of 3D printing. However, it is not without its own restraints, which is why specific DfAM skills are essential to successful adoption. As with any manufacturing process, there are good designs and there are bad designs, and understanding this is essential for successful outcomes.”

Assuring AM quality without bottlenecks

There are many different factors that determine whether a part is in specification. The quality of the powder used in printing is a major one, which is why it is closely monitored for contaminations and moisture content. Traceability plays a big role here, in tracking how the material is transported, stored and handled. “Also, we need to monitor process control from engineering, into production and beyond into post-processing. So much in this chain can affect the quality of outcomes, from internal machine issues such as laser path and intensity all the way through to design of support structures.” It’s important to have a good framework of quality control and quality assurance methods to mitigate these challenges and reduce production difficulties, which also aids in increasing production efficiency and, therefore, cost-reduction.

Catania also mentions that even in a highly automated industry like AM, human error still plays a large role. In the early stages of design and setting process parameters, a “disproportionately high” one even. After that, manual checks during printing and later inspections all increase the risk of human error.

The answer

“To clear the path to the easy adoption of 3D printing for industrial production, it must be acknowledged that these issues first and foremost really do have to be addressed. Quality management in 3D printing needs to be addressed with an end-to-end approach, first looking at material, then DfAM, then build parameters and build, and then post-processing. How rigorous this approach is, is driven to a large extent by the specific applications, and the required level of precision and accuracy. The focus is quality assurance in design and build instead of just a focus on the quality of the part produced as would be the case in traditional manufacturing processes,” says Catania.  

It's no surprise with these highly specialised problems that many companies who use 3D printed prototypes and components rely on outsourcing the production of them to specialists. The dedicated, specialised quality assurance methods for the AM methods are sure to play a vital role in the continuing expansion of the industry.