Celebrating AM! Exploring the Design Impacts of Innovation

At the end of 2023, we saw a lot of conjecture about the demise of 3D printing and the rise of Additive Manufacturing (AM). Tim Simpson and I took the route where we distinguished 3D printing from AM: One is about shapes and the other about parts. This led us to further considerations, such as the infamous 7 AM families. When looking at the original definitions, they have sustained well over time, but fail to include newer processes. This is due to continuous innovation and creation of new hybrids that do not always fit within existing definitions. However, this is a positive, as the processes keep evolving until technically and financially optimized.

So, what is an engineer supposed to do? It is beneficial to have broad descriptions to facilitate the start of any presentation to senior management. Another aspect, indicative of the industry’s maturity, is that if we consider the case of vat photopolymerization, it started roughly 30 years ago with the invention of Chuck Hull. Then, with the introduction of digital light processing (DLP) and Carbon, our perspective changed along with a fresh take on the original process. Most recently, Holo AM has emerged, transforming what was thought to be a polymeric process into a refined metal printing technology.

At the Barnes Global Advisors (TBGA), for similar reasons, we developed the Simplified View of AM. For an engineer, answering the three basic questions—how is the layer formed, how is the material applied, and how is the energy applied—can effectively summarize and begin forming a process specification for any new process.

Figure 1: TBGA’s Simplified View to describe AM process technologies

Fine…It’s in Details

We grew curious upon observing an inadequacy in the design ambit for small components, particularly in supporting AM process technologies. Our intrigue led us to conduct a thorough study with the competent assistance of TBGA Laboratory. We discovered Holo AM and its unique methodologies, which further piqued our interest.

• The formation of layers using a lithographic process or commonly known as DLP.
• The usage of fine metal powders suspended in slurry instead of predominant Metal Injection Molding (MIM) and binder jetting.
• The use of thermal energy to debind and sinter these metal powders into a solidified form.

This practice of creating parts interestingly dovetails DLP. Notably, DLP is armed with superior software and efficient process workflow software support. The maturity of the software employed for DLP processes remains unrivaled by other AM families. This leads to automated auto-generation of supports with impressive accuracy, along with 3-D nesting of buildable parts.

The slurry technique stands out as creators aren’t limited by the ballistic and denudation outcomes apparent in L-PBF and BJP. Binder jetting can often lead to a rough surface finish and limited precision. A study by Carnegie Mellon University emphasized how the binder’s ballistic impact, as it hits the powder bed’s surfaceusually around 8 m/s, affects the process. (Real-time observation of binder jetting printing process using high-speed X-ray imaging, Scientific Reports 9(1):2499). DLP (Digital Light Processing) should provide a uniform layer of metal powders, proving to be a superior approach.

As both BJP and Holo rely on sinter-based process technologies, we must account for shrinkage during the sintering process. We should see similar shrinkage in the X, Y, and Z dimensions using the DLP approach. BJP however, usually results in similar shrinkage in the X and Y directions, with the Z direction needing different distortion to achieve accurate final dimensions. Once the scaling factor for a material is known in the slurry technique, it can uniformly be applied to each new part, streamlining the non-recurring engineering requirements for producing new parts.

The sintering process is somewhat simpler due to the small size of parts. However, preserving details and dimensions is always a challenging task. The DLP process is expected to result in less and uniform distortions unlike in conventional powder bed technologies where factors such as binder bombardment or laser effects could erode the surface finish and dimensional detail.

For our study, we selected a few parts from the TBGA Exemplar library. We chose scaled versions of the impeller and vane segment and added a heat sink with some fine detail. We used our process economic tools to evaluate the costs associated with part production via MIM (Metal Injection Molding), Binder Jetting, Laser Powder Bed Fusion (LPBF), and Holo.

Process Economics

We established the costs to produce the parts with various processing methods. We set up the per part costs along with the required investment to create the parts. Consider this as recurring costs versus non-recurring costs, the latter being the cost of printers, tooling, and so on. Within this calculation, we then determined the number of parts necessary to offset the non-recurring costs. This factor becomes relevant as it would be challenging to justify if production numbers need to be high. Further, we evaluated the ability to maintain tolerance, that is, whether each process produces a consistent output (i.e., can they all reach the specified dimensions?).

Figure 3 is the average part cost for the exemplar geometry as processed by L-PBF, DLP, and BJP. The L-PBF was selected as a competitive PBF entry in a quad laser configuration, despite its finest features being significantly larger than those of DLP-based processes. A more suitable L-PBF comparison could be the 3DMircroprinting GmbH DMP 70, particularly for creating smaller, detailed parts. Nonetheless, we still lack process economics data for this system.

We evaluated several common BJP approaches, such as the HP S100 Metal Jet, Desktop Metal P1, and Desktop Metal X160 Pro, whose costs were similar and therefore averaged to represent typical industry costs. While their costs are akin to those of the Holo machine, they lack the feature size, repeatability, and accuracy offered by the DLP-based method. It is worth noting that the MarkForged PX100 (formerly Digital Metal) uses a finer pixel pitch when printing, making it the best BJP technical comparison. We used qualitative indicators – green (meets), amber (might meet), or red (does not meet) – to denote whether technical requirements of resolution and dimensions were met.

Non-Recurring Expenses and Part Volume

Figure 4. Non-recurring and volume of parts comparison

It’s shown in Figure 4 that non-recurring costs are divided by the total amount of parts to be manufactured. Simply put, initial manufacturing cost for MIM is high due to tooling expenses, but once this is established, mass production becomes feasible. However, it is important to note that if your project requires only smaller quantities, MIM may not be the most cost-effective choice. Alternative additive manufacturing (AM) methods may present a more economical route, even if individual parts are slightly more expensive. AM also offers flexibility in avoiding fixed tooling strategies, thus allowing for modifications in the design if needed. This information is provided for a more comprehensive view of the situation.

When compared to traditional high-resolution manufacturing processes like MIM, both AM techniques considerably simplify the amortisation of non-recurring costs (Engineering + Tooling) because of the expenses associated with injection mold tooling. The availability of automation software for DLP and improved process consistency make Holo an even less expensive option compared to BJP.

Time is Money

We often hear that ‘time is money’, and this saying holds exceedingly true within the manufacturing industry. Seeing the importance of this adage, we have conducted a time analysis to estimate the duration for achieving Low Rate Initial Production (LRIP), as depicted in Figure 5. Please note, due to the fact that MIM tooling usually exceeds 4 weeks, it has been omitted from this graph. Upon examination, it can be seen that the iterative nature of BJP and L-PBF extends the time needed to achieve LRIP. On the other hand, Holo, and the DLP + Sinter strategy results in quicker results. The automated and well-integrated software tools of the DLP drive this efficiency, and Holo directly benefits from this legacy. The maturity of the software tools for the BJP and L-PBF processes however, lags in comparison. Our experience has shown that a majority of preliminary prototypes designed for BJP and L-PBF do not pass the first prototype trial, with issues involving inappropriate sintering setters design, uneven shrinkage for BJP, and potential improvements in build orientation and support design to further minimize distortion in L-PBF. Therefore, for each newly conceived part, a minimum of two Design -> Simulate -> Build Prototypes -> Inspect cycles are usually required, represented in Figure 5 for BJP and L-PBF.

I Need Some Space – Some Design Space

We all need our space at times. Most of us appreciate the design space for different processes. There is some overlap, but this small, detailed part world is relatively new to AM. In this design space, we need to be concerned about factors that can affect surface finish and the precision ability to hit a resolution and feature size. To expand into this small space further, we investigated the resolution and minimum feature size of several processes, not just the ones included in the prior analyses. Based on this information, the DLP + Sinter approach (Holo) has the smallest minimum feature size. Table 1 also adds a dimension to the economic analysis because, after all, parts have requirements, and if you can’t meet the requirement, the cost is somewhat irrelevant.

Table 1. Resolution and Feature Size of Various AM Printers

Requirements, Requirements, Requirements

Can we meet the requirement? From our demonstrated prototypes, it might seem forced to claim we have, as they’re only model parts. However, we did manage to produce some genuine parts and it appears that the introductory bunch adhere to the requirement using the DLP + Sintering method. Based on previous projects, we believe that the DLP method will deliver superior surface finishing and dimensional accuracy than that of BJP – within the same budget. It may be possible to enhance feature resolution by reducing layer thickness and voxel conditions, but this is likely to inflate costs. The lithographical method is fundamentally superior in creating small, intricate parts.

Can we justify this from a business perspective? Financial and temporal constraints often provide clarity. DLP + Sintering and BJP are virtually equal in terms of part cost. DLP + Sintering has the financial edge when it comes to producing a smaller quantity of parts because of existing DLP software. Both BJP and DLP + Sintering benefit from avoiding a sizable initial and fixed tooling cost. Ultimately, the cost-per-part at large quantities is essentially the same for DLP, BJP, and MIM.

The advantage of Additive Manufacturing (AM) methods, especially those leveraging DLP legacy, is apparent when it comes to Lead Time for Rate Production (LRIP).

Does Size Matter? An Age-Old Question

When dealing with small parts, attention to detail is paramount. The recent validation of our process economics with Holo was exciting, though we wish we had more time to delve deeper into the dimensions.  The exploration of finer details, notably internal ones like the impeller and heat sink, emphasizes the need for accurate measurement to ensure compliance.  Smaller features and parts present a compounded measurement issue, which, in effect, is a worthwhile challenge.  The idea of CT scanning the parts to analyze their features and measurements is intriguing.  However, assessing the mechanical properties in small samples can be complex and costly, thus more pertinent data is desirable.

Opting for a slurry-based approach with lithography offers a smoother surface finish and less likelihood of needing setters.  It allows us to evade the problems typically associated with fine powder, which has a more intricate backstory.  Using a slurry effectively prevents free-floating powder and related safety hazards.  Handling the slurry is also simpler compared to fine powders, thus shaping it into a particular form should require less effort.

It’s exciting to see the design space for AM expand again. The small and detailed parts space was underrepresented in metals. The economics of the space also enable good ‘time to first part’ and AM enables the user to get initial parts made without the outlay of cash in tooling. With tooling comes other burdens, namely that the design is then very hard to change or modify and tools have to be maintained and stored.

Let’s make some parts. Long live AM!

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