Is METAL Additive Manufacturing disruptive?

#AdditiveManufacturing (AM) / #3Dprinting, the umbrella term for layer-wise deposition of build material to produce functional components from digital models encompasses diverse operating principles ranging from the selective thermal fusion of powder particles to the UV curing of photoreactive monomer resins. These processes are enabling organizations to change the manufacturing philosophy from “Designing for Ideal Manufacturing” to “Manufacturing the Ideal Design”. As such, the generic advantages associated with AM claim to challenge the existing paradigm of centralized mass manufacturing and reinvent the #SupplyChain. The question is, are these claims “Too Outrageous”, given the economic constraints to the wider adoption of AM over conventional manufacturing or is there any truth to these claims? First, let's look into the economic and technical challenges associated with AM processes, and then explore the solutions available for users to reap maximum economic benefits from these processes.

Is AM disrupting manufacturing?

To answer this question, let's compare AM with conventional manufacturing processes. Compared to the traditional subtractive manufacturing and formative fabrication techniques, in AM processes many of the tooling related constraints on the geometries can be avoided. The high degree of fidelity and flexibility of operation associated with AM processes brings the following advantages with AM processes:

• Design freedom,
• Part consolidation,
• Production of near-net-shapes with relatively little scrap,
• Product life extension,
• Cost reduction due to logistics and inventory management

Although AM processes are associated with the above-mentioned benefits, the reality is the current AM processes do not match the speed and mass scale production capabilities of many conventional manufacturing processes such as injection molding, machining etc. However, AM processes reap significant economic benefits in specific areas, such as:

• High volume manufacture of complex parts with expensive metals such as Ti6Al4V or Inconel or Tool Steels,
• Low volume manufacture of; customized medical components such as implants (polymers) and machine tools (metals),
• Repair of critical structural components such as molds, turbine blades, precision engineered tools, fuel nozzles etc.

Figure 1: CAD model of an industrial spur gear

In short, the single biggest advantage of AM processes (polymers and metals) is design freedom. Consider the case of a simple industrial spur gear (Figure 1), available at ~$8-$10/piece. Additive Manufacturing of the same will cost ~$35/piece at ~10 hrs/piece processing time, and does not look economically attractive. The advantage that AM poses is including complexities in the geometry to reduce weight or enhance stiffness. While with AM including complexity is literally free, with milling the average increment in processing cost is ~$2/piece/feature, provided the feature is machinable.

Figure 2: Distribution of AM business

In-fact with AM mass customization is already a reality as it significantly reduces the cost of logistics and inventory management. Interestingly, the fact that AM could also be used as a complementary tool to traditional manufacturing was already highlighted in the Wohlers’ Report of 2017. Consider CNC machining and 3D printing, even though both are completely opposite in principle, yet actually, they complement each other extremely well. Naturally, the question arises: Can using the new hybrid 3D printer/CNC machines, reap tangible economic benefits? Fact is using AM in conjunction with CNC machining reduces the lead time by ~50%. So long answer short, yes AM is causing widespread disruption across SPECIFIC industry verticals ranging from automotive ancillary to medical devices. That being said, before jumping on the bandwagon of AM disruption let’s look at the many challenges that essentially exist for AM processes.

Challenges in AM

Let's divide the challenges for the diffusion of AM into the existing manufacturing ecosystem into the economic and technical aspects. Unlike traditional manufacturing, the cost associated with the AM system itself is huge, both the capital investment as well as the operational time (Figure 3). For example, while short wavelength (~1064 nm) Nd: YAG or Yb-fiber lasers are suitable for processing metals, higher wavelength CO2 lasers are suitable for polymers and ceramics. So, besides the complex physics of laser-material interaction, minimum print resolution and their effect on the quality of the build, there is a huge economic component involved in the selection of the laser itself. I will discuss these details in later posts. Additionally, the size of the build chamber and effective utilization of the build chamber volume dictates the operational costs associated with the process.

Consider this. For processing a 10 cm × 10 cm × 10 cm steel block, even though the cost associated with running a metal AM machine (~₹ 3000/hr.) is comparable to CNC machining, the primary area of concern in AM is the operational time (~100-300 hr.). Note that, metal AM machines do not run in isolation. Class D fire extinguishers, electrostatic flooring and humidity- and temperature-controlled spaces for storing powders, oven/furnace, wire Electro Discharge Machine (EDM) for support removal post build are some of the necessary auxiliary pieces of equipment. The auxiliary pieces of equipment additionally contribute to the operational costs.

Figure 3: Challenges in AM processes

As with traditional manufacturing, full utilization of the available machine capacity forms a prerequisite for efficient operations in AM as well. However, unlike traditional manufacturing, in AM once the technology is utilized effectively in terms of build volume utilization - repetition hardly produces any substantial economic wins. Fortunately, with the continuous advances in laser technology and material research, the capital investment on AM machines and consumables (i.e. materials) is expected to reduce significantly in the coming years. Independent researchers conclude that by 2020, the cost of metal AM systems will reduce by ~50% along with a significant drop in AM material price (polymer by ~60% and metal by ~40%). Therefore, for AM processes to reap sustainable benefits, the analyses of “ill-structured” costs are the most important. The “ill-structured” costs are a consequence of the technical challenges and relate to the following:

• Unintended product variation/failure,
• Ancillary post-processing operations (Polishing, Support Removal, Annealing, Hot Isostatic Pressing etc.),
• Slow build speed,
• Lack of in-house expertise

Viable solution

The key to reaping economic benefit from AM lies in overcoming the technical challenges through proper understanding and planning of the printing process are necessary. For example, in metal AM, an incorrect orientation of the part in the build chamber can result in as much as ~160% increase in the energy consumption, besides resulting in unfavorable residual stresses and distortions. While the reduction in various other expense heads, such as machines, material cost will require some time, improving the available process design using simulations can;

• Reduce the operational time and cost,
• Improve part design and quality,
• Reduce/eliminate post-processing efforts,
• Realize the printability of complex shapes (e.g., conformal lattice structures),
• Compensate for the lack of in-house AM expertise

Figure 4: General workflow in AM process

Usually, the very first compromise in the original design of a component happens due to the limitations or imperfections of the manufacturing step in the workflow. In metal AM, the room for such compromise is further limited due to the economics of the process and competitiveness of the finished product. This is the reason why in metal AM, “Design for Additive Manufacturing (DfAM)”, is not a luxury, but a necessity. DfAM introduces multi-physics based pre-processing capabilities within the workflow to reduce the lead time from months to days and thus, increments profit with minimal efforts. Interestingly, DfAM also compensates for the lack of in-house AM expertise to generate “sustainable wins” for the organization.

How?

The road to sustainable wins

An AM process starts with a feasibility study to determine the parts that AM would most benefit, followed by design of the component and post-processing operations, before the actual printing process. Note the crucial multi-physics analysis coupled with topology optimization to realize DfAM in Figure 4. The post-processing operation is the most crucial component in the AM workflow to print components for sustainable profit. Importantly, a detailed thermal and structural Finite Element (FE) analysis of the actual build process (virtual build) can take ~2-6 hours and help identify:

1. The location of the support structures,
2. The residual stresses developed in the build part as well as in the support structures,
3. The distortions in the part on the removal of the support structures,
4. Correct part orientation for a successful build,
5. Optimal nesting configuration effective build chamber utilization etc.

Note that the authenticity of these results is dependent on the robustness of the FE solver, the material model and the ability of the user to incorporate process physics in the simulation. More into these details in later posts.

Now returning to the importance of AM workflow. The ease of operation associated with most of the recent AM systems from EOS, Concept Laser, Trumf, SLM etc. or even the desktop printer suppliers ensures a relatively narrow learning curve for an experienced CNC operator. Imagine the cost associated with build failure during and post-printing, without pre-processing.

It’s enormous.

Add to it the increase in lead time.

The solution lies in using DfAM along with process mechanics simulation to generate the STL file which can accurately compensate for the part distortions, leaving the machine operator to examine the G-codes for laser scan and effectively process the powders.

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Santanu

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