Perspective Chapter: Breaking the Barriers – Additive Technologies (AX) for Integrated Process Chains and Integrated Devices (IDs) for Hybrid Product Architectures

*Matthias Dahlmeyer and Sebastian Noller*

## **Abstract**

Additive technology has evolved from rapid prototyping to rapid tooling and manufacturing of load-bearing parts for productive use. Application potential is limited by constituent strengths and weaknesses. To enfold its full potential, research, development, and industrial application have to facilitate combinations of additive and conventional technology. The concept of additive parts manufacturing has to be expanded to a mature technology contributing and facilitating hybrid products and integrated process chains. From a two-dimensional reference model, approaches to integration are derived, and their status is briefly outlined: Efforts to facilitate postprocessing by design for additive manufacturing (DfAM) and hybrid manufacturing have been raised to awareness and are being worked on. Yet, integration of pre-fabricated structures is hardly accounted for, although it bears the potential for a paradigmatic shift in manufacturing: With a wider concept of layer-based processes, Additive Technology could form the core technology for integration of components and functions to Integrated Devices, following the model of the Integrated Circuits and packaging technology in microelectronics and Microelectromechanical Systems. First developments are outlined, but research and development effort has to be dedicated to novel additive processes for this application. Finally, workflows for product developers need to be modified and trained to plan hybrid product architectures already in conceptual phases.

**Keywords:** additive technologies (AX), integrated process chains, integrated devices (IDs) hybrid product architecture, design for additive manufacturing (DfAM), packaging of integrated structures, additive joining, additive coating, material grading, selective liquid-phase sintering (SLPS)

## **1. Introduction**

Additive processes have developed from rapid prototyping purposes for nonfunctional demonstrators, via rapid manufacturing of specific single parts, to a regular manufacturing technology for load-bearing parts on industrial scale. However, additive parts manufacturing (AM) application still focuses mainly on specific parts that are complex, require customization, often with short lead time, and low production volume. Although existing processes are continuously improved and new ones created, it is unlikely that additive processes will overcome their own limitations to actually substitute conventional processes. In order to meet typical requirements of—or even transform—industrial reality from the perspective of a complete product, AM should not be conceived as an alternative to conventional technology, but an interoperable contribution as a specific link in a process chain to realize hybrid products.

This chapter outlines critical factors for process and product integration and expands the current predominant perspective of additive parts manufacturing (AM) to a more comprehensive concept, furtherly referred to as *Additive Technologies (AX)* as a prerequisite to realize an *Integrated Device (ID)*. It identifies factors and approaches to break barriers:


4.for the wider industrial adoption and capitalization of AX.

First, the strengths and weaknesses of additive processes and approaches to regard them in product design are recapitulated. Based on a frame of reference, possible dimensions of integrations are introduced to derive approaches for integration. The status for each approach is summarized and illustrated by own examples, and the need for further research on one promising approach is defined.

## **2. AM processes: light, shadow, and the exploitable potential between**

The broad range of established additive processes of today offers significant economic and technologic advantages over traditional formative or subtractive parts manufacturing. Placing material selectively in space allows directly building up complex shapes, with hollow sections, undercuts, delicate, or inner structures without the costs and building time of part-specific tooling and without the design constraints of conventional processes, e.g., for tool accessibility, material flow, demolding, or machining forces.

On the other hand, additive processes imply constraints of their own, affecting their fitness to fulfill requirements for the growing industrial interest. As additive processes are highly diverse, constraints can vary significantly. For industrial manufacturing of mainly load-bearing industrial metal parts, the main focus here will be processes from the categories powder bed fusion (PBF) and directed energy deposition (DED).

Process constraints include:

• Current process principles require that the building space to be enclosed in the machine.

*Perspective Chapter: Breaking the Barriers – Additive Technologies (AX) for Integrated Process... DOI: http://dx.doi.org/10.5772/intechopen.104891*


These influences affect key target variables, such as


Furthermore, PBF processes constitutively require a powder bed of costly raw material to fill the working space—even if only an insignificant fraction of it is actually processed into smaller, delicate, or hollow structures. For single piece or small batch production, the effectively used powder may be a fraction of the excess. If subsequent parts or runs require powder of identical material and grade, the excess powder may be reconditioned (usually by sieving), but efficiency is limited by its coagulation, material alteration, and other contamination (depending on process parameters such as thermal energy applied in the process): Typical is an equal mix of fresh powder, powder from the reservoir, and from the actual bed (distant from the volume affected by the LASER).

DED processes do not require a powder bed, but require a minimum continuous stream of comparably flowable, coarse powder, accelerated by a carrier and shielding gas. This results in comparably high powder delivery rates that have to be matched with a high application heat (LASER) energy. Overall, benefits from higher buildup rates at concession of less resolution and thicker walls result in a "near-net shape" that requires substantial postprocessing. In general, the coarser surface quality may not fulfill functional requirements and may lead to a reduced fatigue life of parts [1].

Overall, AM (as a process group, and each process for itself) has a specific profile of strengths and weaknesses—ideal for some purposes and adverse for others. While the rise of AM may be a disruptive landmark of manufacturing technology, AM does not supersede the range of manufacturing processes but complement them. Many technical applications will require AM to concur rather than to compete with other processes—deploying each process where it is superior and yielding to others where it is inferior. Consequently, a key to capitalize on additive technology will be to expand the focus from process development toward process integration for hybrid architectures of products, assemblies, parts, and features.

## **3. Integration by design: design for additive manufacturing (DfAM)**

The connection between product design and production technology is heavily interdependent: Product design leads its implementation in production—but it has to proactively regard opportunities, limitations, and costs for processes downstream in the value creation chain. Consequently, design rule sets have been developed to design for subsequent processes from early on, ideally already in conceptual phases—allowing for a foresighted, holistic product design. Initial design rules were implemented for manufacturing as *Design for Manufacturing (DfM*), then for assembly (*DfA*), and then for more aspects (such as transport, testing, service, sustainability), converging to the discipline *Design for X (DfX)*, sometimes paraphrased *Design for eXcellence*. As a new technology, the novel opportunities and limitations as described above require specific design rules and approaches. This is represented in the new research field of *Design for Additive Manufacturing (DfAM)*.

On the one hand, the novel possibilities from selectively placing material spawned visionary approaches and methods, such as topology optimization, lattice or cell-based structures, or multi-material design. While these attracted much attention, there was (and still is) also the need to systemize the specific limitations for reliably designing parts for AM processes and their typical subsequent processes in the more fundamental meaning of DfX. This concerns more the potential and restrictions of specific processes, and how they can be considered to generate parts workably, effectively, and economically. In the past, this has been subject to practical experience and therefore a secret of trade of specialized AM service companies. With regular availability and maturity of processes and machines, publications have increasingly covered systematic Df(A)M guidelines for process limits, achievable feature properties (e.g., dimensions and tolerances of walls, gaps, holes, overlap angle, etc.), and workable and effective buildup strategies (e.g., how to plan part orientation, support structures, etc.). This chapter on integration will focus these more fundamental aspects of DfAM.

Collections of process- and buildup-specific design rules are specified in guidelines such as the German VDI guideline 3405 [2]. A compilation of design rules of various categories, based on the analysis of a complex enclosure for a satellite-based X-ray spectrometer measurement system, was presented in [3].

## **4. Dimensions of integration: a frame of reference**

In order to derive integrative approaches integration, a systematic frame of reference will be used (**Figure 1**).

The *dimension of process sequence* extends the scope along the process chain, opening up the potential for the *integration of precedent and subsequent processes*. There is a growing awareness for *downstream* processes (e.g., finishing, treatment, handling, testing, assembly, and transport).

As the current focus on additive processes is mostly limited to a concept of exclusive generation of parts from scratch (with all downsides), there is no substantial coverage of interoperation with *upstream* conventional processes.

The *dimension of product structure* extends from the AM part up and down the product hierarchy, creating touchpoints for the *integration of subordinate and superordinate product elements*. Due to the drawbacks of AM technology, AM parts had to be considered early on, either as semifinished goods for conventionally finished or treated net shape parts or as components in conventionally joined for *higher-level* assemblies and products (with other conventionally or AM fabricated other parts).

*Perspective Chapter: Breaking the Barriers – Additive Technologies (AX) for Integrated Process... DOI: http://dx.doi.org/10.5772/intechopen.104891*

#### **Figure 1.**

*The origin represents the currently predominant focus on the additive processing and on the additive part. It bears the potential for integration of concurrent hybrid processing (alternating, or maybe simultaneously).*

Corresponding with upstream processes, applying AM processes to *lower-level* prefabricated elements (such as semifinished goods, parts, assemblies, or even products) is factually unaccounted for even in DfAM as of today.

Overall, integration of subordinate components, pre-fabricated, precedent to AM processing, would open up potentials currently hardly covered even in research. However, this would require:


From the frame of reference, the following points of process and product integration can be derived:


4.*Facilitate hybrid product architectures* to methodologically regard the whole process chain and product architecture together from the start.

The following subsections outline the status and potential for each of these aspects.

## **5. Facilitate external postprocessing of additive structures**

For early single-piece rapid prototypes, manual postprocessing such as cutting clean, joining, filling, and painting has been a frequent implicit necessity. Most industrial-scale additive metal parts today still require postprocessing to achieve the required geometric and surface qualities [4]. Therefore, DfAM has increasingly adopted design rules in order to systematically plan for typical postprocesses, such as:


Further successive processes may include testing, transportation, utilization, maintenance, or recycling. However, although these processes need to be regarded


*Perspective Chapter: Breaking the Barriers – Additive Technologies (AX) for Integrated Process... DOI: http://dx.doi.org/10.5772/intechopen.104891*


*\* In analogy to typical guidelines for DfM for casting.*

#### **Table 1.**

*Excerpt of design rules for post-processing of additive parts (based on [3]).*

systematically, their systematic consideration is part of the regular established design literature design engineering, specifically *Design for X (DfX),* and not specifically covered here. An exception may be the testing of AM-specific characteristics such as material properties (e.g., relative density) that require dedicated design considerations.

Lee et al. [1] concludes that based on the existing ISO/ASTM standards, only less than 1% ASTM standards related to the surface finishing of metal AM components and proposes vast R&D opportunity in these areas.

**Table 1** shows an excerpt, of design rules specific to postprocessing of additive parts, based on [3].

## **6. Facilitate hybrid processing**

Hybrid AM has been a focus of investigation increasingly over the past decade [4]. Hybrid manufacturing systems compensate the limits of AM processes by alternating or concurrent application of conventional processing to combine advantages of both worlds: high material utilization and complex and internal shapes (AM) combined with high productivity, feature accuracy, and surface quality of conventional machining.

Two approaches can be distinguished:

In a *multi-setup*, additive and nonadditive processes are combined across multiple, separate machines for conventional processing between additive buildup steps. This essentially logistic approach to integration allows to process differently progressed parts in parallel on separate machines (e.g., one part is machined while the next part is still being built up).

However, the main focus of hybrid (additive) manufacturing is a *single setup* in one hybrid machine that combines technologically


Compared with an exclusively additive process or a hybrid multi-setup, advantages of hybrid single setup are as follows:


• Since all production steps are automated on one machine via CAD/CAM interface, the probability of human errors is reduced.

On the other hand, limitations and challenges have to be considered, such as:


## **7. Facilitate additive processing of externally pre-fabricated elements**

Some problems of AM can be compensated by subsequent or hybrid postprocessing. Other problems remain or originate from adverse effects between additive structures and conventional processing, in the first place. These specific problems can be attributed mainly to the predominant traditional process order "generate or build up material, then subtract from it, and assemble." In consequence, they can be addressed by reversing or stacking this order to "finish material, then add material to it."

This essentially means that otherwise finished parts could be extended by, or be incorporated in, hybrid or monolithic buildups, furtherly referred to as *Integrated Devices (IDs)*.

## **7.1 Integrated devices (IDs): a new potential for the macromechanical world**

In the 1950s, a disruptive invention revolutionized electronic circuitry and their production: Traditionally, discrete electric and electronic components were produced separately, and afterward wired point-to-point, or soldered to a circuit board. Based on preceding developments of a planar process with structured layers on a substrate, the integrated circuit (IC) was developed, as the hybrid IC (incorporating different functional elements into a single buildup, patented by Jack Kilby), and as the monolithic IC (a completely integral buildup of functional elements on one substrate, patented by Robert Noyce). ICs reduced cost, increased processing performance, and paved the road for today's world of ubiquitous microelectronic in industrial and end user products. Especially the hybrid IC with additional packaging processes also facilitated the production of microelectromechanical systems (MEMS).

By applying the same principles to the macromechanical world, the concept of *Integrated devices (IDs)* can be postulated: Rather than fabricating separate components and then assembling them component-to-component, a unit (part, assembly, or product) could be built up by structured layers in an additive process, incorporating premanufactured conventional or additive components, i.e., machined, purchased, or standard parts, complete assemblies up to full products.

IDs could open up completely new application potential for the group of additive processes: Rather than deciding *whether or when* a part should be processed conventionally *or* additively, it could be distinguished *where* (*which features)* to process conventionally *and* where to build up additively. This would allow to tailor the process chain for a given unit to make use of the advantages of additive technology to where it is superior and to avoid its disadvantages where it is not. Substructures too precise, too massive, or too cost-inefficient for AM could be created externally and then integrated into an additive buildup—even where postprocessing or joining is impossible or uneconomic, due to geometry, accessibility, or structural stability and stiffness to withstand machining or clamping forces with typically complex, delicate parts.

## **7.2 Additive technology (AX) for IDs**

In order to produce IDs that incorporate or package nonadditive features, a processing technology will require not only the primary shaping of structures, but also their extension and alteration (i.e., buildup, joining, and conditioning).

There are examples of packaging-like processes for limited purposes in generative manufacturing, e.g., plastic injection molding around metal inserts. But it is the group of additive processes that bears a striking resemblance to the packaging of ICs and MEMS, by additive buildup of functional units in structured layers.

The current concept of additive manufacturing is mostly focused on (as the designation suggests) parts manufacturing. Additive processes are widely conceived as a subtype or alternative to generative processes. For example, the current (2020) revision draft of the German industry standard DIN 8580 "Manufacturing processes - Terms and definitions, division" [5] attributes group "1.10 Primary shaping by additive manufacturing" clearly to the main group "1. Primary shaping." Consequently, parts integration is implicitly mostly limited to monolithic IDs, where external components and their assembly are substituted by integral AM parts. Also, as-built assemblies (e.g., plastic roller bearings for nonproductive use) from one continuous AM process have demonstrated the fundamental feasibility of monolithic IDs.

However, hybrid approaches to IDs, combining the benefits of additive and conventional processing (as analyzed in Section 2 and 4), are currently not focus of discussion, published research, industrial application, or standardization. This approach would require packaging-like applications of additive processes, such as additive joining and assembly, additive finishing, or additive surface treatment (e.g., melting alloy components into the surface). For distinctiveness of further discussion, the broader concept of *Additive Technology (AX)* shall be used to refer to the technology of applying *additive processes (A)* for *diverse purpose (X)* (not only parts manufacturing).

**Table 2** shows a set of examples where design problems can be solved (or solved better) with an AX approach where a pure AM or AM with postprocessing approach is problematic.

Instead of screwing precision-turned elements to complex part with machined threads and joining surfaces, a bolt or nut could be integrated into the additive counterpart for assembly—or the additive section could simply be built up directly around the conventional component without the need for additional joining. Instead of drilling holes and cutting threads, standard purchased nuts could be embedded in a part. Instead of building up massive structures with delicate extensions layer-by-layer, a machined massive core could be extended by additive mountings or surface structures.

*Perspective Chapter: Breaking the Barriers – Additive Technologies (AX) for Integrated Process... DOI: http://dx.doi.org/10.5772/intechopen.104891*


**Table 2.**

*Examples for benefits of the AX approach over AM.*

## **7.3 Developing processes for AX**

Established additive processes were developed mainly for parts manufacturing. The extended applications in AX require additive processes that fulfill a different requirements profile, allowing


Typical PBF or DED processes do not fulfill this profile:

PBF processes can create net shapes of reasonable as-built quality. But they usually do not allow parts to protrude from the powder bed because they would collide with the doctor knife that dresses each layer. The powder bed allows access only from the top, follows a Cartesian working principle with an invariable buildup direction. As the powder is provided as a filled bed, switching to a different material takes a lot of effort. However, the thermal influence on the existing buildup is comparably small.

DED processes, on the other hand, share the working principle with LASER cladding where material is applied to existing parts (e.g., for repair) while it is liquified with a direct energy source (usually, LASER, electron beam, or wire arc). Using a 5-axis-kinematic, material could even be applied from the sides. By using different heads or powder feeds, it is basically possible to alternate between or combine different materials. However, DED processes require a continuous delivery of flowable, coarser powder and carrier (shielding) gas, with adequately high application of energy—resulting in high buildup rates, creating comparatively thick and bulging layers and rough tolerances (depending on the process, up to several millimeters). Results from DED processes are usually designated as "near-net-shape" and require substantial postprocessing.

At the *Hochschule für Technik und Wirtschaft Berlin*—University of Applied Sciences (HTW Berlin), research about AX processes has resulted in two approaches, which are currently in development [6]:

Based on regular PBF processes, workflow and control can be modified to incorporate pre-fabricated inserts with a level top surface. The modified process is described in **Table 3**.

Furtherly, the novel additive process principle "Selective Melt Dispersion (SMD)" was developed in order to fill the niche between PBF and DED. Like DED, it allows parts to protrude out of the buildup and to vary buildup direction, without a voluminous homogeneous powder bed. But the working principle was developed for finer resolutions and tolerances of the as-built net shape: Other than in the regular powder-based DED processes, the powder is not propelled by a shielding gas stream in a mix nozzle and also not heated directly in-delivery. Instead, the directed energy source selectively melts a surface spot of the already built material. Unheated solid metal powder is dispersed onto this melt pool with a separate delivery system, e.g., by a newly developed vibration-operated dropdelivery dispenser. The powder adheres to the liquid surface and is embedded as the working progresses along its continuous track and the pool of metal solidifies as the new layer. This layer is melted again fully to receive the next layer (or for finishing as the final layer).

Separating the powder delivery from the shielding gas stream and the directed energy source allows finer control of each factor, resulting in:

• ability to process fine powder grades, because no mixing nozzle is used that could be clogged with less flowable powder,

*Perspective Chapter: Breaking the Barriers – Additive Technologies (AX) for Integrated Process... DOI: http://dx.doi.org/10.5772/intechopen.104891*


### **Table 3.**

*Modified PBF process for pre-fabricated inserts (based on [6]).*


## **8. Facilitate hybrid product architectures: DfAM methodologies**

Introduction of AM to industrial production often fails where regular parts are simply converted to AM parts without a full redesign, starting on product level. This can be attributed to the fact that conventional designs often do not make effective use of the potential of AM, but are substantially affected by its constraints. For workable results, an AM part, its environment, and the complete product should ideally be redesigned or specifically developed.

However, DfAM expertise is still not amply available in many regular product engineering and design departments, and a relatively new part in regular engineering education programs—which is a substantial barrier for a more comprehensive application of AM on industrial scale.

Consequently, the interest of DfAM has expanded in recent years to more integrative approaches, such as the design for postprocessing of AM parts, and product development and design methodologies with specific regard to AM parts as part of the overall product development process [7], more detailed in the thesis [8] (in German).

But overall, AX and DfAM need to be incorporated strategically into regular product and process development departments of branches where AX can make a difference. For regular AM, there are vocational trainings as AM specialist engineers (including modules about design rules and principled for product designers), e.g., since July 2017 by the Association of German Engineers VDI [9]. Also, AM is becoming a regular component of engineering education programs.

## **9. Conclusions**

AM is a mature technology for industrial application. Like all other manufacturing technologies, it has strengths and weaknesses that make it an unlikely "do-all" substitute for conventional processing. Instead, AM is most effectively applied as for specific elements or features, in combination with features from other processes—as one interoperable contribution to an integrated process chain for a complete product. Integration can involve subsequent processes and assemblies, concurrent hybrid processing, and pre-fabricated elements from precedent processes.

Systematic consideration of postprocessing in AM is currently being focused in research, literature, and application. However, it has to be implemented in regular development workflows, requiring systematic competence development, in development staff training and engineering education.

First machines for concurrent hybrid processing are already in the market, research is ongoing. Again, awareness of and competence for the technology and their benefits and constraints have to be systematically implemented in development workflows and the respective staff.

However, the additive working principle bears the potential of a disruptive innovation for micromechanical products: Following the principle of Integrated Circuits (ICs) in microelectronics and MEMS, additive processes can be used to build and package monolithic or hybrid products as Integrated Devices (IDs). In order to package pre-fabricated elements into a hybrid product, the current scope of additive processing would have to be extended from primarily Additive Manufacturing (AM) of parts to novel purposes such as additive joining, additive finishing, and additive treatment. This extended concept of Additive Technology (AX) requires the development of new processes that allow additive processing of pre-fabricated elements.

*Perspective Chapter: Breaking the Barriers – Additive Technologies (AX) for Integrated Process... DOI: http://dx.doi.org/10.5772/intechopen.104891*

Research and development will have to acknowledge IDs by AX as a significant future prospect, prioritize efforts to develop processes suited for AX, and systematically implement them in product development workflows. Only then, additive and conventional processes can be combined over the full integrated process chain, and additive and conventional features can be planned on all levels of the integrated product architecture—resulting in a more consequent deployment and capitalization of additive processes.

## **Acknowledgements**

The patent application and content for [6] were developed under participation of David Grüning, M.Sc., before graduating from HTW Berlin, with internal research funding from internal research funding from the HTW Berlin.

## **Conflict of interest**

The authors declare no conflict of interest.

## **Author details**

Matthias Dahlmeyer\* and Sebastian Noller Hochschule für Technik und Wirtschaft (HTW) Berlin, University of Applied Sciences, Berlin, Germany

\*Address all correspondence to: matthias.dahlmeyer@HTW-Berlin.de

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## **Chapter 6**
