MEPCA - Design for Additive Manufacturing

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DESIGN FOR ADDITIVE MANUFACTURING

The role played by 3D Printing in the manufacturing sector continues to advance. I am old enough to remember when, under the label rapid prototyping, the technology involved the computer controlled cutting out of cardboard sheets to build layer-by-layer mock-ups of products. In its most common forms, what is now more widely referred to as additive manufacturing still works on the principle of building the end product in layers. But what the layers are made of and how they are formed has advanced significantly in the last 30 years.

The evolution in additive manufacturing has meant that, while it still plays an important role in design and prototyping, its applications in product manufacturing are expanding. This is partly due to the constant development of new materials able to offer end products with a growing range of properties, but it is also driven by cost reductions as the equipment manufacturing parts evolves.

This evolution is not unlike traditional printing. Not so long ago, if you wanted just a handful of brochures printed, the cost was prohibitive. You probably needed to print several hundred or even thousand to make it worthwhile. But now you can print single brochures, and order books which are printed, singularly, on demand. Indeed, you probably have a colour printer, capable of good quality results, a few feet away. And if you need to, you might be able to print a passable brochure on it. But you would, in all likelihood, go to a dedicated printer if you wanted more like 100 – or if you needed any special finishes.

In this context, additive manufacturing is similar, albeit some years behind 2D printing. Perfectly capable ‘desktop’ 3D printers are well within reach. And a growing number of manufacturers are using them beyond prototyping, with tooling being a common use case. But if it comes to using 3D printing for manufacturing, and there are a growing number of circumstances where it is the most cost-effective solution, then working with a dedicated additive manufacturing specialist is the way to go. Not only do they have equipment far more advanced and capable, like a traditional printer, but they also have a deep knowledge and extensive experience in delivering the best quality in the most cost-effective way.

In this special issue of MEPCA we have brought together a series on design for additive manufacturing from specialist 3DPRINTUK, which looks at many of the pitfalls in designing products for this form of production. And it demonstrates the advantages a depth of experience in additive manufacturing can bring.

In many applications, particularly those traditionally using injection moulding, additive manufacturing has become a viable short-run production method, with the definition of shortrun stretching all the time. So, now might just be the time to talk to an additive manufacturing specialist, to find out how it could work for you.

Chris Callander, Editor

@Mepcamagazine

Optimising outcomes with 3D printing: A historical perspective

In the first of a series of articles exploring design for additive manufacturing, Nick Allen, Managing Director of 3DPRINTUK, addresses the evolution of product design. He provides context in terms of the state of the design industry when 3D printing first emerged and how digital design and 3D printers have evolved alongside each other.

The history of 3D printing or additive manufacturing (AM) dates back almost 35 years, and as a technology set, it proved to be disruptive across many industrial sectors and continues to evolve and disrupt to this day.

Back at the beginning, what is now referred to as AM or industrial 3D printing began its journey as a technology universally referred to as rapid prototyping or RP. This was because it was viewed as a technology that singularly allowed design engineers and manufacturers to easily, quickly and cheaply produce physical prototypes of their new products and components.

It is also pertinent to remember that back in the 1980s, digital design was also still relatively new. Indeed, it was progress with 3D CAD that went some way to facilitating 3D printing itself. Product development – including design – is an iterative process, and getting a product from idea to manufacture involves a great many steps, often in a linear/circular way. This includes going through numerous iterations of a product to optimise it — factoring in market research feedback and manufacturability. Designing for the manufacturing process of choice has always been a thing.

When 3D printing really broke through as a means of rapid prototyping in the 1990s, it offered companies a viable and economically attractive way of producing multiple design iterations to optimise the final product without extending lead times and often shortening them. It is also vital to note that rapid prototyping and 3D printing – then and now –are used as umbrella terms for several different additive processes. There are seven additive manufacturing process types in total.

The first process was Stereolithography (SLA), a VAT polymerisation process that used resin materials, which resulted in the first

commercial 3D printing system – the SLA-1 –from 3D Systems Inc. This was closely followed by two more: the Selective Laser Sintering (SLS) process, originally developed at the University of Texas and commercially licensed by DTM Corp; and the Fused Deposition Modelling (FDM) process developed and commercialised by Stratasys Inc. SLS now falls under the generic process name of Powder Bed Fusion (PBF), while FDM comes under the Material Extrusion process name. The other four additive manufacturing processes that are now firmly established are Material Jetting, Binder Jetting, Directed Energy Deposition, and Sheet Lamination.

The major advantage that 3D printing offered for rapid prototyping, and the reason it took hold, is that it enabled a concurrent or simultaneous engineering approach that eliminated the existing linear/circular over-thewall silo culture of product development and drastically reduced design to market times and costs.

3D printed prototypes remain a universally

accepted and dominant application of the technology set today.

The thing to note here, though, is that 3D printing offered a way of improving the product development process – it did not affect the nature or methodology of the design itself. It essentially embedded itself originally as a useful tool for improving the development process (including improving the design through iterative feedback) for existing, traditional manufacturing processes.

Throughout the 90s, early adopters highlighted progression by including tooling managers in the product development process much earlier – sometimes just days into the product life-cycle rather than the traditional weeks or months it would usually take. As a result, they could provide valuable input that helped avoid costly mistakes and speed up time-to-market. Further evolution saw tools themselves become a key application of 3D printing — cue the moniker rapid tooling. This application area provided a highly cost-efficient way of producing tools

Komodo simulation – 3D printed helicopter control stick.

for low and medium volumes of products. Again, this is still a viable application of AM technologies today.

As time moved on – and really getting traction in the last ten years or so – 3D printing began to evolve from being a prototyping or tooling technology to a true production technology, highlighted in the terminology used to describe it today: Additive Manufacturing or industrial 3D printing.

With this shift, the ability for AM to continue its disruptive role was redoubled, as now the focus was on if and how the various AM processes, together with new and improved materials for AM, could truly replace or complement traditional manufacturing processes. The development of more robust, accurate, speedy, repeatable and cost-efficient machines, especially with the PBF process, has reinforced the importance of industrial 3D printing as a true production technology, and today opportunities exist for the intelligent and judicious use of it as a viable and competitive serial production solution.

However, this shift has also meant that design engineers who are developing products that will be produced with AM –or considering it – have had to alter their approach to design. As I mentioned before, designing for the manufacturing process has always been a thing, whether for injection moulding, casting, or CNC machining. The point here is that for Additive Manufacturing,

the design rules are a bit different; in fact, they kind of break the mould.

In the next part of this series, we will look at just how different design for additive manufacturing is from traditional design for manufacturing approaches, the opportunities

this brings in terms of product innovation and functionality, and the ability to optimise products in a way that reduces weight and material usage.

www.3dprint-uk.co.uk

Rapid tooling for Brushtec’s various brush designs.

The SLA 1 – the first commercial 3D printing system.

Optimising outcomes with 3D printing: Design for additive manufacturing

In part 1 of this series Nick Allen, Managing Director of 3DPRINTUK, provided a historical perspective of additive manufacturing/3D printing, centred around the evolution of the technology and its impact on the product development process. Here in part 2, Nick looks at how 3D printing has evolved to the point where it can be considered a serial production technology, how it has impacted the design process itself and considers the different design approaches required for 3D printing compared with traditional manufacturing processes.

As design engineers and manufacturers assess the possibilities that exist for the use of industrial 3D printing to replace or, more likely, integrate with traditional manufacturing processes, there needs to be a quantum shift in the way that they approach the entire design to manufacturing process.

Necessarily this begins with re-evaluating product design, and the subject of design for additive manufacturing (DfAM) has become a fertile area for discussion and debate. Indeed, DfAM is a key factor that can drive the uptake of additive manufacturing (AM) as a production technology insomuch as it can leverage the key advantages of 3D printing.

This issue centres around the fact that DfAM requires a very different approach compared with traditional design for manufacturing and assembly (DfM&A). The latter focuses on designing products so that manufacturing and assembly costs and difficulties are reduced, while DfAM aims to capitalise upon the unique capabilities of AM to design and optimise a product or component, thereby promoting innovation. Key here is the utilisation of the characteristics of AM to improve product functionality according to the capability of the AM process. This typically indicates that designers can tailor their designs to utilise the advantages of AM for complex geometries and light-weighting opportunities whilst taking the AM process limitations into consideration, to ensure the manufacturability of the product.

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 and bad designs, and understanding this is essential for successful outcomes. For many design engineers and manufacturers, however, this is a leap into the unknown, and it can be a barrier to adoption.

But the rewards are there to be reaped.

Design optimisation

Whether for a new or a redesigned product or component, design optimisation focuses on two key aspects:

• topology optimisation — stronger and lighter parts, and

• part consolidation — reducing assemblies from multiple components to fewer or even a single part.

Both of these aspects are unique to AM, and cannot easily or cost-effectively be achieved with traditional manufacturing processes.

Essentially, industrial 3D printing can produce components that are either impossible

or too difficult/expensive to achieve using injection moulding, such as components that are hollow in certain areas or products that require an internal lattice structure. This is possible because 3D printing is an additive process, whereby material is added layer by layer and material density can be altered in predetermined areas of the part. Thus, not only can some areas be hollow, but other critical areas can be reinforced. This means that 3D printing is a key facilitator when it comes to lightweighting with increased strength and functionality.

Topology optimisation is a methodology that uses software tools to optimise material distribution within a design. It is a powerful design technique that allows for the reduction of the weight of a product by removing material where it is not required, while maintaining, sometimes even increasing, the overall functional requirements of the part. This often results in complex geometries, something that only 3D printing as a

Complex part designed by Komodo Simulations.

manufacturing method can fulfil.

Part consolidation is another capability that the increased design freedom of 3D printing opens up by enabling the creation and production of complex internal geometries and complete complex products that incorporate the functionality of multiple components that cannot be made via conventional manufacturing technologies. While 3D printing processes are relatively agnostic to increased part complexity, it is important for design engineers and manufacturers to understand the limitations and capabilities of the particular AM process chosen for production, the system-level design intent, and the implications in terms of inspection, validation, and post-processing.

While it is generally accepted that part consolidation can improve structural performance compared to conventional multipiece assemblies, this may not always be the case. For example, 3D printed materials are directionally weakened, usually in the “build” direction, and this can compromise design intent and ultimate part functionality.

For manufacturers that are assessing the feasibility of the use of industrial 3D printing for manufacturing and production, there are various considerations that need to be addressed. Nobody is denying that it is a relatively steep learning curve when it comes to design and achieving optimal outcomes in respect of part functionality, cost savings, and time savings.

As a result, there are benefits for

manufacturers in forming strategic partnerships with service providers that have the breadth and depth of knowledge of 3D printing that allow them to achieve project success. 3DPRINTUK is extremely well-positioned in the 3D printing sector as a company with considerable expertise and experience to support clients in maximising the opportunities and avoiding the pitfalls for a wide range of 3D printing applications.

Some of our most recent case studies better illustrate this point:

• ecoSUB Robotics has benefitted from 3D printing through understanding Design for AM and the management of the 3D printing process to maximise efficiencies and therefore reduce costs per part. In addition, the company has benefitted from the ability to customise designs for individual clients enabled by the innate capability of 3D printing as a direct manufacturing process.

• Komodo Simulations have developed realistic helicopter control systems for home Flight Sim Pilot and Professional Flight Simulators. These control systems, which are traditionally manufactured in many different parts, can be printed as a single part, which eliminates assembly and significantly reduces production costs. In addition, 3D printing allows for hollowed-out internal parts and little to no limitation on the design of complex curved parts. The capability to produce high surface detail also means that textured grip surfaces can

be included in the design.

• DfAM provided Kongsberg with new opportunities too. According to the company: “By deciding to 3D print this pivotal part in a new design right from the word go, we were able to shrink the size while integrating features and functionality that are simply unavailable through other manufacturing methods.”

• For Brushtec, a world-class designer and manufacturer of innovative brushwear, 3D printing has unlocked a new level of innovation and enabled the company to design complex SLS parts without being restricted by the limitation of standard machining.

For design engineers, using AM enables them to look past the constraints around traditional DfM and DfA. In so doing, there is much greater design freedom in terms of complexity. Parts can be produced using 3D printing that are more ergonomic and incorporate multiple parts and features that would be impossible or prohibitively expensive to achieve via the fabrication of highly complex tooling required for injection moulding.

The opportunities are endless; however, there are caveats. Of course. 3D printing for production applications does have its own constraints. In part 3 of this series, we will consider these in more detail and highlight how to work around them to ensure success.

www.3dprint-uk.co.uk

Charles Duffy, Plexus

Optimising outcomes with 3D printing:

Avoiding the pitfalls

In the third part of our series exploring design for additive manufacturing, Nick Allen, Managing Director of 3DPRINTUK, shares some of the most common pitfalls which can be experienced when designing parts for 3D printing with SLS and MJF 3D printing processes and how to avoid them.

Different industrial 3D printing processes (see part 1, MEPCA April 2022) have different constraints that can affect designed parts in production. Some constraints are universal across the different processes; some are more specific to the type of process used.

At 3DPRINTUK, we specialise in the powder bed fusion (PBF) process, so this is where our expertise lies. To date, our expertise is specifically with polymer materials.

It is essential to understand the technology you are working with to maximise its potential as a production method. With this understanding, it is possible to design around the general limitations of additive manufacturing (AM) as well as the specific process constraints that could impact a product or part. As I have mentioned, design

for manufacture (DfM) is not a new concept; however, the rules for designing for additive manufacture (DfAM) require a different approach for design engineers.

While we are strong advocates of 3D printing and what it can achieve, the key to our success for and on behalf of our clients over more than ten years lies in fully understanding the limitations of the process too, and also in managing expectations.

Wall thickness

Wall thickness is a critical consideration for parts being designed for AM, both in terms of the part itself and any post-processing that may be required. For our service, we recommend a maximum wall thickness to prevent shrinkage deformation during cooling, while our minimum wall thickness is recommended to ensure parts withstand

our automated post-processing techniques without damage.

1 mm is our guaranteed minimum wall thickness for unfinished parts, but it is important to note exceptions where thickness should be increased. Exceptions include vulnerable unsupported structures, skeletal structures, weight-bearing walls, and specific functional/performance requirements.

• 1.5 mm is our guaranteed minimum thickness for parts that will be postprocessed using our polishing or shot peening options. Again, there are exceptions for vulnerable unsupported features, weight-bearing walls, and performance requirements.

• Our recommended maximum wall thickness is 5 mm. Anything beyond 10 mm may require the wall of the part to

be hollowed out to prevent shrinkage deformation, build failures and excessive print times.

In most cases, a 3 mm wall thickness provides a rigid part with little or no flex, while a 1.5 mm wall thickness results in some flex, depending on the length and/or structural support.

Surface details

The nature of PBF processes means that parts come off the printer with a granular surface, and sometimes layer lines can be visible. This is why post-processing options such as polishing or shot peening are often required to achieve a smoother injection moulding-like finish. With this in mind, if specific surface details are designed into a product or part, certain design rules are pertinent here.

Surface details can vary depending on which surface they have been applied to. The top side may include a raised burr of the laser around the outer edge, whilst the underside can appear more muted. Thus, for most parts, the best outcome is achieved by applying the text on the side skins for the best and most consistent visibility. Other recommendations are as follows:

• Minimum 0.5 mm wide and 0.5 mm deep. The same depth and width measurement results in superior clarity.

• Embossed text is safer than extruded text, as small details and edges can be vulnerable to break.

• Avoid embossing or extruding the surface details too far – try to keep them to around 0.5 mm – further out can result in damage in post-processing, and too deep can result in trapped powder.

Solid versus hollow parts

Hollowing can prevent the part from deforming and achieve higher levels of accuracy and reliability. However, the PBF processes work with powdered material, and hollow parts can result in trapped powder within the sintered shell. When designing a hollowed part, there are a few design options that avoid trapped powder, such as designing in powder escape holes, removing unwanted surfaces altogether (for example, bases), or including a locating lid.

We will automatically hollow larger parts before printing when above 15-20 mm on a case-by-case basis, so there is no need to do this yourself if you don’t want to. If you do want us to print it solid, then please let us know, and we can advise accordingly.

Interlocking/ mechanical parts

When designing interlocking or mechanical parts, including a clearance between parts is essential. This is because a gap between the sintered surfaces prevents them from fusing together and becoming a merged part. The tighter the tolerance, the more likely it is to fuse together. Some general design rules for this are:

• In nearly all cases, a clearance between moving parts must be at least 0.5 mm for us to guarantee a result.

• Contacting surfaces must be kept to 5 mm or below to guarantee them not fusing – longer shafts are likely to be too difficult or impossible to free up.

• Think about how the trapped powder between the surfaces can be removed. Sometimes a little force is enough to remove the powder, but designing powder removal holes may also be needed.

• Dense volumes can refract more heat and harden the powder between the surfaces. This means that the clearance may have to be increased if this is flagged as a concern or if the part does not function as intended.

Holes and channels

One of the key advantages of 3D printing is the ability to design and produce complex geometries without the need for expensive or ‘impossible’ tooling. However, designers still have to be mindful of the complexities they design into parts, especially when it comes to holes and channels running through the part. The nature of the PBF process comes into play here, specifically, the amount of heat that parts are exposed to during the build process. Thus, holes and channels with small diameters can result in fused powder within them. To prevent this, the recommendation is to design them greater than 3 mm. For long internal channels over 50 mm, the same problem applies, and it can be difficult to remove all of the powder; therefore, diameters greater than 5 mm are recommended for internal

channel features. The same rule applies to curved holes too.

Maximum Build Size

This might seem like an obvious one, but all 3D printers – whether desktop, mid-range or full production systems – have a maximum build size. You would be amazed how often this can be overlooked.

Across our fleet of industrial-scale 3D printers, our maximum build sizes are:

• For SLS PA12: 300 x 300 x 600 mm

• For MJF PA12: 350 x 255 x 350 mm.

• SLS Flexible TPU: 180 x 120 x 120 mm

Unlike other service providers, 3DPRINTUK will always position parts in a build to get the best possible outcome – no matter the original orientation of the file. The only exception to this is if a client locks the orientation while placing the order.

Summary

Designing for 3D printing is a really important facet of successful outcomes with the technology. Hopefully, this overview will provide a useful primer for anyone coming to the technology for the first time or some fresh insight for anyone working with the technologies on new products or parts. At 3DPRINTUK, our experienced build operators will always work with our clients to support the most successful outcomes for them.

www.3dprint-uk.co.uk