How to make design for AM your step to success

Making yesterday's products with tomorrow's technology is not a smart strategy. Additive manufacturing (AM) is an incredibly flexible technology, but that doesn't mean that it's wise to use it to make just any old design. Thoughtful design for AM (DfAM) is critical to success. DfAM helps us to extract the maximum benefit of additive technologies, whilst also minimising its associated costs. Profitable AM applications combine high product performance with cost-effective production and efficient post-processing. If we want to make a successful AM business, great DfAM is a must.

In this article, we will see how AM products can be designed to out-perform their conventional counterparts. Giving ourselves the maximum design freedom by looking beyond the boundaries of the component, we can unlock further opportunities to innovate. We will explore how efficient, light-weight design creates a disruptive, virtuous circle to deliver a successful business case. Finally we will look at some of the important practical considerations to ensure that our innovative designs are efficient to produce.

Why do we need DfAM?

As we transition from 3D printing and rapid prototyping to industrial AM, our priorities change. Series production is much more demanding than model-making. Instead of crafting one-off 'shapes' in a short lead time, now we are concerned more with maximising product performance, ensuring consistent quality and minimising manufacturing cost. Effectiveness must be combined with efficiency. This only happens by design.

So, DfAM is an essential contributor to a successful AM application. Our goals with design for AM are threefold. AM products must:

1. Provide higher performance than conventional components – this creates the value driver for our AM business
2. Be built cost-effectively in series production – our build process must be efficient in its use of capital and materials
3. Require minimal post-processing & quality assurance – it’s no use saving cost on the build if we rack it up again in finishing and testing

We must get all of these aspects right if we are to produce a profitable AM application.

Levels of AM deployment

Companies can deploy AM technologies in many different ways, illustrated by this staircase.?Many start by making prototypes and tooling, using AM to speed up new product development cycles.?In regulated sectors, the next step is often to use AM to make legacy parts, replacing out-dated processes with a simpler, digital build technique, reducing lead-times and inventories.?The higher staircase levels make use of more of the unique capabilities of AM to handle complexity.?Part consolidation, for instance, helps with light-weighting, streamlines production and eliminates troublesome joints.?The top step is where designers really exploit AM to deliver performance that simply couldn’t be provided by conventional products.

As we move up through these levels, we create increasingly valuable products.?But the commitment in terms of design effort, product and process certification, and the knowledge required to master the fine details of AM techniques, also increases.?You get out from life what you put in, and so it is not surprising that the best business cases tend to be found at the upper levels.

Business impact of industrial AM

Our AM business case is driven by two sorts of benefit: production benefits that are accrued whilst we are making the product, and product benefits that are reaped once that product is in use. It is the larger product benefits that underpin the demand side of the AM growth equation. DfAM is the key to unlock this profit potential.

Innovative AM product design

Let’s look at some ways in which innovative product design can be unleashed by the freedom that AM gives us.

Reduced weight

Light-weighting is a key driver for AM deployment in fields such as motor-sport, aerospace and automotive.?Additive allows us to place metal just where we need it and to omit it where we don’t, supporting the production of more ‘organic’ shapes that can be more efficient than traditional formed or machined components.?Parts can also be hollow or filled with low-density lattice structures, enabling structural parts to provide the required strength and stiffness whilst using less material.?As we will see, light-weighting also benefits part costs.

Strong material properties are critical to light-weight product design. We should choose alloys with a high specific strength and we must ensure that the components are free from defects to ensure that we secure the full potential performance of the material. Consistency is key, as this allows us to reduce the design safety factor, so that we are not carrying extra weight just in case the part is weaker than we expect.

Reduced space claim

The complexity of AM parts can also save space.?Consolidating multiple parts into one removes joints and fixings, freeing up space around the part for other more useful features.?Such space savings often lead to weight savings elsewhere in the system in a virtuous circle.

Increased heat transfer

Intricate channels with thin wall sections and high surface areas can also bring fluids closer together, enabling greater heat transfer between them.?Heat exchangers are a great application for AM, which not only raises thermal efficiency but also enables neat integration with surrounding pipe-work. Conformal cooling of mould tools is another application where AM enables a more efficient design.

Efficient fluid flow

Fluid flow is a critical function of many industrial and transport applications.?Hydraulic manifolds and actuators can be made more efficient by optimising fluid channels to minimise pressure drops.?Complex gas manifolds with ideal profiles and intersections optimise engine efficiency.

Effective joining

Joining our AM component to the rest of the system in which it must work also offers new possibilities.?The fine detail that AM can provide can be used to enlarge the surface area at the interface, enabling a stronger bond.?Joining of metal parts to composite tubes, for instance, can be enhanced by ‘double lap’ joints in which the carbon fibre tube is glued into a conforming inner- and outer-sleeve to produce an incredibly strong bond.?In medical applications, by contrast, the bonding is done by the human body, where lattice coatings on implants promote bone in-growth for superior osseo-integration.

Customisation

Medical implants are perhaps the best example of where customisation can make an impact. No two patients are the same, so why should their implants be the same? In orthopaedics,?patient-specific implants are designed to fit the unique anatomy of each person, so that healthy bone need not be ground back to suit a standard implant.?This leads to faster surgery and better patient outcomes.

Expand your design space

Another way to maximise the impact of AM is to think beyond the boundaries of the component. The more freedom that we give ourselves to change aspects of the system within which an AM part must function, the greater the benefit that we can generate. We should seek to maximise our 'design space'.

The examples shown here are possible designs for a hydraulic manifold, comprising a simple circuit consisting of two check valves, a solenoid valve and their associated outlet ports (male insert type). For more details, see DfAM strategy - create 'design space' for maximum AM impact.

Direct part replacement

At one extreme, we may have no freedom to change the part design at all - i.e. AM?is being used simply for direct part replacement.?The AM part must be a form-, fit- and functional-replacement for the existing part, with no changes to its shape or to its interfaces with other elements of the system.?The only change is the process - i.e. a switch to AM,?which can production benefits, but the build time is likely to be very long and so part costs will not be attractive.

Component-level adaptation?

If our design space expands to?the component level, then we can make changes to the form of the component to take account of AM process capabilities and limitations.?Here the?AM part is a?fit- and functional-replacement for the current part, but we have freedom to change both the process and the part form.?In this case we can?adapt for AM,?often delivering significant weight, cost and performance advantages.

System-level 'clean sheet' design

If our design space extends beyond the component and out to a system or sub-system level, then we can truly?design for AM?(DfAM).?We?have the opportunity to create a 'clean sheet' design that fully exploits the capabilities of AM.??Now even the component's function may be open for change as we consolidate neighbouring components, as well as its fit,?form and the?process used to make it.?

By influencing design decisions at a system level, we can optimise the performance of the product, not just the part. Ideally, we should be looking one, or preferably two layers higher in the bill of materials, to find opportunities for consolidation and improvement. In this way, we maximise the beneficial impact of AM on product performance, whilst also minimising product costs.

Lightweight AM parts are cheaper

So, AM product design can be transformative.?It is also vital if we are to produce AM parts cost-effectively.?As we will see, light-weighting and efficient AM builds go hand in hand.

Subtractive and additive process economics

The economics of subtractive manufacturing (e.g. machining) and AM are very different.?In subtractive manufacturing, low-weight components are often expensive, since the manufacturer must go to extreme lengths to remove any excess material, or resort to exotic alloys to hit a weight target.?Heavier parts will be cheaper to produce from a processing cost standpoint, but the material cost starts to become more significant. The minimum overall cost is found when we find the best trade-off between processing complexity and material costs. A typical cost-v-mass curve is shown below. For more details, see How steel can be as light as titanium - and why it matters.

The cost-v-mass curve for additive manufacturing is quite different.?In powder-bed fusion processes, the cost of the material in the part and the processing costs are both directly related to part mass.

There is a virtuous circle in AM:

Lower part mass = lower AM part costs

Ideal AM product positioning

We can now see how important DfAM is – it is the lever that influences the economics of the AM process.?Get this wrong, and we have an expensive alternative to a conventional product that no one will want.?Get this right, and we have a ‘killer application’ for AM that can be truly disruptive.

Many industrial products are used in multiple market sectors - they perform the same basic function and there will generally be common requirements such as performance and reliability that all sectors expect. Where market sectors may differ, however, is in the value that they assign to product weight and size. For some customers, the product must have the lightest possible weight and make the smallest possible space claim. For others, space and weight are not at a premium, and cost is the prime driver. In a market served by products made using conventional manufacturing processes, these customers will select different product variants from different positions on the cost-v-mass curve, as shown here.

The disruptive impact of AM on a product market depends on to what extent we can make AM products that meet the needs of each these various market sectors.?Whether we can do this depends on the relative position of these two cost-v-mass curves and how far down the AM curve we can move through good product design.

With advanced DfAM, where we select a cost-effective material, use a productive AM machine and minimise post-processing, it might be possible to move to a point where our ultra-lightweight product matches the minimum cost conventional product.

The impact of this could be profound. Instead of a wide range of different products optimised for each market sector, we just have one. Product configuration and sales processes can be simplified, inventories can be reduced, servicing can be streamlined.

Buildability considerations

We have seen how, if we take full advantage of the freedoms that AM gives us, we can create high-performance, efficient and disruptive designs. But to make a compelling business case, they must also be straightforward to build, finish and certify. With additive, it is essential that designers and manufacturing engineers work closely together. There are several factors that must be considered at the design stage to make life easier for us here.

Orientation and supports

Powder bed fusion processes deploy supports in overhanging regions to make them buildable. Supports conduct heat away from thermally isolated regions of the build, and also anchor vulnerable structures to the build plate to resist deflection and stress. Supports represent waste in terms of additional material, build time and post-processing costs, and so every effort should be made to minimise their use in production builds. Reliance on supports is a sign of poor design for AM.

The key is to design our build at the same time as thinking about the design of our part. Consider the orientation in which the part will be built, to enable the part to carry itself using the minimum of material. Aim for self-supporting designs, such as those shown here, integrating supporting structures into the part itself and putting them to good use. Where supports cannot be avoided, then these should be designed in CAD rather than added as an afterthought in build processing software. For more details, see Can you build AM parts without supports?

This thinking also applies when we are using advanced design techniques such as topology optimisation. Here the secret to buildability is to ensure that the fixed design space - shown in green in the left hand image below - is itself self-supporting. This makes for far fewer adjustments to the resulting optimised design. For more details, see Is topological optimisation really optimal?

Stackability

With smaller parts, we want to build as many as we can in a single set-up to maximise machine utilisation and minimise part costs. With careful thought, it is often possible to stack parts on top of one another with simple 'snap-off' connections between them to create an efficient production build. This automotive headlight heat-sink build, developed by Betatype, is a great example.

Residual stress

Residual stress is a natural consequence of the rapid heating and cooling inherent to the laser powder-bed fusion process. Shear forces build up as each new layer is added, which can lead to part distortion and even fracture.

By selecting an appropriate scan strategy and using techniques such as elevating the build temperature, we can reduce the accumulation of residual stresses, but generally it will not be possible to avoid them altogether. These stresses may lead us to build parts that are not quite the right shape. In these instances, we may need to mitigate this distortion to produce conforming parts. For more details, see Want to build accurate AM parts? No stress!

Modern design tools and simulation techniques can be deployed to evaluate the likely stress and distortion in a proposed build. Anticipated distortion can be compensated by applying a mirror image of the error to the part geometry, so that the counter-distorted component 'pulls itself straight'.

Finish machining and inspection

Without sufficient up-front thought, we can face very real challenges with post processing. Post-processing is often needed to produce tight tolerance features for interfacing with other parts.?Light-weighting often has the effect of reducing the stiffness of our AM parts, which can mean that they do not stand up well to the machining process.?Their complex form also makes them hard to grip securely without causing damage.?Finally, it is common to produce the datum features on additive parts after the build itself, and so setting up components for finishing can be tricky.

Work-holding can be a particular challenge.?In the case of this microwave guide, we need to machine the end flanges to precise tolerances, but clamping the part near to the flanges using conventional fixtures is difficult due to its curved shape.?The part’s lack of stiffness makes it prone to tool chatter, whilst deflections under cutting loads affect the feature precision.?A solution here is to use AM to make plastic jaws that encapsulate the part such so that it is well supported during the metal cutting process, enabling it to stand up to the loads that its will experience.

Another key consideration is part set-up.?Since we have no precise datums on the part, we have to find the good part within the shape that we have produced, so that we can clean it up with a machining operation.?Metrology is essential here.?We can use probing on our 5-axis machine tool or on a robot-loaded gauge to establish the material condition of the built part in numerous locations, performing an iterative best fitting operation to find the best alignment. For more details, see You can build it, but can you finish it?

Summary

AM success is driven by design. Innovative AM products take full advantage of additive’s unique capabilities to perform better than was previously possible.?Product performance creates that value on which AM business cases rest.

We can maximise the impact of AM design by designing at a sub-system or system level, thinking beyond the boundaries of our component to eliminate waste, consolidate parts and simplify manufacturing. We should give ourselves the maximum 'design space' in which to innovate.

Good design is also a factor in the cost side of the equation.?A virtuous circle exists in AM in which a lighter part is also cheaper.?As AM technology advances and part costs fall, this provides a unique opportunity for market disruption.?Innovative firms will use AM to undercut conventional competitors and introduce new products and services.

Designers must also take account of the capabilities and limitations of the AM technology that they select.?Whilst these are changing over time, they must be built into design thinking – it’s not sufficient just to design for function and think about buildability later.

Companies have a choice to make about the type of competitive play that they want to make with additive.?Those companies that take additive most seriously - for whom AM is a business strategy - have their product designers fully engaged in designing products specifically for AM.?By contrast, those firms that are asking manufacturing engineers to adapt unsuitable designs are acting tactically rather than strategically.?Businesses that adopt a true 'design for AM' strategy will reap the greatest competitive rewards.

Next steps

Visit?www.renishaw.com/amguide?for more education resources and to access downloadable versions of LinkedIn articles by Renishaw authors.

Readers may also find the following articles useful:

• DfAM strategy - create 'design space' for maximum AM impact.
• How steel can be as light as titanium - and why it matters
• Can you build AM parts without supports?
• Is topological optimisation really optimal?
• Want to build accurate AM parts? No stress!
• You can build it, but can you finish it?