Design for Additive Manufacturing Essentials
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This document discusses design considerations for additive manufacturing (AM) with metals. It outlines that while AM provides design freedom, there are still capabilities and limitations to consider. Key factors for metal AM include minimum feature size due to laser spot diameter, avoiding large overhangs and interior holes that require supports, minimizing supports through feature shape and part orientation, and preventing part distortion from residual stress. The document presents a case study comparing a conventional hydraulic manifold design to designs adapted and purposefully designed for AM, showing increased mass savings as the design leverages more AM capabilities. True design for AM allows for an extremely efficient design that consolidates parts and is self-supporting. Understanding AM characteristics is important for successful design.
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Design for Additive Manufacturing Essentials
- 1. Design for Additive Manufacturing (DfAM) Essentials with Metals
- 2. So I’ve got complete design freedom, right ? Not quite! Like any manufacturing process, AM technologies have their capabilities and their limitations Design for AM (DfAM) considerations for laser melted metal parts include: • feature size • surface finish • overhanging features • minimizing supports • avoiding component distortion
- 3. Feature Size In machining, minimum feature size is governed by cutting tool size In AM, the minimum size of solid feature is limited by the laser spot diameter: • Spot heats powder and creates a weld pool • Molten metal cools to form a dense solid • Spot size and laser power determines minimum feature size
- 4. Minimum Producible Feature Size Sintering of neighboring powder means minimum feature size is larger than laser spot size, dependent on: • Thermal conductivity of powder • Energy imparted With a 70 µm spot: • Lattice struts down to 140 µm • Wall thicknesses down to 150 – 200 µm
- 5. Overhangs Avoid large overhangs • Green builds OK • Yellow poor surface finish • Red distorts Avoid overhang angles greater than 45 degrees to vertical Shallow overhangs may deform or have poor surface finish Vertical edges are OK < 45° > 45°
- 6. Lateral Holes • Holes in the side of parts create overhangs • Small holes (< 10 mm) do not distort • Large holes will need supports, or to be modified to reduce overhangs
- 7. Minimizing Supports – Feature Shape Overhangs can be built using supports Supports have to be removed after the build is complete Changing the shape of lateral holes can remove the need for supports Interior supports needed for large bore Teardrop and diamond holes do not need supports
- 8. Minimizing Supports – Re-orientation Re-orientation can be used to minimize supports • May require addition layers and build time Interior supports needed for horizontal bore Minimal supports & wasted material Re-orientate
- 9. Residual Stress AM is a welding process, although spot size is small and energy density is high • Stress can build up in thick cross-sections, or where cross sections vary in thickness
- 10. Part Distortion Stress (particularly thick sections) • Avoid thick part sections • Thin and consistent sections are best • Use thicker build plates where stress is likely to be high Standard and thick build plates
- 11. • Adaptation for AM (AfAM): – The redevelopment or modification of existing product designs to better suit the design constraints imposed by additive manufacture; leveraging AM specific benefits – Existing product design specification (PDS) and system-level design reduce available ‘design space’ • Design for AM (DfAM): – The wholesale ‘blank sheet’ design and development of a new product; fully exploiting the opportunities the technology provides – Considerably more open design space and ability to influence system-level design decisions Slide 114/12/2016
- 12. Slide 124/12/2016 Conventional AfAM DfAM Design evolution Product Specification
- 13. • Hydraulic manifold for a circuit operating at pressures in the order of 200-500bar • Weight limited application • Simple circuit consisting of two check valves, a solenoid valve and their associated outlet ports (male insert type) Hydraulic Manifold Case Study Slide 134/12/2016
- 14. Conventional Solution: Block Manifold Slide 144/12/2016 Benefits • A simple solution to the problem • Easy to design • Fast to manufacture Limitations • Sub-optimal performance due to cross-drillings • Massively inefficient use of material • 8 additional components in the form of pressure plugs Mass: 4.6kg (10lbs)
- 15. AfAM Design Flow Slide 154/12/2016 Extraction Scaffold Machining Ops
- 16. Adapted for AM Slide 164/12/2016 Benefits • A significant reduction in mass • Improved hydraulic performance • ‘Drop-in’ replacement for conventional part • Pressure plugs no longer needed Limitations • Horizontal passageways need support and machining allowances can’t be too aggressive • Removal of material reduces rigidity and complicates machining Mass: 1kg (2.2lbs)
- 17. • True DfAM products are always clean sheet designs • Customer has a specific product application in mind • Adherence to a product development methodology as per any other conventional design process • Engineering due diligence: cost/benefit, concept evaluation, design optimisation, compromises for manufacture etc. DfAM Checklist Slide 174/12/2016
- 18. Designed for AM Slide 184/12/2016 Benefits • Extremely efficient use of material • Alignment of valves allows for entirely self-supporting part • Consolidation of outlet ports into design Limitations • High degree of CAD complexity/difficulty • System-level engineering and design must be flexible in order to react to and incorporate the potential advantages of DfAM MASS: 0.4kg (0.89lbs)
- 19. Version Mass (kg) Saving (%) Conventional 4.6 - AfAM 1 76.3 DfAM 0.4 91.2 Slide 194/12/2016 Conventional AfAM DfAM Summary
- 20. Minimizing Supports – Case Study AM beer bottle opener • Original sleek design (left) • First optimisation to reduce weight (right) resulted in several overhangs (orange circles), needing supports (grey)
- 21. Minimizing Supports – Case Study AM beer bottle opener • Second iteration (left) included modifications to the shape to minimise support • Third iteration (right) involved a re-orientation, leaving only self-supporting overhangs (grey circles), needing just one tiny support to connect the bottle opener to the build plate
- 23. Summary • Awareness of AM characteristics & limitations is critical to success • DfAM rules encourage reduction in part weight, build time and cost • Modern build preparation software simplifies and speeds up the DfAM process
- 24. Thank You! Your product design Renishaw expertise Your AM process Global support
Notas do Editor
- Good afternoon. Thank you for being here with us today. Introduction – My name is Robert Chiari, Regional Sales Manager with Renishaw, Inc. Primary focus and responsibility with our metals AM technologies. Additive manufacturing (AM) gives us tremendous freedom to create components with free-form and intricate features, designs which would be impractical - if not impossible - to produce conventionally
- Like any manufacturing process, the various AM technologies have their capabilities and their limitations. In this presentation, we'll take a look at some of the key Design for AM (DfAM) considerations for laser melted metal parts. We will consider feature size, surface finish, overhanging features, minimizing supports, and avoiding component distortion.
- In machining processes, the size of detail feature that you can produce is limited by your choice of cutting tool. The cutting tool size determines the minimum size of holes and slots in the part. In AM, a similar rule applies, with the tool size being the spot size of the laser. The size of the spot, along with laser power and modulation, controls the size of the weld pool and hence the size of the structure that is built.
- The minimum producible feature size is generally somewhat larger than the spot size due to thermal conductivity. Detailed structures such as lattices, where strut dimensions down to 140 microns can be built using a 70 µm laser spot. Wall thicknesses as low as 150 – 200 µm can also be achieved.
- The rule of thumb is that overhang angles greater than 45 degrees to the vertical should be avoided, with 30 degrees being preferred. Overhang angles greater than this will require supports.
- As a general guide rule, circles or holes with a diameter less than 10 mm can be self-supported without causing distortion. Review all three images – small hole, larger hole, teardrop
- One answer to the problem of overhangs is to support the overhanging feature. However, supports are effectively waste and have to be removed after the build is complete: they enable the AM process to succeed, but add complexity and cost further down the process line. So a key part of the DfAM process is to assess how to build the part with the minimum of supports. This means eliminating overhangs by angling the part, and by modifying the design of overhanging features such as holes, slots and channels. We are programmed to design round holes because that is what we can most easily produce subtractively. In cases where roundness is critical, then it is best to orientate a hole so that its axis is vertical with no overhangs. If the hole must be in the side of the part, then consider whether it needs to be round or if it can be modified to make it more buildable - into a 'teardrop' or diamond shape, for instance. In the example on this slide, the round lateral hole requires internal supports - the teardrop and diamond holes require none – they are self-supporting.
- Orientation is another way to avoid supports, although this can come at the expense of additional layers and build time. In the image on this slide, employing the 45 degree rule, we have tilted the component so that none of the interior of the cylindrical hole requires supports.
- AM is essentially a high precision micro welding process. This can lead to stress in large cross sections or in parts with varying cross sections. That stress tries to break through the edge of the part, as shown in the image.
- This stress can cause warping, and in extreme cases, can cause the part to pull away from its supports, or even to crack. Where thick sections have to be built, it is wise to select a thicker build plate to resist these bending forces. Where blocks of material are essential, consider filling them with lattice to reduce stress, weight, material cost and build time.
- AfAM (interim) – relies on a pre-existing component that was designed to be manufactured with a conventional process, and needs to be modified for AM. DfAM – is a new component, specifically planned to be produced with the AM process, this is where optimal design can be achieved.
- Power curve of efficiency in product design
- Let’s dive into an example of the design of a hydraulic manifold
- Simple, easy, fast to manufacture – or is it? Limited component performance Inefficient use of raw materials – means a lot of waste Secondary components, processes and assembly are required
- Emphasis on functionality – improved flow performance Scaffold integrates handles and creates free-standing component Following 45º rule diamond shape eliminates need for internal supports Secondary machining is still required for some internal channels
- Listed are the nominal benefits when Adapted for AM …and some of the limitations based on the constraints of modifying a design that was originally for a conventional process.
- So we will move on from Adaptation for AM to Design for AM. DfAM breaks away completely from design constraints of conventional manufacturing processes Application, function and AM all play equally in the design considerations
- The same hydraulic manifold when designed for AM Though it requires expert level CAD abilities, the gains far out weigh the limitations
- Results! Conventional – blocky, cumbersome, inefficient flow, and use of materials AfAM – gains limited by pre-existing design DfAM – optimal design and functional performance, and over 90% savings in raw material
- Let's look at one more example of dealing with overhangs. Renishaw's AM beer bottle opener was originally conceived as the sleek design shown left. Our first attempt to optimize this part for AM involved eliminating weight by creating a more intricate structure shown right. Highlight teardrop design. This resulted in several overhangs (circled in orange), necessitating additional support material (grey).
- So we tried again, this time with some additional structures to minimize the supports needed (left). By inverting the part (right), we were able to design a build with self-supporting overhangs (circled in grey). Only a tiny support to connect the bottle opener to the build plate was needed. Facilitating removal from the build substrate by hand.
- And here they as built are on the build plate. Cheers!
- AM gives us huge freedom to design parts differently, but we do need to be aware of some of the characteristics and limitations of the process, so that we create parts that can be built successfully. The DfAM rules described above are not too onerous in practice, and actually encourage us to consider ways to make parts that are lighter, faster to build, and more cost-effective. One final note: Modern design and build preparation software helps enormously to find an optimum design, orientation and support strategy so that we can produce consistent parts economically.