MIND OF METAL: LIGHTWEIGHTING
Four Additive Design Benefits When Lightweighting Metal 3D Printed Parts
Of the vast benefits offered by additive manufacturing, this is one of the most often cited. The incremental ‘layered’ building process allows for inclusion of component variations and complexities that would be impossible in traditional manufacturing.
The application and benefits of additive design can be evidenced in many ways, but one of the most dramatic examples is its impact on the process of ‘lightweighting’. As you might expect, lightweighting is the term used for the process of making components lighter. It is a growing trend in transportation, tooling, energy, health care, and a host of others.
- Lighter components offer wide ranging benefits: from enhancing fuel efficiencies in transportation to greater viability as implants or prosthetics. For example, a study released by the Massachusetts Institute of Technology estimated that weight reduction in vehicles could reduce energy consumption by between 12-20%. Citing a similar study, the US Office of Energy suggests that for each 10% reduction of vehicle weight, energy consumption can be reduced by between 8-12%.
- Lightweighting allows for different material considerations. Pending application, optimized lighter materials can be used to replace heavier components, or the inverse – components can sometimes be produced using heavier, less expensive materials to replicate the benefits of lighter, more expensive materials.
- More efficient use of material and the energy required in production make them more environmentally friendly and address a growing concern among policy makers and consumers alike.
- Cost reduction. Less material per component means less capital per component.
Additive manufacturing helps break down many of the hurdles to the production of lightweight components. Here are four ways additive manufacturing/3D printing can produce lighter components:
Method I – Lattice Structures
Additive manufacturing makes the use and scale of lattice structures far more accessible. Lattice structures feature a high strength-to-weight ratio. This is what makes them so useful in architectural and engineering applications (e.g. the Eiffel tower or a lattice truss bridge).
Lattice structures are three-dimensional open-celled structures composed of one or more repeating unit cells. These cells are defined by their dimensions and connectivity of their constituent struts, which are connected at specific nodes. Lattices can achieve the ideal balance of engineering strength, toughness, durability, statics, dynamics and manufacturing cost.
The relative density of crystal lattice, the shape, size, and material are adjusted by periodically duplicating a large number of single cells for design and manufacture, so as to adjust the mechanical properties of the structure, such as strength and toughness.
A 3D lattice structure offers a high degree of spatial symmetry which can evenly disperse an external load, reduce weight and increase load bearing capacity. In addition to engineering applications, there are healthcare applications: a hollow lattice structure features a ‘gap’ (or adjustable aperture), which can facilitate integration into the human body and the implant tissue in the application of the implant.
Lattice design is very flexible and lattice elements with different shapes, sizes and porosity can be customized to suit their use. When high structural strength is required, the shape and density of lattice cells can be adjusted accordingly with larger cells and a more complex strut-structure. Similarly, when requirements call for weight reduction, a hollow lattice structure can be integrated into the design. The hollow structure can be arranged regularly or randomly to form irregular pores. In addition, the hollow structure can also present gradient transition arrangement of variable density and thickness to meet the requirements of the overall gradient strength of the components.
Method II – Hollow Interlayer / Thin-walled Stiffened Structural Design
Additive gives the designer a wide range of design options not easily available when relying on traditional processes.
First, wall thickness of less than 1 mm can be achieved, allowing for significant weight reduction. The use of different infills (interlayers) and wall settings and thicknesses allows the designer to reduce the net weight of the component, but also to compensate for the various loads and stresses the component will have to bear.
Use of infills will then disperse external pressures across the lattice. How does this work? Consider a simple curtain rod, under a flexural (bending) load where the surface material bears most of tensile and compressive stresses. Now imagine a core infill has been added to the rod. This will help disperse the load. The strength of the rod has been improved without having to resort to a solid metal rod or even having to increase wall thickness.
In sum, interlayer structure has the advantages of offering net weight reduction, high bending stiffness and flexural rigidity, strength, greater stability, fatigue resistance, sound absorption and heat insulation.
Infills are widely used to reduce weight in the automotive and aviation applications, for wind turbine blades, and in ships and trains.
Method III – Topological Optimization
3D printing is the most efficient method of optimizing component design topology; that is to say, of identifying and removing excess material that does not affect the functionality of the part.
First, optimal material distribution within required parameters is determined. Once topology has been optimized, the structure is simulated and analyzed to complete final modeling. It is not unusual for optimized components to be more than 45% lighter than their non-optimized counterparts.
Although some designs can be produced using traditional methods, the same degree of topology optimization is not possible. For instance, a 5 axis CNC router can be used to reduce net weight and achieve desired topology, but such subtractive methods produce waste in proportion to the material removed.
The additive process of 3D printing, on the other hand, often eliminates waste material. Even where supports are used for the product being created, waste material will be far less than in a subtractive process. Additive manufacturing is material-efficient and topology is truly optimized.
Method IV – Integrated Component Assembly
Anyone who has assembled a piece of IKEA furniture can attest to this sentiment: why so many parts!? The advantage for IKEA is, of course, cost savings for the company and its consumers in flat-packing. The sacrifice, often, is structural integrity.
Integrated product design focuses on reducing the number of components traditionally used. A unit traditionally produced from multiple components can often be 3D-printed as one complete unit. Not only does this enhance the strength and integrity of the overall structure, but it also renders connection structures (flanges, welds, etc.) unnecessary.
Though the focus here is lightweighting, integrated components can also offer broader benefits of reduced assembly time and required maintenance.
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