MIND OF METAL

MIND OF METAL: LIGHTWEIGHTING


Four Additive Design Benefits When Lightweighting Metal 3D Printed Parts

Design freedom.

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.

Why?

  • 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:


A 3D printed intake manifold for the Ford F-150 pickup truck. Photo via Ford.

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.


Examples of different lattice configurations
Sample component with dense lattice structure produced on the Eplus EP-M250

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.

Honeycomb infill used in piston design/production by German automotive engineering firm IAV. Picture supplied by IAV.
Linear infill in this radiator design has the additional benefit of improving heat exchange area and heat dissipation efficiency. Picture by Eplus.

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.

Topology optimization flow (picture by 3Dprint.com)
Optimized exhaust bracket designed and produced by Eplus using the EP-M250

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.


As we’ve tried to illustrate in this post, lightweighting affects far more than design aesthetics. The design freedom afforded by additive manufacturing provides very tangible benefits for the functionality of the end product.

Click here to request a copy of the Minds of Metal white paper.


*This article was produced in collaboration with Eplus3D Additive Manufacturing.

Additive vs. Subtractive

Who wins in this match-up? 

You might expect we are going to tell you that the winner is additive manufacturing? 

Not necessarily.  Each has advantages.

Let’s have a look at both processes.  We’ll compare additive manufacturing with more traditional forms of production in a real-life contest and reach a better appreciation for the circumstances where each is more effective. 


CASE STUDY ROUND ONE – THE SIMPLE GEAR

Let’s assume your organization needs to produce a simple gear to replace an existing one. Perhaps you need one like this one to the left. This is a 45-tooth gear and it measures 8mm x 6.25mm (3.15” x 0.25”). And it cannot be purchased outright from a supplier.

CONTESTANT: Conventional Manufacturing

You could ask a conventional manufacturer to reproduce the gear for you.  This simple gear is too complex to cut out accurately by hand, and the size variables alone make off-the-shelf dies impractical.

They might use laser-cutting to cut a sheet of high-density polyethylene (HDPE) and create your gear. They inform you that there will be a one-time set up fee of $105.00, plus the cost of the plastic ($0.50).  They also charge $1.00 per cutting inch.  Including the octagonal shape in the center, this will come up to roughly 11 inches, or $11.00. The total cost of one gear using conventional subtractive methods will be $116.50 plus applicable taxes.

Because the setup time for the production of more than one gear will not change much, if you needed two gears, the cost would be $105.00 + (2 x $11.50) = $128.00.  Averaged out between two gears your cost will be $64.00 per gear. So the unit cost goes down. For three gears, $46.50. For ten gears, $22.50 per unit. For 100 gears, $12.55 per unit, and so on.

Depending on how many gears you expect to need, a mold might be fabricated in order to further cut costs.

Your gear is a small component, but it does have some finer details, so the estimated cost for a mold would place it at approximately $1,500. However, once the mold is in place your cost, including material, cooling and labor, now drops down to $0.50 per gear. In order to justify the capital cost of the mold over laser-cutting, you will need to produce at minimum 125 to compare with laser cutting. However, if you need 1,500 gears, having a mold produced would be the economical choice.  Your unit cost will now be $1.50 — and less with every gear produced.

Of course costs may vary from supplier to supplier, and from region to region, but the basic principle remains the same. It both cases, the average cost per gear goes down as the number of gears goes up.

CONTESTANT:  Additive Manufacturing

You decide to produce this same gear using your 3D printer.  Your costs will be very different from traditional manufacturing.

Production of this same gear requires precisely 8.55 grams of material and will take one hour to produce. Perhaps you decide to use HDPE filament which you purchased at a cost of $35/1,000 g, or $0.035/g. Of course as a business-owner you will want to take into account the electricity used and the operating time of the machine into account.  You calculate that these operating costs increase your unit cost by an extra $0.30/gram, for a total of $0.335/g, multiplied by 8.55 g of material.  Your cost is $2.86 per unit.

Note that the cost for additive manufacturing is flat. It does not reduce with volume unless the producer chooses to discount. If you need 10 gears instead of just the one, it will take 10 hours and the cost will be $2.86 x 10 = $28.60. If you need 100, it will take 100 hours and the cost will be $286.00.

A cost equilibrium is reached between Additive Manufacturing and Conventional Manufacturing when the cost of producing a part using either method is the same.


CASE STUDY ROUND TWO – THE HELICAL GEAR

CONTESTANT: Conventional Manufacturing

For conventional manufacturing methods, an inverse cost relationship exists with regards to the complexity of the item being produced. The more complex the item, the more costly it will be to make.

There are a few different reasons for this, starting with availability of machines to produce simpler items. For example the flat gear above can be cut by a laser cutter or a water jet cutter.  In fact, because it is a polymer gear, probably various smaller cutters could work.

What if your organization required a helical gear instead? There are good reasons for such a choice. Helical gears have slanted teeth.  They reduce noise and vibration, and are stronger.

However, using conventional methods, helical gears also prove a bit trickier to produce. They cannot simply be cut out of a flat sheet of plastic or nylon with a laser cutter.  Instead they must be carefully machined out of a thicker chunk of plastic using special processes such as hobbing or milling.  Producing only one gear can be cost-prohibitive — $500 for machine set-up and charges for machine down-time from other projects are not unusual.

Creation of a mold to allow for mass production of helical gears similarly requires more time and higher capital costs than for our first gear.  More attention must be paid to the mold to ensure proper dimensions and uniform cooling time, especially when using polymers.

CONTESTANT: Additive Manufacturing

What about producing a helical gear using additive manufacturing?  Well, complexity of the gear really isn’t as big a concern. 

The same helical gear can be produced – layer by layer – using the exact same costing method discussed above (material weight x material weight cost).

Again, as with the quantity/cost graph, the complexity/cost bar continues to be relatively flat for additive manufacturing.  Occasionally, it can be helpful to print very complex items more slowly.  And occasionally, use of temporary support materials is needed with extremely complex designs.  However, the complexity of an item often has little bearing on the over-all cost.

THE VERDICT?

Unless your business can justify the cost of a mold, additive manufacturing will offer the cheaper, faster process and the best per-unit production cost.  If the item has a complex design?  This will be all the more true.

What about your business?  Could additive manufacturing improve your production?  We’d love to talk to you about that. 

WEBINAR: 3D metal production overview

Shining3D senior application engineer Enis Jost hosts this great webinar featuring a ‘design-to-print’ overview of a neat little bottle opener.

The overview touches on everything from design considerations to production and lastly inspection.

Check it out!

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