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Printed Casting: 3D-printed moulds and cores for lightweight construction and electromobility

British company Brooks Crownhill Limited (BCP) relies on 3D printing systems from voxeljet to produce housings for electric motors. For many of its automotive parts, BCP has prototypes produced using 3D sand printing well before they are ready for series production. The advantage is the ability to design highly complex parts without having to keep expensive tools on hand. This is possible as rapid prototyping allows end users to thoroughly inspect and extensively test the newly designed components before the production tools are manufactured, thus saving a vast amount of time and money. As we know, moulds made of sand are relatively cost-effective and sufficiently refractory for the application in steel and, above all, aluminium foundries, which is why sand moulding continues to enjoy great popularity, especially in the automotive industry. Over 60 per cent of all metal castings are produced by sand casting. However, modern industrial 3D printing has offered completely new possibilities for foundries – with the help of 3D printing systems, such as the binder jetting systems from voxeljet – even highly complex moulds and cores can be manufactured.

Co-operation with suppliers is irreplaceable

Lee Henderson, sales director at Brooks Crownhill, comments on the collaboration with voxeljet: “We have been using 3D printing and casting, or printed casting, for quite some time now. The immense advantages are obvious. The process is fast, cost-effective and gives designers enormous creative freedom. This is important for rethinking established components and saving as much material as possible, for example by optimising the topology of the components.” BCP largely manufactures engine components and, more recently, housing components for electric motors for its customers in the automotive sector. “We have to make our parts lighter and lighter. And we need to do this while maintaining, or even better increasing, load-bearing capacity and extending the service life of the parts. This is where voxeljet comes to our aid with its 3D sand printing.”

So-called lightweight design is one of the most important design trends of recent years. Customer designs are being pushed further and further to the limits of manufacturability: thinner wall sections of the entire casting and higher tolerance bands for positional accuracy. “3D sand printing is therefore irreplaceable. Not only because it allows us to realise geometries that would not be possible using conventional processes such as milling or core shooting, but especially when we want to test brand new designs, we need the optimised prototypes quickly. We then take a close look at these with specific integrity tests, non-destructive testing (NDT), before we give the go-ahead for series production,” says Henderson.

Impact of 3D printing on metal casting: design possibilities and feasibility

“In modern engineering, 3D printing means above all that we can print complex inner cores as one part. This saves us a lot of work in casting preparation. And we can be confident that all tolerances on wall thickness and the associated stability of the cores will be maintained during the enormous stresses of metal casting,” says Henderson. “Further economic opportunities are opened up by time-saving printed castings when you reduce potential costs and conventional assembly time on complex core-stack assemblies line-side. This has a direct impact on the business model, ongoing costs and delivery times to the customer.”

However, Henderson also notes that the benefits of additive manufacturing of moulds and cores are not yet one hundred per cent clear in the minds of engineers. “3D printing, unfortunately, still has a niche existence. It is increasingly recognised within the foundry industry as a fully-fledged manufacturing process for casting moulds, but I’m not sure to what extent the advantages are even known by both engineers and the key buyers. There are still unimagined design and cost opportunities that could be leveraged here.”

Designed for manufacturing versus designed for functionality

Greater latitude in the design of 3D printed sand moulds is closing the gap between ‘design for manufacturing’ and ‘design for functionality’. Casting expert Henderson says: “Today, engineers can use finite element analysis (FEM) to optimise functionality and then directly 3D print the designs. This makes the design of engine parts, for example, a lot faster and, more importantly, the components are stronger, which in turn allows drastic weight reductions. This is extremely attractive, especially in the wake of current environmental regulations such as lightweight construction, and the associated energy savings.”

3D printing offers more than mere product optimisation

But the advantages do not stop there. “With 3D printing, we can plan gas channels into the sand cores and moulds during the design stage. These are used for venting and outgassing during the casting process, making our job much easier, and have a great effect on the quality of the cast parts, in terms of density and surface quality,” Henderson explains. “Adding structural tie rods for better transportability of the parts is also possible and simplifies the handling of the printed parts.”

BCP also relies on the use of different sand systems for each application. For example, high-strength and high-temperature cores to ensure stability and concentricity of the inner cores during the casting process of high temperature alloys. BCP is a precision engineering company specialising in all aspects of castings, including CNC machining, CNC tool making, assembly and associated processes. Partners for product development and production, established in a range of markets including automotive, motorsport, military, electronic, renewable energy, marine, broadcast, and medical.

www.bcplimited.co.uk

voxeljet is a leading provider of high-speed, large-format 3D printers and on-demand parts services to industrial and commercial customers. The company’s 3D printers employ a powder binding, additive manufacturing technology to produce parts using various material sets, which consist of particulate materials and proprietary chemical binding agents. The company provides its 3D printers and on-demand parts services to industrial and commercial customers serving the automotive, aerospace, film and entertainment, art and architecture, engineering, and consumer product end markets. www.voxeljet.com

The binder jetting process for printed castings – how it works

The 3D printing system spreads a 300-micrometre thin layer of sand on to the building platform. The print head then uses a binder to bond the sand grains together wherever the casting mould is to be created. The build platform lowers by one layer thickness and the process starts again until the mould is completed. The excess sand is then removed, and the mould is ready for casting. The printed moulds and cores can also be combined with simple, conventionally produced casting moulds at any time.