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Digitisation pushes the boundaries of additive manufacturing

10 July, 2020

3D printing (additive manufacturing, or AM) has hit the headlines with its role in producing emergency ventilator parts and supplies of PPE. But is it a serious competitor to established mass manufacturing methods? Andy Pye looks at how the boundaries are being extended.

Injection moulding is the linchpin of plastics manufacture. It has improved immeasurably over the years, with inventions including soluble forms of cellulose acetate, screw injection machines, gas-assisted injection moulding process, and an extensive range of material options. It has progressed from simple objects such as buttons and combs, to the complex products now seen in industries such as automotive, aerospace, healthcare, consumer products and packaging.

At the other end of the scale, despite the industry's dislike of its original name of Rapid Prototyping, 3D printing or additive manufacturing has struggled to evolve beyond a prototyping method, or at best a manufacturing option for small batches.

Nevertheless, some design features, such as hollow infill patterns, are too complex for traditional methods and are exclusive to AM. It is also possible to include multiple materials into a single object, which allows different colours, textures and mechanical properties to be mixed and matched. Digital texturing enables complex, aesthetically pleasing parts within a single run without extra design and processing time.

3D printing has been given a sizeable boost by digital manufacturing: a part can be designed, manufactured in-house on a professional 3D printer, and tested, in a few days. The CAD-to-production speed makes it a perfect candidate for Low Rate Initial Production (LRIP), getting to market much faster, with the option to switch to the mass manufacturing processes when tooling is ready or when higher volumes are needed. After the initial investment to create the appropriate tools and moulds, injection moulding can be automated and the part rapidly mass-manufactured. This significantly decreases the amount of time needed per part.

For any specific part, there is a crossover "breakeven" point of production volumes. It may be as few as 150 units manufactured, or more than 1000. At these lower production numbers, the cost of each injection moulded part can be 10 to 100 times as much as it would be using tool-less digital production.

But by its nature, 3D printing is a layer-by layer process with a fixed time per part, meaning that the first component will always take the exact same amount of time to create as the last. To move the crossover point to the right, away from small batch production towards a genuine mass production option, suppliers are coming up with better and smarter 3D printing machines, but these are unlikely to eliminate traditional methods of manufacturing. Larger 3D printers are available, but these are expensive, and there is a trade-off between size and cycle time. Improving part quality also means 3D printing using laser-based systems at extremely high resolutions, which means the parts will take a lot longer to manufacture.

A developing approach is digitalising not only the main 3D printing process, but also the activities happening around it. This underlines 3D Systems' Figure4 Technology. Much like digital photography, digital printing and digital video, direct digital production has come about through a confluence of complementary technologies that have been intelligently choreographed for speed, accuracy and efficiency.

Based on stereolithography, Figure4 Technology is a tool-less, easily scalable, AM process which is built around discrete and automated modules for each step of direct production. It is offered in three configurations that vary in footprint, capacity and versatility and uses a range of proprietary polymeric materials.

• Standalone: a single build unit for ultra-fast and affordable same-day printing of prototypes and low volume production parts.

• Modular: a scalable, semi-automated 3D manufacturing process that permits users to add more printer modules to grow capacity as the need to scale arises.

• Production: fully integrated in-line production cells.

According to 3D Systems’ benchmark tests, within 11 days, a Figure4 array with eight modules can turn out 10,000 units of a textured automotive vent, while the injection moulding process was still in the design stage. By the time 10,000 units of the automotive vent could be produced using traditional injection moulding, a manufacturer using Figure4 could have produced nearly 14,000 units.

Accelerating adoption

Also moving towards digitalised additive manufacturing is Siemens Digital Industries Software. The Siemens Additive Manufacturing (AM) Network is designed to accelerate the adoption of AM for industrial processes and applications. Partners include Decathlon, HP and Materialise. The network is designed to provide an end-to-end digital process that connects the demand for parts with a supplier network and provides a cloud-based environment to foster collaboration. The order-to-delivery process is also digitalised.

Siemens is engaging the network to validate a new process called the AM Path Optimizer a beta technology integrated in the NX software. It is designed to help solve process overheating, reduce scrap and increase production yield, this time in parts manufactured in metal powder. AM Path Optimizer complements a digital twin manufacturing strategy and addresses errors originated from suboptimal scan profiles and process parameters. The technology combines physics-based simulation with machine learning to analyse a full job file in a few minutes before execution on the machine.

Metal powder

3D printing is not only feasible with polymers, but also with metal powders. Selective LED-based melting (SLEDM) – the targeted melting of metal powder using high-power LED light sources – is a patent-applied technology developed by a team led by Franz Haas, head of the Institute of Production Engineering at Graz Technical University (TU Graz) in Austria. The technology is similar to selective laser melting (SLM) and electron beam melting (EBM), in which metal powder is melted by means of a laser or electron beam and built up into a component layer-by-layer. However, SLEDM solves two time-consuming problems of these powder bed-based manufacturing processes: the ability to produce large parts and avoiding manual post-processing.

The LEDs are equipped with a complex lens system in which the diameter of the LED focus can be easily changed between 0.05 and 20mm during the melting process. This enables larger volumes to be melted without having to dispense with filigree internal structures, reducing the average production time of components by a factor of 20.

A demonstrator of the process is already being constructed at the Medical University of Graz, where the first laboratory for medical 3D printing was opened in October 2019. The process will be used to produce bioresorbable metal implants. These are screws made of magnesium alloys used for bone fractures and which dissolve in the body after the fracture has mended. A second operation, which is often stressful, is therefore no longer necessary. Thanks to SLEDM, the production of such implants is now possible in the operating theatre itself, because "an LED light is naturally less dangerous for the operation than a powerful laser source," says Haas.

A second line of exploration is producing bipolar plates for fuel cells, or components for battery systems.

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Table 1 Factors pushing breakeven point of 3D printing towards higher production numbers

• Process Speed: shortens the time of liquid material in the vat, enabling a wider range of hybrid materials that mirror those used in traditional moulding processes

• Improved dimensional accuracy

• Design needs to address functionality only, not the draft angles, undercuts, side inserts and other features required for injection moulding.

• Development of CAD/CAM software that enables design for the unique capabilities of 3D printing, including organic and complex designs, consolidation of parts within an assembly, and use of lighter-weight materials with greater strength.

• Advanced robotics systems that enable fast connections between modular operations and a high level of scalability. Robotic arms take the parts through each step of the primary and secondary processes, including the washing, drying and curing operations.

• Being able to move continuously (and autonomously) among manufacturing steps.

• Digital inspection involving the sensor and data capture practices of Industry 4.0.

• Real-time communication using industry standard protocols both locally on the factory floor and remotely via web and cloud connectivity.

• Operation within automated production lines, allowing fast and flexible switching of production between different parts and long and short-run batches.

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