Product design of high-value metal components: adopting new rules for Selective Laser Melting

Selective Laser Melting (SLM) enables component geometries and functions that are almost impossible to produce using other machining or moulding processes. This new, unconventional process modifies manufacturing work-flows and generates creative design approach to provide innovative solutions for cases deemed impractical. With SLM, there is no trade off between complexity and costs. It is an alternative manufacturing technique to be considered when limitations and constraints of existing manufacturing methods impact the ability of manufacturing a desired product practically, efficiently or affordably.

Ref [1]

Where tooling access need considered for substrative machining, and cast molds limit structures obtainable, SLM ensures access to greater design freedom.  When complex shapes  that are time consuming in process planning  and operation, demand specialised equipment, tooling  and operators, generating high production costs, SLM can ensure manufacturing in a 1-step process and significantly reduce delivery time to market.

New design rules for SLM

Yet, to take full advantage of the technology, engineers need to shift their conventional approach to engineering design and adapt to new SLM-specific design rules and guidelines. Understanding the process fully, both advantages and limitations to make the most of the technology. Ensuring manufacturing consideration during product design will improve part quality and production yield.

So far, this experience-based know-how is only held by engineers who have learnt on-the-jobs rules by working and experimenting with SLM machines on a daily basis. Yet, building components specially (re)designed to take advantage of SLM technology have revealed financial and performance benefits.

3 practical high-value benefits gained from redesigning components for SLM

1.      Improving delivery time to market: 3D printing assemblies using appropriate build direction.

Aircraft NOS PT6A Turbine Engine Combustion Chamber Liner King Air.

Where it usually took 6 months to cut, punch, machine various elements of an assembly, and get on with the different production stages (welding, brazing, post-processing,…), it’s now possible to save 6 months time by building a high-value  metal aerospace components in a single step. 

2.      Improving lubricating and cooling performance by integrating complex internal channels

Internal channels can be integrated into SLMed products that can not be produced by any other means of manufacturing. Such features have been demonstrated to have lower manufacturing costs and added performance values over conventional processes. For instance, improving cooling rate of a car engine turbocharger enhanced the maximum RPM, decreased fuel consumption and CO2 emissions.

High performance turbocharger with water-cooled casing. Ref [2]

3.      Improving functionalisation with cellular lattices structures

Typically, lattice cellular structures are investigated for medical applications such as bones implants, where they can create variable rigidity as the cells density or size vary.
Other actual products include cross-flow heat exchanger made from stainless steel and copper, and heat-sinks made of aluminium. These could not be made any other way so cheaply and efficiently with conventional machining. 

Ref [3]

Ref [4]

Introducing new SLM-specific design rules

These 3 practical examples show that knowing and using SLM-specific design rules can:

• Save product delivery time;
• Save manufacturing costs;
• Improve functionalization;
• Give access to tailored rigidity in mechanical parts;
• Improve sub-components and assemblies’ performances.

These rules include guidelines to improve production yield, limit post-processing and ensure easy functionalization. We’ll get to these in the next part. Keep tuned!

References
[1]      M. Wong, S. Tsopanos, C. J. Sutcliffe, and I. Owen, “Selective laser melting of heat transfer devices,” Rapid Prototyp. J., vol. 13, no. 5, pp. 291–297, 2007.
[2] High performance turbocharger with water-cooled casing
[3] K. Hazlehurst, C. J. Wang, and M. Stanford, “Evaluation of the stiffness characteristics of square pore CoCrMo cellular structures manufactured using laser melting technology for potential orthopaedic applications,” Mater. Des., vol. 51, pp. 949–955, Oct. 2013.
[4] R. E. Winter, M. Cotton, E. J. Harris, J. R. Maw, D. J. Chapman, D. E. Eakins, and G. McShane, “Plate-impact loading of cellular structures formed by selective laser melting,” Model. Simul. Mater. Sci. Eng., vol. 22, no. 2, p. 025021, Mar. 2014.