Design for SLM - high value case study: electronics enclosure

ref[2]

Components best suited for commercially viable SLM display one of the following characteristics [1]

• Geometric complexity, such as internal structures
• Demanding form or aesthetics requirement
• Ease of parts consolidation
• Low volume production requirement
• Customisation requirements
• Use of multi or dual material within a single component

In this geometry complexity study, an electronics enclosure is redesigned for RM to identify potential performance improvements and costs reduction. 

This safety-critical casing is used to protect electronic components driving the control systems of a subsonic unmanned aerial vehicle (UAV) used in military reconnaissance missions. Originally made up of aluminium alloy that can cause interferences, the enclosure is redesigned for Selective Laser Sintering of polyamide powder in order to avoid white noise.

casing ref[2, 3]

Case study: design study of avionics enclosure 
Objective: assessing SLS use and specific redesign rules to improve a subsonic unmanned aerial vehicle (UAV) enclosure
Challenges: tooling costs, delivery schedule: 2 weeks for full design and development of 2 finished components, stringent customer requirements: light weight / waterproof /  able to withstand electromagnetic interference, cost effectiveness.

Even though IMAdMan usually focuses on metal-based AM, in this scenario, we step away from metal SLM to concentrate on plastic SLS as this material exhibits properties better suited to the final application.

electronics casing ref[2]

Given the (lack of proper) budget and the short design-to-delivery timeframe (2 weeks), SLS is preferred to injection molding.

In this scenario, the design has to comply with stringent temperature, vibrations and stress requirements outlined by the customer. Easy installation and secure fastening of electrical and electronics components drive the design, starting with the outer geometrical shape that has to be fitted in the front of the UAV. The inner features of the casing are designed used parametric CAD software. 

Combining customers’ requirement with practical experience of SLS characteristics allows significant direct design innovations impossible with injection moulding:

• customised internal chassis and supports to hold electronics
  
• snap fit hooks to secure and fasten components
  
• mounting bosses
  
• integrated cable support.

mounting bosses ref[2, 3]

Some challenges remain such as a lack of (certified) material data specification describing mechanical behaviour. As a result, the actual part required expensive testing following manufacturing. Significantly reduced electromagnetic interferences compensated for these additional testing costs.

Following this study, specific re-design and use of SLS was also successfully employed on a follow-up project [3], and has since established itself as the way to produce deliverable, performance enclosures specifically for UAVs. [3]

References
[1]    M. J. Burton, “Design for rapid manufacture : developing an appropriate knowledge transfer tool for industrial designers,” Loughborough University, 2005.
[2]    S. Maidin, R. I. Campbell, I. Drstvensek, and P. Sever, “Design for rapid manufacturing – capturing designers ’ knowledge,” in Advanced Research in Virtual and Rapid Prototyping - Proceedings of VR@P4, 2009, pp. 311–317.
[3]    P. du Plessis, “A Functional Application Of RM In A Military Environment,” in TCT Conference, 2008.