Solutions ready for the harshest conditions?
Creating product for extreme environments poses challenges throughout the design process...from understanding what the exact requirements are for a product to survive, to the details in manufacture that determine eventual success.
At KD, we consider an extreme environment to be where the use conditions are at an abnormal level and could involve any one of: temperature, vibration, shock, impact, chemical exposure, pressure, moisture, dust, vacuum or incident radiation.
Some of these abnormal conditions require very particular engineering analysis and design approaches. However there are also some key points that should go into the development of any product designed for harsh environments.
Here, we explore these key areas and consider a few examples.
Understand the needs
When designing for an extreme environment there may be additional complications in first determining the user and product requirements. Consider the user in extreme conditions of cold:
Will they be wearing protective gloves and equipment that may hamper operation?
Will they even be able to access the product?
To fully understand the user needs we apply insight and research testing, preferably with mock-up devices or processes, so that our engineers have the greatest possible understanding of the demands of the product.
In harsh conditions, the engineer must also consider the greater scope of research that goes into understanding the environment’s effect on materials and components. At these extremes, the data that forms the typical bedrock of engineering analysis may not be applicable. Plastics can be substantially affected by extremes of temperature, ultra-violet, chemicals, vacuum and moisture. Even metallics are not immune, for example some aluminium alloys experience appreciable strength reduction at temperatures above 150 °C.
Solutions for the environment
Creating initial ideas that tackle the extreme environment early in the design process is the most efficient method of development. So that, when the idea is established as part of the final design, the major hurdles to environmental performance have already been considered.
Taking the example of a deployable sensor fitted in the engine compartment of heavy plant equipment; the sensor shall experience extremes of temperature, near continuous vibration and exposure to fuel and lubrication oils. By considering feasible material options for the enclosure and the means of sensor attachment at the very first stages of the project, the riskier elements of the product development can be identified and addressed.
The complication of this approach resides in the uncertainties of the requirements. For the sensor example, vibration frequency and amplitude vary greatly between machine types and their condition. In this instance, we applied assumptions of vibration levels used for the design of military vehicle hardware to create inputs for calculation of the in-service loads experienced by the attachment system and the enclosed electronics. Based on this, an early stage mathematical analysis was used to assess feasibility of the concepts, allowing early risk reduction.
For this sensor to survive inside the engine compartment of off-road machinery it needs to withstand extremes of temperature, chemical exposure and vibration. To reduce development risk the early ideas for sensor attachment were analysed to ensure their feasibility before integration into the product.
Proving the principles
While preliminary analysis can be effective in screening problematic designs from later development phases, there is still the need to prove the design as it matures. This requires a more complete analysis, coupled with prototype testing.
For delicate electronic systems in harsh environments, a casework provides protection from moisture and dust ingress, typically using elastomer seals between parts. Using computational finite element analysis, the performance of the seal and casework structure can be analysed. More advanced techniques can employ non-linear models for the elastomer deformation and consider the effect of geometric tolerance variation in the sealing quality.
For even greater understanding, virtual prototyping may be supplemented with physical test prototypes. These prototypes are especially useful when observing complex phenomena such as impact and shock damage. Testing of this nature may be also improved by using data acquired through high-speed video, allowing improved analysis of failure sequences during impact.
Finite element analysis of casework deformation and gasket compression in a plastic enclosure. This process was used to optimise the number of fasteners and case thickness for reduced size in a ruggedized military radio handset.
Applying the details
For the design engineer, the last development hurdle is often the transfer to manufacture. Until this point, all activities will have used either virtual or physical prototyping of the product to gain the best possible approximation. However final performance will be affected by the chosen processing method and applied controls.
The ingress sealing performance of moulded elastomer seals is sensitive to the presence of knit lines, created where flow fronts in the injected polymer meet, component distortion. Many of these issues can be identified early in the design but working with the manufacturer to determine correct positions for injection gates and moulding parameters is critical to successful implementation.
Finally, once initial production samples are available, measurement of the product against the starting requirements, through a robust programme of verification testing is imperative in gaining enough confidence for a successful launch.
Thales Squadnet radio communicator, designed to meet military standards for rugged design, where detailed design of the casework over-mould was used to improve ingress sealing.