What’s the issue?
There is rarely a requirement for electronics with no enclosure, but the choice of materials, types, and performances must be properly linked to client needs. The scope can vary from a bespoke and complex form of enclosure with demanding engineering requirements to one that can be supplied off the shelf – and obviously the costs of the former far exceed those of the latter. This article answers questions about the fit, form and function of such enclosures and gives advice about choices.
What type of enclosure is best for the application?
There are always options and choices to be made, and these will depend on the application and market requirements. Basically, the following routes are available for production (not prototyping) quantities:
- An off the shelf box (plastic/metal) from a company like Fibox. These can be obtained from the big distributors (Farnell, RS, Digkey, etc.) is preferred. If quantities are low and aesthetics not of prime importance this may be the most economic route. Off the shelf boxes are usually quite cheap per item if the quantity is low but not price competitive at higher volumes. Clearly, compromising and accepting standard offerings is part of taking this route.
- A bespoke shape plastic enclosure tuned to the size and shape required made from folded plastic sheet. These are just one level above a standard box and offer some level of bespoke fitting and the aesthetics may be acceptable for a testing or industrial environment – a judgement would need making whether or the aesthetics are good enough for the market in question. Like standard enclosures, these may be a practical choice for relatively low volumes. The cost/item will get progressively less acceptable as volumes increase. One company that offers this service is Custom Design Technologies.
- Machined metal boxes. are often overlooked because machine shops generally consider them of low specification. An aluminium enclosure can turn out to be cheaper that a plastic one – volume dependent. Another option is to use extruded, anodised aluminium with screw on front and back panels – very cost effective method because the metal work is a minimum and the extruded aluminium is standard. The drawback may be that the aesthetics aren’t good enough, but an extruded aluminium enclosure can look very neat. There are numerous companies offering this through Google, e.g., RS Components
- 3D print is left out here because it isn’t really a practical method for volume manufacture – excellent prototyping tool but not really suitable for volume manufacture.
- Sometimes there is no escaping the need for something special, but possibly also with a very cheap price/item. If this solution happens to be metal (would probably be chosen as such for engineering reasons), it is actually easier (not cheaper) than if it were plastic. A bespoke and complex metal enclosure doesn’t usually require special tools. What will require though is detailed design and manufacture by a competent machining company. ANR Ltd can provide such services.
- When there is a need for high volume, low manufacturing cost, and aesthetics well suited to the given application and market, it is very difficult to beat injection moulding. The problem is that there is a complex design process and very expensive tooling involved. The tooling will cost tens of thousands of pounds, which is usually little compared to the costs of designing and commissioning a plastic enclosure via injection mould. The advantage is that a beautiful, tuned to purpose enclosure that is very cheap results, but there must be very significant volume so that payback on tooling and design is quick. This topic is definitely one on which expert guidance is necessary. 3P1 is a company that can provide this.
What types of enclosure are suitable for prototyping?
These days, the universal answer is 3D printed ones. 3D printing is so flexible that it perfectly lends itself to prototyping, and it is even possible to get metal 3D printed parts. Machined metal parts or the types listed in the first 3 bullets of the former section can also be considered. On top of this a technique called SLA moulding, which has been largely supplanted by 3D printing, can be used. It is recommended that expert advice is sought on this section unless the prototypes are conceptual and have no need to be presentable, in which case any standard enclosure will do. Advice on anything in this section is available from 3P1.
How do I balance the needs of fit, form and function?
The fit, form and function of a device are different elements of design that must receive focus. There is no point in designing/using an enclosure that will not withstand service conditions, but equally a design that is costly because it’s over-engineered is likely equally pointless.
- Fit: obviously any contents of the enclosure must not only fit but have all outward facing elements precisely positioned – LEDs, switches, screens, etc. The important issue to get covered is requirement. Does the device need to be as small possible? If it does it is known in the electronics industry as a shoehorn design that will require iterative and expensive design work between mechanical and electronics disciplines. It is understood that some products need this, but it is very necessary to be aware the cost, time and risk factors all increase once this is demanded. If the design doesn’t need to be as small as possible, be very sure to remove this as a requirement from specifications – significant cost saving. Also, note that even when a design does need to be a shoehorn, it may make sense to make early prototypes without placing size restrictions on the process – can be quicker because basic functionality is more quickly achieved before later iterations work on minimisation. 3P1 is a good company to discuss this with.
- Form: Does the design need to look exceptionally good and be crafted such that its use blends seamlessly with its form? If the answer is no, make sure the enclosure type picked from the first section doesn’t apply onerous product design demands. If it is yes, a product design company will be required to take the design through a full conceptual phase before the details for prototyping and injection moulding are started. It is advised that product design experts are approached for this (3P1).
- Function: There are a multitude of requirements that could affect the use of an enclosure, so the list below endeavours just to state the most common:
- The device may need to be proofed against water or other material to varying degrees. This is covered by the IP rating system – just specify the IP rating the design requires in the specification – definitions of IP ratings. Pick only the level that’s needed – over specification adds to budget.
- It may be necessary to ensure the enclosure is safe for use in hazardous areas. This can be partially or completely covered by the enclosure and connector systems chosen. The specifications that are relevant are ATEX and SIL. A requirement to work in a hazardous environment is usually demanding -Click CONTACT to have the EM give direct assistance with this.
- R.F. (radio frequency) performance may be important. Wireless signals don’t propagate through metal. If a wireless system (say Bluetooth BLE) is implemented inside a metal box with cut-outs as outlets or an external aerial, there is a risk that the wireless will not work particularly well because propagation through the metal enclosure is not efficient. Plastic enclosures are normally used for products that have a need to transmit wirelessly. Click CONTACT to have the EM give direct assistance with this.
What is the best kind of user interface (UI) for the enclosure?
The advent of Bluetooth, WiFi and other easily accessible wireless technology has improved the options and economy of bespoke user interface design on embedded products. The list below gives ideas for hardware implementation of UIs and discusses advantages and disadvantages.
- The traditional and basic interface type is made up of momentary buttons, switches and LEDs, with screen print on the enclosure covering the definition of buttons. This remains an option, and may be the quickest and best one for early prototypes, but wireless options following give the option to remove the user interface on the product and transfer an enhanced form of it to a smart phone, tablet or computer.
- Touch screens can be used on a product, but the efficacy of such solutions must be challenged because the same can be achieved by via remote wireless interface.
- Membrane keypads took a bit of a hit with the advent of the touchscreen, but applications requiring quick resolution and physical robustness still find application through membranes. RHT is a good source of these.
- One of the most significant movements in the market over the last decade has been the use of wireless technologies to remove user interfaces to smart phones. This transfers the cost and responsibility of user interfaces to client. It is very neat and reduces the manufacturing cost of the product.
The EM would be delighted to give you further guidance if you need it – please click CONTACT US and we’ll take it from there.
