Putting the cart before the horse… why early enclosure selection ensures efficient product design

Our experience shows us that design engineers tend to follow a logical sequence when a new product is being designed. It goes something like this: first there is the brief, then the design, sourcing components for the assembly and then finally finding a housing to enclose the whole lot. Although this seems reasonable, by actually following this sequence many things can start to go wrong, just when time is of the essence and pre-production is about to take place. Paul Raynor, JPR Electronics, explains

What if the final assembly is too big for an available enclosure? Diecast enclosures are invariably more expensive as the depth required increases. The die required for a deep casting is not easy to create and such manufacturing tools are invariably a high cost item; even when amortised over the final selling price of the casting. A tall assembly limits the choice of enclosure, increasing the time required to find a suitable housing. A larger box than actually required means paying extra for unnecessary space, a smaller box may need a circuit or component redesign. More time, more money. Some equipment manufacturers choose to make their own custom tooling, adding time and expense to their production costs and increasing their risk if the product doesn’t sell well.

What if all is ready to go into production but the chosen enclosure isn’t in stock and has a long lead time? Only limited options are available: choose an alternative enclosure with possible redesign of components or simply wait until the stock is available. Both choices entail frustration, delays and possibly lost sales.

What if the chosen enclosure is cheap, the right size, readily available initially and then either loses quality or is no longer available once full scale production of the project is taking place? Company credibility suffers when explaining to clients and their end customers that their heavily promoted product has to undergo changes in size, shape and cost.

What happens when it is discovered that the IP rating, the flammability rating or EMC rating of the project design depends on a special enclosure? Enclosures with special ratings have correspondingly high prices and should be included in the budget from an early stage.

These are all typical examples of what I call “putting the cart before the horse.” I suggest trying a different scenario, designing from the outside – in, where choosing an enclosure comes right at the very beginning of the process of product development. Once the brief is decided it will be known whether the enclosure needs to be weather proof, have special IP or flammability ratings.

Once the type of enclosure is decided, the next step is to choose an ideal size for the product and design to fit the box. The process becomes infinitely more efficient and cost effective.

By making early decisions over enclosures any customisation can be agreed and time and money can be saved. By designing circuitry to fit the enclosure, costings are already in place and sizing of the product is already well defined. Changes can be implemented if necessary either to the circuitry or to the enclosure while there is still time but when the enclosure is deemed satisfactory, it can be ordered ahead so that production can proceed without time lost waiting for stock to arrive.

Of course, it is important to ensure that there is reliability of quality and continuity of supply. Cheap may be attractive initially but as many OEMs have found to their dismay, often cheap items may have a quality problem or simply don’t appear once production is underway. If the customer is willing to place a scheduled order, they will ensure that buffer stocks are held for the customer to be delivered as and when they are required. JPR only work with reputable, well established suppliers who are able to produce quality products over the long term, hence their growing relationship with Hammond Manufacturing.

JPR directors, Paul Raynor and Melissa Jaques

JPR’s close working relationship with Hammond along with their excellent facilities in guiding customers, help them to make the right choices early on in the process. CAD drawings of enclosures are easily downloaded so that specifications can be integrated right from the beginning. Machining, printing and drilling are carried out in the factory, all saving time and money.

We have found that by working together with our customers and key suppliers like Hammond from the start of a new product, design and production times are optimised. There are less false starts and frustrations and the end product is on time and on budget. The horse and cart are a team, not just separate entities.

By taking a holistic approach to design it is common sense to choose first the item that is the most difficult to alter at a later stage. It is a fallacy to assume that in the last stages of the project design, it will be easy to find an appropriate enclosure from the thousands available. Decision making at this point is time consuming and often fruitless. While components and circuitry can often simply be reorganised so that internal form alters while still maintaining function, the enclosure can only remain static.

The moral is, of course, to choose the enclosure first.

www.jprelec.co.uk

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