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PSM Water Level Alarm/Indicator

PSM Instrumentation is a UK designer and manufacturer of specialised process measurement and control instrumentation for the Marine, Chemical, Water and Food & Beverage industries. Their unique Water Level Alarm/Indicator provides a simple, robust and reliable solution where an immediate visual warning is needed of the possible hazards of flooding, for example in underground high voltage sub-stations.

Their requirement was for 8,000 units, and whilst 3T RPD Ltd are specialists in the fast, accurate production of one-off prototype components, they also offer the economical manufacture of small series parts as final products; namely Rapid Manufacturing. Using Selective Laser Sintering (SLS) technology, Rapid Manufacturing is a fast, flexible and cost-effective method of generating otherwise 'impossible' end-use parts directly from CAD data, with no tooling required.

PSM's design consisted of a multi-component unit of four parts requiring subsequent assembly, together with an integrated magnet, and sealing at one end to make it waterproof.

Float Body, Lid & Reed Switch Housing	Assembled float

The physical attributes required by the main housing took full advantage of the SLS process, as it enables part design to be unconstrained and functionality-led. The float housing could be built in one piece as the 'selective' nature of the SLS process enables complex geometries to be achieved, such as holes and cavities, with the 'unsintered' or loose material simply being removed and recycled for future use. The internal workings incorporated undercuts, levers and living springs essential to its mechanical function.

Float assembly with reset levers (cut)

The design required a lightweight production material to aid the buoyancy of the product. The Nylon used in the SLS process proved ideal, and the ease with which the parts could be assembled enabled the unit to be sealed and made waterproof without any additional post-processing work.

When the float rises with incoming floodwater, the internal spring mechanism 'latches' at the highest recorded level. The flexibility and 'spring-like' action of the SLS material enables the latching function to work extremely efficiently. Furthermore, the float needed to be of high visibility, so 3T's revolutionary colouring process was used to colour the parts a bright orange and yellow. Requiring no surface dressing, functionality of the part is unaffected whilst giving a high visual impact.

(L) SLS part    (R) Part after colouring

3T produced the parts in batches of 1,000, with the smaller components being built on a laser sintered 'bridge' so that all the individual pieces were held together, making the break-out of the build and removal of the surrounding powder much easier.

Parts built on a laser sintered 'bridge'

Sean Lane, Technical Support at PSM Instrumentation Ltd, says "SLS was the preferred method of manufacture as due to the shape of the components it would have been too expensive to have them machined from anything solid or cast, and the leadtimes would have been much longer than offered by 3T's technology. The parts also needed to be very lightweight to aid the buoyancy of the float mechanism, and the nylon material lent itself perfectly to this application. The durability of the components was important as the location and installation of the equipment required them to be extremely strong, and SLS again provided these qualities."

Fully assembled unit	Unit in situ

The use of Rapid Manufacturing for this particular application proved extremely successful, resulting in a convincingly attractive product that is fully functional and durable enough to be used as a production part in its working environment.

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3T RPD LTD
Fulton Court, Wofford Way, New Greenham Park, Newbury, Berkshire, RG19 6HD, UK
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