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Gauging accuracy – when you need an accurate part fast

Supplier: Rapid Pro
15 August, 2012

Monitor Sensors is an Australian company that designs and manufactures a full range of meteorological and environmental monitoring instruments.

The prototype: rain gauge bucket

A tipping bucket rain gauge has several components that allow it to accurately measure rainfall. As precipitation falls it lands in the funnel of the rain gauge. The precipitation travels down the funnel and drips into one of two very carefully calibrated ‘buckets' balanced on a pivot.  In order to develop a rain gauge bucket that gives consistent readings of rainfall, it must be designed and produced with an easily repeatable, accurate eccentric mass.

The client: Monitor Sensors

All instruments, data loggers and software from Monitor Sensors are manufactured in Caboolture, 15 minutes north of Brisbane, Queensland.

The rapid prototyping process: fused deposition modeling (FDM)

Monitor Sensors have used several types of rapid prototyping technologies to design and test their monitoring instruments and data loggers. They had previously prototyped this part from 3 metal castings which were made in three separate moulds before being individually stamped and punched through.

The three castings were then soldered together and powder coated. Producing prototypes in metal castings proved to be an inaccurate, expensive, lengthy and daunting process. It took several weeks to produce moulds, was difficult to make design changes, and the minimum order was too high at 50 units.

They moved to 3D printing using fused deposition modeling (FDM) technology to save lead time and to ensure accurate repeatable parts.

With FDM they were able to order the quantity they required (maximum of 10), for a fraction of the cost in only a couple of days — and most importantly, all parts were identical and fully repeatable.

FDM is a popular prototyping process used during the developmental phase of product design as it caters to various design modifications without the need for expensive re-tooling, as well as providing parts quickly and inexpensively for form, fit and function testing.

The prototyping material chosen for the rain gauge was Black ABS-M30 because of its appearance, strength and durability. The prototype was then chemically etched for an improved visual finish and to ensure the part was watertight.

The result

Ralph Loveday, Monitor Sensors' design engineer, said: "The previous version (of the rain gauge bucket) was made from three metal castings which were individually stamped and punched through.

"Repeatability was difficult and the accuracy of the hole locations were sometimes skewed. Our previous process also had minimum order prerequisites that meant that we had to store these extra parts until they were needed if at all.

"We chose RapidPro's FDM technology because it gave us consistent, accurate parts and simplified assembly. For example, we can now use a stainless steel M8 bolt as a standard counter weight. When we used metal castings to prototype, the buckets did not have the same weight distribution due to manufacturing inaccuracies.

"With FDM, the weight distribution is always the same so we no longer need to individually calibrate the buckets to achieve consistent measurements.

"We have been able to shave months off the design cycle, have improved our accuracy and can order fully repeatable parts in quantities that match our manufacturing schedules."