Product design brief
The client is a manufacturer of rugged PPE and fire-fighting equipment containers for the Offshore energy and commercial marine sectors. The client saw an opportunity for a high quality fire hose cabinet for use on commercial ships, where the market was currently swamped by low quality glass fibre cabinets. The client wished to use injection moulding to create a robust, attractive and cost effective product which requires less time and effort to assemble than GRP or blow-moulded containers.
Injection moulded boxes of a similar scale to the proposed product generally fit into two categories. The first category is thin walled storage boxes, designed to be economical to produce, but not structurally strong or durable due to the limited stress they will be subjected to. The second category is ‘mil-spec’ storage boxes and flight-cases. These are incredibly tough, but contain a large volume of plastic within large wall thicknesses and multitudes of ribs and buttresses. These flight cases are expensive to produce and their material volume means that they are only manufacturable by a very limited number of moulders. HPDL were required to strike a balance - structural rigidity while using only a limited amount of material in order to be economical to produce.
The design stage
A definition for a minimum internal volume for the cabinet was required in order to ensure that the product was fit for purpose after material reductions had been undertaken. This was achieved using physical test rigs where the contents of the cabinet were placed inside a unit with adjustable internal walls. Test subjects of a variety of ages, heights and strengths were recorded approaching the cabinet and removing the contents. This served to identify common behaviours which should be allowed for, as well as verifying the suitability of the chosen cabinet volume.
Hillside Product Design used FEA extensively to assess structural rigidity and identify any potential stress or failure points. This enabled the design to be optimised while incrementally reducing material volume to within manufacturer specified limits. FEA-derived deflection values showed how much the walls of the cabinet would deform and deflect under load. The design was altered until the deflection was within acceptable ranges which could be mitigated for with gaps between door and base while still presenting an obstacle to water ingress – a factor which may cause corrosion and damage the items stored within.
Following the design and material reduction stages, a full-size prototype was sourced which was as close as practicable to the final specification. This required HPDL to find a supplier who was able to prototype the two principle components from single billets of material in their entirety. This was to ensure that the walls of the cabinet prototype would behave similarly to moulded parts, something that was not guaranteed if walls contained joints or welds between segments.
The prototype was reviewed with the moulding supplier and optimised using DFM and mould flow analysis. Hillside Product Design were actively involved in reviewing the tool design and tool sampling to ensure that the design intent was preserved and the client received parts which met their specification.