Unfortunately, production prototypes are often expensive, and approaches to their development have not always kept pace with other areas of design, engineering and manufacture.
The accurate manufacture of prototype parts and assemblies is vital for almost every engineering sector. In most instances, the prototype will be the only component subjected to every testing and performance validation procedure, which ultimately influences key decisions on design modifications, published performance attributes, warranties and service intervals.
At this stage, consistency and accurate process documentation are key. In the testing stage, for example, it’s important for prototypes to remain as faithful to the original design as possible. Any deviations – whether in shape, thickness or material – can render test results unreliable, or even invalid.
These results are vital to the progression of a design, which is why they need to be as accurate as possible. If not, individual parts, or even the whole assemblies, must be examined, remanufactured and reconfigured, all of which can lead to substantial delays and additional costs. Worse still, if inaccurate data is carried forward into the next stage of production, the ramifications can be severe: from a shortened service life or a failure to meet warranted standards, to a catastrophic failure while in service. For these reasons, a prototype must be the best and most accurate part a company ever produces.
The problem with prototyping
Unfortunately, this field has not always received the attention it deserves. This could be for a variety of reasons. For one, production prototypes are often expensive, particularly when you compare it to the cost-per-unit of the component in its final form. There has also, arguably, been an inconsistent approach to prototype development, which has meant that it has not kept pace with its design, engineering and manufacturing counterparts.
Unlike the mass-production of finished parts - which involves detailed operations sheets, photos, precise written instructions and guidance on correct handling and fixing – prototype assembly often works based on a CAD representation at best. As a result, quality and repeatability can suffer. With most projects working to strict deadlines, re-engineering a component at a later stage incurs project delays and budget overruns
Why, then, has the manufacture of prototypes been so neglected? Traditionally, prototypes have been prioritised and progressed according to timeframe. Product development and project managers tend to focus on ensuring that all the required components are available by a certain date. In the worst cases, only once the components have arrived do engineers start worrying about how, and indeed whether, these components will fit together.
The number of tolerance and assembly issues identified at this stage is higher than many would care to admit. Fixturing can also cause problems, because investment in adequate workholding equipment when adding remaining components is often the first to go in the drive to reduce project costs. This is, of course, a false economy: awkward working processes caused by incorrect fixturing can result in both damage to, and sub-standard assembly of, the prototype.
A solution to the prototype problem
It’s clear that prototype development needs a new approach. By focusing on wider objectives of getting a product to market and into production, the solution is challenging but achievable.
Each step in the prototype manufacture and assembly process must be driven by the objectives of final production. Overall risk, cost and time can be reduced, while increasing the chances of accurate production, reducing final assembly time and lowering the cost of re-work.
Production Oriented Prototyping (POP) is a novel approach to prototype development that involves both the individual component and full assembly designers from the start of the application development phase. The aim is to build production standards into the prototype, while minimising cost and delivery time, as well as optimising safety.
Using virtual builds, simulation and validation via CAD, manufacturers can ensure that all the components fit together for each design release and can be accessed and manipulated during the build. Any issues with component compatibility, design or accessibility can be tackled at a much earlier stage and, crucially, before time and money have been invested in one-off component manufacture for the prototype.
Using this methodology, the team can develop operation sheets as they go, making the final assembly process easier and more intuitive. Fixturing and work-holding are also considered at an earlier stage, meaning that manufacturers have more time to specify and produce a bespoke system, if required.This is especially true when dealing with larger or more complex assemblies, which do not lend themselves to easy movement or manipulation.
In effect, assembly process design – including process, flow, tooling and fixturing – is completed before the physical components are ready to be assembled.
By adopting this holistic approach, it’s easier to identify and fix issues faster than would be achieved during final assembly, with programme time savings of over 25% often achievable.What’s more, the extra efficiency afforded by POP allows assembly technicians to identify cost reduction opportunities for components and processes through ‘practice runs’ for future assembly.
Productiv has been developing and testing this method, and the results have been impressive. In one instance, we were able to reduce the assembly time for the first prototype build of a complex transmission for an automotive manufacturer from their typical eight weeks, to just eight days.
The benefits of the POP approach can be applied in any sector for which precision and replicability are vital to enable accurate testing and validation. In fact, any engineering business can achieve lower costs and a faster route to market. We hope this will finally give prototypes the attention they deserve.
About the author
Alan Francis is head of supply chain and operations at Productiv