Part 2: Prototyping considerations for the move to low-volume production
Once prototypes have been validated in terms of fit, form, function and aesthetics, development can move to low-volume production. This stage of manufacturing consists of batches of parts that range from 50 to several hundred of several thousands, scheduled to match production needs, providing parts that are delivered to meet fluctuating demand. For certain projects, low-volume production can be the actual, and final, method of production.
1. Do your parts produce useful insights?
A designer’s main concern at this stage should be to have parts produced that provide useful insights in terms of fit, form, and function, but which are also optimised for manufacturability. It’s one thing to have a physical prototype that confirms that a part or product will perform the intended task, and quite another to have a physical prototype where the means of producing it have been optimised for manufacturability.
2. Why optimise for manufacturability?
For low-volume production, a primary aim of optimised manufacturability is to tweak prototype designs so that moulding tooling can be manufactured more quickly, or more cheaply—or both, in conjunction. In addition to these tooling considerations, a manufacturer will usually want to achieve optimised mouldability, as well. Potentially, for instance, a small change to a mould’s draft angle can deliver significant improvements in part ejection and therefore both surface finish and strike rate.
How to achieve this optimisation? In an ideal world, a manufacturer’s choice of prototyping and low-volume production provider will have taken this requirement into account, and selected a provider that can offer both insights delivered through human-based application engineering skills, as well as automated tools that can cost-effectively provide an initial rough-cut optimisation analysis automatically, without human intervention.
3. Can design optimisation be automated?
Indeed, in many cases, it can prove possible for automated design optimisation tools to completely deliver a degree of optimisation that is perfectly adequate for low-volume production. Usefully, when such tools are delivered through high-powered compute clusters, this optimisation can be achieved at minimal delay to the part production process—which is usually important, as achieving a rapid time to market remains a primary objective.
At Protolabs, for instance, when designers upload a 3D CAD model to the website, a quote is returned within a few hours which highlights detailed sections of the model that are in need of draft angles, and which even offers suggested changes to improve the draft on those sections.
Rapid injection moulding works by injecting thermoplastic resins into a mould, just as in production injection moulding. What makes the process “rapid” is the technology used to produce the mould, which is often made from aluminium instead of the traditional steel used in production moulds.
Moulded parts are strong and can have excellent finishes. It is also the industry standard production process for plastic parts, so there are inherent advantages to prototyping in the same process if the situation allows. Almost any engineering-grade resin can be used, so the designer is not constrained by the material limitations of the prototyping process.
Typically, an intelligent prototyping strategy will reflect on both the rate at which the project is expected to ramp up to low-volume production phase, and the time—or rather, total output—that this phase of production is envisaged to take to complete.
Often, the production rate takes on greater significance during low volume production, and as aluminium tooling does not retain heat to the same extent as steel tooling, mould tools are both quicker to reach temperature, and allow faster cooling prior to ejection or release, potentially leading to a higher output rate.
And given that well made low-volume or ‘bridge’ aluminium tooling can last for thousands of cycles—with some tools capable of producing over 200,000 parts—it definitely makes sense for manufacturers to view such tooling as a viable alternative to more expensive steel tooling. Steel tooling may be required eventually, but there is little point in discarding perfectly serviceable aluminium tooling, if aluminium can do the job well indefinitely