In a previous article about the quality standard for prototypes, we explained why most development prototypes don’t need to look as good as mass-production products. Those early prototypes are useful for validating the product’s ability to “do its job”, to confirm that users like the general form factor, and so on, but they are generally not used to sell to a wide audience.
(There are exceptions, of course, such as the samples used for a crowdfunding campaign video, to be used by a sales force to pre-sell to retailers, and so forth.)
In this article, we will start from two examples – one about a plastic part, the other about a metal part – and we will explain what the typical limitations of prototyping methods imply. In short, achieving the intended effect before production processes are used can be near impossible, and it can lead to heavy extra costs.
1. A product that has a plastic enclosure
During product development (before tooling is produced), making prototypes look good means they have to be 3D-printed, polished, and painted by the engineers. And, even then, there are different levels of visual quality:
- Thin layers of paint will be better for dimensional control (and the ‘fit’ between the plastic parts), but the color may not be exactly what the customer wants.
- Thicker layers of paint provide a color closer to what the customer wants, but the parts are physically larger and it comes with its issues.
- High requirements of finishing quality often require the engineers to apply paint, remove it, and so on until the desired effect is reached. That’s a very time-intensive process.
The need for paint disappears once the plastic injection molds are ready, as the plastic polymer is mixed with pigments. Once the initial setup is done, thousands of parts can be injection molded with exactly the right color, without the need for systematic rework.
2. A product that has a cast metal enclosure
During product development (before tooling is produced), prototypes can either be produced by conventional 3D printing processes such as SLA, SLS, and FDM and even 3D metal printing or with the use of CNC machining. All of these come with their own set of issues.
Development prototypes produced by 3D printing
- With conventional 3D printed processes that are resin or plastic-based, the prototype will only be good for a visual representation, as it will not have any of the mechanical properties associated with a metal product.
- 3D metal printing can have lower dimensional accuracy and surface finish compared to die casting due to factors like layer lines, shrinkage, and support material removal. This can lead to issues with functionality and assembly.
- 3D metal printing will not have the same mechanical properties as a pressure die-cast part and this could create issues with product testing and validation showing early failures on certain functional tests.
- 3D-printed parts often require post-processing like heat treatment or machining, adding cost and complexity. Die-cast parts typically require less post-processing.
So as you can see, producing prototypes via 3D printing, either plastic or metal, will come with limitations if you are trying to compare them against the final production method.
Development prototypes produced by CNC machining
Prototypes produced by CNC machining will be machined from a solid block of metal that will have the mechanical properties of the final product. We also need to consider the limitations and issues that come with this process:
- CNC machining offers exceptional flexibility in creating complex geometries due to the computer-controlled toolpath. However, intricate designs with internal cavities or undercuts might require multiple setups or specialized tools, increasing complexity and cost.
- In some cases, the complexity of die casting may not be possible with CNC machining due to undercuts and cavity geometry that would be possible in a die-cast product.
- CNC machined parts often require post-processing like deburring, polishing, and heat treatment depending on the desired finish and functionality. This adds cost and time to the process.
- CNC machining typically generates more material waste compared to die casting, making it less environmentally friendly.
- While faster than die-casting tooling, CNC machining lead times can still be longer than production due to programming and machining setup.
Limitations of development prototypes and considerations for you
Both plastic and metal development prototypes come with limitations compared to their final production counterparts. Here’s a breakdown:
Key limitations of development prototypes
- Dimensional Accuracy and Surface Finish: Prototypes, regardless of the method (3D printing, CNC machining), often struggle to match the precise dimensions and smooth finish achieved in mass production methods like die casting or injection molding. This can impact functionality, assembly, and visual appeal.
- Material Properties: While CNC machining offers closer material representation, prototypes often lack the exact mechanical properties of the final production material due to limitations in the prototype process itself. This can lead to misleading results in functional testing and validation.
- Production Volume and Cost: Prototype methods like 3D printing and CNC machining are typically slower and more expensive for larger quantities than mass production methods. This can hinder cost-effectiveness and production timelines.
- Design Complexity: While offering flexibility, CNC machining might not be able to replicate the intricate geometries achievable with die casting due to limitations in tool access and undercuts.
- Post-Processing: Prototypes often require additional finishing steps like painting, machining, or heat treatment, adding cost and time compared to the minimal post-processing needed for production parts.
- Environmental Impact: CNC machining typically generates more material waste compared to die casting, making it less environmentally friendly.
- Lead Time: While faster than die-casting tooling, CNC machining lead times can still be longer than production due to programming and setup requirements.
Considerations
- The ideal choice between prototypes and production methods depends on your specific needs and priorities. Consider factors like required volume, accuracy, material properties, budget, and design complexity.
- Prototypes remain crucial for early design iteration, visual representation, and limited testing. However, their limitations highlight the importance of transitioning to production methods like die casting or injection molding for accurate testing and mass production.
In short, you need to ask yourself, ‘do we really need the prototypes to look & feel nice, or can we wait until the tooling is ready?’. If you really need look-like samples with a high standard of finish and/or dimensional accuracy, expect costs to escalate quickly.
Remember, our product engineers are happy to give you some no-strings advice about your product in development and explain how we may be able to help you, too. Just get in touch and let us know.
