Key Considerations for Custom Prototype Manufacturing: Materials, Process, and Development
Isaac Maw posted on November 22, 2019 |

In today’s competitive markets, companies must respond to market demand instantly and find ways to speed time to market in order to survive. Across industries, design and manufacturing engineers need custom prototypes for fit check, testing and other technical and business purposes. Prototyping is an important part of the product lifecycle.

But what’s the best way to make and source prototypes? While larger companies may have the resources to produce prototypes in-house, smaller companies and design firms may not have the equipment and expertise required to manufacture single prototypes or small runs of parts. Global manufacturing service bureaus such as Shenzhen-based Wayken Rapid Manufacturing, which specializes in prototyping services and short-run manufacturing, are one option for small and medium enterprises.

When manufacturing prototypes, it’s important to consider the materials and process technology to use for each project. While some prototypes, such as functional or engineering prototypes, must be made of the same material as the production part, other prototypes—such as those for concept or presentation—may be made of a lower-cost or faster-to-build material or process.

What Materials are Used in Prototyping?

While some prototypes must be made of the same material as the final production part, different materials may be used for prototypes in cases such as presentation prototypes, where strength, stiffness and other material properties are not necessarily required.

Machined aluminum and steel parts are often made for automotive assembly prototypes, for example, as well as any prototype which is required to closely simulate the appearance and function of the production part.

Urethane Resins

For urethane casting, a wide variety of urethane resins are available—from soft elastomers to rigid resins. Optically clear resins are available and commonly used for automotive lighting prototypes. A range of colors and Shore hardness are possible. Urethanes can even simulate engineering plastics such as ABS, PMMA, PP and PA. Glass-filled resins are available for high toughness, and even properties such as impact, fire and heat resistance.

Because of this wide range of properties and options, urethanes can be an excellent choice for prototype parts which closely resemble injection molded production parts, at a lower cost.

How to Choose the Right Prototyping Techniques

Today, inexpensive desktop 3D printers are often used to produce concept and design prototypes, but these parts may lack the strength, quality and other functional characteristics of production parts. For plastic parts or other custom prototypes, urethane casting, vacuum forming, low volume injection molding and even CNC machining are often a better choice.

CNC Machining vs 3D Printing: Which is Better for Your Prototyping Process?

The most obvious difference between these two manufacturing technologies is that 3D printing is capable of building geometries that are impossible or impractical to machine, such as curved deep holes, interior square corners or fully enclosed hollow sections. CNC machining, on the other hand, offers speed and accuracy.

Aside from these designed-for-additive manufacturing features, it can be difficult to identify the most effective technology for a given prototype.

CNC machining has a much faster cycle time per part than additive processes, but this is far less important for low-volume production and small batch prototypes than for mass production. CNC machining is capable of very high accuracy and fine surface finish. Prototyping using CNC machining also allows engineers, machinists and tool path programmers to optimize the design for efficient manufacturability, ironing out the kinks in the translation from CAD to CAM to cutting metal. If the production part is to be machined, a CNC made prototype may reveal secrets useful to tool path programming of production machines.

Of course, CNC machining technology is used in the process of other manufacturing techniques, such as moldmaking and toolmaking. For parts that will be produced via these techniques in final production, prototypes may simply be machined directly from metal stock, saving time and avoiding multi-step processes.

Additively manufactured parts by a variety of processes, including FDM and SLS, may have a rough surface finish which limits the accuracy of features such as mating surfaces or holes. The roughness of the surface may also be a factor, especially when a high gloss finish is needed for cosmetic purposes. Many additive parts, especially in metal materials, require machining as a secondary operation after printing. SLA printing typically delivers a much more precise finish due to the low layer height of deposition, but this depends on the scale of the part and the printing parameters.

Consider the geometry and functional requirements of the part: if a part is blocky, made of basic shapes and with features like holes and flat surfaces, machining may be best.

If a part is complex, would require multiple CNC operations to complete, and would not require post-processing after printing, it may be more cost-effective to 3D print it.

Urethane Vacuum Casting

Vacuum casting is a fast, inexpensive way to produce prototype parts that will, in final production, be made via plastic injection molding. This process should be considered when a small batch of plastic or resin prototype parts are needed.

In urethane casting, a mold master is first created via CNC machining or SLA. Because this casting method transfers fine details and surface finish from the master mold to the cast parts, precision machining may be needed to produce a fine surface finish on the master. The master mold is then suspended in a box with gates, vents and risers attached. Silicone is poured around the master and cured in an oven. The resulting mold can be used to produce 10-20 parts depending on the complexity of the part and the quality and surface finish requirements of the prototypes. If more parts are required later, the master can be used again to make new molds.

Low Volume Injection Molding

Injection molding uses a metal machined mold capable of making volumes ranging from hundreds to hundreds of thousands of parts. It is a high-labor, skilled task; low volume injection molding requires an investment of time and money into cutting and polishing the mold. For small, low-volume production runs, this investment is not amortized across a large quantity of parts. So, why use injection molding for prototypes?

In some cases, a prototype must be made using the same production technology as the finished part. This ensures that the design of the part is manufacturable and free of design defects, preventing delays and rework during production. It can also validate the material choice and help the molder establish initial parameters for the production run, such as melt temperature, masterbatch validation and cooling strategies.

Prototype to Production: The Role of Prototypes in the Product Development Process

Effective prototypes can provide many benefits in the product development process. They can be used as part of an iterative design process to realize and explore concepts. Proof-of-concept prototypes can help build product ideas into a manageable scope while working to establish the critical details and fully understand the design intent at the beginning of the product lifecycle, especially when working with an external client or contractor. A physical prototype is a powerful communication tool. This can help a project move forward with clear, actionable feedback on design, manufacturability and product lifecycle considerations.

Functional prototypes, on the other hand, can be used to test design iterations in applications such as fit check and performance. This can reveal issues to be corrected before the design is finalized, reducing business risk and improving quality during the prototyping services. Functional prototypes can be made in several versions, with low cost commodity materials used for fit check and form validation and smaller numbers of test articles made with more expensive, production equivalent materials. At this stage, functional prototypes may be used to validate alternate materials to those originally specified, whether from a new raw material suppler, or as a substitute material to lower cost or improve performance.

Accurate, low-cost product prototypes help designers and engineers verify the design, engineering and manufacturability of the product before running into issues during full production, which is costly and causes delays—especially if issues are discovered after a significant investment in tooling or molds. This helps get the product to market faster.

Faster, high fidelity, cost-effective prototypes, including functional and design prototypes, are an essential tool for the engineer and designer to improve and optimize designs and ensure production goes smoothly. A little money spent here can pay big dividends later.

To learn more about prototype manufacturing services, check out WayKen.

WayKen Rapid Manufacturing has sponsored this post.  All opinions are mine.  --Isaac Maw

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