Prototyping is one of the most important steps in the product development process. Prototypes allow product developers to find design flaws and/or test different design options quickly by providing tangible models that can be evaluated for form, fit, and functionality before committing to full-scale production tooling. Different types of prototypes can be used during different phases of the project, including clay mock-ups, 3D printed parts, machined parts, and cast and injection molded parts. Due to advances in the speed of mold fabrication, prototype injection molding has become one of the most popular methods of producing both functional plastic prototypes and visual concept models in any design phase due to its ability to accurately replicate final production parts on a short timeline.
Selecting the right prototype injection molding tooling requires navigating the inherent tradeoff between speed and quality. Generally, the faster a prototype mold can be produced, the lower fidelity the parts are to final product specifications. On the other hand, while achieving extremely precise prototypes is the best option for advancing the design, producing high-quality prototype tooling adds time and costs to the iterative design process.
Finding the right balance depends greatly on the priorities and objectives during the development phase. Understanding these tradeoffs allows product developers to produce prototypes that meet their needs in an optimal time frame without either overspending on unnecessary precision or working with inadequate approximations with low-fidelity prototypes. The key is aligning the quality and speed with the purpose of each round of prototypes. This article explores the factors influencing both speed and quality in prototype tooling and how to find the right balance.
Factors Impacting Prototype Tooling Speed
Complexity
The complexity of the mold design directly correlates with the machining and assembly time required before prototype parts can be molded. Intricate molds with multiple cavities, side actions, or complex geometries necessitate longer manufacturing lead times than simple, single-cavity open and closed molds (see Part Design).
Durability
The durability of the mold material also impacts production speed. Prototype molds constructed from less robust materials, such as 3D-printed resins or soft metals, are faster to produce but may degrade more quickly, limiting the number of cycles before the part geometry starts changing. This may be acceptable, since prototype runs are usually in the hundreds or thousands; these types of molds are durable enough to produce these quantities..Conversely, molds machined from hardened steel offer extended lifespans but require additional fabrication time. When tens of thousands of parts are needed for an extended user study, this type of tooling may be required.
Part Design
Part complexity is another significant factor affecting prototype injection mold fabrication speed. Designs incorporating undercuts, threaded features, or small features increase the intricacy of the tooling and the associated manufacturing time. Features that cannot be created in the primary mold cavities in the direction of the mold opening must be created using slides or core pins, which take time to fabricate. Deep, thin ribs cut into the tool require the use of small diameter, long cutting tools and extended machining time. The bigger the cutter that can be used, the faster the mold can be made. Avoid small radii when possible (< 0.016”) and think about the spacing of features and the size of the tool required to make those features in a mold. Simplifying part designs, particularly in early prototyping stages, can optimize injection mold fabrication time and reduce production timelines.
Precision
If a prototype part must meet strict tolerance specifications, then a machined prototype injection mold is preferred. Aluminum or brass mold cavities are usually sufficient, but fragile mold features, such as long, small diameter pins, may need to be inserted as stainless steel features into the mold to increase robustness. Molds printed in aluminum or stainless steel are not strong enough for small features, must be polished post-printing, and therefore, cannot be expected to produce parts that require precision tolerances.
By carefully considering these factors and making strategic design decisions, product development teams can minimize mold fabrication lead times, optimize injection molding cycles, and accelerate the prototype tooling process while still achieving the required part functionality and quality.
Factors Impacting Prototype Tooling Quality
Material
The material used for the mold significantly affects the quality of the surface finish. Surface finish is essential for visual models and user interaction points but less critical for prototypes intended to test structural integrity or function. However, if high-polished parts (SPI-A1) are required, the mold must be fabricated in stainless steel (SS). A mirror finish is impossible with 3D-printed mold parts, and only SPI-A2 can be achieved with aluminum tools. Selecting the right mold materials can still emulate tactile feels and visible quality, while post-molding treatments can further enhance surfaces.
Molding Press
Measurement variability affects the consistency of each shot in a prototype run. While tighter process controls and appropriate machine parameters can enhance accuracy and repeatability, hobby injection molding machines often struggle to maintain part tolerances due to inconsistent parameters. Achieving repeatability requires high-quality production molding machines with tightly controlled parameters. Striking the right balance involves optimizing resin selection, machining methods, and process tuning steps to enhance quality, even if it extends timelines.
Finding the Right Balance Between Speed and Quality
Finding the optimal balance between speed and quality in prototype injection molding tooling requires strategic decision-making around project goals. The product development team must align on clear objectives for each prototyping round. Some rounds may prioritize visual models to assess industrial design concepts or ergonomics. Others may focus on functional prototypes, aiming to demonstrate real-world viability on critical features, even if cosmetics are crude.
An assessment is needed around must-have quality attributes versus those that can be sacrificed for expediency. Factors like rigidity, strength, and durability often cannot be compromised, even for prototypes. However, perfect color matching or mirror-polished chrome finishes may be unnecessary until production tooling. Keeping prototypes as fast and affordable as possible while achieving core goals for the phase should be the goal.
Creating critical function prototypes is another way to help de-risk areas of uncertainty within the overall project. For example, instead of investing in detailed housing molds solely to evaluate how assembly snaps work, a simple mold can be created with snaps on a simple support structure that mimics the housing but with minimal detail. This approach saves significant mold fabrication time while still allowing thorough testing of the critical functionality, ensuring that design uncertainties are resolved quickly and efficiently.
With priorities set, reasonable schedule expectations can be built, factoring in part size, complexity, batch sizes, and service shop bandwidth availability. Then, as prototypes are evaluated after each round, the team can adjust levers like design revisions vs. mold rework needs, surface finishes, measurement standards, and testing criteria to reassess the right speed and quality balance for the next phase. Finding this equilibrium enables affordable progress between the initial concept and full production release.
Optimize Speed & Quality with Protoshop: Your Injection Molded Prototyping Partner
If striking the right speed vs quality balance for your next injection molded prototypes seems complex, don’t go it alone. Partner with the knowledgeable Protoshop team to fast-track learning critical information about your product designs, no matter the development phase. We build high-quality aluminum molds in 3-5 days and mold parts within 1-2 days. Reach out today to learn more about our services that balance your need for speed with must-have quality standards.
