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Prototype Injection Molded Parts – Process Guidelines 

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A Guide to Injection Molding Prototypes

Prototype injection molding is a manufacturing process that involves creating a physical plastic prototype or sample of a plastic product using injection molding techniques. It is a highly versatile and efficient method of producing small quantities of complex plastic parts with precision and speed. 

Prototype injection molding is widely used across various industries to streamline the product development process, reduce design risk, reduce time-to-market, and ensure the optimal design and performance of new products before investing in high-cost, multi-cavity production tooling.

What are Prototypes?

A prototype is a preliminary physical model of a new or revised product or its components. These initial prototypes allow product development personnel to test and refine designs or critical portions of the design before committing to full-scale manufacturing tooling. Prototypes can vary in complexity depending on what needs testing – some might only mimic certain aspects of the end product, i.e., critical functions or form, while others can be fully functional models. 

Why is Prototyping Important?

Prototyping allows the developers to collect feedback from users or stakeholders about the product’s look and feel, functionality, and usability before the public release. It also helps reduce unnecessary costs by revealing areas for improvement, identifying faults and usability issues, and improving team efficiency and collaboration.

Teams build prototypes with varying degrees of fidelity to capture design concepts, perform functional testing, and test them with users. Designs can be refined and validated with prototypes to ensure that the product is viable and meets user needs without wasting time and resources by fully committing to an untested design, building expensive production tooling, and waiting three months for the tooling to be completed, only to find out that the design is flawed. Because of this, prototyping is a cost-effective way to learn early and quickly from failure, promoting innovation and creativity and improving project timelines.

Sometimes in the product discovery phase, the product team has numerous compelling ideas. However, many initial uncertainties exist (e.g., technical feasibility, seamless process fit, user acceptance, etc.). The best way to avoid letting uncertainties drive the decision is to test the concept. Prototyping allows one to test the initial ideas and decide whether to drop them or push them forward.

What Method of Prototyping is Optimal?

Production-like prototypes can be manufactured in many ways, including 3D printing, vacuum forming, casting, machining, and injection molding, to name a few. At the beginning of the design process, 3D printing is the quickest and least expensive way to obtain physical prototypes without expensive tooling costs. 

Three-dimensional printing allows engineers to quickly create a realistic design replica using a computer and printing machine. The 3D parts can be used to identify flaws or areas that need adjustment and can be easily modified based on observations and testing. The prototype file simply needs to be digitally redesigned and the part printed again. 

Machined prototypes are great for making and testing preliminary designs as well. While it is more difficult to machine organic shapes, and some fixturing may need to be built to hold the part during machining, the design can be readily changed after testing and machined again. Other methods require tooling fabrication to create the parts, and if the design changes, the tooling must be modified or re-created.

However, once the initial design considerations are flushed out, 3D-printed prototypes can be limited in their effectiveness. 3D-printed components cannot fully replicate the form and function of an injection-molded part because the materials are not the same, the strength and surface finish are not the same, small features cannot be printed and could break easily, the dimensional accuracy is not adequate, and elastomeric materials are not robust and don’t feel or function the same as molded elastomers. Machined parts contain inherent stresses that change the strength of the parts, can be expensive, and some materials are difficult or impossible to machine. 3D printing or machining can also become costly if numerous parts are needed. 

If the ultimate manufacturing process for the plastic part will be injection molding, an injection molded prototype will likely be needed to fully de-risk the design.

What Is an Injection Molded Prototype?

An injection molded prototype is a production-equivalent plastic part made using the same injection molding materials and processes that will be used in mass production. The difference between prototype and production injection molded parts lies only in the construction of the tooling and the number of cavities in the tool. 

Production injection molds are CNC machined from hardened stainless steel. Prototype injection molds are typically made in aluminum or brass; the metal is softer and can be machined more quickly (and therefore less expensively). While aluminum and brass are less robust than stainless steel over hundreds of thousands of molding cycles, molds constructed in these softer metals will typically still produce tens of thousands of parts and, depending on geometry, can produce many more without sacrificing dimensional accuracy.

When Do You Need Prototype Injection Molding?

Production-equivalent plastic parts are necessary for complex designs or innovative products with many unknowns. While 3D printing and machining can get you part way initially, there are many reasons to then graduate to a higher fidelity, production equivalent, prototype injection molded components before committing to expensive, full-scale production tooling:


Injection molding produces larger quantities of parts at a lower cost per unit than machining or 3D printing, making it perfect for user trials or functional testing. A good rule of thumb is that if you print or machine more than 30 prototypes, you could have purchased a prototype mold for the same cost and have parts that more closely replicate the ultimate production part.

High Precision

This process allows for complex shapes and intricate designs to be produced with high accuracy that can’t be achieved through 3D printing or machining.


Injection molding accommodates various plastics, offering flexibility in material selection based on the end product’s requirements. Parts made through injection molding are also more resistant to wear and tear and can be used in medical IVD (In Vitro Diagnostic) testing and clinical trials.


Prototype molds can be modified as the design changes, even if the design requires a non-metal safe change to the cavity; the metal is simply plugged and the new geometry is machined into the mold. The design can be iterated and parts can be produced multiple times as the engineers work out the kinks.

Faster Production Time

Prototype injection molding tools are typically single cavity, and can be produced in 1-2 weeks, depending on the complexity of the geometry. Production tools can take 8-16 weeks to fabricate. 

Once the prototype tool is fabricated, injection molding produces parts faster than CNC machining or 3D printing. With a typical cycle time of 45-60 seconds, injection molding is one of the fastest methods for producing plastic parts.

Production Equivalency

The parts are identical to parts produced by standard injection molding methods. This means that the parts will function as ultimately intended and can be used in functional testing and clinical trials to meet design verification/validation requirements well before the production tooling has been completed.


Prototype injection molding allows for parallel design paths during development for minimal tooling cost commitment; more ideas can be explored using the “Fail early, fail fast, fail often, fail better” principle. 


Excess materials or rejected parts can often be recycled back into the production line, reducing waste and increasing efficiency.

Designing Prototypes for Injection Molding/ IM Process

The design of the prototype is a crucial step in the injection molding process that requires careful consideration of factors like functionality, aesthetics, materials, and injection mold design.

The prototype injection molding process starts with creating a design for the part that meets design needs but is also compatible with injection molding requirements. Simply, this means that the part should have close to constant wall thickness and that the design should reflect how the mold will open to remove the part. For example, in injection molding, any features on the part that are not in line with the direction of the mold opening/closing must be made with side-action slides. To keep the cost of the tool and the parts lower, side actions should be minimized as much as possible.

Once the part design is complete, a mold is designed using the 3D part model file and is CNC machined in aluminum or brass. The metal mold is loaded into the injection molding press, and the mold cavity is filled with molten plastic under high heat and pressure, after which the plastic cools and hardens into the shape of the desired part. Once the plastic has cooled, the mold open, and the part is ejected from the molding machine. In prototype tooling, features requiring side-actions are made with core pins manually loaded into the mold and removed from the part after the part is ejected. 

The design of the prototype is a crucial step in the injection molding process that requires careful consideration of factors like functionality, aesthetics, materials, and mold design.

Contact Protoshop to discuss how to optimally design your part for prototype injection molding.

Contact Protoshop for Your Prototype Injection Molding Needs

If you’re developing new products regularly or working with intricate designs that require precise specifications, then prototype injection molding should be an integral part of your strategy. It helps mitigate risks associated with scaling up production and ensures high-quality output from inception through launch.

Ready to make your vision a reality? Let us help you navigate this complex process. At Protoshop Inc., we’re more than just a prototype injection molding company; we’re committed partners. We offer comprehensive services to our customers, including design assistance to prepare your part for injection molding and fabricating highly accurate molds and molded parts. Typically, molds can be fabricated in 3-5 days, and parts molded within 1-2 days. 

Based on 7 reviews
Dana Taylor
Dana Taylor
If you're in need of a molding prototype shop, Dylann and Jimmy at Protoshop are sure to not only meet but exceed your expectations. Their team demonstrates remarkable responsiveness and proactiveness, contributing to an exceptionally efficient overall process. The speed at which they deliver top-notch work is truly impressive. Protoshop's commitment to customer satisfaction is apparent in their flexibility and willingness to closely collaborate with clients to address specific needs. An exemplary instance of this was their accommodation of our request to have our customer onsite for part evaluation and mold changes while we were present. What sets Protoshop apart is not solely their technical proficiency but also their dedication to providing valuable insights and design advice. Their expertise extends beyond standard projects, showcasing proficiency in handling complex components for diverse applications, be it over-molded sealing parts or flexible components. In conclusion, if you're on the lookout for a reliable and efficient partner for your manufacturing and molding requirements, I wholeheartedly recommend Protoshop. Their combination of expertise, responsiveness, and commitment to customer satisfaction makes them an exceptional choice for a variety of projects.
Brittany Mason
Brittany Mason
I have worked with Photoshop on several mold designs over the past year. From the moment I reached out to them with an inquiry, they were prompt in their communication and eager to assist me. I have greatly appreciated and benefited from their extensive expertise and prompt feedback. They consistently offering valuable suggestions and insights that ultimately saved us money in the overall design. As for the quality of work they provided, Dylann and her team have always come through. If any issues do arise, they have been quick to offer solutions and kept us up to date throughout the whole process. If you're looking for a reliable partner for your plastics molding needs, I would check them out.
Stacie Depner
Stacie Depner
Having worked with Dylann and Jimmy prior to Protoshop, I knew the immense level of expertise they have for this business and it proved to carry through. They are honest straight shooters that will help guide you and find the best solution for your molds. We needed a mild that could be versatile and allow us to easily change out one side of the design. Dylann helped us come up with an approach that will allow us to continuously iteration the design without having to make a whole new mold every time.
Chad Follmar
Chad Follmar
Dylann and team are wonderful to work with. On multiple programs, they have delivered quality product in a matter of days. The design for moldability support is unparalled to ensure your part is ready to order.
Garrett Garner
Garrett Garner
We work regularly with Protoshop on a variety of complex components for various projects. They are an excellent company to work with providing a vast history of experience to help their clients optimize designs. We have worked with them on microfluidic chips with small feature sizes, over molded sealing parts and flexible parts. They have experience working with many materials including Topas (COC), polycarbonate, TPE, PE, and PP. I would highly recommend reaching out on your next project. The team is very responsive to design changes as well as delivering to tight timelines. They also offer design advice and best practices which have helped expedite design iterations.
Steven Soeder
Steven Soeder
Great experience with Protoshop. Dylann is extremely responsive and great to work with. Very fast turn-around. Worked with us on our order to get what we needed. I was able to drop ship 3d printed parts from another vendor to Protoshop to have them match-fit and incorporated into our tooling. I will be back again.
Wendell Woidyla
Wendell Woidyla
Dylann at Protoshop is excellent to work with: highly responsive and proactive. This is possibly the fastest, high-quality work I have ever witnessed. 1 week...from payment (start) to delivery (after CTQ measurements at Protoshop), we had 100 test samples of a component we intend to use in high volume manufacturing. Thank you for the tremendous work! I would highly recommend Protoshop, and will plan to use Protoshop services in the future.