Proto Molds Fabrication and Prototype Injection Molding

Is it absurd to use proto molds and prototype injection moulding? As most designers know, plastic injection molding is best used for large quantities of production-quality (i.e., non-prototype) items. It’s possible that you’ve also heard that aluminum injection molds are meant for smaller volumes, steel injection molds for larger numbers, and both kinds of proto molds are too costly.

Should any of this resonate with you, it’s time to reconsider your production and prototyping alternatives as well as unlearn some of the advice you’ve been given. Injecting plastic is indeed a high-volume manufacturing method. However, it can also be used for low-volume production and prototyping at times. It’s not simply aluminum vs. steel when it comes to injection molds.

Are proto molds expensive? Yes, however as this article will show, there are ways to cut costs. Does it take a long time to make injection molds? You’ll be happily surprised to hear that the proper manufacturing partner can generate tooling in a matter of weeks, if you were expecting mold-making to take several months. Consider your part design, material choice, tooling costs, and machining times while keeping an overall perspective. Additionally, keep in mind that you can get assistance when you share the part design with us. For instance, our DFM specialists will recommend a higher draft angle if your design doesn’t have enough draft to ensure that your parts eject cleanly.

Part Design and Prototype Injection Molding

The maturity of your part design plays a pivotal role in determining the next steps. If you haven’t reached the manufacturing phase, chances are you’re still immersed in the prototyping stage. But the type of proto molds you require depends on your specific objectives:

Proof-of-Concept Prototypes: These prototypes serve to evaluate scale, form, and sometimes basic functionalities.

Looks-Like Prototypes: Designed to provide a visual representation of the final product’s appearance.

Works-Like Prototypes: Intended for the validation of form, fit, and functionality.

Pre-Production Prototypes: These prototypes combine the validation of the product’s final appearance and its utility.

While these categories aren’t the only way to classify prototypes, they provide a structured framework for the discussion of proto molds that follows.

3D Printed Prototypes vs. Injection-Molded Prototypes

For many proof-of-concept and looks-like prototypes, the expenditure on an injection-molding tool may not be justified. Typically, in these early stages, designers only require a limited quantity of one or two parts. The cost of an injection mold, when divided among such a small production run, often makes it an impractical choice.

However, when it comes to works-like and pre-production prototypes, the scenario changes. Designers often necessitate part quantities in the tens rather than single digits. Depending on the volume required, it might be more economical to opt for injection molding instead of 3D printing, even though injection molding involves tooling expenses and isn’t the intended production process.

Consider this scenario: molding one proof-of-concept prototype versus crafting 100 pre-production prototypes, both requiring a $10,000 tool. The per-part tooling cost for one proof-of-concept prototype is $10,000, while for 100 pre-production prototypes, it’s a significantly reduced $100—a substantial cost differential.

When comparing 3D printed prototypes with injection-molded counterparts, several key factors should guide your decision:

For 3D Printed Prototypes:
3D proto molds appropriate for evolving designs in the conceptual phase.
Suited for very low quantity requirements.
Lead times typically range from 1 to 15 days.

For Injection-Molding Prototypes:
Proto molds Ideal for finished designs that demand real-world testing.
Best for prototype quantities exceeding 100 pieces.
Lead times typically span 2 to 5 weeks.

Now, consider the concept of design for manufacturability (DFM), a process that focuses on designing parts for ease of manufacturing. Let’s say you 3D print certain components and assemble them seamlessly, allowing you to test the product’s functionality effectively.

While this may be promising, it’s crucial to recognize that achieving perfection in 3D-printed proto molds doesn’t guarantee a smooth transition to equally flawless injection-molded parts. The production process can introduce new challenges and variables that demand a comprehensive evaluation, emphasizing the significance of thorough testing and validation.

Design Rules, Part Features, and Tolerances

It’s important to consider the differences in design rules, part features, and tolerances between 3D printing and injection molding. These factors play a significant role in the success of production injection molding and can impact the quality and functionality of the final parts.

One crucial aspect to remember is that 3D printing and injection molding have different design rules, including minimum wall thickness. Walls that are too thick, too thin, or non-uniform can often lead to failures in production injection molding. To avoid such issues, proto molds and prototype injection molding is recommended as it allows you to identify potential production challenges and make necessary adjustments.

Additionally, the file formats used in 3D printing and plastic injection molding differ. 3D printing relies on STL files, which define objects as a triangle mesh, while injection molded parts are typically defined using CAD files that are parameter-driven. To utilize 3D printing files for injection molding, a conversion process is required to transform the mesh into a shape and then into a solid.

Tolerances, which refer to the allowable part-to-part variations, also differ between 3D printing and injection molding. Most additive manufacturing technologies have dimensional tolerances of at least 0.1 mm, resulting in greater deviations compared to injection molding. Moreover, injection molding typically involves two types of tolerances: commercial and fine.

The good news is that we offer expert Design for Manufacturability (DFM) assistance through 3D visualization for injection molded part design. Additionally, we provide an online checklist that can help you determine if you’re ready to transition from 3D printing to injection molding. It’s worth noting that you can request injection-molded samples even before your parts are fully production-ready, allowing you to evaluate the results and make any necessary refinements.

Material Selection and Prototype Injection Molding

Proto molds or Prototype injection molding and production injection molding share the ability to utilize the same plastics. However, it’s crucial to be aware that certain abrasive materials, such as glass-filled nylon, can accelerate wear and tear on proto molds. This is primarily because proto molds are typically crafted from softer materials. Nonetheless, if your intention is to prototype 100 parts, the issue of wear becomes less critical compared to the wear and tear associated with a full-scale production run of 10,000 parts.

Commodity Plastics vs. Engineering Plastics

When your part design is still in its early stages, you might contemplate the use of more cost-effective commodity plastics, even if they do not possess the same mechanical properties as your intended production materials. As an illustration, consider PEEK, an engineering plastic frequently employed in medical devices. PEEK comes at a notably higher cost compared to other polymers and might involve a high minimum order quantity (MOQ) if your supplier does not purchase it in quantities substantial enough to secure a discount.

For a works-like prototype, you may opt for a less expensive material, such as polyphenylsulfone (PPSU), which can be a suitable choice. However, it’s important to note that selecting a material other than PEEK might not offer a comprehensive assessment of your part’s moldability. Given that both PPSU and PEEK are available as 3D-printing filaments, you might explore the possibility of utilizing additive manufacturing instead. This approach not only reduces tooling costs but also grants you the flexibility to use your preferred plastic material. It seems straightforward, doesn’t it?

All Part Samples Aren’t Created Equal

However, this approach may not always fulfill your requirements. 3D-printed materials do not replicate the end-use properties found in their injection-molded counterparts. For instance, 3D-printed PEEK may not possess the same level of strength as injection-molded PEEK. In situations where your part is intended for use in a medical device, obtaining representative samples for the first article inspection (FAI) becomes imperative.

The most effective way to obtain these representative samples is by employing the same material and production process you intend to use for full-scale production, which typically involves injection molding. If you have any questions or uncertainties regarding your part design, our team of Design for Manufacturing (DFM) experts is readily available to provide you with further information and

Prototype Injection Molds: Steel vs. Aluminum

When it comes to proto molds, the choice of materials goes beyond the traditional steel versus aluminum debate. While production molds can be constructed from either steel or aluminum, the versatility extends to proto molds, which can also be fashioned from both steel and aluminum, with variations within each category.

SPI Classes and the Significance for Prototypes

In assessing mold finish, SPI (Society of the Plastics Industry) Classes play a crucial role, with SPI Class 105 being the designated class for prototype quantities. However, SPI encompasses a range of mold classes, each tailored to specific production volumes:

SPI Mold Class 101: Designed for high volume, with a cycle life exceeding 1 million.

SPI Mold Class 102: Suited for medium-to-high volume, with cycles ranging from 500,000 to 1 million.

SPI Mold Class 103: Geared for medium-volume production, with cycles falling below 500,000.

SPI Mold Class 104: Intended for low-volume manufacturing, with cycles numbering less than 100,000.

SPI Mold Class 105: Specifically for prototype production including proto molds, with cycles totaling less than 500.

Aluminum vs. Steel Molds
The choice of mold material is of paramount importance. While aluminum is the most cost-effective option, it may not deliver injection-molded parts with the tight tolerances required for precision applications. Steel molds, on the other hand, excel in achieving precise tolerances, with the capacity to machine to tolerances as tight as +/-0.001 inches, a marked contrast to aluminum’s typical +/-0.005 inches.

Soft and semi-hardened steel molds, despite being pricier than aluminum, offer an excellent compromise for proto molds. These steel variants can attain tighter tolerances while remaining reasonably easy to machine, reducing the time required for tool creation, often within a timeframe of 10 to 14 days.

Hardened steel is typically reserved for production molds, given its greater durability (i.e., more cycles) and the ability to achieve stringent tolerances. For applications demanding tight tolerances, such as in the medical or aerospace sectors, aluminum falls short.

Diverse Mold Materials and the Role of MUD Dies

One advantage of injection molding is the adaptability in choosing various mold materials. For instance, the base of proto molds can be crafted from aluminum or soft/semi-hardened steel, while the inserts may be made of soft, semi-hardened, or hardened steel. Additionally, if your mold requires movable components like lifters, these elements can also be fashioned from steel.

Master Unit Die (MUD) inserts, featuring a standard mold frame with customizable, removable inserts, provide a cost-effective alternative for initial tooling, potentially reducing costs by up to 66%. Despite the cost savings, MUD molds maintain the complexity often needed for proto molds designs, allowing for efficient modifications to the insert in response to design changes.

Precision in Gate Selection and Mold Flow
Lastly, proto molds and prototype injection molding is designed to ensure that your mold incorporates the appropriate gate type and location. This guarantees even filling of the mold cavity and the application of adequate pressure to yield parts with consistent quality. While mold-flow-analysis software can be utilized, proto molds and prototype injection molding offers a tangible, real-time solution to place the finished part directly in your hands, making it a valuable choice for rapid prototyping.

In summary, the selection of mold materials and the consideration of SPI classes play a pivotal role in achieving your goals for proto molds and prototype injection molding, allowing you to strike the right balance between cost, tolerances, and production volumes.

Custom Proto Molds and Injection Molding Prototypes

As a manufacturer with 20 years of manufacturing experience, at Sungplastic we can assist you with the entire product lifecycle, from prototyping to manufacturing. You may use the procedure that you need when you need it because we provide a wide range of capabilities through a single platform, including 3D printing, CNC machining, and injection molding. We offer comprehensive services to clients worldwide, and we are able to create intricate components—including proto molds and prototype parts and products—to meet particular requirements.

Are you prepared to begin? Talk to us about the manufacture and design of your part.

Related Resources:

Prototype Mold for Injection Molding – Rapid Tooling

CNC Prototyping from Custom Prototypes to Production

3D Prototyping: Guides To 3D Rapid Prototypes Manufacturing

Injection Molding Prototyping Service