Questions You Should Know about plastic mold design company

To some people, DFM (design for Manufacturability) might seem a little overkill or an unnecessary step in the already lengthy process of developing a new product. However, it is one that we at Sofeast take seriously and is a step that pays off time and time again resulting in saving time, money, and headaches down the line. Here's why tooling DFM is crucial for successful injection molding.

Let's look at a scenario where you are thinking about skipping tooling DFM: you think you have a great design, and you move straight into mold tool production, however, during mold tool production, unexpected challenges arise. The design needs modifications, leading to delays, rework costs, and a dent in your budget. Tooling DFM would have helped you avoid this nightmare scenario.

By proactively identifying potential issues early on, Tooling DFM saves you from costly fixes later. It analyzes your design through the lens of manufacturability, highlighting areas that could lead to expensive mold modifications or production delays. Addressing these concerns early in the design phase minimizes rework and keeps your project on track, both financially and temporally.

But DFM doesn't stop there. It also helps you choose the right material for your needs, minimizing waste and reducing material costs. Additionally, a DFM-optimized design translates to smoother production with less downtime and potential machine adjustments, further saving you operational costs. In essence, DFM helps you get the most out of your investment, ensuring every penny counts towards a successful outcome.

DFM also plays a key role in ensuring your injection molded parts meet the highest quality standards. It considers critical factors like wall thickness, draft angles, and gating, minimizing the risk of shrinkage, warpage, and other defects that can impact part quality and functionality.

In the image below you can see our own internal feedback during DFM on a product about the size of the gate and the requirement to add some material on the inside of the rim which shows the level of detail the team goes into during a DFM review to ensure that we have the absolute minimum gate mark on the surface of the product.

We get asked about plastic injection molding cost on every project we manage and it is not always that easy to answer. Let's break it down into two parts, first, the cost of the mold tools and second, the cost of the injection molded parts.

A. Injection mold tooling cost

When it comes to injection molding, the tooling itself is the most expensive part, but what factors contribute to all the cost?

The complexity, size, and material of the mold heavily influence its cost. Here's a closer look at each factor:

• Complexity: Simple, single-cavity molds with basic geometries are naturally cheaper than intricate, multi-cavity molds with complex features like undercuts or tight tolerances. The more intricate the design, the more machining and finishing work is required, driving up the cost. Simple, single-cavity molds for small parts might cost around $1,000-$5,000, while complex, multi-cavity molds for high-volume production can soar to $25,000-$80,000 or even more.
• Size: Larger molds require more material and machining time, resulting in a higher price.
• Material: Steel is the most common mold material due to its durability and heat resistance. However, it's also the most expensive. Aluminum offers a cost-effective alternative for simpler molds or low-volume production but with potential limitations in durability and heat tolerance. These days, aluminum tools are not very common in China as most toolmakers prefer to go directly to steel.

Where would the mold tooling usually be fabricated?

Most mold tooling is fabricated in China; mostly around Dongguan and Ningbo, where there is a very dense network of toolmakers and prices are quite competitive. Here's our advice for you when requesting quotes from mold tooling shops in China.

B. Plastic injection molding cost for parts

Several factors will determine the plastic injection molding cost for your parts with the material selection having a significant part in this equation. We have already touched on some of the plastics commonly used, however, it is not the cost of the material that should influence the selection, it has to be the required properties like strength, heat or chemical resistance, etc.

Another factor that will impact the cost is volume. High-volume production benefits from economies of scale, bringing the cost per part down especially if multiple parts can be molded with a single shot (multi-cavity tooling). Conversely, low-volume projects might have a higher per-unit cost due to mold setup and processing costs.

We've written more about the costs of tooling and purchasing process in these blog posts:

• How to avoid paying in full for your tooling
• Buy China Tooling For Plastic Production Abroad? (Benefits & Risks)
  
• Should Tooling Fabrication and Plastic Injection Molding Be Done Together?

As with the question about costs, the answer to how long it takes to make a mold tool is not a straightforward one as no two projects are the same.

Mold complexity is probably the single most influencing factor to the time it will take to fabricate your mold tooling. Single-cavity molds with basic geometries are quicker to create, often taking 2-4 weeks. But intricate designs with multiple cavities, tight tolerances, or complex features like undercuts can push the lead time to 6-8 weeks or even longer. The more intricate the design, the more steps and time required.

The second part of this complexity equation is the mold size. The more cavities involved, the larger the mold itself, the larger the mold, the more machining is involved which increases the time.

Another factor to take into consideration is the mold maker's schedule. With a busy workshop, your mold may have to wait its turn which adds to the overall lead time. On top of the mold maker's lead times, you have the supply chain to consider where material shortages or delays in components like cooling systems can add unexpected waiting periods.

Key factors to remember when planning the build of your mold tool are:

• Estimates are your friends: Experienced mold makers can provide an initial estimate based on your design and requirements. Keep in mind, that this might change depending on unforeseen circumstances.
• Communication is key: Stay in touch with your mold maker throughout the process. Understanding potential delays and adjustments helps manage expectations and adapt your timeline accordingly.
• Planning is crucial: Factoring in the mold lead time when planning your overall project timeline is essential. Rushing the mold creation often compromises quality and can lead to costly rework later.

An example of the difference in mold tool fabrication lead times between China and India, and why they're not the same.

China is still the fastest place to have mold tooling fabricated. The same mold might get made in 3 weeks in China (not including DFM, mold design, first trial, etc.), and 7 weeks in India, simply because Chinese toolmakers have automated the processes much more than in India where a lot of the finishing is done by hand (which is a more labor-intensive process).

Prototype plastic injection molding is a must for prototyping your design before mass production for many businesses, as it is crucial for identifying flaws, refining functionality, and ensuring a smooth transition into the tooling phase. While 3D printing has emerged as a popular prototyping tool, various injection molding-specific methods offer distinct advantages and cater to diverse needs. Here we will look at the different prototype tooling methods, exploring their materials, lead times, limitations, and what they can produce:

For more information, please visit plastic mold design company.

Rapid Injection Molding (RIM):

This method utilizes simplified, single-cavity molds often crafted from aluminum or epoxy resin. These molds are quicker and cheaper to create compared to their production counterparts, offering faster lead times and lower upfront costs.

• Materials: Aluminum, epoxy, nickel-plated steel (for higher durability)
• Lead Time: 2-4 weeks for simple designs, longer for complex geometries
• Limitations: Limited part size and complexity, lower durability and repeatability compared to production molds, potential dimensional deviation from the final part
• Applications: Functional testing, design validation, low-volume production runs

Prototype Insert Molding (PIM):

PIM leverages inserts made from materials like aluminum or beryllium copper, integrated into a standard production mold base. This offers faster lead times than full production molds while delivering closer quality to the final product.

• Materials: Aluminum, beryllium copper (for higher heat resistance), steel (for complex geometries)
• Lead Time: 4-6 weeks for simple designs, longer for intricate features
• Limitations: Can be more expensive than RIM, limited to mold base configurations, might still not be a replica of the final production part
• Applications: Functional testing, design verification, pilot production runs, pre-production validation

3D Printing for Injection Molding Patterns:

The 3D printing rapid prototype approach utilizes 3D-printed patterns to create sand molds for casting metal molds. It offers a relatively fast and affordable way to produce prototype molds, particularly for simpler geometries.

• Materials: 3D printing materials like ABS, SLA resins, SLS nylon (for better heat resistance)
• Lead Time: 1-2 weeks for simple designs, longer for complex geometries
• Limitations: Limited material options, lower mechanical strength, and heat resistance compared to metal molds, not ideal for complex geometries or high-precision parts
• Applications: Initial design verification, early testing, low-volume prototypes with simple shapes

In many cases, going straight from 3D printing to hard steel tooling makes sense when one considers the overall lead time of the project. One common exception is product designs that rely on technical assumptions that can only be validated by getting parts in the right polymer coming out of a mold.

Read more: We have created a guide to rapid tooling prototyping which discusses other options for rapid tooling.

Aluminum seldom makes sense if a mold is fabricated in China (which we cover later). Steel is the most common injection mold material, but choosing the right injection mold steel material is similar to selecting the foundation for a building: it dictates the mold's durability, performance, and ultimately, the quality of your parts. As engineers, we understand the critical nature of this decision.

Let's delve into the three most common types of hard steel and pre-hardened steel utilized in injection molding:

Hard Steels:

1. / / H13: This trio offers a workhorse option. After hardening, they achieve a Rockwell C hardness of 49-53 HRC, making them suitable for ordinary hardening molds. Their versatility allows for applications across various projects.

ESR: This steel takes the performance of the previous group a notch higher. It boasts the same hardness range (49-53 HRC) after hardening but excels in applications demanding both durability and a highly polished finish.

S136 / S136SUP / : Don't be fooled by the 'steel steel' reference ' these are actually high-performance stainless steels. Their strength lies in corrosion resistance, making them ideal for molds processing materials like POM and PVC, which can be corrosive to standard steels. Additionally, they hold their own when it comes to achieving a polished finish.

Lifespan: Mold tooling made from hard steels like 1.#, #, and # will usually last for around 300k-500K shots, but can reach 1 Million if the mold structure is simple.

Pre-Hardened Steels:

S50C / S55C: These steels offer a cost-effective option for mold bases, providing adequate strength and machinability. However, their lower hardness limits their suitability for high-wear applications.

718 / 718H: Renowned for their toughness and ability to achieve a good surface finish with standard polishing techniques, 718 and 718H are popular choices for mold cavities and inserts. Their well-rounded properties make them a versatile option for various applications.

738 / 738H: Offering superior rigidity compared to 718 grades, 738 and 738H excel in core and insert applications. While their polishing capabilities are considered 'ordinary,' their rigidity often outweighs this limitation for specific applications.

A Note on P20: It's important to clarify the perception of P20 steel in China. While technically encompassing a series that might include materials like 718 or 738, the term 'P20' in China often refers to a lower-grade steel with potentially less desirable properties compared to the 718/738 series.

NAK80 / XPM: The champion of pre-hardened steels, NAK80 boasts a hardness of 37-43 HRC. This, coupled with its excellent polishing capabilities, makes it the go-to choice for molds requiring high-precision parts from materials like PC, PA+GF, and PC+GF.

Remember, this is just a starting point. Selecting the optimal steel grade requires careful consideration of factors like part complexity, plastic-type, production volume, and budget. Consulting with experienced mold makers and material suppliers is crucial to ensure you make the best choice for your specific project.

Lifespan: For pre-hardened materials the mold life is usually 100K-300K shots.
In particular:

• 278#; 718#; p20#: 100k-200K;
• NAK80; XPM: 200-300K

Watch these videos on how to test steel's properties which may help you to select the types you require.

When we talk about tonnage or the term 'tonne' in the injection molding process, it means the injection molding press machine capacity regarding the clamping force it can exert. It has nothing to do with the weight of the machine.

So, if you encounter a statement like 'this mold requires a 120 Tonne machine,' it essentially means that the mold needs a press capable of exerting a minimum clamping force of 120 tonnes (metric tons, specifically) to hold the mold halves tightly shut during the injection molding process. This force ensures:

• Proper mold closure: Prevents molten plastic from leaking out under high pressure (known as flash).
• Dimensional accuracy: Maintains the mold cavity shape for precise part formation.
• High-quality parts: Minimizes warpage and other defects caused by insufficient clamping force.

It's important to understand that injection molding machine capacity isn't the only factor to consider when choosing a plastic injection molding press. Here are some additional key parameters:

• Shot size: The volume of molten plastic the machine can inject into the mold. This needs to be compatible with the part size and material selection.
• Injection pressure: The pressure applied to force the molten plastic into the mold cavity.
• Clamping stroke: The maximum distance the mold halves can travel during opening and closing. The size of the injected parts needs to be removed between the two halves of the mold when it is open.
• Platen size: The dimensions of the movable and stationary platens that hold the mold.

You may also like to read: How To Check The First Production From A New Plastic Injection Mold?

The allure of speed and affordability often leads to the question of soft tooling, particularly aluminum molds. While this approach might seem appealing at first glance, let's delve deeper to understand why, in many cases, hard steel molds remain the preferred choice for the average plastic injection molding process:

Cost Considerations in China

In China, the cost differential between hard steel and aluminum molds is often surprisingly minimal. This eliminates the initial cost advantage that aluminum might seem to offer elsewhere.

Automated Process

Modern injection molding facilities leverage automation extensively.  While machining hard steel does take slightly longer due to its inherent hardness, the difference is typically measured in days, not weeks. This automation advantage significantly diminishes the time-saving argument for soft tooling.

Durability and Production Efficiency

Aluminum molds, by their nature, are less durable than their hard steel counterparts. This translates to shorter lifespans, more frequent replacements, and ultimately, higher overall costs, especially for high-volume production runs. Hard steel molds provide significantly more cycles, maximizing production efficiency and minimizing downtime for mold changes.

Part Quality and Precision

Soft tools can struggle to maintain the same level of dimensional accuracy and surface finish as hard steel molds over extended use. This can lead to part quality issues, increased scrap rates, and the need for additional finishing steps. Hard steel molds ensure consistent part quality throughout their lifespan, minimizing rework and maximizing yield.

Our Experience

We've been approached about soft tooling in the past, and after careful analysis, we've consistently concluded that hard steel molds offer the best overall value. Their durability, efficiency, and ability to deliver superior part quality make them the smarter long-term investment, even when considering the slightly longer machining times.

The Takeaway about Aluminum Molds

In China, the combination of readily available steel, efficient machining practices, and economies of scale often shrink the cost gap between hard steel and aluminum molds.  When you factor in the superior durability, longer lifespan, and higher production efficiency of hard steel molds, they often become the more cost-effective choice in the long run, even for initial production runs.

The world around us is shaped by injection molding, a technology that transforms concepts into tangible realities. This guide has hopefully answered some of your key plastic injection molding questions and equipped you with the knowledge to use this intricate process with confidence.

We've covered critical factors like material selection, steel options, runner systems, and gate design, allowing you to optimize production efficiency and achieve superior part quality.  We've also explored important considerations often overlooked, such as quality control and environmental impact.

But the journey doesn't end here.  Our expertise extends far beyond this guide. 

Ready to transform your innovative ideas into real-world products?

First, delve into how Sofeast can help organize and look after your mold tooling in China: Tooling management for plastic injection molds in China.

Second, get help from our China-based injection molding subsidiary to design and fabricate your tooling and produce your injection molded parts in China.

Third, contact us today! Our team of injection molding specialists in China is here to answer your questions, discuss your project requirements, and help you leverage the immense potential of injection molding to achieve manufacturing success.  Together, we can turn your vision into reality.

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