Introduction

From the gears within the 3D printer to the robust, lightweight prosthetic limbs changing lives, the injection molding process shapes the world around us. As engineers, we focus on precision, repeatability, and the power to materialize ideas. Injection molding delivers on all fronts, transforming even the most intricate CAD station designs into the high-tolerance physical components that bring ideas to life.
This plastic injection molding process resource answers the key questions that will help you navigate through some of the complexities of bringing your visions to life through the power of injection molding.

Here at Sofeast, we have managed more than a hundred new product development projects, the majority of which require some parts that are injection molded. We get asked so many questions related to this subject that we put together these answers to the top plastic injection molding process questions we’re usually asked.

Plastic Injection Molding Process Q&A: Table of Contents

1. What are the main injection molding benefits?

In the world of manufacturing, versatility and efficiency rule, and when it comes to plastic parts, injection molding is king (you can better understand it here). There are a host of injection molding benefits that make it the go-to choice for engineers and manufacturers that span all industries. Here we look at some of the key benefits that make the injection molding process reign supreme for many manufacturers:

  • Mass production of identical parts: The plastic injection molding process is efficient at producing large volumes of identical plastic parts. This makes it ideal for products like bottle caps, toys, electronic housings, and consumer electronics where consistency and affordability are crucial.
  • Minimal waste through greater efficiency: Compared to machining or other subtractive processes, injection molding generates minimal material waste. Molten plastic precisely fills the mold cavity, leaving little excess. Even the waste plastic produced during the injection process can be recycled and reused.
  • Repeatability and consistency: Injection molding excels at delivering consistent part dimensions and quality across high production volumes, a key factor in ensuring product reliability and smooth assembly. This meticulous process guarantees dimensional precision and material consistency, leading to seamless assembly, predictable performance, and ultimately, highly reliable products.
  • Complex designs and shapes: Unlike many traditional techniques for component manufacture, one of the key injection molding benefits is that it allows for complex geometries with intricate details, undercuts, and varying wall thicknesses. This opens doors for innovative product designs.
  • Wide material selection: A diverse range of plastic materials with specific properties (strength, flexibility, heat resistance) caters to various functionalities and performance requirements encountered across a spectrum of industries.
  • Economies of scale: Another key benefit is that plastic injection molding is almost unrivalled when it comes to the cost of producing parts in large quantities:

Reduced per-unit cost: As the production volume increases, the cost of tooling and setup (which can be significant) is spread across more units, leading to a lower cost per part.

Increased efficiency: With high volumes, manufacturers can optimize their processes for speed and efficiency. This might involve investing in automated systems, dedicated production lines, and bulk material purchases, all of which lead to further cost reduction.

Improved quality control: High-volume production often necessitates implementing robust quality control systems. These systems can identify and address issues early on, reducing scrap and rework, ultimately leading to higher-quality products.

Watch these videos for more of an introduction to plastic injection molding.

2. What are the key disadvantages of injection molding?

We have looked at some of the advantages of injection molding when we discussed ‘what is the purpose of injection molding’ at the start of this guide, but the disadvantages of injection molding (or its limitations) are often overlooked and not discussed. Let’s highlight some of the disadvantages here:

Cost Considerations

  • Upfront Costs: The biggest hurdle for many is the initial investment. Mold design, fabrication, and setup can be expensive, particularly for complex designs or high-volume production. This cost barrier can be prohibitive for smaller projects or startups. For example, below you can see an exploded view of a mold we fabricated for our product which shows how many separate parts are required just to make a relatively small two-cavity mold with four sliders (and other molds can get more complex than this):
exploded plastic injection mold parts view
  • Limited Design Flexibility: Injection molding imposes some geometric constraints compared to other methods. Tight tolerances, undercuts, and certain shapes might be challenging or even impossible, requiring design modifications or alternative techniques, potentially inflating costs.
  • Material Restrictions: While a wide range of plastics is available, not all materials are suitable for injection molding. Some options might require specialized molds or processing conditions, impacting feasibility and cost.

Time Management

  • Long Lead Times: As discussed previously, mold creation takes time, ranging from weeks to months for complex designs. This can significantly delay your project timeline compared to faster prototyping and low-volume production techniques like 3D printing.
  • Limited Volume Flexibility: While excelling in high-volume production, injection molding becomes less cost-effective for small quantities. Exploring alternative methods like CNC machining or 3D printing might be more suitable for low-volume needs.

Quality and Maintenance:

  • Quality Control Challenges: Maintaining consistent part quality during the injection molding process demands careful monitoring and process control. Defects like shrinkage, warpage, or surface imperfections can occur, jeopardizing functionality and aesthetics, and potentially requiring additional costs for rework or scrappage.
  • Rework and Modifications: Making changes to the mold after it’s built can be expensive and time-consuming. It’s crucial to finalize and thoroughly review your design before proceeding with mold creation to avoid costly rework.

Environmental Impact:

  • Plastic Waste and Energy Consumption: Plastic waste and the energy used in the plastic injection molding process raise environmental concerns. Opting for sustainable materials, optimizing processes, and implementing responsible end-of-life solutions can help mitigate these negative impacts. Although recyclable plastics exist, people are increasingly calling for plastic-free options these days, especially for items like packaging.

3. Why do I need a tooling DFM process for injection mold design?

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.

injection mold tool gate analysis

Furthermore, DFM ensures your design aligns with the mold’s capabilities, this means parts that not only look good but also perform reliably. Consistent quality across your entire production run becomes a reality, solidifying your brand reputation and ensuring customer satisfaction.

In summary, skipping a tooling DFM review before injection mold design carries substantial risks that can be easily avoided. While it might seem unnecessary, DFM offers significant benefits across cost, time, quality, and performance. In short, tooling DFM is an investment that pays off by ensuring a smooth, cost-effective, and high-quality injection molding process from design to final product.

4. What is the best plastic for injection molding?

The world of plastics used in injection molding is vast and diverse, offering plastic materials suited to virtually any need. Here’s a breakdown of some popular options of plastic for injection molding and why they’re beneficial

High-Volume Commodity Plastics:

  • Polypropylene (PP): Known for its flexibility, chemical resistance, and affordability, PP is widely used in packaging, toys, and household goods.
  • Polyethylene (PE): Divided into subtypes like High-Density PE (HDPE) for rigidity and Low-Density PE (LDPE) for flexibility, PE offers excellent chemical resistance, moisture barrier, and cost-effectiveness for bottles, bags, and films.
  • Polystyrene (PS): Often used for disposable items like cups and cutlery, PS is lightweight, affordable, and easily moldable, but with limited heat resistance.

Engineering Plastics for Enhanced Performance:

  • Acrylonitrile Butadiene Styrene (ABS): Offering a balance of strength, impact resistance, and good surface finish, ABS is popular in electronics housings, automotive parts, and toys.
  • Polycarbonate (PC): Renowned for its high strength, clarity, and heat resistance, PC is ideal for demanding applications like safety glasses, medical devices, and electronic components.
  • Nylon (PA): Available in various subtypes with diverse properties, nylon generally offers high strength, wear resistance, and good lubrication, making it suitable for gears, bearings, and other mechanical parts.

Speciality Plastics for Unique Applications:

  • Acetal (POM): Known for its exceptional stiffness, dimensional stability, and low friction, acetal is used in gears, cams, and other precise mechanical components.
  • Polytetrafluoroethylene (PTFE): Offering unmatched chemical resistance, low friction, and heat tolerance, PTFE is used for non-stick coatings, bearings, and seals in demanding environments.
  • Thermoplastic Polyurethane (TPU): Providing a combination of flexibility, strength, and abrasion resistance, TPU is used in footwear, hoses, and other elastic applications.

Read more: You can explore the many resources about the different thermoplastics we’ve created to help you make the right selection.

5. Why pay attention to injection molded plastic durability?

Injection molded plastic durability depends on several factors, making it impossible to give a one-size-fits-all answer. However, we can break it down to help you understand the variabilities and nuances that come into play:

  • The Importance of Material Selection
    Different plastic materials possess inherent strengths and weaknesses. Polycarbonate (PC), for instance, shines in demanding applications like safety glasses due to its exceptional strength and clarity. In contrast, polystyrene (PS), commonly used for disposable cups, offers limited durability. Choosing the right plastic for your specific needs is crucial. Consider factors like strength, impact resistance, heat tolerance, and chemical resistance, all of which vary significantly between different plastic types.
  • Processing Makes a Difference
    Even with the right material and design, improper processing during injection molding can compromise durability. Incorrect temperature or pressure settings can lead to internal stresses, voids, or weak areas within the part, ultimately reducing its lifespan. Precise control of processing parameters is essential for achieving consistent and reliable durability in your final product.
  • Environment Conditions
    The environment your injection molded plastic part encounters plays a significant role in its longevity. Constant exposure to sunlight, UV radiation, extreme temperatures, or harsh chemicals can accelerate the degradation of certain plastics. Understanding the expected environmental conditions your part will encounter is crucial in selecting a material and design that can withstand these external factors.

As you can see, there is no clear answer about injection molded plastic durability and it’s important to remember that molded plastic can be incredibly durable when approached strategically. By carefully considering the material selection, design optimization, and controlled processing, you can achieve the desired level of durability for your specific application. Consulting with experienced professionals (including our plastic injection molding team at our subsidiary Agilian Plastic & Molds) can further guide you toward the optimal combination of factors, ensuring injection molded plastic durability resulting in parts that stand the test of time.

6. How much does plastic injection molding cost?

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:

7. What are some common injection molding quality control challenges?

As engineers, we understand the importance of quality control in any manufacturing process. During the injection molding process, maintaining consistent part quality requires vigilance, as even minor deviations can lead to costly downtime and rejections. Performing plastic injection pilot runs can help find and iron out the quality issues we will discuss. To ensure molded parts meet the requirements of the highest standards, let’s have a look at some of the common injection molding quality control challenges:

  • Warpage and Shrinkage: As the molten plastic cools it tends to contract and this contraction leads to warping, shrinkage, and dimensional inaccuracy. With careful mold design, material selection, and process optimization, these issues can be mitigated.
  • Surface Defects: Defects such as flow lines, sink marks, and weld lines are common problems, however, they can all be overcome with correct mold design and process optimization. Software programs such as mold flow analysis will help identify any potential areas of concern and these can be addressed to mitigate surface defects.
  • Short Shots: Incomplete filling of the mold cavity due to insufficient pressure or material flow can lead to undersized or malformed parts. This results in scrap parts and a financial loss due to waste and repeat cycle time to achieve the desired result and yield output. Optimizing injection pressure, gate design, and material viscosity are key to preventing short shots.
  • Flash and Burrs: Material exceeding the mold cavity can create unwanted protrusions (flash) or sharp edges (burrs). Proper mold design, gating, and ejection mechanisms are essential for preventing flash and burrs as well as using the correct machine tonnage for the job.
  • Material Degradation: Overheating or prolonged exposure to high temperatures can degrade the plastic, affecting its mechanical properties and potentially causing discoloration. Selecting the right material for the application and controlling processing parameters are crucial.

Read more: We wrote an article that explained Avoiding 9 Plastic Injection Molding Defects: Key Preventive Measures.

8. How long does it take to make a mold tool?

fabricating injection mold tooling

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).

10. What are the options for prototype plastic injection molding?

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:

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.

11. How to add mold surface textures to tooling?

Injection molding’s versatility goes beyond simply shaping plastic. By incorporating mold surface textures into your tooling’s design, you can unlock a new dimension of functionality and aesthetics for your final product. But how do you add these textures to the mold itself? Let’s explore the various mold texturing techniques at your disposal during the injection molding process:

1. Mechanical Methods

  • Sanding and polishing: Offers basic texture control for flat surfaces. Grain size determines roughness. Ideal for simple patterns and matte finishes.
  • Grinding and milling: Precisely creates grooves, channels, and other raised features. Suitable for functional textures like gripping surfaces or anti-slip patterns.
  • Machining and engraving: Advanced technique for intricate details and logos. CNC machines achieve high precision but are costlier.

2. Non-Mechanical Methods

  • Laser etching: Offers extreme precision and control, enabling complex logos, patterns, and textures. Works on various materials, but can be expensive.
  • Chemical etching (photo etching): Creates detailed textures using light-sensitive resists and chemical etching. Ideal for fine lines and lettering, but requires specialized equipment.
  • Texturing pastes: Applied to mold surfaces, creating specific textures upon molding. It offers versatility and affordability but is limited to simple patterns.
  • Spark erosion (EDM): Uses electrical discharges to erode the mold surface, creating precise and complex textures. Suitable for deep pockets and undercuts, but costly and time-consuming.

Choosing the Right Method for Adding Mold Surface Textures

The ideal technique depends on several factors:

  • Desired texture complexity: Simpler textures might be achievable with mechanical methods, while intricate details require non-mechanical options.
  • Material compatibility: Ensure the chosen method works with your mold material without compromising its integrity.
  • Cost and lead time: Compare the cost and time required for each option to fit your budget and project timeline.
  • Production volume: High-volume production might justify the investment in expensive techniques, while low volumes might favor simpler methods.

Beyond Aesthetics

Mold surface textures provide benefits beyond visual appeal:

  • Improved grip: Textured surfaces enhance user interaction and safety by providing a better grip.
  • Reduced glare: Textured finishes can minimize light reflection, improving product usability.
  • Functional features: Textures can incorporate channels for fluid flow, ventilation, or heat dissipation.

You may benefit from obtaining a mold texture book that will give you hundreds of tangible samples (on plastic or metal tiles) to help you visualize how the texture will look on your product.

YS texture book

12. What are the tooling design questions the designer should ask upfront?

While the product designer’s inquiries are crucial, the tooling designer has their own set of tooling design questions to ensure a smooth translation from concept to reality. Here are some key inquiries the tooling designer might pose to you, exploring beyond the initial specifications, and brief explanations of why they need to know:

Part Geometry

  1. Are there any thin walls or sharp corners that could cause sink marks or flow issues? This helps determine if design modifications are necessary for optimal material flow and part strength.
  2. Can any undercuts be avoided or redesigned for easier mold ejection? Undercuts require complex mold designs, increasing costs, and potential ejection problems.
  3. Are there any critical tolerances that require special attention in mold design and production? Tight tolerances demand high-precision molds, impacting cost and lead time.

Material Selection

  1. Have you considered shrinkage rates for the chosen material? Shrinkage can affect part dimensions, requiring adjustments in mold design or material selection.
  2. Are there any concerns about the material’s compatibility with the molding process (e.g., heat resistance)? Incompatible materials can lead to warping, discoloration, or even mold damage.
  3. Are there any special surface finishes or textures required? These can necessitate specific mold features or post-processing techniques, impacting cost and lead time.

Production and Cost

  1. What is the desired surface finish (e.g., matte, glossy)? Different finishes require different mold polishing levels, affecting cost and lead time.
  2. What is the acceptable level of parting line visibility and flash (excess material)? Balancing aesthetics with production realities helps determine mold complexity and cost.
  3. Are there any specific gate locations or types preferred? Different gate types affect flow patterns, potentially impacting part quality and requiring mold design adjustments.
  4. How many cavities per mold are desired for production efficiency? More cavities increase production speed but also raise mold cost and complexity.

Additional Considerations

  1. Do you have any specific requirements for mold materials (e.g., corrosion resistance)? Special mold materials might be needed for certain applications, impacting cost and lead time.
  2. What are your expectations for mold maintenance and repair? Discussing maintenance needs upfront helps determine mold design features and potential future costs.
  3. Do you have any existing quality control standards or specifications for the parts? Understanding these helps ensure the mold meets specific requirements and avoids rework or scrap.

Be aware that if you are working with a Chinese tool fabricator, they may have very different expectations from you about the final ownership of the tooling if they have worked on designing and creating it.

13. Selecting your injection mold steel material. What is the right steel for the Job?

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:

1.2344 / 8407 / 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.

2344 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 / 2083: 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 1.2344#, 2343#, and 8407# 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.

14. Why is it important to use the right injection molding press?

plastic injection molding presses

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?

15. Hot Runner vs Cold Runner, what system is best?

When it comes to injection mold design, a critical decision revolves around the runner system – the channel that delivers molten plastic from the sprue to the mold cavities. Two primary options dominate the landscape: hot runner vs cold runner. Understanding their distinct characteristics empowers you to select the most suitable approach to use in your injection molding process.

Hot Runner system

  • Function: Employ a heated manifold system that maintains the plastic in a molten state throughout the runner. This eliminates solidification and the need to remove a solidified runner after each cycle.
  • Advantages:
    • Faster cycle times: No need for runner removal translates to quicker production cycles, boosting efficiency.
    • Reduced material waste: Molten plastic in the runner is reused, minimizing material consumption and cost.
    • Improved part quality: Consistent flow and temperature control lead to better part quality and reduced sink marks.
  • Disadvantages:
    • Higher initial cost: Hot runner systems are generally more expensive due to their complex design and heating elements.
    • Limited material compatibility: Certain heat-sensitive plastics might not be suitable for hot runners.
    • Increased maintenance: Maintaining the heating system requires additional attention.

Cold Runner system

  • Function: Utilize unheated runner channels. The plastic solidifies in the runner after each injection cycle.
  • Advantages:
    • Lower initial cost: Simpler design translates to a more affordable option.
    • Greater material compatibility: Can handle a wider range of materials, including heat-sensitive ones.
    • Simpler maintenance: Less complex system requires minimal maintenance.
  • Disadvantages:
    • Slower cycle times: Removing the solidified runner after each cycle adds time to the production process.
    • Material waste: The solidified runner becomes scrap, increasing material consumption and cost.
    • Potential for quality issues: Inconsistent flow and temperature control can lead to defects like sink marks.

How to Choose Between Hot Runner vs Cold Runner?

The optimal selection between hot runners and cold runners hinges on your specific project requirements. Consider factors like:

  • Production Volume: High-volume production often favors hot runners due to their faster cycle times and reduced waste.
  • Part Complexity: Complex parts might benefit from hot runners to ensure consistent flow and minimize sink marks.
  • Material Selection: Heat-sensitive materials or frequent color changes might make cold runners a better fit.
  • Budget: Initial cost considerations might favor cold runners, but long-term savings with hot runners due to reduced waste need to be factored in.

By carefully evaluating these factors and the unique properties of hot and cold runner systems, you can make an informed decision that optimizes your injection molding process for success. Remember, consulting with experienced injection molding professionals can guide you towards the most suitable runner system for your project.

16. Demystifying the Gateway: A Guide to Injection Molding Gates

Within the intricate world of plastic injection molding, a seemingly small detail – injection molding gates – plays a significant role in part quality and production efficiency. This section delves into the most common injection mold gate types and shapes, guiding you towards the optimal choice for your specific project.

Understanding the Gate’s Role

The injection molding gate serves as the critical entry point for molten plastic into the mold cavity. Beyond simply allowing plastic flow, it also influences factors like:

  • Filling balance and part quality: A well-designed gate ensures uniform filling, minimizing voids, weld lines, and warpages.
  • Surface finish: Gate type and placement can affect the aesthetics of the final part, especially when dealing with highly visible surfaces.
  • Cycle time and material waste: Efficient gate design minimizes material waste and optimizes production cycle times.

Now, let’s explore the various gate types and their applications:

1. Edge Gate

  • Description: A simple, rectangular gate sheared directly from the runner’s edge.
  • Applications: Well-suited for thin and flat parts with good flow characteristics. Commonly used for electronics housings, lids, and containers.
  • Limitations: Can leave a visible gate mark on the finished part, requiring additional finishing steps. Not ideal for thick parts or those requiring high structural integrity.

2. Submarine Gate (Tunnel Gate)

  • Description: Located on the parting line of the mold, often positioned below the part surface. Requires a post-molding operation to remove the vestige (the remnant material left behind at the gate).
  • Applications: Ideal for parts requiring a flawless surface finish, such as cosmetic components and high-visibility applications. Commonly used for housings, lenses, and medical devices.
  • Limitations: Adds an extra step to the production process for vestige removal. Might not be suitable for parts with deep cores or undercuts.

3. Pin Gate

  • Description: A small, cylindrical gate formed by a pin inserted into the mold cavity. The pin is ejected with the part, leaving a tiny mark that can be easily finished or hidden on a non-critical area.
  • Applications: Perfect for small, intricate parts or those with limited gate placement options. Commonly used for connectors, gears, and electronic components.
  • Limitations: Requires precise pin placement to ensure proper flow and avoid stress concentration points. Might not be suitable for very large or thick parts.

4. Fan Gate

  • Description: A wider version of the edge gate, spreading the flow of plastic into the cavity in a fan-like shape.
  • Applications: Ideal for parts requiring balanced filling, particularly those with thick sections or uneven wall thicknesses. Commonly used for housings, brackets, and gear housings.
  • Limitations: Can leave a visible gate mark that might require finishing, depending on the application. Not suitable for very thin parts or those with limited gate placement options.

5. Sprue Gate

  • Description: The simplest gate type, formed directly from the sprue (the main runner channel).
  • Applications: Primarily used in low-volume production or for simple parts with minimal aesthetic requirements. Can be helpful for initial prototypes or testing purposes.
  • Limitations: Generally not recommended for high-volume production due to material waste associated with the sprue. Can lead to unbalanced filling and potential quality issues in complex parts.

6. Tab Gate

  • Description: Similar to an edge gate, but features a short, extended tab that projects slightly into the cavity. This tab helps to improve flow initiation and reduce shear stress on the plastic.
  • Applications: Well-suited for thin parts where minimizing gate mark size is important. Often used for electronic components, lids, and packaging applications.
  • Limitations: May leave a small visible mark on the part, depending on the tab size and material used. Not ideal for thick parts or those requiring high structural integrity.

7. Diaphragm Gate

  • Description: Utilizes a thin membrane (diaphragm) within the runner system that ruptures under pressure, allowing molten plastic to enter the cavity. The ruptured diaphragm material remains within the runner and is discarded during the recycling process.
  • Applications: Ideal for applications demanding a virtually invisible gate mark, such as cosmetic parts and high-precision components. Often used for lenses, housings for electronic devices, and medical equipment.
  • Limitations: Increases mold complexity and cost due to the diaphragm mechanism. Might not be suitable for highly abrasive materials or those with high viscosity.

8. Valve Gate (Hot Runner Gate)

  • Description: Employed exclusively with hot runner systems, valve gates feature a shutoff mechanism that controls the flow of molten plastic into the cavity. This allows for precise control over injection timing and pressure, minimizing waste and optimizing part quality.
  • Applications: Ideal for high-volume production runs, parts requiring superior quality and minimal gate marks, and applications with strict material usage requirements. Commonly used for automotive components, medical devices, and electronic components.
  • Limitations: Significantly increases mold complexity and cost compared to simpler gate designs. Requires specialized equipment and expertise for setup and maintenance.

How to Choose the Right Injection Molding Gates for Your Project?

As previously mentioned, the optimal injection molding gate selection hinges on several factors, including:

  • Part geometry: Consider factors like wall thickness, surface finish requirements, and presence of undercuts.
  • Material properties: The flow characteristics of the plastic material play a role.
  • Production volume: High-volume production often benefits from efficient gates like valve gates, while aesthetics might be prioritized for low-volume parts.
  • Cost considerations: Balance the initial mold cost with potential savings in material waste and finishing processes.

What does a Gate look like on the Injection Mold Tool?

You can see a gate for a product we made from the image below. It is made in such a way that the resulting parts are clean with no marks, which consumers of electronic devices would usually demand.

Product injection molding gate example

17. Can we use aluminum molds to reduce the cost/timeline?

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.

Our Conclusion to this Injection Molding Process Guide

The world around us is shaped by the injection molding process, a technology that transforms concepts into tangible realities. This comprehensive guide has hopefully answered some of the questions you have and equipped you with the knowledge to navigate 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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