The reason behind the diverse use of injection molding technology lies in its variations. Several types of injection molding techniques are used in industrial manufacturing. Not only plastics but some of them can produce metal, ceramic, and foamed products.
If you want to make an injection mold tooling or full-scale production, choosing the right technology is essential for optimal quality and cost savings. This article will cover the technical guidance to choose from, including characteristics of classified types, applications, selection considerations, and how to order injection molding parts.
What is Injection Molding Technology?
Injection molding technology produces desired parts or products by shaping the molten material into a cavity. The geometry of the cavity outlines the 3D shape of the designed products. Typically, high pressure is applied during injection to facilitate material flow and maintain compactness once the material is solidified.
The history of injection molding can be traced back to 1872; two American brothers(Hyatt and Isaiah) invented a simple hydraulic plunger plastic molding machine. Since then, it has continuously evolved and become more accurate, cost-effective, and diverse.
Recent innovations and advancements like micro-molding, metal injection molding, muti-component molding, robotics, and automation are why electronics, automotive, medical, consumer, and toy industries heavily use this technology.
Specialized Injection Molding Techniques
Let’s discuss some of the specialized techniques in plastic injection molding; the classifications are based on their specialized working mechanism;
Gas-Assisted Injection Molding
As the name refers, gas-assisted injection molding involves introducing a compressed air flow( typically inert gases, 0.5 Mpa to 300MPa) into a mold cavity through specific gas channels after injecting ~70 to 80% liquid plastic. These channels are incorporated during the mold design.
The gas flow pushes the molten plastics toward the cavity wall, maintaining the structural integrity and smooth finish.
It not only produces parts with hollow sections but also enhances the material flow and helps reach complex sections, like deep corners.
OverMolding
Overmolding means creating final parts by molding two materials one over another. For example, soft-touch materials like rubber or silicone are molded over the hard base of polycarbonate in tool handles.
First, the base section is made and then inserted into the mold, followed by the injection of secondary material. Meanwhile, the bond is strong and does not act as the layers.
Moreover, the parts or products requiring grip, vibration damping, or sealing are preferable to make with this technique.
Insert Molding
In insert molding, a pre-made solid part( typically metal or hard plastic material) is placed into the mold cavity before the injection process, either with automated inserting or by hand. For example, electrical plugs involve brass prongs as inserts. This technique eliminates the need for assembly and emphasizes simple product designs.
The compatibility of the insert material is essential for strong bonding; besides that, the surface needs to be abrasive. Consequently, precisely designing the insert location and supporting mechanism (if needed) also influences the final quality.
Water-Assisted Injection Molding
The Water-assisted technology involves high-pressure water flow that displaces the molten core and forms a hollow structure. Depending on design, water can occupy 20 to 50% of the cavity volume.
The waterjet makes parts with partial (or full) hollow-section, ensuring uniform wall thickness and smooth internal surfaces—for instance, fluid pipes, chair legs, car handles, and cooling ducts. Consequently, short cycle time is another advantage. The water flow helps to solidify the material quickly.
Fusible (Lost, Soluble) Core Injection Molding
Sometimes, complex parts like those with deep cavities and undercuts are impossible to make with removable cores. Here comes the role of Fusible core or lost core injection molding.
A core made with fusible material, such as soluble polymer, is used to match the final part’s internal geometry. After the injection of hot material, the core fuses with the part. It means you need to remove the core by melting, dissolving, etc.
A few application examples are parts with undercut and tight bends, like automotive manifolds and medical micro-lumens.
Structural Foam Injection Molding
Structural foam molding is popular for lightweight components(10 to 30% less) with a foam core and a solid outer layer. The process involves mixing the blowing chemical in molten resins, which need to be injected into the cavity with inert gases. This expansion causes the formation of cellular structures like sponges or honeycombs. However, the exterior surface is smooth and compact.
Using this method, you can make thick parts of ABS, Nylon, Acrylic, Polypropylene, PVC, etc.
Typical thickness range → 2 to 12.70 mm (0.500 to 0.080″)
Injection Molding Technology Based on Material Type
Each material has a distinct flow behavior, solidification rate, and thermal stability. These characteristics influence the molding process variables, potential defects, and overall quality. Therefore, manufacturers often classify the technology based on material types to streamline manufacturing processes and optimize the final results.
Thermoplastic Injection Molding
Thermoplastic melts immediately while heating and solidifies easily upon cooling, which makes it perfect for injection molding. E.g., ABS, PP, PC, and PE. Various recyclable parts are possible with these materials: packaging, automotive, aerospace, transparent prototypes, etc. All you need is suitable thermoplastic pallets as the raw materials.
Thermoset Molding
Unlike thermoplastics, thermosets include a cross-link and strong molecular chain, making it impossible to melt and solidify reversibly. So, the malleable form of the thermoset material is forced into the heated cavity, where it flows and shapes itself.
You can create harder and more durable parts with thermoset molding; the additives and bonding chemicals in the material charge enhance the strength. Epoxy, polyurethane, phenolic, and other thermosets are compatible with molding.
Liquid Silicone Molding (LSR)
This method molds the liquid form of silicone into functional prototypes and parts that are flexible and durable. The LSR molding process involves mixing base polymer liquid and curing agent in a chamber and injecting under high pressure. Then, vulcanization forms cross-linked bonds as solidification begins.
Moreover, This type of rubber molding is suitable for medical seals, gaskets, baby care products, sensors, vibration dampers, etc.
Metal Injection Molding (MIM)
Injection molding technologies are also capable of molding metals like aluminum alloys, stainless steel, titanium, etc. The mechanism differs slightly from plastic molding; the feedstock consists of atomized metal powder (spherical, ⌀ < 20 µm) and the binding agent. Then, a molding press shapes the feedstock material by high compression force in a die. This way, you can create high-strength and intricate metal parts for medical, dental, firearms, electronics, automotive, and general industrial manufacturing.
Ceramic Injection Molding (CIM)
Ceramic injection molding produces simple consumer products to advanced engineering items. It involves forcing the heated feedstock of ceramic powder and binding agents, along with some other additives, and removing the compact part after curing. Then, debinding process melts the binder resin, and the sintering causes ceramic particle bonds to tighten.
Some examples of products are semiconductor insulators, sensor components, industrial nozzles, and decorative items.
High-Precision and Advanced Techniques
Now, let’s briefly examine some advanced injection molding technologies used in modern manufacturing.
Thin Wall Molding
First, thin wall molding is characterized by the flow length ratio, the ratio between wall thickness and flow length of the process ( Wall Thickness/ Flow Length). In standard techniques, this ratio is maximum up to 20:1, whereas it can be as high as 50:1 in thin wall injection molding.
Another way of defining this is “ all molding products with less than 1 mm wall thickness.”
This technique suits complex, thin-walled plastic parts, where precision matters for functionality and desired performance criteria. Moreover, mold design, cycle time, shot size, and other parameters are crucial for final quality.
Micro Injection Molding
Micro molding is popular for healthcare and micro-optic components, washers, locks, and several other tiny-sized applications—the main difference from the standard technique is the specialized injection unit and the shot size. Meanwhile, EDM and CNC machined micro-molds are used in the process.
High-Pressure Injection Molding
High pressure refers to a range of 500 to 2000 bar; it improves the flow and speed. A heated screw mechanism implies pressure into plastic pallets, which melts and pushes pallets into the injection mold gate.
High-pressure injection is ideal for parts with intricate designs, surface texture, and tight tolerance levels. However, you must consider high-strength materials for mold, like tool steel, to withstand high pressure.
Low-Pressure Injection Molding
This is a consistent production process in which low injection pressure allows for higher control over the process and provides excellent repeatability. A typical pressure range is 1.5 to 40 bar.
This process is slower than high-pressure molding and best fits plastic prototyping and low volume injection molding. However, the simple tooling and low heat requirement make the process cost-effective.
Cube Molding
This method incorporates a cube-shaped mold that can rotate into different faces to intake molten material. Each face can include a different cavity shape or similar ones. This way, manufacturers can achieve higher production efficiency.
The multi-face mold is mounted on a rotational mechanism with a motorized turntable or hydraulic actuator for automated face-switching.
2-Shot Molding
This advanced technique is favorable for multi material components. A specialized injection molding machine with two injection units injects two different materials simultaneously to form a single integrated part/product.
It might sound like overmolding, but the main difference between two-shot vs. overmolding is that a single machine cycle executes the whole process in two-shot. In contrast, a pre-made solid Overmolding adds secondary material over an existing part, often made separately.
Co-Injection Molding
Co-injection molding is specialized for multi-layer parts. First, an injection unit injects one polymer that flows across cavity walls to form outer skin. Then, another material is injected to form the core inside that skin. This applies to the packaging industry for making rigid containers with barrier layers to preserve and protect food, medical items, and consumer goods.
Decorative and Multi-Component Molding
In-Mold Decoration (IMD)
The appearance of molding items can also be customized during the in-process, which involves inserting a premade decorative film inside the cavity before introducing molten material. The material forces the film into the exterior and bonds together on solidification. So, first, you need to print the decorative film/foil separately.
IDM is ideal for producing decorative items and adding aesthetics to consumer products, from flower pots to enclosures of home appliances.
In-Mold Labeling (IML)
Like IMD, the parts are molded over pre-printed label film inside the cavity, which becomes parts of the final product. The difference is more in the application preferences; IML is mainly used to add label graphics during molding. Electronics, gaming, automotive, and other industries apply for label finishing their components.
Multi-Component Molding
This injection molding technology produces different parts from separate materials with a single mold tooling. It allows manufacturers to make injection molded products with multiple components efficiently. Consequently, you can also use this for parts with multiple colors.
Runner System Types
The runner system refers to channels that transfer the injected material charge from the nozzle tip to the cavity. The runners can be of two types: cold and hot. Cold runner involves passing the material without further temperature control; the injection charge might lose some heat as it approaches the cavity. On the other hand, hot runners maintain the same temperature until the material reaches the cavity.
There are also some design differences between hot and cold runner injection molds. Hot runner molds are more complex due to heating & insulation elements, whereas cold runner molds are simpler.
Hot Runner Injection Molding | Cold Runner Injection Molding |
The heated runner keeps the plastic molten | Not heated; plastic solidifies in the runner |
Minimal waste as runners stay molten | It generates more waste due to solidified runners |
Higher initial cost due to complex system | Lower initial cost, simpler design &installation |
Ideal for high-volume and essential for heat-sensitive materials | Best for low-volume and prototypes |
Reaction Injection Molding(RIM)
In the RIM technology, two distinct polymers react inside the heated mold. Then, a chemical reaction causes expansion and solidification. A popular material combination for RIM is polyol and isocyanate, which react and form strong and lightweight plastic components.
Instead of injecting separately, a liquid mixture of two polymers is injected, whereas heated mold triggers the chemical reaction.
Furthermore, this low-temperature and pressure molding produces strong, lightweight, and durable parts, regardless of complexity and feature detailing. You can opt for this one, especially for large single-piece parts.
Application examples are;
- Industrial Machinery Enclosures
- Automotive Parts like DashBoardd, Bumpers, and other Exterior Items
- Housing for Home Appliances
- Sporting Goods
- Protective Gears
High-Gloss Injection Molding
Molding parts or products with high gloss finishes ( smooth & mirror-like) starts with creating a polished injection mold. The cavities are precisely machined and polished, whereas the material captures this smooth exterior for high-gloss.
It is not only for an appealing appearance but also to enhance the feel, touch, hygiene, and comfort. E.g., automotive dashboard components, medical devices, and household goods.
Moreover, the use of high-quality polymers with excellent flowability is also critical for a high-gloss finish. For instance, ABS, PC, and PMMA.
- Precise temperature control and minimal surface defects
- Often, post-processing (like polishing) is applied to enhance the gloss.
- Higher cost for polished and chrome-plated molds
Rotational Molding
Applying heat and rotating the mold with powder inside, the heat and rotation force the powder toward the wall, leaving a hollow section around the center of the rotational axis. Rotation molding is mainly for polyethylene (PE), PVC, and PA plastics.
You can choose this molding technology for manufacturing large, hollow, or double-walled items that require uniform wall thickness and durability.
- It is ideal for seamlessly producing large hollow items like tanks and pipes.
- The centrifugal force from mold rotation distributes material evenly.
- Mold and other tooling costs for the rotational method are less expensive.
- Longer time for molding cycles
Key Advantages of Injection Molding
Cost-benefit in high volumes, molding efficiency, materials range, and capability of complex geometries are the key advantages of adapting injection molding techniques in your manufacturing project.
Let’s discuss these a bit more;
Cost Effective for High Volumes
The hard mold tooling can run up to millions of cycles, producing identical designs with consistent quality. This widespread distribution of tooling costs reduces the per/part production cost. Additionally, high speed and low material wastage further reduce the cost.
Typically, per/part production costs for high volume molding projects are almost 30 to 50% less than CNC machining or 3D printing.
High Production Efficiency
The fast cycle times and low machine downtime justify the high injection molding efficiency; it takes 2 sec to 3 minutes to produce a part, whereas the maximum machine downtime between the cycles is 20 sec. Furthermore, the automation of injection equipment allows it to run 24/7, making the technology more efficient.
Complex Part Geometry and Detailing
The detailed molds and automatic injection units enable the production of complex part geometry with a precision of ±0.005 inches and a minimum wall thickness of 0.5 mm.
Moreover, it can mass-produce parts with complex geometrical features like undercuts, deep cavities, internal channels, etc. E.g., gears, medical items, microfluidic chips, robotics components, etc.
Material Versatility
First of all, there are numerous thermoplastic choices: ABS, PC, PVC, PA, etc. Then, thermosets, ceramics, rubbers, metals, and alloys are also compatible with molding technology. These countless options allow you to customize your product’s final properties and color.
Consistent Part Quality
Injection molded items are consistent across the batches, even for medium to high volumes. In most precision projects, defect rates are as low as 0.1%. A stable setup with minimal variations in process variables is important for higher consistency.
Low Waste and High Material Utilization
The injection molding process leaves minimal material wastage, plus the scrap materials can be recycled for future use or even for the same project. This high material utilization is beneficial for both cost reduction and sustainability.
Applications of Different Injection Molding Technologies
If you look around yourself, you will find many products made from injection molding technology: plastic bottle caps, toothbrushes, toys, electronics housing, keyword keys, and components in your car.
Let’s look at what can be made for different industries;
Automotive Industry
Injection molding for automotive is crucial to produce lightweight, high-quality, durable results. Both as-assisted molding and RIM create lighter parts, consume less fuel, and thereby improve the ride.
Standard Molding | Car bumpers, dashboards, and interior trims |
Gas-assistant Injection Molding | Door handles and structural frames |
Reaction Injection Molding(RIM) | Outer body like bumpers and fenders |
Electronics
Producing small and complex components for electronics and consumer items offers good reproducibility, reduces assembly requirements, and improves strength. Laptops, tablets, phones, TVs, PCs, gaming controllers, and other products use injection molding technologies.
Standard Injection Molding | Casings for electronics items and custom parts |
OverMolding | Phone casing, game controllers, tool handles, etc. |
Micro Injection Molding | Small connectors, switches, and circuit parts |
Consumer Goods
Injection molds also significantly produce everyday consumer products, offering durability, aesthetic appeal, and cost-effectiveness. It ensures high quality in mass-produced items like toys and kitchenware.
Standard Injection Molding | Toothbrushes, food containers, and bottle caps. |
Overmolding | Soft-grip handles for tools and kitchen utensils. |
Thin Wall Molding | Lightweight packaging and disposable cutlery. |
Medical Devices
The production of medical devices and components with injection molding technology ensures quality, biocompatibility, tight tolerances, and standard safety rules. With medical injection molding, you can make products that meet FDA, ISO, and other regulatory requirements.
Micro Injection Molding | surgical instruments, microcatheters, implants, and microfluidic devices. |
Liquid Silicone (LSR) Molding | Biocompatible and heat-resistant tubing and seals, respiratory masks, etc. |
Standard Molding | Housings for diagnostic devices, syringe barrels, and IV connectors. |
Choosing the Right Injection Molding Technology for Your Project
The diversity of technologies offers the freedom to transform unique designs in real life, but deciding which technology best fits your project in terms of quality, efficiency, and cost is equally important.
The following are some major considerations for choosing the right technique;
Consider Material Type
Consider the type of raw material you are using and the compatible technologies for that. Some of the materials are only compatible with specific technologies. For instance, thermoplastics are best for standard molding, whereas polyurethane suits reaction injection molding.
⟶ Identify which material you are using and shortlist the compatible technologies.
Production Volume Factor
Production volume also influences your choice. Standard technologies like gas-assisted molding are suitable for high volumes. On the other hand, micromolding or low-pressure techniques are more favourable for small batches and prototypes. Consequently, high volume productions are difficult to customize and adjust the designs.
⟶ Consider the desired production volume and which technologies are feasible for that, both technically and economically.
Analyze Part Design and Complexity
Designs with complex geometries, high detailing, and joining features require advanced and specialized technologies like muti-shot. Next, rotational and water-assistance techniques are best for hollow designs.
Over-molding and insert molding work best for parts made from multiple materials. Meanwhile, micro-injection molding is perfect for making tiny, complex parts used in medical devices and electronics.
⟶ Consider the complexity of the design and analyze which techniques can produce those designs.
Take Cost into Account
One of the key factors is the cost associated with the short-listed technologies; examine the per/part production cost to find out which offers high production value at a low cost. Similarly, choosing highly precise techniques for simple projects also drives up the cost.
⟶ While trying to choose low-cost technologies, do not forget the quality sacrifice. You must balance cost-effectiveness with the desired quality.
Consider Lead Time
Some injection molding technologies have longer cycle times and extensive work for mold tooling, increasing the lead time for your projects. Meanwhile, standard and large-sized molding has relatively quicker leads. So, analyze which techniques can deliver the results early.
⟶ Ensure the lead time of the chosen technology matches your project timeline.
RapidDirect: Your Trusted Injection Molding Expert
Once you decide which injection molding technology fits your requirements, there are three criteria to achieve optimal results: the capability of equipment, the experience of working on similar projects, and the expertise of human resources involved in production.
In this Domain, RapidDIrect has been working for more than a decade, providing comprehensive Injection Molding Services for diverse applications. We handle general injection moldings, insert moldings, overmolding, and other various technologies.
If you have your drawing ready, our engineers can help you from the beginning, with design optimization and mold making to surface finishing. Meanwhile, automated injection molding equipment in our factory runs 24/7 for consistent, high-quality parts or products with quick leads.
Have further doubts or want to quote your design? Drop your file and queries at our online portal.
Conclusion
We have discussed several types of injection molding technologies, which shows that each has unique production capabilities and material preferences. With the correct technique, manufacturers can produce identical items in large volumes at competitive prices. At the same time, considering your end requirements, material type, design complexity, and project timeline can guide you in the selection process.
FAQs
The common types of injection molding in manufacturing include gas-assisted, insert, 2-shot, co-injection, micro-injection, thin wall, and overmolding.
Generally, injection molding machines are categorized by their driving mechanism (hydraulic, electric, or hybrid) and injection method (plunger or screw-type).
Thermoplastic, thermosets, and elastomers are the leading injection molding materials. However, it is also possible to mold metal and alloys with proper equipment and tooling.
● ABS
● PolyCarbonate
● Nylon
● Epoxy
● Phenolic
● Silicone Rubber, and many more.
Mold classifications (Class 101 to 105) indicate the durability and lifespan of molds based on production volume and material. For example, class 101 refers to high-precision and durable molds, whereas 105 means a low-cost and short-run mold.
The exact cost varies on mold complexity, size, material, and production volume. For example, simple molds cost a few thousand dollars, while complex ones exceed $100,000. Additionally, there are extensive expenses on molding equipment and related systems. So, it is recommended to outsource from a secondary manufacturer for cost benefit.