Injection moulding is one of the most widely used manufacturing processes for mass-producing high-quality plastic parts. This process involves injecting molten material into a custom-designed mould, where it cools and solidifies into the desired shape. From plumbing fittings and medical devices to consumer electronics and clothing, injection moulding enables the mass production of complex, durable, and cost-effective parts, producing thousands to millions of identical parts with minimal waste.
This guide comprehensively explores injection moulding, covering its process, types, key considerations, materials, applications, advantages, and Limitations. Whether you’re evaluating manufacturing options for a project or looking to understand more about the injection moulding process, this guide provides invaluable information.
What is Injection Moulding?
Injection moulding is a formative manufacturing technology that creates parts by injecting molten material into pre-fabricated custom moulds. The material flows into the mould, filling all channels and cavities. Upon cooling, the material solidifies in the exact shape of the mould, replicating highly detailed features. While variations of injection moulding exist for different materials, plastic injection moulding is the most common application. This technology is compatible with both thermoplastics and thermosets. However, thermoplastics are the predominant materials for injection moulding due to their properties, such as low melting point, high flowability, rapid solidification, and thermal stability, which make them well-suited for the process.
Injection moulding is one of the most widely used manufacturing processes, surpassing CNC machining and 3D printing services in applications. This technology is mainly applied in the mass production of identical parts. Injection moulding can produce highly complex parts with a standard tolerance of ± 0.05 mm, depending on the mould’s accuracy. Precision plastic injection moulding achieves tolerances tighter than ± 0.05 mm. Injection moulding can also produce various build volumes, from less than 5 mm³ to over 1 m³.
Injection moulded rubber parts.
A Brief History of Injection Moulding
Injection moulding began in 1872 when John Wesley Hyatt and Isaiah Hyatt patented the first machine for moulding celluloid, an artificial plastic. The process involved melting the celluloid in a barrel and forcing it into a connected mould using a plunger.
A major breakthrough came in 1946 when James Watson Hendry developed the screw-type plastic injection moulding machine, which improved material mixing, flow control, and consistency. This innovation laid the foundation for modern plastic injection moulding and cemented James’s place in the history of injection moulding. By the 1970s and 1980s, CNC machining enhanced mould fabrication, while the introduction of electric injection moulding machines in the 1980s and 1990s improved energy efficiency and precision.
James Watson Hendry’s screw-type injection moulding machine
Today, the injection moulding process benefits from automation, robotics, and real-time process monitoring, making it the leading method for mass-producing plastic parts in various industries. Ongoing advancements in smart manufacturing, sustainable materials, and 3D-printed moulds continue to shape its future.
The Injection Moulding Process
Having explored injection moulding’s history, the next important question is, how does injection moulding work? The injection moulding process from conceptualisation to finished product comprises five stages.
Mould design and fabrication: Creating a custom mould tailored to the part’s specifications.
Machine setup: Configuring the injection moulding machine with the correct parameters.
Material preparation: Selecting and conditioning the raw material
Injection moulding cycle: The core process where molten plastic is injected, cooled, and ejected
Post-processing: Additional steps like trimming, finishing, or quality control
Each of these stages involves multiple individual steps, each critical to ensuring consistent quality, durability, and functionality of the final product.
The injection moulding process
1. Mould design and fabrication
The first stage of an injection moulding project is mould design and fabrication. While it is technically not a part of the actual moulding process, mould fabrication is an all-important preliminary step. In this step, designers first design a 3D replica of the mould using CAD (Computer-Aided Modelling) software. In addition to designing the negative (mould cavity) of the desired geometry, designers incorporate clamping, flow, mounting, ejection, and cooling features, such as runners, gates, and channels, into the design. Designers account for every feature of the final product, including minute details, such as text, screw holes, and surface roughness, incorporating these features into the mould. Engineers create the mould after design and DFM (Design for Manufacturing) optimisation. The image below displays a mould design process in CAD software.
Precision CNC machining and electrical discharge machining (EDM) are the most common technologies for mould fabrication due to their ability to produce highly complex geometries with tight tolerances. EDM is particularly useful for machining extremely hard materials and creating intricate mould features, such as internal channels, deep cavities, and sharp internal edges, which are difficult to achieve with 5 axis CNC machining. In addition, advancements in metal 3D printing have made it possible to 3D print moulds. The image below is a CNC-machined injection mould.
2. Machine setup
After mould creation, the next step in the injection moulding process is setting up the machine. Operators attach the mould to the machine using clamping devices. The mould is connected to the material delivery system, typically a heated barrel containing a helical screw.
Once the mould is in place, the injection moulding machine’s heating system is turned on and set to heat the barrel to the appropriate temperature for the specific material. The mould is also heated to enhance molten material flow and minimise thermal shock. The table below shows the appropriate mould and material temperatures for different. The specific temperature may vary based on materials and operating conditions. Note that heating may not be necessary for certain resins.
Injection moulding temperature chart
3. Material preparation
After setting up the injection moulding machine, operators prepare the raw material. For thermoplastics, this process involves mixing plastic pellets with any necessary plastic additives. Additives alter and enhance various aspects and characteristics of the raw material and the final product, such as colour, mechanical strength, weatherability, fire resistance, aesthetics, and biodegradability. They can also impact the injection moulding process, enhancing flowability, thermal stability, cohesion, and various other factors. Popular injection moulding additives include:
Reinforcements: Improve the final product's strength, stiffness, and other mechanical properties. Examples are glass fibres and carbon fibres.
Lubricants: Minimise friction between the material and the mould, preventing sticking and easing part ejection. Examples are waxes and silicones.
Colourants Provide pigmentation and improve the aesthetics of the final product. Examples include dyes, pigments, and masterbatches.
Plasticisers: Reduce the viscosity of the molten material, improving flow and lowering injection pressure. Examples: Phthalates and citrates.
Flame Retardants: Improve fire resistance of the final part. Examples: Brominated compounds and phosphorus-based additives.
Anti-static Agents: Prevent static buildup, reducing material clumping. Examples: Ethoxylated amines and quaternary ammonium compounds.
Fillers: Increase raw material volume to reduce costs. Modify properties like density, thermal conductivity, or stiffness. Examples: talc and calcium carbonate.
Geomiq utilises process-enhancing additives when necessary. We also offer numerous product-enhancing additives. Simply upload your CAD model and requests on our instant quoting platform, or contact us for recommendations based on your project requirements.
Plastic injection moulding raw material
4. Injection moulding cycle
The Injection moulding cycle is where the actual moulding takes place. It takes a complete cycle to manufacture each injection moulded part. The injection moulding cycle involves the following steps.
Injection
Packing/dwelling
Cooling and solidification
Ejection
An operator or automated system feeds the raw material into the injection moulding machine barrel, typically via a hopper. The screw within the barrel rotates, moving the raw material forward as it melts and homogenises inside the heated barrel. The screw pushes the molten material to the end of the barrel, where it gathers in a shot, significantly increasing pressure. A shot is the volume of material required to fill the mould at a time plus approximately 10%. When enough material and pressure build-up, material flows into the mould, with the built-up pressure forcing the material through all channels and cavities. Some injection mould machines utilise a plunger/piston-type mechanism to inject the molten material.
The machine maintains a holding/packing pressure as the mould fills to compensate for material shrinkage, a process known as dwelling. The mould holds the part as the material cools and solidifies. Injection moulding machines typically feature cooling systems that pass fluid (air, water, or oil) through designated paths in the mould. Once the part cools to a sufficient temperature, the mould opens, and an ejector mechanism pushes out the solid part.
Depending on the material, size of the part, and the machine set-up, the injection moulding cycle from injection to ejection can take between two seconds to two minutes. Several critical parameters, such as injection pressure, material temperature, cooling period, shot volume, and injection speed, are precisely monitored and controlled throughout the injection moulding process to ensure optimal execution and prevent injection moulding defects.
5. Post-processing
The primary injection moulding post-processing step after ejection is trimming, also known as deflashing. This process involves removing excess material that forms around the edges of the part during moulding. Injection moulded parts exit the machine with material deposits around the gate, runners, and sprue: areas where molten material flows into and through the mould. Additionally, flash, a thin excess layer of material that seeps out at the mould-parting lines, forms around the part. These excessive materials are removed, and the markings are sanded to ensure a clean, precise final product. Trimming and deflashing can be performed manually using cutting tools, mechanically with specialised trimming machines, or through advanced methods such as cryogenic deflashing, where parts are exposed to extremely low temperatures to make the excess material brittle for easy removal. The image below is an injection moulded part before and after deflashing
Numerous injection moulding secondary post-processing operations exist. These operations, which are applied to achieve specific functionalities or aesthetics, include the following:
Sanding and Polishing: Sanding removes surface imperfections, smooths rough areas, achieves specific surface roughness, and prepares parts for coatings. Different grits of sandpaper are used. Polishing creates a high-gloss finish, especially for transparent plastics. Methods include mechanical polishing, polishing compounds, and flame polishing.
Blasting: Manufacturers blast finished parts with fine media (glass, ceramic, or plastic beads) at high pressure to achieve a uniform matte finish, improve grip, or enhance aesthetics. Operators take care to prevent deformation in softer plastics.
Coating: While plastics can be pigmented during moulding, post-processing methods such as painting, dyeing, and functional coatings (e.g., UV-resistant or wear-resistant layers) enhance durability and aesthetics. Some coatings also improve grip or reduce reflections.
Marking and Texturing: Pad printing, laser etching, or silk-screening add logos, serial numbers, barcodes, or decorative textures.
Plating and Metallisation: Manufacturers use techniques such as electroless plating and vacuum metallisation to apply a metal layer (e.g., nickel, chrome, or gold) to plastic parts to enhance their durability, conductivity, or decorative appeal.
A crucial aspect of injection moulding postprocessing is surface finish: the texture of a finished part's surface without coating or painting. The mould’s machining surface roughness impacts the injection moulded part’s surface finish. However, several techniques exist to achieve very specific surface finishes.
Injection Moulding Surface Finish
The plastic manufacturing industry standardises injection moulding surface finishes according to SPI guidelines. Outlined by the Plastics Industry Association (formerly known as the Society of the Plastics Industry), these guidelines categorise and define surface finishes for injection moulded parts. The table below shows industry-standard plastic injection moulding surface finishes.
Another common but less popular surface finish guideline is the VDI (Verein Deutscher Ingenieure) guideline. See our injection moulding surface finish guide for more information. The VDI guidelines are less comprehensive than the SPI, hence its reduced popularity. See our injection moulding surface finish guide for more information. The image below is a visual representation of standard SPI injection moulding finishes.
Geomiq offers SPI-A2 (high polish), SPI-B1 (600 grit paper), SPI-C1 (600 stone), Bead blast - light texture, and Bead blast - medium texture as standard finishes via our instant quoting platform. You can request any other finish you require.
Order high-quality injection moulded parts from Geomiq
An injection moulding machine comprises several key components, each performing key roles in the plastic injection moulding process. These components are grouped into five major systems and units - Mould, Injection unit, Clamping unit, Power system, and Control system.
1. Injection Unit
The injection unit is responsible for melting and injecting the material into the mould. It consists of the following components:
Hopper: Holds and feeds the raw plastic pellets into the barrel.
Barrel: Houses the screw and provides a chamber where the plastic is heated and melted.
Screw: Rotates to mix, melt, and convey the plastic material towards the mould.
Heaters: Surround the barrel to provide the necessary heat for plastic melting.
Nozzle: Directs the molten plastic from the barrel into the mould cavity.
2. Clamping Unit
The clamping unit holds the mould in place and applies the necessary force to keep it closed during injection and cooling. It also features an ejector system for dislodging the solidified product from the mould. It includes:
Clamping Mechanism: Applies force to keep the mould shut during injection and cooling.
Movable and Stationary Platens: Secure the mould halves in position.
Tie Bars: Provide structural support and guide the movement of the movable platen.
Ejector System: Pushes the finished part out of the mould after cooling.
3. Mould
A mould is a precisely engineered injection moulding tool that shapes molten material into the desired part geometry. It determines the final part's shape, dimensions, and surface features and is custom-made for each product design. It is the most critical component in an injection moulding machine as various aspects of this tool, such as the material, design, quality, tolerance and surface roughness, significantly affect product outcome. In addition to the hollowed-out negative of the part, the mould includes features such as runners, gates, and cooling channels to guide the flow of material, ensure proper filling, and regulate the cooling process for optimal part quality.
The mould is an intricate tool comprising the following components, features, and systems:
Cavity and Core: The negative and positive impressions of the final part. The cavity forms the part's external shape, while the core defines its internal features.
Sprue, Runners, and Gates: The sprue is the main channel through which molten plastic enters the mould from the injection nozzle. From there, runners distribute the material to one or multiple cavities, and gates control the final entry point of the plastic into the mould.
Cooling System: Cooling channels circulate water or oil to regulate the mould’s temperature, ensuring uniform heat dissipation. Effective cooling reduces cycle times and minimises defects such as warping or sink marks.
Ejector Pins: Ejector pins push the part out, while air blasts and stripper plates assist in releasing delicate or complex geometries.
Venting System: Small vents in the mould allow trapped air and gases to escape during injection, preventing defects such as short shots, burn marks, and incomplete filling.
Mould Base and Plates: The mould base houses and supports all the mould’s components, ensuring structural integrity. Clamping plates secure the mould to the injection moulding machine, while support plates provide stability during operation.
Mould Manufacturing
Manufacturers commonly fabricate moulds using CNC machining services, such as CNC milling and CNC turning, due to their ability to produce complex components with high precision and tight tolerances. Electrical Discharge Machining (EDM) is also widely used in mould fabrication, particularly for creating intricate features such as deep cavities, sharp corners, and undercuts that are challenging to achieve with conventional CNC milling. EDM machining is also highly effective for machining extremely hard materials, making it indispensable for working with hardened steel moulds. Advancements in metal 3D printing services now make it possible to create prototyping moulds cost-effectively.
Mould Material
Depending on the application requirements, plastic injection moulds are usually made of metals, typically aluminium and steel. Considerations in material selection for moulds include cost, speed, tolerance, durability, and production volume. Aluminium moulds typically cost less and are easier and faster to machine, given aluminium's machinability. These moulds are suitable for prototyping and low-volume production. However, their relatively inferior mechanical properties, temperature-induced dimensional variation, and susceptibility to wear and damage after repeated clamping and injection cycles make them unsuitable for very high-volume productions and parts requiring extremely tight tolerances. Note that these limitations do not apply in many applications. Aluminium moulds are perfectly suitable for up to 10,000+ production cycles, depending on factors like aluminium grade, part material, and design complexity.
On the other hand, steel moulds are better suited for full-scale, continuous industrial production. These moulds, typically made from H13, S136, and P20 tool steels, are extremely durable and capable of withstanding high temperatures, pressures, and long production runs. While they cost 1.5 to 3 times their aluminium counterparts, steel moulds are capable of 100,000 to millions of production cycles. Conversely, steel has a lower thermal conductivity than aluminium, resulting in longer heating and cooling times during the injection moulding process. Material selection is a vital aspect of mould fabrication. Geomiq's team of experts analyses your project's specific requirements and selects the most appropriate mould material, balancing cost, durability, speed, and efficiency.
4. Power system
Injection moulding machines are powered by either a hydraulic or an electric system, which drives the movement of the injection and clamping units. This system provides the required force to turn the screw or plunger. It consists of:
Servo Motors (in electric injection moulding machines): Provides the torque that turns the screw.
Hydraulic Cylinders (in hydraulic injection moulding machines): Provide force to move the clamping and injection mechanisms.
Pumps and Valves: Regulate hydraulic pressure and flow (in hydraulic systems).
5. Control System
The control system manages the operation of the entire plastic injection moulding machine. It controls monitors and controls parameters such as pressure, temperature, and speed. This system also controls and automates the physical movements of the machine’s components. The control system includes:
Sensors: Monitor and adjust variables such as temperature, pressure, and injection speed.
Actuators: Physical controls machine components based on control inputs.
Computer/Controller: The brain of the injection moulding machine. It automates machine functions based on inputs and control feedback.
User Interface: Allows operators to program the injection moulding process, stipulating parameters such as temperature, pressure, and cycle time.
Types of Injection Moulding
Several injection moulding technologies/techniques exist, each suited for different materials, part geometries, and performance requirements. These techniques are variations of the conventional injection moulding process, with differences in mould design, injection moulding machine, and process execution.
Thermoplastic injection moulding
Also known as plastic injection moulding, thermoplastic injection moulding is the most common injection moulding process. In most contexts, the term “injection moulding” refers to this process. Regarded as conventional injection moulding, plastic injection manufactures parts from thermoplastic materials using the standard moulding process: thermoplastic material is melted and forced into a pre-fabricated mould. This material cools and solidifies in the shape of the mould. The following variations of the conventional injection moulding process exist:
Micro Injection Moulding: Used for manufacturing extremely small and precise plastic components. The plastic injection moulding machine and mould are relatively small, corresponding to the part's size.
Thin-Wall Injection Moulding: Designed for lightweight parts with reduced material usage, commonly used in packaging and consumer electronics. The moulds in this plastic injection moulding process are specifically designed to produce thin walls. Moulding parameters are very closely monitored to prevent warping and shrinkage.
Low-Pressure Injection Moulding: This process is ideal for producing delicate components, such as encapsulating electronics, where high pressure could damage internal parts. Using lower injection pressures ensures that the moulded parts are formed gently without compromising the integrity of sensitive components.
Gas-Assisted Injection Moulding: This process involves injecting gas into the molten plastic to create hollow sections, reducing weight and material usage while improving dimensional stability. The plastic injection moulding machine and the mould feature parts that facilitate gas flow.
Gas-assisted injection moulding process
Thermoset injection moulding
Thermoset injection moulding is a variation of injection moulding designed for thermosetting plastics, a class of plastics that undergo an irreversible chemical reaction when heated, resulting in a permanently rigid structure. Unlike thermoplastics, cured thermosets do not remelt when heated. In thermoset injection moulding, the raw material, usually a liquid or viscous thermoset paste, is injected into a preheated mould under controlled pressure. Once inside the mould, the heat and pressure trigger a chemical reaction that causes the material to cure and harden. The polymer molecules form irreversible crosslinks, ensuring that the final part retains its shape and mechanical properties.
Reaction injection moulding
Liquid silicone rubber injection moulding
Liquid silicone rubber injection moulding is a process for manufacturing silicone rubber parts using liquid silicone. Liquid silicone rubber is a thermoset material that is injected in its liquid form into a preheated mould cavity. The material is then cured by heat or a chemical reaction inside the mould, forming a flexible, durable silicone part. Liquid silicone rubber injection moulding is very similar to thermoset injection moulding, the main difference being the elastomeric nature of liquid silicone rubber.
Liquid silicone rubber injection moulded parts
This process is often used for medical devices, seals, consumer wearables, food packaging, etc., where flexibility, precision, and resilience are key requirements. Liquid silicone rubber's low viscosity also allows for the production of intricate designs and fine details, even in very thin sections.
Insert Moulding
Insert moulding is a plastic injection moulding process in which a pre-made component or insert, such as metal parts, screws, or electrical contacts, is placed into a mould cavity before injection. The thermoplastic or thermoset material is then injected around the insert, which is encapsulated by the material. This process allows for the creation of parts that combine the strength and functionality of the insert with the versatility and design freedom of the plastic material. Examples of everyday items manufactured via insert moulding are USB connectors, audio jacks, screw knobs, and cable clips. You'll notice a fusion of metal and plastic materials in each of these items.
Insert moulding is commonly used in applications requiring reinforcement or functional integration, such as tools, connectors, and fasteners. Its main advantage is the ability to combine multiple materials and processes in a single moulding step, improving efficiency and reducing the need for additional assembly.
Overmoulding
Overmoulding is similar to insert moulding but involves injecting material over an existing substrate. The substrate could be a previously moulded part or another material, such as rubber over plastic or plastic over metal. In this process, one material is injected onto a substrate to create a multi-layered part with enhanced aesthetic appeal, ergonomics, or functionality. The substrate serves as the core material, while the overmould adds properties like soft-touch surfaces, sealing capabilities, or improved mechanical strength. The image below is an overmoulded part with
Overmoulding is frequently used for products requiring multi-material components, such as consumer goods, tools, and sporting equipment. Specific examples include toothbrush handles, game controllers, razors, and protective gear. Overmoulding allows for the creation of parts that are both visually appealing and durable, with the ability to meet specific functional needs.
Metal injection moulding
Metal injection moulding is a specialised powder metallurgy process that combines the flexibility of injection moulding with the strength and durability of metals. In this process, fine metal powders are mixed with a binder material to create a feedstock, which is then injected into a mould cavity under high pressure. The part is then sintered in a furnace to remove the binding, fuse the metal particles, and achieve the final part's density and strength.
Metal injection moulding is used to produce complex metal parts in high volumes, with applications ranging from aerospace and automotive to medical and consumer electronics. It is particularly useful for producing small, intricate parts with tight tolerances that would be difficult or expensive to manufacture using traditional metalworking techniques.
Injection Moulding Materials
The injection moulding process is compatible with a wide range of thermoplastics, thermosets, elastomers, and metals. These materials offer a diverse set of characteristics that influence performance criteria, such as strength, flexibility, heat resistance, and chemical compatibility. Choosing the right material is crucial to achieving the final product's desired mechanical properties, durability, and cost-effectiveness. Geomiq offers over 50 injection moulding materials.
Thermoplastics
Thermoplastics are the most commonly used materials in injection moulding. These materials start as pellets; they soften when heated and harden when cooled, allowing them to be remelted and reshaped multiple times without significant degradation. This characteristic is the primary difference between thermoset vs thermoplastic materials.
Their ubiquity in injection moulding is a result of their characteristics, such as high flowability, thermal stability, and rapid cooling, which perfectly suit the injection moulding process. Furthermore, numerous types of thermoplastics exist with varying beneficial characteristics, making these materials appropriate for countless applications. Common plastic injection moulding thermoplastics include:
Polypropylene (PP): Lightweight, flexible, and resistant to chemicals and fatigue. Used in automotive interior components, medical syringes, food containers, and hinges (e.g., living hinges in bottle caps).
Acrylonitrile Butadiene Styrene (ABS): Strong, impact-resistant, and easy to machine. Commonly used in electronic housings, automotive dashboards, tool casings, and LEGO bricks.
Polyethylene (PE): Available in different densities, primarily HDPE and LDPE, offering durability and chemical resistance. Injection moulded applications include caps and closures, storage bins, wire insulation, and rigid industrial parts.
Polycarbonate (PC): High impact strength and transparency. Commonly used in protective eyewear, LED light covers, automotive headlamp lenses, and durable enclosures.
Polyamide (Nylon, PA): High wear resistance, toughness, and low friction. Found in gears, bushings, brackets, cable ties, and structural automotive components.
Polyoxymethylene (POM/Acetal): Excellent dimensional stability, low friction, and wear resistance. Used in precision parts like gears, bearings, fuel system components, and pump housings.
Polystyrene (PS): Available in both general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS). Injection moulded applications include disposable cutlery, plastic casings, laboratory trays, and lightweight consumer goods.
Polyethylene Terephthalate (PET): While commonly associated with blow moulding for bottles, PET is used in injection moulding for preforms, rigid trays, cosmetic packaging, and mechanical components.
Thermosets
Thermosetting plastics differ from thermoplastics in that they undergo a permanent chemical crosslinking reaction when heated and moulded. Once cured, they cannot be remelted or reshaped, making them ideal for applications requiring high heat resistance, mechanical strength, and dimensional stability. Common thermosets include:
Epoxy Resins: Used in high-strength composites.
Phenolic Resins: Heat-resistant and commonly used in electrical components.
Polyurethane (PU): Used in reaction injection moulding (RIM) for lightweight, rigid structural parts.
Elastomers
Elastomers are flexible, rubber-like materials with excellent elasticity and durability. These materials can be either thermoplastic (TPE) or thermoset (silicone rubber). Examples include:
Thermoplastic Elastomers (TPE): These can be reprocessed like thermoplastics while retaining rubber-like properties and are used in grips and seals.
Liquid Silicone Rubber (LSR): A thermoset elastomer with high heat resistance and biocompatibility, ideal for medical devices and automotive seals.
Metals
Metal injection moulding is used to produce small, high-precision metal parts by injecting a metal powder-binder mixture into a mould. The binder is later removed, and the part is sintered to achieve full density. Common metal powders used include:
Stainless Steel: Corrosion-resistant and widely used in medical and aerospace applications.
Titanium: Lightweight and biocompatible, often used for medical implants.
Copper Alloys: Excellent thermal and electrical conductivity, used in electronic components.
Metal injection moulding is more appropriate than CNC machining for applications requiring cost-effective, large-scale production. It is also used for metal parts with highly complex geometries.
Injection Moulding Design Tips
Designing for injection moulding is a complex, multifaceted process. In addition to designing the product, designers need to design the mould considering several critical factors. The product design itself has to account for the specifics of the injection moulding process. Therefore, a 3D model for 3D printing may not be suitable for injection moulding. The following are a few design tips:
Maintain Uniform Wall Thickness: This ensures even cooling and reduces warping, sink marks, and stress concentrations. If variations are necessary, use gradual transitions to avoid defects.
Incorporate Draft Angles: This allows easy part ejection from the mould, reducing the risk of sticking or damage. Depending on the part's complexity, we recommend a typical draft angle of 1–3° per side.
Avoid Sharp Corners: Sharp corners create stress concentrations and increase the risk of cracking. Use fillets or rounded edges to improve material flow and structural integrity.
Optimise Rib and Boss Design: To prevent sink marks, ribs should be 40–60% of the nominal wall thickness. Bosses (used for fasteners) should have filleted bases and be connected to ribs for strength.
Ensure Adequate Venting: Proper venting prevents air traps, burn marks, and incomplete fills. Vents should be 0.01–0.05 mm deep to allow air escape without plastic leakage.
These design tips enhance part quality, reduce production costs, minimise defects, and improve the injection moulding process. See our comprehensive injection moulding design guide for many more design tips and rules.
Applications of Injection Moulding
Injection moulding’s ability to turn a variety of materials into finished products with complex shapes, tight tolerances, and high consistency has made it one of the most widely used modern manufacturing technologies. As a result of this ability and the ubiquity of plastic, the injection moulding process is used in a plethora of applications across numerous industries, predominantly in plastic parts manufacturing. In an over 20 billion pounds plastic manufacturing industry (UK alone), injection moulding is responsible for the majority of all plastic products, from insulation fixtures in construction to shoes.
Due to its repeatability, scalability, and speed, injection moulding is mainly used in medium- to large-scale parts production. Injection moulding machines are typically incorporated into fully automated production lines featuring other manufacturing, conveying, inspection, and packaging technologies. Whether you require 500 units or a million plus units, Geomiq’s injection moulding service can handle your injection moulding project.
Building and Construction
Injection moulding is used in construction to manufacture pipe fittings, electrical conduit boxes, window and door frames, fasteners, insulation components, and panel clips. Durable plastics like PVC and polypropylene are popular for these applications.
Automotive and aerospace
Many interior and exterior components are injection-moulded, such as dashboards, bumpers, door panels, grilles, air vents, lighting housings, and fluid reservoirs. Under-the-hood parts, including clips, brackets, and cable insulation components, are also produced using variations of the injection moulding process.
Electrical, Electronics, and Telecommunications
Injection moulding is critical in the electrical and electronics industry for manufacturing switch housings, circuit board enclosures, connectors, sockets, protective casings, cable management components, router and modem casings, fibre optic junction boxes, and countless other electronic components.
Sports and fashion
Sports injection moulding is essential for producing helmets, mouthguards, protective padding, footwear soles, fitness equipment components, and various sports accessories. High-performance polymers ensure that these products offer superior impact resistance and durability.
The injection moulding process is widely used in the production of shoe soles, sunglasses frames, jewellery, watch casings, and handbag hardware. It allows for the mass production of stylish and durable fashion accessories, often with intricate designs and superior finishes.
Medical, Healthcare, and Biotechnology
Injection moulding is crucial for making syringes, IV components, surgical instrument handles, inhalers, diagnostic test kits, prosthetic components, laboratory consumables, and diagnostic device casings. Biocompatible plastics are selected for these products to ensure patient safety and the ability to withstand sterilisation.
Consumer Goods
Many everyday products, such as toys, kitchen utensils, storage containers, furniture parts, phone cases, and appliance housings, are made through injection moulding. This process ensures cost-efficiency, durability, and precision in high-volume manufacturing.
Advantages of Injection Moulding
Injection moulding is one of the most used manufacturing technologies worldwide today, especially for the large-scale production of plastic parts. This ubiquity results from the many beneficial characteristics and advantages of this technology. Some of the advantages of the injection moulding process are as follows.
Complex geometries
Injection moulding can create highly complex geometries through functional moulds. Advanced mould fabrication technologies, such as electrical discharge machining and metal 3D printing, allow manufacturers to create moulds with very limited geometry limitations.
High part quality
The injection moulding process does not negatively impact the final quality of fabricated parts. Rather, it allows you to significantly improve the quality of finished products by adding product-enhancing additives.
Repeatability
After the initial set-up, a single injection moulding machine and a single mould can produce hundreds of thousands of identical products without variations in quality or geometry. This is one of the main advantages of injection moulding, which makes it excellent for large-scale production.
Speed
Injection moulding is a highly rapid process. The cycle, from injection to ejection, can take between two seconds and two minutes. This means that an injection moulding machine can produce 30 to 1,800 units per hour, compared to CNC machines and 3D printers, which can take multiple hours to produce a part, depending on its size and complexity. Speed is another significant advantage of injection moulding that supports large-scale production.
Low cost per unit for large productions
Injection moulding offers one of the lowest costs per part of all manufacturing technologies. Plastic, the main injection moulding material, is relatively inexpensive. In addition, the injection moulding process is fast and requires minimal human intervention. The main cost of an injection moulding project is the mould. However, this cost is spread over several units, driving down per-unit costs through economies of scale. These factors make injection moulding a highly cost-effective process for large-scale production.
Versatility
Injection moulding is a highly versatile and capable process. This technology can be adapted to various build volumes from less than 5 mm³ to over 1 m³. It is also compatible with various plastics and metals, can produce different surface finishes, and allows you to modify part properties with additives.
Disadvantages of Injection Moulding
While the injection moulding process has many benefits, it also has certain limitations that make it unsuitable for certain projects and applications. Some of the disadvantages of injection moulding are explored below.
High set-up cost
Injection moulding has significantly high set-up costs, with injection moulding machines costing as much as £1 million. In addition, moulds cost around £1,000 for simple, low-volume production to well over £100,000 for large, complex moulds used in full-scale production.
Inefficient for prototyping and small production
Because of the time, cost, and effort involved in mould design and fabrication, the injection moulding process is not efficient or cost-effective for prototyping or one-off productions. Engineers typically spend days to weeks designing and manufacturing a mould, making it impractical to expend this time and cost on a one-off part.
Material limitations
Injection moulding is limited to thermoplastics, thermosets, elastomers, and a few metals. While it is compatible with numerous plastics, the injection moulding process is not as material-compatible as technologies such as CNC machining, which is compatible with metals, plastics, wood, glass, paper, stone, and ceramics.
Is Injection Moulding Appropriate for Your Project? Factors to Consider
After reviewing the applications, capabilities, advantages, and limitations of injection moulding, the next step is determining whether it is the appropriate manufacturing method for your specific project. Injection moulding is highly efficient and cost-effective for many applications, but it may not always be the best choice, depending on the factors:
Production volume
Part geometry and complexity
Material selection
Lead time and production speed
End-use
Note that these factors are interconnected and should be jointly considered.
Production volume
Injection moulding requires a high initial investment in tooling, particularly for creating precision-engineered moulds. However, this cost is offset over large production runs due to low per-unit costs. Therefore, it is best suited for high-volume production where economies of scale make the process cost-effective. We recommend starting from thousands of units. Five hundred units remain relatively cost-effective but with less expensive moulds. Alternative technologies such as 3D printing and CNC machining should be considered for numbers lower than this. The chart below compares cost and production volume for custom manufacturing technologies.
Part geometry and complexity
Injection moulding can produce highly detailed parts with intricate geometries, including thin walls, undercuts, and fine surface textures. It is best suited for parts with consistent wall thickness, well-planned draft angles, and features that can be formed using a split mould. It is also great for hollowed geometries. Conversely, injection moulding is not ideal for extremely large parts (due to mould size constraints), highly variable wall thickness, solid designs, or thick solid geometries. Injection moulding offers more geometry freedom than CNC machining (especially when the mould is manufactured via EDM) but less than 3D printing.
Material Selection
The process is compatible with various thermoplastics, thermosets, and elastomers. The material must withstand the high pressures and temperatures of the injection process. Thermoplastics like ABS, polypropylene, polycarbonate, and nylon offer excellent flowability and durability. Injection moulding is incompatible with materials with poor flow characteristics, extreme brittleness, or degradation at high temperatures. CNC machining remains the best option for non-plastic materials. 3D printing is also an option for metals.
Lead Time and Production Speed
Once the mould is fabricated, injection moulding enables rapid, high-volume production with short cycle times. However, initial tooling development can take weeks or months, making injection moulding best suited for projects with long-term production needs and high volume demands. It is not ideal for urgent, short-run projects. Faster alternatives like CNC machining or 3D printing may be more practical. The chart below compares lead time and number of parts.
End-use (Mechanical properties)
Injection moulding produces parts with uniform grain structure. An injection-moulded part is a homogeneous solid unit of plastic with anisotropic properties. When the molten material enters the mould, it solidifies as a unit, maintaining the mechanical properties of the part. This makes injection moulding ideal for moving and load-bearing parts. On the other hand, while industrial 3D-printed parts are sufficiently strong for most applications, they exhibit some weakness in the Z plane due to the layer deposition technique of 3D printing.
Getting Started With Injection Moulding
Once you’ve determined that injection moulding is the ideal manufacturing technology for your project requirements, the next step is to plan and execute the process effectively, beginning by selecting an injection moulding manufacturer. Geomiq is your ultimate injection moulding service provider, offering expertise in mould design, precision manufacturing, and material selection to ensure the highest quality parts for your project. The following steps will take you from conceptualisation to delivered parts. Let’s get started!
Step 1: Upload design and select preferences
Upload a 3D CAD design of your required part on our instant quoting platform, and select your preferences, including material, tolerance, surface finish, markings, inserts, intended production cycles (for the mould), and QC requirements. Place your order, make payment, and we will take over from here. However, while our instant quoting platform is designed to analyse your design and provide an instant quote, most injection moulding projects require manual quoting due to the many variables involved. This brings us to step 2.
Step 2: Design Validation
First, we ensure your part design is suitable for injection moulding. Design validation involves evaluating the material choice, geometry, and overall manufacturability to ensure the design can be efficiently produced. Based on these factors, our engineers will present a quote. Our design and manufacturing experts provide recommendations when required or requested.
Step 3. Mould Design
Once the part design is validated and the order is placed, we will proceed with creating a mould design. This includes determining the best approach for the mould's structure, cooling system and features to ensure optimal production.
Step 4. Prototype Development
For complex designs, a pre-production sample is created, typically through rapid prototyping methods such as 3D printing. This helps to verify the part's functionality and design fit before proceeding to full-scale production.
Step 5. Lead Time Estimation
During this stage, we assess the lead time needed for manufacturing the mould, procuring materials, and setting up the production process. This timeline will help plan for delivery and any potential delays.
Step 6. Mould Fabrication
With the design finalised, the actual mould is fabricated. This step involves precision machining to create the cavity and core and any necessary cooling and ejection features. The fabrication time depends on the complexity of the mould.
Step 7. T1 Sampling
The first test injection cycle (T1) is conducted to produce initial parts. This stage helps identify any mould or part design issues, such as material flow or cooling inconsistencies. Adjustments can be made if needed. We send you this sample for review.
Step 8. Full-Scale Injection Moulding
Once the T1 sampling is validated, we proceed with full-scale production, continuously monitoring and optimising the process to ensure consistent quality and efficiency. Geomiq has the capacity to handle continuous production runs of millions of units. We also store your moulds to save on costs for any future projects.
Step 9. Inspection and QC
All finished injection moulded parts undergo a series of standard inspection and quality control processes to ensure thatgle defective part is included in the final delivery. In addition to our free standard QC procedures, customers can request additional inspections, such as FAIR AS9102 and CMM Inspection with Dimensional Report.
Step 10. Delivery
Geomiq delivers your finished product right to your doorstep, anywhere in the world.
Want to get started with injection moulding - upload your parts here
Mechanical Engineer, Founder and CEO of Geomiq, an online manufacturing platform for CNC Machining, 3D Printing, Injection Moulding and Sheet Metal fabrication. Our mission is to automate custom manufacturing, to deliver industry-leading service levels that enable engineers to innovate faster.
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