A Guide for Designers and Engineers
If you’re new to the world of injection moulding (or Injection Molding if you’re in America) or simply want to brush up on industry terminology, this guide is for you. Whether you’re a product designer or engineer, procurement specialist or technical buyer, understanding these terms will help you communicate more effectively and make informed decisions throughout the manufacturing process.
At Roland Plastics, we work with customers across a broad range of industries, such as automotive, medical, aerospace, defence, and consumer goods, supporting projects from prototype through to production. Based in Suffolk, we specialise in plastic component manufacturing using high-performance injection moulding . Let’s explore the essential terminology every industry professional should know
Injection Moulding
Injection moulding is a manufacturing process used to produce parts by injecting molten plastic material into a mould cavity. It is known for its speed, repeatability, precision, and ability to produce complex plastic components at scale. Injection moulding offers high-volume with excellent value per unit.
Thermoplastics
Thermoplastics are plastic polymers that become soft and mouldable when heated and solidify upon cooling. They are widely used in injection moulding due to their ability to be remelted and reshaped. There are literally thousands of different thermoplastics, but common examples include ABS, Polypropylene (PP), Nylon (PA), and Polycarbonate (PC). Different materials also offer different properties such as impact and chemical resistance, strength, flexibility and UV stability depending on the final product’s requirements. You can learn more about the types of plastics on our moulding overview page.
Mould Tooling
Also referred to as tooling or simply “the tool” or “the mould“, this is the metal mould used to shape plastic during the injection process. Tooling can be made from aluminium or hardened steel, depending on production volume and material, both of which offer distinct advantages and disadvantages. Speak to our team and we’ll advise you on the best tooling options for your project
Cavity and Core
The cavity is the hollow space inside the mould where the plastic forms the outer shape of the part. The core forms the internal features and moveable parts of the mould. Together, they create the negative space that the plastic fills during the moulding cycle.
Cycle Time
Cycle time is the total time required to complete one moulding cycle, from mould closing and plastic injection to cooling and ejection.
Clamping Force
Measured in tonnes, clamping force refers to the pressure required to keep the mould halves closed during plastic injection. Roland Plastics operates injection moulding machines from 30 to 320 tonnes, allowing us to manufacture a wide variety of part sizes.
Gate
The gate is the entry point through which the molten plastic flows into the mould cavity. Different gate designs, such as edge gates, pin gates, or hot runner gates, affect how the plastic flows and cools, influencing final part quality.
Runner System
The runner system is the network of channels in the mould that directs the molten plastic from the injection nozzle to the gate and into the cavity.
Sprue
The sprue is the main channel that connects the injection moulding machine’s nozzle to the runner system.
Ejection System
Once the plastic has cooled and solidified, ejector pins push the finished part out of the cavity after the tool has re-opened.
Flash
Flash is excess plastic that seeps out between the parting surfaces of the mould during injection. It is considered a defect and typically results from worn tooling, excessive injection pressure, or poor clamping force.
Parting Line
The parting line is where the two halves of the mould meet. It often leaves a faint seam on the finished component, which must be considered in the part design and may require post-mould finishing.
Sink Marks
Sink marks are small depressions on the surface of a moulded part caused by uneven cooling or excess material. Proper mould design and process control can minimise these cosmetic defects.
Overmoulding
Overmoulding is a process in which a second material is moulded over a base component. This technique is often used to create ergonomic grips, soft-touch surfaces, or ruggedised seals between a product and it’s cable.
Insert Moulding
Insert moulding involves placing a metal or non-plastic insert into the mould before injecting plastic around it. Think the handle of a screw driver or a kitchen utensil!
Multi-Impression Tooling
A multi-impression mould produces multiple identical parts in a single cycle to improve productivity and cost-efficiency for high-volume production. At Roland Plastics, we can support both single and multi-impression tooling and can design your tool depending on your exact product requirements.
Tolerance
Tolerance defines the allowable variation in part dimensions. Injection moulding can achieve very tight tolerances, making it suitable for precision applications like aerospace, medical or defence components.
Tool Transfer
Tool transfer refers to physically moving your injection moulding tool from one location to another. This could be for maintenance purposes, or for changing to a new injection moulding company.
Prototyping
Prototyping allows product designers to test and validate a component before investing in full-scale tooling. Roland Plastics offers design support and prototyping to help customers across the East of England and beyond to bring their products to market quickly and confidently.
Venting
Vents are small openings in the mould that allow trapped air or gases to escape during injection. Proper venting ensures complete cavity filling and minimises defects with the ejected part.
Whether you’re working on a new product concept or a need new reliable UK-based manufacturer to take-over your existing requirements, understanding injection moulding terminology will help you streamline communication and avoid costly misunderstandings.
At Roland Plastics, we work closely with clients across Norfolk, Suffolk, Essex, Cambridgeshire and beyond, offering expert guidance from concept to final delivery. (We also offer 3PL and storage for your products too!)
If you’re ready to discuss your next plastic manufacturing project, get in touch today.
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