Why Choose Injection Moulding?

Plastic and rubber parts of automotive manufacturing by high precision mold injection in the industrial factory

Why Choose Injection Moulding?

October 2, 2019

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Injection Moulding

Injection moulding is the process of manufacturing parts in large quantities. It is mostly used in occasions where the same parts are being produced thousands or millions of times at a time. One of the advantages of using injection moulding is the ability to produce in masses. After the initial cost has been paid, the prices per unit in the process are extremely low. The prices also drop further as more parts are produced. Some of the other advantages of the injection moulding process include:

injection moulding infographic

It Produces Low Scraps and is Repeatable

When compared to other manufacturing processes like CNC machining, the rate at which scraps are produced in plastic injection moulding is very low. CNC is known to cut off substantial percentages off the original plastic block. However, injection moulding can also not be compared to processes like 3D printing which has even lower scraps. The waste produced in plastic injection moulding services come from four areas: the runners, the sprue, gate locations, ejector pins, and the runner system. The sprue is the part that guides molten plastic from the spout of the injection moulding machine to the injection moulding tool. The runner consists of channels that meet with the sprue.

Their function is to guide the molten plastic to cavities within the plastic injection moulding tool. The gate is the part that comes after the runners leading directly to the part cavity. After the injection process, the cooling plastic leaves solid pieces along with the sprue, runners, and gates, if not appropriately contained. After the first part has been created, the second and the rest that follows are practically identical from shape to part size. This is a brilliant characteristic, especially when trying to keep up with brand consistency as well as high volume production of parts.

What Is the Down Side To Injection Moulding?

The process has an upfront cost which is usually very high due to the testing, design, and tooling requirements. Now that the other parts look identical to the first one produced, you will need to make sure that you get the first part right when producing in high volumes. Otherwise, the process that follows including thousands of parts will be a mess. For the first part to be perfect, you will need to:

•    Design and the prototype the part itself to specification- The prototype is first designed on a 3D printer using a different material such as ABS plastic.

•    Design an injection unit tool for the initial production- This is required for generating 300-1000 prototypes with the production material.

•    Refine all surface finish in the injection moulding tool before mass production.

Injection moulding requires uniform wall thickness. For instance, if you were to cut a cross-section, you would realise that the wall thickness is about 2-3mm. This prevents uneven cooling and deformation of part shapes, their wall thickness, and strength. Some of the potentially negative aspects of injection moulding include:

Metal tool for molding rubber products

High tooling cost and large lead times

Tooling is quite a huge process by itself and is only a phase in the whole moulding process. The high cost and time needed come about because you’ll first need to produce a prototyping part before producing the actual moulded part. After the prototype is made and perfected, you’ll now need to come up with a perfect mould tool that can produce duplicates in large volumes with zero error. As you can now see, getting a prototype right and moulding tool with fine details for mass production requires both time and money.

Difficult to make changes

These tools are typically made of steel, so making any changes to them is quite a hustle. In cases where you need plastic added to the tool, you can always make larger cavities by cutting away steel or aluminium depending on what the tools made of. If in your case you need plastic removed from the metal, then what you need to do is decrease the mould cavity size by adding metal to it.

Material Suitable for Injection Moulding

One of the most important factors to consider during injection moulding is the type of material used. These plastic materials directly affect the moulding manufacturing process and performance as well. For you to choose the right material, you have to consider its function and environment. Other factors to consider in thermoplastics are material strength, flexibility, durability as well as color and cost. Below is a list of the most commonly used materials:

Injection moulding machine used for the forming of plastic parts using plastic resin and polymers


Due to its toughness and high melting temperature, nylon is mostly used to produce plastic products like gears and bearings. It is best known for resisting chemicals as well as tear and wear and is cost-effective.


This material is used to produce transparent parts like lighting equipment, window panes, and walls. Due to its tensile strength, it’s often used as an alternative to glass. It’s also scratch-resistant. One of the most common uses is to create food containers. This is as a result of its tasteless and odourless nature hence making it perfect for food preparation and storage.


Often used for making parts that would be made of metal, this material is used for the production of hardened plastic parts. Its chemical compound makes it very strong, rigid, and tough. Its common uses include making knife handles, gears and ball bearings.


What makes a material suitable for use in injection moulding machines or not depends on what is being manufactured. The materials used should meet property requirements as well as be resistant to the environment of the application. For instance, parts that are often used in the kitchen or as part of a moving mechanism would require the use of Polyoxymethylene due to extreme heat and clamping. Places that need lighting or translucent walls like public offices would mean that the material used for construction be made of acrylic material. There are many other considerations to make during the injection moulding process. It all depends on the purpose of the parts being produced.