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When you look at a small plastic cap, it’s hard to imagine the level of technical knowledge that’s gone into making it. Although plastic components may just be one small part of a much larger product or machine, it’s essential that they perform, both in terms of quality and function.

Just a small change in the tolerance or a slight fault in the production of a component can cause problems for your process or your customers, for example:

  • A cap that doesn’t cover a valve properly can cause dirt and ingress to enter a system, or mean that materials leak from the process, threatening manufacturing downtime
  • A motion component that doesn’t operate correctly in a washing machine can cause, at best, consumer inconvenience and at worst real threats to a customer’s safety and your company’s reputation tarnished
  • An electrical part that malfunctions in a car can be a real threat to people’s safety and cause significant damage to the vehicle


This guide will explain the considerations that experienced manufacturers take into account to ensure they are creating accurate components. This means you can be aware of the variables involved in the process and can make an informed decision about the components manufacturer you choose.


What affects the consistency of injection moulded components?

To make sure that plastic components are of a consistent high quality, it is essential that the injection moulding process is as accurate and efficient as possible. As a highly complex process, there are several variables in injection moulding which will influence the final quality and consistency of an injection moulded component.


An established manufacturer will have an in-depth knowledge of injection moulding variables and will also:


  • Understand the effects of changes in pressure and temperature
  • Know the complexities of mould design and polymer selection
  • Select the appropriate machinery for each type of component, experienced manufacturers provide consistent and high-quality component products.

As part of this guide, we’ll examine five different areas of the injection moulding process and the controls needed to ensure a consistent final product, namely:

  • Pressure
  • Temperature
  • Mould design
  • Polymer choice
  • Machine specification

This will help you to have a greater understanding of the process so you can ask the right questions and guarantee you get the component quality you need.



The impact of pressure

Usually, the injection moulding process involved two different types of pressure, injection pressure and hold pressure. Injection pressure is the force with which molten plastic is pushed into the moulding tool. Hold pressure is the tension with which the cavity and core, the two halves of the tool, are pressed against each other to pack the final component into the correct form and size. Getting the balance of these two pressures is essential to ensuring that the final product has high material qualities and moulds into an accurate form.

With injection pressure, it’s important to consider the characteristics and volume of the polymer that is being used in the process. Particular polymers, such as nylon, are sensitive to intense pressure, so injecting it at a high speed will damage the plastic and mean that a final part isn’t formed correctly. Alternatively, injecting the polymer at too low a pressure will mean that the coverage of the polymer within the moulding tool will not be correct, causing faults in the aesthetics and strength of the final part.

The injection pressure also needs to be considered alongside the volume of polymer that’s being injected, as dependent on the size and design of the moulding tool, it will be filled to around 95% and 98% of its final form. The greater the volume of polymer, the more pressure that needs to be applied and vice versa. Getting this right also means that the polymer won’t get stuck in the gate or leak out of the moulding tool.

The hold pressure is equally challenging to get right as not only do manufacturers need to consider the capacity of the tool to handle the applied force (a smaller, more delicate tool won’t take as much pressure) but also consider the force that needs to be applied so there’s an even distribution of the polymer within the tool. Too little pressure and the component won’t form correctly, with polymer potentially leaking outside of the tool. Excessive pressure will affect the structural integrity of the part, potentially causing warpage or distortion in the part.


Considering the mould design

There are many important elements of the tool design manufacturers consider when creating a high-quality consistent part.

In combination with the design of the tool, manufacturers need to balance the polymer type and cycle time to ensure the plastic has adequate time to form and cool before being ejected. The more complex the design of the part or the more cavities it has, and the higher temperature the plastic can be heated to, the longer the cycle time needs to be to ensure the component is fully formed.

Aesthetic elements play a part in mould design too. The location of where the two halves of the tool, the cavity and core, come together is an important consideration, as it will leave a parting line at the join, affecting the final aesthetics if the mould tool isn’t positioned correctly.

Similarly, the position of where the ejector plates or pins push out the formed part needs to be considered and an experienced manufacturer will be able to advise how best to create the mould tool to avoid these aesthetic imperfections.


The importance of accurate temperature

Similarly to pressure, there are two types of temperature that have to be tightly controlled during the injection moulding process. Barrel cylinder temperature (which is the temperature of the heaters which surround the barrel feeding the injection moulding tool and shear heat temperature) is caused by the friction of the screw against the polymer during the screw back phase.

In addition, thermoplastics are the most common type of polymer used in injection moulding and are highly sensitive to temperature differences, meaning that even a decimal point change in temperature will have a huge impact on the final aesthetic and functional quality of a part.

By balancing the temperature of the barrel cylinder and that caused by screw back, manufacturers will prevent the plastic from becoming too liquid or too solid. As well as causing the polymer to become too molten and not fix into the correct shape in the tool, high polymer temperatures can also cause aesthetic damage to a component such as burn marks and flash, particularly if the tool becomes too hot to mould the part correctly. A lack of heat in the barrel however will cause inconsistent polymer flow into the tool, potentially causing blockages in the barrel or gate or leading to a lack of plastic distribution within the moulding tool.

It’s also important for manufacturers to take the cooling time of a polymer into account when designing the mould for the part because, as the polymer material cools, the part will start to shrink. By taking the cooling rate into account, manufacturers can ensure that the design of the tool will produce the correctly sized component and ensure that the hold pressure isn’t released before the component is fully packed and formed.


Selecting the correct polymer

Choosing a plastic that’s right for the aesthetic and functional needs of your component is a fundamental decision to make in the process.

Thermoplastics are the most common polymer used to create injection-moulded components. However, no two types of thermoplastic have the same materials characteristics. There are two main categories of thermoplastics, amorphous and semi-crystalline. The major difference between these two types of plastic is their molecular structure, causing them to behave differently under certain conditions.

The randomly ordered molecular structure of amorphous plastics means they gradually soften as temperature increases making them a more stable plastic to mould, with greater tensile strength and resistance when cooled. In contrast, semi-crystalline plastics have a highly ordered structure, meaning they’ll melt quickly at a specific temperature. This makes them tricky to mould with but tougher under stress, wear and loads.

The ultimate function, aesthetic and material qualities of your part will help you decide which type of plastic you need. Your manufacturer should be able to advise on this and adjust the injection moulding process and mould design to your selected polymer.


Using the right spec of machine

No single injection moulding machine is able to create all types of parts consistently and accurately. Different types, shapes and sizes of components require different machines, so ensuring that a manufacturer has the right spec of machine for the complexity of a part and the scale at which it needs to be produced.

If your business needs a range of different component types manufactured at scale, then it’s key you choose a company that has a variety of machine specs for different types of tooling and production scales. Also, making sure a manufacturer has a good maintenance and machine replacement strategy is essential to reducing the likelihood of production downtime and delays in delivering the parts you need. In short, a manufacturer with a variety of machine specs can deliver a wider range of accurate components.


How does Essentra Components consistently create high-quality components?

The key to making sure our components are of a consistent high quality is in the expertise we employ within our global workforce. As well as employing experienced technical experts who oversee the injection moulding process and develop both our standard and custom components for customers, we have distribution teams who regularly ship more than 17,000 orders each week across the world.

Our manufacturing and distribution expertise helps us to deliver thousands of consistent components efficiently from our 12 global sites. This means that customers can get the high-quality parts they need when they need them, reducing lead times and preventing disruptions on the production line, as well as ensuring that your final product or system functions and looks its best.

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Whether you’re designing or assembling a new product, ensuring that your plastic components are made of the best materials and to the closest tolerances is essential.

As well as affecting the quality of the final product, selecting an inaccurate part can cause faults in its function and lead to increased costs and customer dissatisfaction.

Plastic injection moulding is one of the most popular manufacturing methods for producing plastic components across the Australia and wider world. 

However, to guarantee a consistent level of quality, manufacturers have to consider and control a range of parameters within the process, such as temperature, mould design and machine efficiency. For engineers and assemblers to ensure they have the highest quality parts possible, they need to choose a manufacturer who’ll offer expertise at each stage of the process.


How to choose the right manufacturer

Customers seeking a plastic parts manufacturer should be aware of what’s involved in the injection moulding process and what level of input to expect from a components provider at each stage.

Our Global Process Development Manager, Chris Butler, also offers assemblers and engineers advice on the types of questions to ask manufacturers before ordering parts from them:

  • Does the supplier have a good history and background in manufacturing the type of products that the customer requires?
  • What are the manufacturing capabilities of the company?
  • What manufacturing and quality systems are in place to ensure delivery of good quality parts at the correct costs?
  • Have you addressed considerations around their manufacturing capabilities, tooling, machinery and process control?
  • Do you have a full picture of their capacity, quality control measures and staff competences?
  • What are their OTIF measurements and on-time-in-full delivery performance like?

By focusing both on the process and the service the manufacturer provides, designers and assemblers can ensure their parts will be both high-quality and produced efficiently.


Creating an accurate mould

Finding out about the expertise a manufacturer will provide at each stage of the process will help to ensure you have a full picture of how their components are created.

At the centre of the injection moulding process is the mould that’s used to shape the part. The development of this mould requires expertise and experience to ensure it’s accurate enough to avoid faults in the final part, such as flash, warpage or an excessive parting line.

During mould development, good manufacturers should offer the opportunity to try out prototypes, particularly if you’re creating a custom part. This will ensure that the mould is producing a consistent, high-quality part, as well as the design characteristics you’re looking for.


Choosing the right plastic

Making sure your part has the material characteristics you need is essential to both the tensile and aesthetic quality of your final product. For example, whether you’re looking for custom colours, textures or qualities (such as the need to be washable or strong).

Some of the most common thermoplastics used in injection moulding are:

  • Acrylonitrile-Butadiene-Styrene (ABS)
  • Nylon (PA)
  • Polycarbonate (PC)
  • Polypropylene (PP)

Although all of these can be heated and used for parts, they all have individual characteristics which suit certain types of components best.

For example, ABS is strong and chemically resistant but isn’t suitable to be used outdoors, making it a popular choice for automotive interiors and computer equipment. Alternatively, PC is resistant to heat, transparent and can be used for outdoor components, making it suitable for eyewear, greenhouses or test tubes.

If they’re compatible with each other, plastics can be mixed to combine different characteristics into one material. Different colour resins can also be added to the plastics to get a desirable aesthetic finish. This means that with advice from an experienced manufacturer, assemblers and engineers should be able to find a material that combines the material and aesthetic qualities they need.


Efficiency of the injection moulding process

As well as delivering high-quality parts, a manufacturer’s injection moulding process should be efficient enough to produce a high number of components quickly with as minimum waste as possible.


Reduce and recycle waste

Experienced manufacturers will work to reduce waste from the mould development stage by ensuring the right amount of plastic is injected at the correct pressure and the tool is tight enough to prevent material from escaping. In addition, some manufacturers recycle their flash waste material by reheating it and mixing it with virgin plastic ready to be used to create new parts.

Also, the hot runner systems in certain machines keep the plastic liquid between injections. This saves energy because the plastic doesn’t need to be reheated and reduces the amount of plastic that’s wasted. This helps to reduce the costs passed onto customers, as well as lower the environmental impact of the process.


Machinery maintenance

In addition to using materials efficiently, maintaining machinery is essential to minimising downtime and delayed delivery times. By selecting the right type of machinery and harnessing predictive maintenance technology, manufacturers can ensure they maximise efficiency.



By asking for a manufacturer’s Original Equipment Effectiveness (OEE) score, you can quickly discover how efficient their machinery is. Our injection moulding machinery has a score of around 90%, with the majority of our factories using Sumitomo Demags, which enable us to achieve quicker cycle times and a stable process.

As Chris explains, the machines also bring advantages with maintenance: “On average against our older machines we see savings of around 1 second just on movement and open-close profiles. The equipment manufacturers can also dial in remotely and actually see how well our machines are running, if they’re in calibration, and advise on a routine maintenance programme.”


Choosing a manufacturer with the right machinery

Although the basic process each machine completes is the same, there are many variations in the types and specifications of injection moulding machines. Machines can be run by either electric, hydraulic or hybrid (a combination of the two) power, providing manufacturers different mechanisms and levels of efficiency.

Choosing a manufacturer with efficient machinery is important, but making sure the machines are the right specification for the parts you need is also essential, as Chris explains: “It’s so important to choose the correct specification when purchasing new injection moulding machines. Purchase the wrong one and it can have a catastrophic impact on manufacturing - you won’t be efficient, you won’t hit your costed cycle times and you can end up making out-of-spec parts.”


Using Industry 4.0 to maintain quality

Our machinery is also Industry 4.0 enabled. By harnessing these advances, we’re not only able to maintain our machinery for maximum efficiency and uptime, but ensure that our components are of a consistent level of quality.

At our Kidlington site, we use 3D printers to help develop prototypes for custom parts. Using this technology helps both to reduce cost and increase the efficiency of the design process, as we don’t have to create an injection moulding tool to test out a component’s design and can quickly produce a number of prototypes for testing. Installing robotics and monitoring technologies, such as predictive maintenance in our machinery, also helps us to maintain efficiency during the production phase.

Chris explains that this move towards smart factory technologies is essential for future-proofing our production: “Pace, the ability to get products to market and across the line quickly, is where smart factories really strike out. 3D printing means you can have prototypes on your desk the same day rather than waiting a week for the parts to come back.”


Look for great service with efficient process

Although part quality is important, which is why we ensure we consistently meet international quality standards, finding a manufacturer that can produce the amount of components you need and deliver them quickly is also essential.

Not only will this save you headaches in the long run, but ensure there are no delays in your production schedules and the resultant wasted cost. Chris explains: “At Essentra, we completely control every aspect of the process from order intake through to manufacture and dispatch to the customer; and with the wide range of tooling and machinery we have on our sites we can produce good quality parts in a short space of time.”

“For example, the size ranges of our PVC grommets and standard LD/PE protection caps are vast and, likewise, the number of different industries they are supplied to is equally broad. We manufacture millions of these types of products on a huge scale to an extremely high standard.”



We know that when you’re designing a new product, ensuring that each component meets close tolerances and accurate sizes is essential. So we put together some guidelines and advice on how to make sure your manufacturer is delivering the high quality components you need.

The ability of the injection moulding process to produce accurate and complex components at scale is the main reason why it’s a popular method with manufacturers worldwide. However, if a manufacturer isn’t experienced in delivering the types of components you need, it’s likely that they’ll be inaccurate in terms of quality, size and tolerances.

By giving you advice on what a skilled manufacturer should offer you during component production and the injection moulding process, we’ll help you to make sure you get the right component for your final product.


Why is component accuracy important?

A range of industries use plastic injection moulded components in their final products. Their design and material flexibility make them a popular choice for engineers in sectors from automotive to construction.

Although accuracy and quality need to be the main consideration when manufacturing components for any sector, it’s important that each component is considered within the context of how it will be used. With so many variable designs of just one product type, engineers may not always be aware of the full selection available to them, but manufacturers should be able to help recommend a standard or custom solution.

As Manufacturing Director for Components Europe David Barker explains: “The consequences of poor quality are far-reaching. Not only do you incur the cost of resolving the concern, with collection, sorting, scrap and re-manufacturing, but there is also the damage to customer confidence and the reputational damage this brings. We differentiate ourselves through our service, so quality is something we take exceptionally seriously.”


Inaccurate components can affect a product’s function

Faults in the design or material selection for a component can have a huge effect on the function of the final product. To avoid difficulties in the final assembly, a manufacturer should offer you CAD designs for their standard products, or a significant prototype development phase for a custom component.

By harnessing CAD technology and 3D printed prototypes, it’s possible to remove any design errors before production even begins. An experienced manufacturer should be able to advise you on the best design of standard or custom component for your final product, as well as an appropriate material for the functional characteristics you’re looking for.


It can affect how safe the final product is

Selecting a material with appropriate characteristics, whether it be blunt edges, low toxicity or a soft texture, is key to ensuring that a final part meets safety requirements for specialist products. Also, if an engineer is working for a sector such as automotive, looking out for manufacturers with industry-specific safety certifications (for example, IATF 16949) will give you a good indication as to the quality of their components.


It can ruin final aesthetics

Injection moulding is a highly accurate process but, if used by an inexperienced manufacturer, can result in faulty components. Some of the most common faults that can result from a bad process affect a parts aesthetics as well as their strength and material quality.

Often aesthetic faults, such as flash, are caused by manufacturers using incorrect pressures and temperatures within the injection moulding process. Flash occurs when molten plastic escapes the mould tool, this can be through a fault in the tool or a lack or excess in moulding pressure.

However, as experienced manufacturers will know, ensuring that the moulding tool is designed correctly, with final aesthetics in mind, is also essential. Whether it is the position of the parting line or the location of the ejector plates or pins, making sure that the tool design takes into account the final aesthetics of the part and product is essential to meeting high quality standards.


The importance of accurate tool design

There are three elements of the injection moulding process which can have a significant effect on the quality and accuracy of the final component:

  • Tool design
  • Material selection
  • Choice of machinery

As well as ensuring the correct size of the product, the tool design has a huge impact on the aesthetics of the final part. It defines where parting lines will appear, as well as any impressions or indentations from the ejection phase.

Even if you’re selecting a standard product, getting advice from your manufacturer on how best to adapt your tool design to the complexities of the injection moulding process and your desired material. As Chris Butler, Global Process Development Manager, explains: “At Essentra, the quality of our tooling, both in design and manufacture, coupled with a robust trials and approvals process, enables us to produce high quality products in a consistent and repeatable way.”


Why selecting the right material is essential

All thermoplastics are not created equal. Although they’re all heated up and turned molten before they’re moulded, they have completely different characteristics and reactions to levels of heat and pressure.

Manufacturers should be able to advise you on the best choice of material for your component. With a greater awareness of the range of plastics that are available, they’ll be able to match the characteristics you need for your part, the component’s design and the parameters of the injection moulding process together to create a part which is accurate and high-quality.



Check your manufacturer’s machinery

Making sure your chosen manufacturer has the machinery and processes available to create the type of part you need at the capacity is fundamental to ensuring you get top levels of service and quality.

Chris is responsible for outlining the specifications for injection moulding machines across the majority of our 12 global manufacturing sites and explains why it’s important to ensure your manufacturer has the right type of machine for the job. He says: “It’s so critical that you spec the correct machine up in line with the components, the materials and the type of tooling that you’ll be running.

“Get it wrong and it can have a catastrophic impact on manufacturing. Engineers can end up with out-of-spec parts, manufacturers won’t be efficient and won’t hit their customers’ costed cycle times and that’s before you consider the technical issues around the actual injection moulding process.”


Are your manufacturers’ components accurate?

As well as enquiring about their injection moulding process, tooling and machinery, one of the main ways of comparing the accuracy of manufacturers’ components is by asking about the tolerances of their products.

As David explains: “The tolerances on our products vary depending upon their size, but typically they’re between +/-0.1mm to +/-0.25mm. We have non-contact measuring equipment such as computerised maintenance management systems and Shadowgraph to ensure we accurately verify product before releasing to production.”

By examining the tolerances and the validation processes of a manufacturer, you can be assured that the components they’re producing are of the highest quality, even when they’re produced at scale. Building this level of relationship with your manufacturer will also ensure that their supply chains can continue to deliver the parts you need in the future, with hassle-free service and continuous quality.

David says: “We continuously invest in the business. Not only on new cutting-edge injection moulding machines and tooling, but most importantly, in our people. We have a programme to continuously develop the technical capability of our workforce, who we believe are the most important element of any manufacturing organisation.”

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