So, you have decided that injection moulding is the way you intend to manufacture your components; but you now face a choice as to which polymer or combination of polymers is best suited to your needs. Most importantly, that will meet the design criteria for the part and provide the physical properties demanded by the application.

Plastic injection moulding relies on thermoplastics, a very wide range of polymers, that can tolerate repeated melting and solidification, without significant change to the chemical structure and properties of the material.

Where to start?

There are many grades of engineering thermoplastic resins to choose from and deciding which one is right for your product can be daunting. Fortunately, these resins fall into distinct polymer categories, each of which is likely to offer the end-use properties that you are seeking.

It is important to determine the operating conditions under which the part will be expected to function without risk of failure, as well as the environmental extremes that it is likely to encounter.

Questions to ask might include:

• Does the part need to be tough and flexible, and able to take significant impacts and shock?
• Must it have a high degree of stiffness and rigidity, have a glossy or specially textured surface?
• Is resistance to chemicals and fuels important, and is it necessary to ensure that the surfaces of the part do not degrade in the presence of UV light?
• Will the part be subjected to temperature extremes?
• Does the part need to be resistant to abrasion or wear, and offer low sliding friction?
• Can the injection moulded part accept post production processes such as machining?
• Does the material have to meet regulatory requirements for food or clinical uses?

And then, of course, there are variations on a theme. You can add significant value to your parts using two-, three-, even four-shot injection moulding techniques that use specially designed moulds into which different polymer resins with specifically desired properties are injected in a series of separate ‘shots’ to create overlays, inserts and other interesting features in various colours. One very common method is a two-shot process that over-moulds a specific area of a rigid plastic component with a flexible elastomer to enable the component to be more easily gripped.

Material choices should be discussed at the earliest stages of the design process, and a dialogue established between the designer and the injection moulding company’s materials experts before final decisions on material choices are made.

Popular resins and their properties

The scope of this article doesn’t allow anywhere near full treatment of this subject, but the following six classes of resins give some idea of the breadth of choice that is available:

• ABS (Acrylonitrile Butadiene Styrene) – a tough, impact resistant plastic used in the manufacture of power tool housings, automotive components and similar parts subject to rough, day-to-day handling.

• PC (Polycarbonate) – a highly impact resistant transparent plastic that tolerates high temperatures and which produces glossy, crystalline finishes when injection moulded. Often blended with other polymers, PC is frequently used in the manufacture of medical devices, lenses, electronic housings and automotive components.

• PA (Polyamides) – more commonly referred to as nylons, which come in many grades to provide strength, chemical resistance and good high temperature performance. Widely used in the manufacture of machine components (gears, shims and so on) and, when mixed with fillers, some structural parts.

• PE (Polyethylene) – a low cost resin, notable for its high ductility, abrasion resistance, and chemical resistance. Available in Linear Low Density, Low Density and High Density (LLDPE, LDPE and HDPE) versions, the resin is widely used in the manufacture of large packaging and bulk containers.

• POM (Polyoxymethylene) – a low friction, tough resin more commonly referred to as acetal. Its slippery surface and resistance to fuels and lubricants makes it ideal for use in automotive plain bearings.

• PP (Polypropylene) – another widely used, low cost resin offering toughness and high flexibility. It is a favourite of the packaging industry, which uses the material to make lids and bottle tops.

OGM’s offer

As one of the UK’s leading trade plastic injection moulders, with over 50 years of experience, our comprehensive range of injection moulding machines gives us the flexibility to fulfil the diverse scope of our customers’ requirements. Processes we carry out include conventional injection moulding, over-moulding, insert moulding and clean room moulding.

We select and source high-quality materials from proven suppliers and have experience in processing most thermoplastics. We manufacture a huge variety of injection moulded parts, including housings, aesthetic parts, two-part mouldings, clear mouldings/lenses, internal technical parts and high-tolerance parts.

Why not speak with one of our industry experts today to see how our plastic injection moulding service can help you.

But before we answer that question, let’s take a broader look at the industrial uses of plastic injection moulding. How it has become such an important tool in the manufacture of an extraordinarily wide range of components, many of which we are likely to encounter in our everyday lives.

Plastic injection moulding is a universal manufacturing technique that can produce many different types of parts or components.  Indeed, the vast majority of manufactured products rely to some extent on the use of plastic injection moulded parts. These can be produced economically in large volumes and at high speed, sometimes at rates that are expressed in terms of tens of thousands of parts per hour.  Typical applications range from extremely small high precision components, such as gears or spindles used in desktop printers, to large automotive parts, such as bumpers and interior panels. 

Plastic injection moulding is capable of producing parts from a variety of thermosetting and thermoplastic resins. These are generally specified according to end-use requirements for strength, impact resistance, durability, flexibility, finish and so on.

There are many reasons for companies to choose injection moulding; you can read more about those in our recent blog post Choosing to use Injection Moulding.

Injection moulding process

The essential process of plastic injection moulding is to convert the polymer resin, introduced in the form of solid pellet or bead, into an easily flowing, viscous liquid state. This is done by the application of direct heat and the shear action of the resin feeding system. Then injecting the hot molten resin under pressure into the cavities of a mould.

A combination of good mould design and sustained high pressure ensures that the molten resin reaches every part of the mould cavity without voids or inclusions.

On completion of the injection phase, the molten resin is cooled under carefully controlled conditions to form the final shape of the component, as defined by the contours of the mould. The component is ejected after an appropriate length of time (in as little as a few seconds to several minutes), depending upon the size of the component and the rate at which the resin is allowed to cool.

Injection moulding machine

Converting resin pellets or beads into a hot viscous liquid, injecting it at considerable pressure into a mould and finally releasing the cooled, moulded component requires a machine with three distinct elements: the feeding and injection stage, the mould and its retaining system and a hydraulically powered clamping mechanism.

• Injection – Resin pellets are transferred to a motor-driven, reciprocating screw feeder via a hopper. The screw feeder chamber (called the barrel) is enclosed by a heating element and it is this, in combination with the shear action of the screw that heats the resin and causes it to become molten.

This molten polymer resin is conveyed forward by the screw to the nozzle of the barrel (called the sprue orifice) and is prevented from flowing backwards by means of a check ring. This arrangement ensures that the resin arrives at the point of injection at the right pressure and in a homogeneous state.

• Mould – Molten resin enters the split mould assembly (comprising a platen-mounted moving core and a stationary cavity) via runners that direct the flow away from the sprue orifice towards the part cavity. Runners end in gates at the cavity boundary, with the type, size and location of these gates having a significant influence over the quality of the final moulded part. Moulds incorporate internal channels through which liquids are pumped following the injection phase to aid part cooling prior to ejection.

• Clamp – The clamp, which in most cases is hydraulically actuated, must keep the two parts of the mould tightly closed together to sustain the extremely high pressures generated during the injection stage. Most injection moulding machines are defined, in terms of size, by the achieved clamping force (usually expressed in tonnes). The clamp is released when the part is properly cooled, allowing it to be ejected before the machine is readied for the next cycle.

That concludes our guide on how an injection moulding machine works. If you work in an industry that operates in fast-moving and time sensitive markets, why not speak with one of our industry experts today to see how our plastic injection moulding service can help you.

A new solution to improve part quality and cycle rates

One of the challenges when manufacturing injection mould tools is how best to incorporate channels that allow even and effective cooling of the tool, to ensure that part quality while reducing cycle times.

The traditional approach to conformal cooling

To date, cooling channels are generally produced as drilled holes running in straight lines through injection mould tool cores and inserts. Bringing these straight runs close enough to the mould surface to provide optimal cooling is impossible when parts have curved or complex shapes, thin profiles or large numbers of intricate features. Additionally, drilled water holes have to compete for space with ejector holes; in box-shaped parts such as enclosures and housings, these need to be located in the same place at each corner.  In most cases, cross channels have to be drilled between two parallel channels and then sealed at each end, with ‘bubblers’ being used to make water run in and out of cores in a plane perpendicular to the drilled holes. These techniques are, however, a compromise aimed at achieving the best cooling possible within the limitations of machining straight holes.

Conformal cooled injection mould tools

What is needed for high-quality results is ‘conformal cooling’. In this approach, water channels closely follow the surface contours of the injection mould tool inserts. To date, however, this has been slow and costly to produce for most applications, due to the limitation of the available technology. For example, to engineer conformal channels using conventional subtractive machining, engineers need to build mould tools in a series of layers. Each layer is machined separately, and then stacked and bonded to form a finished tool. This is slow, expensive, prone to failure and unsuitable for many tools.

Metal additive manufacturing

The advent of additive manufacturing technology now creates new possibilities. Using direct metal laser sintering, powder materials can be formed into complex shapes, which contain cooling channels of almost any shape and size.  To date, however, the surface of injection mould tool inserts that have been laser sintered is relatively rough and requires further machining to create a high quality injection mould surface; this adds to time and cost.

Driving down injection mould tool cost

A new hybrid technology now combines additive manufacturing and CNC machining in an integrated system, producing injection mould tool inserts in a single operation. This technology is being offered as a new service from OGM; branded ConformL Cool, it makes true conformal cooling a viable option.

We have the first hybrid metal additive manufacturing system of its kind in the UK. Steel injection mould tool inserts are built layer by layer by laser sintering, with an automatic secondary CNC machining process providing a precise surface finish. Conformal cooling channels are incorporated as part of the build process, which has an extremely high degree of dimensional accuracy, with a fine finish on both internal and external surfaces. There is generally no need for separate finishing work, which means the process is faster and more economical.

The precision and flexibility of this technology enables channels to be printed in whatever shape or configuration that best matches the required characteristics of each injection mould tool. Channel cross sections can be round, elliptical, rectangular or teardrop-shaped to maximise heat transfer in different situations. It is also possible to incorporate special features that encourage turbulent water flow, to keep channel surfaces smooth and free of trapped debris or fungal growth.

Reducing injection mould lead times

In addition to its inherent efficiency, and resulting cost-effectiveness, the new hybrid technology offers consistent levels of quality. With us being located in the UK, lead times, compared to offshore manufacturing, can be significantly reduced from around 12 weeks from overseas suppliers to just 4 weeks or less.

To find out how OGM can help you with your next project, contact us now.

Speed is of the essence in the production of injection moulded components. Manufacturers need to get their designs from concept to production as quickly as possible. Moulders also need to achieve the shortest possible part production cycle times to maximise productivity and keep unit costs down.

The manufacture of mould tools suitable for the high-volume production of complex parts is a time-consuming process; lead times of up to four months between design sign-off and first part production are not uncommon. Moreover, the performance of a tool determines the cycle time, quality and overall productivity of the moulding process.

Conventional Cooling Channels

Conventionally, these cooling channels are drilled through the mould material during tool manufacture; and while this approach is simple, where the part geometries are more complex, it can be difficult to run straight cooling channels close enough to the mould cavity for efficient heat transfer.

A further complication arises when cooling channels have to compete with certain features for space within the tool. Illustrative of this is the production of box shapes, where the best position for the ejectors is usually at the more structurally strong corners. Unfortunately, these points are also the hardest to cool and even minor shrinkage at the corners of a box due to inadequate cooling can lead to significant distortion of adjacent walls.

Sometimes, it is impossible to provide a straight cooling path through the tool and often requires elaborate workarounds during tool manufacture. These all add cost and complexity to the mould making process, while some mould features may be too small to accommodate them altogether.

Conformal cooling

The ‘conformal cooling’ approach has been around for a long time, but it is rarely used in production applications, as there is significant manufacturing complexity involved in building the tools.

Using conventional subtractive machining, conformally cooled tools require moulds to be created in laminations. The cooling channels are machined into the surface of these laminations, which are then stacked on top of each other to create the finished tool. The technique adds significant time and cost to the toolmaking process; it can also result in less durable tools and does not provide a solution for all part geometries.

More recently, additive manufacturing technologies have provided an alternative method of incorporating conformal cooling channels in plastic injection moulds. Direct metal laser sintering allows the formation of complex shapes from powder metallic materials, enabling channels of almost any shape to be incorporated into a design.

Hybrid additive manufacturing

There is now a new technique which promises to overcome some of the barriers that have prevented the wider uptake of conformal cooling by the industry. Combining additive manufacturing and conventional CNC machining technologies, we can build steel mould tools complete with conformal cooling channels layer by layer using a laser.

As each layer is deposited, an automated secondary CNC machining process removes excess material to provide a dimensionally accurate, fine surface finish. The material produced by this process is hard enough to meet the needs of many production applications without subsequent heat treatment.

Cooling channel designs are able to make optimal use of the capabilities offered by this process. For example, as well as allowing cooling channels to take any route through the tool, the process also removes the necessity for those channels to be round. Elliptical, rectangular and even teardrop designs can maximise heat transfer for a variety of applications. Moreover, special ‘trip’ features can be incorporated within the channels to promote turbulent coolant flow which increases the heat transfer rate.

The technology developed to manufacture complex conformal cooling channels, which can significantly improve the in-mould cooling of complex parts, not only boosts part quality but can also cut moulding cycle times by up to 20%.

To find out how OGM can help you with your next project, contact us now.

A revolution in toolmaking technology is driving up the quality and speed of manufacture of injection mould tools that produce plastic parts. At the heart of this revolution is the way additive and subtractive equipment work together in an integrated process.

Mould tools incorporate cooling channels to prevent distortion in the moulds they form. These so-called ‘conformal channels’ enable cooling water to be directed close to the surface of the injection mould tool to optimise cycle times and the quality of finished parts.

This forces moulders into a difficult trade-off. Either accept higher levels of distortion or slow the production process to allow the part to cool in the mould for longer, increasing the overall cycle time, damaging productivity and driving up part costs.

Hybrid metal additive manufacturing solution

There is, however, a solution, which is based on a new hybrid metal additive manufacturing and machining technology. The resulting conformal cooled inserts can incorporate complex curved, shaped or spiral cooling channels that are easily formed in small, narrow or awkwardly-shaped inserts.

This allows the creation of a new generation of mould tools, with consistent and accurate cooling across the entire forming area. It also eliminates many of the problems of distortion and poor part quality traditionally associated with inefficient cooling.

Benefits of hybrid technology

ConformL Cool hybrid machines combine laser sintering and milling in a single process to manufacture injection mould tools quickly and accurately, with conformal cooling channels, in an integrated build process.

But the benefits don’t stop there:

• Injection mould tools are often manufactured in the Far East to drive down cost, but it typically takes between 12 and 14 weeks before they are available for use in the UK. Using a hybrid machine locally can cut these lead times in half.
• The ability to build complete mould tools with complex cooling channel geometries and designs in a one-hit automated process also helps shorten design-to-part lead times.
• Hybrid machines allow mould tool parts to be built in a range of metals, with conformal cooling channels printed in complex circular shapes that accurately follow the profile of the tool surface.
• The hybrid manufacturing process allows better control of fluid flow within the channels themselves. Special features encourage turbulent flow to increase heat extraction while maintaining a smooth surface finish within the channel to prevent blockages caused by mould growth or trapped debris.
• Applying ConformL Cool technology in production applications allows cycle time reductions of up to 20% and dramatically reduces defect rates on challenging parts.

To find out how OGM can help you with your next project, contact us now.

Leading industry magazine, Machinery, has featured an editorial from Marcel Gowers. The editor, Andrew Allcock recently visited our production facilities in Oxford. The article explains how we incorporated the new metal hybrid manufacturing process into our facilities as well as the benefits it brings to our customers.

Read the full article online

Leading industry magazine, Controls Drives & Automation, has featured an editorial from Marcel Gowers. A recent step change in technology is set to revolutionise the manufacture of mould tools for plastic parts. The article explains this development and how the new service overcomes many barriers and makes conformal cooling a much more viable option.

Read the full article online

Leading industry magazine, Production Engineering Solutions, has featured an editorial from Marcel Gowers. Creating more effective conformal style of cooling channels, particularly within complex shaped moulds, can be challenging. The article describes a novel hybrid tool manufacturing technique that overcomes the many hurdles to producing conformal cooling channels and other complex mould features.

Read the full article online

Leading magazine for the plastic and rubber industries, British Plastics & Rubber, has featured an editorial from our Additive Applications Engineering Manager, Marcel Gowers. The article outlines how injection mould tools can now be created in the UK in half the time required for conventional toolmaking.

Read the full article online

An innovative new service from OGM, a leading UK injection moulding specialist, has been introduced to reduce the lead-time for producing mould tooling by up to 50%. Based on the combination of conventional subtractive machining and the latest additive manufacturing processes, to form a hybrid technology, the new Rapid Production Mould Tools (RPMT) service will help both to compress lead-times and enhance still further the quality and finish of most types of mould tool inserts.

Read More “Hybrid technology from OGM reduces injection mould tooling lead-times by 50%”