Polycarbonate Injection Molding: The Complete Guide

If you’re in the helmet visors, face shields or goggles industry, then you should try polycarbonate injection molding.


It is a versatile polycarbonate fabrication technique, allowing you to make complex designs and shapes.

And, in today’s guide, you’re going to learn everything about polycarbonate injection molding – from the basic definition, techniques, process parameters and much more.

By the end of this guide, you should be able to implement injection molding in your manufacturing processes.

Let’s get started…

What is Polycarbonate Injection Molding?

Listen to this fact:

Polycarbonate material is arguably the strongest one currently used in various industries.

So what does that imply?

It is simple!

It means that you need to get the proper method of making sure it suits your particular application.

Polycarbonate injection molding refers to the efficient process that you can use to produce polycarbonate parts in almost any shape.

Yes, this is the reason why many industries are opting for this technique given that it allows you to design this material suitably.

Polycarbonate injection molding is, of course, a manufacturing process which has to take place in well-equipped laboratories.

The bottom line nonetheless is that this process involves the production of polycarbonate parts by injecting molten polycarbonate into a mold.

Again, this process involves feeding of thermoplastic pellets into a heated barrel, mixed and then forced into a mold at extremely high pressure.

So that after some time, the heated thermoplastic shall cool down and later on harden.

Afterward, it shall form a part which takes the precise shape of the mold.

Another important aspect regarding this technique is that you have to take into account several elements.

Some of these elements include molding machine, desired shape, as well as the features of the part.

We’ll discuss all these factors later on in this guide to enable you to understand the effects and significance of the overall polycarbonate injection molding process.

Polycarbonate sheet

Polycarbonate sheet

And as you’ll come to notice, this technique is quite intensive and requires intense attention to yield better results.

Injection Molded Visor

Injection molded visor

At the moment though, let’s first find out some of the benefits of polycarbonate injection molding in the next section as we move on.

Benefits of Polycarbonate Injection Molding

The fact that polycarbonate material is an incredibly useful plastic for several applications, it provides alternatives for many materials.

And so injection molding makes it possible for you to attain the desired shape for the particular need.

For that reason, it would be ideal if we look into various advantages that this particular technique brings.

Undeniably, its benefits are quite several and therefore, we shall only look at the key ones that cut across in different applications.

Injection molding machine

 Injection molding machine

1. Fast cycle time

The injection molding process of polycarbonate material is a process that takes the shortest time possible.

What this means is that it is a comparatively fast process which takes little time to complete.

Indeed this is beneficial given that you’ll have to manufacture your particular polycarbonate mold and get the desired shape quite faster.

Moreover, the fact that you get fast cycle time with this process, it means that you can manufacturer quite a number of molds from this process.

And in the long run, you’ll notice that the fast cycle time helps you in a great way to cut on cost, reduce time wastage and better utilization of raw materials.

2. Helps in creating parts with tight tolerance

One of the most important elements which you have to know when dealing with polycarbonate parts is tolerance.

You see, there is a need for getting a polycarbonate part that has a tight tolerance for the effectiveness of the application.

Fortunately, injection molding is one of the best techniques that guarantee you the particular tight tolerance which you require.

It happens that during the process, there are some specific parameters which you have to consider.

Therefore, it becomes easy for you to create the parts which have the tight tolerance, ideal for the specific application you want to undertake.

3. Allows you to accommodate a variety of part sizes

Well, what this simply implies is that injection polycarbonate molding makes it possible for you to create a wide range of part sizes.

In any case, you’d prefer to create polycarbonate parts of different sizes; then this is the best technique that you need to use.

Most of the injection molding machines in the market come with various settings that enable you to get the right or somewhat desirable size.

Furthermore, you can also incorporate other numerous parameters in making sure that you obtain the correct size of the part.

Therefore, injection molding should be your ultimate choice if at all you’re looking for a suitable method for creating polycarbonate parts of different sizes.

4. Produces excellent part-to-part repeatability

You see, it is always fundamental to maintain consistency when it comes to manufacturing a particular set of polycarbonate parts.

Undeniably, this also depends on the specific application.

Nonetheless, finding the best approach that can yield the necessary consistency is key in this aspect.

Injection molding, even so, makes it easy for you to produce excellent part-to-part repeatability.

It is arguably easy when using this method especially when you are using some of the high-quality molding machines.

5. Helps in producing parts in large quantities

Like I did mention earlier on in this section, injection molding is the only technique that guarantees faster and massive production of polycarbonate parts.

In most instances, you’ll notice that the need for producing large quantities or polycarbonate parts may arise.

Therefore, you’ll need to get a technique which of course guarantees you not the only production of large quantity but efficiency too.

And injection molding is a suitable method that you can choose to use.

In most instances, it is easier and effective to produce polycarbonate parts using this particular technique hence beneficial.

6. Helps in eliminating surface defects

In many instances, you might notice that after completing the process, you’ll still have some form of defects on the surface of the material.

This indeed is occasioned by several factors including a wide range of parameters that you probably did not meet.

But then, injection molding of polycarbonate material guarantees you the smoothest surface of all by eliminating any surface defects.

Of course, this is beneficial because at the end of the day you’ll have a seamless polycarbonate part.

Moreover, it enables you to get the best desirable results by making it possible for you to have physically attractive parts.

7. Effective utilization of the raw materials

You see, one of the many reasons that often make the entire processing of a particular polycarbonate part relatively costly is wastage of raw materials.

Remember raw materials is a critical aspect of any manufacturing process hence the need for making sure that it’s utilized appropriately.

Injection molding allows for better utilization of the raw materials from the beginning to the end of the process.

Also, it makes it easy for you to determine the right quantity of raw materials you need to use when thinking of creating a particular type.

Nonetheless, this is essential because at the end of it all you’ll notice that you’ll be saving on cost significantly.

8. Relatively low labor cost

In most instances, you’ll be using injection molding machines to create a number of polycarbonate parts.

As you’ll find out later on, most of these machines come with various settings that determine different operating parameters.

So in other words, what I’m trying to say here is that you’ll be able to cut down on cost related to labor since the machines will be performing most tasks.

The importance of this is that it helps you to attain high efficiency which leads to better productivity and high revenue.

9. Production of items with different designs and shapes

Injection molding of polycarbonate material is somewhat a flexible process which makes it easy for you to get different part designs and shapes.

Remember you have to heat the material to an extremely high temperature.

This is a clear indication that you can as well easily design this material to form any kind of shape that suits your needs.

Incidentally, this is the reason why in most instances you would come across different unique shapes and designs of polycarbonate material.

It is quite apparent that injection molding makes it easy for you to attain the best results in terms of designs and shapes.

Well, these are some of the key benefits of this particular polycarbonate processing technique.

As I did tell you earlier on, the list could be endless, and perhaps we cannot necessarily discuss all of them here.

Even so, let’s also look at some of the shortcomings of using this method in producing different polycarbonate parts.

Disadvantages of Polycarbonate Injection Molding

The truth of the matter is that polycarbonate injection molding is a highly preferable process among many manufacturers.

Injection molding process

Injection molding process

As we have seen in the previous section, it has quite a number of benefits.

Nevertheless, it also has a few disadvantages, which include the following;

1. Costly for small run polycarbonate parts

Let’s get the gist here!

The ordinary operations requirements of this process are somewhat demanding in one way or the other.

In fact, you’ll realize that whenever you choose to use this method to process polycarbonate material, you’ll have to put quite a lot of elements into consideration.

What I’m trying to say here is that this process is evidently suitable for producing continuous large parts of polycarbonate material.

This way, you’ll surely get value for your investment all-round.

However, for small run polycarbonate parts, you’ll end up spending quite a lot of resources which ends up being quite costly.

In other words, injection molding for polycarbonate material is only ideal for large run polycarbonate arts as opposed to small run.

2. It has restrictions on part design

Well, this is also another obvious disadvantage of using this process, even though many people may not necessarily realize it.

You see, when you decide to create certain parts using this method, you’ll need to adjust the settings of the machine accordingly.

So this somehow restricts you from creating part design unless you change the machine settings and other related parameters.

Now, this can be tiresome especially if you desire to create different part designs concurrently during the process.

Also, this prevents you from actualizing some form of creativity that you might be having in your mind during the process.

3. The high initial cost of machinery and tooling

Let’s face it!

The truth of the matter is that investing in formidable machinery and tooling for polycarbonate injection molding can be quite costly.

What happens most of the time is that you have to be specific on what you require when it comes to the actual machinery.

Moreover, there are also other many factors surrounding the initial installation of such machines and other related tools.

So at the end of the day, you’ll notice that you have to spend quite a lot of money and other resources before you finally kick start the process.

And for that reason, you have to be somewhat financially stable when investing in this technique if at all you need to yield better results.

As you can see, it is quite obvious that the pros of polycarbonate injection molding supersede its cons.

Therefore, it shows that investing in this process is worth it hence making it a viable option for any serious polycarbonate parts’ manufacturer.

And talking about viable options, we now want to look at some of the critical techniques of injection molding polycarbonate.

Polycarbonate Injection Molding Techniques

Now, this is where the rubber meets the road.

What happens is that as you can see from the above sections of this guide, injection molding of polycarbonate is quite an intensive process.

But that notwithstanding, you also ought to understand that this process involves quite a lot of elements to make it efficient.

Injection molded goggles

Injection molded goggles

On that note, it also fundamental to understand that you can use different types of techniques to create a particular polycarbonate part.

And for that matter, let’s now look at some of these injection molding techniques in details and find out more regarding the same.

a) Optical molding polycarbonate

This is apparently one of the leading techniques currently used in injection molding of polycarbonate material.

Optical molding ideally refers to a replicative process which enables the production of high precision optical components from polycarbonate without polishing or grinding.

Some resources may also refer to this process as ultra-precision thermoplastic pressing.

It is ideal for manufacturing a number of polycarbonate parts for different consumer products.

Nowadays, the use of a precision polymer is somewhat becoming a necessity.

This is as a result of the fact that most products require sophisticated light handling parts to attain the desired results.

And if you’re keen enough, you’ll notice that development of many devices nowadays integrates the use of polymer optics.

Furthermore, optical molding polycarbonate has the ability o combine optical surfaces with mounting features on a comparatively economic basis.

Nevertheless, you also ought to realize that the unique nature of polycarbonates and injection molding process call for a disciplined approach.

Of course, this is in regards to the entire process from component design all through to the prototyping and production phase.

Apparently, this technique works best when you understand the manufacturing process.

b) Thin Wall Molding Polycarbonate

This is the other predominant technique used for injection molding of polycarbonate parts.

This process refers to a specialized form of conventional injection molding which focuses on the manufacturing of mass plastic parts.

In most instances, this technique requires molding machinery and tooling designed and built to endure higher stresses and injection pressures.

2k Automotive Glazing Injection Molding Maschine

Thin wall injection molding machine – Photo courtesy: COVESTRO

The outstanding feature of this process is that the plastic parts produced are thin and light.

Therefore, it makes it easy to cut cost on materials and reduces the cycle times as much as possible.

Indeed, what this means is that shorter cycle times will always result in relatively high productivity as well as low cost per part.

Incidentally, this technique revolves around the size of the part in comparison to its wall thickness.

What this implies is that as the wall thickness of any particular plastic part reduces, the harder it becomes to manufacture using injection molding process.

In other words, the size of the polycarbonate part plays an integral role in putting the limit on how thin the thickness of the wall can be.

One advantage of this technique is that it reduces resource consumption as well as cutting weight hence decreasing fuel usage.

Additionally, it enables faster cycle times which is ideal for injection molders since it reduces delivery cut time and cost per part.

c) Water Assist Molding Polycarbonate

Water assist injection molding technique is one of the recent and most promising developments in this industry.

Injection molded visors

Injection molded visors

Primarily, it refers to a technology which uses fluid under intense pressure to core out a hollow thermoplastic part in the mold.

This technique integrates high water injection pressure which helps in making sure that the necessary evenness in wall thickness distribution and smooth surfaces are attained.

Some of the benefits of this technology include lower tool cost, lower material cost as well as more part consolidation.

Water assist molding polycarbonate also features a direct cooling inside the part.

One of the reasons why this technology is becoming increasingly popular these days is because it can produce a smooth internal part surface.

This, of course, in addition to the fact that the technology produces comparatively more even-wall thickness and somewhat less residual

What’s more is that this technique is suitable for creating larger void spaces as well as a longer hollow section in polycarbonate parts.

Even so, it is also important to understand that it is essential to drain away the water used in this particular process.

At the same time, you also need to understand that water assist molding polycarbonate needs components with markedly wider diameters,

The essence of this is to ensure that water can easily penetrate the melt relatively fast.

d) Two Component Molding Polycarbonate

Well, this refers to the molding process which takes place when two or more thermoplastic materials form a single product.

It ideally involves the injection of the different materials into the cavity first then altering the hole in the mold as you inject second material and so on.

Injection molded car head lamp

Injection molded headlamp

In this process, you combine molding resins with different properties to a single part as a form of enhancing functionality and aesthetics.

As you can see, this technique varies from the relatively typical single-component injection molding process.

This technique is quite fundamental since it allows you to manufacturer combinations of soft and hard plastics and a combination of different colors.

Nevertheless, it is essential to take note of the fact that you can use several ways to attain a two-component injection molding process.

Some of these techniques include the following;

· Mixed materials

It is considered as the simplest mode of two-component injection molding.

In this process, you tend to feed two different materials into the injection machine concurrently and nix them as they’re heated.

This process is particularly ideal for mixing materials for aesthetic purposes.

Furthermore, you can as well use it to attain a different physical property than merely one resin would offer.

For instance, you can choose to mix a somewhat harder resin in a bid for strengthening a piece made from some soft plastic.

· Bi-injection molding

This technique involves feeding of different materials into a mold cavity at various points and different hollows.

So it happens that these different materials begin to harden even before their meeting point within the cavity.

· Co-injection molding

This particular technique involves injection of two full material shots into the cavity immediately after another.

This leads to hardening of materials around each other while becoming fully bonded.

Ideally, co-injection molding is suitable for manufacturing softer rubber exterior around a relatively hard plastic core.

· Over-molding

This process involves the construction of multi-component pieces through an “add-on” type of operation.

Well, this necessarily implies that one component is constructed and fully allowed to cool down and harden.

After that, you can use it as a core or base as another portion is molded around or over it.

The good thing with over-molding is that it enables extensive flexibility with materials as well as construction.

The reason for this is that the core piece does not essentially need to be injection molded.

· Multi-shot molding

Other resources refer to this process as sequential molding.

In this technique, you tend to attain a layering effect by injecting partial shots of material in sequence into the mold cavity.

At this point, the materials hardly mix nor harden around each other, preferably, these materials stack into a finished piece.

So these are the different ways that you can use to achieve injection molding.

What’s more is that as you can see, all these various techniques tend to yield different results as well as effects.

With all the available options, it is quite clear that two-component molding polycarbonate is suitable and advantageous in several situations.

Therefore, you can think of undertaking one depending on the application as well as your particular needs.

Even so, let’s continue looking at other injection molding techniques;

e) Injection Compression Molding Polycarbonate

This refers to a process of technology which enables manufacturing of relatively low stress, thick-walled elements without sink marks but with high contour accuracy.

In other words, this process involves injecting molten resin into a mold and forming the injected resin by clamping mold with closed compression.

Compression molding

Compression molding

What happens in this process is that a preset quantity of plastic material is injected into an open hollow.

So it is this hollow that is then compressed to complete filling as well as packing.

At the end of it, you’ll notice that this process provides uniform distribution of the resins hence yielding extreme accuracy.

This process is preferable especially in the event that you’re dealing with components that contain decorative adornments or inserts.

An outstanding feature of this technique is that it reduces stress on the component during production.

The essence of this is that it allows the formation of more delicate or lightweight components.

Additionally, this process is suitable for large comparatively large flat parts or those that need a downstream heat cycle.

You should nonetheless understand that this process is relatively complex and needs detailed knowledge of the process as well as high-end machinery.

f) Structural Form Molding Polycarbonate

This refers to a molding technique which allows you to produce relatively large structural parts.

It primarily involves the addition of a blowing agent as well as modification of process factors that form a sandwich construction.

And this solid construction has a solid skin on the external layers and a foam core in the center.

In this process, what usually happens is that a blowing agent tends to form a cellular structure and at the same time allowing hard skin to form.

Structural form molding

Structural form molding

One benefit of the process is that it requires lighter and less expensive materials.

Moreover, it is also associated with relatively low initial investment compared to other forms of injection molding.

You also need to understand that product you from this process usually have excellent strength to weight ratios.

Of course, this is an addition to the fact that they possess better acoustic and thermal insulation properties compared to products from other processes.

Primarily, these are the key polycarbonate injection molding techniques that you’re likely to come across.

As you can see, each of these techniques involves a number of different processes hence the need to understand the specific one suitable for you.

As you’ll find out later in this guide, several factors ideally determine the choice of a suitable injection molding polycarbonate technique.

And to get a better understanding of the same, it would be imperative also to figure out several aspects revolving around such processes.

For that reason, let’s get straightaway to the next section and discuss a myriad of elements surrounding the parameters of injection molding polycarbonate.

Polycarbonate Injection Molding Process Parameters

This is the thing;

Polycarbonate injection molding is a process.

And for any procedure, several parameters tend to determine a wide range of factors leading to its efficiency or inefficiency.

The truth of the matter is that this process is not an exception.

And for you to get the best results from this particular process, you must understand most if not all of its parameters.

In this section, I want us to keenly look at some of these factors in detail to find out the effect they have in realizing the overall efficiency in this process.

Injection molding process

Injection molding process

What’s more is that it will enable you to have an idea of what it takes to attain proper results as you undertake this process.

So without taking much of your time, let’s get straightaway and have a look at the key parameters of the injection molding process;

· Injection molding temperature

Listen, the temperature is one of the fundamental aspects which determine the quality of the polycarbonate parts you’re manufacturing.

Injection molding temperature

Injection molding temperature

In fact, I usually say that quality temperature control in polycarbonate injection molding is what makes the entire difference in the part.

What I mean here is that you have to determine the ideal temperature control throughout the injection process.

Undeniably, you have to factor in quite a number of considerations in a bid of attaining proper temperature control.

Some of these factors, of course, include the type of polycarbonate material, residence time, mold temperature, mold size, and material melting point.

Additionally, you also need to consider the coolant type as well as mold heating cooling channels for a quality polycarbonate part.

Injection molding temperature has a fundamental effect on the purpose of formability as well as the appearance of the product.

Proper temperature control in this process can also help reduce the cooling stress by improving the properties of the same.

Injection molding temperature, however, has a wide range of structures, which also determine the quality of the product.

Some of them include the following;

· The temperature of the screw barrel

A screw barrel is a significant component in an injection molding machine.

It is what forces the heated polycarbonate resin into the mold as it provides the pressure which enables the molten material to flow through the mold in open areas.

This then leads to the formation of the part which has been tooled.

Injection molding machine screw barrel

Injection molding machine screw barrel

So as you can see, setting or controlling the temperature of this component is necessary for the formation of quality polycarbonate parts.

Incidentally, most of the modern injection molding machines come with barrel heating zones set with a gradual temperature rise.

So it is somewhat easier to handle and regulate the temperature of the screw barrel when using such machines.

· Polycarbonate Melt temperature

This is yet another aspect of temperature that plays a vital role in the quality of product part manufacturing in injection molding.

It refers to the actual temperature of the polymer at the moment it exits the nozzles and enters the mold.

This temperature is essential, and it’s measured by an air shot technique or in some instances, nozzle.

It plays a crucial role in determining the overall effectiveness of the process and the quality of the polycarbonate part in the molding process.

Polycarbonate melting temperature

Polycarbonate melting temperature

The injection cylinder settings of a particular machine for achieving melt temperature depends on shot size, molding cycle, screw rotational speed, and back pressure.

· A constant temperature of the barrel

Apparently, for the quality production of polycarbonate parts, it is vital to ensure that you set and maintain a consistent barrel temperature.

Remember this is the aspect which determines whether or not the molten resin will attain the required temperature parameters.

And for that reason, it is always essential to ensure that you set the temperature of the barrel to remain constant throughout the process as necessary.

· Mold temperature

This is also another imperative variable in the injection molding of polycarbonate material.

You see, if you want to reduce the unit cost of injection molding, you have to attain an ideal temperature control.

The essence of mold temperature is to make sure that it keeps the surface of the molten resin for a long time to form pressure in the cavity.



In an ideal world, what happens is that the mold temperature is essential to producing injection molded parts.

Therefore, you have to realize that it plays a fundamental role hence making it a key parameter to look into the overall injection molding process.

· Polycarbonate injection molding temperature

This is another fundamental parameter that plays a crucial role in the injection molding process.

First of all, it is imperative to understand the temperature range that a polycarbonate material meltsat.

The reason for this is that it will make it possible for you to ensure that you get quality molds that yield better polycarbonate parts.

A fact to also note is that measurement and control of injection molding temperature is essential in this particular process.

The truth nonetheless is that high injection molding temperatures increase the flow rate of polycarbonate in filling the cavity.

Polycarbonate molding temperature

Polycarbonate molding temperature

But at the same time, you need to understand that extreme high temperature can lead to the degradation of the material.

So it is equally vital to make sure that you take control of this particular temperature during this process.

Generally, if the injection molding temperature is high, there is a tendency of plastic filling the cavity relatively fast.

However, this has the possibility of introducing flashes, shrinkages as well as internal stress.

On the other hand, if the injection molding temperature is low, the material will have relatively fewer flashes, and internal stress will reduce.

Nonetheless, it will introduce little mold and a high parting line.

Some of the elements surrounding injection molding temperature include the following;

· Injection pressure

Injection pressure is essentially what causes the material to flow.

To yield better results in injection molding, it is important to note that control of the injection pressure is necessary.

The injection pressure is apparently the driving force which overcomes the resistance of polymer melt, hence pushing the material to fill and pack mold cavity.

Most injection molding machines come with integrated pressure sensors.

So, if you place these sensors along the flow path of the material melt, you can easily obtain the pressure distribution in the polymer melt.


Figure 17 Injection molding pressure

On the same note, you also have to realize that different elements affect the requirements of injection pressure.

For instance, a part design which includes thickness and surface area play a fundamental role.

Again, gate design such as the size as well as flow length is among other variables that influence the injection pressure requirements.

Moreover, a number of processing conditions including, ram speed, melt temperature, as well as coolant temperature, also affect the need for this parameter.

· Back pressure

This refers to force in an injection molding machine which is exerted by the material the moment is injected into the mold.

It is important to understand that during injection molding, the material also tends to exert pressure.

And this pressure is often equal and opposite to the pressure of the molten material.

Creation of back pressure usually happens during the return action of the screw immediately after injecting the material.

For better results, it is always advisable to keep the back pressure as low as possible.

Experts state that in any event, this pressure should never go beyond 20% of the machine’s maximum rated injection molding pressure.

You should also understand that the role of back pressure is never to raise the temperature of the resin.

What’s more is that this pressure helps to enhance better melt uniformity in temperature and viscosity.

· Holding pressure

Holding pressure is often applied in injection molding as compensation for resin shrinkage that often occurs as a result of cooling.

It is always appropriate to ensure that you maintain the ideal holding pressure in pushing the molded screw.

This is important because it helps to continue injecting molten resin into the cavity.

The most significant aspect of holding pressure you ought to know is that it influences product shrinkage rate greatly.

For that reason, you can increase this pressure to make the product bigger hence essential for shrinkage compensation.

At the same time, you also need to note that holding pressure should never be too high since it causes mechanical force and residue stress.

All these lead to product deformations.

So in other words, you need to ensure that you get the right setting for holding pressure if at all you need to attain better results.

It is also advisable that you gradually decrease holding pressure during the process to reduce pressure difference within the cavity rather than setting it uniformly.

· Injection Speed

Just like injection molding temperature and pressure, speed is also another fundamental element in the entire molding process.

This speed refers to the rate of injection of the molten material in the mold.

Usually, it is controlled by a piston or injection screw which exerts the pressure on the molten resin especially in hydraulic molding machines.

This parameter is quintessential in injection molding in several ways.

First of all, it helps the molten material to fill inside the mold as fast as possible which enhances the production rate.

Secondly, it prevents any incidences of the molten material staying within the injectors.

Remember this can make the viscosity of the material to increase and end up solidifying within the injector.

· Screw speed

Well, this is yet another essential parameter of the injection molding process which you ought to understand.

It merely refers to the speed of rotation of the screw for mixing the pellets.

In many instances, the screw speed needs to be moderate, of course depending on other factors that influence the process.

Injection molding screw

Injection molding screw

For example, if the screw speed is too high, air tends to mix inside the molten plastic which makes the occurrence of a gas generation quite easy.

At the same time, if the screw speed is too low, you won’t attain sufficient kneading and can thus make the material quality to fluctuate.

While at it, you also need to understand that extreme screw speeds at both ends may lead to different adverse effects to the end product.

For that reason, you need to ensure that you figure out the ideal screw speed, of course depending on several factors.

· Residual Stress

This refers to process-induced stress frozen in a relatively molded part.

This element can either be thermal-induced or flow-induced.

This parameter is also a vital consideration in the injection molding process because it affects a part similarly to visibly applied stresses.

In most cases, it is the residual stress that causes warping and shrinkage of the part.

Some process conditions, as well as design elements which reduce shear stress during cavity filling, helps in decreasing flow-induced residential stress.

· Gate system

Listen, this is one of the interesting aspects of the injection molding process.

Gate, particularly, in this process refers to a small opening designed to allow the melted plastics into the mold cavity.

Ideally, a successful gate design is determined by various factors including gate type, location, dimensions as well as mold plates.

What happens here is that the gate system is responsible for directing the molten resin from the nozzle of the machine to cavity of the tool.

You should also understand that the gate design, as well as its location, tend to affect the cycle times, lead times, tooling cost and other potential defects.

In terms of location, the gate system affects the overall quality of the finished product directly.

And that’s why improper gate location can lead to part distortion in case the build volume whole part is filled disproportionately.

Another thing worth noting is that gate design can also affect the quality of the part.

You see, these gates force molten material under pressure into the cavity, which then accelerates and heats the plastic as it continues doing so.

In such a case, it creates a number of effects which may require changing the strategy of gate design.

What you also need to know is that the several types of gates can be used in the injection molding process.

Some of the notable examples include edge gates, submarine gates, fan gate and direct gate among others.

· Barrel equipment

This is also another essential element which plays an integral role in the overall injection molding process.

Barrel equipment in ordinary circumstances tends to support reciprocating plasticizing screw.

It offers a vital effect in determining the quality of the final product.

Most modern machines incorporate this element and have appropriate settings to that effect.

Therefore, you have to ensure that you integrate the settings accordingly to help in yielding desired results.

· Metering stroke

It is yet another fundamental aspect of the polycarbonate injection molding process.

In simple words, we can describe this parameter as a stroke of the screw which happens to determine the quantity of melt to be injected.

What happens with this parameter is that as it increases, the effective length of screw also tends to decrease.

So in that case, it results in a variation of shearing on the melt as well as residence time.

At this time, the melt tends to move through the screw as it amasses on metering.

For that reason, it is an essential element which you have to understand if at all you want to attain the best results from this process.

Recovery rate

Last but not least, the recovery rate is the other equally significant element which you need to know about in injection molding.

It is the weight or volume of specified of any material that can be processed and discharged from screw per unit of time when operating at 50% injection capacity.

In general, the impact of this parameter is that when it is high, the chances of shortening the cycle time increases.

The importance of this is that it helps to eliminate the possibilities of using a nozzle shut-off valve.

So these are some of the main parameters which you need to understand in as far as injection molding polycarbonate process is concerned.

If you look at them keenly, you’ll notice that all of them affect the overall quality of the final product.

Thus, you have to ensure that you integrate all of them appropriately to enable the best results, convenience, and effectiveness all the time.

Polycarbonate Injection Molding Process

Listen, polycarbonate injection molding process is an intricate but straightforward process.

That is the truth.

In other words, you need to know so many aspects surrounding the process including the parameters that we have discussed in the previous section.

Injection molding process

 Injection molding process

Even so, looking at any of the injection molding machines around, you’ll notice that this process is quite intensive.

In this section, I want us to look at various aspects of polycarbonate injection molding process to enable you to get an idea of what it takes.

So let’s get straightaway and find out more.

First of all, you need to know that the injection molding process of polycarbonate incorporates four major phases, including the following;

  • Filling Phase
  • Switchover phase- This is where the peak pressure happens after a small delay
  • Pressure phase
  • Cooling phase

As you can see, all these phases tend to give you somewhat an idea of what the entire process takes to eventually come to reality.

What you also need to understand is that when analyzing the part design, you also need to consider the injection molding process carefully.

Step 1: Prepare the mold

This step involves cleaning the mold as a way of removing mold protection.

At the same time, you also need to ensure that you clear the tool vents as a manner of preventing issues to do with gassing.

While at it, you must ensure that you lubricate the machine accordingly to enhance the functionality of the process.

Step 2: Prepare the material

This is yet another critical stage.

Preparation of material primarily involves issuing the required quantity of thermoplastic material to finish the production run.

It also involves removing moisture from the material in a dedicated dryer depending on the processing parameters.

At this point, you now need to mix the material with masterbatch to attain the desired colour.

Step 3: Set up the process

This step is also crucial because it also plays a significant role in achieving the efficiency and convenience of the process.

In this case, what you need to do first is to clamp the mold tool in the press.

You also need to configure the ejection system of the entire mold tool in the machine.

And while at it, you should never forget to set the guide process parameters which also include temperature control.

At the same time, ensure that the working area is appropriate and prepare it with extra ancillary equipment as required.

Some of this equipment include conveyor belts, workbenches, tool shielding among others.

After you’re over with the setup process, you now load the polycarbonate granules to the machine via the feeder hopper.

And then you can start adjusting the settings accordingly to meet all the necessary expectations.

Step 4. The injection molding process

Now, this is where real action starts.

Here is where all other aspects including cooling, plasticizing the resin, ejection, and removal of the runner and packaging takes place.

At this stage, once you pour the thermoplastic granules into the hopper, they funnel down into the machine to the screw which in turn heats to melt the plastic.

The barrel also heats at different set temperatures hence enabling the material to solidify and then move along the screw.

As the screw rotates, it moves the material forward with the speed and pressure aimed to fill the cavity effectively.

So by the time the molten resin exits the nozzle, it is injected into the feed channels of the mold tool.

While at it, the feed channels also enable this material to flow into a relatively open cavity of the tool where it starts forming the part shape.

You have to hold the mold tool at a constant temperature to enable ease of material flow as well as drawing out heat from the product after injection.

This helps the molten resin to set off to solid form.

You then subject the material to a predetermined cooling time then open it after retracting the moving platen carrying the ejection half.

It thus triggers the mold tool to open up while holding the product in the ejection half of the tool.

The ejection tool then shifts forward hence releasing the product from the mold tool.

As the process comes to an end, the material amasses in the collection box once the cycle is complete.

You can then start picking the parts from the machine as necessary.

But you also need to know that on some occasions, you will need to undertake additional post molding work to get the final desirable product.

So there you have it, the primary polycarbonate injection molding process.

But one thing you should also not forget is that this process also comes with its fair share of challenges.

And in the next section, we want to look at some of these problems and understand how to better tackle them in any event that you experience them.

Common Problems in Polycarbonate Injection Molding

Here is the thing;

We can never dismiss the fact that injection molding is arguably the most versatile technique for producing parts and products.

It happens that this process is somewhat fast, works with numerous plastic materials and can provide a durable and highly detailed final product.

Even so, you need to understand that the process itself is a bit complex and comes with several challenges.

Injection molding problems

 Injection molding problems

The good thing nonetheless is that these challenges are quite easy to resolve.

So in this section of the guide, we want to look at all the major problems you might encounter and possibly how you can fix them.

i. Flow lines

These refer to the off-tone lines or patterns that tend to appear on the parts.

The cause of flow lines varies from slow injection speed to fluctuating flow rates.

The former would make the molten resin to solidify at different stages.

Fixing this problem is quite simple, depending on the actual cause.

One is that you can choose to increase the injection speeds and the pressure.

This helps in making sure that filling of all cavities.

Moreover, you can also choose to raise the temperature of the molten resin or mold as a way of preventing the material from cooling too fast.

ii. Flash

It refers to the condition that occurs when some molten resin tends to escape from the mold cavity via the ejector pins or parting lines.

In most instances, the cause could be due to loose or expired mold clamps.

It could as well be as a result of too much injection pressure thus forcing the molten plastic outside the mold.

The solution for this is to substantially increase clamp pressure and also making sure that it never requires cleaning or maintenance.

At the same time, you also need to evaluate your mold temperature, injection pressure as well as injection speed.

iii. Sink marks

These are small depressions that you find in thicker areas of the injection molding once the final product shrinks.

It could be as a result of an incorrect mechanism or cooling time, which means that the material does not cool down sufficiently while inside the mold.

In other instances, it could be as a result of excess heat at the gate or pressure issues inside the cavity.

An ideal way of dealing with this problem is by reducing the mold temperature and increasing the holding pressure.

iv. Weld lines

These are basically the seam that you are likely to see where two sections of the molten material meet.

The cause for this problem is normally relatively more flow fronts as well as poor bondage between the two bonds.

You can handle this by trying to increase the temperature of the molten material or the old.

Additionally, you can also choose to increase the injection speed, change to a less viscous plastic material or simply adjust the flow pattern to single-source flow.

v. Jetting

It refers to the condition when the molten resin fails to adhere to the surface of the mold and instead form wavy folds on the part’s surface.

In most instances, this problem often results from a combination of several things which happen simultaneously.

They may include, low melt temperature, highly viscous plastic material as well as low injection speed.

Fixing this problem requires careful thought regarding the specific issues that tend to happen all at once.

Furthermore, you need to make sure that there is a sufficient amount of contact between the mold and the molten plastic.

vi. Warping

It is defined as the condition where the finished product appears twisted, bent or uneven is some areas due to various unintentional reasons.

In most cases, the cause of warping is normally non-uniform cooling due to varying cooling rates.

What it means is that plastics tend to get stressed in many different instances especially when cooling at different rates.

The suitable way of handling this is by making sure that you’re not rushing your cooling process.

Also, you may need to ensure that the wall thickness within the mold is uniform.

vii. Vacuum voids

These are the air pockets which appear to be stuck close or inside the surface of an injection molded part.

They are often as a result of inadequate holding pressure which of course makes the molten plastic to condense inside the mold.

It could also be as a result of the improper alignment of the mold halves as well as non-uniform curing.

A proper way of fixing this problem is by placing the gate system closer to the thickest part of the molding.

You may as well reconsider using less viscous plastic resin as a way of preventing trapping of gas.

viii. Burn marks

These are rusty discolorations which appear on the surface of a particular part you’re creating from the injection molding process.

Prototypes with burn marks may be as a result of excessive heating or relatively fast injection speeds.

Also, it may be due to overheating trapped air and forming etches on the surface of molded parts.

The only suitable approach for dealing with this problem is by reducing your injection speeds and enhancing degassing quality.

Alternatively, you may also attempt to reduce and regulate the melt and mold temperatures.

ix. Surface delamination

It refers to the layers which tend to appear on a part surface that you can easily peel off.

Contamination is the most likely cause of this problem, which may imply that a foreign material possibly got into the material.

Excessive use of release agents might also lead to this problem.

However, pre-drying the plastic adequately before molding could be the best approach for preventing it.

Furthermore, you may also consider the need for using mold release agents if you want to solve this problem.

x. Short shots

This one refers to the situation when the molten resin fails to fill the mold cavity fully.

Incorrect calibration capacity might be a leading cause for this problem.

Furthermore, excessively viscous plastics may also be a cause for this problem.

Improper degassing also causes this problem because trapped air may prevent molten material from occupying space.

A suitable way of fixing this problem is by working with less viscous materials.

Also, increasing the mold or melt temperature would be fundamental since it helps in improving flowability.

You also need to adjust the tools accordingly so that you may account for any gas trapped in the mold.

Plastic injection molding

Plastic injection molding

Top 10 Polycarbonate Injection Molding Machine Brands

Get this in your mind;

The machines used for injection molding polycarbonate are somewhat some of the most complex you can ever find in the market.

Indeed this makes perfect sense given that the process itself requires an understanding of several aspects for best results.

In other words, you also need to know at least the basic knowledge of operating the machine as well as some of the elements revolving around the same.

Expectedly, several brands of injection molding machines are in the market.

So it can be quite challenging to select the best one which suits your needs.

Plastic injection molding machine

 Plastic injection molding machine

In this section, let me guide you on the leading machines for injection molding that you need to consider if you’re searching for one.

  1. Negri Bossi
  2. Arburg
  3. Toyo
  4. Toshiba
  5. Nissei
  6. Husky
  7. Battenfeld
  8. Sumitomo
  9. Engel
  10. Newbury

These are the top brands which you need to have in mind whenever you’re thinking of acquiring one for your needs.

However, you also need to ensure that irrespective of the brand you’re purchasing, it has to be within your budget and able to meet your needs.

Applications of polycarbonate injection molding

So far, I’m sure you have so many ideas of what revolves around the process of injection molding of polycarbonate.

And for one reason or another, you probably might be wondering where on earth do products from this process applicable.

In that case, let me take through a few key applications of polycarbonate injection molding to have an idea.

Funny thing is you’ll notice that most of these applications are things you’ve seen or exposed to on several occasions.

They include the following;

· Electronic components

Well, most of the electronic components that you see around, whether in residential or commercial premises are made using parts from this process.

Of course, they undergo different processes depending on various factors determining the type of particular component.

Injection molded electronic components

Injection molded electronic components

The process is ideal for these components since it helps in producing durable and quality parts for the same.

· Medical apparatus

This is also another are where the use of polycarbonate injection molding is common.

If you are keen enough, you’ll notice that most of these apparatus are made of some polycarbonate parts.

Medical face shield

 Medical face shield

And for that reason, it is always ideal in making sure that their quality and durability is top notch, hence preferring this process to produce the parts.

Automotive industry

It is yet another key area where the use of this process in manufacturing different parts seems to be common.

Motorcycle helmet visor

Motorcycle helmet visor

Numerous parts of vehicles are made of polycarbonate materials.

And these materials also factor in the fact that the parts have to be sturdy and of high quality.

Therefore, you’ll find that this process becomes the ideal one for manufacturing such products.

· Construction materials

You see, modern day construction of buildings and related elements incorporate various types of materials.

And those made from polycarbonate materials are among the commonly used in various spheres of construction.

Polycarbonate profiles

Polycarbonate profiles

Such parts are made from this process hence necessary to understand that it plays a fundamental role in boosting the standards of the industry.

· Aviation industry

Just like in the automotive industry, parts from injection molding process are also widely used.

In fact, for aviation, polycarbonate injection molding parts seem to be preferable.

Augmanted Reality Visor

Augmented reality visor

Of course, the main reason is the quality they present as well as the ability to withstand different physical and environmental conditions.

· LED and Optical media

One thing that you ought to understand is that injection moldingis molding is in producing some of the ideal parts used for LED and optical media.



Most of the parts such as computer screens, mobile phone screens among others are products of these process.

And it is the reason it has become common since the parts present quality and durability at the same time.


Well, this guide is quite exhaustive, and I believe that by now, you understand various aspects of injection molding polycarbonate as promised.

In fact, it is always good to have some basic ideas regarding this type of process at least it helps you to appreciate what it involves.

The most important thing nonetheless is knowing that this process helps produce quality and durable parts for different applications.

And for that reason, this guide enables you to know what revolves around this particular process.

But if you still have any questions, recommendations, suggestions or inquiries, don’t hesitate to leave a comment.

Alternatively, you can contact us and we’ll surely get back to you to offer the necessary assistance.

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