Acrylic Molding: The Ultimate Guide
Acrylic molding is a versatile technique you can use to make a range of products from acrylic material.
But first, you should get this right.
An acrylic is a synthetic plastic sheet which has one or more acrylic acid derivatives.
In simple terms, you can refer to it as plastic that has glasslike properties.
At times, you may desire to form complex shapes using an acrylic.
In such a case you will have to mold the acrylic.
Acrylic injection molding is, therefore, the process of shaping acrylics by injecting hot materials into a mold.
You can be able to mold an acrylic into any shape through acrylic injection molding.
Acrylic Plastic Properties
What are the basic properties of acrylics?
Well, the basic properties of acrylics at room temperature are as follows:
Mechanical Properties of Acrylic
i. Tensile Strength ranging between 8000 to 11000 psi
ii. Tensile Modulus ranging between 350,000 to 500,000
iii. Tensile elongation at break percentage at 2%
iv. Flexural strength ranging between 12,000 to 17,000 psi
v. Flexural modulus 350,000 to 500,000 psi
vi. Compressive Strength ranging between 11,000 to 19,000 psi
Thermal Properties of Acrylic
i. Coefficient of linear thermal expansion 5 – 9 degrees F
ii. Heat Deflection temperature varies between 65 – 100 degrees centigrade at 264 psi
iii. Melting temperature at 130 to 140 degrees centigrade
iv. Maximum operating temperature 65 to 93 degrees
v. Thermal Conductivity at 3.9 (BTU –in/square foot
Electrical Properties of Acrylic Sheet
i. Dielectric Strength at 400 V/mil
ii. Dielectric constant at 60Hz
iii. Dissipation Factor at 60Hz
Optical Properties of Acrylic Sheet
i. Minimum light transmission at 92%
ii. Refractive Index ranging between 1.48 – 1.50
The above information on the acrylic sheets will vary according to the type of acrylic sheets.
Therefore, you should expect it to change depending on the type of acrylic you intend to use.
From this information, you should expect acrylic to have numerous benefits.
Let us find out more about the benefits of the acrylic molding in the next section.
Benefits of Acrylic Molding
You may ask why you need to mold acrylics?
Well, the acrylic molding will enable you to achieve quite a number of distinct acrylic shapes.
Other benefits of acrylic molding include:
Molded acrylic – Photo credits: The Daft Club
i. Excellent Optical clarity
ii. Excellent resistance to sunlight
iii. Excellent weatherability
iv. Rigid with excellent impact strength
v. Low mold shrinkage
vi. Excellent dimensional stability
vii. Stretch forming that increases the bi-axial toughness
viii. Excellent resistance to most of the aqueous solutions.
ix. Low rate of water absorption
x. No toxic composition
xi. You can recycle acrylic molds
The above factors make it very easy for you to mold acrylic into any form.
Disadvantages of Acrylic Molding
Apart from the numerous benefits, acrylic molding also has its demerits.
Therefore, whenever you wish to fabricate acrylic sheet using molding technique, it is important to pay attention to these disadvantages.
Since it is a product of different chemical combinations it may have a couple of demerits.
Let me walk you through some of the disadvantages.
i. Poor solvent resistance
ii. Combustible and can self-ignite at very high temperatures and burn with an open flame.
iii. Unavailability of flexible acrylic molds
iv. It is subject to cracking under stress
v. The service temperature cannot exceed 200 F degrees as it might melt.
Factors Affecting Quality of Injection Molding Acrylic
Injection molding is a simple and straightforward process.
Despite the simplicity, you may experience a few issues that will affect the quality of the final product.
You may experience these issues during the designing, fabrication assembly, testing and even during use.
Let us walk through the main factors influencing the quality of injection molding acrylic.
Injection molding machine layout
i. Mold Tool Design
Tool design is a significant part of the injection molding process.
Injection molding acrylic using different tool designs will affect the final quality of the acrylic product.
For example, designing an acrylic product with a cooling machine you can manage intelligently improves the quality.
It can reduce the distortion of the product of the final product and improve the tightness of manufacturing tolerance.
You should ensure that the tools you are using are fit and of the right quality for molding acrylic.
Apart from that, the tool design can have a great impact on the manufacturing speed, productivity and unit cost.
ii. Acrylic Product Wall Thickness
The thickness of the wall is a very important consideration when molding acrylics.
The thicker the wall the stronger the acrylic mold and, therefore, the better the quality.
Despite the strength from the thick walls, the product may suffer from warping.
The thicker the wall, the longer it takes to cool and the more the product will shrink.
It is important to reduce the thickness of the acrylic mold for the following reasons:
- Thinner parts use less material thus saving on the cost
- Thinner walls cool faster reducing the chances of excess shrinkage
The thickness of the wall will depend on the final product requirements.
iii. Acrylic Product Behavior OverTime
As you design an acrylic product, you should consider the factors that it will endure on a daily basis.
These factors will greatly affect the period which the acrylic product will last.
You should bare the following factors in mind when you are starting an acrylic molding project:
- Creep – stressing acrylic plastic over time thus affecting the original shape.
- Fatigue due to excess strain that results to material failure
- Wear due to erosion of a material under a lot of friction over time
- Weathering due to exposure to weather conditions thus affecting the color and other properties of the material.
You can mitigate such problems by molding:
- Chemical resistant plastics
- Flame redundant plastics
- High strength plastics
Shrinkage will occur due to a difference in the volume and density in acrylics in its solid and molten state.
You need to control the cooling process of the acrylic mold to avoid Control shrinking and warping.
You can use water or control the cooling time to avoid such issues during the cooling process.
You should follow the instructions above to make sure that the final acrylic mold is of very high quality.
Now! Before we proceed to the actual molding process.
You should know some of the molding specifications for injection molding acrylic plastics.
Well, let us look at the specifications in the next chapter.
Mold Specifications for Injection Molding Acrylic Plastic
Before you begin the process of molding acrylics, there are key parameters that you need to specify.
Injection molding acrylic material
· Pre-drying the Acrylic
First, you should pre-dry the acrylic before you begin the molding process.
Acrylic sheets are somehow hygroscopic and may have moisture.
Moisture can lead to serious aesthetic defects on the final acrylic product which you do not want.
Pre-drying is the process that make you remove certain amounts of moisture from the acrylic sheets.
Normally the amount of moisture that you need to remove from the acrylic sheets depend on the injection molding temperature.
For example, you need to remove 0.05% of moisture from acrylic sheets for low barrel temperature injection molding.
For high barrel temperature injection molding, you have to make sure that the moisture level is at 0.02%.
The drying process requires you to use a dehumidified system with a dew point ranging between -29 and -40 degrees.
You should note that the drying temperature and time vary according to the type of acrylic sheet you are using.
For most acrylic brands, the drying temperature and time is often set at 82 degrees Celsius for about 4 hours.
The time factor will also vary according to the size of the acrylic sheet you are working on.
After making sure that the moisture content is at standard levels, we will proceed to the next specification.
· Choosing a Suitable Injection Molding Equipment
There are quite a number of injection molding machines that you can choose from.
The type of machine you will choose will depend on the process you intend to take the acrylic sheets through.
In the case of injection molding, you can opt for the screw injection molding machine.
The main specifications of the injection molding machine are:
i. Acrylic feed zone should be at least 50%
ii. The compression zone should be at least at 25%
iii. The metering zone should be at 25%
iv. The ratio of the screw length to diameter should range between 18:1 and 24:1
v. The screw compression ratio should range between 2:1 and 3:1
vi. The machine should have a short and free flow nozzle.
Apart from the machine, you will need to have a mold.
Mold is a shape that you would desire to form from the acrylic.
A good mold should have the following specifications:
i. Mould surface with a fine polish
You can use stainless steel mold or high chrome tool steel.
ii. Better water circulation due to better coring of the mold.
You should have the freedom of adjusting the temperature of water for good cycle time and balance.
iii. Have a variety of gating systems to choose from such as sprue, tab, edge, tunnel among others.
iv. It should give shrinkage space range between 0.003 to 0.008 mm/mm.
v. Better ventilation to eliminate any gas in the mold traps.
With all the factors in mind, it is time to proceed to the main process of molding acrylics.
Step-by-step Acrylic Molding Process
Acrylic molding process is simple and straightforward.
In this section, you are going to go through every step in the process of acrylic molding.
Let’s dive right in:
Step One: Preparing and Cleaning all the Relevant Materials
You need to prepare all the necessary materials you need for the molding process.
i. Bringing all the acrylics from the drying chambers
ii. Making sure that you have all the protective gear on.
iii. Cleaning the feeder hopper to prevent possible contaminations.
Step Two: Feeding Acrylic Pieces into the Barrel
After drying the acrylic, you will need to cut it into smaller pieces.
You need to cut the pieces of acrylics so that they fit well into the barrels of the machine.
Feed the small pieces of the acrylic into the barrel.
Step Three: Start the Molding Process
You can start the molding process by switching on the machine.
The machine will start operating by turning the screw.
The screw will turn and heat the acrylics to a particularly suitable temperature.
Apart from heating, the machine will mix all the acrylic materials.
After that, you will pour the molten acrylic into the mould.
It will assume the shape of the mould that you are pouring it into.
Step Four: Cooling the Now Acrylic Mold
In this stage, all you need to do is to allow the acrylic mold to cool off.
As it cools off, the acrylic mold will harden.
You need to control the cooling time and process to avoid excess shrinkage and warping of the acrylic mold.
You can use cooling agents such as water to assist in cooling the acrylic mold.
Are you looking forward to custom injection molding?
You have to understand some specifications before you proceed with injection custom molding.
Walk with me into the next section and find out more about it.
Specifications for Custom Injection Molding
You need to specify the type of acrylic plastic mode that you desire to allow your manufacturer to prepare tooling system.
Acrylic injection molding – Photo credits: Xcentric
Some of the factors that you need to specify include:
- Dimensions of the acrylic plastic mold in terms of size, length, width in millimeters
- Weight of the acrylic plastic mold
- The shape of the acrylic plastic mold
- The thickness of the acrylic plastic mold
- The end use of the acrylic plastic mold.
These specifications will allow the manufacturer to have all the custom machines ready for molding your products
It also gives them time to outsource the tooling system if it is not available.
Finishing Operations for Injection Molded Acrylic Parts
After cooling the acrylic mold, you need to pass it through the final finishing of injection molding of acrylic.
Most of the finishing techniques are often to improve the aesthetic image of the acrylic plastics.
You have to include the additional finishing processes when computing price regardless of the reason for finishing.
Let us go through the main finishing processes of the acrylic plastic molding.
Acrylic injection molding
In the molding process, there are gates that allow compounds to pass through the mold cavities.
This can result in protrusions and intrusions on the final product.
You have to remove the protrusions and intrusions as part of the finishing process through the degating process.
After degating the acrylic mold, you need to remove excess materials from the sides of the mold.
The excess materials can be in the form of flash, or excess compounds and resin bleeds.
You can remove them through the process of deflashing to eliminate imperfections on the acrylic mold.
Some excess material or leftovers might still stick to the acrylic mold.
These materials could compromise other finishing processes such as decorating acrylic molds.
You should thoroughly clean the acrylic mold and ensure it is spotless.
Depending on how and where you will use the acrylic mold.
You may want to decorate the acrylic mold.
Even though it is for aesthetic value, the process of decorating acrylic molds is very important.
Decorating acrylic molds will ensure that it is as presentable as possible.
How are you going to choose the right acrylic molding machine?
Find out more about it in the next section of this guide.
How to Choose Acrylic Molding Machine
Whenever you are looking for a good acrylic molding machine.
You have to look at certain specific factors.
Some of the major factors to look out for include:
Acrylic molding machine
1. Type of Acrylic Molding Machine
Since there are different types of molding machines, you need to specify the type of molding you need.
In this case, you need to go for an injection molding machine.
In this case you have a number of options to choose from.
You can decide on electric, hydraulic, manual, or pneumatic actuation for your machine.
3. Machine Orientation
You can either go for the vertical or the horizontal orientation of the machine.
4. Clamping Force
This is the pressure that machines exert on the acrylic to prevent it from opening due to process pressure.
You need to specify the amount and type of clamping force for acrylic molding.
It is the distance that the moving platen will cover as it operates.
You have to specify the stroke according to the acrylic mold you desire.
6. Daylight or Opening
You have to specify the distance available for fitting different thicknesses of acrylic materials.
7. Shot Size
It is the maximum amount of resin that the machine you want can shoot in a thrust.
8. Injection Pressure
You need to specify the amount of pressure the machine will use in injecting the resin.
Let us have a look at some of the applications of acrylic molding technology.
Applications of Acrylic Molding Technology
You can use acrylic molding technology in a number of different applications.
Acrylic safety goggles
Some of the major applications include:
- Molding different shapes of medical appliances
- Molding different types of home appliances such as refrigerator drawers and plastic glasses
- Molding different types of industrial equipment such as protective goggles.
- Molding different shapes of automotive products
- Molding acrylic sheets to form different structures for the construction industry
I believe that all your hesitations are a thing of the past.
You have all the information that you need to successfully mold an acrylic.
Do not hesitate to visit your dealer and order for the best acrylic sheets for molding.
Apart from that, you can easily choose the best acrylic molding machine using information from this guide.