Thermoforming Acrylic: The Ultimate Guide

Today we want to learn about Thermoforming Acrylic.

In this guide, I will take you through the definition of thermoforming acrylic, thermoforming basics, its advantages, and disadvantages.

We will also look at the factors affecting the quality of acrylic thermoforming process and techniques used for thermoforming.

We will look at Drape, Pressure, and Vacuum forming an acrylic sheet.

Apart from these, we will also journey through common problems in thermoforming acrylic, machine buying and the applications.

Acrylic Thermoforming Basics

Thermoforming is a plastic molding technique. It refers to the process of heating thin acrylic sheet material until it reaches a pliable temperature.

Then, the hot plastic sheet is manipulated to form a three- dimensional shape. This is then trimmed into a finished product that can be used.

Plastic thermoforming

Thermoforming plastic material

Thermoforming is a process mainly used as a packaging for consumer and large customized products.

It can be divided into two categories: thin and thick gauge thermoforming.

Thin -gauge use less than 0.060 inches to manufacture food and medical packagings like blisters, disposable cups, and poultry trays.

Thick-gauge, on the other hand, uses 0 .120 inches to manufacture industrial products like refrigerator liners, plastic pallets, and enclosures.

Let us now have a close look at some of the basics in acrylic thermoforming.

Design in Thermoforming Acrylic

All thermoforming projects must begin with a design.

In most cases, thermoforming acrylics are used for large products. They are always the outer protective covering of equipment.

Nevertheless, thermoformed products start as a CAD model or drawing. Manufacturing companies use CAD files.

Visor design

Visor design – Photo courtesy: Autodesk

Through their engineers, they refine the model into shapes that work well with acrylic manufacturing processes.

Material Selection

When the design is ready, we can now select acrylic as our material for use.

The factors affecting the choice of material here include functional reasons like fire-related and high heat materials.

Acrylic material

Acrylic material

We can also select colored and textured acrylic so that we can end up with an enhanced final product.

Tooling for Acrylic Thermoforming

This is the creation of a mold where the acrylic will be heated over.  Aluminum molds are commonly used.

Thermoforming tooling

Tooling set for thermoforming – Photo courtesy: Research gate

Depending on the size and complexity of equipment, several individual parts are combined to form a single mold. This helps in reducing the tooling cost, material cost and production time.

The parameters for thin-gauge tooling include maximum mold size of up to 30 inches wide. It also has a maximum depth of draw of about 8.0 inches and a maximum sheet thickness of 0.8 inches.

Other parameters are aluminum mold, which is temperature controlled, and steel rule dye for trimming.

Thermoforming Process

The acrylic is formed to the mold by heating it to a pliable temperature.  Thereafter, shape it to the mold using either a vacuum pressure or air pressure, or a combination of both.

Once it has been formed onto the mold, it is cooled and then removed from the mold in its final shape.

Because the final product cools against the mold surface under ambient temperature, its finished parts have zero residual stress.

Trimming Acrylic Sheet

After the final product has cooled, some parts need to be trimmed off. Fully robotic 5 and 6-axis trimmers can be used to quickly cut both complex and precise shapes.

These trimmers are very important in this process because they aid in faster production, more accurate and flexible cuts. This provides an excellent finishing for the products.

The trimmers can sometimes be used to perform secondary operations like cutouts, through-hole and anything that requires the removal of material.

Secondary Operations

After thermoforming and trimming, other secondary operations like painting, silk-screening, EMI/RFE shielding and the installation of inserts are performed.

Also, fastening devices, assembly of hinges, handles, and other hardware are carried out during this stage.

Goggles

Goggles

They all form an important step in acrylic fabrication process.

When all these are done, the acrylic thermoformed products will be ready to integrate with their manufacturing processes.

Advantages of Thermoforming Acrylic

Some of the main advantages of acrylic thermoforming include:

  • Offers a fast tooling production which can be available within 2-3 weeks.
  • It is cost effective in terms of tooling. It saves up to about 90% of tooling cost as compared to other molding types. If you desire to modify tools and parts of acrylic, it is achievable quickly and this is also very economical.
  • It is a faster process as compared to other manufacturing methods. This is because once the design has been confirmed, thermoformed parts can be ready within a month or less. This speed in production enables delivery on time.
  • Acrylic has the ability to tolerate the expansion of dimensions as far as 6 feet by 10 feet. The typical tolerance for thermoforming processes include forming: part to part +/-.025 and perimeter Die cut: +/- .060
  • It is compatible with numerous types of engineered thermoplastics.
  • Thermoformed acrylic has a flexible ordering with short lead times of about four to six weeks. Therefore it allows shipment to be scheduled conveniently, thus reducing inventory.
  • This process is ideal for both small and medium-sized part runs between 50-5000 pieces.
  • Its parts with small thickness to area ratio can easily be fabricated, even though extremely large parts can also be fabricated.

They are flexible and can be used to produce any desired shape and size. It can also be produced in a variety of colors and textures. This provides an opportunity to produce a wide variety of products that enables competition in the market.

  • Acrylic thermoforming uses high-quality plastic sheets which are durable as compared to those used in other methods. It produces good dimensional stability.

Disadvantages of Acrylic Thermoforming

Before you start thermoforming acrylic sheet, it is important to note the following:

  • Acrylic sheets in a pliable state can break due to excessive stretching under a certain temperature. When this happens, it leads to wastage. Also, about 20% more acrylic will be used, and this will result in higher acrylic thermoforming processing cost.
  • The fact that high-quality acrylic plastic sheet is used means the acrylic thermoforming method is not cost effective. It costs around 50% more as compared to other methods like injection molded parts.
  • Because it uses molds, only one side of the product is defined by the mold. Therefore, itcan produce non-uniform wall thickness due to film stretching.
  • Also, the parts that have sharp bends and corners are very difficult to produce. Due to this, the internal stress of the product is very common.
  • This process is limited to the geometry since parts with undercuts cannot be produced.
  • At times, parts have a poor surface finish and therefore have to be trimmed.
  • It is difficult to mold ribs and bosses and very thick acrylic sheets cannot be formed.

Factors Affecting Quality of Acrylic Thermoforming Process

There are a number of factors that affect the final acrylic product.

This section covers some of the most common factors and procedures that affect the quality of acrylic thermoforming process.

Acrylic thermoformed letter

Acrylic thermoformed letter

· High Water Content in Acrylic Sheet

When the sheet has high water content, it is essential that it should be dried before forming. This will help in reducing the length of the forming cycle.

Failure to do this may result in blistering of the sheet during forming, thus compromising the quality of the product.

The sheet should, therefore, be dried in a spare oven, and immediately be transferred into the forming oven at 80ºC.

· Unheated Clamping Frame

The frame should be heated first to a temperature of between 60-82ºC before clamping acrylic sheet on it.

This helps in reducing stress when the sheet becomes hot while the clamped edges remain cold.

Using unheated frame can lead to tearing, edge distortion and formation of asymmetric shapes that were not intended.

· Temperature Distribution

The thermoforming acrylic process requires that the temperature be distributed evenly across the entire sheet’s thickness.

Normally, acrylic sheet forms at a temperature of between 142-160ºC. The temperature of the sheet must be higher than the desired one so that cooling occurs before forming begins.

The machines that have specifications for oven temperatures make it easy for adjustments and control.

However, others have no such specifications. Therefore, it is required that you find an approximate temperature by using a pyrometer calibrated for plastics.

Alternatively, you could use thermometer papers that show the sheet’s surface temperature by color change.

Nevertheless, the requirements for temperature depend on forming conditions like the degree of shaping/stretching and the forming rate.

Therefore, if you want to prevent pimples, blisters, shading, and other damages, you have to avoid unnecessarily high temperatures.

· Heating Time

This depends on the acrylic sheet thickness and the heating method. Time for heating is influenced by the velocity of the air in the oven and panel-to-heat distance.  It is also determined by thermal conductivity.

Thicker acrylic requires more heating time. For instance, when the acrylic volume is larger, thermal conductivity is small and therefore the heating time becomes long.

To understand how long an acrylic sheet should be heated, you have to determine this by running a test cycle.

· Forming Rate/ Speed

When a sheet has stretched without exceeding its strength and fracturing, it’s said to have reached its maximum forming rate. The minimum forming rate should be fast to prevent the sheet from cooling appreciably.

It should take long to form a colored sheet as compared to a colorless or a transparent one.

Acrylic sheet develops stress when the forming rate is excessively fast, and this causes low craze resistance.  To minimize this stress, you should use moderate forming rate.

You should also ensure a uniform temperature distribution over the surface of the sheet and across its thickness.

Therefore, for forming of large parts, low forming temperature is relevant with Infrared heating while the part is being formed. High forming temperature is ideal for greater draws.

When forming parts that have a varied thickness, always increase both the temperature and the forming speed for thicker parts. This will help you to get better results.

· Molding Pressure

Acrylic has the ability to resist deformation, but when heated, it becomes elastic and begins to form over a mold. This pressure varies with the thickness of the sheet and the temperature subjected to it.

Acrylic Thermoforming Techniques

There are many acrylic thermoforming techniques. However, we shall look at the most common three. They are drape forming acrylic sheet, pressure forming acrylic sheet and vacuum forming the acrylic sheet.

1) Drape Forming Acrylic Sheet

This is one of the earliest thermoforming processes dating back to early Egyptian times. The Egyptians heated tortoiseshell in hot oil so that it can be formed.

This process uses a vacuum or air pressure to force the sheet against the mold. Acrylic sheet is heated to the desired temperature and then draped over a male mold/a fixture to stretch.

This is done either by lowering the sheet into the mold or by raising the mold into the sheet. The sheet part that touches the mold first will cool and then cease to stretch.

It is used to manufacture products that require gradual curves or bends like windshields, machine guards and POP displays.

There are machines that have been developed to make drape acrylic form with superior accuracy and produce many parts per sheet. This machine has eliminated secondary trimming operations because it uses cut-to-size sheets and this has greatly reduced the production cost.

Sometimes, techniques like power drape forming are used. Articulating clamp frames are used in this case to increase the normal sag of the sheet.

Drape forming acrylic sheet

Drape forming acrylic sheet

This helps in approximating the depth of the mold more closely. It also reduces the pressure on the mold surface of the sheet resulting in fewer mark-offs being apparent in clear parts.

Advantages of Drape Forming Acrylic Sheet

  • Tooling cost is relatively low as compared to other methods of forming the acrylic sheet. This means that it can be used in low-level production providing an opportunity to produce small quantities economically.
  • During drape forming, acrylic sheet is not typically stretched. Therefore it retains its full dimensional thickness in a flat sheet of material.
  • When acrylic sheet that has been used is either clear or textured, it will retain its surface features even post-processing.
  • It produces products with beautiful gradual bends.
  • This technique is ideal for both small and large parts. For example, it can be used to process parts that are between 0.060 – 0.50 inches.

Disadvantages of Drape Forming Acrylic Sheet

  • Very little details can be achieved with this process since there is no pressure to shape the acrylic.
  • During forming, the acrylic sheet in a pliable state can break due to excessive stretching when subjected to a certain temperature. This can lead to wastage and increase the use of more sheets to about 20%. Therefore, with this problem, it can be costly.
  • The use of high-quality sheets makes this method expensive to around 50% more than the use of other techniques.
  • Sharp bends and corners are not so easy to produce, and because of this, internal stresses are common.

1) Pressure Forming Acrylic Sheet

This is a more advanced process for forming the acrylic sheet into a finely detailed molded shape. A pressure box is added to the tooling package.

It’s more related to vacuum forming although air pressure is 4 times higher as compared to that in vacuum forming.

Once the plastic is heated, it is placed on the mold surface. Air pressure is applied quickly above the acrylic sheet resulting in high pressure between the softened sheet and pressure box. This leads to deforming of the sheet into the mold cavity in a short while.

The formed sheet remains in the mold cavity for a few seconds as it cools down and thereafter, is ejected.

The picture below illustrates pressure forming

Pressure forming acrylic

Pressure forming acrylic

Advantages of Pressure Forming Acrylic Sheet

  • It is possible to form fine details such as surface texture on the mold without having to incur additional costs.
  • This is a cheaper way of forming acrylic sheets for both low and medium volume runs. It can also form very large parts and complex shapes at a cheaper cost.
  • It has a quick and cheap tooling process.
  • Pressure forming acrylic sheet can form pieces with vents and louvers.
  • Pressure forming can also be used to form acrylic in projects that require tighter tolerance.
  • Normally, it is faster to market with quick prototypes
  • It can be used to produce items with a variety of colors and textures.

Disadvantages of Pressure Forming Acrylic Sheet

  • It is limited to shape complexity and thin-walled parts.
  • Once the acrylic has been used, its scrap cannot be re-used.
  • For you to have a great finishing of its products, trimming must be done using a hand saw.

1) Vacuum Forming Acrylic Sheet

In this process, the parts are formed by heating acrylic to a suitable temperature. Place the acrylic sheet on the mold surface and fixed using a clamping unit.

Heat it until it becomes soft and then quickly apply the vacuum.

Using a surge tank, quickly pull the air out from between the mold and the sheet. This will trigger the formation of a cavity on the mold.

The heated sheet will then conform to the shape of the mold cavity, cool and be ejected from the cavity.

Vacuum forming is a reliable method used in creating numerous types of props and costume accessories.

The diagram below shows vacuum forming

Vacuum forming acrylic

Vacuum forming acrylic

Advantages of Vacuum Forming Acrylic Sheet

  • This method is cheap compared to other acrylic forming methods.
  • The tooling process if quicker here.
  • Vacuum forming acrylic sheet technique has the ability to form very large parts.
  • It allows for the forming of products with sharper details, texture, different colors and undercuts.
  • It has tighter tolerance.

Disadvantages of Vacuum Forming Acrylic Sheet

  • Vacuum forming has restrictions. It is only ideal for applications that use shallow acrylic parts which are formed into cavities.
  • It is limited to shape complexity and thin-walled parts.
  • Its scrap cannot be re-used.
  • Trimming must be done for a neat finishing.

Common Problems in Thermoforming Acrylic

Like many manufacturing processes, thermoforming acrylic also has some problems which interfere with its successful process. Most of these problems are tool related.

They include:

Vacuum forming acrylic sheet

Vacuum forming acrylic sheet – Photo courtesy: FORMEC

  • There could be warping caused by improper temperature controlled tool design and manufacturer. This results in unequal heating and cooling of acrylic material surface area.
  • Sometimes, there are dimensional inconsistencies which also results from improper temperature controlled tool design. When the form/mold is in the process of production, the temperature will not be consistent over a batch of parts. This yield inconsistent parts shrinkage.
  • Inconsistent Acrylic part thickness is another problem.  This occurs when there is inadequate and or improper vacuum venting in tool design and manufacture.

When the parts are forming over the mold, these inconsistencies occur due to inadequate venting.

  • Another problem is the lack of detail in part geometry. This is also as a result of inadequate vacuum venting in tool design and manufacture.

It happens when the parts are forming over the mold with inadequate venting in areas of geometry or aesthetic design.

This will result in a failure to produce the desired results.

  • Poor quality surface finishes due to the texture of gloss variation. This can be caused by improper tooling materials selection or inadequate tool surface finishing.

When the tool surface is porous, it may result in unwanted surface texture, dimpling or even gloss reduction.

  • Chill marks are another challenge. It occurs when there is inadequate or improper vacuum venting and temperature control in tool design and manufacture. This causes wavy undulations in the acrylic surface when air is trapped, resulting in unequal material cooling.
  • Web or unwanted wrinkles usually form around the mold particularly when you use the vacuum method of forming acrylic. This affects the final product in a negative way.
  • Surface markings resulting from improper mold surface and dirt on the sheet.

Reduce this by using proper mold covering like foam, felt and flocking. You can also clean the mold surface with deionized air.

  • Bubbles which occur due to an application of heat too rapidly, uneven heating or excess moisture in acrylic sheet.

The remedy here is to lower temperature by increasing the distance between heater and sheet. Also, pre-dry, pre-heat, and keep masking on the sheet until formed and use older materials first.

  • When the mold or tool is positioned too high in relation to its base area.
  • Sharp vertical corners which have minimum draught angles.

In this case, you should add draught angle corners to allow the materials to flow over the mold or pattern.

  • Deep male mold placed in close proximity to each other.

The remedy here is to use a female tool to prevent the webbing.

  • Cracking in corners due to stress concentration.

To avoid this mess, heat the acrylic sheet evenly and use heated frames. You can also add supplemental heat to the corners.

  • Raised corners as a result of excessive stress.

To minimize this, the frame should be heated to temperature before clamping the sheet. In addition to this, you can also add supplemental heat to the corners.

You can minimize all these tool-related issues by utilizing proper tooling designs, material selection, and adopting high-quality manufacturing. By so doing, you will raise your initial tooling investment thereby saving the production cost.

You will also have benefits associated with reduced lead-times, reduction in part defects, increased aesthetics and high-quality parts.

Buying Acrylic Thermoforming Machine

These machines can be bought in many countries like China, Taiwan, and Turkey. You simply place an order, which will be protected right from payment to delivery through a service supported by all suppliers.

Send your machine specifications and a quotation will be sent to you. You can then place your order depending on the purpose for which the machine is intended and your budget.

These machines exist in a variety of capacities with different price allocations. The cost ranges from as low as 2000- 100,000 USD or even more.

Plastic thermoforming machine

Plastic thermoforming machine

There are those that are distinctly made to carry out pressure forming or vacuum ones.

Some are only meant for a single specific product. For example, there is a high-speed vacuum acrylic sign forming machine, acrylic bath-tab vacuum forming machine, among others.

Applications of Thermoforming Acrylic Sheet

This is a versatile and reliable process for any number of applications. They are affordable and dependable for consumer goods, medical components, and office equipment. Application areas include:

Acrylic components

Acrylic components

· OEM Equipment Covers

Thermoformed acrylic sheets provide protection from impact, elements, ultraviolet radiation and corrosion to all types of OEM equipment.

The acrylic gives flexibility to design and durability that is needed to protect this equipment.

· Medical Equipment Covers

The acrylic molding process is a reliable method for producing high-quality products that are very important in the medical industry. For example, it is used to produce the covers that enable clean and dry storage of medical instruments and equipment.

The equipment covers that use this application include IV pumps, ventilators, and liquid oxygen systems.

Radiotherapy masks for cancer patient treatment, burn victims pressure masks and parts of wheelchairs are also applications for this process.

· CRTs Housings, Touch Screen, Liquid Crystal, Flat Panel or Plasma Displays

Thermoformed acrylic sheet produces good quality protective housing for consumer, business and medical displays. They are formed through pressure method to add logos, sharp corners, and detailed designs.

· Agricultural Equipment

Acrylic sheet molding process of vacuum forming is used to create numerous types of agricultural equipment. These include panels, roofs, interior components for tractors and farm machinery, sprayer shells, feed/water containers, and livestock housings.

Seed trays, flower tubes, and lawn mower enclosure are also made through this process.

This application is very relevant here because acrylic can be exposed to UV radiation and elements. It is resistant to corrosion, impact, chemicals, and stains.

· Automotive Components

Thermoformed acrylic has also been applied in the automotive industry. For example, it is used to produce components like panels, doors, seating parts, dashboards, bumpers, and air ducts.

In addition to these, it is also used to produce truck bed liners, floor mats, and headlight covers.

Vacuum forming is very ideal for the larger and shorter-run components like bumpers and interior panels.

On the other hand, pressure forming is used to make precise, sharp detailed and attractive surfaces like logos stamped.

· Skylights

They can be made very well using thermoformed acrylic sheets.  This is because they are more transparent than glass and they have shutter proof grades.

They are either vacuum or drape formed depending on the shape and aesthetic needs of a particular application.

· Building and Construction Industry

This process aids the production of building and construction materials. For instance, drain pipes, anti-drip fittings, roof lights, internal door liners and PVC door panels.

In addition to these, mold for concrete paving stones and special bricks, molded features for ceilings and fireplaces are also manufactured.

· Aeronautics

Aeronautical manufacturers use this application to make interior trim panels, covers cowlings and internal sections for (NASA) space shuttle.

· Chocolate Industry

The industry has found this application relevant because they use it to process chocolate molds for special occasions. They also use it to make chocolate packages.

· Computer Industry

Through this process, they produce surroundings of computer screens, soft transparent keyboard covers, enclosures, and ancillary equipment.

· Packaging and Related Industries

The packaging industry uses this application by manufacturing point of purchase, trays, plates and cosmetic cases. They also make electronic cassette holders, blister and skin pack products, food trays and fast food containers.

Conclusion

Thermoforming acrylic is a very crucial process that has been adopted by many manufacturing industries. This is because it’s cheap, has short lead time, non-corrosive and resistant to external factors like a stain.

It’s a flexible process that is ideal for small and medium productions, large and small in size parts.

The parts can also be produced in different colors, with details and different designs.

This technique enables the production of parts that are cheaper since the whole process is cost effective.

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