The Vacuum Forming Porcess -The Most Detailed Explanation

Ditaiplastic SINCE 1997!

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What Is Vacuum Forming?

Vacuum forming is an invention that dates back to 1930 and has increased its relevance over time. It is a simplified thermoforming version and a very common way of processing plastic material. The vacuum forming process operates under the principle of a hard, flat plastic sheet that gets softened by heating, the vacuum is sucked to the surface of the preferred mould and then cooled to permanently take up the shape of the mould. It is considered the best way of forming both permanent and recyclable plastic products.

Things About Our Factory

Ditaiplastic since 1997, is one of China’s largest vacuum forming/thermoforming processing factories! Up to now, we have a factory covering 12,000 square meters with over 60 processing machines. Also, we have over 80 employees, 6 engineers, and lots of experienced people! We can design for free, and develop and produce all elements in-house; from design and tooling/molds to forming and CNC cutting. We are even able to carry out complex assembly of the final product for you.
Keeping all aspects in-house allows us to maintain unparalleled quality control as well as speed up the entire process from concept to product delivery. Clients also benefit from us being a single point of contact for all their manufacturing needs. And we are so proud of our large volume machines, we have the largest vacuum forming machine in Guangdong! That being said, no project is too small, and we will happily speak with you about how we can help you with your project requirements.

The Steps Involved in Vacuum Forming Process 

The entire vacuum-forming process consists of different steps through which, a flat Plastic sheet will be moulded into a preferred shape. The steps involved are clamping, heating, sheet levelling, pre-stretching, vacuum, plug assist and cooling. Let’s elaborate on these significant steps below.

Video Shows How To Extrusion Plastic Sheets And The Package

Chose The Best Plastic

We all agree that plastics are increasingly becoming very popular and equally controversial. They have by far provided practical solutions for quite a number of modern-day problems. We are urged to use plastics ethically, minimize the quantity and increase quality by ensuring the plastics are reusable and or recyclable. To have a successful forming, it is very advisable to commence by choosing the best plastic for forming. The following are some best plastics for the vacuum-forming process.

Acrylonitrile Butadiene Styrene (ABS)

ABS is popularly known as ABS. It is described as a hard and rigid plastic with high resistance to impact. It also has high weather resistance qualities making it ideal for forming vehicle parts and accessories.

High Impact Polystyrene (HIPS)

HIPS is a rigid, tough plastic with high resistance to impact just as the name suggests. It is available in a wide variety of colours and it is very affordable. It is ideal for forming toys, point-of-sales displays, and signs.

High-Density polyethene (HDPE)

HDPE has a very high strength and resistance to impact and still maintains its flexibility. It can easily be fabricated and supports welding. It is low-cost and ideal for forming vehicle and caravan parts.

Polyvinyl Chloride (PVC)

 PVC is a low-cost forming plastic with a strong range between medium and high strength levels. It has the ability to resist fire and chemical effects. It supports machining, welding and fabricating making it ideal for forming automotive parts, electronics and packaging materials.

Polypropylene

Polypropylene is a common plastic with high impact resistance and is equally flexible. It has desirable aesthetic qualities and is chemical resistant. It is mainly used in chemical tanks, medical applications, food containers and automotive parts.

Acrylic 

 Acrylic plastic is very easy to fabricate and easily bonds with solvents and adhesives. It has a high quality, impressive strength and versatility making it fall in the bracket of high-cost forming plastics. It’s mainly used to form display shelves, signs and baths.

Polycarbonate

Polycarbonate is a highly rigid and hard plastic with a recommendable impact resistance. It has a self-extinguishing property making it under the expensive forming plastics. This same feature has makes it in high demand in the aerospace industry, machine guards, visors and riot shields.

Acrylonitrile Styrene Acrylate (ASA) 

Acrylonitrile Styrene Acrylate (ASA) plastic is highly durable with impressive impact resistance strength. It also has Ultraviolet (UV) resistance properties making it ideal for use in outdoor settings. Its demand is high in the forming in automotive industry, signage and garden furniture and accessories.

Polyethylene Terephthalate Glycol (PETG)

Polyethylene Terephthalate Glycol (PETG) is high impact resistance and also resistance to a wide range of alcohols, acids and oils easing the sterilization process. It is popularly used in the forming of medical applications and food packaging materials since it can be moulded and trimmed precisely without exposing it to structural integrity.  

Clamping

As the dictates, the clamping stage is used to hold and bind firmly the plastic sheet into place. The clamp frame of the vacuum-forming machine needs to be strong enough to firmly hold even the thickest material in place. Considering the vacuum forming machines are either single heating machines or twin heating machines, they can handle plastic thicknesses of between 6mm to 10mm in thickness. In order to ensure the operator is safe at all times, the moving parts of an automated machine need to be interlocked and safely guarded. The safety guard needs to be fabricated or a light curtain to maximize the operator’s safety during operation.

Heating

After the flat plastic sheet is firmly clamped, we now move to the heating stage. The heating stage of the vacuum forming process is facilitated by the following parts;

Infrared Elements – they are mounted within a reflector place made of aluminium. This is to ensure that the heating is done uniformly on the surface of the material and into its thickness – the flat plastic sheet.

The Pyrometers – the heaters are fitted with pyrometers that accurately control the temperature since it has the ability to sense the sheet’s melting temperature.

Readout – pyrometer interacts closely with the operating process control of the machine. The operator is able to see the temperature through the readout on the computer-controlled system that works in unison with the pyrometers.

The Heating Control System – is an extension of the process controller that facilities rapid heater zoning visual interpretation.

Thyristor Modules – provides precise temperature control.

When forming thick materials it’s advised to use twin heaters since they help in providing more uniform heating and faster cycle times. Quartz heaters are preferred due to their less thermal mass which enables their rapid response times. The twin quartz heater is mainly used when dealing with thick materials that require critical heating.

Sheet Level Monitoring

There is a gap between the plastic sheet and the heater there is a photo-electronic beam. It is there to ensure that the plastic sheet does not sag. In the event the plastic sheet sags, it interrupts the photo-electronic beam – it means that the plastic sheet is sagging. To correct that the machine blows pressurized air to lift the plastic sheet back into position. This is to ensure that there is a consistent finish.  

Pre-Stretch

Once it has reached the forming stage, the plastic sheet is pre-stretched so that the thickness can be consistent. With an even thickness, it will be maintained when the vacuum is applied. The feature is very important when forming deep draw parts, high-detail mould surfaces and minimum draw angles. The purpose of pre-stretching or controlling the bubble is to ensure we obtain consistent results. To enhance more consistent results, optional aids such as plug assist and mandatory Vacuum and air pressure are used on the heated and pre-stretched plastic sheet.

Vacuum

The plastic sheet now is heated and pre-stretched and has attained the correct temperature. A vacuum can now be applied to draw the air that’s trapped between the mould and the plastic sheet. Simultaneously, the mould is moved upwards towards the plastic sheet. At this stage, the vacuum pump will suck the air out and once the air is all sucked up, the plastic sheet will be sucked into the mould. The vacuum machines are expected to uphold a differential pressure of approximately 27” mercury. This is to ensure the process is done with haste to ensure the heated and pre-stretched plastic sheet does not lose its moulding temperatures. In larger machines, a two-stage vacuum of a fusion between a large vacuum reservoir and a large capacity vacuum pump to ensure hast moulding.

There are basically two types of moulds;

Mold

Male Molds – it’s also referred to as positive and convex in shape. The plastic sheet is placed on its top – prioritizing the interior dimensions over the external dimensions.

Female Molds – it’s also referred to as negative moulds and it is concave in shape. The plastic is formed inside the mould – making the exterior dimensions a priority over the internal detentions.  

Plug Assist

The plug assist is the use of a male plug tool with a hydraulic or pneumatic mount that is situated at the forming area. It’s responsible for forcing the heated and pre-stretched plastic sheet into the female cavity found in the moulding area. It facilitates the complex and deep raw moulds to form without webbing and attain an even distribution of thickness. It ensures that there is enough material in the cavity right before the launch of vacuum pressure. Leather lining or felt reduces the risk of premature chilling on contact. Resin plugs are the most preferred alternative since they are good insulators and have no effect on the pressure of the sheets. The plug assist is ideal when forming multiple male mould impressions since they can be placed at a very close range without the risk of material webbing.

Cooling And Releasing

This is considered the last stage where the heated, pre-stretched and vacuumed plastic sheet is now allowed to cool before it’s released. If the moulded plastic is released before cooling, it may result to reject parts. The forming machine comes fitted with high-speed fans that are activated to speed up the cooling process. There is also the option of spraying the plastic sheet with chilled water – the water nozzles are attached to the fans and directed to the sheet. The combination of the high-speed fans and chilled water emitting nozzles shortens the cooling process greatly.

Using the moulding temperature control, the temperature is regulated to provide an accurate and even cooling process.

The Materials Used In Vacuum Forming

Plastic is the most common material used in vacuum forming. Here is a list of the plastics used in vacuum forming and an outline of key characteristics and properties.

Acrylic Perspex (PMMA)

  • It is hygroscopic
  • It has high-temperature sensitivity
  • It can become brittle when exposed to high temperatures
  • It has a 0.3% to 0.8% shrinking rate.
  • It has prone to shattering.
  • It is good to work with manually.
  • Safe to use cellulose and enamel sprays.
  • Available in different colours – can also be transparent or opaque.
  • It is very suitable for applications where clarity is important.

ASA

  • It is hygroscopic
  • It is strong.
  • It forms easily to a high definition.
  • It has a 0.3% – 0.8% shrinking rate.
  • It is easy to cut/saw
  • It can take all types of paints
  • It has great UV resistance for outdoor use
  • It is hard and rigid to withstand impact.
  • Has the ability to resist weather hazards.

 Acrylonitrile Butadiene Styrene (ABS)

  • It is hygroscopic
  • It is strong.
  • It forms easily to a high definition.
  • It has a 0.3% – 0.8% shrinking rate.
  • It is easy to cut/saw
  • It can take all types of paints
  • It has an unlimited colour range
  • It is hard and rigid to withstand impact.
  • Has the ability to resist weather hazards.

Polycarbonate

  • It is hygroscopic
  • It is very strong.
  • It forms well to a high-definition product
  • It has a 0.6% – 0.8%shrinking rate
  • It can be machined, tapped, ultrasonically welded and drilled.
  • It can take the spray.
  • It is a clear, embossed texture, translucent, and solid colours, and opal and diffuser patterns.
  • It has a great resistance against both fire and impacts

Polyethylene (HDPE)

  • is not hygroscopic.
  • It is very strong
  • The PE component is alone challenging to Form.
  • It best forms under low temperatures.
  • It has a 2.3%- 3.5% shrinking rate
  • Does not take paint but can be printed on with specific paint.
  • Has black, white and other colours.
  • It has good chemical resistance.

Polyethylene Terephthalate (Glyco/CoPolyester PETG)

  • It can be used without being pre-dried.
  • It is strong.
  • It is good for forming high-definition products.
  • It has a 0.3% – 0.7% shrinking rate.
  • It can be cut, sawn and routered.
  • It can be punched and die-cut to a limited extent.
  • It can be printed with paints and inks suitable for polyester.
  • It has a limited colour range but is mostly clear.
  • It can be safely sterilized with alcohol and acidic oils.
  • It is not recommended to use alkaline solutions on it.
  • It is very easy to form.

Polypropylene (PP)

  • is not hygroscopic
  • It is very strong
  • It is challenging to form.
  • To form it requires precise temperature and sheet level.
  • It has a 1,5% – 2.2% shrinking rate.
  • Cannot be sprayed on
  • It is translucent and available in white, black and other colours.
  • It is hard to form –prone to sheet sag

Polystyrene (HIPS)

  • is Not hygroscopic
  • It forms well and can support high definition.
  • Has a 0.3% – 0.5% shrink rate
  • It machines well but it needs a special primer to get sprayed.
  • It has a wide range of colours, textures and patterns.
  • It has poor UV resistance.
  • It is very easy to form.
  • Supports non-sterile packaging.

In Summary:

The Application Of Vacuum Forming Process 

Over the years, vacuum forming has grown in its popularity and has been adopted by different companies such as; Aeronautical Manufacturers to make covers, interior trim panels and cowlings. Agricultural Suppliers make seedlings trays, animal feeding containers, machinery parts and covers. Architectural model makers to develop models and prototypes. Automotive Industry to develop vehicle parts and accessories such as wheel caps, and mudguards. Construction industry to make plastic moulds, ceilings, and PVC door panels. Boat industry to make boat dashboards, electrical insulation, cover, etc. Food products for making chocolate mould, packaging etc. The electronics industry develops Plastic housing like television and computer back covers. Education sector to the development of plastic study dummies. Entertainment in the making of PVC costumes such as masks. Medical and Hospitals use parts of mobility assistants like wheelchairs. Packaging Industry in making PVC containers and containers.

Ditaiplastic SINCE 1997!

WhatsApp: +86 13825780422 Email: amy@dgdtxs.com.cn

Kindly visit us at: https://www.ditaiplastic.com

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