CN
Twin Sheet Thermoforming Provides One-step Solution
T W I N S H E E T T E C H N O L O G Y PROVIDES AN EFFICIENT SOLUTION TO THE PRODUCERS OF VERY DIFFERENT PLASTIC PARTS. WE LEARN MORE IN THIS INTERVIEW WITH ZVI RAPAPORT OF CANNON ERGOS.
Cannon News: Could you define in few words the Twin Sheet thermoforming technology? Zvi Rapaport: It is a production method of manufacturing thermoformed parts by bonding two heated sheets of plastics in a single operation using a double female mould, resulting in a hollow three dimensional structural part. This space inside the part may remain hollow, contain structural inserts or expanded foam bonded to the hot sheets during the forming stage. Compressed air or gas can be injected and sealed after the part is cooled to create an actively responsive part.
CN: Which advantages can you highlight for this technology? ZR: The structures obtained by the two bonded sheets can solve numerous functional and aesthetic problems, providing an industrial finished solution in a single process that often also has economic benefits. It is a smart alternative to blow-moulding, rotational moulding and other plastics processing technologies, since it allows for the positioning of inserts within the hollow part, allows for the use of different compatible thermoplastic materials in addition to the ability to use different thicknesses and colours on each of the side of the part.
CN: Could you illustrate the most recent achievements in this specific niche of the thermoforming market? ZR: I can disclose some details of an interesting project we delivered this year to an Italian Tier One supplier of mechanical components to the automotive industry. Cannon Ergos was commissioned to develop a large and flexible Twin Sheet thermoformer for the manufacturing of custom industrial pallets. These custom-made rectangular supports are used to hold large mechanical components or bulk materials precisely and safely on their trip from the Tier One production plant to the OEM ' s car assembly line. Thermoformed by Twin Sheet technology, they are composed by two sheets of HDPE( High Density Polyethylene) bonded during the forming operation. The hollow structure obtained is able to withstand the substantial weight and severe impacts while protecting a number of mechanical assembled components during the trip and in intermediate storage areas. The client manufactures these pallets in different sizes and shapes using a dedicated Cannon Twin Sheet thermoformer designed to optimise the cycle time while keeping high flexibility in terms of final product. This machine features a forming area of 2,500 by 1,500 mm and has a closing force of several hundreds of kN. The thermoformer is designed to handle plastic sheets in the 1 to 10 millimetres thickness range, this specific application typically uses 4.5 mm thick HDPE sheets. Two banks of halogen heating elements efficiently heat the sheets according to a user defined heating pattern. A precise, highly responsive, computer temperature control system guaranties correct temperature is maintained
throughout the heating process. Dual sag control is achieved as the lower mould box and the volume between the two sheets are sealed and pressurized. An array of sensors monitors the sag of the sheets and opposes it by increasing the pressure in the sealed spaces. This feature is extremely useful to optimally heat the material and optimize material thickness distribution during the forming process. The forming clamp locks the two mould halves and a closing force of hundreds of kN is applied to bond the two sheets into a cohesive three dimensional structure. Pressurized air is blown between the two sheets, to ensure the best reproduction of the mould details and to provide an initial cooling effect. After cooling, the mould and the moving intermediate frame( the“ cartridge”) open, to release the formed pallets. A robot in the heart of the production cell unloads the formed parts from the machine and immediately puts in place another set of four pre-heated sheets to restart the cycle. A production cadence of 5 minutes and a generous working area – to simultaneously produce two pallets of 1,200 by 1,000 mm side by side – contribute to high production rates. Fast tool change is achieved by automatically adjustable reduction plates and clamp frames. All tooling has automatic quick locking systems. Servo movements with encoders and proportional valves for process control ensure the process is stored and retrieved when needed. The ability of producing single sheet parts complete the flexibility of the machine. I can disclose only a few details of another project, a machine designed for high-speed, high-precision, extremely repeatable production. It makes small parts that require a high degree of accuracy. The machine uses two independent sheet transport rails with ample space between them. The independent transport rails allows for flexible forming sequence and the space allows the ability to place inserts inside of the Twin Sheet part. A robot places inserts inside the cavities of the first formed sheet while the second sheet is still heating in the oven. Once the inserts are placed the second sheets is transported to the forming area to be formed and bonded to the first sheet. The latent heat bonds the inserts
Twin Sheet thermoforming equipment requires a special design to guarantee perfect handling and bonding of two hot plastic sheets.
Industrial plastic pallet obtained with Twin Sheet forming technology, using two thick HDPE sheets.
26