Professional manufacturer of thermoforming machines.
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Professional manufacturer of thermoforming machines.
Principle of Vacuum Forming Machine: Vacuum forming is also called thermoplastic forming, This process involves heating and softening thermoplastic sheets (e.g., PVC, PET, PP) and using a vacuum pump to shape them over molds, producing items such as vacuum-formed covers, blister trays, and clamshell packaging.
Vacuum forming machine includes several parts such as clamping system, heating system, vacuum and compressed air system and mould.
When plastic sheet is moulded, the sheet is fixed on the clamping device. In the thermoforming of general-purpose and composite thermoforming machines are used to facilitate the fixing of various sizes of sheet clamping device. In some cases, the entire moulding machine is equipped with a set of clamping frames.
The clamping system should be optimized with automated controls to achieve rapid operation, thereby enhancing part quality and production efficiency.
Thermoplastic sheet and film of vacuum forming process, one of the main processes is sheet heating.Heating duration and effectiveness depend on factors including heater design, radiation surface thermal inertia, sheet-to-heater distance, material absorption coefficients, and the material's thermophysical properties. Commonly used heaters are electric heaters, crystal emitters and infrared heaters.
Vacuum system consists of vacuum pumps, tanks, valves, piping and vacuum gauge, etc., often used in vacuum forming a separate type of vacuum pump, the vacuum of such pumps should reach 0.07 ~ 0.09 Mpa (520mmHg) or more. The gas storage tank is generally a cylindrical box welded with thin steel plates and has an oval bottom. The capacity of the gas storage tank should be at least half the capacity of the largest moulding chamber. Vacuum piping must be equipped with appropriate valves to control the narrow capacity of the vacuum.
The vacuum pump's motor power (typically 2-4 kW for large/high-speed systems) is determined by equipment size and production demands. Vacuum pipelines require precise flow control valves. The size of the vacuum central system depends on the specific production and development requirements of the factory.
The pneumatic system consists of compressors, air tanks, valves, and pipelines. Molding machines typically require 0.4-0.5 MPa compressed air, supplied either by integrated piston compressors or centralized plant screw compressors. Can also use large screw air compressor whole plant supply.
Compressed air in addition to a large number of should be used in forming, there is when a part of the mould for the first products outside the cooling and manipulation of the mould frame and running sheet and other machine parts such as the power of action.
In order to improve production efficiency,vacuum forming products are often required to be cooled before demoulding. Ideally, the inner and outer surfaces of the parts in contact with the mould are cooled, and it is preferable to use moulds with internal cooling coils. For non-metallic moulds, such as wood, plaster, glass fibre reinforced plastics, epoxy resin and other moulds, because it is not possible to use water cooling, can be changed to air cooling, and can be added to the water mist to cool the outer surface of the vacuum forming parts.
Natural cooling produces stress-relieved parts with enhanced impact resistance. While water cooling increases productivity, it may induce higher internal stresses.
Demolding involves ejecting the product from the mold, which may be concave or convex. In most cases, thermal contraction causes the part to adhere tightly to the mold. Demolding is therefore achieved by applying reverse air pressure through vacuum ports or compressed air channels.
Especially for the moulds with small release slope or with concave moulds, the mould is also released by using the release mechanism of bumping or vibration, sometimes by applying release agent on the sheet and the mould, or by spraying the surface of the mould with Teflon treatment.
Control system generally includes the vacuum forming, finishing and other processes, including instruments, meters, pipelines, valves and controlling parameters and actuating mechanisms. Control methods are manual, electromechanical automatic control, computer control, etc.
Professional manufacturer of thermoforming machines.
