Strech Forming

A plastic sheet forming technique in which the heated thermoplastic sheet is stretched over a mold and subsequently cooled. It is quick, efficient, and has a high degree of repeatability.

Advanced pre-stretch forming or mechanical assisted forming techniques require thermoforming equipment with both top and bottom platens. Automatic machine sequence control is also usually required.

The only real advantage of this process is that only a male form is needed. The disadvantages are many, and include requiring the male form to beconstructed strong enough to resist thelarge forces exerted by the mechanicalequipment that is needed to stretchmany lineal inches of plastic in onedirection. That force may reach manytons.Additionally, minor dirt particles on,or minor deviations of the molds exteri-or surface, will show up as opticaldefects (mark-off) on the concave innersurface of the part. Such defects arevery difficult to remove by later effortsusing abrasives and polishing products.Other problems are excessive thin-ning of the plastic at the deepest por-tion of the formed part and the intro-duction of severe internal stresses thatusually result in early failure when thepart is exposed to sunlight

Strech Forming

A plastic sheet forming technique in which the heated thermoplastic sheet is stretched over a mold and subsequently cooled. It is quick, efficient, and has a high degree of repeatability.

Advanced pre-stretch forming or mechanical assisted forming techniques require thermoforming equipment with both top and bottom platens. Automatic machine sequence control is also usually required.

The only real advantage of this process is that only a male form is needed. The disadvantages are many, and include requiring the male form to beconstructed strong enough to resist thelarge forces exerted by the mechanicalequipment that is needed to stretchmany lineal inches of plastic in onedirection. That force may reach manytons.Additionally, minor dirt particles on,or minor deviations of the molds exteri-or surface, will show up as opticaldefects (mark-off) on the concave innersurface of the part. Such defects arevery difficult to remove by later effortsusing abrasives and polishing products.Other problems are excessive thin-ning of the plastic at the deepest por-tion of the formed part and the intro-duction of severe internal stresses thatusually result in early failure when thepart is exposed to sunlight

Inline Thermoforming

The in-line thermoforming process is designed to take advantage of the hot sheet coming off the extruder- The sheet is mechanically conveyed directly from the extruder through the oven to maintain the sheet at a forming temperature and then to the forming station. The forming step must be synchronized with the extruder take-off speed. This type of thermoforming is usually limited to sheet 0 125" or thinner and applications that do not require critical thermoforming. i.e.. optimum material distribution and close tolerances· This process Is more difficult to control than other thermoforming processes· The major disadvantage is that with the extruder and former being tied directly together an upset In one causes a shutdown in both. The majority of roll-fed machines or in-line machines are commonly used for the production of thin-walled products such as cups, trays, lids. internal packaging, and other finished products with a finished wall of 0.003 to 0.060+ in· in thickness. Because of the speed of these machines, secondary operations are incorporated within the unit. These may consist of printing, filling, sealing, die cutting, scrap cutting, or automated removal and stacking of finished product. The normal roll-fed machines consist of the roll station, upper and lower heating banks. form Station, cooling station, and trim station.

Inline Thermoforming

The in-line thermoforming process is designed to take advantage of the hot sheet coming off the extruder- The sheet is mechanically conveyed directly from the extruder through the oven to maintain the sheet at a forming temperature and then to the forming station. The forming step must be synchronized with the extruder take-off speed. This type of thermoforming is usually limited to sheet 0 125" or thinner and applications that do not require critical thermoforming. i.e.. optimum material distribution and close tolerances· This process Is more difficult to control than other thermoforming processes· The major disadvantage is that with the extruder and former being tied directly together an upset In one causes a shutdown in both. The majority of roll-fed machines or in-line machines are commonly used for the production of thin-walled products such as cups, trays, lids. internal packaging, and other finished products with a finished wall of 0.003 to 0.060+ in· in thickness. Because of the speed of these machines, secondary operations are incorporated within the unit. These may consist of printing, filling, sealing, die cutting, scrap cutting, or automated removal and stacking of finished product. The normal roll-fed machines consist of the roll station, upper and lower heating banks. form Station, cooling station, and trim station.

Twin Sheet Forming

Twin sheet forming

Twin-sheet thermoforming is a process of vacuum or pressure forming two sheets of plastic essentially simultaneously, with a separate mold on the top and bottom platens. Once the plastic has been molded, it remains in the molds, and while still at its forming temperature the two molds are brought together under high pressures, and the two sheets are welded wherever the molds dictate a weld. The process creates 3 dimensional parts with formed features on both sides. The parts are typically very strong, stiff, and quite light-weight. Step 1: Two preheated thermoplastic sheets are simultaneously heated between the two molds till they are are entirely plasticized.

Step 2: On reaching the the specific temperature the two molds move together. The
two Sheets are deep-drawn and tightly molded to each other in one step. No
adhesives are used. There are neither resulting pressure nor strain.

Step 3: To achieve a high level of detail or precision, the forming can be supported by high pressure or (and) vacuum.

Step 4: ... and the hollow body, without solvent, molding additives and adhesives,
is finished. Furthermore, there are no inner strains.

Materials

• H.M.W. HD Polyethylene
• ABS
• PC/ABS
• Polycarbonate

Typical applications are:

pallets, industrial dunnage, portable toilets, medical housings, surfboards, fuel tanks, air/ventilation ducts, electrical enclosures, recreational boats, cases, toys, marine products, doors, tables, spine boards and numerous transportation-related products.

Main Advantages

• Increased Structural Integrity and Rigidity
• Enclosed Cross-Section Capability
• Low Tooling Cost
• Internal Reinforcement Options: Structural Member, Rigid Foam, Etc.
• The process has some distinct advantages over blow-molding and rotomolding.

The process has some distinct advantages over blow-molding and rotomolding.

Compared to blow-molding, the twin-sheet process:

• Tooling and machines are more cost-competitive for small to modest run sizes.
• Each sheet may be a different thickness, material or color.
• More flexibility with parting line structure is possible.

Compared to Rotomolding, the twin-sheet process:

• Many more resin types are available in twin-sheeting.
• More structural beams can be created in twin-sheeting
• Much higher production rates

Twin Sheet Forming

Twin sheet forming

Twin-sheet thermoforming is a process of vacuum or pressure forming two sheets of plastic essentially simultaneously, with a separate mold on the top and bottom platens. Once the plastic has been molded, it remains in the molds, and while still at its forming temperature the two molds are brought together under high pressures, and the two sheets are welded wherever the molds dictate a weld. The process creates 3 dimensional parts with formed features on both sides. The parts are typically very strong, stiff, and quite light-weight. Step 1: Two preheated thermoplastic sheets are simultaneously heated between the two molds till they are are entirely plasticized.

Step 2: On reaching the the specific temperature the two molds move together. The
two Sheets are deep-drawn and tightly molded to each other in one step. No
adhesives are used. There are neither resulting pressure nor strain.

Step 3: To achieve a high level of detail or precision, the forming can be supported by high pressure or (and) vacuum.

Step 4: ... and the hollow body, without solvent, molding additives and adhesives,
is finished. Furthermore, there are no inner strains.

Materials

• H.M.W. HD Polyethylene
• ABS
• PC/ABS
• Polycarbonate

Typical applications are:

pallets, industrial dunnage, portable toilets, medical housings, surfboards, fuel tanks, air/ventilation ducts, electrical enclosures, recreational boats, cases, toys, marine products, doors, tables, spine boards and numerous transportation-related products.

Main Advantages

• Increased Structural Integrity and Rigidity
• Enclosed Cross-Section Capability
• Low Tooling Cost
• Internal Reinforcement Options: Structural Member, Rigid Foam, Etc.
• The process has some distinct advantages over blow-molding and rotomolding.

The process has some distinct advantages over blow-molding and rotomolding.

Compared to blow-molding, the twin-sheet process:

• Tooling and machines are more cost-competitive for small to modest run sizes.
• Each sheet may be a different thickness, material or color.
• More flexibility with parting line structure is possible.

Compared to Rotomolding, the twin-sheet process:

• Many more resin types are available in twin-sheeting.
• More structural beams can be created in twin-sheeting
• Much higher production rates

Match Die Forming

Matched Die Forming

In this process, both halves of the part are formed by molds with no vacuum or air pressure. The sheet is heated until it is soft, and then both mold halves clamp together to form the part. Used with parts that do not have large draws. Advantages excellent definition and dimensional contol on both sides. complexity high tolerances

Match Die Forming

Matched Die Forming

In this process, both halves of the part are formed by molds with no vacuum or air pressure. The sheet is heated until it is soft, and then both mold halves clamp together to form the part. Used with parts that do not have large draws. Advantages excellent definition and dimensional contol on both sides. complexity high tolerances

Pressure Forming

Pressure Forming

Pressure forming is a variation of vacuum forming that utilizes both vacuum and compressed air to force the plastic sheet against the mold. As the platens are closed, the vacuum pulls on one side of the sheet and compressed air pushes on the other. Specially shaped tooling is used to match the top and bottom halves of the mold creating a seal to maintain pressures of up to 500 psi, therefore, the platens must be locked together. This compressed air pressure reduces the cycle time and makes it possible to run at lower temperatures, it also improves the distribution of the material creating a more even wall thickness and enhances the detail of the part to a nearly-injection-molded quality. After the part has been formed, the platens unlock and one of the platens moves out of the way to speed up the cooling process. The increased air pressure will require a stronger mold and a locking device for the platens so consequently a higher tooling expense will be incurred.

Steps Material is heated to proper temp then moves over the mold. Platens close and lock. Vacuum and air pressure are applied. Materials Theoretically, any thermoplastic material can be pressure formed. However, some materials are more difficult to work with than others. Polyethylene, for instance, flows easily and causes few problems for pressure formers. With vacuum alone, polyethylene can be intricately formed. On the other hand, polycarbonate, which chills quickly, can cause manufacturers to be concerned about tool design and plug assists. Medical device manufacturers usually specify that their products should be formed of a material that passes the Underwriters Laboratories (UL) 94 V0 or 94 5V tests for flammability. The resins most commonly used in pressure-formed medical products are flame- retardant grades of acrylonitrile butadiene styrene (ABS). In many cases, assists are used to help distribute material evenly and to coin it into sharp or narrow corners. Depending on its complexity, the design of a product's tooling may require the former to use matched heated molds and assists; otherwise, assists can be made of low-heat-transferring materials such as wood. Advantages Sharp, crisp lines and details Low tooling costs Short lead time Textured surfaces and molded in colors Formed in undercuts Ideal for short runs Zero degree draft on sidewalls Embossed and Debossed areas Highly detailed openings Superior, uniform tolerance control Applications Use pressure forming when the part will be the "face" of the product expecting a long life. You can pressure form a company logo or model designation with styling lines, surface texture or other features in a light weight and durable part. Use pressure forming when you have undercuts or rims and a greater depth of draw.

Pressure Forming

Pressure Forming

Pressure forming is a variation of vacuum forming that utilizes both vacuum and compressed air to force the plastic sheet against the mold. As the platens are closed, the vacuum pulls on one side of the sheet and compressed air pushes on the other. Specially shaped tooling is used to match the top and bottom halves of the mold creating a seal to maintain pressures of up to 500 psi, therefore, the platens must be locked together. This compressed air pressure reduces the cycle time and makes it possible to run at lower temperatures, it also improves the distribution of the material creating a more even wall thickness and enhances the detail of the part to a nearly-injection-molded quality. After the part has been formed, the platens unlock and one of the platens moves out of the way to speed up the cooling process. The increased air pressure will require a stronger mold and a locking device for the platens so consequently a higher tooling expense will be incurred.

Steps Material is heated to proper temp then moves over the mold. Platens close and lock. Vacuum and air pressure are applied. Materials Theoretically, any thermoplastic material can be pressure formed. However, some materials are more difficult to work with than others. Polyethylene, for instance, flows easily and causes few problems for pressure formers. With vacuum alone, polyethylene can be intricately formed. On the other hand, polycarbonate, which chills quickly, can cause manufacturers to be concerned about tool design and plug assists. Medical device manufacturers usually specify that their products should be formed of a material that passes the Underwriters Laboratories (UL) 94 V0 or 94 5V tests for flammability. The resins most commonly used in pressure-formed medical products are flame- retardant grades of acrylonitrile butadiene styrene (ABS). In many cases, assists are used to help distribute material evenly and to coin it into sharp or narrow corners. Depending on its complexity, the design of a product's tooling may require the former to use matched heated molds and assists; otherwise, assists can be made of low-heat-transferring materials such as wood. Advantages Sharp, crisp lines and details Low tooling costs Short lead time Textured surfaces and molded in colors Formed in undercuts Ideal for short runs Zero degree draft on sidewalls Embossed and Debossed areas Highly detailed openings Superior, uniform tolerance control Applications Use pressure forming when the part will be the "face" of the product expecting a long life. You can pressure form a company logo or model designation with styling lines, surface texture or other features in a light weight and durable part. Use pressure forming when you have undercuts or rims and a greater depth of draw.

Drape Forming

Drape Forming Drape forming is similar to straight vacuum forming except that after the sheet is framed and heated, it is mechanically stretched, and a pressure differential is then applied to form the sheet over a male mould. In this case, however, the sheet touching the mould remains close to its original thickness. It is possible to drape-form items with a depth-to-diameter ratio of approximately 4 to 1; however, the technique is more complex than straight vacuum forming. Male moulds are easier to build and generally cost less than female moulds; however, male moulds are more easily damaged. Drape forming can also be used with gravitational force alone. For multi-cavity forming, such as tote trays, female moulds are preferred because they do not require as much spacing as male moulds.

Step 1. The plastic sheet is clamped in a frame and heated. Heating can be timed or electronic sensors a can be use to measure sheet temperature or sheet sag.

Step 2. Drawn over the mold - either by pulling it over the mold and creating a seal to the frame, or by forcing the mold into the sheet and creating a seal. The platen can be driven pneumatically or with electric drive. In some very small machines the platen can be manually moved up or the clamped sheet can be manually pushed over the mold.

Step 3. Then vacuum is applied through the mold, pulling the plastic tight to the mold surface. A fan can be used to decrease sheet cooling time.

Step 4. After the plastic sheet has cooled, the vacuum is turned off and compressed air is sent to the mold to help free it from the plastic. The platen then moves down pulling the mold from the formed part. The formed sheet is unclamped, removed, and a new cycle is ready to start.

Main techniques, differing by the position of the mold during the first stage. 1) 1st Method: The sheet (without masking) is placed on top of the mold in its basic, flat state. Both sheet and mold are then slid into a hot-air circulating oven and heated to about 150-155°C (300-312°F). When the sheet (and mold) reaches the required temperature it sags and drapes over the heated mold. Both are then pulled out of the oven and quickly helped, by gloved hands, to conform more precisely to the mold. It is then allowed to cool down. 2) 2nd Method: The sheet is placed into a hot-air circulating oven (without masking), and heated to about 150-155°C (300-312°F). When the sheet reaches the required temperature it is quickly pulled out of the oven and placed on top of the mold. there the sheet sags, aided quickly by the gloved helping hands, and takes the accurate shape of the mold. For better results we recommend pre-heating the mold to about 80-100°C (175-210°F) before putting the heated sheet on top. Then it is, likewise, allowed to cool down. Advantages better part dimensional control on inside of part lower mold costs ability to grain surface (tubs, showers, counter tops, etc.) faster cycle times. Disadvantage is more scrap due to larger clamps and trim area. Applications: Drape forming is widely used for large panels that require retaining a simple non-flat shape as in a curved display wall. Another useful application of this process is for the construction of wide sections of odd-shaped walls that will still retain overall even material thickness.

Drape Forming

Drape Forming Drape forming is similar to straight vacuum forming except that after the sheet is framed and heated, it is mechanically stretched, and a pressure differential is then applied to form the sheet over a male mould. In this case, however, the sheet touching the mould remains close to its original thickness. It is possible to drape-form items with a depth-to-diameter ratio of approximately 4 to 1; however, the technique is more complex than straight vacuum forming. Male moulds are easier to build and generally cost less than female moulds; however, male moulds are more easily damaged. Drape forming can also be used with gravitational force alone. For multi-cavity forming, such as tote trays, female moulds are preferred because they do not require as much spacing as male moulds.

Step 1. The plastic sheet is clamped in a frame and heated. Heating can be timed or electronic sensors a can be use to measure sheet temperature or sheet sag.

Step 2. Drawn over the mold - either by pulling it over the mold and creating a seal to the frame, or by forcing the mold into the sheet and creating a seal. The platen can be driven pneumatically or with electric drive. In some very small machines the platen can be manually moved up or the clamped sheet can be manually pushed over the mold.

Step 3. Then vacuum is applied through the mold, pulling the plastic tight to the mold surface. A fan can be used to decrease sheet cooling time.

Step 4. After the plastic sheet has cooled, the vacuum is turned off and compressed air is sent to the mold to help free it from the plastic. The platen then moves down pulling the mold from the formed part. The formed sheet is unclamped, removed, and a new cycle is ready to start.

Main techniques, differing by the position of the mold during the first stage. 1) 1st Method: The sheet (without masking) is placed on top of the mold in its basic, flat state. Both sheet and mold are then slid into a hot-air circulating oven and heated to about 150-155°C (300-312°F). When the sheet (and mold) reaches the required temperature it sags and drapes over the heated mold. Both are then pulled out of the oven and quickly helped, by gloved hands, to conform more precisely to the mold. It is then allowed to cool down. 2) 2nd Method: The sheet is placed into a hot-air circulating oven (without masking), and heated to about 150-155°C (300-312°F). When the sheet reaches the required temperature it is quickly pulled out of the oven and placed on top of the mold. there the sheet sags, aided quickly by the gloved helping hands, and takes the accurate shape of the mold. For better results we recommend pre-heating the mold to about 80-100°C (175-210°F) before putting the heated sheet on top. Then it is, likewise, allowed to cool down. Advantages better part dimensional control on inside of part lower mold costs ability to grain surface (tubs, showers, counter tops, etc.) faster cycle times. Disadvantage is more scrap due to larger clamps and trim area. Applications: Drape forming is widely used for large panels that require retaining a simple non-flat shape as in a curved display wall. Another useful application of this process is for the construction of wide sections of odd-shaped walls that will still retain overall even material thickness.

Vacuum Forming

Vacuum-snap back is an excellent and often used process for forming deep draw products with uniform wall thickness. Vacuum is used to pre-stretch the hot plastic before the mold makes contact with the sheet. Vacuum snap-back, while more complex than plug assist, can produce deeper drawn products with better wall uniformity and less mark-off. A vacuum pre-stretch box is required. The pre-stretch box is sealed against the hot sheet and vacuum is applied. The plastic is drawn into the box as a hemisphere with the height of the hemisphere usually controlled by a photocell. Other methods can be used to control the hemisphere height, but a photocell works well.

The steps of vacuum snap-back are:

• After the plastic sheet is heated and the sheet cart returns to the forming station, the bottom platen moves up sealing the vacuum pre-stretch box against the hot sheet. Vacuum is then applied. When the stretching plastic crosses the photocell beam, vacuum is turn off.
• The mold is moved into the formed hemisphere. When the mold is sealed against the hot plastic, vacuum is applied to the mold and vacuum is released from the pre-stretch box causing the plastic to snap to the contours of the mold.
• The pre-stretch box is then lowered and cooling air is blown against the hot plastic. After the plastic cools, the mold vacuum is released, air eject is applied through the mold and then the mold is removed from the formed plastic part.
• Placing the mold on the bottom platen and the pre-stretch box on the top platen will also work for vacuum snap-back.

Advantages

• well controlled part thickness

though longer cycle times

Vacuum Forming

Vacuum-snap back is an excellent and often used process for forming deep draw products with uniform wall thickness. Vacuum is used to pre-stretch the hot plastic before the mold makes contact with the sheet. Vacuum snap-back, while more complex than plug assist, can produce deeper drawn products with better wall uniformity and less mark-off. A vacuum pre-stretch box is required. The pre-stretch box is sealed against the hot sheet and vacuum is applied. The plastic is drawn into the box as a hemisphere with the height of the hemisphere usually controlled by a photocell. Other methods can be used to control the hemisphere height, but a photocell works well.

The steps of vacuum snap-back are:

• After the plastic sheet is heated and the sheet cart returns to the forming station, the bottom platen moves up sealing the vacuum pre-stretch box against the hot sheet. Vacuum is then applied. When the stretching plastic crosses the photocell beam, vacuum is turn off.
• The mold is moved into the formed hemisphere. When the mold is sealed against the hot plastic, vacuum is applied to the mold and vacuum is released from the pre-stretch box causing the plastic to snap to the contours of the mold.
• The pre-stretch box is then lowered and cooling air is blown against the hot plastic. After the plastic cools, the mold vacuum is released, air eject is applied through the mold and then the mold is removed from the formed plastic part.
• Placing the mold on the bottom platen and the pre-stretch box on the top platen will also work for vacuum snap-back.

Advantages

• well controlled part thickness

though longer cycle times

Free Forming

This method of thermoforming does not use a mold. Instead, an acrylic sheet is clamped in a frame and either a vacuum or compressed air draws the material to a desired depth. An electric eye determines when the proper depth has been reached and cuts off the pressure. Since only air touches the sheet of material, there is no markoff. Free forming is used to create windshields for planes, skylights, or anything where optical quality is necessary.

Advantage is achieving high clarity.

Free Forming

This method of thermoforming does not use a mold. Instead, an acrylic sheet is clamped in a frame and either a vacuum or compressed air draws the material to a desired depth. An electric eye determines when the proper depth has been reached and cuts off the pressure. Since only air touches the sheet of material, there is no markoff. Free forming is used to create windshields for planes, skylights, or anything where optical quality is necessary.

Advantage is achieving high clarity.

Billow Forming

Billow Forming - a method of thermoforming sheet plastic in which the heated sheet is clamped over a billow chamber. Air pressure in the chamber is increased causing the sheet to billow upward against a descending male mold.

Similar to vacuum snapback except the heated sheet is blown upward into a bubble shape and then the plug or mold is driven into the pre-stretched sheet from the top plate.

Using compressed air produces greater stretching forces but requires a much stronger pre-stretch box.

Billow Forming

Billow Forming - a method of thermoforming sheet plastic in which the heated sheet is clamped over a billow chamber. Air pressure in the chamber is increased causing the sheet to billow upward against a descending male mold.

Similar to vacuum snapback except the heated sheet is blown upward into a bubble shape and then the plug or mold is driven into the pre-stretched sheet from the top plate.

Using compressed air produces greater stretching forces but requires a much stronger pre-stretch box.

Plug Assisted Forming

Plug assist forming is a widely used forming technique and requires the use of a female (cavity) mold. The limited depth of draw of female molds is improved by the use of plug assist. With plug assist the plastic sheet is mechanically pre-stretched by a plug that is pushed into the hot plastic before the application of vacuum to the mold. The plug has a geometry that is usually 10 - 30 percent smaller than the interior of the female mold cavity. The plug is constructed of materials with low thermal conductivity or is heated. Low thermal conductivity plugs or heated plugs must be used to keep the plastic sheet from cooling when the sheet comes in contact with it. Materials such as wood, syntactic foam, and cast thermoset plastics can be used to make a low thermally conductive plug. This insulator type plug can be covered with felt to reduce mark-off. Aluminum with temperature controlled electric heaters can also be used. Aluminum plugs produce excellent results but are usually more costly than insulator type plugs. Different wall and bottom thickness can be produced by controlling how deep the plug goes into the mold and by controlling and varying plug temperatures.

The steps in plug assist forming are: After the sheet is heated and the sheet cart moves back to the forming area, the bottom platen moves up to the plastic sheet and seals. The top platen with the plug moves down pushing the plug into the hot plastic. After the plug reaches the required depth, vacuum is applied to the female mold forming the plastic to the contours of the mold. The top platen moves back up and cooling fans cool the plastic covering the inside of the female mold.

Advantages

• better wall thickness uniformity especially for cup or box shapes
• reduces stretching or thinning of material during forming.

Plug Assisted Forming

Plug assist forming is a widely used forming technique and requires the use of a female (cavity) mold. The limited depth of draw of female molds is improved by the use of plug assist. With plug assist the plastic sheet is mechanically pre-stretched by a plug that is pushed into the hot plastic before the application of vacuum to the mold. The plug has a geometry that is usually 10 - 30 percent smaller than the interior of the female mold cavity. The plug is constructed of materials with low thermal conductivity or is heated. Low thermal conductivity plugs or heated plugs must be used to keep the plastic sheet from cooling when the sheet comes in contact with it. Materials such as wood, syntactic foam, and cast thermoset plastics can be used to make a low thermally conductive plug. This insulator type plug can be covered with felt to reduce mark-off. Aluminum with temperature controlled electric heaters can also be used. Aluminum plugs produce excellent results but are usually more costly than insulator type plugs. Different wall and bottom thickness can be produced by controlling how deep the plug goes into the mold and by controlling and varying plug temperatures.

The steps in plug assist forming are: After the sheet is heated and the sheet cart moves back to the forming area, the bottom platen moves up to the plastic sheet and seals. The top platen with the plug moves down pushing the plug into the hot plastic. After the plug reaches the required depth, vacuum is applied to the female mold forming the plastic to the contours of the mold. The top platen moves back up and cooling fans cool the plastic covering the inside of the female mold.

Advantages

• better wall thickness uniformity especially for cup or box shapes
• reduces stretching or thinning of material during forming.