Mesin Injection Molding: Desain, Operasi, Aplikasi, Kelebihan & Kekurangan
Injection molding is an important industrial method. It is little bit similar to die casting but difference is in raw material used. In die casting we use metals which require extremely high temperature for melting but injection molding is mainly done on glasses, elastomers dan most commonly thermoplastic dan thermosetting polymers but this technique is widely used for fabrication of thermoplastic materials. This process is done by heating of raw material dan injecting them into mold cavity by applying pressure at specific temperature without any change in their chemical composition.
Injection Molding:
Main parts of Injection Molding Machine:
Main parts of Injection molding machine are material hopper, barrel, an injection ram/ rotating screw type plunger, heating device (heater), movable pattern, ejectors, dan a mold inside mold cavity.
Generally injection molding machines works in horizontal manner. Injection molding machine consists of a barrel (cylindrical pipe). A hopper is located at one end of barrel. A hydraulic ram or rotating screw runs by electric motor used of providing force is located inside barrel. A heating element (heater) is attached to barrel circumstantially used for melt molding material comes down from hopper.
On other side of barrel a mold cavity attached. Mold is located inside mold cavity dan a moveable pattern is used in whole manufacturing. Mold is generally made up of copper, aluminum dan tool steels. Life cycle for different material molds are different. This can be selected as per requirement.
Working:
Working of injection molding similar to extrusion dan it works like an injection as name suggest. Molding material/ raw material pour into hopper by feeding device. After that molding material goes down under action of gravity into cylinder (barrel) as shown in diagram. A circumferential heater which is located on barrel is used to melt material. When powder form of molding material goes dawn into barrel from hopper it starts melting dan a hydraulic ram or rotating screw pushes material forward into mould by applying some pressure. Molten plastic material is injected into a closed mould attached on other side of barrel; in this split mold is used. Molding material goes forward continuously by rotating screw. Pressure applies by hydraulic system. Injection pressure is generally 100-150 MPa. After injection; pressure is applied for some time or locked at same position with some force.
After whole process is done parts manufactured is cooled sufficiently. Then mold is open dan some ejectors are used for proper removal of part without damage. After removing part mold is closed again. This process is very fast dan automatically repeated. Here complex shape parts can be easily manufactured. Production capacity of injection molding is 12-16 thousand parts per cycle.
Process parameters:
- Process parameter varies according to condition dan requirements.
- Weight of parts produced by this process is generally 100 to 500 g.
- Cycle time for produce a single part is generally 5 to 60 seconds depends upon parts manufacture.
- Heating temperature of molding material is 150-350 degree centigrade.
- Injection capacity of molding machine is 12,000 to 2.2×10^6 mm^3.
- Injection pressure is 100-150 MPa.
- Locking force is 0.1 to 8.0 MN.
Advantages:
- Main advantage of this process is that complex shapes components having small wall thickness (5-15 mm) can be easily molded dan removed from die without damage.
- Parts which are made by injection molding have good dimensional tolerance.
- Major advantage of this technique is that scrap produced by this is very less as compare to some other processes.
- Parts made by injection molding process are competing with parts made by investment casting dan complex machining parts.
- This process is having high production rate as compare to other techniques.
Disadvantage:
- Initial cost/ setup cost of this process is very high due to design, testing dan tooling of whole equipment.
- Investment molding is generally limited to some special kind of materials like thermoplastic materials atau some polymers only.
- High tooling cost i.e. mould used is made by several processes dan testing overall cost of making single mold is very high. For different parts different kind of molds are required.
Applications:
- Injection molding is used for making complex shape parts of various sizes having less wall thickness.
- Typical parts like cup, containers, toys, plumbing fittings, electrical components, telephones receivers, bottle caps, automotive parts and components.
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