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Injection molding

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Injection Molding By Engr. M Aslam (Manufacturing Processes-II)

Published in: Technology
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Injection molding

  1. 1. Plastics Injection Molding Safety helmet Tooth brush Toys Comb Table Telephone
  2. 2. Injection molding • There are two types of injection molding machines – Manual molding machine (like orange juice machine) – Automatic machine (like mincing machine)
  3. 3. Injection molding • Injection molding is a manufacturing process for producing parts from both thermoplastics and thermosetting plastic materials. • Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity.
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  7. 7. Injection molding • The injection molding process requires the use of an – Injection molding machine – Raw plastic material (Granular/Powder form) – Die • The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part. Bins and boxes Snow sled
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  12. 12. Injection molding • Injection molding is used to produce thin-walled plastic parts for a wide variety of applications, one of the most common being plastic housings. • These housings are used in a variety of products including household appliances, consumer electronics, power tools, and as automotive dashboards. • Other common thin-walled products include different types of open containers, such as buckets. Tableware
  13. 13. Injection molding • Injection molding is also used to produce several everyday items such as toothbrushes or small plastic toys. • Many medical devices, including valves and syringes, are manufactured using injection molding as well. Pulley
  14. 14. Injection molding Doll
  15. 15. Injection molding (Process) Process: • Clamping • Injection • Cooling • Ejection Syringe Steering wheel Hair dryer body
  16. 16. Injection molding (Process) Clamping: • Prior to the injection of the material into the die, the two halves of the die must first be securely closed by the clamping unit. • One half of the die is attached to the injection molding machine and one half is allowed to slide. Bemis
  17. 17. Injection molding (Process) Clamping: • The hydraulically powered clamping unit pushes the die halves together and exerts sufficient force to keep the mold securely closed while the material is injected. • The time required to close and clamp the mold is dependent upon the machine - larger machines (those with greater clamping forces) will require more time. Bike frame
  18. 18. Injection molding (Process) Clamping: Clamp force: • The force that is applied to a mold by the molding machine in order to keep it securely closed while the material is injected. • The clamp force is typically some factor of safety greater than the separating force, which is the outward force exerted on the mold halves by the injected material. Bucket
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  20. 20. Injection molding (Process) Clamping: • This time can be estimated from the dry cycle time of the machine. Dry cycle Time: • The cycle time of a process that results from no material or workpiece being used. Mouse
  21. 21. Injection molding (Process) Clamping: • The dry cycle time is typically a measure of machine performance that indicates the time for the machine to perform the actions necessary to manufacture a part, without the part actually being produced. • This time will always be less than the actual cycle time. Dashboard
  22. 22. Injection molding (Process) Injection: • The raw plastic material, usually in the form of granulers, is fed into the injection molding machine, and advanced towards the mold by the injection unit. • During this process, the material is melted by heat and pressure. • The molten plastic is then injected into the mold very quickly and the buildup of pressure packs and holds the material. Glass frame
  23. 23. Injection molding (Process) Injection: • The amount of material that is injected is referred to as the shot. • The injection time is difficult to calculate accurately due to the complex and changing flow of the molten plastic into the mold. • However, the injection time can be estimated by the shot volume, injection pressure, and injection power. Bicycle pedals Bottle caps
  24. 24. Injection molding (Process) Injection: Shot: • The amount of material that is injected or poured into a mold. • The shot volume includes the volume of all part cavities, as well as the feed system which delivers the material. • The amount of material forming the parts relative to the total shot volume is the material yield. • The shot volume must be less than the shot capacity of the machine being used. Car bumper
  25. 25. Injection molding (Process) Cooling: • The molten plastic that is inside the mold begins to cool as soon as it makes contact with the interior mold surfaces. • As the plastic cools, it will solidify into the shape of the desired part. • However, during cooling some shrinkage of the part may occur. • The packing of material in the injection stage allows additional material to flow into the mold and reduce the amount of visible shrinkage. Body of TV
  26. 26. Injection molding (Process) Cooling: • The mold can not be opened until the required cooling time has elapsed. • The cooling time can be estimated from several – Thermodynamic properties of the plastic and – The maximum wall thickness of the part. Kitchen ware
  27. 27. Injection molding (Process) Ejection: • After sufficient time has passed, the cooled part may be ejected from the mold by the ejection system, which is attached to the rear half of the mold. • When the mold is opened, a mechanism is used to push the part out of the mold. • Force must be applied to eject the part because during cooling the part shrinks and adheres to the mold. Glass
  28. 28. Injection molding (Process) Ejection: • In order to facilitate the ejection of the part, a mold release agent can be sprayed onto the surfaces of the mold cavity prior to injection of the material. • The time that is required to open the mold and eject the part can be estimated from the dry cycle time of the machine and should include time for the part to fall free of the mold. • Once the part is ejected, the mold can be clamped shut for the next shot to be injected. Razor body
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  32. 32. Injection molding • After the injection molding cycle, some post processing is typically required. • During cooling, the material in the channels of the mold will solidify attached to the part. • This excess material, along with any flash that has occurred, must be trimmed from the part, typically by using cutters.
  33. 33. Injection molding • For some types of material, such as thermoplastics, the scrap material that results from this trimming can be recycled by being placed into a plastic grinder, also called regrind machines or granulators, which regrinds the scrap material into pellets. • Due to some degradation of the material properties, the regrind must be mixed with raw material in the proper regrind ratio to be reused in the injection molding process. Lighter
  34. 34. Injection molding (Defects) Flash: • The occurrence of molten material seeping out of the mold cavity and solidifying. • Once the part is ejected, a thin layer of material will have formed attached to the part along the parting line. Causes: • Injection pressure is too high. • Clamp force is too low. Pen
  35. 35. Injection molding (Defects) Warping: • The permanent bending of a part that occurs when certain section of the part shrink faster than others, as result of a non-uniform cooling rate. Causes: • Non-uniform cooling rate
  36. 36. Injection molding (Defects) Bubbles: • Balloon shaped cavities. Causes: • Injection temperature too high • Too much moisture in material • Non-uniform cooling rate
  37. 37. Injection molding (Defects) Unfilled sections: • Incomplete parts Causes: • Insufficient shot volume • Flow rate of material too low Bus lights Bottle crate
  38. 38. Injection molding (Defects) Sink marks: • When molten material is injected into a mold, voids can occur if certain sections solidify first. • The remaining material will fill these voids as it continues to cool and shrink. • This shrinkage causes marks on the part where the material sunk into the void.
  39. 39. Injection molding (Defects) Sink marks: Causes: • Injection pressure too low • Non-uniform cooling rate/Non-uniform wall thickness Storage rack
  40. 40. Injection molding (Defects) Ejector marks: • A part defect in the form of small indentations that are made where the ejection system pushed the part out of the mold. Causes: • Cooling time too short • Ejection force too high
  41. 41. Injection molding Assignment: Marks: 05 (Lab) • Write the names of the industries along with products relying on injection molding process for their products.

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