1. What is the primary purpose of an injection moulding machine?
An injection moulding machine primarily heats plastic until it becomes molten and then injects it into a mould cavity to shape it into a desired product.
2. Which of the following is NOT a main component of an injection moulding machine?
A welding torch is not a part of an injection moulding machine. The main components include the hopper (for feeding plastic), barrel (where plastic is heated), and screw (which pushes molten plastic into the mould).
3. The function of the screw in an injection moulding machine is to:
The screw in an injection moulding machine rotates and mixes plastic pellets, heats them through friction, and then pushes the molten plastic into the mould cavity for shaping.
4. What type of plastic is commonly used in injection moulding?
Thermoplastics like ABS, polypropylene, and polyethylene are commonly used in injection moulding because they can be melted, shaped, and re-melted without losing their properties.
5. Which step follows injection in the moulding process?
After injection, the molten plastic cools and solidifies inside the mould before the next steps, which include ejection of the finished part.
6. The process of forcing molten plastic into a mould is called:
In injection moulding, molten plastic is injected into a mould cavity under high pressure to take the desired shape.
7. What is the purpose of the ejector system?
The ejector system pushes the solidified plastic part out of the mould once it has cooled and taken the desired shape.
8. What material is used to make moulds in injection moulding?
Moulds in injection moulding are typically made from steel or aluminum due to their durability, precision, and ability to withstand high pressure and temperature.
9. What determines the cooling time of a plastic part?
The cooling time depends on factors like the type of plastic, thickness of the part, mould temperature, and cooling system efficiency.
10. Which of the following is an advantage of injection moulding?
Injection moulding allows for high production speed, making it an efficient process for mass-producing plastic parts with minimal waste, excellent surface finish, and complex designs.
11. What are the main types of injection moulding machines?
Injection moulding machines are classified into hydraulic, electric, and hybrid types based on their power source and control system.
12. Which injection moulding machine is the most energy-efficient?
Electric injection moulding machines are the most energy-efficient because they use servo motors instead of hydraulic pumps, reducing power consumption and improving precision.
13. What is the main advantage of hydraulic injection moulding machines?
Hydraulic injection moulding machines provide a high clamping force, making them ideal for large and complex moulds.
They are also more cost-effective for heavy-duty applications compared to electric machines.
14. Hybrid injection moulding machines combine:
Hybrid injection moulding machines combine the precision and energy efficiency of electric systems with the high clamping force of hydraulic systems, offering a balance between speed, power, and efficiency.
15. Vertical injection moulding machines are used for:
Vertical injection moulding machines are commonly used for insert moulding, where pre-placed components (such as metal inserts) are overmoulded with plastic. Their gravity-assisted design helps in precise placement and reduces material waste.
16. What is the purpose of the clamping unit?
The clamping unit applies force to keep the mould tightly closed while molten plastic is injected, preventing leakage and ensuring the part is properly formed
17. Which component is responsible for melting plastic?
The barrel contains a heated section where plastic pellets are melted by heaters and the rotating screw before being injected into the mould.
18. The screw inside the barrel rotates to:
The screw inside the barrel rotates to mix, heat, and move the molten plastic forward before injecting it into the mould cavity.
19. What is the function of the sprue in moulding?
The sprue is the channel through which molten plastic flows from the injection unit into the mould cavity, ensuring proper filling
20. The injection pressure is measured in:
Injection pressure in moulding is typically measured in Pascals (Pa) or Bars, which indicate the force applied to inject molten plastic into the mould cavity.
21. What is the most common defect in injection moulding?
A short shot occurs when the molten plastic does not completely fill the mould cavity, leading to an incomplete or improperly formed part. It is one of the most common defects in injection moulding
22. A short shot occurs when:
A short shot happens when there isn't enough molten plastic to completely fill the mould cavity, resulting in an incomplete or improperly shaped part.
This can be caused by low injection pressure, incorrect temperature settings, or blockages in the mould.
23. What causes sink marks in moulded parts?
Sink marks occur when the outer surface cools and solidifies faster than the inner material, causing depressions or indentations.
24. Flash is an injection moulding defect caused by:
Flash occurs when molten plastic escapes from the mould cavity, usually due to excessive injection pressure, worn-out moulds, or improper clamping force.
25. How can warping be prevented?
Increasing the cooling time allows the material to cool more evenly, which can reduce the chances of uneven shrinkage and prevent warping.
A thicker mould (option 2) can also help, but increasing cooling time is generally the more common solution.
26. What defect occurs due to trapped air in the mould?
Trapped air in the mould can cause bubbles to form in the material, leading to surface defects. These bubbles occur because the air gets trapped as the molten material fills the mould cavity and cannot escape, resulting in visible air pockets or bubbles in the final product.
27. Jetting marks are caused by:
Jetting marks are caused by high injection speed, which leads to the molten material entering the mould too quickly.
This can cause the material to flow in a jet-like manner, creating irregular flow patterns and surface defects such as jetting marks.
28. Which defect is caused by poor bonding between layers of plastic?
Weld lines occur when there is poor bonding between two or more flow fronts of plastic during the injection molding process.
This can happen when the material flows through different parts of the mould and meets at a point, but the bonding between the layers isn't strong enough, creating visible marks or weak spots.
29. The presence of moisture in plastic can lead to:
The presence of moisture in plastic can cause bubbles and voids during the injection molding process. When moisture in the plastic is heated, it turns into steam, which creates bubbles and voids in the final molded product.
This can lead to defects and reduced strength in the part.
30. How can burn marks be prevented?
Burn marks occur when the material moves too quickly through the mould, generating excessive heat.
Reducing the injection speed allows the molten plastic to flow more smoothly, giving it enough time to fill the mould without creating localized overheating, which prevents burn marks.
31. What is the function of a hot runner system?
A hot runner system is used in injection molding to keep the plastic in the runner system heated and flowing, reducing waste.
It prevents the plastic from cooling and solidifying before it reaches the cavity, eliminating the need for additional runner material that would otherwise be discarded.
32. The runner system allows plastic to flow from:
In an injection molding machine, the runner system is responsible for directing the molten plastic from the screw (or injection unit) to the mould cavity, where the plastic will take the shape of the part being produced
33. Multi-cavity moulds are used for:
Multi-cavity moulds are used in injection molding to produce multiple identical parts in a single cycle. This is an efficient way to increase production output while maintaining consistent quality for each part
34. What is insert moulding?
Insert moulding is a process where metal or other materials (like brass, steel, etc.) are placed into the mould, and plastic is then injected around these inserts to create a part that integrates both materials.
This is commonly used for producing parts that require both the strength of metal and the flexibility or insulating properties of plastic.