Purpose of cores in casting: In metal casting practice, why are cores placed inside a mould cavity?

Introduction / Context:
Cores are indispensable when a casting requires hollow sections, undercuts, or passages that cannot be formed by the pattern alone. They shape the internal geometry and can be removed after solidification, enabling complex castings such as engine blocks and pump bodies.

Given Data / Assumptions:

• Sand casting with either green sand moulds and separate baked or chemically bonded cores.
• Core prints on the pattern support positioning.
• Venting and core strength are adequately designed.

Concept / Approach:
The principal function of a core is to create internal voids or negative features. While a core’s surface quality indirectly influences the internal surface finish, its purpose is not to improve the overall mould surface. Cores are separate from the green sand mould body, though they are assembled inside it; they are not synonymous with the mould itself.

Step-by-Step Solution:
Define core: a shaped body (often sand + binder) placed to create internal cavities.Relate to geometry: forms holes, ports, and internal channels.Identify best answer: “form internal cavities in the casting”.Eliminate distractors that confuse ancillary effects with purpose.

Verification / Alternative check:
Production drawings show internal passages matching core geometry; removal after shakeout confirms the function.

Why Other Options Are Wrong:
Improving mould surface is not the primary function.

Cores are inserted into, but are not themselves, the green sand mould.

Changing pour temperature is unrelated.

Common Pitfalls:
Confusing core sand with moulding sand; inadequate core support causing core shift and dimensional defects.

Final Answer:
form internal cavities in the casting