23-Ind-B2 Manufacturing Processes · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Examinations, December 2019 — 17-Ind-B2 Manufacturing Processes. 3-hour closed-book exam; candidates may use a Casio or Sharp approved calculator. Any five questions constitute a complete paper (only the first five as they appear are marked officially); all seven are answered below as a full study resource.
Reference texts. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 6th ed. (primary text for this subject — material selection, casting, polymer processing, machining, and composites).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
As a closed-die (impression-die) forging nears the end of the stroke, excess material is squeezed out through the narrow gap at the die parting line to form flash. Because this gap is thin, the flash cools quickly and its resistance to further outward flow rises sharply — that back-pressure is exactly what forces the bulk of the workpiece material to flow into the fine corners and details of the die cavity instead of continuing to escape as flash. Statement (2) is therefore true: flash formation genuinely enhances the flow of material into the die. Flash also always requires a separate trimming operation after forging to remove it, which is an additional processing step that lengthens the overall manufacturing cycle (forging plus trimming) beyond the forging stroke alone, so statement (1) is also true. Statement (3) is false: flash is not purely a disadvantage — it is a deliberately designed, functionally necessary part of impression-die forging that guarantees complete die fill, even though it does cost extra material and a trimming step.
Answer: d. (1) and (2).
Cooling (solidification) time dominates the injection-molding cycle because the mold itself remains far cooler than the melt throughout the run, so heat must diffuse slowly out through the part wall to the mold surface; this commonly accounts for the majority of the cycle, consistent with statement (1)’s 75% figure. Statement (2) is false and is the classic trap in this question: solidification does not wait for the cavity to fill — the melt begins freezing the instant it touches the cold mold wall, forming a solid skin layer while the core is still filling, well before packing/holding begins. Statement (3) is true: as the part cools and shrinks, the still-molten core cannot always be fed enough material from the (already-freezing) gate to compensate for the shrinkage, so the core is left with a void or porosity rather than the surface simply caving in.
Answer: d. (1) and (3).
Sheer complexity, on its own, does not make a technology more commercially viable — a more complicated process is generally harder and more expensive to implement, scale, and train a workforce on, which works against adoption rather than for it, so statement (1) is not a driver of viability by itself. A technology that is grounded in deeper science (2) tends to be harder for a competitor to reverse-engineer from observation alone and is more defensible through patents, because its working principle is not obvious from inspecting the product; this is reinforced by statement (3) directly — a technology that is difficult to copy protects the innovating company’s competitive advantage and lets it recoup its development investment, which is the core requirement for commercial success. Statements (2) and (3) work together (scientific depth is one of the main reasons a technology resists copying), while (1) alone can be a barrier to commercialization rather than a help.
Answer: d. (2) and (3).
