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.
Given. Four descriptions of a cast part, each stated in terms of surface finish, presence/absence of a parting line, and defect level.
Find. The casting technology consistent with each description.
Approach. A parting line is left wherever the mold is made in two (or more) separable halves; its absence means the mold is a single-piece (e.g. ceramic shell) mold. Surface finish is set by what the metal touches while it freezes — a permanent metal mold gives a smooth surface, sand gives a rough one. Defect level (mainly gas porosity) is set by how turbulently and how fast the mold is filled.
| Part | Description | Casting technology | Why |
|---|---|---|---|
| (i) | Smooth surface, has a parting line | Permanent-mold (gravity die) casting | Reusable, machined two-piece metal mold gives a smooth surface finish; the mold halves leave a parting line, and gravity (not high-speed injection) pouring keeps porosity low. |
| (ii) | Rough surface, parting line, some defects | Sand casting | The sand mold's granular surface texture is directly imprinted on the casting (rough finish); the cope-and-drag flask leaves a parting line; sand's permeability and the mold's one-time, less-controlled fill commonly trap some porosity/inclusions. |
| (iii) | Smooth surface, no parting line | Investment (lost-wax) casting | The ceramic shell mold is built as a single continuous piece around a wax pattern (no mold halves), so there is no parting line; the fine ceramic slurry against the wax pattern gives an excellent, smooth as-cast finish. |
| (iv) | Smooth surface, many defects | (High-pressure) die casting | The reusable, machined metal die gives a smooth finish and a parting line (two die halves, as in (i)), but molten metal is injected at very high speed to fill the die before it freezes — this turbulent, fast fill traps air, producing more porosity/defects than the slower-filled permanent-mold process in (i). |
