25-Comp-B8 Computer Integrated Manufacturing · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
98-Comp-B8, Computer Integrated Manufacturing — National Exams, May 2015. Open-book, 3 hours, non-communicating calculator permitted; six questions of equal value (each 20%), most requiring an essay-format answer; ANY FIVE constitute a complete exam (all six answered below as a complete study resource).
Reference texts: Groover, Automation, Production Systems, and Computer-Integrated Manufacturing, 4th ed. — numerical control (Ch.6–7, Q1), industrial robotics and control resolution (Ch.8, Q2), artificial intelligence and process planning in manufacturing (Ch.24–25, Q3–Q5), computer-integrated manufacturing and manufacturing cells (Ch.1, 19, 24–25, Q4–Q5), and flexible manufacturing systems (Ch.19, Q6); Kalpakjian & Schmid, Manufacturing Engineering and Technology, 7th ed. — CAD/CAM and process planning (Ch.38–39, Q4).
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.
Numerical control (NC) replaces a human operator's manual manipulation of the machine slides with a stored program of coded numerical instructions that drive the axis motors directly. The chief advantages flow from removing the operator from the position-and-feed-rate control loop. Because the same program is re-executed identically every cycle, part-to-part accuracy and repeatability are far higher than with manual machining, and scrap and rework fall accordingly. Non-productive time — positioning the tool, indexing between operations, measuring in-process — is largely eliminated because the controller executes these moves automatically at machine speed rather than at the pace of a human reading a print. This also shortens lead time for a new part: once a program exists it can be run without building the special jigs, templates, or cam-and-tracer tooling that hard automation or manual methods require, so NC is far more flexible to engineering changes — a design revision is a program edit, not a new fixture. A stored program can also be re-run on demand for repeat orders with no loss of the process knowledge embedded in the original setup, and NC handles complex, multi-axis geometry (contours, compound angles) that would be difficult or impossible to hold manually. Collectively these advantages let a shop economically produce a wider range of part variety without a proportional increase in special tooling.
The disadvantages are mainly economic and organizational. The capital cost of an NC machine, its controller, and supporting software is substantially higher than an equivalent manual machine. The shop must employ or train skilled part programmers (and, for conversational/CAM-driven programming, CAM software and trained operators), which is a real and ongoing cost distinct from machine-operating skill. NC equipment is electronically and mechanically complex, so maintenance requires specialized technicians and downtime for a controller or servo fault can be costly. Programming errors can produce a run of scrap parts before they are caught, and for very simple, very high-volume work a dedicated hard-automation transfer line can still out-produce NC at lower unit cost, so NC is not automatically the cheapest choice at every point on the volume/variety spectrum. Finally, the pace of controller and software change creates a real risk of technological obsolescence of the investment.
NC is most economically justified for batch (medium-lot, medium-variety) production — the middle ground between high-variety/low-volume job-shop work (where programming overhead is hard to amortize over one or two pieces) and very high-volume work of one part type (where dedicated hard automation or a transfer line is cheaper per unit once volume is large enough). Within that band, NC suits parts that require many separate machining operations in one setup, since the controller performs the tool changes and repositioning that would otherwise demand several manual setups or special fixtures. It is especially advantageous for parts with complex geometry — contoured surfaces, multiple compound angles, close-spaced hole patterns — that are difficult to hold accurately by hand. Parts subject to frequent engineering design changes or likely to be reordered after the original run benefit because the program, not a physical jig, carries the process knowledge forward. NC is also preferred where the cost of a scrapped part is high (expensive stock, extensive prior machining) because of its superior accuracy and repeatability, and where several similar parts can be grouped into a part family (group technology), letting one master program be adapted with small edits across the family rather than written from scratch for each member.
