1. Unit 3 Advantages of NC Thursday, May 10th, 2007

2. Lead-in questions  How would the time be spent on a part from the time it arrived at a plant as a rough casting to the time it was a finished product?  What are the major advantages of NC?  Which industries did NC develop originally for use in? Which industries employ numerical control machinery now?

3. Notes  Fraction 一小部分  Assume  Rapid

4. Translate the following sentences:  Recent studies show that of the amount of time an average part spent in a shop, only a fraction of that time was actually spent in the machining process.  Let us assume that a part spent 50 hours from the time it arrived at a plant as a rough casting or bar stock to the time it was a finished product. During this time, it would be on the machine for only 2.5 hours and be cut for only 0.75 hour.  The rest of the time would be spent on waiting, moving, setting up, loading, unloading, inspecting the part, setting speeds and feeds, and changing cutting tools.

5.  Some of the major advantages of NC are as follows: 1.There is automatic or semiautomatic operation of machine tools. The degree of automation can be selected as required. 2.Flexible manufacturing of parts is much easier. Only the tape needs changing to produce another part. 3.Storage space is reduced. Simple workholding fixtures are generally used, reducing the number of jigs or fixtures which must be stored. 4.Small part lots can be run economically. Often a single part can be produced more quickly and better by NC. 5.Nonproductive time is reduced. More time is spent on machining the part, and less time is spent on moving and waiting.

6. 6. Tooling costs are reduced. In most cases complex jigs and fixtures are not required. 7. Inspection and assembly costs are lower. The quality of the product is improved, reducing the need for inspection and ensuring that parts fit as required. 8. Machine utilization time is increased. There is less time that a machine tool is idle because workpiece and tool changers are rapid and automatic. 9. Complex forms can easily be machined. The new control unit features and programming capabilities make the machining of contours and complex forms very easy. 10. Parts inventory is reduced. Parts can be made as required from the information on the punched tape.

7.  Since the first industrial revolution, about 200 years ago, NC has had a significant effect on the industrial world. The development in the computer and NC have extended a person’s mind and muscle.  If industry’s planning and logic are good, the second industrial revolution will have as much or more effect on society as the first industrial revolution had.  Computer-assisted manufacturing (CAM) and computer- integrated machining (CIM) are certainly where the future of manufacturing lies, and considering the developments of the past, it will not be too far in the future before the automated factory is a reality.