Chapter Five NUMERICAL CONTROL AND CAD/CAM

Chapter Five NUMERICAL CONTROL AND CAD/CAM

NUMERICAL CONTROL Principle of Numerical Control (NC) A system in which actions are controlled by direct insertion of numerical data.

NC Machine Tool Foundation for > Robotics > Flexible Manufacturing Cell > Flexible Manufacturing > CAD/CAM System > Computer-Integrated

Manufacturing Traditional Machine Tools Milling Machines Lathes Drilling & Boring Machines Grinders

Advantages of NC Flexibility Capability for Complex Work-pieces Manage Large Work-pieces Reduced Jig & Fixture Cost Higher Quality

NC System Components Machine Tool Machine-Control Unit > Data Processing Unit (DPU) DPU processes coded data from hard drive & passes to CLU. > Control-Loops Unit (CLU) Motion control duties. Operates drives Feedback on actual

position. Acts as a translator for machine commands (motor on/off, tool speed, distance). Direct Numerical Control Advantages: > Library of programs > Instant modifications > Links with CAD

> Increase Information Response > Instant Reports Computer Numerical Control (CNC) Advantages: > CRT allows review/editing > Pre-check/simulation

> Interface allows more capability > Accurate positioning > More functions CAD/CAM Computer Aided Design Computer Aided Manufacturing Advantages:

> Eliminate blueprints > Database of parts > Production Schedules > BOM > Process instructions NC Motion Control Objective Execute precise motion in a given

set of reference frames. > Generally described by Cartesian space X-Y-Z. NC Position Movement Incremental > Taking the Last position as the zero position. Absolute

> Locations on Part Fixed Reference Frame with Home position for reference. Degree of Motion Control Point-to-Point (PTP) > Good for holes & slots > Position tool over point.

Contouring > Complex curved surfaces > Computers needed for complex calculations > Motion control to motors: varying voltages to DC servo motors. NC Part Programming Block Formats

> Each block is a statement. Computer Language > Programming language designed to execute complex geometrical outlines. >>> APT (Automated Programming Tool) Geometrical data with motion statements or NC.

Available Block Formats Fixed Sequential Block Address Tab Sequential Word Address** > Used by CNC controller systems. Alphabetic character is used as a code at the beginning of each word. Utilize words that describe an address (identifier) & a number that

specifies its content. Example of Word Address N01 G02 X1500 Y2000 F4 S400 T10 N: identification number G: preparatory command X: x axis Y: y axis

Z: z axis I,J,K: coordinate values F: feed rate S:spindle speed Binary-Coded Decimal (BCD) Machine code used for numerical control.

> Easier to read than binary. > Four binary digits are required to represent 0 to 9. > Code that is saved in RAM. Example: 439 = 10000111001 ASCII uses channels 1 - 4 for digits; channels 5 7 indicate which group (numbers or alphabetic); channel 8 is for parity.

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