Chapter 7: Computer Numerical Control
Three Type of Software Programs used for CNC Systems
- Operating System Software -Machine Interface Software -Application Software
Types of Memory
- Read Only Memory (ROM) -Random Access Memory (RAM)
Advantages of CNC Machine
-Can be operating during two shifts -Can combine several operations into one setup -Setup time set to a minimum
Disadvantages of a CNC Machine
-Expensive -Higher Maintenance -Part Programming
Basic Components of a CNC System
-Part Program -Machine Control Unit -Process Equipment
Four Common Machining Operations
-Tooling -Drilling -Turning -Grinding
Three Possible Mechanical Errors
1- Play between the screw and the worktable 2-Backlash between gears 3-Deflection of machine components
Machine Control Unit
A microcomputer and related control hardware that stores the program and executes it by converting each command into a mechanical action
Open Loop
A positioning system w no feedback
CAD
Computer Aided Design
CAM
Computer Aided Manufacturing
Microcomputer
Computer Numerical Control is a Numerical Control systems whose MCU is a dedicated
Facing and Shoulder Facing
Cutting down an object in size
Parabolic and Cubic Interpolation
Free form curves using higher order equations
CAD/CAM
Integrating the design engineering and manufacturing engineering functions
Operating System Software
Interpolate the NC Part programmers and generates the corresponding control signals to drive the machine
ROM
Main memory, operating system software and machine interface programs are starting here
Two Types of Positioning Systems
Open Loop Close Loop
Process Equipment
Performs the actual productive work
Cutter Offset
Positioning your cutter with respect to its radius
RAM
Secondary Memory
Application Software
The NC Part programs that are written for machining operations
Origin
The part programmer must decide where the _____ of the coordinates axis system should be located
Part Program
The set of detailed step by step commands that direct the actions of the processing equipment
Feed Rate
The travel rate of the machine tool cutter or machine tool table
Concerning interpolation, the maximum error between the nominal (desired) surface and the actual (machined) surface can be controlled by the lengths of the individual line segments (T OR F)
True
Contouring is used for simultaneous control of two or more axis in machining operations (T OR F)
True
Close Loop
a positioning system with feedback
Threading
adding a thread to a hole
Circular Interpolation
circular arc path, tool path consists of a serious of straight line paths
Helical Interpolation
combines the circular interpolation schemes for two axises with w/ linear movement of the third axis
Optical Encoder
is a device for measuring rotational speed, position, and direction that consist of a higher source and a photodetector on either side of a disk
Computer Numerical Control (CNC)
is a form of programmable automation in which the mechanical actions of machine tool or other equipment are controlled by a program containing coded alphanumeric data
Mastercam
is a leading CAD/CAM software package for CNC part programming
CNC Turning Center
is a machine tool capable of performing multiple machining operations on a single workpiece in one setup
Machining
is a manufacturing process by which the geometry of the work is produced by removing the excess material
Repeatability
is the ability of the positioning system to return to a given addressable point that has been previously programmed
Interpolation
is the capability of moving only in discrete, small steps, rather than continuous motion
Operator Control Panel
is the interface by which the machine operator communicates to the CNC system
Accuracy
is the maximum possible error that can occur between the desired target point and the actual position taken by the system
Distributed Numerical Control (DNC)
is the networking of CNC Machine tools
Pocket Milling
is the type of milling when machines a shallow into a work part
Cutting Speed
is the velocity of the milling cutter relative to the work surface
Post Processor
is when a program is converting into a low level code that can be interpreted by the CNC controller
Adaptive Control
is when the MCU measures and analyzes machining variables such as spindle torque, power, and tool tip temperature, and adjust cutting speed and or feed rate to maximize machining performance
Computer Assisted Part Programming
is when the machine instructions are written in English like statements that are subsequently translated by the computer into the low level machine code that can be interpreted and executed by the machine tool conroller
Postion Set
is when the machine tool axis are referenced to the location of the fixture using a target point or set of target points on the part or fixture
Incremental Positioning
is when the position of the tool is defined relative to the previous location of that tool
Absolute Positioning
is when the position of the tool is defined relative tot he origin of the coordinate system
Contour Turning
making a three dimensional reproduction of the shape of a template
Linear Interpolation
straight line path
Depth of Cut
the distance the tool penetrates below the original surface of the work
Control Resolution
used in optical coders, is the distance separating two adjacent addressable points in the axis movement
Machine Interface Software
used to operate the communication link between the CPU and the machine tool to accomplish the CNC Auxiliary functions