19-11-2012, 11:55 AM
CNC MILLING
CNC MILLING.ppt (Size: 1.7 MB / Downloads: 230)
PROGRAM TRANSFERS
PROGRAM PREPARATION WITH CAD CAM
PROGRAM DATA TRANSFER FROM PC TO CNC M/C
PROGRAM DATA TRANSFER FROM PC TO DNC OPERATIONS
SAFETY PRECAUTIONS
SAFE HANDLING OF TOOLS
SAFE HANDLING OF EQUIPMENTS
RIGHT WAY TO CNC OPERATING.
CLEANLINESS OF CNC MACHINE & SHOP
What is a CNC Machine?
CNC : Computer and Numeric Control
Conventionally, an operator decides and adjusts various machines parameters like feed , depth of cut etc depending on type of job , and controls the slide movements by hand. In a CNC Machine functions and slide movements are controlled by motors using computer programs.
For a CNC machine control unit (MCU) decides cutting
speed, feed, depth of cut, tool selection , coolant on off
and tool paths. The MCU issues commands in form of
numeric data to motors that position slides and tool
accordingly.
Overview
A numerical control, or “NC”, system controls many machine functions and movements which were traditionally performed by skilled machinists.
Numerical control developed out of the need to meet the requirements of high production rates, uniformity and consistent part quality.
Programmed instructions are converted into output signals which in turn control machine operations such as spindle speeds, tool selection, tool movement, and cutting fluid flow.
By integrating a computer processor, computer numerical control, or “CNC” as it is now known, allows part machining programs to be edited and stored in the computer memory as well as permitting diagnostics and quality control functions during the actual machining.
All CNC machining begins with a part program, which is a sequential instructions or coded commands that direct the specific machine functions.
The part program may be manually generated or, more commonly, generated by computer aided part programming systems.
Basic CNC Principles
All computer controlled machines are able to accurately and repeatedly control motion in various directions. Each of these directions of motion is called an axis. Depending on the machine type there are commonly two to five axes.
Additionally, a CNC axis may be either a linear axis in which movement is in a straight line, or a rotary axis with motion following a circular path.
Motion control - the heart of CNC
The most basic function of any CNC machine is automatic, precise, and consistent motion control.
Rather than applying completely mechanical devices to cause motion as is required on most conventional machine tools, CNC machines allow motion control in a revolutionary manner.
All forms of CNC equipment have two or more directions of motion, called axes. These axes can be precisely and automatically positioned along their lengths of travel.
The two most common axis types are linear (driven along a straight path) and rotary (driven along a circular path).
Basic CNC Principles
Each axis consists of a mechanical component, such as a slide that moves, a servo drive motor that powers the mechanical movement, and a ball screw to transfer the power from the servo drive motor to the mechanical component.
These components, along with the computer controls that govern them, are referred to as an axis drive system.
Work Positioning
The method of accurate work positioning in relation to the cutting tool is called the “rectangular coordinate system.” On the vertical mill, the horizontal base line is designated the “X” axis, while the vertical base line is designated the “Y” axis. The “Z” axis is at a right angle, perpendicular to both the “X” and “Y” axes.
Increments for all base lines are specified in linear measurements, for most machines the smallest increment is one ten-thousandth of an inch (.0001). If the machine is graduated in metric the smallest increment is usually one thousandth of a millimeter (.001mm).
The rectangular coordinate system allows the mathematical plotting of points in space. These points or locations are called “coordinates.” The coordinates in turn relate to the tool center and dictate the “tool path” through the work.
Tools
Most are made from
high speed steel (HSS),
tungsten carbide or ceramics.
Tools are designed to direct waste away from the material.
Some tools need coolant such as oil to protect the tool and work.
Tool Paths, Cutting and Plotting Motions
Tool paths describes the route the cutting tool takes.
Motion can be described as point to point, straight cutting or contouring.
Speeds are the rate at which the tool operates e.g. rpm.
Feeds are the rate at which the cutting tool and work piece move in relation to each other.
Feeds and speeds are determined by cutting depth, material and quality of finish needed. e.g. harder materials need slower feeds and speeds.
Rouging cuts remove larger amounts of material than finishing cuts.
Rapid traversing allows the tool or work piece to move rapidly when no machining is taking place.