The core of the CNC machine tool is the numerical control device. This is actually a control computer. It is the main component that performs the calculation function and directs the CNC machine tool for automatic machining. Over the years, with the development of technology, the functions of CNC systems have been expanding and people have become increasingly convenient to use. Therefore, learning the function of the numerical control system and clarifying its concept is an important part of the introduction of numerical control.
It is well known that the purpose of using CNC machine tools is to efficiently produce qualified parts with high quality. The so-called qualified parts must be products that meet the requirements of the drawings. How does the machine know the requirements of the drawings? This must be told by people. In what way, by what rules and conventions do people tell the machine? This requires the development of rules for the programming of CNC machine tools. In other words, we must represent the drawing size, routing, cutting parameters, etc. of the part with the numerical and text codes that the CNC machine can accept, and then make the input medium according to the code form (such as punched tape, tape, card, etc.). Then, the information recorded on the input medium is input into the numerical control device, so that the machine tool can be automatically controlled for processing.
This process from part drawing to making input media is called programming of CNC machine tools. The programming of CNC machine tools is divided into manual programming and automatic programming. The general steps of manual programming include process processing, coordinate calculation of motion trajectories, filling out program listings, preparing input media, and program checking. The automatic programming process is also performed as described above, except that most of the work is done by a computer or an automatic programmer. According to different input methods, automatic programming is divided into three modes: language input, graphic input and voice input. Common programming languages ​​are APT, SKC-1, ZCX-1, etc. In order for the machine to receive the programmed program, there must be corresponding regulations. These concepts are described separately below.
1, punched tape and code
There are two ways to read information on CNC machine tools: one is manual input mode; the other is automatic input mode. Therefore, there are two types of control media as information carriers for CNC machine tools: one is perforated tape, punched card, tape, disk, etc. when it is automatically input; the other is keyboard, band switch, manual data input when the console is manually input ( MDI) and so on. Due to the mechanical fixed code hole, the perforated belt is not easily affected by the environment (such as magnetic field), is convenient for long-term storage and reuse, and the program has a large storage capacity, so it is still the main information input method of many CNC machine tools.
2, the program segment format
When programming a CNC machine program, first determine the coordinate value based on the pulse equivalent of the machine tool, and then program the NC program according to its block format. The so-called program segment refers to the combination of the function "words" required to complete a certain action. A "word" is a set of code symbols that represent a function. For example, X2500 is a word indicating that the X dimension is 2500; F20 is a word indicating a feed rate of 20. The block format refers to the order in which the words in a block are arranged and their expressions. There are three commonly used block formats, namely fixed-sequence block format, fixed-sequence block format with delimiter, and word address block format. Since the block is composed of the function "word", the following describes the common function word first, and then introduces the block format.
1) Common function words
In a program segment, in addition to the serial number word (N×××) consisting of three digits headed by the address character N, commonly used function words are: preparation function word G; coordinate function word X, Y, Z; auxiliary function word M; feed function word F; spindle speed function word S and tool function word T, etc.
(1) Prepare the function word. The preparation function word is preceded by the address character G followed by two digits (G00-G99). The provisions of the ISO 1056 standard for the preparation function G are shown in Table 1. China's standard is JB3208-83, which stipulates that ISO1056-1975(E) is equivalent. These preparation functions include: coordinate movement or positioning method specification; interpolation mode designation; plane selection; thread, tapping, fixed cycle, etc.; specification of spindle or feedrate; tool compensation or tool offset Designation, etc. When designing a machine tool numerical control system, it is necessary to select a part of the preparatory function suitable for the system in the G function specified by the standard as the basis for hardware design and programming. The "not specified" preparation functions in the standard can be used to specify the special preparation functions of the system when necessary.
Table 1 Provisions for the preparation of function G by the ISO standard
Code
Features
Description
Code
Features
Description
G00
Point positioning
G57
XY plane linear displacement
G01
Linear interpolation
G58
XZ plane linear displacement
G02
Clockwise circular interpolation
G59
YZ plane linear displacement
G03
Counterclockwise circular interpolation
G60
Accurate positioning (fine)
Positioned according to specified tolerances
G04
time out
Pause for a period of time before the execution of this paragraph
G61
Accurate positioning (middle)
Positioned according to specified tolerances
G05
Not specify
G62
Accurate positioning (coarse)
Positioned to a larger tolerance
G06
Parabolic interpolation
G63
Tapping
G07
Not specify
G64-G67
Not specify
G08
Automatic acceleration
G68
Internal angle tool offset
G09
Automatic deceleration
G69
Outer angle tool offset
G10-G16
Not specify
G70-G79
Not specify
G17
Select XY plane
G80
Cancel the canned cycle
Cancel the canned cycle of G81-G89
G18
Select ZX plane
G81
Drilling cycle
G19
Select YZ plane
G82
Drilling or reaming cycle
G20-G32
Not specify
G83
Drilling deep hole circulation
G33
Pitch rotation
G84
Tapping cycle
G34
Cutting increased pitch
G85
Pupil circulation 1
G35
Cut and cut the pitch
G86
Pupil circulation 2
G36-G39
Not specify
G87
Pupil circulation 3
G40
Cancel tool compensation
G88
Pupil circulation 4
G41
Tool compensation - left
Looking at the direction of movement,
The tool is on the left side of the workpiece
G89
Pupil circulation 5
G42
Tool compensation - right side
Looking at the direction of movement,
The tool is on the right side of the workpiece
G90
Absolute value input method
G43
Positive compensation
Tool compensation value added to a given coordinate value
G91
Incremental value input method
G44
Negative compensation
The tool compensation value is reduced from the given coordinate value
G92
Prefabricated deposit
Modify size word
No movement
G45
For tool compensation
G93
Reciprocal feedrate by time
G46-G52
For tool compensation
G94
Feed rate (mm/min)
G53
Linear displacement function canceled
G95
Feed rate
(mm/r (spindle))
G54
X-axis linear displacement
G96
Spindle constant line speed
( m/min )
G55
Y-axis linear displacement
G97
Spindle speed
( r/min )
Cancel the designation of G96
G56
Z-axis linear displacement
G98-G99
Not specify
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