The technological capabilities of CNC machines, other things being equal, are determined by the number of controlled coordinates.
By the number of controlled coordinates machines are:
1. Two-coordinate ( X, Y).
2. 2.5-coordinate ( X, Y and separately for Z).
3. Three-coordinate ( X, Y, Z).
4. Four- and more-axis (multi-purpose machines and machining centers).
Particular attention should be paid to machines with index coordinate axes, usually marked, for example, not “5 axes”, but “3 + 2 axes”. This means that the 2 axes of this machine have the ability to discretely rotate or move at idle speed, fix the working part of the machine in this position and subsequently process the workpiece without moving along the index axes.
Marking of CNC machines
The marking of CNC machines is similar to the marking of universal machines, but to designate the CNC system, the letter “F” with a number is entered at the end of the mark:
F1 – CNC system with preset;
F2 – CNC positional system (CNC drilling and boring machines) (see Fig. 1.1);
F3 – CNC contour system (CNC lathes and milling machines) (see Fig. 1.2);
F4 – combined CNC system (F2 + F3) (multi-purpose machines).
Examples of marking of CNC machines: 16K20F3 – screw-cutting lathe with CNC contour system; 2Р135Ф2 – vertical drilling machine with CNC positioning system; 2451ПМФ4 – drilling and milling boring machine with a combined CNC system.
It should be noted that the above-described principle of marking CNC machines is valid only for equipment produced in the Soviet Union. Manufacturers of modern CNC machines (including foreign ones) overwhelmingly use the internal standards of their enterprises, which are poorly correlated with the standards of other manufacturers.
Methods for programming CNC machines
Exist three programming methods processing for CNC machines:
1. Manual programming.
All CNC machine operators and programmers should have a good understanding of manual programming techniques for writing a control program directly on the machine's CNC rack or correcting an existing program.
2. Programming on the CNC console (dialogue programming using high-level languages).
In this case, programs are created and entered directly on the CNC rack. Currently, modern high-level NC development systems are used on CNC machines. Such systems allow the operator-programmer to prepare a part processing program, determining the sequence of transitions proposed by the system only with an indication of their parameters. The machine operator can check the correct operation of the NC directly on the CNC rack of the machine with visualization of the processing.
3. Programming using CAM systems.
Programming using CAM systems eliminates the need for labor-intensive mathematical calculations and uses tools that significantly increase the speed of software development. This programming method is often used to write programs for manufacturing complex parts. However, to adapt the developed CP to a specific machine, a postprocessor is required that converts control programs into the phase space of this machine.
Information coding, regardless of the programming method used, is carried out in G-code with an alternative name ISO-7bit. Code ISO-7bit The UE defines frames in an address manner and is based on the binary-decimal system.
The information presented in any control program is divided
into 3 types:
· geometric(set of movement by coordinates);
· technological(setting processing modes, tools, etc.);
· logical(turning on/off cooling, setting spindle rotation, etc.).
Questions and tasks for self-control
1. What is numerical control of a machine tool?
2. Define a numerical control system.
3. What is a machine numerical control device called?
4. What is the purpose and main applications of positional and contour control?
5. What is a control program?
6. What is called discreteness of movement?
7. What is equidistant?
Tests for the section
1. Numerical program control of a machine tool is:
a) control of the processing of the workpiece on the machine according to the control program;
b) a set of functionally interrelated technical and software methods and tools that provide machine control;
2. Numerical control system is:
a) a set of functionally interrelated technical and software methods and tools that provide numerical program control of the machine;
b) a set of functionally interrelated software methods and tools that provide software control of the machine;
c) a set of methods and tools that provide numerical program control of the machine.
3. The numerical control device for the machine is:
a) part of the CNC system, made as a single whole with it and issuing control actions on the executive bodies of the machine in accordance with the control program and information about the state of the controlled object;
b) part of the CNC system that issues control actions to the executive bodies of the machine in accordance with the control program and information about the state of the controlled object;
c) part of the CNC system, made as a single whole with it and issuing control actions on the executive bodies of the machine in accordance with the control program.
4. Positional control is:
a) control in which the working parts of the machine move to specified points without specifying a trajectory;
b) control, in which the working parts of the machine move at a given speed along a given trajectory;
5. Contour control is:
a) control, in which the working parts of the machine move at a given speed along a given trajectory;
b) control, in which the working parts of the machine move to specified points without specifying a trajectory;
c) control in which the working parts of the machine move at a given speed along a given path or without specifying a motion path.
PU systems – cyclic and numeric
Cyclic– allow you to program the sequence and speed of movement of the moving parts of the machine. Currently not applicable.
With CNC the entire machine operating program is recorded on a program medium in the form of combinations of signals expressing numbers, as well as letters and other symbols.
Such a program also includes numerical values of the movements of the moving parts of the machine, which is the fundamental difference between a CNC machine and a machine with a cyclic control.
The control program for processing on a CNC machine is written on a program medium in the form of separate blocks of information or frames, separated by certain characters. Each program frame contains information necessary for the machine to execute a certain group of commands.
One frame may include: the required values of tool movements along the coordinate axes, feed, spindle rotation speed, as well as other data necessary for the machine to perform a given work cycle, for example, commands to turn cooling on and off, instructions on the direction of movement of the working parts of the machine, etc. .
In practice, in production conditions, a control program is a program carrier with information printed on it in one code or another about the full cycle of processing a workpiece on a given machine. The source documentation for developing a control program is drawing, processed workpiece, routing, as well as a calculation and technological map (RTC) or a diagram of the movement of tools during processing. This documentation, when preparing programs manually, allows the programmer technologist to fill out a programming card according to which the control program is produced.
CNC systems, based on the nature of controlling the movement of the working parts of the machine, are divided into two groups: positional (coordinate) and contour (continuous)
Positional control (GOST 20523-80) is a numerical program control of a machine tool, in which the movement of its working parts occurs at specified points, and the movement trajectories are not specified.
Contour control (GOST 20523-80) is a CNC machine tool in which the movement of its working parts occurs along a given path and at a given speed to obtain the required processing contour. Contour systems can also operate in positional mode, but are very expensive.
In addition to those mentioned, there are: digital position indication systems and digital indication systems with manual data entry. At the same time, the numerical values of the coordinates of the moving parts of the machine are continuously indicated on the screen of such a system. Used on universal machines.
In accordance with the considered classification of systems by the nature of control, a special one has been introduced. indexing in the designation of CNC machine models
C - machines with cyclic control; F-1 – machines with digital position indexing, as well as manual data entry; F-2 – machines with PSPU; F-3 – machines with contour control systems.
In addition, indices reflecting the design features of the machine associated with automatic tool change are displayed: P – tool change by rotating the turret; M – tool change from the magazine; MF3 is a machine with a contour control system with a tool magazine.
In the designations of some machine models, the following indices are used: F4 and F5. Assigned to machines of the OC group. F4 – OC with a positional control system; F-5 with contour.
The location and designation of coordinate axes corresponding to the directions of independent controlled movements are adopted in accordance with the JSO-R841 standard.
It is based on the first coordinate system with axes X, Y, Z, which indicate the positive directions of movement of the tools relative to the stationary workpiece.
If the tool is not movable, but the workpiece moves relative to the tool, then its corresponding positive movements directed in opposite directions are indicated by the letters X`, E`, Z`
Positive directions of movement of movable organs are taken to be those movements in which the tool and the workpiece move away from each other.
On a horizontal boring machine, the following are taken as positive: the movement of the spindle head up the stand and the movement of the table sled in the direction from the spindle head; For a quill, its movement in the opposite direction is considered positive.
In addition to the listed principles of axes location, the following rules are used: the X axis is always positioned horizontally, and the Z axis is combined with the axis of rotation of the tool. Only in lathes is the Z axis combined with the axis of rotation of the workpiece.
If in the machine, in addition to movements along the three main coordinates, there are programmable movements of other organs in parallel directions, then the corresponding secondary and tertiary axes are designated by letters: U, V, W - secondary axes; P,Q,R - tertiary axes.
Circular movements of the tool relative to the workpiece are considered positive in a counterclockwise direction when looking at the tip of the corresponding coordinate axis.
Coordinate reference methods– absolute and relative.
When absolute, the position of the origin remains fixed for the entire processing. The absolute values of the coordinates of successively located reference points are recorded on the software carrier. The advantage is that the machine works from the same point every time, there is no accumulation of errors. The origin can be selected anywhere within the working passages and moving parts. "floating zero". This method of reference is used mainly in positional systems on boring and drilling machines and OCs with position control. With the absolute method of measuring dimensions, it is advisable to use the coordinate method of setting dimensions in the workpieces being processed.
In systems with a relative method of coordinate reference, the position of the executive body that it occupied before moving to the next reference point is taken as zero each time. In this case, the program records coordinate increments when moving from the previous to the next point. The first reference point of the program is called the origin or start point. It is verified when setting up the machine and plays the role of the origin of coordinates from which the processing program for this particular workpiece is calculated. The most rational way is to set dimensions in a chain, which results in the accumulation of movement errors. Recently, there has been a trend toward absolute coordinate reference in contour CNC systems.
According to the number of controlled movements (coordinates), CNC systems can be 2,3,4,5 or multi-axis. For contour systems, an important characteristic is the number of simultaneously controlled coordinates. However, some CNC contour systems do not carry out coordinated movements along all coordinates simultaneously, but only in the absence of movement along one of the coordinate axes. Such systems with one incomplete coordinate are sometimes denoted by a fractional number, adding another half coordinate to the whole number of simultaneously and coordinated coordinates. For example 3.5 (four coordinates with one incomplete). The number of controlled coordinates is an important technological characteristic of the machine.
To process the workpiece lathe the machine is enough 2 x coordinates, for machines with two calipers – 4(1734F3). Drilling CNC machines are usually two coordinate. For boring machine tools – 3 x coordinate. Milling not less 3 x simultaneously controlled coordinates.
The most rational ones are five-axis milling machines, in which rotations of the workpiece and tilts of the tool are additionally programmed.
On modern CNC machines, it changes processing modes and is available for manual editing.
Currently, many programming languages are used to program CNC systems, based on the universal ISO 7-bit language. However, each manufacturer brings its own features, which are implemented through preparatory (G-codes) and auxiliary (M-codes) functions.Functions with address G- are called preparatory, they determine the operating conditions of the machine associated with programming the geometry of the tool movement. A detailed description of G-codes can be found in the chapter ISO 7 bit code.
In this chapter we will consider in detail the purpose of auxiliary functions.
Functions with address M- are called auxiliary(from English: Miscellaneous) and are designed to control various modes and devices of the machine.
Auxiliary functions can be used alone or in conjunction with other addresses, for example the block below installs tool number 1 into the spindle.
N10 T1 M6, where
T1– tool number 1;
M6– tool change;
In this case, under the M6 command on the CNC stand there is a whole set of commands that ensure the process of tool replacement:
Moving the tool to the change position;
- turning off spindle speed;
- moving the installed tool in the store;
- tool replacement;
The use of M-codes is allowed in frames with tool movement, for example in the line below the cooling will turn on (M8) simultaneously with the start of the cutter movement.
N10 X100 Y150 Z5 F1000 M8
M-codes that turn on any machine device have a paired M code that turns off that device. For example,
M8– turn on cooling, M9– turn off the cooling;
M3– turn on the spindle speed, M5– turn off the speed;
It is allowed to use several M commands in one frame.
Accordingly, the more devices a machine has, the more M commands will be involved in its control.
Conventionally, all auxiliary functions can be divided into standard And special. Standard auxiliary functions are used by CNC manufacturers to control the devices found on each machine (spindle, cooling, tool change, etc.). Whereas special programs program modes on one specific machine or group of machines of a given model (on/off the measuring head, clamping/unclamping the rotary axes).
The picture above shows the rotating spindle of a multi-axis machine tool. To increase rigidity during positional processing, the machine is equipped with rotary axis clamps, which are controlled by M codes: M10/M12– enable clamps for axes A and C. M11/M13– turn off the clamps. On other equipment, the machine manufacturer can configure these commands to control other devices.
List of standard M commands
M0 – program stop;M1 – stop on demand;
M2 – end of the program;
M3 – turn on the spindle rotation clockwise;
M4 – turn on the spindle rotation counterclockwise;
M5 – spindle stop;
M6 – automatic tool change;
M8 – turn on cooling (usually coolant);
M9 – turn off the cooling;
M19 – spindle orientation;
M30 – ending the program (usually with resetting all parameters);
M98 – subroutine call;
M99 – return from the subroutine to the main one;
The machine manufacturer describes special auxiliary functions in the corresponding technical documentation.
Have you repeatedly wanted to know the capabilities of a CNC milling machine? Before you start looking for such a machine for your purposes, you need to determine what exactly you will use it for. The size and functions of a CNC router for different materials can vary significantly, but in general they are similar for all types of machines.
What to look for when choosing a machine
First of all, you need to decide on the size of the machine and make sure that there is enough space for it in the room (workshop or workshop). Then you need to study the latest news in the CNC world and make sure that the machine you are buying complies with all innovations (only if this is important and not financially critical).
One of the significant factors influencing the choice of a CNC router is the cost of purchase and installation. CNC, which stands for Computer Numerical Control, is the process of controlling an automatic machine using a computer program. In the recent past, quality cars were very expensive, but now their prices have dropped significantly.
Before purchasing, be sure to find out about the accuracy of the purchased machine and its speed, as well as how their change will affect the cost.
Faster machines that can cut and mill to specific tolerances will cost more, while slower, smaller and less accurate machines will cost less. For amateur purposes or a home workshop, a machine with a low operating speed is sufficient, but for professional use, in order to cope with the entire workload, it is better to opt for an automatic machine with high processing speed and high accuracy.
Classification of CNC milling machines
The classification of CNC milling machines is quite different. Some machine models will differ in design, namely, the ability of the CNC milling machine to independently change the tool. This function allows the machine, selecting according to the program, to replace the working tool (mill) without human intervention. The machine knows which cutter to select and use for certain tasks, allowing it to continuously process the workpiece without stopping.
Cheaper machines require manual cutting tool changes, which adds work to the operator and slows down the overall process. The machine cuts edges and even shapes inside the workpiece, where changing tools is difficult, using rapidly rotating cutters mounted on a motor. Manually replacing a working tool will require constant attention to the process.
Other features to consider when choosing a CNC router are:
- spindle cooling system (air or liquid);
- a wide platform on which you can easily attach a part for milling;
- high quality frame materials such as steel and aluminum;
- ease of use of CNC Programs.
Which CNC router should you choose based on these features?
One of the very useful options for a milling machine is a dust collection and removal system (exhaust), which removes dust directly from the cutting site, which allows you to keep the work area clean. The dust collection system will prevent fine particles from accumulating in the air, thus avoiding breathing problems, poor visibility, etc.
How to choose the right CNC machine
There are many types and manufacturers of CNC machines. When purchasing a new or used (used) CNC machine, there are a number of key features to look for.
The figure shows a simple design of a CNC milling machine, it consists of the following parts:
- X axis;
- Y axis;
- Z axis;
- X-axis drive;
- Y axis drive;
- Desktop;
- Spindle;
- Chuck for installing cutting tools;
- Machine body (in this case aluminum).
Let's look at the most important characteristics of the machine:
Number of axes
This is the most fundamental quality of any CNC machine. In most basic designs, the cutting head moves in three directions - X, Y and Z - and the tool itself is always pointing down and aligned with the Z axis. This design is a bit limited compared to multi-directional machines containing a fourth and even fifth axis.
Material from which the machine is made
Cast iron or steel construction provides a higher level of rigidity and the ability to fabricate even the largest workspace, but is very heavy. If you do not plan to move the machine around the workshop, then this option is optimal, but if frequent rearrangements are planned, then it is better to pay attention to aluminum machines; they are much lighter and are almost as strong as steel ones.
If you will be processing soft materials and the machine will not experience heavy loads during operation, then you can opt for a design made of polymer materials (acrylic, PVC).
Using a specialized spindle
The spindle connecting the motor and the rotating tool has a great influence on the accuracy of the CNC machine. Its main task is to ensure that the rotation of the tool is concentrated at one point, has minimal vibration, and that these conditions are met even under maximum load.
A higher quality spindle increases accuracy by reducing the overall amount of lateral oscillation and also reduces the difference between the intended and actual tool diameter.
For non-ferrous metals, wood, plastics and other similar materials, a high spindle speed is recommended. When cutting soft materials at low spindle speeds, the grooves on the end mills will become clogged with chips and ruin the part. The only way to avoid gumming cutters in soft materials at low spindle speeds is to reduce the feed speed.
Mechanical movement ranges
Large tool travel ranges allow you to machine a larger workpiece area in one pass. To determine the dimensions of the machine you need, think about the maximum size of the product you are going to produce on it.
Travel speeds
There are many factors that influence the amount of time it takes to complete a particular workpiece, but the main one is always the performance of the CNC machine itself. “Why not process at maximum speed?” - you ask. As already written above, high speed of movement does not always have a positive effect on the quality of the finished product. For example, acrylic, at high feed speeds, begins to melt and deform, the wood becomes charred, this has a bad effect on the working tool, and the cutters also “burn.”
If you are asking the question: “How to choose a CNC milling machine?”, then it is very important to pay attention to the maximum speed of movement if it is not used for amateur purposes.
Stepper motor or servo drive: advantages and disadvantages
The types of drive motors for each axis are divided into stepper motors and servos.
Servo drives have higher accuracy than stepper drives and are much more expensive. The main advantage of the servo system is that it checks its position with each movement relative to an independent measuring device - a glass scale. It's a whole complex.
Depending on the type of work performed, milling machines are:
- engraving and milling,
- drilling and milling,
- turning and milling and many other types.
Milling can process materials such as:
- tree,
- plastic,
- graphite,
- as well as all types of metals and their alloys (steel, cast iron, aluminum, brass, bronze, copper, etc.)
The cutting tools used, cutters, are also very diverse. The complex design of the machines allows them to perform a wide range of operations for processing materials: engraving, drilling, milling, carving, cutting large slabs and much more.
The operating principle of the milling machine is such that it allows, within the framework of one program being executed, to automatically change the tool - the cutter, change the rotation speed of the cutter and the angle of rotation of the spindle. All of the listed functions and properties of the equipment open up very great opportunities for the use of milling machines in a wide variety of fields and industries. They can be used to perform both cutting and cutting of large slabs and fine processing of the smallest parts.
For example, a milling and engraving machine, despite the impressiveness and massiveness of its design, can perform, in addition to drilling, cutting and cutting materials, very delicate engraving, accurately and clearly transferring the smallest details of the original image onto the workpiece. The engraving accuracy of a properly adjusted machine is a fraction of a millimeter.
The latest generation milling machines allow you to process not only flat parts, but also process workpieces using 3D programs, creating three-dimensional shapes. Such universal capabilities of CNC machines are appreciated by manufacturers of modern furniture. The machines allow you to realize the most complex design solutions: bent furniture facades, carved furniture overlays, complex cutting of furniture boards, decorative milling on both sides of a furniture board.
It is impossible to do without milling machines at woodworking enterprises specializing in country house construction. Carved stairs with elaborate balusters made of ash, oak or walnut, doors with complex ornaments, wooden arches and other decorative and functional interior elements cannot be made without the use of universal CNC milling machines.
The enormous advantages of such universal equipment as CNC milling machines have opened the way for them into all areas of modern production. Among the most important advantages, it is worth noting the high productivity and manufacturability of various products, easy control, quick entry into a working production line, almost complete absence of defects in the manufacture of parts, since CNC milling machines are controlled by a computer, which eliminates the human factor influencing production.
