Before starting to prepare a machining program, you must know well the machining that is going to be carried out on the lathe, the dimensions and characteristics of the starting material, as well as the number of pieces that make up the series that must be machined. With this prior knowledge, the system for fixing the piece on the lathe, the technological conditions of machining in terms of cutting speed, feed and number of passes are established.

Likewise, the geometric parameters of the machining are established, indicating the arrival and departure levels of the tools, and the tools to be used and their qualities are also selected.

Head rotation speed. This data depends on the characteristics of the material, the degree of machining desired and the type of tool used. The program allows you to adapt the rotation speed at any time to the most convenient speed. It is represented by the letter (S) and can be expressed as cutting speed or revolutions per minute of the head.

Work progress. There are two types of advance for the cars, one of them very fast, which is the approach advance or retreat to the starting point, and another which is the working advance. This is also a function of the type of material, machining quality and degree of surface finish. The program allows you to adapt the most convenient progress at any time. It is represented by the letter (F) and can be expressed in millimeters per revolution or millimeters of advance per minute.

Another important factor to determine is that every program must indicate the position location that has been chosen to reference the part, which is called "piece zero." Starting from part zero, all the geometry of the machining program is established.

Numerical control is a machine tool that helps us in the machining of metalworking parts. SH.

La estructura de un programa de torneado está conformado por una serie de secuencias y funciones donde se van programando las tareas que debe realizar la máquina de acuerdo con los parámetros de la pieza y las condiciones tecnológicas de su mecanizado. Existen varios fabricantes de ordenadores para tornos. En este artículo para ejemplificar un tipo de programación se toma referencia el modelo 8050 que fabrica la empresa española Fagor.[11]​.

Sequence number N

The set of non-contradictory orders that can be given to the machine at once is called a sequence. They are identified by the letter N, and on a normal lathe up to 9999 successive orders can be given. If the program is not very long, it can be numbered 10 by 10, in case it is necessary to introduce an unforeseen complementary order, thus we will have N10, N20, N30, etc. or we could have, N10, N11, N20, etc.[12]​.

Preparatory functions G

Under the letter G accompanied by a number, a wide variety of functions are grouped that allow the lathe to perform the appropriate and necessary tasks for its work.

There are five basic types of preparatory functions:

1- Mobility functions The most important mobility functions are the following:.

G00. Quick scroll. Indicates the fastest possible movement of the tool carriage, from the reference point to the point where each tool begins work. Special care must be taken when using this function since the trajectory is not controlled by the user but rather the lathe acts based solely on the maximum travel speed. It is never mechanized with it. It only acts at the beginning of the program, each time a tool change occurs, and at the end of the program when returning to the reference point.

G01. Linear interpolation. Indicates that the tool is moving at the programmed work feed, allowing the classic turning and facing operations as well as the machining of cones "Cone (geometry)").

G02 Circular interpolation to the right (clockwise) It is used when it is necessary to machine spherical or radial areas with controlled speed.

G03. Circular interpolation to the left (counterclockwise). It is used when it is necessary to machine empty spherical areas, or left-hand radii.

There are other G mobility functions, which are less important and depend on the equipment installed in the machine.

2- Technological functions The technological functions are those that refer to the way of programming the speed of the head and the work progress. The head rotation speed can be programmed to the desired revolutions per minute, for which function G97 will be prefixed, or it can be programmed to rotate at a constant cutting speed in m/min. In this case it is indicated with function G96. The same happens with the work advance, if you want to program the advance in mm/rev, the G95 function is prefixed and if you want to work in mm/min, the G94 function is prefixed.

3- Conversion functions The most important function of this group is the one that corresponds to the origin transfer to locate the piece zero that is carried out using the G59 function. There are also functions if the dimensioning is in inches or millimeters. Although it has already pre-established the one that will be used normally. Another case of conversion is if it is programmed with absolute dimensions or incremental dimensions.

4- Special machining functions. The most popular of these functions is the one that corresponds to a threading cycle represented by function G33. Other functions of this type are facing, drilling, tapping, reaming, etc.

5- Modal functions. In CNC programs, there are functions that, once programmed, remain active until a contrary function is programmed, or the program is terminated. These functions are called modal functions. As many functions as desired can be programmed in a block, as long as they are not incompatible with each other. For example, functions G00 and G01 cannot be programmed in a block.[13]​.

X-Z coordinate programming

Dimension programming is understood as specifying in the program the paths that the tools must perform to form the profile of the piece in accordance with its plane. Programming can be done using X and Z coordinates or polar coordinates. Also using the appropriate G function, the dimensions can be programmed in both millimeters and inches. To correctly program the dimensions, it is necessary to know well the excess material that must be removed, to determine the number of passes that must be made as well as the surface roughness that the machined finishes must have, as well as the way to hold the part in the machine and its rigidity.

T-D Tool Programming

Numerical control lathes have a front drum where a variable number of tools can be housed, generally from 6 to 20 different tools. The tools are programmed with a letter T followed by the number it occupies on the drum, for example T2, the letter T is the initial of this word in English (tool). As each tool has a different length and a different cutting tip radius, it is necessary to enter the correct values ​​for each tool into the program so that the program can run normally.

Apart from the length of the tool, there are G functions to introduce a correction according to the value of the radius of the tool at the cutting tip. Tool radius compensation is of great importance in machining, especially in parts that contain irregular profiles. Lathe tool plates always have rounded tips, this way they are more rigid. The smaller the radius of the tip, the less tendency it has to splinter.[14]​.

F-S technological factors

The technological factors that must be taken into account when developing a program are the following:

These factors are what will determine, among other things, the following elements.

Auxiliary functions M

Auxiliary functions are used to establish the operation of the machine. Such as starting and stopping the main drive or end of the program.[15]​.

Advantages:.

The following can be indicated as disadvantages:

The lathe has evolved so much that it is no longer just about removing material at high speed, but the parameters that make up the process have to be closely controlled to ensure the final results of economy, quality and precision.

The way of treating the chip becomes a complex process, where all the technological components of machining are involved, so that it can have the size and shape that does not disturb the work process. If this were not the case, masses of long, fibrous chips would quickly accumulate in the machining area, forming tangled and uncontrollable skeins.

The shape that the chip takes is mainly due to the material being cut and can be ductile material as well as brittle and fragile.

The feed at which you work and the depth of the pass are quite responsible for the shape of the chip, and when it cannot be controlled with these variables, you have to resort to choosing the tool that incorporates an effective chip breaker.[17]​

Greater efficiency than a normal lathe means greater speed.

Today dry turning is completely viable and is used in numerous applications. There is a recent trend to carry out dry machining whenever the quality of the tool allows it.

A higher cutting temperature zone can be a positive factor in many cases.

However, dry machining is not suitable for all applications, especially for drilling, threading and boring to ensure chip evacuation.

It is necessary to carefully evaluate operations, materials, parts, quality requirements and machinery to identify the benefits of eliminating the refrigerant contribution.[18]​.

In turning there are six key parameters:.

CNC lathes, due to their operating mechanisms, allow the machining conditions to be adjusted to the maximum and therefore achieve the best possible turning time.[19]​.

These parameters are related by the following formulas:.

Generally, the optimal cutting speed of each tool and its feed rate are indicated by the tool manufacturer or, failing that, in the machining technical manuals.

Contenido

Las características propias de los tornos CNC respecto de un torno normal universal son las siguientes:.

Motor and main head

This motor limits the real power of the machine and is what causes the rotary movement of the pieces. Current CNC lathes normally equip a direct current motor, which acts directly on the spindle with a pulley transmission interposed between the location of the motor and the spindle, making any type of gear transmission unnecessary.

These direct current motors provide an almost infinite variety of rotation speeds from zero to a maximum determined by the characteristics of the motor, which is programmable with the execution program of each part. Many motors incorporate two speed ranges, one for slow speeds and the other for fast speeds, in order to obtain the most favorable torques. The spindle has at its end the adaptation for the corresponding claw plates and a hole to be able to work with a bar.

The characteristics of the main motor and spindle of a CNC lathe can be the following:[4]​.

Bench and movable carts

On the other hand, the structure of the bed determines the maximum dimensions of the parts that can be machined. Example of the specifications of the bed of a CNC lathe:[6]​.

Carriage positioning adjustment

Despite the quality of the elements involved in the mobility of the longitudinal and transversal carriages, there is no total guarantee of being able to achieve the position of the tools at the programmed level.

To correct possible positioning errors there are two electronic systems, one of them direct and the other indirect system. The direct positioning adjustment system uses a measuring ruler located on each of the bench guides, where an optical reader acts) that exactly measures the position of the carriage, transferring the deviations that exist to the CPU (Central Processing Unit) where it is automatically reprogrammed until the correct position is achieved.[7]​.

Tool holder

The CNC lathe uses a drum as a tool holder where six to twenty different tools can be located, depending on the size of the lathe or its complexity. The tool change is controlled by the machining program, and with each change, the carriages return to a position where the rotation and selection of the appropriate tool occurs to continue the machining cycle. When the machining of the part is finished, the carriages return to the initial position of withdrawal from the work area so that it is possible to change parts without problems. The tool holder drum, known as a revolver, has a built-in servomotor that makes it rotate, and a hydraulic or pneumatic system that locks the revolver, thus giving a precision that is normally between 0.5 and 1 micron of a millimeter. The tools have to be adjusted to appropriate coordinates in an accessory external to the lathes according to the dimensions indicated by the program. In most cases, we work with interchangeable carbide inserts, so when the insert needs to be replaced, it is not necessary to remove the tool holder from its housing.[8]​.

TOOL SETTER

This accessory allows us to facilitate the setting of the tools to be used in machining. The tool setting probes are easily installed in machining centers and CNC turning centers, which allows automated operation with the following benefits:.

Accessories and peripherals

Machine accessories are those pieces of equipment that are purchased from an external supplier as part of the machine, because they are universally applicable to that type of machine. For example, a car battery is an accessory.

All machines that have built-in CNC operation require a series of accessories, which in the case of a lathe are specified in the following:[9]​.

CPU (Central Processing Unit)

The UCP or CPU is the calculation brain of the machine, thanks to the microprocessor it incorporates. The computing power of the machine is determined by the installed microprocessor. Any of the CPUs on the market can be installed on each machine, for example: FAGOR, FANUC, SIEMENS, etc. The normal thing is that the client chooses the characteristics of the machine they want and then chooses the UCP that best suits them in terms of features, price, service, etc.

The main functions entrusted to the UCP are to develop the command and control orders that the machine must have in accordance with the machining program that the programmer has established, such as calculating the exact position that the tools must have throughout the work process, by controlling the displacement of the corresponding longitudinal and transverse carriages. It must also control the technological factors of machining, that is, the spindle revolutions and the work advances and rapid movement as well as the tool change.

On the other hand, the CPU integrates the different system memories, which can be EPROM, ROM, RAM and Buffer, which serve to store programs and act as a hard drive of any computer.

As an input peripheral "Peripheral (computer science)"), the most significant and important is the keyboard "Keyboard (computer science)") which is installed on the machine's control panel, from where corrections and modifications can be made to the initial program, including the creation of an individual machining program. There are many types of input peripherals with greater or lesser complexity, which if they have to be built to be proof against aggressive environments such as those found in workshops.

The most important output peripheral "Peripheral (computer science)") is the monitor, which is where we are informed of the machining execution process and we can see all the values ​​of each sequence. We can also control the manual movement of the carts and other mobile elements of the machine.[10]​.

Before starting to prepare a machining program, you must know well the machining that is going to be carried out on the lathe, the dimensions and characteristics of the starting material, as well as the number of pieces that make up the series that must be machined. With this prior knowledge, the system for fixing the piece on the lathe, the technological conditions of machining in terms of cutting speed, feed and number of passes are established.

Likewise, the geometric parameters of the machining are established, indicating the arrival and departure levels of the tools, and the tools to be used and their qualities are also selected.

Head rotation speed. This data depends on the characteristics of the material, the degree of machining desired and the type of tool used. The program allows you to adapt the rotation speed at any time to the most convenient speed. It is represented by the letter (S) and can be expressed as cutting speed or revolutions per minute of the head.

Work progress. There are two types of advance for the cars, one of them very fast, which is the approach advance or retreat to the starting point, and another which is the working advance. This is also a function of the type of material, machining quality and degree of surface finish. The program allows you to adapt the most convenient progress at any time. It is represented by the letter (F) and can be expressed in millimeters per revolution or millimeters of advance per minute.

Another important factor to determine is that every program must indicate the position location that has been chosen to reference the part, which is called "piece zero." Starting from part zero, all the geometry of the machining program is established.

Numerical control is a machine tool that helps us in the machining of metalworking parts. SH.

La estructura de un programa de torneado está conformado por una serie de secuencias y funciones donde se van programando las tareas que debe realizar la máquina de acuerdo con los parámetros de la pieza y las condiciones tecnológicas de su mecanizado. Existen varios fabricantes de ordenadores para tornos. En este artículo para ejemplificar un tipo de programación se toma referencia el modelo 8050 que fabrica la empresa española Fagor.[11]​.

Sequence number N

The set of non-contradictory orders that can be given to the machine at once is called a sequence. They are identified by the letter N, and on a normal lathe up to 9999 successive orders can be given. If the program is not very long, it can be numbered 10 by 10, in case it is necessary to introduce an unforeseen complementary order, thus we will have N10, N20, N30, etc. or we could have, N10, N11, N20, etc.[12]​.

Preparatory functions G

Under the letter G accompanied by a number, a wide variety of functions are grouped that allow the lathe to perform the appropriate and necessary tasks for its work.

There are five basic types of preparatory functions:

1- Mobility functions The most important mobility functions are the following:.

G00. Quick scroll. Indicates the fastest possible movement of the tool carriage, from the reference point to the point where each tool begins work. Special care must be taken when using this function since the trajectory is not controlled by the user but rather the lathe acts based solely on the maximum travel speed. It is never mechanized with it. It only acts at the beginning of the program, each time a tool change occurs, and at the end of the program when returning to the reference point.

G01. Linear interpolation. Indicates that the tool is moving at the programmed work feed, allowing the classic turning and facing operations as well as the machining of cones "Cone (geometry)").

G02 Circular interpolation to the right (clockwise) It is used when it is necessary to machine spherical or radial areas with controlled speed.

G03. Circular interpolation to the left (counterclockwise). It is used when it is necessary to machine empty spherical areas, or left-hand radii.

There are other G mobility functions, which are less important and depend on the equipment installed in the machine.

2- Technological functions The technological functions are those that refer to the way of programming the speed of the head and the work progress. The head rotation speed can be programmed to the desired revolutions per minute, for which function G97 will be prefixed, or it can be programmed to rotate at a constant cutting speed in m/min. In this case it is indicated with function G96. The same happens with the work advance, if you want to program the advance in mm/rev, the G95 function is prefixed and if you want to work in mm/min, the G94 function is prefixed.

3- Conversion functions The most important function of this group is the one that corresponds to the origin transfer to locate the piece zero that is carried out using the G59 function. There are also functions if the dimensioning is in inches or millimeters. Although it has already pre-established the one that will be used normally. Another case of conversion is if it is programmed with absolute dimensions or incremental dimensions.

4- Special machining functions. The most popular of these functions is the one that corresponds to a threading cycle represented by function G33. Other functions of this type are facing, drilling, tapping, reaming, etc.

5- Modal functions. In CNC programs, there are functions that, once programmed, remain active until a contrary function is programmed, or the program is terminated. These functions are called modal functions. As many functions as desired can be programmed in a block, as long as they are not incompatible with each other. For example, functions G00 and G01 cannot be programmed in a block.[13]​.

X-Z coordinate programming

Dimension programming is understood as specifying in the program the paths that the tools must perform to form the profile of the piece in accordance with its plane. Programming can be done using X and Z coordinates or polar coordinates. Also using the appropriate G function, the dimensions can be programmed in both millimeters and inches. To correctly program the dimensions, it is necessary to know well the excess material that must be removed, to determine the number of passes that must be made as well as the surface roughness that the machined finishes must have, as well as the way to hold the part in the machine and its rigidity.

T-D Tool Programming

Numerical control lathes have a front drum where a variable number of tools can be housed, generally from 6 to 20 different tools. The tools are programmed with a letter T followed by the number it occupies on the drum, for example T2, the letter T is the initial of this word in English (tool). As each tool has a different length and a different cutting tip radius, it is necessary to enter the correct values ​​for each tool into the program so that the program can run normally.

Apart from the length of the tool, there are G functions to introduce a correction according to the value of the radius of the tool at the cutting tip. Tool radius compensation is of great importance in machining, especially in parts that contain irregular profiles. Lathe tool plates always have rounded tips, this way they are more rigid. The smaller the radius of the tip, the less tendency it has to splinter.[14]​.

F-S technological factors

The technological factors that must be taken into account when developing a program are the following:

These factors are what will determine, among other things, the following elements.

Auxiliary functions M

Auxiliary functions are used to establish the operation of the machine. Such as starting and stopping the main drive or end of the program.[15]​.

Advantages:.

The following can be indicated as disadvantages:

The lathe has evolved so much that it is no longer just about removing material at high speed, but the parameters that make up the process have to be closely controlled to ensure the final results of economy, quality and precision.

The way of treating the chip becomes a complex process, where all the technological components of machining are involved, so that it can have the size and shape that does not disturb the work process. If this were not the case, masses of long, fibrous chips would quickly accumulate in the machining area, forming tangled and uncontrollable skeins.

The shape that the chip takes is mainly due to the material being cut and can be ductile material as well as brittle and fragile.

The feed at which you work and the depth of the pass are quite responsible for the shape of the chip, and when it cannot be controlled with these variables, you have to resort to choosing the tool that incorporates an effective chip breaker.[17]​

Greater efficiency than a normal lathe means greater speed.

Today dry turning is completely viable and is used in numerous applications. There is a recent trend to carry out dry machining whenever the quality of the tool allows it.

A higher cutting temperature zone can be a positive factor in many cases.

However, dry machining is not suitable for all applications, especially for drilling, threading and boring to ensure chip evacuation.

It is necessary to carefully evaluate operations, materials, parts, quality requirements and machinery to identify the benefits of eliminating the refrigerant contribution.[18]​.

In turning there are six key parameters:.

CNC lathes, due to their operating mechanisms, allow the machining conditions to be adjusted to the maximum and therefore achieve the best possible turning time.[19]​.

These parameters are related by the following formulas:.

Generally, the optimal cutting speed of each tool and its feed rate are indicated by the tool manufacturer or, failing that, in the machining technical manuals.