What Is CNC?
(Computer Numerical Control, Hereinafter referred to as CNC), Which refers to the use of discrete digital information to control the operation of machinery and other devices, which can only be programmed by the CNC operator.
Application of CNC Technology
The application and development of CNC technology are quite rapid, which greatly improves the productivity of mold processing. Among them, the CPU with faster operation speed is the core of the development of CNC technology. The improvement of the CPU is not only the improvement of operation speed, but the speed itself also involves the improvement of CNC technology in other aspects. It is precise because CNC technology has undergone such great changes in recent years that it is worth making a review of the current application of CNC technology in mold manufacturing.
Block processing time and the performance of CNC manufacturing has improved significantly due to the increased processing speed of CPUs and the adoption of high-speed CPUs by CNC manufacturers into highly integrated CNC systems. A more responsive, more responsive system achieves more than just a higher program processing speed. In fact, a system that can process part programs at a relatively high speed may also operate as a low-speed system, because even a fully functional CNC system has potential problems that can become the limiting bottleneck of processing speed.
Most mold shops and CNC manufacturers today realize that high-speed machining requires more than just shorter program processing times. In many ways, the situation is similar to driving a racing car. Does the fastest car always win the race? Even an occasional spectator knows that many factors other than speed affect the outcome of a race.
First, the driver’s knowledge of the track is important: He must know where there are sharp turns so that he can slow down just enough to get through the corners safely and efficiently. In the process of CNN machining, a mold with a high feed rate, the to-be-machined trajectory monitoring technology in the CNC service can obtain information about the appearance of sharp curves in advance, and this function plays the same role.
Likewise, the driver’s responsiveness to other driver actions and uncertainties is similar to the amount of servo feedback in a CNC machining center. Servo feedback in the CNC machining center mainly includes position feedback, speed feedback, and current feedback.
When a driver is driving around the track, the continuity of the action and whether he can brake and accelerate proficiently have a very important impact on the driver’s on-the-spot performance. Likewise, the CNC manufacturing system’s bell-shaped acceleration/deceleration and track-to-be-processed monitoring functions use slow acceleration/deceleration instead of sudden shifting to ensure smooth acceleration of the machine.
Beyond that, there are other similarities between racing cars and CNC manufacturing systems. The power of the racing engine is similar to the CNC drive and motor, the weight of the racing car can be compared with the weight of the moving components in the machine tool, and the stiffness and strength of the racing car are similar to the strength and rigidity of the machine tool. The CNC machining center‘s ability to correct certain path errors is very similar to the driver’s ability to keep the car in the lane.
Another parallel with the current CNC manufacturing is that the cars that are not the fastest tend to require well-rounded drivers. In the past, only high-end CNC cutting could ensure high machining accuracy while cutting at high speed. Today, it is also possible to do the job satisfactorily with the capabilities that are available in low- and mid-range CNC manufacturing. While a high-end CNC precision machining has the best performance currently available, there is also the possibility that you are using a low-end CNC cutting with the same machining characteristics as a mid-to-high-end CNC precision machining in its class. In the past, the factor that limited the maximum feed rate for mold processing was the CNC cutting, but today it is the mechanical structure of the machine tool. Even better CNC machining center won’t improve performance when the machine is already at its performance limit.
Intrinsic Characteristics of CNC System
The following are some basic CNC machining center characteristics in the current mold machining process:
1. Non-Uniform Rational B-Spline (NURBS) Interpolation of Curved Surfaces
This technique uses interpolation along the curve, rather than a series of short straight lines to fit the curve. Many of the CAM software currently used by the die and mold industry offer an option to generate part programs in NURBS interpolation format. At the same time, the powerful CNC machining center also provides 5 axis machining interpolation function and related features. These properties improve the quality of surface finishing, improve motor smoothness, increase cutting speeds, and enable smaller part programs.
2. Smaller Command Unit
Most CNC machining systems transmit motion and positioning commands to the machine tool spindle in units of not less than 1 micron. After making full use of the CPU processing power to improve this advantage, the smallest instruction unit of some CNC machining systems can even reach 1 nanometer (0.000001mm). After the command unit is reduced by 1000 times, higher CNC machining accuracy can be obtained, which can make the motor run more smoothly. The smooth operation of the motor enables some machine tools to run at higher acceleration without increasing the vibration of the bed.
3. Bell Curve Acceleration/Deceleration
Bell curve acceleration/deceleration, also called the S curve acceleration/deceleration, or crawling control. Compared with the way of using linear acceleration, Bell curve acceleration/deceleration this way can make the machine for better speedup. Compared with other acceleration methods, including the linear method and exponential method, the bell-shaped curve method can obtain smaller CNC precision machining positioning error.
4. Track to be Processed Monitoring
This technology of track to be processed monitoring is widely used and has numerous performance differences that differentiate the way it works in low-end CNC manufacturing control systems from the way it works in high-end CNC manufacturing control systems. Generally speaking, the CNC company realizes the preprocessing of the CNC turning program through the monitoring of the machining trajectory, so as to ensure better acceleration/deceleration control. Depending on the performance of different CNC machining, the number of blocks required for the monitoring of the track to be processed varies from two to hundreds, which mainly depends on the shortest processing time of the CNC turning parts program and the time constant of acceleration/deceleration. Generally speaking, in order to meet the CNC turning parts processing requirements, at least fifteen track monitoring blocks to be processed are required.
5. Digital Servo Control
The development of digital servo systems is so rapid that most machine tool manufacturers choose this system as the servo control system of machine tools. After using this CNC manufacturing system, CNC manufacturing companies can control the servo system in a more timely manner, and the CNC operator’s control of the machine tool also becomes more accurate.
The functions of the digital servo system of CNC machining are as follows:
1) The sampling speed of the current loop will be increased, coupled with the improvement of the current loop control, thereby reducing the temperature rise of the motor. This not only prolongs the life of the motor but also reduces the amount of heat transferred to the ball screws, improving the accuracy of the ball screw. In addition to this, the faster sampling speed can increase the gain of the speed loop, which can help improve the overall performance of the machine tool.
2) Since many new CNC machining centers are connected to servo loops using high-speed sequences, more motor and driver information can be obtained through communication links. This improves the maintenance performance of machine tools.
3) Continuous position feedback allows high precision CNC machining with high-speed feed. The speed of CNC machining center operation makes the rate of position feedback become the bottleneck restricting the speed of machine tools. In the traditional feedback method, with the change in the sampling speed of the external encoder of the CNC machining center and electronic equipment, the feedback speed is restricted by the signal type. With serial feedback, this problem will be solved very well. Precise feedback of CNC machining parts accuracy can be achieved even when the machine is running at very high speeds.
6. Linear Motor
In recent years, the performance and popularity of linear motors have improved significantly, so many machining centers have adopted this device. To date, Fanuc has installed at least 1,000 linear motors. Some advanced CNC machining technologies from GE Fanuc allow the linear motor on the machine to have a maximum output force of 15,500N and a maximum acceleration of 30g. The application of other advanced CNC machining technologies has reduced the size of the machine tool, reduced the weight, and greatly improved the cooling efficiency. All these CNC machining technologies advancements give linear motors greater advantages when compared to rotary motors: higher acceleration/deceleration rates; more accurate positioning control, higher stiffness; higher reliability; internal dynamic control move.
Additional features: Open CNC system
Machine tools using open CNC systems are developing rapidly. At present, the communication speed of the communication system available for selection is high, so there are many types of open CNC manufacturing structures. Most open systems combine the openness of a standard PC with the functionality of a traditional CNC router. The biggest advantage of this is that even if the hardware of the machine tool is outdated, the open CNC machining center still allows its performance to change with the existing technology and machining requirements. With the help of other software, other functions can also be added to the open CNC manufacturing. These properties can be closely related to mold processing, or they can be less related to mold processing. Typically, open CNC systems used in mold shops have these common functional options:
Inexpensive internet communication;
Adaptive control function;
Interfaces for bar code readers, tool serial number readers, and pallet serial number systems;
The ability to save and edit a large number of cnc parts programs;
Collection of stored program control information;
File processing function;
CAD/CAM technology integration and workshop planning;
Universal operation interface.
This last point is extremely important. Because the mold processing to the operation of simple CNC manufacturing demand is increasing. In this concept, the most important thing is that different CNC machining centers have the same operation interface. In general, operators of different machine tools must be trained separately because different types of machines, and machines from different CNC manufacturing services, use different CNC interfaces. Open CNC systems create the opportunity for the entire shop to use the same CNC control interface.
Now, the owner of the machine tool can design his own interface for CNC operation even if he does not know the C language. In addition, the controller of the open system allows the machine to operate in different ways according to the individual’s needs. In this way, operators, programmers, and maintainers can set up according to their own requirements. When in use, only the specific information they need appears on the screen. In this way, unnecessary page displays can be reduced, which helps to simplify CNC operations.
CNC 5 Axis Machining Introduction
CNC 5-axis machining is becoming more and more widely used in the manufacture of complex molds and complex parts. With CNC 5 axis machining, the number of tooling or/and machine tools required to machine a part can be reduced, the amount of equipment required for the CNC machining process is minimized, and overall CNC machining time is reduced. The ever-increasing capabilities of CNC manufacturing have allowed CNC manufacturers to offer more five-axis machining features.
Functions that used to be only available in high-end CNC are now also used in mid-range CNC products. These features make CNC 5-axis machining easier for those who have never used it before. Using the current CNC technology for 5 axis machining, five-axis machining has the following advantages:
Reduce the need for specialized tools;
Allows setting the tool offset after completing the part program;
Support the design of common programs, so that the post-processed programs can be used interchangeably between different machine tools;
Improve the quality of finishing;
It can be used for machine tools of different constructions so it is not necessary to specify in the program whether the spindle or the workpiece is rotating about the center point. Because this will be solved by the parameters of the CNC manufacturing and CNC machining center.
We can use the example of compensation of spherical milling cutters to illustrate why CNC 5 axes are particularly suitable for mold machining. In order to accurately compensate the offset of the spherical milling cutter when the part and the tool rotate around the central axis, the CNC machining center must be able to dynamically adjust the compensation amount of the tool in the three directions of X, Y, and Z. Ensuring the continuity of the cutting contact of the tool is conducive to improving the quality of finishing.
In addition, the use of 5-axis CNC machining is also reflected in Characteristics associated with rotating the tool around the spindle, characteristics associated with rotating parts around the spindle, and characteristics that allow the operator to manually change the tool vector.
When the central axis of the tool is used as the rotation axis, the original tool length offset in the Z-axis direction will be divided into three components in the X, Y, and Z directions. In addition, the tool diameter offset in the original X and Y-axis directions is also divided into three components in the X, Y, and Z-axis directions. Since in cutting engineering, the tool can be fed in the direction of the axis of rotation, all these offsets must be dynamically updated to account for the continuously changing orientation of the tool.
Another feature of CNC 5 axis machining called “tool center point programming” allows programmers to define the path and center point speed of the tool, and the CNC ensures that the tool moves according to the program through commands in the direction of the rotary axis and linear axis. This feature makes the center point of the tool no longer change with the change of the tool, which also means that in the CNC 5-axis machining, the tool offset can be directly input as in the three-axis machining, and it can also be explained by post-programming again. Change in tool length. The motion of the spindle by making it rotate simplifies the post-processing of the tool programming.
By using the same function, the workpiece can be rotated around the central pivot, and the machine tool can also obtain rotational motion. The newly developed CNC machining center can adjust the fixed bias and rotation axis dynamically to match the movement of parts. CNC systems also play an important role when operators use manual methods to achieve slow machine feed. The newly developed CNC system also allows the shaft to be fed slowly along the direction of the tool vector and to change the direction of the tooltip vector without changing the position of the tooltip.
These features make it easy for operators to use the 3+2 programming method currently widely used in the mold industry when using a five-axis machine tool. However, with the gradual development and acceptance of new CNC 5-axis machining capabilities, true 5-axis tooling machines may become more common.