2021 – Page 31 – CNC Machining & Turning, Milling, Metal parts

Advantages of CNC computer gong processing

Master the processing principle and process. When using the common CNC machining technology, the processor should follow the principles of rough machining first, then finish machining, preventing the workpiece from thermal change, reducing vibration and so on. At the same time, also have the ability to deal with all kinds of unexpected problems, such as: how to adjust the tool speed.
Familiar with automatic or manual operation of CNC machining. The machinist should know clearly what process needs manual operation, what is the normal operation state of the machine tool when it is operated manually, what process is suitable for automatic operation, and what state the machine tool should be in. Professional CNC processing staff said, familiar with the above operation, help to carry out the processing work, and can deal with any situation freely.

The above is the basic skills of professional CNC processing personnel. Only by mastering these skills can we complete CNC processing operation independently. In order to become a qualified CNC machining worker, only by constantly asking questions and practicing in the work can we make our technology more solid.

Collision detection of NC machining simulation system

Due to the high cost of NC machining, in order to save the cost, a NC machining simulation system is developed. NC machining simulation system can reduce or even completely eliminate the process of trial cutting and manual verification. Before the actual processing of new NC machining program, the programmer can use NC machining simulation system to carry out virtual machining environment and machining process on the computer, and detect the possible problems in the program design.

In the process of NC machining, it is easy to over cut, under cut and other phenomena. At the same time, the damage of the tool, or the processing of waste products, the interference and collision between parts and tools, tools and fixtures, tools and worktable, will cause a certain waste of cost to the production. The NC machining simulation system can simulate the relevant programs well and reduce the loss to the greatest extent.

Before the actual processing, the programmer can confirm whether the finished cutting product is consistent with the original design drawing through the simulation system, and can make better detail analysis.

collision detection

In the actual processing, five axis NC machining has more advantages than three-axis NC machining, can achieve a wider range, has faster material and efficiency, can reduce processing time and improve surface accuracy. However, because of the high degree of freedom of the two additional rotating shafts, it is easy to collide and damage the machine tool.

Therefore, before the actual processing, we need to use the NC machining simulation system to detect the collision. The main detection algorithms are as follows

The machine tool includes many parts, but the collision detection algorithm between different parts is similar. The simulation system takes the tool, workpiece and fixture as the main research object to detect the possible global collision.

According to the tool location, the grid voxel model of the cutter head scanning body and the grid voxel model of the cutter handle scanning body are solved respectively. The tool holder scanning body is used to detect whether there is a global collision between the tool, workpiece and fixture, and the tool head scanning body is used to calculate the intersection between the tool and workpiece.
A feature attribute of voxel model is cuboid envelope box, which is used for rough judgment. If the envelope box does not intersect, the objects surrounded in the envelope box must not intersect. At this time, the position data information of the object envelope box is updated, and other information remains unchanged, so as to prepare for the generation of the next cutter scanning volume and collision detection. Rough judgment can speed up the detection Speed.
Once a collision occurs, the system stops reading the data and reports the error information and the exact location of the collision. If there is no collision, the system will continue the teaching operation between the cutter head and the workpiece.

How to install workpiece in CNC machining center

Selection of machining center positioning datum:

There are three basic requirements for selecting benchmarks

(1) The selected datum should be able to ensure the accuracy of workpiece positioning, convenient and reliable loading and unloading.

(2) The calculation of the selected datum and the size of each processing part is simple.

(3) Ensure the machining accuracy.

6 principles for selecting positioning datum:

(1) Try to choose the design datum as the positioning datum;

(2) When the positioning datum and design datum cannot be unified, the positioning error should be strictly controlled to ensure the machining accuracy;

(3) When the workpiece needs to be clamped for more than two times, the selected datum can complete the machining of all key precision parts in one clamping and positioning;

(4) The selected benchmark should ensure the completion of as many processing contents as possible;

(5) In batch machining, the positioning datum of parts should coincide with the tool setting datum of workpiece coordinate system as far as possible;

(6) When multiple clamping is needed, the datum should be consistent.

Determination of machining center fixture:

Basic requirements for fixtures:

(1) The clamping mechanism shall not affect the feed, and the processing part shall be open;

(2) The fixture can be installed directionally on the machine tool;

(3) The rigidity and stability of the fixture are better.

Common fixture types:

(1) General fixture: such as vice, dividing head, chuck, etc;

(2) Modular fixture: modular fixture is composed of a set of general components with standardized structure and standardized size;

(3) Special fixture: fixture designed and manufactured for one or several similar processing items;

(4) Adjustable fixture: the combination of modular fixture and special fixture can ensure the machining accuracy and more flexible clamping;

(5) Multi position fixture: it can clamp multiple workpieces at the same time;

(6) Group Fixture: it is specially used for clamping workpieces with similar shape, size, positioning, clamping and processing methods.

Selection principle of machining center fixture:

(1) On the premise of ensuring machining accuracy and production efficiency, general fixture is preferred;

(2) Simple special fixture can be used for batch processing;

(3) Multi position fixture and high efficient special fixture for air pressure and hydraulic pressure can be considered for mass processing;

(4) When group process is used, group fixture should be used;

The best clamping position of the workpiece on the worktable of the machine tool: the clamping position of the workpiece should ensure that the workpiece is within the processing stroke range of each axis of the machine tool, and make the length of the tool as short as possible to improve the processing rigidity of the tool

How to process part curved surface with computer gong

Using CNC machining center to process the surface of these heterogeneous parts, the key work is to work out a reasonable processing program and select the appropriate processing tools. The latter work is relatively simple and can be completed quickly according to the die drawing and process requirements. The preparation of processing program is the most important part of the whole processing preparation work, and also the most important and most important part of the whole die processing One of the main jobs.

1、 Establish mathematical model

Before establishing a model, we should first consider the order and method of establishing each feature of the model, what to do first, what to do next, what method to use, and which modeling function to use. We must deal with this relationship properly when establishing a mathematical model.

2、 Determine machining coordinate system

The establishment of solid model is based on the working coordinate system, while the generation of tool position source file of NC machining center is based on the working coordinate system. The origin position of machining coordinate system should be convenient for rapid and accurate tool setting and dimension calculation.

3、 Planning tool position source file

According to the structural characteristics of different product surfaces, we can select three machining modules, plane milling, cavity milling and fixed axis contour milling, which have their own characteristics and complement each other to plan the machining tool position source files of various types of surfaces.

In a word, we should flexibly grasp the application characteristics of each module according to the processing of mold surface and contour surface, so that we can process our satisfactory products with high quality and high efficiency through CNC machining center.

Basic knowledge of CNC machining center

1、 CNC machine tool and CNC system

CNC means computer numerical control.

CNC machine tools

(1) for metal cutting

Hole processing, tapping, boring, milling, turning, thread cutting, cutting plane, contour processing, surface grinding, cylindrical grinding, internal grinding, etc.

(2) wire electrode cutting machine.

(3) punch, step punch, stamping, metal forming, bending and other machine tools.

(4) industrial robots.

(5) injection molding machine.

(6) testing and measuring machine.

(7) woodworking machinery.

(8) special material processing machinery: such as processing stone, glass, radioactive mineral, etc.

(9) special processing machinery

Laser processing machine, gas cutting machine, welding machine, drawing machine, printing machine, etc.

With the development of electronic technology, computer technology and it technology, at present, these machine tools and processing equipment can be controlled by numerical computer with numerical data, which is called CNC control. Is a metal processing machine tool – vertical machining center of the general structure.

CNC system

CNC system means computer numerical control system. It is the basic configuration diagram of a CNC system. CNC control of machine tool is a kind of integrated control technology, which is a typical CNC control system.

A CNC system includes:

(1) CNC control unit (numerical controller part).

(2) servo drive unit and feed servo motor.

(3) spindle drive unit and spindle motor.

(4) PMC (PLC) controller.

(5) input / output (I / O) list of control signal of machine tool strong current cabinet (including tool magazine)

Yuan.

(6) position measurement and feedback unit of machine tool (usually included in servo drive unit).

(7) external shaft (Mechanical) control unit. Such as: tool magazine, exchange table, upper

Drive shaft of cutting manipulator, etc.

(8) information input / output equipment. Such as computer, disk drive, memory card, keyboard, special information equipment, etc.

(9) network. Such as Ethernet, hssb (high speed data transmission port), RS-232C port and local area network of processing site. I / olinki servo amplifier and motor are used to drive and control external machinery. The hardware of CNC unit (controller part) is actually a special microcomputer. It is the core of machine tool control designed and produced by CNC equipment manufacturer.

Basic skills of professional CNC processor

Master the processing principle and process. When using the common CNC machining technology, the processor should follow the principles of rough machining first, then finish machining, preventing the workpiece from thermal change, reducing vibration and so on. At the same time, also have the ability to deal with all kinds of unexpected problems, such as: how to adjust the tool speed.
Familiar with automatic or manual operation of CNC machining. The machinist should know clearly what process needs manual operation, what is the normal operation state of the machine tool when it is operated manually, what process is suitable for automatic operation, and what state the machine tool should be in. Professional CNC processing staff said, familiar with the above operation, help to carry out the processing work, and can deal with any situation freely.

CNC computer gong processing to prevent collision

collision detection

Therefore, before the actual processing, we need to use the NC machining simulation system to detect the collision. The main detection algorithms are as follows

According to the tool location, the grid voxel model of the cutter head scanning body and the grid voxel model of the cutter handle scanning body are solved respectively. The tool holder scanning body is used to detect whether there is a global collision between the tool, workpiece and fixture, and the tool head scanning body is used to calculate the intersection between the tool and workpiece.
A feature attribute of voxel model is cuboid envelope box, which is used for rough judgment. If the envelope box does not intersect, the objects surrounded in the envelope box must not intersect. At this time, the position data information of the object envelope box is updated, and other information remains unchanged, so as to prepare for the generation of the next cutter scanning volume and collision detection. Rough judgment can speed up the detection Speed.
Once a collision occurs, the system stops reading the data and reports the error information and the exact location of the collision. If there is no collision, the system will continue the teaching operation between the cutter head and the workpiece.

Characteristics of CNC machining center

CNC machining center has good processing consistency and economic benefits. Compared with other CNC machine tools, it has the following characteristics

When the workpiece is complex and the process flow is very long, it can eliminate the human interference factors in the process flow, and has high production efficiency and quality stability.
Due to the centralized working procedure and the automatic tool changing device, the workpiece can complete the complex processing of milling, drilling, boring, expanding, reaming and tapping with accuracy requirements after one clamping.
When there is an automatic exchange table, when a workpiece is being processed, the other table can realize the clamping of the workpiece, so as to greatly shorten the auxiliary time and improve the processing efficiency.
The larger the tool capacity is, the wider the machining range is, and the higher the flexible program is.

Steps of CNC machining precision parts

CNC machining mainly refers to the use of digital information recorded on the media to control the machine tool, so that it can automatically perform the specified processing tasks. Numerical control machining can ensure the products to achieve high machining accuracy and stable machining quality; the operation process is easy to achieve automation; high productivity, short production cycle; can reduce a large number of process equipment to meet the needs of rapid product upgrading; it is usually closely linked with CAD to achieve the transformation of design ideas to the final product.

In the whole CNC process, we should focus on the relationship between the processes and the significance of each step. Broadly speaking, the whole process consists of product analysis graphic design process planning path generation path simulation path output processing inspection.

Product analysis through product analysis should obtain certain composition information and some specific processing requirements.
Graphic design graphic design should be based on the detailed analysis of the product, determine the type of graphics by analyzing the processing requirements, and draw through the graphics software.
Path generation the process of path generation is that we realize the process planning by software, and optimize the tool path by setting parameters.
Through the analysis of the appearance and processing requirements of the workpiece product in the early stage of process planning, each processing step is reasonably established from the overall situation of processing.
After the path simulation path is generated, we generally have no intuitive sense of its final performance on the machine tool. Here we can check the possible problems through path simulation, so as to reduce the scrap rate of actual processing. The general inspection focuses on the effect of the workpiece appearance, whether it is overcut or undercut, and whether the process planning of the path is reasonable.
Path output path output is a necessary step for software design and programming to realize on the machine tool. Through path output, the intermediate reference can establish a connection between the two. If you have NC professional background, it can also be understood as the post-processing of tool path.

Deviation of processing accuracy of computer gong

With the rapid development of CNC machining center, the replaceable headstock machining center has appeared. It is equipped with a number of automatically replaceable multi axis headstock with cutting tools, which can process the workpiece at the same time. After decades of development, the current CNC lathe has achieved computer control and has been widely used in industry, especially in the mold manufacturing industry. Horizontal machining center generally has indexing turntable or numerical control turntable, which can process all sides of the workpiece; it can also make joint movement of multiple coordinates to process complex space surface. The vertical machining center generally does not have a turntable, only for the top surface processing. In addition, there are compound machining centers with vertical and horizontal spindles, and vertical and horizontal adjustable machining centers whose spindles can be adjusted into horizontal or vertical shafts. They can process five surfaces of the workpiece.

The automatic tool changing device of CNC machining center of milling machine is composed of tool magazine and tool changing mechanism. There are many kinds of tool magazine, including disc type and chain type. The storage capacity of chain magazine is large.

The tool change mechanism exchanges tools between the machine tool spindle and the tool magazine, commonly known as the manipulator; there are also no manipulator and the spindle directly exchanges tools with the tool magazine, known as the armless tool change device.

High precision and stable quality. It is processed according to the instruction given by the digital pattern. Under normal circumstances, there is no need for manual interference in the labor process, which eliminates the deviation caused by the dominator. When planning to manufacture CNC machine tools, many methods are adopted to make the parts of CNC machine tools reach higher accuracy and stiffness. The movement equivalent of CNC machine tool worktable is widely up to 0.01 ~ 0.0001mm, and the reverse clearance of feed transmission chain and screw pitch deviation can be compensated by CNC device. The high-grade CNC machine tool adopts the closed-loop control of grating ruler for worktable movement. The machining accuracy of CNC machine tool has improved from ± 0.01 mm to ± 0.005 mm or even higher. The positioning accuracy has reached ± 0.002mm to ± 0.005mm in the middle of 1990s. In addition, the transmission system and layout of CNC machine tools have high stiffness and thermal stability. By using the compensation technology, CNC machine tool can get higher machining accuracy than its own. In particular, the progress of a unified batch of parts production uniformity, product qualification rate is high, processing quality is stable. The selection of milling cutter diameter depends on different products and production batches, and the selection of cutter diameter mainly depends on the specifications of the equipment and the processing size of the workpiece.

Plane milling cutter

When selecting the diameter of the plane milling cutter, the power required by the cutter should be within the power range of the machine tool, and the diameter of the machine tool spindle can also be used as the basis for selection. The diameter of plane milling cutter can be selected according to d = 1.5D (D is the diameter of spindle). In batch production, the tool diameter can also be selected according to 1.6 times of the cutting width of the workpiece.

end mill

The selection of end mill diameter should mainly consider the requirements of workpiece processing size, and ensure that the power required by the tool is within the rated power range of the machine tool. If it is a small diameter end mill, we should mainly consider whether the maximum revolution of the machine tool can reach the minimum cutting speed of the tool (60m / min).

Slot cutter

The diameter and width of the groove milling cutter should be selected according to the size of the workpiece to be machined, and the cutting power should be ensured within the allowable power range of the machine tool. Before using the CNC machine tool, you should read the manual of the machine tool and other relevant information carefully, so as to operate the machine tool correctly, and pay attention to the following points:

(1) The PLC program of the machine tool is designed by the machine tool manufacturer according to the needs of the machine tool, and does not need to be modified. Incorrect modification, operation of the machine tool may cause damage to the machine tool, or even injury to the operator;

(2) It is suggested that the machine can run continuously for up to 24 hours. If the continuous running time is too long, the service life of the electrical system and some mechanical components will be affected, which will affect the accuracy of the machine

(3) The operators and maintainers of machine tools must be professionals who have mastered the corresponding professional knowledge of machine tools or have received technical training, and must operate the machine tools according to the safety operation regulations and safety operation regulations