CNC Technology – Page 25 – CNC Machining & Turning, Milling, Metal parts

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.

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.

CNC computer gong processing to prevent collision

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.

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

How to process complex parts with computer gong

The continuous fine blanking die for complex parts is the frontier basic technology of fine blanking technology, and it is expected to promote the whole fine blanking technology in China. Taking the synchronizer gear ring, clutch plate, longitudinal compound continuous fine blanking process and continuous fine blanking die for complex parts as the breakthrough point, the key technology of fine blanking die design and manufacturing is studied, so as to realize the rapid improvement of fine blanking die technology in China and shorten the gap with advanced countries as soon as possible.

Study on the life promotion of fine blanking die and its related key technologies

Die life is a comprehensive reflection of die material, small craft and supporting product level,

It can not only solve the problem that the life of fine blanking die is too low, but also promote the technical development of die materials, fine blanking process, supporting tooling and other auxiliary products.

Research and development of fine blanking precision forging composite technology

Precision blanking and precision forging are two advanced manufacturing technologies developed in parallel. If the precision blanking parts are too thick and need precision forging, the precision forging must be too thin. They are closely related. The basic idea of developing precision forging and fine blanking compound process is to find the combination point of the two processes (such as gear parts with wheel hub and cam parts with short shaft). The precision forging in China has a long history and has a high level, so it is a good way to improve the overall level of precision blanking technology in China.

How to program CNC computer gong processing

NC machine tool programming technology is not a very short period of time to learn, need to learn step by step, and slowly accumulate experience. Mastering this technology is not only the theoretical level of engineers, but also the practical experience and practical ability of senior technicians.

This process is the basis of programming. If you don’t know the technology, you can’t say it’s programming. Therefore, to master the programming technology of CNC machine tools, you must first become a craftsman.
Proficient in CNC programming and computer software application.

3, skilled CNC machine tools. It takes 2-3 years to study. In this process, we need to learn how to operate the system, fixture installation, part benchmark alignment, tool presetting, set zero offset, set tool length compensation, radius compensation, tool and handling handle, cutting tool grinding, part measurement (skilled use of vernier caliper, micrometer card, micrometer, micrometer, diameter bar meter), etc.

4, must have good fixture foundation and measurement technology.

Familiar with CNC machine tools. Proficient in CNC machine maintenance.
Cultivate good habits and adapt to the characteristics of CNC processing. In this case, suitable for CNC machining master should be humble, rigorous, calm, serious thinking, orderly and persuasive.

CNC computer gong processing light knife

A set of products usually have several or more than ten parts. The main matching dimensions of these parts are guaranteed by computer gong processing. It is very important to choose a reasonable tolerance, especially some product design drawings do not consider the matching problem. Bottom, surface, shell fit, shape is no doubt 0 to 0 fit, positioning is guaranteed by the mouth, concave mouth and convex mouth tolerance is generally 0.1 mm, unilateral. The fit on the big body is like a transparent mirror. The shape of the general accessories is 0.1 ~ 0.2 smaller than the size on the big body. The shape of the movable accessories on the big body, such as buttons, is 0.1 ~ 0.5 smaller than the shape on the big body. The surface shape of the accessories on the big body is generally consistent with the surface shape on the big body, which can be removed from the big body.

1、 Exit angle (draft angle)

All plastic molds should have a mold angle, otherwise they will be scratched. If it is not indicated in the drawing, you can discuss with the mold maker. The mold angle is generally 0.5 ~ 3 degrees. If the mold is etched, the mold angle should be larger, 2 ~ 5 degrees, depending on the thickness of the etched pattern.

2、 Cutting problem

Most of the time, when the cutter is just milled, the amount of cutting is relatively large, which is easy to cause the cutter to break and bounce. At this time, you can first roughen the lower cutter position, or lift the cutter away, or lower the cutter outside the material in the daytime. In a word, this problem should be fully considered. Grab the knife, spring the knife, drop the knife, when the processing capacity is relatively large, the knife clip is too long, the knife is too small, this often happens. When the processing capacity is relatively large, especially when the concentration feed is large, it is easy to occur. For example, when the depth of the smooth side is 50 mm and the diameter is 3 / 4, we can process it in 25 mm twice, so it is not easy to occur. Tool clamping is too long, the length of the tool is very important for processing, should try to clamp short, beginners are easy to ignore this problem, the program paper must indicate the length of the tool clamping. It’s easy to grab the knife when turning the corner. The solution is to use a smaller knife to clear the corner layer by layer, and then change the larger knife to smooth the side.

3、 Sharpen a knife

The shapes of computer gongs are different, so we often need to grind all kinds of knives. When all kinds of molding knives are worn out, we also need to grind them. Only when we reach the following points can we grind a usable knife.

The four corners of the tool should be the same height.
A is higher than D.
The forward (tool face) of the tool is higher than the back, that is, it has a certain back angle.

4、 Milling direction

The reason is that the rigidity of the computer gong is relatively good, it is not easy to let the cutter, the back clearance is small, and the milling shape or inner groove is left compensation. When machining left and right symmetrical shapes, the profile tool path cannot be mirrored, otherwise the processing effect of the mirrored side is not good. In order to communicate with the operator of the machine tool, the program paper should include:

Program name
Tool size and length
Method of machining tool path
Machining allowance
Rough or light knife
Drawing file name 4

Process benchmark of high speed CNC machining

High speed CNC machining can change the shape and size of products, which plays a very important role.

The broad meaning of benchmark is “basis”. The datum in mechanical manufacturing refers to the points, lines and surfaces used to determine the geometric relationship between the geometric elements on the production object. According to different functions and applications, datum can be divided into design datum and process datum, and process datum can be divided into process datum, positioning datum, measurement datum and assembly datum.

The technology of high-speed CNC machining is the premise to ensure the production of high-quality parts.

On lathe, the shape and size of the blank can be changed by the rotary motion of the workpiece and the linear or curvilinear motion of the cutter, and it can be processed to meet the requirements of the drawing. Ordinary machine tools are more and more difficult to meet the needs of processing precision parts, at the same time, due to the improvement of production level.

The price of CNC machine tools is falling from time to time. CNC precision parts processing mainly includes ultra precision turning, mirror grinding and grinding.

The primary premise of CNC precision parts processing is the accuracy of process datum. Datum on mechanical drawings are represented by capital letters a, B, C, D, etc. with a specific reference symbol with circle. When the reference symbol is aligned with the surface and its extension line or the dimension limit of the surface, the surface is taken as the datum. When the datum mark is aligned with the dimension line, it means that the solid center line of the dimension is taken as the datum. It is a more general statement that the process is accurate.

Assembly benchmark refers to the precision used to determine the position of parts in components or products during assembly.

Measurement datum refers to the specification for the size and position of the machined surface to be measured during the inspection of parts. Positioning datum refers to the datum used for positioning the workpiece in the machine tool or fixture during machining.