肯堂 – Page 8 – CNC Machining & Turning, Milling, Metal parts

CNC precision machining circuit

When the machining precision of ultra precision parts is nanometer, or even atomic unit (atomic lattice distance is 0.1 ~ 0.2 nanometer), the machining method of ultra precision parts can not adapt to it. It needs to use the method of special precision parts machining, that is, the application of chemical energy, electrochemical energy, thermal energy or electric energy, to make these energies exceed the binding energy between atoms, so as to remove the surface defects In order to achieve the goal of ultra precision machining, some atoms are attached, combined or lattice deformed. This kind of processing includes mechanical chemical polishing, ion sputtering and ion implantation, electron beam exposure, laser beam processing, metal evaporation and molecular beam epitaxy.

The characteristic of these ultra precision parts machining methods is that the amount of material removed or added to the surface layer can be controlled very finely. However, to obtain the machining accuracy of ultra precision parts, it still depends on precision machining equipment and precise control system, and uses ultra precision mask as the intermediary. For example, in VLSI plate making, electron beam is used to expose the photoresist (see lithography) on the mask to make the atoms of the photoresist polymerize (or decompose) directly under electron impact, and then the polymerized or unpolymerized parts are dissolved by the developer to make the mask. Electron beam exposure plate making requires ultra precision processing equipment with positioning accuracy of ± 0.01 micron.

General principles for drawing up process route of precision parts

There are two steps in the process planning of precision parts. First of all, draw up the process route of parts processing, and then determine the process size of each process, the equipment and process equipment used, as well as the cutting specification, man hour quota, etc. These two steps are interrelated and should be comprehensively analyzed.

The process route of precision parts processing is to make the overall layout of the process. The main task is to select the processing method of each surface, determine the machining sequence of each surface, and the number of processes in the whole process.

General principles of process planning

Machining datum first

In the machining process of parts, the surface as the positioning datum should be machined first, so as to provide the precise datum for the subsequent process as soon as possible. It is called “benchmark first”.

Division of processing stages

Machining quality requirements of the surface, are divided into processing stages, generally can be divided into rough machining, semi finishing and finishing three stages. The main purpose is to ensure the processing quality, to facilitate the rational use of equipment, to facilitate the arrangement of heat treatment procedures, and to facilitate the detection of blank defects.

Face before hole

For parts such as box, bracket and connecting rod, the plane should be machined first and then the hole should be machined. In this way, the hole can be machined by plane positioning, the position accuracy of the plane and the hole can be ensured, and the machining of the hole on the plane is convenient.

Details of CNC machining miscellaneous parts

The parameters of the front center gear are: modulus M = 4, number of teeth z = 9, addendum height coefficient ha = 1, addendum clearance coefficient C = 0.25, radial modification coefficient X = 0.4, number of teeth k = 2, common normal wn = 19.5 + 0.2 + 0.1 (mm). CAXA does not provide professional gear modeling command and can model through function curve, but this method is more cumbersome and more difficult with modification coefficient.

It is difficult to guarantee the size of the curve groove at the lower end of the front side of the part, and the two 90 ° notches are not closed, so it is necessary to close the auxiliary line before programming.

There are two ellipses in different directions on the inner contour edge of the back, inner and outer hexagonal petals composed of arcs in the center, and two arc curve islands at the top and bottom. These elements need to be rounded in processing, so it is more convenient to choose a reasonable shape.

Analysis of parts processing technology

Using CAXA to manufacture engineering parts, there is no need to draw a complete part for reprocessing. Firstly, the downtime is long and the processing time is wasted. Secondly, when selecting local processing, the elements between parts will interfere, which is not convenient to draw the program track.

The software supports rough and finish machining only by drawing the contour line of the part when machining the plane contour elements. Surface machining can be programmed by solid or surface. In order to realize local machining, curved surface must be used, and some finishing commands can only be selected by curved surface.

The rough machining command can not only realize rough machining, but also be used as finish machining command.

The finishing command can use the track translation to form multiple levels and connect the tracks into a whole rough machining command; the rough machining command can change a layer of processing track into a finishing command by setting the layer height.

The plane contour elements of CAXA Manufacturing engineer can use the plane area rough machining and contour finish machining to complete the rough and finish machining of parts, and can also use the contour finish machining to do the rough machining. Surface roughing can use contour roughing, parameter line finishing and three-dimensional offset surface finishing commands for roughing and finishing.

Due to the high dimensional accuracy in the drawing, it is decided to adopt rough machining, semi finishing and finishing to achieve dimensional accuracy. Semi finishing and finishing adopt the same cutting tools and cutting parameters, which can correct various geometric errors of the cutting tools and elastic deformation of the parts. It is easy to ensure the size, and finish machining is also required for the important bottom surface.

The part is processed by FANUC CNC machining center, all tool paths are generated according to FANUC post format, and transmitted by CAXA’s own communication function according to FANUC settings, and large surface programs are processed online; the later processing programming ends with tool path.

Essential knowledge for CNC machining workers

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.

Selection and use of CNC machining fixture

(1) According to the characteristics and processing needs of machining center, the commonly used fixture types include special fixture, modular fixture, adjustable fixture, group fixture and workpiece unified reference positioning clamping system.

(2) The high flexibility of machining center requires that its fixture structure is more compact and simple than ordinary machine tool, clamping action is more rapid and accurate, auxiliary time is reduced as far as possible, operation is more convenient, labor-saving and safe, and enough rigidity and flexibility should be ensured. Therefore, pneumatic and hydraulic clamping devices are often used.

(3) In order to keep all the surfaces to be machined fully exposed, the fixture should be open as far as possible, and the space position of the clamping element should be low as possible, so there must be space for the tool path.

(4) Considering the minimum distance between the machine tool spindle and the worktable and the clamping length of the tool, the installation position of the fixture on the machine tool worktable should ensure that the processing content of the workpiece can be completed within the stroke range of the spindle.

(5) Automatic tool change and worktable exchange can not interfere with the fixture or workpiece.

(6) Sometimes, the positioning block on the fixture is used when installing the workpiece. In the process of processing, in order to meet the processing requirements of the front, back, left and right stations and prevent interference, the workpiece can be removed after clamping. In this regard, we should consider the problem of maintaining the positioning accuracy of the workpiece after removing the positioning element.

(7) Try not to change the clamping point in the middle of machining.

(8) Determine the best position of parts on the machine tool table

Causes of computer gong limit alarm

Cause analysis of positive and negative hard limit alarm of computer gong

Computer gong processing in normal circumstances will not appear this alarm, but what is the reason for this situation?

The contact of travel switch is pressed and stuck (over travel);
The travel switch is damaged;
There is open circuit, short circuit and no signal source in the travel switch circuit;
The limit stop cannot press the switch contact to the action position;
The PLC input point is burnt out.

Many times, due to the improper use of the operation and technical personnel, or the work handover is not in place, there will be some failures in the processing of computer gongs. How can we prevent the deformation of parts in the processing of computer gongs?

In order to meet the requirements of ultra-high speed machining, the computer gong machining will adopt the structure of spindle motor and machine tool spindle, which realizes the integration of variable frequency motor and machine tool spindle. The bearing of spindle motor adopts magnetic floating bearing, hydrodynamic bearing or ceramic rolling bearing. Deformation often occurs in the process of processing, how to prevent it?

1、 In order to reduce the influence of cutting force and cutting heat, the deformation caused by rough machining can be corrected in finish machining.

2、 In order to reduce the influence of clamping force, the following measures are taken to reduce the influence of clamping force

When radial clamping is used, the clamping force should not be concentrated on a radial section of the workpiece, but should be distributed over a larger area to reduce the clamping force per unit area of the workpiece.
The position of clamping force should be selected in the part with strong rigidity to improve the deformation of thin-walled parts under the action of clamping force.
Change the direction of clamping force, change the radial clamping to axial clamping.
In order to reduce the clamping deformation, the computer gong processes the process boss or thread to strengthen the rigidity of the workpiece. When processing, the special structure claw is used to clamp, and the convex edge is cut off at the end of processing.

Introduction of CNC computer gong

Fuselage part:

1) Casting, which is the most important part of the computer gong, directly affects the accuracy, stability, wear resistance of the computer gong and the service life of the machine tool. After the casting is finished, it is not immediately used in the production. The good casting is that it is after wind and rain, sun exposure, natural weathering, and some of them are soaked in sea water. After the casting does not change, it is taken to the processing. The machine tool made in this way is not easy to change, and can maintain the stability and accuracy of the machine tool for a long time.

2) Spindle, the spindle is used to directly face the workpiece, it is driven by the motor to work, high-speed rotation, the spindle is equipped with a tool handle, it can chip the workpiece, meet various production needs, the quality of the spindle will directly affect the processing accuracy, if the internal bearing is worn, it is easy to cause the swing of the spindle, the accuracy of the processed things naturally has a few deviations . At present, the rotation speed of the main shaft is generally about 8000 rpm, and the high-speed machine can achieve more than 20000 rpm, and each machine has only one main shaft.

3) The screw rod is also a part of the fuselage. It is driven by a servo motor and drives the displacement of the worktable through the copper sleeve of the screw rod to meet the processing needs. If there is a gap in the screw rod, it is also directly reflected in the processing accuracy and finish.

4) There are two kinds of motors: servo motor and frequency conversion motor. The servo motor has good stability, high power of spindle drive motor and low coordination rate of three-axis drive motor.

5) The coupling is installed between the screw rod and the motor, which is just a linkage function.

6) The lubrication cooling system consists of an automatic oil pump, a spindle oil cooler and a chip liquid circulation system. When the machine tool is working, the oil can be pumped once every few minutes, and the oil pipe is connected to every corner, such as screw rod, guide rail, etc. if the oil circuit is blocked, the guide rail will be easily worn and the accuracy will be affected. Spindle oil cooling is a circulating cooling system added to cool the spindle. It is necessary or not for the spindle with 8000 revolutions, and it must be equipped for the spindle with more than 8000 revolutions. In the chip liquid circulation system, the oil in the oil tank is pumped up by the oil pumping motor and flushed to the workpiece being processed.

7) Sheet metal, sheet metal requirements are not too high, as long as there is no oil leakage on the line, but also involves the appearance of beautiful, image problems.

In order to improve the service life of stamping die or plastic die (including injection die, extrusion die, blow mold, etc.), the relevant parts of die cavity are generally made of high-strength wear-resistant materials (such as various grades of alloy structural steel, alloy tool steel and stainless steel, etc.), which have high hardness after heat treatment and are difficult to be machined by conventional machining Methods to process. For decades, the best way to deal with this kind of difficult to machine materials is to use special machining.

Discussion on precision mold processing technology

Since its invention in Europe in 1920s, fine blanking technology has experienced more than 80 years. It is one of the most important precision plastic forming methods in the field of thick plate manufacturing. It is a method with high technical content and good economic benefits for the economic production of large quantities, high quality, multi-functional ferrous and non-ferrous metal parts. Fine blanking press completes a stamping process, through the processing of special fine blanking die, one or more high precision forming parts can be produced, which can be directly used for assembly. It has been widely used in the fields of electronics, computer, electric power, home appliances, automobile and aviation. According to incomplete statistics, there are about 4500 fine blanking machines and 10000 parts produced in 40 countries in the world. For example, there are nearly 100 kinds of fine blanking parts in a car (car), including gearbox fork, seat and seat belt angle adjuster, planetary gear, brake shoe and steel back.

China’s fine blanking die technology has made great progress in the Eleventh Five Year Plan period, and has made a series of scientific research achievements in fine blanking process, materials, fine blanking press, die base, die and lubrication. As of the end of 2008, nearly 20 provinces and cities in China have professional fine blanking production equipment, with more than 80 fine blanking presses (excluding hydraulic mold base), more than 5000 fine blanking employees, producing about 2000 kinds of fine blanking parts, and a number of independent fine blanking mold development demonstration bases have been formed. Metal materials are expanded from non-ferrous metal blanking to ferrous metal blanking. The blanking thickness of low carbon steel, low alloy steel and stainless steel can reach 12mm; the blanking thickness of non-ferrous metals such as aluminum alloy and copper alloy can reach 18mm; with the progress of die materials and treatment methods, as well as the spheroidization process of the punched plate Some hard high carbon steel, high alloy steel and other low toughness materials such as nickel base or cobalt base alloy materials are also used in the production of fine blanking parts. In addition, the proportion of self-developed progressive compound fine blanking die, transfer die and modular die in domestic fine blanking die has increased significantly, especially the progressive compound fine blanking die for complex parts of automobile transmission system has basically realized localization.

The research, development and application of finite element numerical simulation technology, structure optimization technology of fine blanking die, intelligent design and knowledge base technology of fine blanking die improve and enrich the technical connotation of fine blanking die in China. However, at present, the fine blanking enterprises are generally small in scale, scattered in resources, low in production efficiency, shortage of talents and incomplete in supporting. Although in the fine blanking die development has a certain development ability.

How to prevent wear of CNC parts

The common wear types in machining include running in wear, hard grain wear, surface fatigue wear, thermal wear, phase change wear and hydrodynamic wear.

Running in wear is a kind of wear under normal load, speed and lubrication, which develops slowly and has little effect on machining quality in a short time.

Hard grain wear is due to the parts themselves or from the outside into the machine tool hard particles, mixed into the processing area, by mechanical cutting or grinding, causing damage to the parts, which has a serious impact on the processing quality.

Surface fatigue wear is a kind of mechanical damage caused by micro cracks or pits under alternating load. This kind of wear is usually closely related to the pressure, load characteristics, parts material, size and other factors.

Hot wear is the heat generated in the friction process, which makes the parts soften and wrinkle. This kind of wear usually occurs in high-speed and high-pressure sliding friction, the destructive wear is relatively large, and accompanied by the nature of accident wear.

Corrosion wear is a kind of chemical action, that is, chemical corrosion causes wear. When the part surface contacts with acid, alkali, salt liquid or harmful gas, it will be subject to chemical erosion, or the part surface combines with oxygen to form hard and brittle metal oxide which is easy to fall off and wear the part.

Phase transformation wear is a kind of wear caused by long-term work at high temperature, the grain of metal structure on the surface of the part becomes larger when heated, and the grain boundary is oxidized, resulting in a small gap, which makes the part fragile and wear resistance decreased.

Hydrodynamic wear is caused by the impact of liquid or particles mixed in liquid on the surface of parts at a faster velocity.

CNC computer gong machining center code

The meaning of letters in NC program

O: Program number

N: Program segment number, set program sequence number

G: Preparation function

X / Y / Z: dimension character, axis movement command

A / B / C / U / V / W: additional axis movement command

R: Arc radius

I / J / K: arc center coordinates (vector)

F: Feed, set feed rate

S: Spindle speed, set the spindle speed

T: Tool function, set tool number

M: Auxiliary function, on / off control function

H / D: tool offset number, set tool offset number

P / X: delay, set delay time

P: Program number instruction, set subroutine serial number (such as subroutine call: m98p1000)

50: Repeat, set the repeat times of subroutine or fixed cycle (e.g. M98 P1000 L2, omitting L for L1)

P / w / R / Q: parameters, parameters of fixed circulation (e.g. tapping g98 / (G99) g84 x)_ Y_ R_ Z_ P_ F_)

Explanation of common G code

G00: positioning or rapid movement

G01: linear interpolation

G02: arc interpolation / helix interpolation CW

G03: circular interpolation / spiral interpolation CCW

G04: dwell time or delay time

For example: G04 X1000 (or G04 x1.0)

G04 P1000 stands for 1 second

G09: accurate stop or accurate stop check (check whether it is within the target range)

G10: programmable data input

G17: select xpyp plane XP: X axis or its parallel axis

G18: select zpxp plane YP: Y axis or its parallel axis

G19: select ypzp plane ZP: Z axis or its parallel axis

G20: Inch input

G21: mm input

G28: return to reference point detection

Format: G91 / (G90) G28 x__ Y__ Z__

Passing through the middle point x__ Y__ Z__ Return reference point (absolute value / increment value instruction)

G29: return from reference point

G91/(G90) G29 X__ Y__ Z__

From the starting point through the reference point back to the target point X__ Y__ Z__ Instruction (absolute value / increment value instruction)

G30 returns to reference points 2, 3, 4

G91/(G90) G30 P2 X__ Y__ Z__ Return to the second reference point (P2 may be omitted). )

G91/(G90) G30 P3 X__ Y__ Z__ ; return to the third reference point

G91/(G90) G30 P4 X__ Y__ Z__ ; return to the fourth reference point

X__ Y__ Z__ : through the middle point position (absolute value / incremental value instruction)

G40: tool radius compensation cancelled

G41: left tool radius compensation (along the feed direction, the tool is on the left side)

G42: right tool radius compensation (the tool is on the right along the feed direction)

G43: tool length compensation + direction

G44: tool length compensation – direction

G49: cancel tool length compensation

CNC computer gong Processing Cam Parts

Research on key technology of design and manufacture of continuous fine blanking die for complex parts

Continuous fine stamping die for complex parts is the frontier basic technology of precision punching technology. 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 the level of mold materials, small arts and supporting products. Taking the life of precision punching die as the leading point to solve the problem of too low life of precision die, it can not only solve the problem of too low life of the die in China, but also promote the development of die materials, fine blanking technology and 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 precision stamping composite process is to find the combination points of these two processes (such as gear parts with hub and cam parts with short shaft). However, precision forging in China has a long history and has a high level. It is a good way to improve the overall level of precision punching technology in China.