CNC Technology – Page 22 – CNC Machining & Turning, Milling, Metal parts

Six advantages of computer gong processing parts

In addition to the characteristics of ordinary milling machine, computer gong processing also has the following six functional advantages:

Parts with strong adaptability and good flexibility, especially complex contour shape or difficult to control size, such as mold parts, shell parts, etc;
It can process parts that can not be processed by ordinary machine tools or are difficult to process, such as complex curve parts described by mathematical models and three-dimensional curved surface parts;
It can process the parts that need to be processed by multiple processes after one clamping and positioning;
High production efficiency, CNC milling machine generally does not need to use special fixture and other special process equipment, when replacing the workpiece, it only needs to call the processing program, clamping tools and adjust tool data stored in the CNC device, thus greatly shortening the production cycle. Secondly, the CNC milling machine has the functions of milling machine, boring machine and drilling machine, which makes the process highly concentrated and greatly improves the production efficiency. In addition, the spindle speed and feed speed of CNC milling machine are continuously variable, so it is beneficial to select the best cutting parameters;
The pulse equivalent of the numerical control device is generally 0.001mm, and the high-precision numerical control system can reach 0.1 μ M. in addition, the numerical control machining also avoids the operation error of the operator;
High degree of production automation, can reduce the labor intensity of the operator. It is beneficial to the automation of production management.

CNC computer gong processing tool requirements

There are specific requirements for the size and accuracy, such as 1 mm plus or minus how many microns, etc. if the size is wrong too much, it will become a scrap. At this time, it is equivalent to reprocessing, which is time-consuming and laborious. Sometimes even the whole processing material will be scrapped, which leads to the increase of cost. At the same time, the parts are definitely unusable.
For the processing of high-precision parts, the main requirements are the size, such as the diameter of the cylinder, there are strict requirements, positive and negative errors within the specified range are qualified parts, otherwise they are unqualified parts; There are also specific and strict requirements for length, width and height, as well as positive and negative errors. For example, if the diameter of an embedded cylinder (take the simplest basic parts as an example) is too large and exceeds the allowable error range, it will cause the situation that it cannot be inserted. If the actual diameter is too small and exceeds the lower limit of the allowable negative error, it will cause the problem that it is too loose and not firm. These are all unqualified products, or the length of the cylinder is too long or too short, which is beyond the allowable range of error. They are all unqualified products, and they have to be scrapped or reprocessed, which will inevitably lead to the increase of cost.
The requirement of high-precision parts processing is actually the most important dimension problem. It must be processed in strict accordance with the additional drawings. The actual size of the processed parts will not be exactly the same as the theoretical size of the drawings, but as long as the processing size is within the allowable error range, they are all qualified parts. Therefore, the requirement of precision parts processing is to process in strict accordance with the theoretical size Line processing.
The second is the advanced precision parts processing equipment and testing equipment. The advanced processing equipment makes the processing of precision parts simpler, higher precision and better effect. The detection device can detect the parts that do not meet the requirements, so that all the products sent to customers can really meet the requirements.

Basis of high precision CNC machining

CNC machining can change the shape and size of products, which plays a very important role. Many friends don’t know the process benchmark of high speed CNC machining.

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.

Computer gong processing machine debugging

Before the debugging of CNC computer gong processing machine tool, the debugging methods for the precision and function of CNC computer gong processing machine tool are as follows:

Using precision level instrument and other testing tools, the main bed level of the computer gong processing machine tool is precisely adjusted by adjusting the pad iron, so that the geometric accuracy of the machine tool can reach the allowable tolerance range;
For the automatic tool changing device, adjust the position of tool magazine, manipulator, stroke parameters, etc., and then check the action with instructions to ensure accuracy;
For the machine tool with APC automatic exchange table, after adjusting the relative position, carry out automatic exchange;
After the adjustment of the machine tool, carefully check whether the parameter setting values in the numerical control system and the programmable controller conform to the data specified in the random index, and then test the main operation functions, safety measures, and the execution of common instructions.
Check the auxiliary functions and accessories of the machine. CNC computer gong NC machining is the basis of modern manufacturing technology, this invention for the manufacturing industry, has epoch-making significance and far-reaching influence.

Introduction of CNC machining center coordinates

Machining center is often divided into vertical machining center and horizontal machining center according to the state of the spindle in the space. The vertical machining center whose spindle is vertical in the space is called vertical machining center, and the horizontal machining center whose spindle is horizontal in the space is called horizontal machining center. Spindle can be vertical and horizontal conversion, known as vertical and horizontal machining center or five machining center, also known as composite machining center. According to the number of machining center columns, there are single column type and double column type (gantry type).

According to the coordinate number of machining center movement and the coordinate number of simultaneous control, there are three axis two linkage, three axis three linkage, four axis three linkage, five axis four linkage, six axis five linkage, etc. Three axis and four axis refers to the number of motion coordinates of the machining center. Linkage refers to the number of coordinates that the control system can control at the same time, so as to realize the position and speed control of the tool relative to the workpiece. Machining center is often divided into vertical machining center and horizontal machining center according to the state of the spindle in the space. The vertical machining center whose spindle is vertical in the space is called vertical machining center, and the horizontal machining center whose spindle is horizontal in the space is called horizontal machining center. Spindle can be vertical and horizontal conversion, known as vertical and horizontal machining center or five machining center, also known as composite machining center. According to the number of machining center columns, there are single column type and double column type (gantry type).

CNC computer gong processing sequence

1、 Face before hole

For the 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 processed by plane positioning to ensure the orientation accuracy of the plane and the hole, and bring convenience to the processing of the hole on the plane.

2、 Machining datum first

Parts in the processing process, as a positioning reference surface should be processed first, in order to provide fine reference for the subsequent process as soon as possible. It is called “benchmark first”.

3、 Finishing

The main surface finishing (such as grinding, honing, finishing, rolling, etc.).

It should be carried out in the final stage of the process road. The surface finish after processing is above ra0.9um. Slight bumps will damage the surface. In Japan, Germany and other countries, after finishing, flannelette should be used for maintenance. It is definitely forbidden to touch the workpiece directly by hand or other objects to avoid damage to the surface of finishing due to the transfer and device between processes.

4、 Distinguish processing stages

The appearance with high processing quality requirements can be divided into three stages: rough processing, semi finishing and finishing. First of all, it is to ensure the processing quality; it is conducive to the rational use of equipment; it is convenient to organize the heat treatment process; and it is convenient to find the defects of blank.

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.

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.