March 2021 – Page 2 – CNC Machining & Turning, Milling, Metal parts

CNC machining center fault inspection

The spindle is the power auxiliary device of CNC machining center. The spindle drives the workpiece to rotate to process the workpiece of the rotating body. Spindle is an important guarantee for high-speed and high-precision machining of CNC machining center, so the maintenance methods and skills of spindle fault are the basic knowledge that operators and maintenance personnel of CNC machining center must master. In the operation of CNC machining center, the spindle will inevitably have some faults. What is the specific reason?

Different types of CNC machining centers adopt different types of spindles. According to the different transmission systems, the spindle system can be divided into the main transmission spindle with variable speed gear, the main transmission spindle with belt transmission, the dual motor drive spindle and the motor spindle integrated spindle. No matter what type of spindle application, the common faults in use are as follows:

Overload.

Fault causes: excessive cutting amount, frequent forward and reverse rotation, spindle motor fault, spindle drive device fault.

The spindle does not rotate

Fault causes: spindle drive failure, CNC device can not output speed signal, spindle motor failure, spindle drive failure, drive belt fracture.

The spindle speed deviates from the command value

Fault causes: motor overload, CNC system output spindle speed command output problem, speed measuring device failure or speed feedback signal disconnection.

CNC machine tool 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 machining is the basis of modern manufacturing technology. This invention has epoch-making significance and far-reaching influence for the manufacturing industry. CNC machining centers are usually classified by the relative position of the spindle and the workbench, which are divided into vertical, horizontal and multi axis linkage machining centers.

1、 Vertical machining center: it refers to the machining center with the spindle axis perpendicular to the worktable. It is mainly suitable for processing plate, plate, mold and small shell complex parts.

2、 Horizontal machining center: it refers to the machining center with the spindle axis parallel to the workbench, which is mainly suitable for machining box parts.

3、 Multi axis linkage machining center: it refers to the machining center that can control the linkage change by processing the angle between the spindle axis and the rotary axis of the worktable, and complete the machining of complex spatial surface. It is suitable for the machining of impeller rotor, mold, cutting tool and other workpieces with complex spatial surface.

Difference between machining center and NC milling machine

CNC milling machine is the abbreviation of digital control machine tool, is a kind of automatic machine tool with program control system. The control system can logically process the program with control code or other symbolic instructions, decode it, express it with coded numbers, and input it into the numerical control device through the information carrier. After calculation and processing, the numerical control device sends out various control signals to control the action of the machine tool, and automatically processes the parts according to the shape and size required by the drawing.

Similarities and differences between machining center and CNC milling machine:

The same as CNC milling machine, machining center is also composed of CNC system, servo system, mechanical body, hydraulic system and other parts.

But machining center is not the same as NC milling machine. The biggest difference between machining center and NC milling machine is that machining center has the function of automatic tool exchange. By installing different tools in the tool magazine, they can pass through in one clamping. In addition, the machining range of the two is different. The functions of machining center include milling workpiece, drilling workpiece, setting space, etc The machine can only mill the workpiece. The automatic tool changing device for Dongguan high-speed computer gong processing changes the processing tools on the spindle to realize various processing functions, such as drilling, boring, reaming, tapping, grooving, etc.

The spindle component of drilling and tapping center is mainly composed of spindle, bearing, spindle quasi stop installation, automatic clamping and chip removal device, which is an important part of the mechanical part of drilling and tapping center. The lubrication, cooling and sealing of the spindle components of drilling and tapping center are several problems worthy of attention in the process of machine tool use and maintenance. So, how to maintain the spindle of drilling and tapping center?

First, good lubrication effect can reduce the working temperature and prolong the service life of the bearing; therefore, attention should be paid in operation and use: grease and oil circulation lubrication is adopted at low speed; oil mist and oil air lubrication are adopted at high speed. However, when grease lubrication is used, the sealing volume of the spindle bearing is usually 10% of the bearing space volume. Do not fill it up at will. Too much grease will aggravate the spindle heating. For oil circulation lubrication, check the constant temperature oil tank of spindle lubrication every day to see whether the oil quantity is sufficient. If the oil quantity is not enough, add lubricating oil in time. At the same time, pay attention to check whether the temperature range of lubricating oil is appropriate.

In order to ensure that the spindle has good lubrication, reduce friction and heat, and take away the heat of the spindle assembly, the circulating lubrication system is usually used. The hydraulic pump is used to supply oil for lubrication, and the oil temperature controller is used to control the oil temperature of the oil tank. The spindle bearing of drilling and tapping center manufacturer adopts advanced grease sealing method for lubrication, and each grease addition can be used for 7-10 years. The new lubrication cooling method not only reduces the bearing temperature rise, but also reduces the temperature difference between the inner and outer rings of the bearing, so as to ensure the small thermal deformation of the spindle. There are two common lubrication methods for spindle. Oil air lubrication is similar to oil mist lubrication, but oil mist lubrication is to continuously supply oil mist, and oil air lubrication is to send oil mist into the bearing gap at a fixed time and quantity, which not only realizes oil mist lubrication, but also avoids the air pollution caused by too much oil mist. In order to achieve the purpose of lubrication and cooling, a large flow of constant temperature oil (3-4l / min for each bearing) is injected into the spindle bearing. Here, the oil injected with larger flow rate must be forced to drain by the drain pump instead of natural reflux. At the same time, the common large capacity and high-precision constant temperature oil tank should be used, and the oil temperature change should be controlled within ± 0.5 ℃.

Second, the cooling of the spindle components is mainly to reduce the bearing heat, invalid control of heat source.

Third, the sealing of spindle components should not only prevent dust, chips and cutting fluid from entering the spindle components, but also prevent the leakage of lubricating oil. There are non-contact seal and contact seal for spindle components. For the non-contact seal, in order to prevent leakage, it is important to ensure that the return oil can be drained as soon as possible and the oil return hole is unobstructed; for the contact seal with felt ring and oil resistant rubber seal ring, pay attention to check its aging and damage. To sum up, in the process of using and maintaining the drilling and tapping center, we must pay great attention to the lubrication, cooling and sealing of the spindle components, and do this work carefully.

Cutting tools for computer gong processing

Roughening: under the maximum load of the machine tool, in most cases of processing, select the largest possible tool, the largest possible feed amount and the fastest possible feed. In the case of the same tool, the feed is inversely proportional to the feed amount. In general, the load of the machine tool is not a problem. The principle of tool selection mainly depends on whether the two-dimensional angle and three-dimensional arc of the product are too small The principle is that the length of the tool is greater than the depth of processing. For large workpieces, it is necessary to consider whether the collet can be lowered. Otherwise, it is necessary to go as follows. 0 I4 Q6 x1 f5 l N& u

The purpose of light knife: to meet the workpiece processing requirements: finish, flying die allowance, copper male spark position, etc., at the same time, as large as possible, as fast as possible, because the precision knife takes a long time, with the most appropriate feed and feed, in the same feed, the larger the transverse feed, the faster. The surface feed is related to the finish after processing, and the feed size is related to the surface shape In the case of no damage to the surface, the minimum allowance should be left, the maximum knife should be used, the fastest Belt should be rotated, and the proper feeding should be carried out.

Clamping method:

All clamps are long horizontally and short vertically;
Vise clamping: the clamping height should not be less than 10 mm. When processing the workpiece, the clamping height and processing height must be specified. The processing height should be about 5 mm higher than the vise plane, so as to ensure the firmness and not damage the vise. This kind of clamping belongs to general clamping, and the clamping height is also related to the size of the workpiece. The larger the workpiece is, the higher the clamping height will be;
Splint clamping: the splint is fixed on the worktable with the code, and the workpiece is locked on the splint with the screw. This kind of clamping is suitable for the workpiece with insufficient clamping height and large processing force, generally medium and large workpieces, and the effect is very good. 1 ` Q( F9 k, n
When the workpiece is large, the clamping height is not enough, and it is not allowed to lock the thread at the bottom, it should be clamped with code iron. This kind of clamping needs to be clamped twice

a. First code the four corners, process the other parts, and then code the four sides and process the four corners. The principle is that during the second clamping, be very careful not to let the workpiece loose, code before loosening,

b. There are also two sides of the first code, the other two sides of the processing, 8 L # y% @ # e’n% p

Code iron has an advantage, large contact area, not easy to deformation, such as aluminum, magnesium within the soft metal must use code iron to prevent deformation;

Tool clamping: diameter more than 10 mm, not less than 30 mm; diameter less than 10 mm, not less than 20 mm,

Note: the impact of the tool on the workpiece can cause: a. the workpiece moves; B. the tool is broken; C. the tool is deformed and the workpiece is damaged; D. the tool is loose, the tool is dropped or the workpiece is not processed correctly

Therefore, the clamping of tool and workpiece should be firm. Strictly prevent Tool Collision and direct insertion of workpiece, & H #: X # {3 W

Classification of cutting tools and their application scope:% Q + e’c. B-Z

By material:

White steel knife: easy to wear, used for roughening of copper and small steel

Tungsten steel knife: used for angle cleaning (especially steel material) and light knife. . g4 k+ L1 U0 h/ s3 P+ T

Alloy knife: similar to tungsten steel knife

Purple knife; used for high speed cutting, not easy to wear

According to the cutter head:, ~. A “{2 s; t

Flat bottom knife: used for plane and straight body side cleaning (plane angle / m3 Z / M)_ , Z

Ball cutter: used for all kinds of surface medium light, light knife) F + I-m: B0 F8 G-V) H

Ox nose knife (one side, two sides and five sides): used for roughening steel (r0.8, r0.3, r0.5, r0.4) – X / F9 x, H: v

Rough leather knife: used to cut rough, pay attention to the remaining method (0.3)

According to the arbor: straight knife: straight knife is suitable for all kinds of occasions 9 a # x E + x0 a% E

Slant bar cutter: but not suitable for straight face and face with inclination less than the inclination of bar (S2 [7 d & D% O6 M0~

How to improve the efficiency of CNC machining

(1) The size and structure of all kinds of parts are very different, and the universality of machine tools and other process equipment is not high.

(2) Many companies are usually faced with the production task of multi variety, small batch and short production cycle, so the process system is required to have a higher response speed.

(3) The structure of product parts is complex and the processing is difficult.

(4) Thin wall, easy to produce processing deformation. There are a lot of thin-walled and deep cavity structures, which are typical weak rigid structures.

(5) It is difficult to select cutting tools and cutting parameters. Because the development of tool industry can’t catch up with the development and application of new materials, and lack of the support of machining database.

So how to improve the efficiency of CNC machining? Generally speaking, the methods to improve the machining efficiency of CNC machine tools are as follows:

1、 Change the understanding of numerical control technology.

Numerical control technology is a comprehensive technology, in addition to the numerical control machine tool, there must be corresponding supporting technology and personnel support, especially in the numerical control processing process, people play a decisive role, the technical ability of management personnel, engineering and technical personnel, engineering maintenance personnel and operators will affect the production efficiency of numerical control machine tool.

2、 Develop effective tool management measures.

For example, the tool is pre adjusted to reduce the installation and adjustment time of the tool on the machine tool, and the tool is managed through the management system to reduce the errors caused by manual management.

3、 Fixture management.

Because the selection of fixture is directly related to the installation time and measurement time of workpiece, the management of fixture should be realized.

Computer gong processing workpiece collision number

After the workpiece is placed on the pad iron, it is necessary to pull the table for the workpiece datum according to the drawing requirements. For the workpiece that has been ground on six sides, it is necessary to check whether its verticality is qualified.

The nut must be tightened after the work-piece is pulled to prevent the work-piece from shifting during the processing due to the loose clamping; pull the work-piece again to ensure that the error does not exceed the tolerance after the clamping.

Number of workpieces touched

For the clamped workpiece, the contact head can be used to set the processing reference zero position. The contact head can be used in photoelectric type and mechanical type. There are two kinds of methods: middle collision number and unilateral collision number

Photoelectric static, mechanical speed 450 ~ 600rpm. Manually move the x-axis of the worktable according to the collision number to make the collision number head touch one side of the workpiece. When the collision number head just touches the workpiece and the red light is on, set the relative coordinate value of this point to zero. Then manually move the x-axis of the worktable to make the collision number head touch the other side of the workpiece. When the collision number head just touches the workpiece, record the relative coordinate at this time.

According to the relative value minus the diameter of the collision head (i.e. the length of the workpiece), check whether the length of the workpiece meets the requirements of the drawing.

Computer gong processing tool setting point

When the machining accuracy is not high, some surfaces on the workpiece or fixture can be directly used as the tool face; when the machining accuracy is high, the tool setting point should be selected on the design basis or process basis of the part as far as possible, for example, for the part with hole positioning, it is more appropriate to take the axis of the hole as the tool setting point. The tool setting point must have a certain coordinate relationship with the positioning datum of the workpiece. In this way, the relationship between the machine tool coordinate system and the workpiece coordinate system can be determined. The selection of tool setting point should be convenient for coordinate value calculation and tool setting. During tool setting, the tool setting point should coincide with the tool position. The so-called cutter site refers to the intersection of the tool axis and the bottom surface of the tool for the flat end end milling cutter; for ball end milling cutter, it refers to the ball center of the ball head part; for turning tool, it refers to the tool tip; for the drill bit, it refers to the drill point; for the linear electrode cutting machine, it refers to the focus of the axis of the wire electrode and the part surface.

Stress and warpage analysis based on two-sided flow technique

According to the analysis results of gate solidification effect and packing pressure and temperature distribution, the stress and warpage analysis module calculates the stress changes with time in the wall thickness and plane direction of the product, and the shrinkage of the product along the wall thickness direction at the time of demoulding. Based on the double-sided flow technique, a special double-layer shell element is used to predict the warpage of the product at the time of demoulding.

Troubleshooting of CNC machining center

Overload.

Fault causes: excessive cutting amount, frequent forward and reverse rotation, spindle motor fault, spindle drive device fault.

The spindle does not rotate

Fault causes: spindle drive failure, CNC device can not output speed signal, spindle motor failure, spindle drive failure, drive belt fracture.

The spindle speed deviates from the command value

Fault causes: motor overload, CNC system output spindle speed command output problem, speed measuring device failure or speed feedback signal disconnection.

The standard of CNC programming program

It takes 1-2 months to be very familiar with. The automatic programming software is a bit complicated and needs to be learned. But it is not difficult for CAD.

In practice, one is:

Readable, well organized, and understood by everyone in the operator.
The program instructions should be as few as possible for the purpose of simple, practical and reliable. From the point of view of programming, I think that the instruction G00 G01 and other auxiliary instructions are convenient for programming.
Easy to adjust. Parts machining accuracy need to be fine tuned is the best without changing the plan. Tool wear, for example, adjustment, just change the tool offset table length, radius.
Easy to operate. Programming will be based on the characteristics of machine operation, conducive to observation, inspection, measurement, safety, and so on. The same parts, for example, the same processing content, in the vertical machining center and horizontal machining center processing, are certainly not the same.

In machining, the simplest method is the best. As long as there is practical experience of the peer, will certainly agree with this sentence!

Skillfully operate CNC machine tools

This requires 1 – 2 years of research, operation delicate feeling, beginners, especially college students, know how to do, can not listen. Learn in this process: operation mode of installation system, clamp, datum alignment, knife, setting zero point offset, setting tool radius, length compensation, compensation, handling of tool and loading and unloading, grinding tools, measurement, skilled use of vernier caliper, micrometer, dial indicator, dial indicator, rod diameter indicator, etc.

CNC machining process of complex parts

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.