Post internship week

First, the development history of China's CNC system
1. Since 1958, China has started research and development of numerical control systems by a number of scientific research institutes, institutions of higher learning and a small number of machine tool factories. Due to the low level of domestic electronic components at that time, the departmental economy and other constraints, failed to achieve greater development.
2. After the reform and opening up, China's numerical control technology has gradually achieved substantial development. After the introduction of foreign technology in the "Sixth Five-Year Plan", the digestion and absorption of the "Seventh Five-Year Plan" and the scientific and technological research of the "Eighth Five-Year Plan" national organization made China's numerical control technology have a qualitative leap. At that time, the products passed the national investigation and appraisal and appraisal. Including the China I type of Beijing Everest Company, the Huazhong I type of Huazhong Numerical Control Company and the Blue Sky Type I of Shenyang High-grade CNC National Engineering Research Center, and other domestic CNC systems that have passed the "National Machine Tool Quality Supervision and Testing Center" test, such as Nanjing Four open company products.
3. China's CNC machine tool manufacturing industry has experienced rapid development in the 1980s, and many tool machine factories have transformed from traditional products to CNC products. However, in general, the technical level is not high and the quality is not good. Therefore, in the early 1990s, the national economy was transferred from the planned economy to the market economy. After several years of the most difficult depression, the production capacity fell. 50%, inventory is more than 4 months. After the "Ninth Five-Year Plan" in 1959, the state started the development of the machine tool market from the expansion of domestic demand, and strengthened the examination and approval of restrictions on imported CNC equipment. The investment focused on supporting key CNC systems, equipment, and technical research, which greatly promoted the production of CNC equipment. The role, especially after 1989, the state invested a large amount of technical reform funds in the defense industry and key civil industrial sectors, making the CNC equipment manufacturing market prosper.

Third, the process and tooling of CNC car reading: 133

The machining process of CNC lathe is similar to that of ordinary lathe, but since the CNC lathe is a single clamping and continuous automatic machining to complete all turning operations, the following aspects should be noted.

1. Reasonable choice of cutting amount

For high-efficiency metal cutting, the material to be processed, the cutting tool, and the cutting conditions are the three major factors. These determine machining time, tool life and machining quality. A cost-effective processing method must be a reasonable choice of cutting conditions.

The three elements of the cutting conditions: cutting speed, feed rate and depth of cut directly cause damage to the tool. As the cutting speed increases, the tip temperature rises, causing mechanical, chemical, and thermal wear. Cutting speed is increased by 20% and tool life is reduced by 1/2.

The feed condition is related to the wear behind the tool in a very small range. However, the feed rate is large, the cutting temperature rises, and the rear wear is large. It has less effect on the tool than the cutting speed. Although the depth of cut has no effect on the cutting speed and the feed rate, in the case of small depth cutting, the hardened layer is produced by the material to be cut, which also affects the life of the tool.

The user should select the cutting speed to be used according to the material to be processed, hardness, cutting state, material type, feed amount, depth of cut, and the like.

The selection of the most suitable processing conditions is selected on the basis of these factors. Regular, stable wear and longevity are ideal conditions.

However, in actual operations, the choice of tool life is related to tool wear, machined dimensional changes, surface quality, cutting noise, and heat processing. When determining the processing conditions, it is necessary to conduct research according to the actual situation. For difficult-to-machine materials such as stainless steel and heat-resistant alloys, a coolant or a rigid blade can be used.

2. Reasonable choice of tools

1) When roughing the car, it is necessary to select a tool with high strength and durability to meet the requirements of large back feed and large feed amount during roughing.

2) When finishing the car, it is necessary to select tools with high precision and durability to ensure the processing accuracy.

3) In order to reduce the tool change time and facilitate the tool setting, the machine clamp and the machine clamp blade should be used as much as possible.

3. Reasonable selection of fixtures

1) Try to use a universal fixture to clamp the workpiece and avoid using special fixtures;

2) The part positioning reference coincides to reduce the positioning error.

4. Determine the processing route

The machining route is the trajectory and direction of the tool relative to the part during the index control tool machining process.

1) The processing accuracy and surface roughness requirements should be guaranteed;

2) The machining route should be shortened as much as possible to reduce the tool idle travel time.

5. The relationship between processing route and machining allowance

At present, under the condition that the numerical control lathe has not yet reached universal use, it is generally necessary to arrange excessive margin on the blank, especially the margin containing the forged and cast hard skin layer on the ordinary lathe. If you must use a CNC lathe, you need to pay attention to the flexible arrangement of the program.

6. Fixture installation points

At present, the connection between the hydraulic chuck and the hydraulic clamping cylinder is realized by the tie rod, as shown in Fig. 1. The hydraulic chuck clamping points are as follows: First, remove the nut on the hydraulic cylinder by moving the handle, remove the pull tube, and pull it out from the rear end of the spindle. Then remove the chuck fixing screw to remove the chuck.
Fourth, carry out effective and reasonable turning processing Read: 102


Effectively save processing time

Index's G200 turning center integrated machining unit features modular, high-power dual-spindle and four-axis linkage, which further reduces machining time. Contrary to other concepts of clamping with the aid of a working axis, the product uses an integrated intelligent machining unit to automatically clamp the workpiece into place and process it. In other words, the automatic clamping does not affect the machining of the other spindle, which can shorten the machining time by about 10%.

In addition, the four-axis machining is very fast, and two tools can be machined at the same time. When the machine tools are put into use in pairs, the efficiency improvement is more obvious. In other words, conventional turning and hard turning can set two machine tools in parallel.

The only difference between conventional turning and hard turning is the tool holder and the centralized constant temperature coolant system. However, unlike conventional machining, conventional machining can be processed with two tool holders and one tailstock; in the case of a hard car, only one tool holder can be used. Dry hard machining is available on both types of machine tools, but the manufacturer of the process solution needs to carefully design a balanced cycle time, and the module structure provided by the Index tool machine makes it more flexible.

Increase productivity with high precision

As production efficiency continues to increase, users place high demands on accuracy. When machining with the G200 turning center, up to 4 workpieces can be machined after a cold start, and tolerances of ±6 mm can be achieved. The accuracy is usually kept at 2mm during processing. Therefore, Index provides customers with a complete solution with high precision and high efficiency. To provide such high-precision solutions, it is necessary to carefully select the functional components such as spindles and bearings.

The G200 turning center has achieved good results in the application of the BMW Landshut automobile manufacturing plant in Germany. The plant not only produces engines, but also produces parts made of light metal, in-vehicle plastic trims and steering shafts. Quality supervisors believe that the machining accuracy is very precise: the tolerance zone is ±15mm and the bearing tolerance is ±6.5mm.

In addition, the processed universal joints use Index's fully automatic intelligent machining unit. The first two turning centers were used for pre-machining the workpiece before it was machined. After processing, it was measured on-line and then sent out by conveyor belt for hobbing, cleaning and quenching. In the final process, a second Index processing system was used. The two G200 turning centers are used to brake the knuckle housing. The in-line measurement is done in the machine tool and sent to the unloading unit. The integrated processing unit is fully integrated into the layout of the shop, meets ergonomic requirements, has a significantly reduced footprint, and requires only two employees to take care of the manufacturing unit.

Five, the magical use of G00 in CNC turning and the guarantee of dimensional accuracy


CNC turning technology has been widely used in the machinery manufacturing industry. How to process workpieces efficiently, reasonably and qualitatively, each engineering and technical personnel engaged in the industry has more or less experience. The author has been engaged in numerical control teaching, training and processing for many years, and has accumulated certain experience and skills. Now take the GSK980T series of machine tools produced by Guangzhou CNC Equipment Factory as an example to introduce several CNC turning machining techniques.


First, the first sentence of the program uses the skill of G00

At present, we are exposed to textbooks and technical books on CNC turning. The first sentence of the program is to establish the workpiece coordinate system, that is, G50 Xα Zβ is the first sentence of the program. According to the instruction, a coordinate system can be set to make the coordinate value of a certain point of the tool in this coordinate system. In this way, the program is written. After the tool is moved, the knife must be moved to the predetermined position set by G50 to process. The process of finding the position is as follows.


1. After the knife is placed, the workpiece blank is clamped;
2. The spindle rotates forward, and the handwheel reference knife flattens the right end face A of the workpiece;
3. The Z axis does not move, release the tool along the X axis to point C, input G50 Z0, and the computer memorizes the point;
4. Program entry mode, input G01 W-8 F50, turning the workpiece to a step;
5. The X axis does not move, release the tool along the Z axis to point C, stop measuring the step diameter γ of the workpiece that is turned, input G50 Xγ, and the computer memorizes the point;
6. In the program entry mode, enter G00 Xα Zβ, the tool runs to the programmed program origin, and then enter G50 Xα Zβ, the computer remembers the program origin.



In the above steps, step 6 is that the tool positioning is important at XαZβ. Otherwise, the workpiece coordinate system will be modified and the workpiece cannot be processed normally. Anyone who has experience in machining knows that the above process of positioning the tool to XαZβ is cumbersome. Once an accident occurs, there is no servo on the X or Z axis, tracking error, power failure, etc., the system can only be restarted, and the system loses after the restart. The memory of the workpiece coordinate value set by G50, "Reset, zero return operation" no longer works, you need to re-run the tool to the XαZβ position and reset G50. If it is mass production, after processing one piece, return to the G50 starting point to continue processing the next piece, and if there is a slight mistake in the operation, it is possible to modify the workpiece coordinate system. In view of the various drawbacks of using the G50 to establish the workpiece coordinate system in the first sentence of the above program, the author tried to fix the workpiece coordinate system on the machine tool, and changed the program first sentence G50 XαZβ to G00 Xα Zβ, the problem was solved. The operation process only needs to adopt the first five steps of the above-mentioned G50 process, that is, after completing steps 1, 2, 3, 4, and 5, the tool is moved to a safe position, the program is called, and the automatic operation is performed. Even if there is an unexpected situation such as power failure, after restarting the system, move the cursor to the block that can be safely processed without affecting the machining process of the workpiece in the edit mode, and continue machining according to the automatic operation mode. The essence of the above program is to use G00 instead of G50 to fix the workpiece coordinate system on the machine tool. It is no longer limited by the G50 Xα Zβ program origin. It does not change the workpiece coordinate system. It is easy to operate and reliable. Unexpected effect. China Metal Processing Online

Second, the skills to control the dimensional accuracy


1. Modify the tool compensation value to ensure the dimensional accuracy

Since the workpiece error exceeds the workpiece tolerance due to the first tool error or other reasons, and the machining requirements cannot be met, the workpiece can be resized to the required size by modifying the tool compensation. The radial dimension is as follows:

Ab. absolute coordinate input method

According to the principle of “large reduction, small increase”, it is modified at the knife repair 001~004. If the workpiece size is 0.1mm when cutting with a No. 2 cutting knife, and the tool compensation display at X002 is X3.8, you can input X3.7 to reduce the No. 2 tool compensation.
b. Relative coordinate method

In the above example, the U-0.1 is input to the 002 tool and the same effect can be obtained.

For the same reason, the control of the axial dimension is also analogous. If you use a No. 1 external circular knife to machine a certain shaft section, the length is 0.1mm, you can input W0.1 at the 001 knife compensation.

2. Semi-finishing eliminates the influence of screw clearance to ensure dimensional accuracy

For most CNC lathes, after a long time of use, the size of the machined workpiece often appears unstable due to the influence of the screw gap. At this time, we can perform a semi-finishing after the roughing to eliminate the influence of the screw gap. If roughing the outer circle with the No. 1 knife G71, you can input U0.3 at the 001 tool compensation point, call the G70 fine car once, stop the measurement, then input U-0.3 at the 001 tool compensation, and call the G70 fine car again. . After this semi-finishing car, the influence of the screw clearance is eliminated, and the dimensional accuracy is ensured.
3. Programming to ensure dimensional accuracy

a. Absolute programming guarantees dimensional accuracy

Programming has absolute programming and relative programming. Relative programming refers to the coordinate system determined by the end point of each line segment on the machining contour curve with the starting point of the line segment as the coordinate origin. That is to say, the relative programmed coordinate origin is often in the transformation, and the cumulative error will inevitably occur. The absolute programming is in the whole process of machining, and there is a relatively uniform reference point, that is, the coordinate origin, so the cumulative error is relatively relative. Programming is small. When numerically turning a workpiece, the accuracy of the radial dimension of the workpiece is generally higher than that of the axial dimension. Therefore, when programming, the radial dimension is preferably absolutely programmed. Considering the convenience of processing and programming, the axial dimension is often relatively programmed. However, for important axial dimensions, absolute programming is preferred.
b. Numerical conversion guarantees dimensional accuracy

In many cases, the dimensional reference on the pattern is inconsistent with the dimensional reference required for programming, so the reference size on the pattern should first be converted to the size in the programmed coordinate system. As shown in Fig. 2b, except for the size of 13.06mm, the other are the programmed sizes obtained by directly converting the dimensions indicated in Fig. 2a. Among them, the three dimensions of φ29.95mm, φ16mm and 60.07mm are the programmed sizes obtained by taking the average of the two extreme dimensions respectively.

4. Modify the program and tool compensation control size

In CNC machining, we often encounter such a phenomenon: after the program is automatically run, the parking measurement, found that the workpiece size does not meet the requirements, the dimensional changes are irregular. For example, the workpiece shown in Fig. 3 is machined with an external cylindrical cutter No. 1 and measured by roughing and semi-finishing. The radial dimensions of each shaft section are as follows: φ30.06mm, φ23.03mm and φ16.02mm. In this regard, the author uses the modified program and knife compensation method to remedy, as follows:

a. Modify the program

The X30 in the original program is unchanged, X23 is changed to X23.03, X16 is changed to X16.04, so that each shaft segment has a uniform tolerance of 0.06mm beyond the nominal size;
b. Change the knife

Enter U-0.06 at No. 1 knife 001.


After the modification of the above program and the knife and the two-pronged, the fine wheel type is called, and the workpiece size can be effectively guaranteed.

CNC turning machining is an automated machining method based on numerical control program. In actual machining, the operator can only produce high-quality machining programs and produce high-quality workpieces with strong program commanding ability and rich practical skills.
Sixth, CNC tool machine troubleshooting methods and their precautions Due to frequent participation in maintenance tasks, some maintenance experience, combined with the relevant theoretical aspects, listed below, hope to throw a brick.

First, troubleshooting methods

Initialization reset method: Under normal circumstances, due to the system alarm caused by transient fault, the hardware reset or the power of the switch system can be used to clear the fault in turn. If the system working storage area is powered off, the plug-in circuit board or the battery undervoltage causes confusion. The system must be initialized and cleared. Before cleaning, pay attention to the data copy record. If the fault cannot be eliminated after initialization, perform hardware diagnosis.

Parameter change, program correction method: System parameters are the basis for determining system functions. If the parameter settings are incorrect, the system may be faulty or a function may be invalid. Sometimes due to user program errors can also cause downtime, you can use the system's block search function to check and correct all errors to ensure that it is working properly.

Adjustment, optimization adjustment: adjustment is one of the easiest ways. Correct system failure by adjusting the potentiometer. If a factory is in maintenance, its system display screen is chaotic and normal after adjustment. For example, in a factory, the main shaft has belt slippage during starting and braking, because the main shaft load torque is large, and the ramp-up time of the driving device is set too small, and it is normal after adjustment.

The optimization adjustment is a comprehensive adjustment method that systematically achieves the best match between the servo drive system and the driven mechanical system. The method is very simple, using a multi-line recorder or a dual-track oscilloscope with storage function, respectively Observe the reverberation relationship between the command and speed feedback or current feedback. By adjusting the speed factor and integration time of the speed regulator, the servo system can reach the optimal working state with high dynamic reverberation characteristics without oscillation. In the absence of an oscilloscope or recorder on site, according to experience, the adjustment causes the motor to start to oscillate, and then slowly adjusts in the reverse direction until the oscillation is eliminated.

Spare parts replacement method: replace the bad circuit board with a good spare part, and do the corresponding initialization start, so that the machine tool can be put into normal operation quickly, and then the bad board is repaired or repaired. This is the most commonly used troubleshooting method. .

Improve power quality method: At present, a regulated power supply is generally used to improve power supply fluctuations. Capacitance filtering can be used for high-frequency interference to reduce power board failure through these preventive measures.

Maintenance Information Tracking: Some large manufacturing companies continually modify and improve system software or hardware based on accidental failures due to design defects in actual work. These modifications are continuously provided to the service personnel in the form of maintenance information. As a basis for troubleshooting, this can be completely and completely eliminated.

Second, matters needing attention in maintenance

When taking out a certain circuit board from the whole machine, you should pay attention to record the corresponding position, the cable number of the connection, for the fixed installation of the circuit board, you should also take the corresponding crimping parts and screws for recording. The pressed parts and screws should be placed in a special box to avoid loss. After assembly, all the contents of the box should be used, otherwise the assembly is incomplete.

The soldering iron should be placed in front of the hand and away from the repair circuit board. The soldering iron tip should be properly trimmed to accommodate the soldering of the integrated circuit and to avoid damage to other components during soldering.

When measuring the resistance between the lines, the power should be cut off. When measuring the resistance value, the red and black test leads should be interchanged twice, and the resistance value is the reference value.

Most of the circuit boards are covered with a solder mask. Therefore, the corresponding solder joints should be found as test points during the measurement. Do not remove the solder film. If some of the boards are covered with an insulating layer, the insulating layer can only be scraped off with a blade at the solder joint.

The printed circuit should not be cut off at will. Some maintenance personnel have certain experience in appliance repair and are used to check for disconnection. However, most of the circuit boards on CNC equipment are double-sided metal orifices or multi-layered orifices. The printed circuit is fine and dense. Once cut, it is difficult to weld and tangent. It is easy to cut off adjacent lines, and then there are points. When cutting a certain line, it cannot be separated from the line. It is necessary to cut off several lines at the same time.

Components should not be replaced at will. Some maintenance personnel, if they do not determine the faulty component, simply change the component and immediately replace it, so that the false positive rate is higher, and the component that is removed has a higher damage rate.

Use the tin and the suction cord when removing the components. Do not take them hard. The same pad should not be heated and removed repeatedly for a long time to avoid damaging the pad.

Replace the new device, the pins should be properly treated, and the acid solder should not be used in the soldering.

Record the switch on the line, the jumper position, should not be changed at will. When performing comparison inspections of more than two poles, or when interchanging components, pay attention to marking the components on each board to avoid confusion, and the good board will not work.

Check the power supply configuration and type of the circuit board. According to the inspection requirements, you can supply power or all power separately. Attention should be paid to high voltage, some circuit boards are directly connected to high voltage, or there is a high voltage generator in the board, which needs proper insulation, and special attention should be paid during operation.

Finally, I feel that maintenance should not be obsessed with stereotypes. The things that move the theory must be combined with the actual situation at the time, broaden the thinking, gradually analyze them, and eliminate them one by one until they find the real cause of the failure.
In summary, the development of numerical control technology is synchronized with the development of modern computer technology and electronic technology, and is also developed according to the needs of production development. Now that CNC technology is mature, the development will be deeper, wider and faster. Future CNC systems will make machinery more usable and cheaper.