December 2020 – Page 5 – CNC Machining & Turning, Milling, Metal parts

Key points in computer gong processing

Try to install the clamping material first and then the cutting tool, so as to prevent the hand from touching the tool when installing the clamping material. If the tool has been installed, the worktable should first be moved to the outside to ensure that the clamping material will not interfere with the tool, so as to avoid injury or breakage of the tool.
When disassembling the tool, you must first observe whether the spindle stops rotating.
When unloading the knife, do not hold or pinch the edge of the knife with force to avoid scratching.
The wrench should be placed in the tool storage area after use, not on the y-axis shield or beam.
In the process of machining, operators are not allowed to observe the cutting position closely to prevent chips from falling into the eyes.
Before processing, check the position of the oil nozzle before opening the oil pump switch to avoid spraying to other positions when flushing oil.
When the machining gap is suspended for observation, the worktable must be moved away from the cutting position.
Inspection: after the machining is completed and before the workpiece is disassembled, we should first carry out the preliminary inspection of the necessary size or appearance. Only after the inspection is qualified can the workpiece be disassembled, so as to avoid the positioning problem of secondary processing and the scrapping of the workpiece

Computer gong processing reduces tool change times

In order to improve the accuracy of the groove width and reduce the number of tool changes, the milling cutter with a diameter of 7 than the groove width can be used to mill the middle part of the groove first, and then use the tool radius compensation function to mill the two sides of the groove.

Ball end milling cutter, ring milling cutter, drum milling cutter, cone milling cutter and disc milling cutter are often used in machining solid curved surface or variable bevel profile.

When the machining allowance is small and the requirement of surface roughness is high, the face milling cutter with cubic boron nitride blade or ceramic insert blade can be selected for high-speed cutting.

According to the principle of NC machining, the overall consideration is made according to the requirements of workpiece processing drawings, the format specified by the CNC milling machine is used for editing, and the processing program input is carried out according to the action sequence. Thus, it is necessary to know the precision machining technology of CNC lathe while compiling the NC program.

Determine the process flow. The processing technology of CNC milling machine is very similar to that of ordinary machine tool. Through analyzing the workpiece, specify the processing route, select the processing procedure, select the machine tool, fixture and cutter. Determine the equipment baseline position and cutting amount. The difference is that CNC machine tools need to program the operation process.
Calculate the tool coordinate value. In order to facilitate the programming and calculation of tool path coordinates. The coordinates of the workpiece and the size and shape of the part must be calculated first, so as to determine the whole machining path of the tool.
Write processing program, for simple workpiece can be written manually, but for complex processing workpiece, automatic programming is needed.
There are many ways to input programs into CNC system, which are mainly accomplished by the operation panel of CNC control system. In addition, the interface between computer and CNC system can be connected to input program by computer.
Comprehensive inspection of procedures. Through the function of graphic magic shadow display or NC milling machine equipment running without load, the running track of machine tool is checked, and whether the cutter movement meets the requirements of capping

CNC machining method of plane peripheral contour

The end mill C is often used when machining the peripheral contour of a plane workpiece.

Ball end milling cutter, ring milling cutter, drum milling cutter, cone milling cutter and disc milling cutter are often used in machining solid curved surface or variable bevel profile.

Determine the process flow. The processing technology of CNC milling machine is very similar to that of ordinary machine tool. Through analyzing the workpiece, specify the processing route, select the processing procedure, select the machine tool, fixture and cutter. Determine the equipment baseline position and cutting amount. The difference is that CNC machine tools need to program the operation process.
Calculate the tool coordinate value. In order to facilitate the programming and calculation of tool path coordinates. The coordinates of the workpiece and the size and shape of the part must be calculated first, so as to determine the whole machining path of the tool.
Write processing program, for simple workpiece can be written manually, but for complex processing workpiece, automatic programming is needed.
There are many ways to input programs into CNC system, which are mainly accomplished by the operation panel of CNC control system. In addition, the interface between computer and CNC system can be connected to input program by computer.

Standard of computer gongs processing

Design datum: the datum used to determine the position of other points, lines and planes on the part drawing, which is called design datum.

Process datum: the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, the process datum of die and mould can be divided into assembly datum, measuring datum and locating datum.

(1) Assembly datum: the datum used to determine the position of parts in parts or products during assembly, which is called assembly datum.

(2) Measurement datum: the datum used to check the size and position of machined surface, which is called measuring datum.

(3) Positioning datum: the datum used for workpiece positioning during machining, which is called positioning datum. For the surface (or line, point) as positioning reference, only the rough surface can be selected in the first working procedure. This positioning surface is called rough datum. The machined surface can be used as the positioning datum in the following processes, and the positioning surface is called the precise datum. Process datum: the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, process datum can be divided into assembly datum, measuring datum and locating datum.

(1) Assembly datum: the datum used to determine the position of parts in parts or products during assembly, which is called assembly datum.

(2) Measurement datum: the datum used to check the size and position of machined surface, which is called measuring datum.

In the process of turning a blank into a finished product, the total thickness of the metal layer cut off on a machining surface is called the total machining allowance of the surface. The thickness of the metal layer cut by each process is called the machining allowance between processes. For the rotating surface such as outer circle and hole, the machining allowance is considered from the diameter, so it is called symmetrical allowance (i.e. bilateral allowance), that is, the actual thickness of the metal layer cut off is half of the machining allowance on the diameter. The machining allowance of the plane is the unilateral allowance, which is equal to the actual thickness of the metal layer removed. The purpose of leaving machining allowance on the workpiece is to remove the machining errors and surface defects left by the previous process, such as the surface cold and hard layer, air hole and sand inclusion layer on the casting surface, oxide scale, decarburization layer and surface crack on the forging surface, internal stress layer and surface roughness after cutting. The precision and surface roughness of the workpiece are improved. The size of machining allowance has great influence on machining quality and production efficiency. If the machining allowance is too large, it not only increases the labor of machining, reduces the productivity, but also increases the consumption of materials, tools and power, and increases the processing cost. If the machining allowance is too small, it can not eliminate the defects and errors of the previous process.

Precision form grinding technology

Precision form grinding technology, and realize the precision coordinate grinding technology of round hole and mold hole with precision hole spacing. EDM and NC WEDM are widely used, which provide the key processing technology for high hard materials. The specialization, serialization and standardization of die materials are realized. During this period, the high development of mold standardization, the full use of standard parts and components in mold production is not only a major achievement and feature of mold industrial production mode, but also an important technical basis for realizing modern mold production mode. With the progress and development of computer and machine tool industry, die CAD / CAM and CAD / CAM / CAE have become widely used production technologies. They are combined with high standardization to form a modern mold production mode, that is to realize the informatization and digital mold production mode of mold design and manufacturing.

Design: during the period of manual workshop mold making and the early stage of industrial mold manufacturing, mold design was not carried out, and mold manufacturing was completely dependent on the experience and skills of mold makers. With the development of industry, the application of die and mould is becoming more and more extensive, the requirement of mould performance and quality is getting higher and higher, and the production technology is constantly improving. Designing and drawing the die structure system diagram and parts drawing, defining the design requirements and manufacturing technical conditions are the first task and core technology in the mold production process, which has been evolving until now.

However, with the progress of computer and CNC machine tool industry, and the wide application of CNC machine tools such as machining center, the mold design method and method have produced substantial and breakthrough progress. Mold design includes the following three aspects: mold part modeling and structure design, mold structure system design, mold structure parameter calculation and setting. Mold design process and content. The die with high precision needs to be processed by high-precision CNC machine tool, and the die material and forming process have strict requirements, and CAD / CAE / CAM die technology is also needed to design and analyze. Due to the special requirements of some parts, the mold also needs to use advanced technology such as hot runner, gas assisted molding, nitrogen cylinder and so on. The manufacturer shall be equipped with CNC, EDM, WEDM and NC profiling milling equipment, high-precision grinder, high-precision CMM, computer design and relevant software. Generally, large stamping dies (such as automobile cover parts mould) should consider whether the machine tool has blank holder mechanism, or even edge lubricant, multi position progressive, etc. In addition to stamping tonnage, punching times, feeding device, machine tool and die protection device should be considered.

Not every mold manufacturer and manufacturer has the means to master the above mold. When choosing a cooperative manufacturer, we must understand its processing ability, not only depending on the hardware equipment, but also combining the management level, processing experience and technical strength. For the same set of mould, there is sometimes a big gap between quotations from different manufacturers. You should not pay more than the value of the mold, at the same time, should not be less than the cost of the mold. Mold manufacturers like you, to make a reasonable profit in the business. Ordering a set of molds with a much lower price would be the beginning of trouble. Users should start from their own requirements and comprehensively measure. Avoid multi cooperation, try to make mold and product processing one-stop, with qualified mold (test piece qualified), not necessarily can produce a batch of qualified products. This is mainly related to the machine tool selection, forming process (forming temperature, forming time, etc.) and the technical quality of the operator.

CNC rough machining and semi finishing machining

Rough machining, semi finishing, finishing of all parts of the processing process, so we must carry out a thorough process analysis, arrange a reasonable processing sequence, select the appropriate cutting tools and cutting parameters, in order to ensure the machining accuracy of parts and improve production efficiency.

Arrange tool position number reasonably. The machining center needs to use a variety of tools, sometimes the shape of the tool is very different, so it is necessary to leave enough space for tool change to avoid tool collision.

In order to improve the work efficiency of high-speed Gong machining, the tool is usually pre adjusted outside the machine tool after it is installed on the tool holder, and the tool parameters are input into the corresponding address of the tool table.

For the convenience of debugging program and adjusting work steps, different working steps can be programmed into subprograms, and the main program mainly carries out tool changing and subroutine calling.

Because there are many steps in high-speed Gong machining, and tool change is required many times, so the error rate of manual programming is high. Therefore, it is necessary to check the program carefully and verify it by trial operation. During calibration, it is better to check the tool path at each plane position. If the main plane is XY plane, elastic pen or water pen can be clamped on the main shaft to draw the running track in trial operation mode. The programming features of the program are that the shape of the workpiece processed by small machining center is complex, and there are many kinds of cutting tools used. The whole process from rough machining, semi finishing to finishing must be completed after one clamping. Therefore, the program is more complex. The following problems should be considered in programming.

Analyze the drawings carefully to determine the reasonable process route.
The size and specification of the tool should be selected, and the actual size measured should be filled into the tool card.
Determine the reasonable cutting parameters. It mainly includes spindle speed, back feed rate and so on.
Sufficient space for automatic tool change shall be reserved to avoid collision with workpiece or fixture. It is suggested that the tool change position should be set at the origin of the machine tool.
In order to check and debug the program, the processing contents of each step can be arranged into different subprograms, and the main program mainly completes tool change and subroutine call. This procedure is simple and clear.
Check and test run the compiled program, and pay attention to whether there is interference between the tool, fixture or workpiece. When checking the m, s and t functions, it can be carried out in the z-axis locking state. Processing programming need to pay attention to the first, do not modify the setting of machine parameters. 2、 Do not change the file format of the computer. 3、 Note that micro connections are added and checked before each incoming. 4、 Remove stamping after the body, if you need to add stamping should focus on inspection, and stamping. 5、 Program file cannot exceed 2, program cannot run. 6、 Stamping sequence from inside to outside, if there is an accurate stamping part will be preferred. 7、 Each width is less than 140 mm or stamping position is less than 40 mm. The length less than 300 mm cannot be punched. (Note: for composite die, except the influence of position, the cutting angle is less than 30 mm, and the clamp should be moved to a reasonable position. When the cutting angle is less than 30 mm or in effect, the distance of clamping position, the reasonable position of 150 mm to 250 mm and the cutting angle clamp on the computer must be the same as the actual position). The digital control system can control the machine tool to automatically select and change the cutting tool according to different working procedures, and automatically change the spindle speed, feed rate, the motion track of the cutter relative to the workpiece and other auxiliary functions. The machining center can complete the processing of multiple processes on several surfaces of the workpiece in turn. In addition, it has a variety of tool changing or selecting functions, which greatly improves the production efficiency. Due to the centralization of working procedure and automatic tool change, the time of clamping, measuring and adjusting of machine tool is reduced, so that the cutting time of machine tool reaches about 80% of the starting time of machine tool (only 15-20% for ordinary machine tools); meanwhile, the time of turnover, handling and storage of workpieces between working procedures is reduced, and the production cycle is shortened, which has obvious economic effect

The importance of CNC motorized spindle

The importance of CNC motorized spindle 1. High speed CNC must first verify the parameters of the input tool starting point. It is strictly forbidden to knock or impact the rotor end of the spindle motor during operation. The operator is required to pay attention to the starting point of z-axis during tool setting to prevent misoperation. It is necessary to avoid the damage to the bearing of spindle motor caused by collision and knife binding during operation. Once there is knife binding phenomenon, stop the machine immediately, so as to prevent the bearing from being damaged by high-speed operation. Then, start running in from low speed, the time is slightly longer than normal running in time, until the motor runs smoothly and normally.

The high-speed CNC should ensure that the cooling circulation system of the engraving and milling machine motor works normally before starting up and using. Then turn on the spindle motor. It is forbidden to use the spindle motor without cooling. The working environment temperature should not be higher than 30 ℃. When the ambient temperature is higher than 30 ℃, air conditioner or refrigerator should be used for forced cooling of spindle motor.
According to the principle of running from low speed to high speed, the spindle motor should be preheated step by step. When the motor reaches the required speed, the no-load operation is stable, and the temperature is cooled, then the processing can be carried out. Only in this way can the better machining accuracy be ensured.
When planning the tool path, it is necessary to ensure that the force of the spindle motor is reasonable, and the engraving process should be carried out according to the knife principle provided by the technical service personnel. It is necessary to prevent the vertical cutting tool and prohibit the spindle motor from overload operation, so as to ensure the normal service life of the spindle motor.
Generally, the spindle motor should be disassembled, cleaned and reassembled for use after running for about one year, so as to ensure the bearing accuracy and prolong the service life. In order to ensure the normal and good work of the spindle motor, its assembly must be carried out by experienced professional operators in a clean and clean environment, as well as using appropriate tools. Do not knock at random. For the temporarily unused motorized spindle, the residual water in the water chamber shall be blown out with compressed air, and the sleeve and shaft head shaft hole shall be oiled for rust prevention and placed in a cool and dry place.

Control system of CNC machine tool

Generally, the control system of CNC machine tool can control the machine tool according to the digital program instruction to realize the automatic start stop, reversing and speed change of the spindle. It can automatically control the feed speed, direction and processing route for processing. It can select the tool and adjust the cutting amount and travel track according to the size of the tool. It can complete all kinds of auxiliary actions needed in the processing. When we use machine tools to process parts, we usually need to control the various actions of the machine tool, one is to control the sequence of actions, the other is to control the displacement of each moving part of the machine tool. When machining with ordinary machine tools, such operations as start-up, stop, feed, change direction, change speed of spindle and switch cutting fluid are all controlled by manual. When automatic machine tool and copying machine tool are used for machining, the above operation and motion parameters are controlled in the form of analog quantity through the designed cam, profiling and blocking device. Although they can process more complex parts, and have certain flexibility and versatility, the machining accuracy of parts is affected by the manufacturing accuracy of cams and profiling machines, and the preparation time of working procedure is also very long 。

When machining parts with large CNC machine tools, it is only necessary to compile program codes in the form of digital information, such as part graphics, process parameters and processing steps, and input them into the control system of machine tools, and then convert them into the command signals of driving servo mechanism after calculation and processing, so as to control the coordinated action of various parts of the machine tool and automatically process the parts. When the processing object is changed, it is only necessary to re write the program code and input it to the machine tool, and then the NC device can replace most of the functions of human brain and hands, control the whole process of processing, and produce any complex parts.

After a speed command is given in MDI mode, the spindle does not move a little bit. At first, it is suspected that the shift signal is incorrect. When the z-axis gearbox is disassembled, it is found that the shift of the spindle gear is normal and in place signal is correct. But the spindle doesn’t rotate. In principle, if the spindle encoder or the spindle is not powered on, it will cause an alarm. Therefore, I have ruled out the above two doubts. Do you want to know what good solutions are available for such problems?

The solution can refer to 1: first of all, we should know whether we can see the parameters after 9000, and if we can see them, whether the parameters are needed. I have encountered such a situation, it is 0i-MC system, all axes are normal, that is, the main shaft does not rotate. Later, we changed the parameters after 9000. I don’t know if 21i is like this

The solution can be referred to 2: there was an oi-m in the company before, and it was found that it was caused by the clamping of the pneumatic valve of the tool arm. After the tool change, the tool arm should be ready for the next knife, but the knife arm did not put down, and there was no alarm. After the valve was replaced, it was ready. And whether there is a hydraulic fixture, the fixture is not tightened, or the clamping signal is disconnected.

Solution can refer to 3: first look at the spindle monitoring, turn the spindle by hand to see if there is a value? Is the value correct? In the past, there is no alarm and the spindle does not rotate. No monitoring value. Adjust the distance. Or replace it with a new one.

CNC machining clamping workpiece

Before the workpiece is clamped, the surface should be cleaned, and there should be no oil stain, iron filings and dust, and the burr on the surface of the workpiece should be removed with a file (or oilstone).
The equal high-speed rail used for clamping must be grinded flat by grinding machine to make it smooth and flat. The weight iron and nut must be firm, which can reliably clamp the workpiece. For some small workpieces that are difficult to be clamped, they can be directly clamped on the vise.
The worktable of the machine tool shall be clean and free of iron filings, dust and oil stains.
The pad iron is generally placed at the four corners of the workpiece, and the equal height pad iron should be placed in the middle of the workpiece with too large span.

Check whether the width and height of the workpiece are qualified according to the drawing.

When clamping the workpiece, according to the clamping and placing mode of the programming operation instruction, it is necessary to consider avoiding the processing position and the situation that the cutter head may encounter the fixture during the processing.
After the workpiece is placed on the pad iron, pull the table according to the drawing requirements. The length direction error is less than 0.02mm, and the horizontal error of the top surface X and Y direction is less than 0.05mm. The perpendicularity of the workpiece which has been ground on six sides shall be checked to see if it is qualified.
After pulling the watch, the nut must be tightened to prevent the workpiece from shifting during processing due to the loose clamping.
Pull the meter again to make sure that the error does not exceed the tolerance after clamping.
Workpiece collision number: for the clamped workpiece, the collision number head can be used to determine the processing reference zero position. There are two kinds of collision head: photoelectric type and mechanical type. The collision selection method can be divided into middle collision number and single side collision number, and the steps are as follows:
Collision counting method: photoelectric static, mechanical speed 450 ~ 600 rpm.
Manually move the x-axis of the worktable to make the colliding head touch one side of the workpiece. When the colliding head just touches the workpiece and the red light is on, set the relative coordinate value of this point as zero; then manually move the x-axis of the workbench to make the collision head collide with the other side of the workpiece, and record the relative coordinates when the collision head just touches the work piece.
According to the relative value minus the diameter of the bumping head (i.e. the length of the workpiece), check whether the length of the workpiece meets the requirements of the drawing.
Divide the relative coordinate number by 2, and the value is the middle value of the x-axis of the workpiece. Then move the worktable to the middle value on the x-axis, and set the relative coordinate value of the x-axis at this point to zero, which is the zero position on the x-axis of the workpiece.
Carefully record the mechanical coordinate value of the zero position on the x-axis of the workpiece in one of g54 ~ G59, and let the machine tool determine the zero position on the x-axis of the workpiece. Once again, check the correctness of the data carefully.
The procedure of setting the zero position of workpiece Y axis is the same as that of X axis.
Prepare all tools according to the programming instruction.
According to the tool data in the programming operation instruction, replace the tool to be processed and let the tool touch the height measuring device placed on the datum plane. When the red light of the measuring instrument is on, set the relative coordinate value of this point to zero.
Move the tool to a safe place, manually move the tool down by 50mm, and set the relative coordinate value of this point to zero, which is the zero position of Z axis.
Record the mechanical coordinate Z value of this point in one of g54 ~ G59. This completes the zero setting of the X, y, z axes of the workpiece. Once again, check the correctness of the data carefully.
The one-sided collision is also to touch one side of x-axis and Y-axis of the workpiece according to the above method. Offset the relative coordinate value of x-axis and y-axis at this point. The radius of collision head is the zero position of x-axis and y-axis. Finally, the mechanical coordinates of x-axis and y-axis are recorded in one of G54-G59. Once again, check the correctness of the data carefully.
Check the correctness of the zero point, move the X and Y axes to the side suspension of the workpiece, and visually inspect the correctness of the zero point according to the size of the workpiece. Two 报错笔记

Operation steps of CNC machine tool

Confirm the model, size and allowance of processing blank according to the program sheet before operation, and sand and grind the blank

After operation, confirm the position of the workpiece and the processing sequence, and complete the table comparison

In the process of centring, if it is necessary to “split the rod”, the rotating speed is 501r / m. if the tool is used to divide the center, the speed depends on the tool. In this process, it should be noted that the data must be taken at the same height to ensure the accuracy of the split. After the separation, the “g0g54 x0y0” can be used for inspection

Before the formal processing, check and confirm whether the position of the workpiece is placed and whether the fetching is correct

C. Precautions in CNC machining

Before machining in each program, it is necessary to strictly confirm whether the tool is consistent with the program
When installing the tool, confirm whether the length of the tool and the selected tool holder are suitable
In the same workpiece, each tool setting should be kept in the same area to ensure the accuracy of tool connection
Try to blow with air in the roughening procedure and spray oil in the light knife program
Clean the aluminum slag in the machine tool before the smooth knife oil injection to prevent the aluminum slag from absorbing oil
During the operation of the machine tool, the operator shall not leave the machine tool or regularly check the operation status of the machine tool. If it is necessary to leave midway, relevant personnel must be designated to check
If too much machining allowance is found in the process of machining, you must use “single section” or “pause” to clear x, y, Z values, and then manually mill them off, and then swing back to “zero” to let them run by themselves
In case of tool collision during CNC processing, the operator must stop the machine immediately, such as pressing the “emergency stop” button or “reset key” button or setting the “feed rate” to zero
It is forbidden to open the door when the machine tool is running to avoid flying knife or workpiece
After the workpiece is off the machine, the burr must be removed in time
When off duty, operators must make timely and accurate handover to ensure the normal follow-up processing
Before shutdown, make sure that the tool magazine is in the original position and the XYZ axis is in the middle position. Turn off the power supply and the general power supply on the operation panel of the machine tool in turn
In case of severe thunderstorm, the power supply must be cut off immediately to stop working