What is CNC machining
What is CNC machining?
Table of Contents
- What is CNC machining?
- The operation process of CNC machining
- The main features of CNC machining
- CNC machining processing principles
- Tool selection for CNC machining
- Operational safety of CNC machining
CNC machining refers to the processing by the control system to issue instructions to the tool to make various movements to meet the requirements, in the form of numbers and letters to indicate the shape and size of the workpiece and other technical requirements and processing process requirements. It refers generally to the process of machining parts on a CNC machine tool.
CNC machine tool is a computer to control the machine tool, used to control the machine tool computer, whether it is a special computer, or general-purpose computer are collectively known as the CNC system. CNC machine tool movement and auxiliary action are controlled by the instructions issued by the CNC system. The instructions of the CNC system is prepared by the programmer according to the material of the workpiece, processing requirements, the characteristics of the machine tool and the instruction format (CNC language or symbols) specified by the system. The CNC system according to the program instructions to the servo device and other functional components issued to run or final break information to control the machine tool’s various movements. When the parts of the processing program is over, the machine will automatically stop. Any kind of CNC machine tools, in its CNC system if no input program instructions, CNC machine tools can not work. Machine tool controlled actions include machine start, stop; spindle start and stop, rotational direction and speed change; feed motion direction, speed, way; tool selection, length and radius compensation; tool replacement, coolant on and off, etc.
The operation process of CNC machining
There are manual (manual) programming and automatic programming methods for CNC machining programming. Manual programming, the entire content of the program is prepared by manual according to the instruction format specified by the CNC system. Automatic programming, i.e., computer programming, can be divided into automatic programming methods based on language and drawing. However, no matter what automatic programming method is used, all need to have the corresponding supporting hardware and software.
It can be seen that the realization of CNC machining programming is the key. But programming alone is not enough, CNC machining also includes a series of preparatory work that must be done before programming and after-processing work after programming. Generally speaking, CNC machining process mainly includes the following.
- (1) Select and determine the parts and content for CNC machining.
- (2) The process analysis of the part drawing for CNC machining.
- (3) The process design of CNC machining.
- (4) Mathematical processing of the part drawing.
- (5) Preparation of machining program sheets.
- (6) Production of control media according to the program sheet.
- (7) Calibration and modification of the program.
- (8) Trial machining of the first part and processing of field problems.
- (9) The finalization and archiving of CNC machining process documents.
In order to improve the degree of production automation, shorten the programming time and reduce the cost of CNC machining, in the aerospace industry also developed and used a series of advanced CNC machining technology. Such as computer numerical control, that is, the use of small or microcomputer instead of the controller in the numerical control system, and the software stored in the computer to perform calculations and control functions, this soft connection of the computer numerical control system is gradually replacing the initial state of the numerical control system. Direct CNC is a computer directly control multiple CNC machine tools, very suitable for small batch short cycle production of aircraft. The ideal control system is to continuously change the processing parameters of the adaptive control system, although the system itself is very complex, expensive, but can improve the efficiency and quality of processing. The development of CNC in addition to the hardware aspects of the CNC system and machine tool improvements, there is another important aspect is the development of software. Computer-aided programming (also called automatic programming) is written by the programmer with the CNC language after the program, it will be entered into the computer for translation, and finally the computer automatically output perforated tape or tape. The more widely used CNC language is the APT language. It is roughly divided into a main processing program and a post-processing program. The former program written by the programmer to translate, calculate the tool trajectory; the latter tool trajectory into the CNC machine tool part processing program. CNC machining, is in the workpiece for processing before the computer in advance to write a good program, and then these programs into the use of computer programs to control the machine tool for command processing, or directly in this computer program control of the machine control panel to write instructions for processing. The process of machining includes: tool walking, tool changing, variable speed, change of direction, stopping, etc., all done automatically. CNC machining is an advanced means of modern mold manufacturing and processing. Of course, CNC machining means must also not only be used for mold parts processing, the use is very wide.
The CNC machining processability of the part being machined involves a wide range of issues, the following combined with the possibility and convenience of programming some of the main elements that must be analyzed and reviewed.
1. Size labeling should be consistent with the characteristics of CNC machining
In the CNC programming, all points, lines, surface dimensions and location are based on the programming origin. Therefore, it is best to give the coordinate size directly on the part diagram, or try to cite the same datum size.
2. Geometric elements of the conditions should be complete and accurate
In the programming, the programmer must fully grasp the geometric elements that constitute the part profile parameters and the relationship between the geometric elements. Because in automatic programming to define all the geometric elements of the part profile, manual programming to calculate the coordinates of each node, no matter which point is not clear or uncertain, programming can not be carried out. However, due to poor consideration or neglect by the part designer during the design process, parameters are often incomplete or unclear, such as whether the arc is tangent to or intersects or departs from the line, arc and arc. Therefore, when reviewing and analyzing the drawings, we must be careful and find the problem in time to contact with the designer.
3. Reliable positioning reference
In the CNC machining, the processing process is often more concentrated, the same benchmark positioning is very important. Therefore, it is often necessary to set some auxiliary benchmarks, or add some process tabs on the blank.
4. Unified geometric type or size
The shape of the part, the cavity is best to use a unified geometric type or size, which can reduce the number of tool changes, but also may apply control procedures or special procedures to shorten the length of the program. The shape of the part as symmetrical as possible to facilitate the use of CNC machine tools mirror processing function to program to save programming time.
The basic principles of positioning and installation
When processing parts on CNC machine tools, the basic principle of positioning and installation is a reasonable choice of positioning reference and clamping program. In the selection should pay attention to the following points.
- 1. Strive to design, process and programming calculations of the benchmark unity.
- 2. Minimize the number of clamping, as far as possible after a positioning clamping, processing all the surface to be machined.
- 3. To avoid the use of the machine manual adjustment type processing program, in order to give full play to the effectiveness of CNC machine tools.
The selection of fixture basic principles
CNC machining characteristics of the fixture put forward two basic requirements: one is to ensure that the fixture coordinate direction and the machine’s coordinate direction is relatively fixed; second is to coordinate the size of the parts and machine coordinate system relationship. In addition, the following points should be considered.
- 1. When the parts processing batch is not large, should try to use combination fixtures, adjustable fixtures and other general fixtures to shorten the production preparation time, save production costs.
- 2. In batch production before considering the use of special fixtures, and strive to simple structure.
- 3. The loading and unloading of parts should be fast, convenient, reliable, in order to shorten the machine stopping time.
- 4. The parts on the fixture should not prevent the machine tool to the parts of the surface processing, that is, the fixture should be open, its positioning, clamping mechanism components can not affect the processing of the tool (such as collision, etc.).
CNC machining error △ number plus is formed by the programming error △ editor, machine tool error △ machine, positioning error △ fixed, tooling error △ knife and other errors combined.
That is: △ number plus = f (△ editor + △ machine + △ fixed + △ knife)
- 1. Programming error △ editor by the approximation error δ, rounding error composition. Approximation error δ is generated in the process of using straight line segment or circular arc segment to approximate the non-circular curve, as shown in Figure 1.43. Rounding error is the error generated by rounding the coordinate values into integer pulse equivalent values during data processing. Pulse equivalent is the displacement of each unit pulse corresponding to the coordinate axis. Ordinary precision level of CNC machine tools, the general pulse equivalent value of 0.01mm; more precision CNC machine tools pulse equivalent value of 0.005mm or 0.001mm, etc..
- 2. Machine tool error △ machine by the CNC system error, feed system error and other reasons.
- 3. Positioning error △ fixed is when the workpiece is positioned on the fixture, the fixture is positioned on the machine tool when generated.
- 4. Tool setting error △ knife is generated when determining the relative position of the tool and the workpiece.
The main features of CNC machining
CNC machine tools are selected from the outset to have a complex profile of aircraft parts as the object of processing, solving the key of ordinary processing methods difficult to solve. The most important feature of CNC machining is that the machine is controlled by a perforated tape (or magnetic tape) for automatic machining. As aircraft, rocket and engine parts have different characteristics: aircraft and rocket zero, large component size, complex surface; engine zero, small component size, high precision. Therefore, the aircraft, rocket manufacturing sector and engine manufacturing sector selected by the CNC machine tools are different. In the aircraft and rocket manufacturing to use continuous control of large CNC milling machine, and in the engine manufacturing both continuous control of CNC machine tools, but also point control of CNC machine tools (such as CNC drilling machine, CNC boring machine, machining center, etc.).
Work order concentration
CNC machine tools generally with automatic tool changer, tool magazine, tool change process automatically controlled by the program, therefore, the process is more concentrated. Process concentration brings huge economic benefits.
- (1) Reduce the floor space of machine tools, saving plant.
- (2) Reduce or no intermediate links (such as intermediate testing of semi-finished products, temporary storage and handling, etc.), both to save time and labor.
CNC machine tool processing, no manual control of the tool, a high degree of automation. The benefits are obvious.
(1) Reduced requirements for the operator.
An ordinary machine tool senior workers, not a short period of time can be trained, and a non-programmable CNC workers training time is very short (such as CNC turners need a week can, will also write a simple processing program). And, CNC workers on CNC machine tools to process the parts than ordinary workers on traditional machine tools to process the parts of high precision, time to save.
(2) Reduce the labor intensity of workers: CNC workers in the processing process, most of the time is excluded from the processing process, very labor-saving.
(3) Stable product quality: CNC machine tool processing automation, eliminating the fatigue of workers on ordinary machine tools, carelessness, estimation and other human errors, to improve the consistency of the product.
(4) High processing efficiency: CNC machine tools such as automatic tool change makes the processing process compact and improves labor productivity.
Traditional general-purpose machine tools, although good flexibility, but low efficiency; and the traditional special machine, although very high efficiency, but poor adaptability of the parts, rigid, poor flexibility, it is difficult to adapt to the market economy under the fierce competition brought about by frequent product changes. Just change the program, you can process new parts on CNC machine tools, and automated operation, good flexibility, high efficiency, so CNC machine tools can be well adapted to market competition.
Machine tools can accurately process a variety of contours, and some contours can not be processed on ordinary machine tools. CNC machine tools are particularly suitable for the following occasions.
- 1. No scrap parts.
- 2. New product development.
- 3. The urgent need for the processing of parts.
CNC machining processing principles
- (1) The processing of the previous process can not affect the positioning and clamping of the next process.
- (2) First inside and then outside, that is, the processing of the internal cavity (inner hole) first, and then the processing of the shape.
- (3) With the same installation or using the same tool processing process, it is best to proceed consecutively to reduce the mis-capacity caused by repositioning or tool change.
- (4) In the same installation, the process that has less impact on the rigidity of the workpiece should be carried out first.
CNC lathe feed processing route refers to the turning tool from the point of tooling (or machine tool fixed origin) to start the movement, until the return to the point and end of the processing program after the path, including the path of cutting processing and tool cutting, cutting out and other non-cutting empty travel path.
The feed route of finishing is basically along the order of its part contour, so the focus of the work to determine the feed route is to determine the roughing and empty stroke feed route.
In CNC lathe machining, the determination of the machining route generally follows the following principles.
- ① It should be able to ensure the accuracy and surface roughness of the machined workpiece.
- ② Make the machining route the shortest, reduce the empty travel time and improve the machining efficiency.
- ③ Simplify the workload of numerical calculation and simplify the machining procedure as much as possible.
- ④ For some reused programs, subroutines should be used.
Make the machining program has the shortest feed route, not only can save the entire machining process execution time, but also reduce some unnecessary tool consumption and machine tool feed mechanism wear and tear of the sliding parts. The shortest feed route types and implementation methods are as follows.
(1) The shortest cutting feed route. The shortest cutting feed route can effectively improve productivity and reduce tool loss. When arranging the shortest cutting feed route, it is also necessary to ensure the rigidity of the workpiece and processability requirements.
(2) The shortest empty stroke route.
- ① Smart use of the starting point. Example of a general case of rough turning using the rectangular cycle method. The tool setting point A is set at a position far away from the blank, taking into account the need for easy tool changes during finishing, etc. At the same time, the starting point is coincident with its tool setting point.
- ② Crafty setting of tool change point. In order to consider the convenience and safety of tool change, sometimes the tool change point is also set at a position far away from the blank.
- If the tool change point of the second tool is also set in the position of no point, the empty travel distance can be shortened.
- ③ Reasonable arrangement of “return to zero” route. In the manual preparation of complex contour machining program, in order to simplify the calculation process and facilitate the verification, the programmer will sometimes return the tool end point after each tool is machined by executing the “return to zero” operation instruction to make it all return to the tool point position, and then execute the subsequent program. This will increase the distance of the feed route and reduce the production efficiency. Therefore, in the reasonable arrangement of the “return to zero” route, the distance between the end point of the previous tool and the starting point of the next tool should be as short as possible. Or zero, to meet the requirements of the shortest feed route. In addition, in the selection of return to the point of instruction, without interference, as far as possible to use the x, z-axis two-way simultaneous “back to zero” instruction, the function “back to zero” route is the shortest.
(3) Step cutting feed route for large margin blanks. Listed two kinds of too much margin blank cutting feed route.
feed route. The step cutting route is wrong, cutting in the order of 1 bucket 5, each cut leaves an equal amount of margin, is the correct step cutting feed route. Because at the same backlash amount.
(4) The continuous cutting feed route for the finishing of the part contour. Finishing of the part profile can be arranged for a knife or several knife finishing process. Its completion contour should be the last knife continuous processing, at this time, the tool into, back position to choose the appropriate, try not to arrange in the continuous contour cut and cut out or change the tool and pause, so as not to destroy the balance of the process system due to sudden changes in cutting force. Causes the part outline to produce scratches, sudden changes in shape or stagnant tool marks.
(5) Special feed route. In the CNC turning process, in general. Longitudinal feed of the tool is along the negative direction of the coordinate feed, but sometimes according to its conventional negative direction of the feed route is not reasonable. It may even damage the workpiece.
Advantages and disadvantages
CNC machining has the following advantages:
- ① Massively reduce the number of tooling, processing the complex shape of the part does not require complex tooling. If you want to change the shape and size of the part, you only need to modify the part processing program, which is suitable for new product development and reshaping.
- ② Stable machining quality, high machining accuracy, high repeatability, adapt to the processing requirements of the aircraft.
- ③ Multi-species, small batch production under high productivity, can reduce production preparation, machine tool adjustment and process inspection time, and due to the use of the best cutting volume and reduce the cutting time.
- ④ Can be processed by conventional methods difficult to process the complex surface, and even processing some unobservable processing parts. The disadvantage of CNC machining is that the machine tool equipment is expensive, requiring a high level of maintenance personnel.
Tool selection for CNC machining
Choose the principle of CNC tools
Tool life is closely related to the cutting dosage. In the development of cutting dosage, should first choose a reasonable tool life, and a reasonable tool life should be based on the goal of optimization. Generally divided into the highest productivity tool life and the lowest cost tool life of two, the former according to the goal of the least number of hours worked per piece to determine the latter according to the lowest cost of the process to determine the goal.
The following points can be considered when selecting tool life based on tool complexity, manufacturing and sharpening costs The tool life for complex and high precision tools should be selected to be higher than that of single-edged tools. For the machine clamping indexable tool, due to the short tool change time, in order to give full play to its cutting performance, improve productivity, tool life can be chosen lower, generally take 15-30min. for the installation, tool change and tool transfer more complex multi-tool machine tools, combined machine tools and automated machining tools, tool life should be selected higher, especially to ensure tool reliability. The productivity of a process in the workshop limits the productivity of the entire workshop, the process of tool life should be selected lower when a process unit of time to share to the plant-wide expenditure is larger, tool life should also be selected lower. When finishing large parts, to ensure that at least one tool is completed, to avoid changing tools in the middle of cutting, tool life should be determined by part accuracy and surface roughness. Compared with ordinary machine tool processing methods, CNC machining of the tool has put forward higher requirements, not only the need for good Gonzales, high precision, but also require dimensional stability, high durability, break and row performance altogether while requiring easy installation and adjustment, so as to meet the requirements of high efficiency of CNC machine tools. CNC machine tools selected are often used to adapt to high-speed cutting tool materials (such as high-speed steel, ultra-fine grain carbide) and the use of indexable inserts.
The choice of CNC turning tools
CNC turning tools are generally divided into type turning tools, pointed turning tools, circular turning tools and three categories. Shaped turning tools are also known as sample turning tools, the shape of the contour of the processed part is completely determined by the shape of the turning tool blade volt and size. In CNC turning processing, the common shaping turning tools are small radius circular arc turning tools, non-rectangular turning groove tools and threaded tools. In the CNC machining, should be used as little as possible or do not use shaped turning tools. Sharp turning tool is a turning tool characterized by linear cutting edge. The tips of these tools are composed of linear main and secondary cutting edges, such as 900 internal and external round turning tools, left and right end turning tools, grooving (cutting off) turning tools and various external and internal hole turning tools with small tip chamfers. Point-shaped turning tool geometric parameters (mainly geometric angle) selection method and ordinary turning is basically the same, but should be combined with the characteristics of CNC machining (such as processing routes, processing interference, etc.) for comprehensive consideration, and should take into account the strength of the tool tip itself.
Second, the arc turning tool. Arc turning tool is a roundness or line contour error is very small arc-shaped cutting edge as the characteristics of the turning tool. Each point of the arc cutting edge of the tool is the tip of the arc turning tool, and the tool position point is not on the arc, but on the center of the circle of the arc. Arc turning tool can be used for turning internal and external surfaces, especially suitable for turning various smoothly connected (concave) shaped surfaces. The radius of the arc of the turning tool should be considered when choosing the radius of the arc of the cutting edge of the two-point turning tool should be less than or equal to the minimum radius of curvature on the concave contour of the part to avoid processing dry shallow The radius should not be selected too small, otherwise not only manufacturing difficulties, but also due to the tip strength is too weak or poor heat dissipation ability of the tool body and lead to damage to the turning tool.
The choice of CNC milling with tools
In CNC machining, milling flat parts inside and outside the contour and milling plane commonly used flat bottom end mill, the tool parameters of the empirical data are as follows: First, the milling tool radius RD should be less than the minimum radius of curvature of the part inside the contour surface Rmin, generally take RD = (0.8 a 0.9) Rmin. Second, the processing height of the part H < (1/4-1/6) RD, to ensure that the knife has sufficient rigidity. Third, when milling the bottom of the inner groove with a flat-bottomed end mill, the bottom of the groove needs to be lapped because of the two walks at the bottom, and the bottom edge of the tool plays a role in the radius Re = R-r, that is, the diameter of d = 2Re = 2 (R-r), the programming takes the tool radius Re = 0.95 (Rr). For some three-dimensional surface and variable bevel profile shape processing, commonly used ball milling cutter, ring milling cutter, drum milling cutter, conical milling cutter and disc milling cutter.
Most CNC machine tools use serialized, standardized tools, indexable machine clamping cylindrical turning tools, face turning tools, such as shanks and bits have national standards and serialized models for machining centers and automatic tool changers, tool shanks have been serialized and standardized provisions, such as the standard code for the tapered shank tool system TSG-JT, the standard code for the straight shank tool system DSG-JZ. In addition, the selected tool, in the use of the tool size before the strict measurement to obtain accurate data, and the operator will enter these data into the data system, by the program call and complete the machining process, so as to process a qualified workpiece.
From what position does the tool actually start moving to the specified position? Therefore, at the beginning of the program execution, it is necessary to determine the position where the tool starts to move in the workpiece coordinate system, and this position is the starting point of the tool movement relative to the workpiece during the program execution, so it is called the program starting point or tool starting point. This starting point is usually determined by tool setting, so it is also called the tool setting point. In the preparation of the program, the location of the tool setting point should be selected correctly. The principle of setting the tool setting point is: easy for numerical processing and simplify the programming. Easy to find the right and easy to check in the process of machining; caused by the small processing errors. Tooling points can be set in the processing parts, can also be set in the fixture or machine tool, in order to improve the machining accuracy of the parts, tooling points should be set in the design of the parts of the benchmark or process base who as far as possible. The actual operation of the machine tool, through manual tooling operations to the tool position point to the tooling point, that is, “tooling point” and “tooling point” of the overlap. The so-called “tool position point” refers to the positioning reference point of the tool, the tool position point of the turning tool is the center of the tool tip or tip arc. The flat end mill is the intersection of the tool axis and the bottom surface of the tool; the ball end mill is the ball center of the ball, the drill is the tip of the drill, etc. With manual tool setting operation, the accuracy of tool setting is low and the efficiency is low. And some factories use optical tool setting mirror, tool setting instrument, automatic tool setting device, etc., to reduce tool setting time and improve tool setting accuracy. When tool change is needed during machining, the tool change point should be specified. The so-called “tool change point” refers to the position of the tool holder rotation tool change, tool change point should be located on the outside of the workpiece or fixture, to change the tool without touching the workpiece and other parts shall prevail.
CNC programming, the programmer must determine the cutting amount of each process, and write the program in the form of instructions. The cutting amount includes spindle speed, back draft and feed rate. For different processing methods, different cutting amounts need to be selected. The principle of cutting amount selection is: to ensure the machining accuracy and surface roughness of the parts, give full play to the cutting performance of the tool, to ensure reasonable tool durability, and give full play to the performance of the machine tool, maximize productivity and reduce costs.
1. Determine the spindle speed
Spindle speed should be based on the allowable cutting speed and workpiece (or tool) diameter to choose. The formula is: n = 1000v/71D formula: v? cutting speed, in m / m dynamic, by the tool durability decision; n one by one spindle speed, in r / min, D for the workpiece diameter or tool diameter, in mm. calculated spindle speed n, and finally to select the machine tool has or closer to the speed.
2. Determine the feed rate
Feed rate is an important parameter in the cutting dosage of CNC machine tools, mainly based on the machining accuracy of the parts and surface roughness requirements, as well as the tool, the workpiece material properties selected. Maximum feed rate is limited by the machine tool stiffness and performance of the feed system. Determine the principle of feed rate: when the quality requirements of the workpiece can be guaranteed, in order to improve production efficiency, you can choose a higher feed rate. Generally in 100 a 200mm / min range to choose; in cutting, processing deep holes or processing with high-speed steel tools, it is appropriate to choose a lower feed rate, generally in 20 a 50mm / min range to choose; when the machining accuracy, surface roughness requirements, feed rate should be selected smaller, generally in 20 – 50mm / min range to choose; tool empty travel, especially Long distance “back to zero”, you can set the machine tool CNC system to set the highest feed rate.
3. Determine the amount of backlash
Back eat tool amount according to the machine tool, workpiece and tool stiffness to decide, under the conditions of stiffness allows, should make the back eat tool amount equal to the workpiece machining allowance as far as possible, which can reduce the number of times to go tool, improve productivity. In order to ensure the quality of the machined surface, a small amount of finishing allowance can be left, generally 0.2 a 0.5mm, in short, the specific value of the cutting amount should be based on the performance of the machine tool, the relevant manuals and combined with actual experience with analogous methods to determine.
At the same time, so that the spindle speed, depth of cut and feed rate of the three can be adapted to each other to form the best cutting amount.
Cutting amount is not only in the machine tool adjustment must be determined before the important parameters, and its value is reasonable or not on the machining quality, machining efficiency, production costs, etc. has a very important impact. The so-called “reasonable” cutting amount is to make full use of tool cutting performance and machine power performance (power, torque), in the premise of ensuring quality, to obtain high productivity and low cost of machining cutting amount.
Operational safety of CNC machining
CNC machine tool is a high degree of automation, the structure of the more complex advanced processing equipment, in order to give full play to the superiority of the machine tool, improve production efficiency, good management, good use, repair CNC machine tools, the quality of technical personnel and civilized production is particularly important. In addition to the operator should be familiar with the performance of CNC machine tools, to achieve skilled operation, but also must develop a civilized production of good working habits and rigorous work style, with good professionalism, responsibility and cooperation spirit. Operation should do the following.
- (1) Strictly comply with the safety operating procedures of CNC machine tools. Do not operate the machine without professional training.
- (2) Strictly comply with the shift and handover system.
- (3) To do a good job, good management of machine tools, with a strong sense of responsibility for the work.
- (4) Keep the environment around the CNC machine tools neat and tidy.
- (5) The operator should wear good work clothes, work shoes, do not wear, wear dangerous clothing items.
In order to correctly and reasonably use the CNC machine tool, to reduce the incidence of its failure, the method of operation. The machine tool management personnel agreed to operate the machine tool.
(1) Precautions before starting the machine
- (1) The operator must be familiar with the performance of the CNC machine tool, the method of operation. Only with the consent of the machine tool manager can operate the machine tool.
- (2) Before powering up the machine, check the voltage, air pressure, oil pressure is in line with the work requirements.
- (3) Check whether the movable part of the machine is in normal working condition.
- (4) Check whether the table is out of position, over the limit state.
- (5) Check whether the electrical components are solid, whether there is wiring off.
- (6) Check whether the machine grounding wire and workshop ground reliable connection (first start-up is particularly important).
- (7) Has completed the preparatory work before starting the machine before closing the main power switch.
(2) Start-up process precautions
- (1) Strictly according to the machine tool manual in the start-up sequence for operation.
- (2) In general, the process of starting the machine must first be carried out back to the machine reference point operation, the establishment of the machine to do the standard system.
- (3) After the machine is turned on, let the machine tool airlift more than 15min, so that the machine tool to reach a balanced state.
- (4) After shutdown must wait for more than 5min before you can start again, no special circumstances should not be frequent start-up or shutdown operations.
(3) Debugging process notes
- 1) Edit, modify, debug the program. If it is the first piece of test cutting must be empty run to ensure that the program is correct.
- 2) Install and debug the fixture according to the process requirements, and remove the iron chips and debris from each positioning surface.
- 3) Clamp the workpiece according to the positioning requirements to ensure correct and reliable positioning. The workpiece should not be loosened during processing.
- 4) Install the tool to be used, if it is a machining center, the tool position number on the tool magazine must be made strictly consistent with the tool number in the program.
- 5) Set up the tool by the programmed origin on the workpiece and establish the workpiece coordinate system. If multiple tools are used, each of the remaining tools will be compensated for length or tip position respectively.
When the CNC is first turned on, the three axes of origin should be restored, and the machine’s guide oil and spindle hydraulic oil should be checked for adequacy. Not enough oil in time to refuel. The size of the machined workpiece should correspond well with the drawing, even if there is only a small gap, you have to ask the above management or programming. In the process of machining, the program is broken, so it is easy to make mistakes when changing the program, so be sure to check in time. In the processing of the need to change the knife to play a single section at the same time will be XYZ axis to zero.
If the depth of processing is not affected after the tool change, then the tool will be directly shaken to the XYZ axis with the hand wheel for processing. If the depth of machining may be affected after the tool change, the tool must be re-set and the three axes must be swung to zero again for machining. This step is quite complicated for beginners, but it is a necessary skill to master in machining. Every program must be run with a tool setting. Forgetting to set the tool is a dangerous operation, which can lead to disability or death. Therefore, we have to keep in mind this step of tool setting. Many times we have scrapped workpieces because the number in the G60 is not zeroed. When we use the G60 in the machining, we should change it in time after using it. If the latter operation did not go to see in time, then the workpiece made later will be a defective product. The method of knife: general time we will choose to use a ten millimeter pin as our usual tool for knife.
Another is to do something without much precision in order to facilitate, we will take the knife directly to the surface of the workpiece method. The former method of operation is to use the handwheel to shake the tool to a certain distance from the surface of the workpiece and below the distance of a ten-millimeter pin while the pin on the surface of the workpiece, and the handwheel slowly shake upward, in the shake to ten millimeters pin just from the bottom of the tool through the time that the tool is successful. Note: This tool is the most accurate, but the workpiece is still a distance of ten millimeters from the pin. Therefore, the subsequent processing has to use the G60 one-way offset in the Z-axis. In the G60Z axis input -10. Then the zero position of the work is just in the surface of the workpiece. These two methods of tooling mixed with the use of such as not careful, is the most likely to collision accidents. Because the zero position of tool setting is not the same, G60 has -10. When you take the method of directly to the surface of the workpiece, you will crash the machine. Therefore, when choosing the tool setting method, you should be careful with the Z-axis value in G60.
Generally speaking, the main processing models with accuracy are pin hole, guide pillar hole, insert slot, key slot, etc.
(1) The processing method when doing the pin hole is: using a ten-millimeter pin hole for example, we would first use a 9.0 drill to punch the bottom hole, then use a 9.8 drill to ream the hole, and then use a ten-millimeter reamer to ream the hole. But here we should note that when we drill the 9.8 drill bit we should try with a 10 mm pin on the pin hole, we can not be sure that the hole drilled by the 9.8 drill bit must be 9.8, there will be a certain error, if we try out the 10 mm pin can not be put in when we continue the drilling process later. After drilling with the reamer also have to pay attention to the reamer strand the first hole when we also have to use ten millimeters of pins for test holes, when found that ten millimeters of pins can just tightly match the time to go back to the program.
(2) Guide pillar holes: guide pillar holes are more precise, we also have to be careful when doing. When we do the guide pillar hole, we may also use the drill and mill to mill a bottom hole first, at this time we also have to use calipers to measure the size of the hole, not to start boring when the hole is too large phenomenon. After that, we will put the boring tool on. Note: The boring tool should be used twice to align the workpiece surface and the side wall of the hole to be bored. When boring, we have to test the tool, usually five millimeters, and after the test tool is ready, we use the inside diameter to measure the actual size of the hole and the size of the hole we want to bore, and then adjust the scale of the boring tool until it reaches the size of the hole on the drawing.
This is the experience of the operator, the beginner may not consider these aspects, since it is experience, then we should keep in mind that the processing of similar places should be brought to their attention.
- 1) Generally, if we don’t pay attention when milling the drop groove, it is very easy to break the knife, and if we don’t knock off the unmilled area in the middle in time when we are about to mill through, the knife will be broken. Since we have experience, of course, we can also avoid, but to watch the program. Because there are times when the program mills more places and the depth is different when you have to watch the situation. If it is all milling drop material, we can take the method of the bottom side to the knife, and then enter the depth of the program to be milled in G60, so that the knife will not be broken.
- 2) In the processing did not pay attention to the processing content on the drawing, we code the mold just where there is processing place will also cause us to break the knife or crash the machine.
- 3) Not machining the tool and cause a broken tool. When finishing machining, we must remember to measure the tool swing. When processing we also have to be familiar with the material of each template, generally there are A3, 45#, CR12, CR12mov, skd11, s45c, SLD, P20 and some other materials. We have to be familiar with the hardness of these materials for processing, and different materials have to be handled differently. To remember some common instructions, for example, we have to know the flexible use of G81, G73, G83 in processing. Tool magazine is used less to do hardware mold, but the general CNC is equipped with a tool magazine. If the programming does not pay attention to the post-processing will generally appear when the tool change instructions, at this time for the general use of the tool magazine is more brain-damaging things. General automatic tool change instructions appear TnM6: Tn refers to how many knife number, M6 is the automatic tool change instructions. Thought the hardware mold is not required to use the tool magazine, when such a phenomenon occurs, we will use M84 this instruction.
- M00 program stop
- M01 selective stop
- M19 spindle positioning
- M30 program end and back to the start position
- M73 Y-axis mirroring OFF
- M74 Y-axis mirror ON
- M75 X-axis mirroring OFF
- M76 X-axis mirroring ON
- M95 Program mirror function ON
- M94 Program mirror function OFF
- M96 Tool arc corner mode
- M97 Tool intersection angle corner mode
- M98 Subroutine call
- M99 subroutine end
On the tool size offset problem: in the processing is not found in a reasonable tool when we can solve the case of their own offset, then do not affect the processing we can take in the G60 offset method. The offset amount is: (theoretical tool size – actual tool size) ÷ 2 = offset amount. We have to determine the direction of the offset with the actual processing. g41 and g42 use: recent time to think carefully about this piece of tooling. 2011-3-22 night made a big mistake, for us to work for three years is not allowed mistakes. We may usually when repairing the mold is generally to find the pin hole sub-center, but we also have to look at the programming of the sub-center place. It is because the programming is too vague to write the place in the distribution of the pins, and the program is divided into a punching hole, the program ran the wrong injury to the knife edge of the stripper plate.
Source: China machining solutions provider – Yaang Pipe Industry (www.machinedsgn.com)