China Shenzhen Perfect Precision Product Co., Ltd. company news

The primary reason for orientation errors in cnc parts machining is the machining errors caused by the gaps and elastic deformation that occur in the transmission of the machine tool cnc parts machining process, as well as the orientation errors caused by factors such as the friction force that the tool head needs to overcome during the machining process. In the open-loop system, the orientation accuracy is greatly affected, while in the closed-loop follow-me system, the orientation accuracy depends primarily on the displacement detection The machining accuracy error caused by the few errors of cnc parts machining. In the processing of CNC machine tools, because of external forces, heat generated in the processing and other external factors, the machine tool's few accuracy is affected, the few deformation of the parts machined in the machine cnc parts can lead to few errors. According to the study, the cnc parts machining few errors have two primary causes: internal factors and external factors. The internal factors that cause cnc parts machining few errors are the few errors caused by cnc parts machining own factors, such as cnc parts machining table level, cnc parts machining guide level and straightness, cnc parts machining things and fixtures few accuracy. From the cnc parts machining long time data analysis and actual operation can be seen cnc parts machining machine tool positioning caused by machining accuracy errors. From the structural point of view, cnc parts machining processing errors are caused primarily by positioning accuracy, cnc parts machining feed system is the primary link affecting positioning accuracy. cnc parts machining machine tool feed system is usually composed of mechanical drive system and electrical control system.

I believe that everyone is no stranger to precision parts processing, in general, to judge the quality and precision of a product is only to see whether it meets the requirements. Then, wire cutting plays a role in the perfection of precision, +/-0.005mm for it is a small case! If you don't know, you may take it literally and understand that wire cutting is not the use of wire to cut products? Yes, it is true that it uses wire to cut products, but this "wire" is not ordinary wire! It is called electrode wire, which needs to have good electrical conductivity and resistance to electrical corrosion, high tensile strength, and the material should be proportional. Often used electrode wire has molybdenum wire, tungsten wire, brass wire and cored wire and so on.   Wire cutting: slow walking wire processing machine tungsten wire high tensile strength, relatively expensive, generally used in many narrow seam finishing. Brass wire is suitable for slow processing, processing surface roughness and straightness is better, less etching chip attachment, but poor tensile strength, high loss, in the slow one-way wire processing is widely used. Molybdenum wire high tensile strength, mainly used in fast wire processing, general China's machinery processing enterprises are mostly selected for the electrode wire molybdenum wire. Wire-cutting: There are three types of wire-cutting in slow-walking processing, and the precision of different types varies, respectively: fast-walking, medium-walking and slow-walking; generally the precision of fast-walking can reach +/-0.02mm, and the surface roughness can reach Ra3.2 ;the precision of medium-walking can reach +-/-0.01mm, and the surface roughness can reach ≤ Ra3.2; the precision of slow-walking can reach +/- 0.005mm, surface roughness can reach Ra0.8, therefore, the slow walking wire in the precision and quality are higher than the other two. Wire-cutting is developed on the basis of EDM piercing and forming processing. It not only makes the application of EDM has been developed, and some aspects have replaced the EDM piercing, forming processing. Today, wire EDM machine tools have accounted for the majority of EDM machines, playing a large role in the processing of precision parts, increasingly popular in today's market.

The accuracy of a CNC machine depends on several factors, some of which are determined by the manufacturer of the CNC machine, and others that can be controlled by the machinist. In order to achieve accurate part machining, the following factors must be considered.   Machine quality: A well-built machine with high-quality components will usually produce more accurate parts than a low-quality machine.   Machine condition: CNC machines contain a myriad of components, so proper maintenance is critical to maintaining their accuracy.   Tool condition: Dull and worn tools that show signs of rear face wear, crescent pits wear, etc. can reduce the accuracy of CNC machines, so it is important to keep them in good condition. Dull tools also increase cutting temperatures, which is another factor that reduces accuracy. On-machine inspection: Feedback tools such as on-machine probes can tell the machinist if the machine is cutting accurately during operation.   These tools can also be used to correct any deviations in real time, thereby improving accuracy.   Temperature and humidity: The working environment can affect machining accuracy. Although the machine is capable of cutting parts in warm conditions, thermal consistency must be maintained to avoid deviations.   Calibration: The machine should be calibrated periodically to maintain accuracy.

Machining accuracy refers to the similarity of measurements after multiple attempts or between multiple copies of a part. In other words, a machine is highly accurate if it hits exactly the same point on multiple copies of a part.   This is different from accuracy because accuracy is not specifically concerned with whether the "points" are the same as those specified in the design! A machine can be so precise that it always cuts 3 mm to the left of the intended mark.   Obviously, it is important to be both accurate and precise. Accuracy means that you are reaching the coordinates specified in the design, while precision means that you are hitting them consistently over multiple units.

In machining, the tolerance is the deviation from the value of the cut. As such, it is related to accuracy, but it is a value specified by the customer, not a property of the machine itself. If the customer requires a feature of the part to be very consistent from cell to cell, they will set tight tolerances on that feature to allow for minimal deviation. In practice, this means that the machine must be operated more slowly and carefully.   If more lenient tolerances are specified - for example on non-machined features - the machining can be done faster. Although the tolerances are defined by the customer, the machine usually specifies its standard tolerances and minimum possible tolerances.

Machining performance is not only related to the interests of the enterprise, but also to safety, which can effectively reduce the probability of safety accidents while bringing economic benefits to the enterprise. Therefore, it is especially important to avoid the deformation of parts during the machining process. Operators need to consider various factors and take appropriate measures to prevent deformation during the machining process so that the finished part can be used properly. In order to achieve this goal, it is necessary to analyze the causes of deformation in the machining of parts and to find reliable measures for the deformation of parts, with a view to laying a solid foundation for the realization of the strategic goals of modern enterprises. First, analysis of the causes of deformation in the machining of mechanical parts   1, the role of internal forces lead to parts machining accuracy change lathe processing, usually using the role of centripetal force, with the lathe's three-jaw or four-jaw chuck, the parts stuck tight, and then the mechanical parts for processing. At the same time, in order to ensure that the parts do not loosen and reduce the role of internal radial force when the force is applied, it is necessary to make the clamping force greater than the cutting force of the machine. The clamping force increases with the increase of the cutting force and decreases with it. Such an operation can make the mechanical parts in the process of machining force stability. However, after the three-jaw or four-jaw chuck is released, the machined mechanical parts will be far from the original, some present polygonal, some present oval, a large deviation.   2, the elastic deformation caused by the action of external forces in the machining of parts in the elastic deformation of the main reasons there are several aspects. First, if the internal structure of some parts contains thin sheets, there will be higher requirements for the operation method, otherwise, when the operator is positioning and clamping the parts, it cannot correspond with the design between the drawings, which will easily lead to the generation of elastic deformation. Second, the unevenness of the lathe and fixture, so that the parts in the fixed on both sides of the force is not uniform, resulting in the cutting of the force on the side of the small role in the force will appear under the action of the translation of the parts deformation. Third, the positioning of the parts in the process is not reasonable, so that the rigid strength of the parts is reduced. Fourth, the presence of cutting forces is also a cause of elastic deformation of the part. These different reasons for the elastic deformation, all illustrate the effect of external forces on the quality of machining of mechanical parts.   3, heat treatment processing is prone to deformation problems for the thin sheet class of mechanical parts, due to its very large long diameter, in its heat treatment is prone to straw hat bending condition. On the one hand, there will be the phenomenon of the middle bulge, plane deviation increases, on the other hand, due to the influence of various external factors, so that the parts produce bending phenomenon. These deformation problems are not only due to changes in the internal stress of the parts after heat treatment, and the operator's professional knowledge is not solid, not quite understand the structural stability of the parts, thus increasing the probability of deformation of the parts. Second, the mechanical parts processing deformation improvement measures   In the actual processing of parts, resulting in parts deformation of many factors. In order to fundamentally solve these deformation problems, the operator needs to seriously explore these factors in the actual work, and combined with the essence of the work, the development of improvement measures.   1, enhance the quality of the blank in the specific operation process of various equipment, enhance the quality of the blank is to prevent the deformation of the parts to ensure that the processed parts meet the specific standard requirements of the parts, to provide assurance for the use of the parts later. Therefore, the operator needs to check the quality of different blanks and replace the problematic ones in time to avoid unnecessary problems. At the same time, operators need to combine the specific requirements of the equipment to choose reliable blanks to ensure that the quality and safety of the parts after processing meet the standard requirements, and thus extend the service life of the parts.   2, increase the stiffness of the parts to prevent excessive deformation in the machining of mechanical parts, the safety performance of the parts is affected by many objective factors. Especially after the heat treatment of the parts, due to the phenomenon of stress contraction, will lead to parts deformation. Therefore, in order to prevent deformation, the technician needs to choose a suitable heat-limited treatment to change the stiffness of the part. This requires the application of the appropriate heat-limiting treatment in combination with the properties of the part, thus ensuring safety and reliability. Even after heat treatment, there will be no significant deformation.   3, the use of special fixtures to reduce clamping deformation in the process of machining mechanical parts, the requirements for refinement is very strict. For different parts, the use of different special fixtures can make the parts in the process of processing is not easy to appear displacement. In addition, before processing, the staff also need to carry out the corresponding preparatory work, a comprehensive check of fixed parts, against the drawings, check whether the position of mechanical parts is correct, in order to reduce the clamping deformation.   4, trimming processing parts after heat treatment is easy to deformation problems, which requires measures to ensure the safety performance of the parts. In the mechanical parts after processing and natural deformation, to use professional tools for trimming. In the finishing process of the machined parts, it is necessary to follow the standard requirements of the industry to ensure the quality of the parts and extend their service life. This method is most effective when performed after the part has been deformed. If the part is deformed after heat treatment, it can be tempered after quenching. This is because residual austenite is present in the part after quenching and these substances are then converted to martensite at room temperature and the object then expands. When processing parts to treat every detail carefully, so that you can reduce the probability of parts deformation, grasp the design concept on the drawings, according to the production requirements, so that the products produced to meet the standards, improve economic efficiency and efficiency, so as to ensure the quality of mechanical parts processing.   5, measures to reduce the clamping force in the processing of poorly rigid parts, you need to take some measures to increase the degree of rigidity of the parts, such as you can increase the auxiliary support. Attention should also be paid to the contact area between the stepping-up point and the parts, according to the different parts, choose different clamping methods, such as processing thin-walled set of parts, you can choose a flexible shaft device for clamping, pay attention to the location of the stepping-up should choose a more rigid part. And for long shaft type of mechanical parts, you can use the two end positioning method. For the very large diameter parts, the need to use the two ends of the clamping method, can not use "one end of the clamping, one end of the suspension" method. In addition, when machining cast iron parts, the design of the fixture should be based on the principle of increasing the rigidity of the cantilevered part. Can also use a new hydraulic clamping tool to effectively prevent the parts in the process of clamping deformation caused by quality problems.   6, reduce the cutting force in the cutting process should be closely combined with the processing requirements to pay attention to the cutting angle in order to reduce the cutting force. You can try to increase the front angle of the tool and the main deflection angle, so that the cutting edge sharp, and a reasonable tool in the turning of the size of the turning force is also critical. For example, in the turning of thin-walled parts, if the front angle is too large, it will make the wedge angle of the tool larger, speed up the wear rate, deformation and friction will also be reduced, and the size of the front angle can be selected according to the different tools. If you choose high-speed tools, the front angle is 6 ° to 30 ° best; if you use carbide tools, the front angle is 5 ° to 20 ° best.

Our working environment is very important, and it can play a big role. In ordinary life, often use to precision mechanical parts, so it is more familiar with it. In the actual machining production process in a variety of heat sources (friction heat, cutting heat, ambient temperature, thermal radiation, etc.) under the action of machine tools, tools, workpieces being machined and other temperature changes will produce thermal deformation, which affects the relative displacement between the workpiece and the tool, resulting in processing errors, and then affect the machining accuracy of the parts. Such as the coefficient of linear expansion of steel 0.000012 / ℃, for the length of 100mm steel parts, when the temperature rises 1 ℃ will elongate 1.2μm. temperature changes in addition to directly affect the expansion of the workpiece, the accuracy of machine tools and equipment also has an impact.   In the precision machining, the machining accuracy of the workpiece and the stability of the accuracy put forward higher requirements. According to relevant statistics, in precision machining, the processing error caused by thermal deformation accounts for 40%-70% of the total processing error. Therefore, in the high-precision precision machining, in order to avoid the expansion and contraction of the workpiece due to temperature changes, the reference temperature of the environment is generally strictly defined. And the deviation range of temperature change is set, 20 ℃ ± 0.1 ℃ and 20 ± 0.01 ℃ of constant temperature processing has appeared. In general, for precision processing with constant temperature and humidity laboratory, in order to avoid the processed workpiece in the processing and measurement of temperature changes due to expansion and contraction, generally strict provisions of the benchmark temperature of the room, and the development of temperature changes in the range of deviation, while the requirements for the relative humidity of the air is not as strict as the precision requirements of textile testing. Such as a national ultra-precision processing laboratory, the required temperature is 20 ℃ ± 0.2 ℃, while the relative humidity is 45% ± 5%.

In the process of precision machining, companies not only need to ensure its quality, but also need to carefully maintain for the external aesthetic aspects. In order to protect the precision parts from the erosion of sweat, air and other components, so that they are always in factory condition and improve the service life. The parts need to be packaged after they come out of the oven in individually sealed packages, and they also need to be wiped down with gasoline or alcohol, a task that requires gloves to work and blow dry, and then isolated with cotton. In the various forms of precision machining, balance screws are difficult to process due to their deep opening slots, small width, small tolerance range of dimensions and other requirements, resulting in a difficult machining process, easy to scratch and difficult to ensure the shape size. From the traditional processing process, combined with the existing measuring tools, the polishing of the mold and the lubrication of the opening slot can be carried out before processing, and a clamping tire tool can also be designed to allow the balance screw and the tire tool to be processed at the same time during the precision machining, with a small gap between the tire tool and the workpiece, which not only improves the rigidity of the opening slot and reduces the chance of deformation, but also enables the balance screw to achieve The requirement of accuracy. The introduction of sine gauge measurement, sine gauge is a lever table with the calibration of the working taper or angle, the measurement block and the sine relationship in the trigonometric function A precision gauge, consisting of two precision cylinders and a precision work plane body, in the machine tool processing can be in the processing of the angle of the workpiece with precision positioning, in the processing of precision mechanical parts, will be placed on the work plate of the sine gauge, the opposite flat against the sine gauge The workpiece on the stop plate is positioned, and its final required size is the sum of the height of the sine gauge and the size of the measured workpiece. After such measurement, the tolerance of the shape and size of the precision parts can be strictly controlled, and the position of the error can be precisely positioned, while the precise data of the workpiece can be easily derived.      

Compared with drilling-expanding-reaming process, the bore size is not limited by the tool size, and the bore has strong error correction ability, which can correct the original hole axis skew error by several tool walks, and can make the bored hole and the positioning surface maintain high positional accuracy. Compared with turning, the quality and productivity of boring are not as high as turning due to the poor rigidity and deformation of the tool bar system, poor heat dissipation and chip removal, and large thermal deformation of the workpiece and tool. As we can see from the above analysis, boring can be done in a wide range of different sizes and accuracy levels, and it is almost the only method for holes and hole systems with large diameter, high size and position accuracy requirements. The machining accuracy of boring is IT9 to IT7 grade, and the surface roughness Ra is . Boring can be carried out on boring machines, lathes, milling machines and other machine tools, with the advantages of flexibility, production is widely used. In mass production, boring dies are often used to improve the efficiency of boring.

Method of work process division   Machining parts on CNC lathe should be divided into processes according to the principle of process concentration, and most or even all surfaces should be finished under one clamping as far as possible. According to different structure shapes, usually choose external circle, end face or internal hole, end face clamping, and strive to unify the design reference, process reference and programming origin. In mass production, the following methods are commonly used to divide the process.   1, according to the part processing surface division process   That is, the completion of the same part of the surface process for a process, for the processing of multiple and complex surface parts, according to its structural characteristics (such as internal shape, shape, surface and plane, etc.) into multiple processes.   The surface requiring high positional accuracy will be completed in one clamping, so as not to affect the positional accuracy of the error generated by multiple positioning clamping. As shown in Figure 1, in accordance with the process characteristics of the part, the outer and inner contours of the rough and finish machining in a process to reduce the number of clamping, which is conducive to ensuring coaxiality.   2、Dividing the process by roughing and finishing   That is, the part of the process completed in rough machining is a process, and the part of the process completed in finishing machining is a process. For the parts with large margin and high processing accuracy requirements, roughing and finishing should be separated and divided into two or more processes. Rough turning will be arranged in the lower precision, higher power CNC machine tools to carry out, the finish turning will be arranged in the higher precision CNC machine tools to complete.   This division method is suitable for parts with large deformation after machining, which require separate rough and finish machining, such as parts with blanks of castings, welded parts or forgings.   Dividing the process according to the type of tool used   3、Dividing the process according to the type of tool used   The same tool to complete the part of the process for a process, this method is suitable for the workpiece surface to be machined more, machine tools work continuously for a long time, the preparation of processing procedures and check the difficulty of the situation.   4, according to the number of times the installation process   A part of the process to complete the installation for a process. This method is suitable for workpieces with little processing content, the processing is completed to reach the state of pending inspection. After serious and careful analysis of the part diagram, the following basic principles should be followed to develop the machining plan - coarse first, then fine, near then far, inside and outside cross, the least number of program segments, and the shortest tool route.   (1) Coarse first and then fine   It means that the machining accuracy is gradually improved according to the sequence of rough turning and half finishing turning. In order to improve production efficiency and ensure the quality of finishing parts, in the cutting process, the roughing process should be arranged first, in a shorter period of time, most of the machining allowance before finishing is removed, while trying to ensure that the finishing allowance is uniform.   (2) Near first and then far   The far and near mentioned here are according to the distance of the machining part relative to the tooling point. In general, especially in rough machining, it is usually arranged that the part near to the tool point will be machined first, and the part far from the tool point will be machined later, in order to shorten the tool movement distance and reduce the empty travel time.   (3) Internal and external crossover   For both the inner surface (inner cavity) and the outer surface of the parts to be machined, the processing sequence should be arranged so that the inner and outer surfaces are rough machined first, followed by the inner and outer surfaces for finishing.   Determine the tool path   Tool path: in CNC machining, the tool position point relative to the workpiece trajectory and direction of motion. That is, the tool from the start of the movement of the tool point, until the 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.   Determine the general principle of the tool path: under the premise of ensuring the machining accuracy and surface quality of the part, try to shorten the tool path to improve productivity; convenient coordinate value calculation, reduce the programming workload, easy programming. For multiple repetitions of the tool route, subroutines should be written to simplify programming. CNC lathe on the processing of parts commonly used tool route.   Analysis of the tool path of turning circular arc   When actually turning a circular arc, multiple tools are required for processing, and most of the residual is removed first before the required arc is finally turned.   Analysis of the groove route   When turning a rectangular groove with low precision and narrow width, use a grooving tool with width equal to the width of the groove, and use the straight feed method to turn it out at one time. The groove with high precision requirements is generally turned by second feed, that is, the first feed groove, both sides of the groove wall to leave a precision turning margin, the second feed with equal width tool trimming.   Turning wider grooves, you can use multiple straight feed method to cut, and leave finishing allowance on the wall and bottom of the groove, and the last knife finishing to size.