In the machining circuit, parts with high precision requirements are often encountered. Now let’s understand the analysis of positioning error in processing technology
In terms of machining process, the positioning error is divided into many cases. The following shall be paid attention to during operation:
Positioning error refers to the positioning error of a machining accuracy parameter in the machining process of machining a part. It is an integral part of the machining error of the machining accuracy parameter.
A process and positioning scheme can produce different positioning errors for several machining accuracy parameters of the process. Therefore, the positioning errors of these machining accuracy parameters shall be calculated respectively.
The premise of analyzing and calculating the positioning error is to use the fixture to clamp and process a batch of parts with the adjustment method to meet the processing requirements.
The positioning error calculated by analysis refers to the maximum positioning error range that may occur when processing a batch of workpieces. It is a limit value, not a specific value of the positioning error of a workpiece.
The most position change of the design basis for processing a batch of parts relative to the fixture tool adjustment basis is the reason for the positioning error, not necessarily the positioning error.
These points simply understand the analysis and calculation of positioning error. There are many reasons for the error affecting the size in the process of precision CNC machining parts and mechanical parts machining.
Nowadays, in the field of machining industry, ordinary machining equipment can not meet the quality requirements. Now CNC machining equipment replaces the traditional machine tool machining, mainly precision CNC machining and CNC lathe machining; Let’s learn about the characteristics of precision CNC machined parts:
Advantages of CNC machining center in precision machining process:
Precision CNC has high machining precision and high machining quality;
CNC machining can carry out multi coordinate linkage, and can process parts with complex shapes;
When precision CNC machining parts are changed, generally only the NC program needs to be changed, which can save the production preparation time;
Precision CNC machining itself has high precision and rigidity. It can choose favorable processing dosage and high productivity (generally 3 ~ 5 times that of ordinary machine tools);
CNC machine tools have a high degree of automation, which can reduce labor intensity;
CNC machining center mass production, easy to control product quality and save labor operation;
The above is about the characteristics of precision CNC machining. Thank you for your attention!
In the field of mechanical parts processing industry, “machining” refers to the process of changing the overall dimension or performance of the workpiece through a kind of mechanical equipment. Can precision machining be used? “Precision machining” belongs to the finishing process in machining. It is divided into cold machining and hot machining according to the temperature state of the machined workpiece. This is the difference between “machining” and “precision machining”!
What is the difference between machining and precision machining in the working process? Precision machining often refers to the processing of parts with special requirements, which should be matched with reasonable processing equipment, such as CNC processing, CNC lathe processing, precision grinder processing, etc; Machining refers to ordinary turning, milling, grinding and other equipment. It can also be said to be one of the differences between “machining” and “precision machining”.
The above is the difference between “machining” and “precision machining”. Thank you for your attention!
In the mechanical parts processing industry, the unreasonable processing technology of precision parts will directly affect the quality. How to ensure precision parts processing, reasonable processing technology is closely related. Let’s take a look at the solution to the tool receiving trace during the processing of aluminum CNC parts:
Finish machining and rough machining shall be separated, and an appropriate amount of finish machining allowance shall be reserved: in order to ensure that the appearance and size of the product meet the standard value, usually there will be a knife path on the part surface before finish machining, so the allowance after rough machining should be guaranteed to be between 0.05mm ~ 0.15mm.
Aluminum material is light and belongs to one of the easy cutting materials. Programming command cutting command, the dialog box will also change due to different programming software, but the cutting tolerance is an indispensable setting parameter in programming, and the size of the tolerance also directly affects the accuracy and appearance of the product.
In the cutting process, optimize the overlap of advance and retreat tools: after optimizing the program, although there will be overlapping traces at the advance and retreat tools, the embossing and tool receiving marks can be eliminated.
It can improve the size and appearance. Selective feed / retract: extend the feed / retract line so that neither feed nor retract will contact the workpiece, making the machining surface smoother.
Finally, check the accuracy of the machine tool, which needs regular maintenance. Using the platform bottom plate for a long time will damage and the machine tool platform will also produce errors.
The above are the solutions to the precision CNC machining process.
In the hardware processing and manufacturing industry, we should not be unfamiliar with slow wire walking processing and fast wire walking processing. They all refer to WEDM machine tools, so these two processing technologies
What’s the difference? Let’s take a look at the following:
Development status of slow wire processing technology
Multiple cutting technology is the fundamental means to improve the machining accuracy and surface quality of slow wire walking. Generally, it is formed by one-time cutting, the accuracy is improved by two-time cutting, and the surface quality is improved by more than three times cutting.
Due to the lag of electrode wire when cutting corners, the corners will collapse. In order to improve the accuracy of corner cutting, more dynamic corner processing strategies are adopted. Such as: automatically changing the processing speed, automatically adjusting the water pressure, controlling the processing energy, etc.
The high-precision finishing circuit adopted by the advanced slow wire machining machine tool is an effective technology to improve the flatness of the machined workpiece, which significantly improves the machining accuracy of thick parts; In order to carry out the micro finishing of small fillets, narrow slots, narrow grooves and micro parts, the CNC low-speed WEDM machine tool can use 0.02 ~ 0.03 mm electrode wire for cutting.
In order to ensure high-precision machining, the mechanical accuracy, pulse power accuracy and servo control accuracy of the machine tool (including the control of mechanical motion, pulse parameters, wire feeding system and working fluid system) have reached a high level. The water temperature cooling device is adopted to make the internal temperature of the machine tool the same as the water temperature and reduce the thermal deformation of the machine tool; The closed-loop digital AC (DC) servo control system is adopted to ensure excellent dynamic performance and high positioning accuracy. The machining accuracy can be controlled within several microns, and the precision positioning can be realized by 0.1 μ M equivalent control; Immersion machining is adopted to reduce the thermal deformation of the workpiece; Motor servo, closed loop electrode wire tension control; The voltage modulation tool setting power supply is adopted to realize high-precision tool setting, and the tool setting accuracy can reach 0.002 mm without damaging the workpiece, whether dry or wet.
Advantages of medium wire walking processing technology
Medium speed wire cut electrical discharge machining (ms-wedm for short) belongs to the category of reciprocating high-speed WEDM machine tools. It realizes multiple cutting functions on the high-speed reciprocating WEDM machine, which is commonly known as “medium speed WEDM”. The so-called medium wire walking processing does not mean that the wire walking speed is between high speed and low speed, but a composite wire walking WEDM machine tool, that is, the wire walking principle is to use high-speed (8-12m / s) wire walking during rough machining and low-speed (1-3m / s) wire walking during finish machining. In this way, the work is relatively stable and the jitter is small, and the errors caused by material deformation and molybdenum wire loss are reduced through multiple cutting, The processing quality can be between high-speed wire walking machine and low-speed wire walking machine. Therefore, what users call “medium wire walking” is actually a reciprocating wire EDM machine, which draws lessons from the processing technology of some low-speed wire walking machines, and realizes stripless cutting and multiple cutting.
Like the second cutting, the wire feeding mode adopts low-speed wire feeding and speed limiting feeding. In the machining process of medium wire walking technology, attention should also be paid to deformation treatment for multiple cutting, because during on-line cutting of workpiece, with the action of original internal stress and the influence of machining thermal stress caused by spark discharge, there will be non directional and irregular deformation, resulting in uneven thickness of cutting draft, affecting machining quality and machining accuracy. Therefore, it is necessary to reserve different machining allowance according to different materials to fully release the internal stress and complete torsional deformation of the workpiece, and there can be sufficient allowance for finish cutting in subsequent multiple cutting, so as to ensure the subsequent size of the workpiece.
Advantages of fast wire walking processing technology
As the name suggests, fast wire walking processing is named because the electrode wire runs at high speed in the cutting process. Fast wire processing machine tool is an electrical processing machine tool created by Du in China. After decades of continuous improvement and development, it has become an important processing means in the manufacturing industry. It can meet the requirements of medium and low-grade mold processing and other complex parts manufacturing, and occupies a considerable weight in the medium and low-grade market.
At present, the technical index of fast wire processing machine tool: the efficiency of one-time cutting is 180 mm ²/ Min, the surface roughness after multiple cutting is RA ≤ 1.0 μ m. At this time, the average efficiency is 50 mm ²/ Min, the machined surface is glossy without obvious cutting stripes, the machining accuracy is 0.01 mm, and the electrode wire loss is ≤ 0.01 mm / 200000 mm ² 。 These performance indicators look good, but it should be noted that all links need to be ensured to obtain these indicators. Once there are differences, such as changes in the concentration of working fluid and the loss of electrode wire, it will affect the stability of processing quality.
Due to the stronger social demand for product diversification and the obvious increase in the proportion of multi variety and small and medium-sized batch production, the traditional ordinary processing equipment used in medium wire walking processing has been difficult to meet the processing requirements of high efficiency, high quality and diversification. However, medium wire walking processing has the characteristics of simple structure, low cost and low use consumption, so it also has its living space. Compared with fast wire walking machine tool, slow wire walking machine tool has obvious advantages in machining efficiency, precision and surface quality. Although the price of slow wire processing machine tool is expensive, with the rapid development of manufacturing industry, it will be more and more used in various processing fields.
With the improvement of the performance of the core processor of CNC system, the feed speed limit of high-speed machining center can reach 80m / min and the empty running speed can reach about 100m / min. At present, many automobile factories in the world, including China’s Shanghai General Motors Company, have adopted the production line composed of high-speed machining centers to partially replace the modular machine tools. The feeding speed limit of the hypermach machine tool of Cincinnati is 60m / min, the fast speed is 100M / min, the acceleration is 2G, and the spindle speed has reached 60000r / min. It takes only 30min to process a thin-walled aircraft part, while the same part takes 3 hours in general high-speed milling machine and 8 hours in general milling machine. Due to the specialization of the division of labor among the components of the mechanism, the high-speed spindle is becoming more and more popular with the development of professional spindle factories. In the past, the models used only for High-speed Automobile Industry (models with more than 15000 revolutions per minute) have become an essential element of mechanical products.
In the field of machining industry, the stability of parts processing on machine tools is very important. For example, for CNC machining, the stability of precision parts machining process is a prominent problem. The machining process must consider the material properties and external dimensions of parts. Now let’s look at the importance of precision CNC machining stability:
Machine tool: precision machining in order to meet the requirements of CNC machine tools, CNC machine tools mostly adopt the overall structure. Gray cast iron, artificial granite, steel plate weldment and other materials are used. The basic support of the whole CNC machine tool is generally used to place important parts such as guide rail and spindle box. In order to meet the machining accuracy of CNC machine tools, the machining accuracy reaches the range of production standards.
Procedure: the programming engineer formulates cutting parameters and CNC machining feed rate according to the part processing process steps. Suitable for rough machining or finish machining. Ensure the machining quality of precision parts.
Selection of cutting tools: parts with high material hardness have high requirements for cutting tools for precision machining. Because of the high-speed cutting hardness of the tool, the material is easy to wear and even break directly. Different materials need to be processed with selected tools.
The above is about the importance of stable CNC processing. For CNC processing manufacturers, it is very important to schedule the delivery date according to the normal production plan. The normal delivery date is often affected by unstable processing.
In the mechanical processing industry, CNC processing is also known as computer gong processing. It refers to the processing steps completed by the NC command of the programmer. Now let’s take a look at the accuracy parameters of CNC machining, which is mainly determined by the level that the specific geometric parameters (specification, shape and position) of CNC parts are consistent with the ideal geometric parameters. Learn the following parameters in detail:
In the process of machining mechanical parts and small batch parts, CNC machining accuracy usually includes three level parameters: specification accuracy, shape accuracy and position accuracy.
Appearance specification parameters of CNC machining
The specific specification of the machined surface of CNC parts or the middle of the surface is consistent with the ideal part specification. The ideal part processing specification refers to the median value of the specification indicated on the part drawing.
Shape accuracy parameters of CNC machining
The specific shape of the machined surface of CNC parts is consistent with the ideal part surface shape. The ideal part surface shape refers to the definite surface geometry shape.
Precision parameters of machining parts of CNC parts
After machining, the specific parts on each surface of CNC parts are consistent with the parts between the surfaces of ideal parts. The position between the surfaces of an ideal part refers to the positive position between the surfaces.
The above is the accuracy parameter control of CNC machining. For different shapes, shapes, simplicity and complexity, it is necessary to select appropriate machining process parameters to improve CNC machining efficiency and ensure the machining accuracy of parts.
As we all know, the reason why the machining of precision parts is called precision machining is precisely because its machining process and process requirements are very high, and the precision requirements for products are very high. The machining precision of precision parts includes the precision of position, size and shape. We summarize the following ten factors affecting the machining precision of precision parts:
(1) The rotation runout of the spindle of the machine tool can produce a certain error to the machining accuracy of the parts.
(2) The inaccuracy of machine tool guide rail can also lead to the error of workpiece shape processed by precision parts.
(3) Transmission parts can also lead to workpiece machining errors, which is also the main factor of workpiece surface errors.
(4) Different types of cutting tools and fixtures will also have different degrees of impact on the accuracy of machining workpieces.
(5) In the process of machining and cutting, the change of the position of the force point will lead to the deformation of the system, resulting in differences, and can also cause varying degrees of errors in the accuracy of the workpiece.
(6) Different cutting force will also affect the workpiece accuracy.
(7) The deformation caused by the heating of the process system often affects the accuracy of the workpiece. The error caused by thermal deformation of the process system. During machining, the process system will produce certain thermal deformation under the action of various heat sources.
(8) The deformation of the machine tool due to heating will lead to the deformation of the workpiece.
(9) The thermal deformation of the tool will have a great impact on the workpiece.
(10) The thermal deformation of the workpiece itself is mainly caused by heating in the cutting process.
In practical application, the higher the precision of precision parts, the more exquisite it is, the more it can reflect the machining level and quality. Therefore, generally speaking, NC machining has incomparable advantages and characteristics in machining, and its product quality is usually higher. What are the characteristics of NC precision parts machining?
NC precision parts processing plays an irreplaceable role in the development of new products. Generally speaking, parts with different complexity can be processed through programming, while the modification and updating design only need to change the program of the lathe, which can greatly shorten the R & D cycle of products.
The production efficiency of NC precision parts processing is higher. NC parts processing can process multiple surfaces at the same time. Compared with ordinary lathe processing, it can save a lot of processes and time, and the quality of parts processed by NC is much more stable than ordinary lathe.
The initial investment is larger than that of ordinary lathe, because the price of NC lathe is very high, and its maintenance cost and first preparation period for processing are long.
The automation of NC precision parts processing is very sufficient, which greatly reduces the physical labor intensity of workers. Workers do not need to operate the whole process like ordinary lathes in the processing process, but mainly observe and supervise lathes. However, the technical content of NC machining is higher than that of ordinary lathe, so it requires higher mental labor than ordinary lathe.
Familiar with the characteristics of NC precision parts processing, we can better operate NC precision parts processing and improve efficiency.
