60 sets of equipment, resulting in long
product turnaround lines and a large area of site occupancy. Its production efficiency is entirely enhanced by the number of equipment breakdown processes and margins. The Way of High CNC Machining Center Cutting Efficiency CNC machining, as a representative of advanced manufacturing productivity in modern manufacturing, plays an extremely important role in the mechanical, aerospace and mold industries. Since the 1990s, countries in Europe, the United States, and Japan have been competing to develop and apply a new generation of high-speed CNC machine tools, accelerating the pace of development of high-speed machine tools. High-speed spindle unit motor spindle speed 15000 ~ 100000r/min, high-speed and high acceleration / deceleration of the moving parts of the rapid transfer speed 60 ~ 120m/min, cutting feed speed up to 60m/min, high-speed machining center feed rate Up to 80m/min, air speed up to 100m/min. The HyperMach machine tool feed rate of CINCINNATI, USA is up to 60m/min, the speed is 100m/min, and the spindle speed has reached 60,000r/min. In terms of machining accuracy, in the past 10 years, the machining accuracy of ordinary CNC machine tools has increased from 10μm to 5μm, precision machining centers have increased from 3 to 5μm to 1 to 1.5μm, and ultra-precision machining precision has begun to enter the nanometer level ( 0.01 μm). The development and application of a new generation of high-speed CNC machine tools, especially high-speed machining centers, are closely related to ultra-high-speed cutting.
1. Differences in cutting level between machining centers at home and abroad
At present, cutting speeds in turning and milling in advanced countries have reached 5,000 to 8,000 m/min or more; spindle speeds of machine tools are more than 30,000 rpm (some as high as 100,000 r/min or more). For example, in the milling plane, the cutting speed in foreign countries is generally greater than 1000 to 2000 m/min, while the domestic equivalent is only 1/12 to 1/15 of the foreign country, that is, domestic dry 12 to 15 hours of life is equivalent to 1 foreign dry hour. According to the survey, the actual cutting time of many machining centers is less than 55% of the working time. Therefore, how to improve the processing efficiency and reduce the scrap rate has become a common issue for many companies. A survey of the cutting efficiency of CNC machining centers in China found that there are many problems such as low tool accuracy, large amount of blade run-out, low processing finish, and unmatched process equipment.
2. Ways to improve cutting efficiency
(1) Reasonable choice of cutting amount
New cutting technologies such as dry cutting and hard cutting represented by high-speed cutting have shown many advantages and strong vitality, and have become the main way for manufacturing technology to improve processing efficiency and quality and reduce costs. Practice has proved that when the cutting speed is increased by 10 times and the feed speed is increased by 20 times, far beyond the traditional cutting “forbidden zone”, the cutting mechanism has undergone a fundamental change. As a result, the metal removal rate per unit power is improved by 30% to 40%, the cutting force is reduced by 30%, the cutting life of the tool is increased by 70%, and the cutting heat remaining on the workpiece is greatly reduced, and the cutting vibration is almost eliminated. The cutting process took an essential leap forward. According to the current situation of machine tools, in order to give full play to the high-speed machining capability of advanced tools, high-speed machining is required to increase the volume of material removed per unit time (material removal rate Q).
While selecting a reasonable amount of cutting, try to choose the dense cutter (the number of cutter teeth per inch diameter ≥ 3), increase the feed per tooth, improve productivity and tool life. Relevant experimental studies have shown that when the line speed is 165m/min and the feed per tooth is 0.04mm, the feed speed is 341m/min and the tool life is 30 pieces. If the cutting speed is increased to 350 m/min, the feed per tooth is 0.18 mm, and the feed rate is 2785 m/min, which is 817% of the original machining efficiency, and the tool life is increased to 117 pieces.
(2) Choose a tool material with good performance
In the cutting process of CNC machine tools, the role of metal cutting tools is no less than steam invented by Watt. The materials used to make the tool must have high hardness and wear resistance at high temperatures, necessary bending strength, impact toughness and chemical inertness, good processability (cutting, forging, heat treatment, etc.), and are not easily deformed. At present, domestic and foreign tool materials with good performance include: cermets, hard alloy coated tools, ceramic tools, polycrystalline diamond (PCD) and cubic boron nitride (CBN) tools. They have their own characteristics, and they adapt to different workpiece materials and cutting speeds. CBN is suitable for cutting high hardness hardened steels and hard cast irons. For example, ceramic cutting tools and CBN cutting tools are used for machining high hardness steels (50 to 67HRC) and chilled cast iron. Among them, workpieces having a hardness of 60 to 65HRC or less can be used for ceramic cutting tools. , And 65HRC above the workpiece is used CBN cutting tool; PCD is suitable for cutting non-ferrous metals, and alloys, plastics and fiberglass, etc., when processing aluminum alloy parts, the main use of PCD and diamond film coating tools; carbon tools Steel and alloy tool steels are now used only for tools such as boring tools, dies, and taps; hard alloy coated tools (such as coated TiN, TiC, TiCN, TiAIN, etc.) have a high hardness and a wide range of workable workpieces. The anti-oxidation temperature is generally not high, so the improvement of cutting speed is also limited, generally in the range of 400 ~ 500m/min processing of steel parts, and Al2O3 coating high temperature hardness, processing in the high-speed range, its wear It is better than TiC and TiN coatings.
In addition, the geometric parameters of the cutting part of the cutting tool have a great influence on the cutting efficiency and the machining quality. In the high-speed cutting, the rake angle of the tool is generally 10° smaller than that of the ordinary cutting, and the back angle is 5°-8°. In order to prevent thermal wear at the tool tip, the tip of the main and auxiliary cutting edges should be used with a round tip or a chamfered tip to increase the local tip angle and increase the length of the cutting edge near the tip and the tool material volume. Improve tool rigidity and reduce tool breakage.
(3) Speed up the development of coating technology
Since its inception, tool coating technology has played an important role in the improvement of tool performance and processing technology. Coated tools have become the symbol of modern tools, and the proportion of tools in the tool has exceeded 50%. At the beginning of the 21st century, the proportion of coated tools will further increase, and it is hoped that the CBN coating technology will be technically breakthrough, and the excellent performance of CBN will be applied to more tools and cutting processes (including sophisticated and complex tools and forming tools). This will comprehensively increase the cutting level of processed ferrous metals. In addition, the development and application of nanoscale ultra-thin ultra-multilayer and new coating materials will accelerate, and coating will become the main way to improve tool performance.
(4) Select high-precision blades
The low accuracy of the blade, the amount of run-out is too high, the surface finish of the face milling cutter will be reduced, and even a ditch will appear. The run-out of the blade on a high-precision CNC machine tool should be controlled at 2 to 5 μm. With the development of CNC machine tools, the appearance of the blade surface modification coating treatment (the substrate is high-speed steel, WCo carbide, Ti-based cermet), to a large extent, improve the accuracy of the blade. At the same time, various new indexable insert structures have emerged, such as efficient squeegee blades for turning, complex-shaped reamer blades, ball end mill blades, and high-speed milling cutter blades that prevent flying Wait. Indexable inserts have entered the new stage of comprehensive development of materials, coatings, and grooves. According to the rational combination of materials, coatings, and groove types in the processing of materials and machining processes, blades with the best machining results can be developed to meet the requirements. Different requirements for high-speed, high-life cutting machining production technology.
(5) Improve the quality of machined surfaces
While maintaining the same cutting efficiency (ie, the same Q value), increasing the cutting speed can improve the chip formation process and increase the cutting damping, suppress the flutter, and accordingly reduce the amount of feed per blade can reduce the formation of traces of the cutting surface track Height, improve the surface roughness, which is conducive to the processing of precision parts and molds.
(6) Establish a reasonable tool inventory
The tools here are high cutting efficiency tools, and the price of these tools is higher. The same diameter of the milling cutter, the price of a good tool may be several times or even more than ten times that of a normal tool. If a company keeps a large number of good tools for a long time, and these tools may not be used for a long time, it will cause a backlog of funds. However, if a tool is not usually reserved, or the number of reserves is too small, it will be used up quickly, and the new tool will not be able to be purchased at a time. This will inevitably affect the efficiency of CNC machining. The tool magazines of most companies' machining centers can accommodate more than 40 cutters, and there are tool magazines with different numbers of cutters such as 60, 90, 120, etc. to choose from. The exchange time between tools is getting shorter and shorter. The tool change time of the BZ-26 from STEINEL in Germany, MCC86 from MAKINO in Japan, and the MAXIM500 from CINCINNATI in the US only takes 3 to 4 seconds.
(7) Simple Designed Sharpening Clamp
Cutter milling cutters have high efficiency and are easy to use. They are welcomed by operators. However, the consumption of blades is high and the cost of use is high. In most cases, the damage of the blades is caused by the cutting edge wear, so the re-grinding and re-use of the blades The factory can obtain higher economic benefits. Cemented carbide inserts have high hardness and low grinding efficiency. The use of single-chip grinding will not achieve the goal of saving. It is necessary to design a high-efficiency and simple fixture to realize multiple clamping at a time.
(8) Selection of processing methods
Processing methods can be divided into two types, crush milling and counter milling. The mechanical transmission system and the structure of the machining center itself have higher precision and rigidity, the friction coefficient of the relative moving surface is small, the clearance of the transmission component is small, the inertia of the transmission is small, and the damping ratio is proper, so the crushing mill can be used. Processing methods to improve processing efficiency. In addition, according to the processing experience, the tool life is increased by more than one time compared to the up-cut milling. The use of an asymmetrical end milling method can increase the tool life by 2 to 3 times.
(9) Choose a reasonable processing route
CNC machine tools, especially four-axis machining centers, are generally one-stage clamping and multi-axis machining, and they all have tool magazines that can automatically change tools and shape them once. Therefore, determining the correct and simple processing route is the basis for guaranteeing the processing quality and improving the efficiency. The principle of determining the processing route during programming is mainly as follows: The requirements for processing precision and surface roughness of the part should be guaranteed; the processing route should be shortened as much as possible, and the tool idle travel time should be reduced; the numerical calculation should be simple and the number of blocks should be reduced to reduce the number of blocks. Programming workload. For hole machining with high requirements for position accuracy and dimensional tolerances, the processing route for hole diameters of less than 18 to 20 mm is: drill hole-drilling-reaming-reaming, and for hole diameters greater than 18-20 mm. The process route is drilling - reaming - rough bore - fine bore.
In addition, through the integrated application of the processing technology, the number of workpiece installations can be reduced, which can effectively shorten the handling and installation time. For example, a five-axis and five-axis machining center and a vertical lathe are combined to form a universal machining center, and most (or all) machining of parts can be accomplished at one time.
(10) Selection of workpiece clamps
Due to the process concentration during CNC machining, comprehensive consideration must be given to the positioning of components, clamping design, fixture selection and design. First of all, the combination jig should be used as much as possible. Due to the poor flexibility of the universal fixture and relatively low positioning accuracy, a special fixture can be designed when the product batch is large and the processing accuracy is high. Second, when selecting tooling, tool exchange and on-line measurement should be facilitated to avoid collision interference.
(11) Auxiliary equipment of machining center must be equipped
In the machining center, measurement devices such as tool presetters, automatic measuring devices, and sophisticated detectors are used. With the automatic measuring device, the operator does not need to ensure the accuracy of the positioning of the parts, and does not require the operator to move and adjust the parts at any time to match certain fixed coordinate systems of the machining program, which can reduce the installation time. With the aid of the measurement, a process that required 2.5 hours, including the mounting time, was reduced to 1.5 hours. In addition, the application of these measuring devices can also reduce machining errors.
(12) Operator skills and knowledge training
The machining efficiency of a machining center largely depends on the ratio of cutting time to the working time of the machining center. The larger the ratio, the higher the machining efficiency. At the same time, the technological content of modern processing equipment is getting higher and higher, and the quality requirements for personnel are getting higher and higher. In actual production, due to the low technical level of personnel and unskilled operation, the time spent on non-processing time such as program debugging and changing workpieces is too long, resulting in low machining center processing efficiency. In addition, their expertise is too little, and they lack scientific guidance on the principles of numerical control processing, numerical control technology, numerical control tools and cutting parameters. Therefore, it is very necessary to establish a comprehensive training system, prepare new teaching materials adapted to the development of modern cutting and processing technologies, strengthen the study of theoretical knowledge by technical personnel, and strengthen the internal and external technological exchanges between enterprises.
Engine crankshaft: After the composite machining replaced the old craft and entered the 21st century, great changes have taken place in the crankshaft of the engine in terms of manufacturing processes, tools, and so on. Leading the multi-knife turning process and manual grinding process for more than half a century, it is gradually withdrawing from the historical stage due to low processing accuracy and poor flexibility. High-speed, high-efficiency composite processing technology and equipment rapidly enter the automobile and parts manufacturing industry, and high-speed and high-efficiency composite machining technology has been applied to a considerable degree in crankshaft processing and production, and will be its inevitable development trend.
Crankshaft processing technology equipment
At present, the older crankshaft production lines in China are mostly composed of ordinary machine tools and special machine tools, and their production efficiency and automation are relatively low. Roughing equipment generally uses multi-knife lathes to turn crankshaft main journals and connecting rod journals. The process quality is poor in stability, and it is easy to produce large processing stress, making it difficult to achieve a reasonable machining allowance. The general machining of crankshafts such as the MQ8260 crankshaft grinding machine is generally used for rough grinding, semi-finishing grinding, fine grinding and polishing. Usually, manual operation is used, and the machining quality is unstable and the dimensional consistency is poor.
One of the main features of the old-fashioned production line is that there are too many common equipments. According to the processing of ductile cast iron crankshafts, a production line has 35 to 40 sets of equipment. The author has examined a domestic forged steel crankshaft production line. Roughing adopts ordinary external milling machining of the main shaft and the connecting rod neck, and then the numerically controlled finishing main shaft and the connecting rod neck, and then passes through multiple grinding procedures and transfers to the finishing machining. Process. Therefore, this production line has more than
The current car engine crankshaft manufacturing industry is facing the following problems:
1. Multi-variety, small-batch production;
2. The delivery time is greatly shortened;
3. Reduce production costs;
4. The emergence of difficult-to-cut materials has made the processing more difficult. There are many issues that need to be addressed in the processing, such as hard-cutting;
5. To protect the environment, it is required to use less or no cutting fluid to achieve dry cutting or quasi-dry cutting;