In addition to the main machine, a machining center should also be equipped with corresponding auxiliary devices, such as hydraulic devices, pneumatic devices, gas-liquid devices, cooling devices, centralized lubrication devices, chip removal devices and minimum quantity lubrication devices, to assist the complete machine in achieving automatic running. Most of these auxiliary devices are installed inside the machining center, and their performance and quality will directly affect the performance and quality of the host machine. Once an auxiliary device fails, the host cannot operate normally, or even the host is in a shutdown state.
6. Minimum quantity lubrication device
Gas-liquid mixed minimum quantity lubrication technology (Minimal Quantity Lubrication, MQL), also known as minimum quantity lubrication, is a new cooling lubrication method for metal cutting. This working method is to mix and vaporize compressed air with an extremely small amount of lubricating oil to form micron-sized droplets, and then spray them into the processing area to effectively cool, lubricate and clean chips. Figure 2-44 is a typical MQL Device structure.
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Figure 2-44 Typical MQL device structure
Minimum quantity lubrication technology has been successfully applied in some domestic mainstream automotive powertrain companies (mainly engine plants and transmission plants): First, in those joint ventures or sole proprietorships with a German Volkswagen background, this technology is mainly used It has been fully applied in the field of crankshaft machining, and was later successfully used in the rough machining station of the connecting rod line, and is being prepared to be applied to cylinder block and cylinder head machining; secondly, in some joint ventures represented by Ford Motor (such as Changan Ford) and some independent brand car companies (such as Great Wall Motors), this technology is mainly used for processing aluminum alloy shell parts, such as transmission shells, engine blocks and cylinder heads.
As a green quasi-dry processing technology, MQL has the following advantages.
1) There is no need to replace the gas-liquid mixed micro-amount lubricating oil during processing. It is only necessary to mix (i.e. add) a small amount of pollution-free lubricating oil into the compressed gas regularly. During the entire operation, no waste liquid is discharged. The generated oil mist can be directly discharged after being purified by the equipment, thus effectively avoiding environmental pollution caused by industrial production.
2) It improves the cutting conditions of the tool, suppresses and reduces the cutting heat generated during the machining process, and increases the tool life. The cutting fluid is supplied as high-speed mist particles, which increases the permeability of the lubricant, improves the cooling and lubrication effect, and improves the surface processing quality of the workpiece.
Since the consumption of lubricating medium is extremely low when MQL is implemented, the consumption per hour is generally only 0.05~0.1L. In comparison, traditional wet machining consumes about 1000L of emulsion per hour, and the actual cutting fluid consumption of MQL is only one ten thousandth of that of traditional machining, thus greatly reducing the cost of cutting fluid. In addition, the tool, workpiece and chips outside the cutting area can be kept dry, which not only avoids the problem of waste liquid disposal, but also effectively reduces the consumption of auxiliary materials and the post-processing cost of cutting fluid.
Simply put, the gas-liquid mixed minimum quantity lubrication system is a set of oil injection devices that accurately control the amount of oil. The system structure mainly consists of three parts: an oil mist supply system, a nozzle and lubricating oil. The system has a simple structure, a small footprint, and is easy to install next to various types of machine tools.
Gas-liquid mixed minimum quantity lubrication systems can be divided into two categories: single-channel systems and dual-channel systems. Among them, the single-channel system mainly consists of the main body (i.e., compact oil mist unit), ball valve, oil supply unit, and corresponding cutting processing unit, while the dual-channel system mainly consists of the main body (i.e., including air supply and oil mist generation/supply It consists of oil composite unit), ball valve and rotary joint. The difference between the two is the different positions where air and lubricating oil are mixed to form aerosol, that is, they are divided into two forms based on the difference in transmission and atomization of trace amounts of cutting fluid. The single-channel system is characterized by the fact that air and lubricating oil are mixed into aerosol in the generating equipment, and then the aerosol is transported to the processing area through the track inside the tool; while the double-channel system is characterized by air and lubricating oil in different The aerosol is transported into the mixing chamber near the processing spindle head to form an aerosol, which is then transported to the processing area. Compared with the two-channel system, the single-channel system is more convenient to manufacture, but the oil mist is easily dispersed when conveying cooling lubricating oil mist, especially in the rotating spindle with strong centrifugal action, which often results in the processing area The oil mist is unevenly distributed, thus affecting the processing quality. The dual-channel system, because after the aerosol is formed, is transported to the processing area at a relatively short distance, the lubricating droplets are smaller than the single-channel system, and the lubrication effect will be better, so the application range is wider.
The gas-liquid mixed minimum quantity lubrication system can also be divided into an internal cooling system and an external cooling system. The gas mist of the former passes through the machine tool spindle, the inner hole and is ejected from the end, or is ejected from the original nozzle position through the original cutting fluid pipeline to achieve the desired performance. The best use effect; while the latter's aerosol is introduced from outside the machine tool and supplied from the outside of the tool.
Generally speaking, the external cooling system is suitable for machine tools that use external cooling tools, such as planers, lathes, milling machines and center sawing machines. Applicable materials include copper, aluminum, magnesium, easy-cutting steel and medium-difficult-cutting steel; while the internal cooling system The cooling system is mainly suitable for CNC lathes, machining centers and hole processing machine tools. It is more suitable for cooperating with the processing of internal cooling tools such as internal cooling drill bits, internal cooling milling cutters and internal cooling taps. Of course, it is also suitable for the use of external cooling tools. occasion. Applicable materials include aluminum alloy, copper alloy, magnesium alloy, various types of cast iron, easy-cutting steel and medium-to-high difficult-cutting steel.
In today's automotive engine industry at home and abroad, the crankshafts of small-displacement gasoline engines are mainly made of cast iron (especially ductile iron). As for the crankshafts of medium- and large-displacement gasoline engines (especially engines with turbocharging functions) Most of the materials are forged steel. As a key component of the engine, the crankshaft not only has a complex structure, but also has high technical requirements. Therefore, in order to process qualified workpieces, various companies will continue to improve and improve the production process based on relatively mature traditional processes. With the increasing emphasis on vehicle lightweighting and green manufacturing technology, novel manufacturing technologies like MQL have also been applied in the actual production of some mainstream engine plants.
