This paper studies the characteristics of different kinds of chips produced in the process of gear machining and gives the corresponding treatment scheme, which provides technical support for the automatic production of gear parts.
The concept of made in China 2025 and industry 4.0 has pointed out the direction for the transformation and upgrading of China's manufacturing industry in the future. The rapid development of industrial robots, the Internet, and high-precision hydraulic fixtures has provided conditions for the automatic processing of parts. Automatic processing can ensure the consistency of product processing quality, improve production efficiency, shorten the product manufacturing cycle and quickly respond to market demand.
As an independent automatic production line in the construction of Wind Power Industrial Park, gear automatic production line forms a group unit of disc gear parts with the same or similar processing process according to the principles and characteristics of group technology. The automatic production line is designed as a linear layout according to the processing process flow of parts, integrating automatic loading and unloading, processing, transportation, cleaning, online detection and information collection of parts. It aims to build a benchmark project of domestic intelligent manufacturing.
Compared with mass-produced parts such as automobile engine shell and train wheel, the processing process of gear parts is long and complex, involving multiple cutting processes, and there are large differences in equipment between each processing process. The main technological processes involved in gear parts are gear hobbing of gear hobbing machine, fine turning of lathe, grinding of grinding machine and grinding of gear grinding machine.
Compared with the processing technology of parts such as shell castings, gears are processed in multiple processes. Each process involves different kinds of processing machine tools, and the processing principles of machine tools are very different. Compared with the single type chip of cast iron, the cooling medium used by gear processing machine tools is different, and the chip produced is also different in shape.
The precision CNC lathe cutting adopts emulsion for cooling, and the chips formed are long curls. Before the chips are discharged into the chip conveyor of the machine tool, they will contact with the coolant of the machine tool, and a certain amount of coolant will remain on the chips. The lathe chip is shown in Figure 1.
The gear hobbing machine is cooled by cooling oil, and the chips formed are fine and short chips. Generally, the brand of cooling oil is Flowserve hfn32le. More cooling oil will remain on the chips, and the cooling oil is expensive. The traditional chip removal system uses the magnetic chip conveyor to transport the chips to the chip removal trolley with filter screen. Part of the cooling oil leaks into the filter screen at the bottom of the chip removal trolley under the action of gravity and is recycled regularly; Most of the cooling oil will be discharged with the chips, causing great waste and polluting the environment. The hobbing chip is shown in Figure 2.
The grinding process mainly processes the inner hole and end face of disc gear parts, and uses emulsion for cooling, which mainly produces flocculent wear debris, which contains a certain amount of coolant. Wear debris cannot be recycled, nor can it be treated together with lathe chips and gear hobbing chips, but can only be discarded. The wear debris of ordinary grinder is shown in Figure 3.
The cooling oil of gear grinding machine generally adopts the brand of Flowserve hsg211le, and the chips formed are sponge gear grinding chips with strong adsorption force. There is a lot of cooling oil left in the grinding debris, and the cooling oil is expensive. The traditional chip removal system conveys the grinding debris to the chip removal trolley with filter screen through the paper belt filter. Part of the cooling oil leaks into the filter screen at the bottom of the chip removal trolley under the action of gravity and is recovered regularly. Most of the cooling oil will be discharged with the grinding debris, causing great waste and polluting the environment. The gear grinding chips cannot be recycled, nor can they be treated together with lathe chips and gear hobbing chips. The grinding debris is shown in Figure 4.
The chips involved in the automatic gear production line are divided into recyclable chips and waste chips according to their characteristics. Recyclable scrap is steel scrap, which can be discharged and collected uniformly. The waste chips need to be recycled separately, and the oily components can be recycled. Collecting and reusing the cooling oil before chip removal not only saves the cost, but also protects the environment.
Most of the wear debris is fluffy waste, which occupies a large space and cannot be discharged together with the steel debris through the chip conveyor. Wear debris contains a large amount of emulsion or cooling oil, which is time-consuming and laborious for direct transportation, and is easy to pollute the workshop. In the automatic production workshop, due to the different process equipment and workshop layout of processing parts, some enterprises adopt the centralized separation and filtration treatment system of central pipeline to treat the chip liquid in the special part of the workshop. The disadvantage of this is that a large amount of cooling medium is required to take away the wear debris. For ordinary grinding machines and gear grinding machines with different cooling medium, similar equipment is distributed, and different chip discharge and liquid return pipelines need to be designed, which is expensive.
Combined with the actual situation of the enterprise, it is more reasonable to select the scheme of hydraulic block extruding machine. Figure 5 shows the grinding chip pressing effect of hydraulic block extruding machine provided by a manufacturer. The grinding debris shall be placed in the special receiving basket after pressing the block, and shall be transported away regularly by automatic tracking trolley or forklift. In order to save the investment cost, we can also consider the scheme of centralized treatment after the chip removal of several gear grinding machines are connected in series, which not only saves the equipment investment, but also reduces the occupied space of the chip removal mechanism of each machine tool and optimizes the on-site environment.
The effect of squeezing oil pressure block is not ideal for the recovery of cooling oil of hobbing chip. According to the test verification, a large amount of cooling oil in hobbing chip can be recovered by centrifugal dryer. A centrifugal dryer is added between the secondary chip conveyor and the main chip conveyor of the machine tool. The dryer can throw out the residual oil in the hobbing chip, recycle and filter it for reuse, and the hobbing chip is discharged through the main chip conveyor.
The dried hobbing chips and crushed lathe chips are uniformly transported to the chip outlet through the centralized chip removal system, and then the block can be pressed intensively, so as to reduce the volume of iron chips by more than 90% and reduce the transportation workload and cost.
The OEM CNC machining of gear parts is long and complex, involving multiple cutting processes. By studying the characteristics of various chips produced in gear machining, especially the treatment of ordinary wear chips and gear grinding chips rarely mentioned in the literature, as well as the recovery and reuse of cooling oil in gear hobbing chips and gear grinding chips, the chips produced in gear machining are divided into two categories: recyclable and waste treatment, The long coil steel chips are discharged and uniformly pressed with the fine coil chips at the end of the chip conveyor. The gear hobbing chips are discharged after centrifugal oil rejection. The gear grinding chips and ordinary grinding chips are packed with oil pressure blocks and processed regularly by automatic tracking trolley or forklift, which provides technical support for the automatic production of gear parts.