Thermal deburring principle (1)
Each drawing of mechanical parts put into machining has technical requirements for deburring. In the deburring process, the craftsman often cannot process the technical documents, usually using boring tools, cloth wheels, abrasive cloths, abrasive belts, etc. to remove the burrs. With the advancement of science and technology and the development of production, artificial deburring can no longer meet the requirements of product quality and production methods in modern market competition. Finishing technology has gradually replaced the traditional deburring process, and it is increasingly being used by people. Attention is paid to the fact that some finishing and finishing of mechanical parts of ** enterprises have been compiled into the technical requirements of drawings by technicians, and standard processes have been formed.
Free abrasive surface finishing technology
Free abrasive surface finishing technology includes four series of cyclone, centrifugal, fork shaft and horizontal, and dozens of models and corresponding abrasive grinding materials, finishing and light through hundreds of mechanical parts The experimental research on the decoration has achieved better results. Have achieved good economic benefits and benefits.
Free abrasive finishing finishing considerations
The practical process of barrel finishing technology is:
Degreasing treatment→ Finishing and deburring→Sorting→Cleaning→Drying→Anti-rust treatment
◆Degreasing treatment: The parts before the finishing should be thoroughly degreased, and the ultrasonic cleaning method is often used. If the oil on the workpiece enters, the cutting force of the grinding block is obviously weakened, the effect of the grinding agent is reduced, the finishing is reduced, the efficiency is lowered, and the surface of the finished part is not bright.
◆ Finishing: Finishing is mainly based on the shape, size and finishing requirements of the finished parts to select or determine the equipment form, equipment specifications, process materials, process parameters and so on.
◆ Post-finishing processing includes three aspects: the separation of the grinding block and the workpiece, the cleaning of the grinding block and the workpiece, and the dehydration and rust prevention of the workpiece.
Common methods for sorting grinding blocks and workpieces are: manual screening, mechanical screening, vibration screening, manual electromagnetic sorting and conveyor-type magnetic sorting, which can be selected according to actual conditions. The cleaning of the grinding block and the workpiece is best by ultrasonic cleaning method, and then rinsed with clear water. Pay special attention to the dehydration drying and anti-rust treatment of the workpiece.
A large number of process tests have found that the surface of the workpiece is smooth and bright after barrel finishing, and the active metal molecules on the surface are exposed to the air and quickly oxidized and blackened, followed by rust, which is the water film left on the surface of the part after cleaning. A layer of electrolyte solution necessary for electrochemical corrosion is formed. Although the ionization of water is small, it can still ionize into H+ and [OH] -, and this ionization process accelerates with increasing temperature. At the same time, CO2, SO2, etc. are dissolved in the water, and they are easily combined with water.
H2O→H+ + [OH]-
CO2 + H2O → H2CO3 → H+ + [HCO3]-
The impurities in iron and iron are immersed in a solution containing various ions such as H+, [OH]-, and [HCO3]- to form an etching battery, iron is an anode, and impurities are cathodes. In general, the water film contains oxygen, the iron on the anode is oxidized to Fe2+ ions, the electrons on the anode are oxygen, and then combined with water to form [OH]- ions. The corrosion reaction is:
2 Fe+ O2+2 H2O=2Fe(OH)2
From this point of view, dewatering and drying, anti-rust treatment after de-oiling treatment and finishing after finishing is very necessary, both are indispensable, and there are many methods. Dehydration drying usually uses an industrial dryer. The main components of the anti-rust oil are lanolin, petroleum sulfonate, sodium petroleum sulfonate and additives.
Abrasive flow polishing
Principle: During the processing of the abrasive flow, the clamp cooperates with the workpiece to form a machining channel, and two opposite abrasive cylinders cause the abrasive to be pushed back and forth in this passage (see Figure 1). The abrasive grinds the surface or corners of the channel evenly and progressively, resulting in polishing and chamfering.
Figure 1 Principle of abrasive flow processing
Machine tools, abrasives and fixtures are the three elements of abrasive flow processing:
◆Extrusion grinding machine: Its function is to fix the workpiece and fixture and control the extrusion pressure. Under a certain pressure, the abrasive is ground to the surface to obtain deburring and chamfering. The machine tool pressure ranges from 7 to 224 kg/cm2;
◆ Abrasive: It is made of a semi-solid carrier with viscoelasticity, softness and cutting property and a certain amount of scrub. The viscosity of the different carriers, the type of sanding, and the size of the abrasive particles can produce different **. Common types of abrasives are: silicon carbide, cubic boron nitride, alumina and gold steel sand. The sand size is between 0.005 and 1.5 mm. High-viscosity abrasives can be used to uniformly grind the walls and large passages of parts; low-viscosity abrasives are used to round the corners of small parts and small channels;
◆ Fixture: Position the part and guide the abrasive to the part to be processed to block the parts that need no machining.
In order to successfully complete the abrasive flow processing of the parts and get the best processing**, there are many influencing factors. In addition to the equipment, it also includes the choice of abrasive, the size of the pressing force, the number of cycles, and the reasonable design of the fixture.
Advantages: Extrusion grinding is to remove the metal material in a small amount, deburring and rounding the intersection of the internal cavity of the part to achieve the purpose of fine processing. Abrasive flow processing is precise, stable and flexible. Widely used in the automotive industry and various manufacturing industries. Its most fundamental advantage is that it can reach parts with complicated and difficult to access parts; the polished surface is uniform and complete; the processing of batch parts is repeated. These processing features improve the performance of parts, extend the life, and reduce the labor of manual labor, greatly reducing labor intensity. For example, when the car inlet pipe is hand polished, its inner surface can only be cut first, polished and then welded. With the abrasive flow processing method, the inner surface polishing can be completed without cutting and opening. In addition to being a polishing method, the abrasive flow process can also perform some micro-grinding of parts with extremely tight surface tolerances and quality requirements.
Application: Abrasive flow processing is suitable for machining different parts and sizes. Small holes as small as 0.2mm or gears of 1.5mm diameter, up to 50mm diameter spline channels, even 1.2m turbine impellers. Machine tools for machining large parts can be equipped with a swing arm or conveyor track.
This process has been widely used in the finishing of automotive parts: intake and exhaust pipes, intake valves, plenums, fuel injectors, injectors, cylinder heads, turbine casings and blades, splines, gears, brakes, etc. . Such as: rough cylinder head castings in the special two-station abrasive flow production line, the production capacity can reach 30 pieces per hour, the roughness from Ra4μm or Ra5μm to Ra0.4μm, can reduce the exhaust emissions by 7%, the engine Power increased by 6% and mileage increased by 5%.
The microporous abrasive flow machine developed in recent years is unique in processing injector nozzles. It performs complex program operations based on the relationship between extrusion pressure, abrasive temperature, and viscosity. During the machining process, when the set flow rate of the injector reaches, the machining stops automatically. The processing time is about 10 seconds, and the flow dispersion can be controlled to ±1%. Also equipped with this processing equipment are flow testers and high pressure cleaning equipment. These devices are available in single or multiple stations depending on the needs of the user. It can also be a complete system with robotic connections, including machining, measuring, and cleaning.