1Overview of CNC engraving lathes imported from abroad, the parts to be processed are often hard-loaded. When it is necessary to process a low-strength thin-walled part on a CNC lathe, it is not allowed to adopt a hard-loading method. In this case, a vacuum suction jig can be used, which not only can clamp the object smoothly and reliably, but also is not easy to damage the surface of the grasped object. . To this end, we designed a vacuum chucking system for vacuum lathes using vacuum suction. The vacuum pump provides a vacuum source, and multiple CNC lathes are connected in parallel on the vacuum main road to achieve multi-channel vacuum adsorption. In order to ensure the vacuum stability of the suction port of the lathe, two vacuum pumps with a flow rate of 15 (1/S) are arranged in the machine room, and a series of control components such as vacuum pressure reducing valves are used next to the lathe to improve the stability of the vacuum. The system is compact in structure, safe and reliable in performance, and simple in operation.

2 working principle 2. 1 vacuum system working principle Vacuum system is mainly divided into vacuum pump system and vacuum generator system according to vacuum generating device. According to the actual configuration of the workshop, the clamp for the numerical control lathe adopts the vacuum pump system. The vacuum pump is a machine that forms a negative pressure at the suction port, the exhaust port directly passes through the atmosphere, and the pressure ratio at both ends is large. Vacuum is used to monitor the vacuum value of the vacuum circuit. When the vacuum pump end suddenly stops pumping, when the vacuum drops, the check valve with the pipe joint 3 can quickly cut off the vacuum circuit, keep the vacuum pressure in the clamp constant, and delay the time for the workpiece to fall off, so as to take safety remedial measures.

Due to the change in the size of the suction required by the semi-finishing and finishing, the vacuum pressure can be adjusted by the vacuum pressure reducing valve 5, and the adjustment range is 0 - 0.1 MPa. The adjustment method is Set the required vacuum pressure value of the sucked workpiece, then turn the switch to the ON state, and turn the knob 2/2-way valve 6 to the suction position to start vacuum extraction.

Since the vacuum chamber of the machine room has sufficient volume, when the vacuum degree of the vacuum adsorption jig 10 reaches the set value of the pressure reducing valve 5, the workpiece can be safely processed by adsorption. When unloading the workpiece, turn the knob type two-position three-way valve 6 to the unloading position, the clamp end is disconnected from the vacuum pump section, close the intake end, open the exhaust end, and adjust the vacuum destruction speed regulating valve 7 to control the deflation as needed. Speed, which controls the speed at which the workpiece is unloaded. The muffler 8 is installed at the exhaust port of the vacuum destruction speed regulating valve 7, which can reduce noise.

A vacuum filter 9 is provided between the vacuum adsorption jig 10 and the vacuum source 1 to filter the oil stain and the powder layer to prevent the components in the vacuum system from being contaminated and malfunction. For a vacuum pump system, it is desirable to have a vacuum adsorption clamp 10 on a branch line of the vacuum line.

But now there are 6 CNC machine tools in the workshop, which often work at the same time, so that the number of vacuum adsorption clamps that are sucked or not sucking the workpiece changes or leaks, which will cause the pressure of the pipeline to change, so that the set value of the vacuum pressure reducing valve 5 It is not easy to set, especially for the case where the small hole of the small workpiece is sucked. In order to reduce the influence of the multiple vacuum adsorption clamps 10 when sucking the workpiece, a vacuum tank and a true air conditioner pressure valve may be added to the loop to improve the stability of the vacuum pressure; at the same time, a vacuum switching valve is installed on each branch, if a vacuum is adsorbed When the fixture leaks or does not attract the workpiece, the possibility of affecting the work of other vacuum adsorption fixtures is reduced. After comparative experiments, it is proved that the above measures can have better effects, but the problem cannot be solved fundamentally.

2. 2 vacuum adsorption fixture working principle The principle of vacuum adsorption fixture for CNC lathe.

When assembling, the soft nylon tube 5 is first threaded through the spindle hole of the numerical control lathe, and then connected to the rotary quick-change joint 4. The holder 3 is positioned and clamped by a three-jaw chuck of a numerically controlled lathe. During processing, the workpiece is first adsorbed by the metal suction cup 1. After the machine is started, the spindle drives the vacuum suction fixture to work. Since the rotary quick-change joint 4 has a built-in sliding bearing and a rotating seal ring, the vacuum degree of the pipeline is maintained when the machine tool rotates, and the soft nylon tube 5 is not rotated with the machine tool spindle. In the design of the vacuum adsorption fixture, the use of the rotary quick-change coupling 4 is the key to the entire fixture. We use a company's KX-type high-speed rotary quick-change coupling, which can meet the speed of 1200 rpm, and the rotational torque is less than 0. 014 Nm.

3 Flow calculation 3. 1 Maximum flow rate Q The inner diameter D of each branch pipe is known to be (7.5 mm, and the pipe length L is 2 m. The maximum flow rate of the piping system from the switching valve to the suction cup is QQ = 11. 1 S = 277. 5(L /m in); where S: the effective cross-sectional area of ​​the pipe is 25 mm 2 3. The response time T 1 when the response time reaches 63% of the vacuum. T 1 = 60 V / Q = 0. 019(m in ) where V: from the piping volume is 0. 088 (L) Q: the maximum flow rate of the piping system from the switching valve to the suction cup is 277. 5 (L / m in) to reach the degree of vacuum The sorption response time T 2 at 95%. T 2 = 3 T 1 = 0. 057 (m in). This time can meet the vacuum adsorption requirements.

3. 3 Leakage amount when the workpiece is sucked Q In order to find the system leak rate, a ZL112 vacuum generator of a company is used instead of the vacuum pump connection control system to perform the suction test. The system shows that the vacuum pressure in the suction cup can only reach - 0. 05 MPa. According to the flow characteristic curve of the vacuum generator, the suction flow rate is 15 L /m in, that is, the leak rate of each lathe branch is 9 L /m. In.

The average flow rate of each lathe branch when 6 lathes work at the same time: Q level = Q total / 6 - Q leak = 285 L / m in > 277. 5 L / m in type Q total: total system flow is 1800 L /m in; Q leakage: The leakage rate of each lathe branch is 15 L / m in, that is, the flow rate of each branch can reach 285 L / m in, and the whole system flow meets the demand within the response time.

The flow rate is set to 277. 5 L /m in. When a branch leaks and is connected to the atmosphere, the leak rate Q of the branch is 1 277. 5 L / m in, the leakage rate Q leakage of each branch when the other 5 lathes work at the same time: Q leak = 15 + 277. 5 /5 = 70. 5 (L / m in) average flow rate per ladle branch Q Flat: Q flat = Q total /5 - Q leak = 289. 5 L / m in > 277. 5 L / m in means that each branch can still guarantee the flow value set by the shut-off valve, in the response time of each system The flow meets the demand. Therefore, when one of the branches has a leak, it does not affect the normal operation of the other branches.

4 Conclusion Outsourcing components are mostly selected from a company's products, and their performance is reliable. After use, the whole system is simple and convenient to operate, and the overall layout is compact, neat and beautiful, and has high economic benefits.

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