Research On Vibration-damping Handle Of Hand-held Grinding Tools

With the continuous improvement of mechanization in China,various tools are constantly appearing and gradually replacing manpower in various fields such as machinery manufacturing and production.Handheld tools are flexible and easy to operate,safe and reliable to maintain,and technical requirements are not high to operators,so it is widely used in various industries and daily life.The application of hand-held power tools is becoming more and more common,and the various vibration and noise problems that come with it are also receiving more and more attention.When using such tools,the strong mechanical vibration generated by the tool not only causes fatigue damage to some parts of the tool,reduces the service life,affects the performance of the tool itself,but also transmits to the operator’s fingers,arms and the whole body through,which reduces the operator’s operational comfort and causes the operator to have negative emotions such as anxiety,irritability,fatigue,affecting work efficiency,and on the other hand causes certain harm to the health of the operator.The main task of the intensive polishing workshop is to polish the surface of the workpiece by means of hand-held grinding machines.The workshop workers are deeply affected by the vibration.Simple vibration-proof measures such as wearing gloves are not enough.Therefore,the subject is aimed at research on vibration reduction of hand-held grinding tools,designing vibration protection auxiliary devices suitable for angle grinders without changing the original structure.The work is supported by the National Key technologies Research&Development program--Research on protection technology and equipment for occupational hazards in labor-intensive industrial enterprises(No.2016YFC0801700)and National Science Foundation project--Hybrid Energy Flow Method for Prediction of Broadband Vibration and Acoustics in Extra Large Structures Such As High-Speed Train Carriages(No.51675306).CRRC Changchun Railway Co.LTD provides research and experimental base for this topic,and vibration tests related to the subject are completed at the Key Laboratory of Vibration and Noise of the Institute of Acoustics,Chinese Academy of Sciences.In this paper,According to the overall idea of "Discovery and proposed vibration problems→ Vibration characteristics analysis→Vibration control strategy research→Vibration reduction scheme design→Simulation analysis and experimental test verification",the SJ125C pneumatic angle grinder used in the intensive polishing workshop is studied to design and develop an auxiliary vibration damping device,which mainly includes the following work contents:1)Analyze the structural characteristics:Disassemble the structure of the pneumatic angle grinder to understand the composition and working principle of the pneumatic angle grinder.The air compressor provides power and transmit the pressure to the end through the internal eccentric rotor system of the cylinder.The gear transmission system,in turn,drives the grinding wheel for grinding.It is clear that the vibration source of the pneumatic angle grinder under different working conditions is different,it is more complicated when grinding the workpiece.The detailed 3D model and finite element model of the pneumatic angle grinder were established,and the modal analysis and harmonic response analysis were carried out to have a better understand of inherent characteristics of the pneumatic angle grinder.2)According to the relevant test standards,the vibration test is carried out under the two conditions of idling and grinding the workpiece.It is found that the pneumatic angle grinder has a broadband vibration axial acceleration spectra,but more vibration energy is distributed in the middle and high frequency bands.At the same time,there are large resonance peaks at some frequencies at low frequency.Aiming at the spectral characteristics of the pneumatic angle grinder,it is more concerned with the vibration of the medium and high frequency bands.Combined with the structural characteristics of the pneumatic angle grinder,the vibration damping design is carried out,and the structural form of the auxiliary vibration damping handle is determined initially.3)Based on the band gap theory of phononic crystals,the inner core structure of auxiliary vibration damping handle is designed.The finite element simulation is used to analyze the influence of material parameters(density,Poisson’s ratio,etc.)and geometric parameters(original cell axial length ratio and radial diameter ratio)of inner core structure on the band gap frequency range.Combined with the spectrum characteristics of vibration source of the pneumatic angle grinder and strength requirements of the auxiliary vibration-damping handle,geometric parameters of the core material and periodic structure of the handle are selected,and the theoretical band gap frequency range of designed structure is obtained through simulation.The overall finite element simulation of the inner core of the handle verifies the bandgap frequency range of the design.4)Refine and improve the vibration reduction scheme,design and process a complete set of auxiliary vibration-damping handle devices,including four levels of vibration reduction:first-level is the vacuum rubber,second-level is the auxiliary handle shell,third-level is the core of auxiliary handle,and fourth-level is the rubber material of the outer surface of auxiliary handle.The auxiliary handle is screwed to the upper casing,and the upper and lower casings are bolted to realize the detachable function of the vibration damping handle.The processed vibration-damping handle is mounted on the pneumatic angle grinder for vibration test.Under the two conditions of no-load and polished workpiece,the vibration spectrum of each vibration-damping system is obtained,which is compared with the original vibration spectrum to verify the vibration reduction effect.