Research On Mechanical Properties Of Thin Film Strain Sensors For Cutting Force Measurement

Strain-type micro-nano film sensors have broad application prospects in machining cutting force measurement and online monitoring.Studying the preparation process of micro-nano film sensors and obtaining better mechanical properties have become the key factors to ensure the accuracy and reliability of cutting force measurement.In this paper,multilayer magnetic thin films such as transition layer,insulating layer,and sensitive layer were prepared on 304 stainless steel substrate by physical magnetron sputtering method and chemical vapor deposition method.Micro-nano thin film strain sensor was constructed and its mechanical properties In-depth research has been carried out on basic theory,preparation test research,mapping relationship between film preparation process and mechanical properties,and mechanical calibration.Firstly,the structure optimization design of the cutting tool was carried out.The structural improvement method of equivalent the tool bar as a cantilever beam and appropriately increasing the force deformation of the tool was used to establish the relationship between the cutting force,strain,and the structure size of each part of the tool bar.Based on the model,a cutting force measurement system with a segmented octagonal structure that can be embedded in a thin-film sensor is innovatively designed.It consists of a cutter head,a flange,a thin-film sensor,an elastomer,an octagonal connecting plate and a tool holder.The structure and size of the substrate,film and resistance grid of the key component thin film sensor are designed in detail.Based on the interface toughness theory,the relationship between film-substrate adhesion and internal stress,bending moment,thickness and other parameters is modeled.The evaluation method to improve the plastic deformation resistance and fatigue strength of the thin film sensor is analyzed.Through theoretical and static tensile test studies,the effects of nickel,nickel chromium,and alumina films as the transition bonding layer between the silicon nitride film and the stainless steel substrate were analyzed and compared.The composite insulating layer of alumina and silicon nitride film had the best adhesion,thus solving the problem of poor adhesion of the crystalline silicon nitride film deposited directly on the stainless steel substrate.The influence of the thickness change of the double-layer film of alumina and silicon nitride on the adhesion was further analyzed,and the adhesion was tested by the tape method.The results show that when the thickness ratio between the two is large,it helps to improve the adhesion of the composite insulating layer.For the preparation of alumina film,the effects of process parameters such as sputtering power,atmospheric pressure and Ar:O₂ flow ratio on the deposition rate,elastic modulus and nano-hardness were experimentally studied.For nickel-chromium film preparation,the effects of process parameters such as sputtering power,atmospheric pressure,negative bias and substrate temperature on the deposition rate,anti-plastic deformation factor and strain sensitivity coefficient were studied experimentally.The results show that the change of the Ar:O₂ flow ratio has a significant effect on the alumina film,and the change of the sputtering power has a greater impact on the deposition rate.When the nickel-chromium thin film was prepared,changes in sputtering power and negative bias had a large effect on its performance indicators.When the substrate temperature reached a certain value,the mechanical properties of the film changed significantly.Finally,a set of process parameters with optimal mechanical properties of the film were selected by grey correlation analysis.Through the test and simulation methods,the strain effect analysis of the cutting force measuring system embedded in the thin film sensor was carried out respectively,and it was found that the maximum strain sensitivity coefficient of the force measuring system was increased by 2.32 times and 2.23 times in turn.Then,the measurement sensitivity of the cutting force measurement system to the main cutting force,feed force and radial force was calibrated by Abaqus software,and the values were 108.77 N/mV,109.67 N/mV and 2934.18 N/mV in sequence.This result achieved the expected effect and laid the foundation for the further development of strain-type thin film sensors.