Magneto-elastic method–a new way to inspect the surface burn of parts

Grinding burns and common inspections, Many important maintenance such as products, fruits, crankshafts, consumption methods, printing methods, sales and universal use, etc., need to be grinded after heat treatment. , The power consumption time per unit material during grinding exceeds that of other processing methods, and most of the converted material will enter the object, so it is easy to produce changes in the surface metallographic structure. In the case of serious selection of process parameters, cooling and abrasive conditions, the earth is prone to a fairly deep structure change layer (tempered layer) during the grinding process, and accompanied by a large amount of recovery endurance, even better , This is the best grinding burn problem. appeared
The performance and lifespan of the product in the burn incident of the ground layer declines, and it can’t even be used completely, causing serious quality problems. Grinding burns occur; on the other hand, strengthen the inspection of parts, find unqualified workpieces in time, and judge the status of the ongoing grinding process
But for a long time, except for the simplest method for the inspection of grinding burns on the surface of the workpiece, the continuation method that has been used for many years has been adopted-acid is to coat the detected surface with acid, or to immerse it in a container according to regulations. In the acid tank. Under normal circumstances, if the condition is normal; and the color does not change after the change, it indicates that the upper burn is present. , As the color becomes deeper and deeper, it means that the surface temperature of the workpiece is higher, which causes more serious grinding burns.Although the traditional inspection method is simple and easy to implement, it has great limitations.

From the above description, it is clear that the pickling method is essentially qualitative inspection, and massage is used for body burns, and traditional methods can no longer be used. Instructions for use

The theory shows that the pickling method can only reflect the decrease in hardness caused by the change of the metallographic structure, and cannot reflect the residual stress on the surface of the workpiece. It is insufficient to fully reveal the degree of grinding burns.
On the other hand, due to the use of acid solution, enterprises have increased the burden of eliminating environmental pollution; the standardization reliability of traditional inspection methods is low, and it is difficult for Collins to formulate strong operability evaluation standards.
A novel and efficient method for grinding burn detection-magneto-elastic method

1. work

The BN method (Barkhansen Noise Method) is a method based on the Barkhansen effect of physics discovered in 1919. It can effectively grind burns for testing. The trial test instrument has been gradually applied in the ground grinding damage detection, and it has given full play to Ability to cut. Magnetic storms (shown in the magnetic power structure of polycrystals) increase regularly. But it may cause the metallographic changes and the possible significant changes after grinding damage can be proved to cause changes in the structure of the magneto-brain. The strength of the magnetic particle is changed with the required magnetic force of the iron material. Figure 1 is a schematic diagram of the working principle of the detection instrument developed on the basis of the BN method.

The “Door Schematic Diagram” in the Detector detects the actual situation of the object formed by the coil being ground and burned by the strong surface of the workpiece produced by the steel, and the scene formed by the object around it will produce the probe in the test. The corresponding electrical signal in the induction coil of the area, which causes the signal to be directly related to the degree of grinding damage to the workpiece. The whole work: the related process caused by the induction coil is detected, and finally the detection signal is generated in the induction head (B, B signals are amplified and suppressed, and the corresponding signals are processed, and the corresponding signals) are displayed and output.

The physical performance of grinding burns is mainly due to the decrease in hardness caused by the change of the surface metallographic structure and the tempered layer, and the residual stress (tensile stress) that appears on the surface. The detection instrument shown in Figure 1 changes with the surface characteristic value Rc of the workpiece to be detected from high to low, and detects that the corresponding B signal amplitude output by the instrument is reduced to large, that is, the corresponding detection signal is high and low. The signal is detected. Large, that is, when changing from negative (pressure) to positive (pull output), the corresponding B signal amplitude of the testing instrument suppresses the change from low to high.

2. Pulsating characteristic value mp and its calibration

The detection signal generated by the excitation circuit and the sensing device designed by the instrument is an effective expression of the Buckhansen magnetoelastic method, and is marked by the characteristic value mn (magnetoelastic parameter). The detected change state of the earth and the earth, if restored to a certain degree, can be displayed and output on the screen of the instrument. To be able to truly achieve one’s own problems must also be accurately described qualitatively, “solved” calibration description. Including two items: ①Determine the scenery of unqualified products. Burn different objects, use the pickling method to produce different results according to their own selection criteria, and obtain the corresponding value from the user in the qualified/unqualified state through the instrument, and then take the judgment as the unqualified particle size; ② Make a selection. It is to select the characteristic value and the pickling method to confirm the correlation of the degree of grinding. Specifically, it is necessary to determine a related MAGN and provide it with the dial on the instrument panel control. The MGAN value ranges from 0 to 99, and may take 5 or 0. Position, when the MGAN value interval on the detection instrument is 5 or 10, use one method to value the mp corresponding to the two sets of mp, such as MGAN30, measure 2 values ​​on the two objects, and get it again when MGAN 40 2 until MGAN=90. After subtracting the two pairs, an estimate is bound to be obtained, and the MGAN value of the client is used as the correlation coefficient and determined on the panel.

Note: In the actual implementation of “calibration”, you can also use the items in the first item to obtain the relevant factor MGAN, and then find out the unqualified products. The limit value brings some deviation.


Although this BN method can be used in a few places in automobiles as a grinding test tool for basic industries, it is unlikely to cut the tool, but the use of each stopper detection is very limited. On the one hand, it is because of the load carrying heavy parts and working conditions in the same process; on the other hand, because the characteristics of different radii of curvature of the wrong tendency may lead to changes in the surface state during grinding, in this case, the chance of grinding scratches will occur. Increase.

Figure 3 is a schematic diagram of the instrument. It is a high-efficiency semi-automatic testing equipment, which is very suitable for use in automobile engine plants and internal combustion engine plants under mass production conditions. First of all, for different camshafts, one needs to be equipped with one. Before starting, it must be carefully adjusted for the reasons on the basis. To ensure the support of the arm’s hidden position and positioning time, after the operator starts the equipment, the object under test starts to hunt The hunting starts at this time. The operator can simply land on the handle on the hand to allow the operator to support a one-key movement in positioning. When the first detection time is reached, the handle positioning locator on the on-site handle will be used. At the same time, the pressure head is on the surface under the action of the force measuring spring, and the dynamic detection is carried out with the rotation of the measuring. After one week of testing, the operator re-accepts the handle on the test stand, and moves the probe away from the first test to be moved to the next measurement until all retests are completed and return to the starting point.

  • 1. Series
  • 2. Sensor and cross arm
  • 3. Drive to add color
  • 4. Death to add color (tailstock)
  • 5. Axial 6. Tailstock handle
  • 7. Axial fixed knob
  • 8. Positioner locator
  • 9. Limit screw
  • 10 .Stop stop

Semi-automatic equipment, but operation guidance, efficiency, thinking of a goal, such as the axis of the industrial cylinder, including loading and unloading to 22 minutes.
At present, burn detection equipment based on the principle of the magneto-elastic method has been commercialized, and many industries have succeeded. It can be designed and manufactured into different types of tools. There are dynamic ways to track points, and there are also vivid continuous dynamic ways. The instrument is equipped with two magnetic frequencies, 3-15kHz and 70-200kHz. The depth is 02~0.2mm
This aspect is already available in China, but the scenes that have been adopted are in addition to the above-mentioned auto industry.

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