Surface property inspection method and apparatus

Patent metadata

Field	Value
Publication number	US-10048227-B2
Application number	US-201415128573-A
Country	US
Kind code	B2
Filing date	Oct 8, 2014
Priority date	Mar 24, 2014
Publication date	Aug 14, 2018
Grant date	Aug 14, 2018

Abstract

The present invention provides a surface property inspection method and apparatus for inspecting the surface properties of a test object subjected to two stages of shot peening. The present invention is an apparatus 1 includes an AC power supply, an AC bridge circuit, and an evaluation apparatus. The AC bridge circuit is constituted by a variable resistor, a reference detector and inspection detector. The inspection detector includes a coil wound so as to oppose the surface property inspection area of the test object M; an eddy current is excited in the test object M by supplying AC power to the coil. A pass/fail judgment of the first shot peening can be made by inspecting the surface properties of a test object subjected to a second shot peening only after the second shot peening is completed.

First claim

The invention claimed is:

1. A surface property inspection method for inspecting a surface property of a shot peened test object, comprising steps of:
an inspection apparatus preparation step for preparing a surface property inspection apparatus, wherein the surface property inspection apparatus comprises:
an AC bridge circuit;
an AC power supply for supplying AC power to the AC bridge circuit; and
an evaluation device for evaluating the surface property of the test object based on an output signal from the AC bridge circuit;
wherein the AC bridge circuit comprises:
a variable resistor configured to vary a divide ratio between a first resistor and a second resistor,
an inspection detector comprising a coil capable of exciting AC magnetism, said coil being configured to excite an eddy current in the test object disposed adjacent to the coil, and
a reference detector, in which a reference test object having the same structure as the test object is disposed, and detecting a reference state which serves as a reference for comparison with an output from the inspection detector; and
wherein the first resistor, the second resistor, the reference detector, and the inspection detector constitute the bridge circuit;

a threshold value setting step for determining a threshold value used in evaluating the surface property of the test object in the evaluation device;
an eddy current excitation step for exciting the eddy current by the inspection detector in the test object, simultaneously with exciting the eddy current by the reference detector in the reference test object, wherein the test object is subjected to a first shot peening for imparting residual stress from a surface into deep portions and then subjected to a second shot peening for performing a lower strength shot peening than the first shot peening, thereby imparting further residual stress from the surface into shallow portions in comparison with the first shot peening; and
a pass/fail judgment step for using the evaluation device to compare the threshold value with the output signal output from the AC bridge circuit during the eddy current excitation step implemented after the second shot peening, and then judging whether the first shot peening was correctly performed
wherein in the eddy current excitation step, a frequency of the AC power supplied to the AC bridge circuit is set so that the eddy current reaches to a depth to which the residual stress is imparted by the first shot peening.

2. The method of claim 1 , wherein the eddy current excitation step is performed under the state that the reference test object which is an untreated object, not subjected to surface treatment, is placed in the reference detector.

3. The method of claim 1 , wherein in the threshold value setting step, the threshold value is determined based on the output signal from the AC bridge circuit when the eddy current is excited in the test object on which the first shot peening and second shot peeing have been correctly performed.

4. The method of claim 1 , further comprising steps of:
a second eddy current excitation step wherein which AC power at a higher frequency than that of the eddy current excitation step is supplied by the AC power supply to excite the eddy current in the test object, and
a second pass/fail judging step wherein the evaluation device judges whether the second shot peeing has been appropriately performed, based on the output signal from the AC bridge circuit when the eddy current is excited during the second eddy current excitation step.

5. The method of claim 4 , wherein the threshold value setting step determines the threshold value determined based on the output signal obtained by supplying a predetermined first frequency AC power to the AC bridge circuit, and a second threshold value determined based on the output signal obtained by supplying a predetermined second frequency AC power to the AC bridge circuit, the second frequency is higher than the first frequency and the threshold value is used to make a pass/fail judgment in the pass/fail judgment step and the second threshold value is used to make the pass/fail judgment in the second pass/fail judgment step.

6. The method of claim 4 , wherein the second pass/fail judgment step is performed before the pass/fail judgment step.

7. The method of claim 3 , wherein in the threshold value setting step, by using an output signal EA from the AC bridge circuit when an untreated test object is disposed in the inspection detector, and an output signal EB from the AC bridge circuit when the test object on which the first shot peening and the second shot peening have been correctly performed is disposed in the inspection detector, the threshold value Ethi is determined according to the expression:
Ethi =( EAav·σB+EBav·σA )/(σ A+σB ),

where EAav: average value of the output signal EA; EBav: average value of the output signal EB; σA: standard deviation in the output signal EA; σB: standard deviation in the output signal EB.

8. The method of claim 1 , wherein the evaluation device comprises a memory device by which identifying information for each test object, and surface property inspection data for said test object, are correlated and stored.

9. A surface property inspection apparatus for inspecting a surface property of a test object subjected to a first shot peening for imparting residual stress from a surface into deep portions by a shot peening apparatus, and a second shot peening for performing, after the first shot peening, a lower strength shot peening than the first shot peening, thereby imparting further residual stress from the surface into shallow portions in comparison with the first shot peening, the apparatus comprising:
an AC bridge circuit;
an AC power supply for supplying AC power to the AC bridge circuit; and
an evaluation device for evaluating the surface property of the test object based on an output signal from the AC bridge circuit;
wherein the AC bridge circuit comprises:
a variable resistor configured to vary a divide ratio between a first resistor and a second resistor,
an inspection detector comprising a coil capable of exciting AC magnetism, said coil being configured to excite an eddy current in the test object disposed adjacent to the coil, and
a reference detector in which a reference test object having the same structure as the test object is disposed, and detecting a reference state which serves as a reference for comparison with an output from the inspection detector;
wherein the first resistor, the second resistor, and the reference detector and the inspection detector constitute the bridge circuit, and

wherein after the second shot peening, the evaluation device evaluates the surface property of the test object to judge whether the first shot peening has been properly performed on the test object by comparing a threshold value and the output signal from the AC bridge circuit, wherein the output signal is obtained by applying AC power to the AC bridge circuit in a state that the inspection detector detects electromagnetic property of the test object, while the reference detector detects the reference state,
wherein the AC power supply supplies the AC bridge circuit with the AC power at a frequency selected so that the eddy current reaches to a depth to which the residual stress is imparted by the first shot peening.

10. The apparatus of claim 9 , wherein the reference test object is an untreated object not subjected to surface treatment.

11. The apparatus of claim 9 , wherein the coil is formed of Litz wire.

Assignees

• Sintokogio Ltd

Inventors

• Makino Yoshiyasu
• Kaga Hideaki

Classifications

• G01N27/9046 Primary

  by analysing electrical signals · CPC title

• B24C1/10

  for compacting surfaces, e.g. shot-peening (for deforming sheet metal, tubes or profiles B21D31/06; as a metallurgical treatment C21D7/00, C22F1/00) · CPC title

• G01N27/9033

  Physics · mapped topic

• G01N27/9006

  Details, e.g. in the structure or functioning of sensors · CPC title