JP2001524669A - Inspection method for machined products - Google Patents

Abstract

(57) [Summary] The present invention relates to a method for determining the presence of a harmful surface change such as an increase in hardness or residual stress in a machined product. In order to achieve a very reliable test result, the present invention proposes to make this determination using an absolute eddy current probe.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for determining the presence of a harmful surface change such as an increase in hardness or residual stress in a machined product made of titanium or an alloy thereof.

[0002] If there is a machining damage to a rotating part of an aero engine, various methods and equipment have long been used to check for the presence of this damage. With respect to parts made of titanium, so-called blue etching is performed on the surface of the titanium material for inspection of the machined surface. However, this method has two problems in inspection. That is, the first problem is that the method is vision-based, requiring the person to see the surface sufficiently (preferably from directly above).
In this case, there is no obstacle to inspecting the edge of the hole, including the wall of the hole that is very close to the edge of the hole, but it is difficult to inspect deep holes. The second problem is that this method is not completely reliable if foreign matter can be present on the surface. In this case, for example, the tool may be damaged, and substances from the tool, such as Si, Cr, Ni, and Fe, may diffuse into the base material, or substances (eg, oxygen) from the surroundings may diffuse into the base material. There are cases.

[0003] Another possible method is to try to find these cracks in the material by means of a fluorescent penetrant, if these are present. However, any machining damage that may be present does not necessarily result in cracking until the damaged part is installed, and usually this crack does not occur during manufacturing, but only during subsequent use.

[0004] Yet another inspection method that is often used is eddy current inspection using a differential probe. When performing this test, two coils are used to observe the signal difference between these coils. This inspection method is also very suitable for locating cracks, but may not be able to detect long-term changes in the material, such as machining damage, which is the purpose of the present invention. .

[0005] To reliably determine whether there is local overheating due to tool wear or machining damage due to tool breakage, etc., go beyond the blue etching, differential probe and permeate methods. Additional inspection methods are highly desirable.

[0006] According to the present invention, the use of an absolute probe optimized for this application is intended for use in rotating parts of aircraft engines, titanium, titanium alloys, superalloys, and workpieces made of steel. It has been confirmed that this is a very effective method for inspecting the holes formed in the holes. With such probes, residual stresses, diffused impurities, and changes in composition, i.e., changes in composition, i.e., during machining, for example, when harmful overheating of the material occurs as a result of tool wear or tool damage. It is easy to find large deformations of the surface microstructure. The invention is further described below with reference to the accompanying drawings.

As is evident from FIG. 1, the absolute probe used in connection with the present invention has the simplest design possible. More precisely, the shape of the body of this probe is
In cross-section, it conforms to the geometry of the inspection surface, and a coil is wound around this body. With this design, the probe senses anything that affects the conductivity or permeability of the material being tested. The probe also senses anything that changes the relationship between the surface of the material and the probe. As a result, minute material changes such as changes in residual stress, changes in the composition of foreign atoms dissolved in a small percentage, and the like can be measured.

A probe according to the invention is connected to an eddy current device and is inserted at a uniform speed into a hole in the workpiece to be inspected. The signal from the eddy current device is digitized and stored in, for example, a PC. Next, the measurement data is processed to facilitate evaluation.

[0009] The body of the cylindrical probe is preferably constructed of plastic and can be long enough to allow easy mounting for automatic measurements. The diameter of the probe is such that the probe passes through a hole in the workpiece.

[0010] Experiments with the probe of the present invention have found damage showing both significantly deformed areas and especially layers with increased proportions of iron and oxygen. In this region, the hardness increased, and cracks occurred in the portion to be used. If these cracks are not found during regular maintenance, these cracks can spread out and cause damage.
The absolute probe of the present invention also makes it possible to recognize the surface of a workpiece that has been damaged during manufacture but has very little effect.

Furthermore, the inspection can be automated, and the inspection time is shorter than other inspection techniques. The evaluation can be automated, and the measured data can be stored for later retrieval and evaluation.

[Brief description of the drawings]

FIG. 1 is a diagrammatic side view, partially in section, of an absolute probe used in accordance with the present invention and inserted into a hole.

FIG. 2 is an example of two of several microstructures of a titanium material.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Anders Franson Sweden 73233 Arboga Gus Tafsbergswegen 27 F-term (reference) 2G053 AA11 AA17 AA19 AB21 BA02 DA01

Claims (1)

[Claims] When a machined product made of titanium or its alloy has a harmful surface change such as an increase in hardness or residual stress, a method of determining the presence of this surface change uses an absolute type change. Using the eddy current probe of the above.