Expertest 3-channel Sound Control

EXPERTEST : a patented multifrequency sound control instrument.

Thanks to the measurement of resonance frequencies of metal parts, EXPERTEST can detect faults of material soundness or form.

Main faults detected :

• Bad nodularity of parts in ductile cast iron.
• Crack or flaw : the size of the faults detected depends on the process of manufacture.
• Teeming arrest on casting.
• Lap on forgings.
• On certain types of cast iron : presence of carbide (cementite).
• Geometrical variation of the parts : lack of material...
• Variation in the heat treatment of the parts.
• Internal form errors : porosity of aluminium parts, important blister...

Principle of the measurement and control :

The measurement of resonance frequency is performed by putting in contact (or approach) a probe with the part to be tested. This probe excites the part by inductive coupling within a determined frequency band, a microphone placed inside this probe measures the signal generated by the part. The analysis of this signal by the expert software of the instrument allows to determine the natural resonance frequency of the part.

The frequencies measured are a function of the elasticity modulus of the material and the geometry of the part. Since these parameters have a different effect depending on the modes of vibration, it is possible to detect the variations by measuring a sufficient number of frequencies. When the EXPERTEST parameters are set up, a support program for the analysis of the measurements made on a batch of standard parts allows to determine the frequencies to be measured, the influence of the variations in weight and sort criteria. During production operation, after measurement of the part, the EXPERTEST sends back one of the following information : « Good part », « Bad part » or « Measurement error » to a manual control unit or an automat.

Advantages of the method :

• Total control of the part : the probe does not necessarily need to be placed near the fault, possibility of detecting various types of faults in one single test.
• Possible correlation of the resonance frequency via the weight of the part to be analysed, in order to increase the quality of the control by compensating the form variations of the parts.
• Methodology of analysis by statistical method of the frequency response of a batch of parts, in order to select the optimum frequency for the control of the parts.
• Possible measurement of several frequencies with one single probe.
• Very good reproducibility of the measurement.
• Insensitivity to ambient noise.
• Fast measurement : in semi-automatic mode 800 parts/hour with weighing, in automatic mode 900 parts/hour with weighing.
• No constraint of surface conditions.
• No use of couplant (oil or water) between the probe and the part.
• Simple to automate : the probe is mounted on a pneumatic cylinder, the part is placed on a support fitted with flexible studs, positioning of the part can be carried out with an accuracy of a few millimetres.
• Statistical follow up of production.

Applications and implementation of the 3-channel EXPERTEST :

• Use in automatic mode for the control of a single part with several measuring probes, or simultaneous control of 2 parts with weighing or 3 parts without weighing.
• Automatic recording of the weight of one or two parts thanks to the connection of one or two digital weighing devices.

nke Instrumentation can carry out feasibility tests of control on standard parts within its facilities. Please contact us.