Ultrasonic testing is a common method of nondestructive testing used in many industries including foundries. Ultrasonic testing consists of transmitting sound through the part and making measurements to determine internal flaws, thickness and nodularity. 

Ultrasonic testing has the ability to:

• Test an entire part without damaging it.

• Allow inspection of every part versus destructive sampling methods.

The common tests and methods of nondestructive testing are:

Surface Examinations

             2.  Magnetic Particle:

• Detection of surface and near surface flaws on the ferromagnetic material (iron, steel, nickel).

• The part is magnetized and magnetic particles are applied to the surface.

• Flaw location indicated by particle patterns.

            3.  Liquid Penetrant:

• Detection of discontinuities open to the part surface.

• Penetrating liquid/dye applied to part surface.

• Penetrates into and indicates location of flaw.

            4.  Eddy Current:

• Eddy Currents are used for detection of surface and near surface flaws, changes in conductivity and dimensional changes.

• Used in thin and small diameter electrically conductive parts.

Volumetric Examinations

            1.  Radiography:

• Use of radiation (X-ray and Gamma ray) to penetrate a part and the flaw location is recorded on film

• Detects flaws which (X-ray and Gammy ray) to penetrate a part and the flaw location is recorded on film

• Not as effective in the detection of planar type flaws (such as delamintations)

            2.  Ultrasonics:

• Detects flaws which present a reflective surface perpendicular to the sound beam

Ultrasonic Testing is Very Versatile

            Ultrasonic inspection is commonly used to satisfy many needs:

• A wide variety of materials can be inspected; metals, plastics, composites

• A broad range of applications including:

Ø       Every inch of weld in pipe manufacturing

Ø       Airplane turbine disks are inspected up to 5 times

Ø       Spot-weld testing in the automotive industry

Ø       Corrosion monitoring of tank walls

Ø       Inspection of railroad wheels and rail

Ø       Inspection of nuclear heat exchanger tubing.

Ø       Plate testing for lamination and thickness 

Ø       Nodularity testing of safety related components for the automotive industry.

The types of testing that can be accomplished with Ultrasonics are:

Thickness Testing:

Sound travels into the part and returns after a measurable period of time.

Flaw Detection:

Sound travels into the part, reflecting from the defect

Flaw Sizing:

Reflector size is determined by signal amplitude

Velocity Testing:

Sound travels through the part at different speeds based on material properties.

The major advantages of ultrasonic testing:

• Non-destructive

• Access to the part may be from only one side

• Safer than radiography

Ultrasonic Methods:

• Pulse Echo Method

• Through Transmission Method

• Resonance Method

Pulse Echo Test Method

The parts of the system shown above include:

1.  Flaw Detector:

• Produced a short duration electrical pulse

• Processes the returning signal for interpretation

• The flaw detector display shows the "time of flight" of the sound through the material.  (Left to right = Time/Distance)

• The height of the signal on the display represents the amount of reflected sound

            2.  Transducer/Probe:

• The piezoelectric element converts the electrical pulse (voltage) into mechanical vibrations (sound)

• The pulse of sound then travels through a material and bounces off a flaw or other reflective surface

• The returning echo is converted back into an electrical signal

            3.  Test Part:

• The part has properties that allow for consistent measurable repeatable results.

The Flaw detector and probe utilize the Piezoelectric effect. When electrical energy is applied, mechanical energy is produced and when mechanical energy is applied electrical energy is produced.

The following shows the types of reflections that would be displayed on the Ultrasonic instrument when testing a piece with internal flaws. 

Nodularity testing consists of measuring the velocity of sound through a cast part and relating the sound speed to the nodularity. Ultrasonic sound velocity varies in different materials and each material has a measurable velocity. The following are the velocity of some common materials:

• Mild Steel = 2.3 inches / sec 10e-5 (MS) Microseconds

• Water = 0.584 inches / sec 10 e-5

• Gold = 1.3 inches / sec 10 e-5

• Lead = 0.87 inches / sec 10 e-5

• Iron = 2.3 inches / sec 10 e-5

• Iron (Cast) = 1.8 inches / sec 10 e-5

For cast irons, the velocity is not constant, but varies according to the degree or spherodisation of the total graphite content. It is this phenomena which we use to measure and check castings.  

Highly critical safety related automotive parts mandate ultrasonic testing:

·         Ford, Nissan, Toyota, and Volkswagen specify an ultrasonic test for their safety related components.

The ultrasonic method is accepted for many test requirements and when the test is put on the production line 100% of the parts are inspected without having scrap with destructive testing. The typical cycle for in line inspection is as follows:

• The operator or the robot loads the part into the immersion tank.

• The immersion tank has a custom fixture for accurately holding the part between the transducers.

• The operator removes his hands from the tank and then the test begins.

• The part is tested.

• An air stamper marks that part if it has passed the test.

• The part is removed or automatically ejected into a good or bad bin.

The system tests both the velocity and the thickness of the part and additional channels can be added to test for flaws. Additional channels do not add to the cycle time and the typical time for a manually loaded system is 3 seconds total cycle time.

This type of system is manufactured by Krautkramer Branson utilizing the USPC-2100 computerized velocity testing machine.

·         The USPC2100 has specific software to make the task simpler

Ø       Part counter

Ø       SPC 

Ø       Strip chart 

Ø       Data Logging

·         Measurements can also be taken with hand held equipment

Ø       DMV DL

The advances in computer technology have also advanced the ultrasonic testing method. Ultrasonic boards are available that convert a standard pentium computer into an ultrasonic instrument. This technology has created a much easier platform for testing allowing:

1.  Easy integration in the foundry floor.

2. Programmable outputs and inputs to configure with robotic controls and PLC.

3. Windows-based operator interfaces that are easy to learn and run.

4. Less downtime and less expensive spare parts inventories.

5. Data logging for recording of results.

6. Networking for remote access.

The end result is that Ultrasonic testing can enhance your business by:

• Increased business through the automotive industry

• Fewer scraps by monitoring the process much closer