the qualification process for an ultrasonic date: …

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THE QUALIFICATION PROCESS FOR AN ULTRASONIC

FACILITY (AEROSPACE SECTOR) FOR THE INSPECTION OF

COMPOSITE PARTS

Date: 2018-01-31

Issue: 01

Topic: ‘THE QUALIFICATION PROCESS FOR AN ULTRASONIC


COMPOSITE PARTS’

Co-Author: Andre Klaassens

Qualification: Ultrasonic Level 3 COSAC AO3-016312

Company: African NDT Centre

Co-Author: Wayne Claassens

Qualification: Ultrasonic Level 3 COSAC A03-012480

Company: BASF / Chemetall

This paper describes the process required for the qualification of an ultrasonic testing facility

for the inspection of thermoplastic carbon fiber composite parts in the aerospace

manufacturing industry, specific to a customers’ requirements.

Taking into account the customers codes, specifications and component acceptance criteria,

a Quality Test Plan (QTP) must be compiled for each type of ultrasonic inspection required.

Upon approval of the QTP the inspection facility will compile a Quality Test Report (QTR)

and the customer will then visit the facility prior to their approval of the process and report.

This paper will further look into the QTP and QTR with regards to, personnel qualifications,

equipment, material specifications, reference standards and written instructions.

To conclude the whole process will be discussed and explained in detail so as to convey the

qualification of the ultrasonic testing facility in accordance with customers’ requirements.

For the purpose of this document and presentation we will be looking only at the Manual Scanning

qualification process of parts that get manufactured by the forming of a pre-consolidated sheet of

Thermoplastic Carbon Fiber Composite (PEEK) into parts.

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Content

1. THE START 3 2. CUSTOMER SPECIFICATIONS 3 3. QUALITY TEST PLAN 4

3.1 General considerations of the qualification process 4 3.2 General features for the 10 families 5 3.3 General features for 90° bending radius. 5 3.4 Applicable specifications 5 3.5 Description of inspection equipment: 6 3.6 Reference Standards (RS) 6 3.7 Manufacturing of a production part with artificial defects. 8

4. PLANNED INVESTIGATION 9 4.1 Certification of the Reference Standards (RS) for flat and bended parts. 9 4.2 Evaluation of inspection process and set-up using the production part

with artificial defects and all the RS 9

5. STATISTICAL ANALYSIS OF INSPECTION RESULTS 10 5.1 Assessment criteria 10

6. PERSONNEL QUALIFICATION 11 7. QUALIFICATION PROCESS OF REFERENCE STANDARDS 11 7.1 Type I Reference Standard 11

7.2 Type II Reference Standard 16 8. CONCLUSIONS 19

9. REFERENCES 19

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1. THE START This process should begin before the first parts are manufactured, but as we all know

NDT is often considered to be the catch-up station/process.

There is always only one question coming our way “can you find a crack?” And we

usually answer, show me …………… (no not that) the part, so than I can have a look at

what type of defects we can expects to find.

So, in the end, this process will most likely run parallel to that of the first parts being

manufactured, this is not ideal, however as NDT people we are kind of used to this.

There will be critical information like the acceptance criteria, inspection rate (so by the

way we need 80 parts inspected by yesterday) ………. coming our way, one or two

days before the first shipment is due.

If this was a perfect world, let us now look at the process as it should be.

2. CUSTOMER SPECIFICATIONS

Having the customers specifications in your possession is in our opinion, the most

important part of this whole process. It is critical that these specifications include the

drawings of the parts that will be manufactured.

The customer usually expects miracles and wonders, this been on a very small and

tight budget. These documents aid us to reach a mutual understanding as well as to

understand the process with regards to the following……. (to name a few)

• Inspection method to be used (UT, PT, ET, ……)

• Part(s) geometry (shape, size, material, …….)

• Manufacturing process (wet layup, forming of the pre-consolidated plates….)

• At what stage during this process will the NDT take place (there can be more

than one NDT inspection phases)

• Personnel requirements (qualifications, numbers, …….)

• Equipment requirements (frequency, size, manual, automated, …….)

• Acceptance criteria

• Reporting and sizing of defects

• Work shop location and layout (address, temperature controlled …….)

• Quantity of parts expected to be inspected (per hour/day/week/month ….)

A great amount of time goes into understanding these specifications and the requirements

within, together with this, International Standards will be referenced and taken into

consideration.

At the end, we will take into account all of these documents to compile the Quality

Test Plan (QTP) and Quality Test Report (QTR).

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3. THE QUALITY TEST PLAN (QTP) In short, the QTP is a manual that is compiled in order to follow a process that sets out

a plan to prove to the customer that you can meet the criteria set out in their documents

and specifications.

Parallel to compiling the QTP you will need to start writing a Written Instruction of how

exactly the inspection will be performed.

So, let us have a look at the makeup of a document like this.

3.1 General considerations of the qualification process: A short description of what and who you intend to do this for. This process only concerns the manual inspection of the following areas of the part

• Radii

• Joggle areas

• Areas not inspected by the automated/semi-automated inspection

• And manual re-inspection after automated/semi-automated inspection (defect conformation)

Applied NDT Technique: Manual single probe transducer pulse echo inspection.

Location of Test facility: 123 Carbon Street Composite Valley

Material: Thermosplastic carbon fiber reinforced PEEK.

Part NDT classification: Class 1. (this is information that is stipulated in your customer’s specifications)

Geometry – main features:

Ply thickness = 0.31 mm, maximum thickness = 4.34 mm

Maximum number of plies: 14

Parts have a constant thickness.

Range of thickness: 6 plies (1.86mm) to 14 plies (4.34 mm).

90° bend with inner radius from 3mm to 4.34 mm

Each clip has a machined edge contour

Applicability: 850 parts per shipset, split into 10 families (6 to 14 plies). Type 1A 44% of the shipset Type 1A joggled 0.6% of the shipset Type 1A with fiber glass 11.8% of the shipset. Stabilizers 26.6% of the shipset. Type 3 no joggle 0.1% of the shipset Type 3 joggled 1.6% of the shipset Type 5A – splice 1 % of the shipset Type 5A – splice 7.4 % of the shipset Type 5B – splice 1 % of the shipset

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3.2 General features for the 10 families

The above 4-part families give us just a sample of all the families, remember

there were 10 families.

The above drawings provide us with vital information to the size and shape of an individual

part.

We can now start forming some ideas as to what is laying ahead.

3.3 General features for 90° bending radius.

Remember in the beginning we said that the parts have 900 bends, it is very

important to now the inner and outer radii of each of these parts.

If the radii on some of the thinner parts is very small, then these parts can be

considered as to small for inspection, ones again all of this information will be in

the customers specification.

3.4 Applicable specifications

This is where you will list all the relevant customers documentation which is

relevant to these parts.

This will also be the first instance that you reference the written instruction.

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In a lot of cases you will also make reference to international standards, this is

more often the case because the customer will refer to them also.

3.5 Description of inspection equipment:

You will now in some detail describe the inspection process and equipment

required to be able to carry out this inspection.

The inspection of the radius will be performed in manual pulse echo mode using

contact single probe transducer. The inspection will be performed from the

outside of the bending.

Confirmation of findings and sizing after automatic or semi-automated inspection

will be performed in manual pulse echo using contact single probe transducer.

The following equipment will be used:

Probe: 5MHZ, 0.25” with 10mm delay line. It can be a good thing if you add

some calculations at this point to show why the 10mm delay.

Equipment: EPOCH 600 or equivalent.

Three probe positioning tools for inspection in radius: 0° axis; 45° axis and 22,5° axis.

Now the first time you will see the words Reference Standard. Without reference

standards this process is not worth the paper it is written on.

Time of flight and TCG calibration will be performed using type II flat laminate

reference standard.

General gain adjustment for the inspection in the radius will be performed using

the bended reference standard.

The evaluation of the A-scans will be performed directly on the equipment display.

Amplitude and time of flight will be analyzed in order to look for attenuation of the backwall

echo and occurrence of intermediate echo.

Porosity will be evaluated according to…….name the customer spec.

Threshold for reporting indications of porosity will be set to 6dB. Where do I get

this from…………… yes, the customer spec.

The inspection process is fully described in the written instruction ………this is

the one you wrote.

3.6 Reference Standards (RS)

A drawing of the reference standard must be drawn and artificial defect sizes and positions

are defined. Also, the type of reference standard being used must be defined.

Yes, there is more than one type of reference standard, more on this later.

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Type II(Working) Reference standard for the calibration of the UT inspection (Note: The

calibration is not for the equipment calibration but for the inspection) of flat and slightly

curved surface.

• Will be used daily for calibration of the inspection process.

• Five flat laminates with overall dimension 123mm x123mm (one for each thickness

6, 8, 10, 12 and 14 plies without glass ply).

• The Reference standard shall be representative of the parts under inspection and

shall be scanned at the same time as the parts under inspection.

• Directly made out of raw material (pre-consolidated PEEK, no forming).

For each thickness, we will define the artificial defect type and size:

• 3 flat bottom holes, diameter 3, 6 and 9mm are drilled at 0,62mm depth.

• 3 countersinks, dimension 3x3, 6x6 and 9x9mm are machined at 0,62mm depth,

with a 1,5mm radius.

• 3 holes, 3mm diameter, drilled through the entire thickness.

• 2 flat bottom holes, diameter 3 and 6 mm, drilled at 0,62mm depth and tangent to

the 3mm through thickness drilled holes.

• 1 countersink 2x4mm, machined

The five RS’s will be validated by automatic or semi-automated C-scan inspection,

after calibration of gain and TCG on an already validated Type I Reference standard.

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Detection of artificial defects will be checked and amplitude will be compared with

that obtained from the Type I RS.

A maximum variation in dB between the Type I and Type II RS’s need to be set.

(according to the customer spec).

The above format will also be used for the RS’s to be used for the inspection of the

900 bended parts.

3.7 Manufacturing of a production part with artificial defects.

This part will form part of the investigation plan that will establish the Probability of

Detection (POD).

The defect sizes, location and depth are of utmost importance, this will be done by

mechanical means like using a Coordinate Measuring Machine (CMM).

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A report will then be drawn up and become a part of both the QTP and QTR.

4. PLANNED INVESTIGATION

4.1 Certification of the Reference Standards (RS) for flat and bended

parts.

The following test/ measurements will be performed on the RS

• A C-scan of the material planned for the use of the RS will be done before

any machining is performed. The scan will be analysed to determine the

Homogeneity of the part

• Conduct thickness measurement before machining

• Machine the part (RS)

• After machining, C-scan the RS, analyse the scan to determine

Homogeneity

Amplitude and time of flight

The detection of the artificial defects

• Conduct mechanical measurements

Size

Depth

Location of all the defects

• Ensure that the RS meets all the requirements of the customer.

4.2 Evaluation of inspection process and set-up using the production

part with artificial defects and all the RS’s.

The A-scan inspection will be performed, in order to evaluate:

• The homogeneity of the backwall echo amplitude.

• Minimum and maximum value of the BWE will be reported

• The detectability of artificial defects (intermediate echo amplitude and

backwall echo amplitude).

Reporting of results will give the following data for each specimen and for each

defect:

• Status regarding detection relative to the threshold.

• Position (X-Y) relative to origin of the specimen.

• Position in depth for the intermediate echo.

• Amplitude (%FSH) of the intermediate echo and of the backwall echo at the

maximum response of the indication.

• Dimensions of the indication (length of the defect in radius and length x width

for the defect in flat and slightly curved surface).

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5. STATISTICAL ANALYSIS OF INSPECTION RESULTS

Reliability of detection will be assessed using the 29/29 method on the 6mm artificial

defects (18).

This inspection will be carried out by three (3) independent inspectors, that meet the

requirements of the customer.

This then provides you with a population of 54 trials. (18 x 3)

The total number of trials (n) and the number of failed detection(d) will be counted in

order to demonstrate the 90% probability of detection of the 6mm diameter defects with

a confidence level of 95% - for example 0 failed in a 29 trials batch or 1 failed detection

allowed in a 46 trials batch.

It is important to Note that this technical qualification is not used to determine the POD

for porosity detection.

5.1 Assessment criteria Assessment criteria for the inspection setup to be qualified:

• All 6mm defects shall be reliably detected.

• A-scan amplitude homogeneity shall not vary by more than 2 dB (in parallel sided

area)

• Assessment criteria for the statistical analysis are given in the table below.

Due to the time constraint we will now look into two areas within the QTR namely:

• Personnel Qualification

• And a bit detail into the qualification process of reference standards

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6. PERSONNEL QUALIFICATION.

In essence your customers specifications will stipulate on how your inspection

personnel are to be certified.

These specifications will most likely reference NAS 410 and/or EN 4179, as aerospace

recognised certification schemes. Both are employer-based schemes and it is left up to

the Level 3 to ensure compliance with these documents when compiling the companies

Written Practice (WP).

Customer specific requirements (specific inspection techniques, equipment,

procedures, experience etc.) will be included in the WP, to ensure personnel are

certified accordingly.

Some regulatory authorities may even require that personnel are qualified

under/through the control/guidance of a National Aerospace NDT Board (NANDTB),

and are then certified by the employer in accordance with the companies WP and in

compliance with NAS 410 and/or EN 4179 requirements.

Why use National Aerospace NDT Board?

Quite often in the aerospace manufacturing industry, the customer requires that your

facility obtains Nadcap approval. Having your personnel qualifications/certifications

under the control of a recognised NANDTB is most beneficial to this cause.

7. QUALIFICATION PROCESS OF REFERENCE STANDARDS

First, why do we need reference standards

• Verification of inspection technique

• Verification of inspection set-up, probes, accuracy and deterioration of equipment

• System calibration

• To prove that our plan will work (QTP)

When manufacturing these reference standards, we need to take the following points in

consideration, but not limited to

• Material

• Manufacturing process

• Material thickness range

• Surface finish

• Geometry

We will be looking at the master (Type I) and one of the flat working (Type II) reference

standards.

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7.1 Type I Reference Standard We need the following to start the process

1. Material (the same as the parts)

2. Drawings

• Material distribution

• Sketch of the RS, and all the artificial defects (position, size and

depth)

Material distribution matrix’s (Type 1 RS)

The grey area will become the RS

The green and turquoise piece’s will be sent to an approved laboratory to determine the

following

Porosity volume Content

Resin polymerization

Tg (Glass Transition Temperature)

Degree of crystallinity

Melting temperature

Fibre volume content

As you can see all of these pieces (grey, green and turquoise) will be for the same piece of

material.

Sketch that indicate all the artificial defects

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Before any machining will take place, the material earmarked for the RS will be inspected for

Homogeneity of the material by means of non-destructive inspection techniques.

Differences in backwall echo amplitude

Max. 2 dB (for minimum 95% of the zones area).

1st peak T (mm)

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Now, the material can be sent for machining, after machining we do some of the same tests

and a few more tests.

Measurements

We will mechanical measure the RS by using CMM or handheld measuring equipment,

these measurements must now be within the tolerance mentioned in the drawing.

1 2 3 4

4.39mm 3.16 1.89 0.94

1 2 3

3.70mm 1.85 0.63

1 2 3 4 5 6 7 8 9

Ø2.90mm Ø2.93 Ø2.92 Ø5.96 Ø5.96 Ø5.93 Ø8.99 Ø8.96 Ø8.93

1 2

155.81mm 290.92

If handheld equipment is use we need to record the serial numbers and provide the

calibration certificate for each one.

a. Vernier ser: AS244

b. Vernier ser: AS548

c. Micrometer ser: AS359

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Inspection after machining by applied method.

Max amplitude (%)

Detection of artificial defects by applied method. (1st peak T (mm))

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If all the requirements are met you can label your reference standard and add it to your

“calibration” register, because annually you need to re-certify your reference standard, as

per customers’ requirements.

The end product Type 1 Reference standard.

(This reference standard is available to have a look at after the presentation)

Inconclusion, we now have a TYPE 1 reference standard that is representative of the parts

that will be inspected in regards to

• Material

• Thickness range

• Surface finish

• Surface geometry (flat and slightly curved areas)

We will now use this reference standard to qualify the rest of the reference standards (Type

2) that will be used daily (working type).

7.2 Type 2 Reference Standards

The whole process will repeat itself except for the lab test, we will make use of a

direct comparison method.

We will be scanning the Type 2 reference standard using the same settings as for

the Type 1 RS and then compare the scans with regards to:

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1. Max amplitude (dB)

Master panel Type 1

Reference panel type II

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2. Max amplitude (%)

3. 1st peak T (mm)

4. Detection of artificial defects by applied method

And this process will be applied for every RS that will get made for this project,

and yes, this will be repeated every year, it will be part of your re-certification

process.

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8. CONCLUSIONS

As you can see this is quite a lengthy process (and we only covered certain

aspects of this process), to begin this process two days or two weeks before

delivery of the first production parts will be extremely difficult.

So, our advice is to get involved with the NDT process as soon as you start

hearing anything about a possible new project.

Thanks for listening, there are some samples here that you can have a look at.

9. REFERENCES

[1] Airbus, document references (AITM’s),

[1.1] AITM6-0011: Non-Destructive Inspection of Composite Parts

[1.2] AITM6-0012: Reference standards for non-destructive inspection methods on fibre

composites.

[1.3] AITM6-4005: Ultrasonic pulse-echo inspection of carbon fibre plastics.

[1.4] AITM 6-4010: Inspection of fibre composites by ultrasonic phased array technique.

[1.5] AITM6-0014: Probability of detection POD.

[1.6] A1083:

[2] NDT Report No ENG1103523_3_Issue 3 by E. PAGNOUX (NDT Expert now

TESTIA), F. SANTOS

[3] NAS 410, NAS Certification & Qualification of Nondestructive Test Personnel

[4] EN 4179, Aerospace Series - Qualification and Approval of Personnel for Non-

Destructive Testing

[5] Nadcap,

[5.1] AC7114 Rev L Nadcap Audit Criteria for Nondestructive Testing (NDT) Suppliers

Accreditation Program

[5.2] AC7114-3 Rev K Nadcap Audit Criteria for Nondestructive Testing Facility

Ultrasonic

the qualification process for an ultrasonic date: …

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