No.6: Contraction of the core fill: when the area filled with resin during potting after cure has a little depression.
No.7: Crushed core: cells crushed. Normally due to an incorrect handling.
No.8: Bubbles/Pores in the union of adhesive: sometimes, after cure, in the resin used for splicing two cores, some pores/bubbles appear.
Once the core has been cut and machined, and after removing the glass fiber fabric, adhesive paper, etc used for these operations, we proceed to clean and store them in polyethylene sealed bags, identifying on the outside of the bag with the P/N of the detail part.
The removal operations of the carbon fibre fabric, adhesive paper, etc shall be carried out in the cutting and machining areas.
Cores shall be handled with clean cotton or polyamide gloves during cutting, machining and cleaning operations and any later operation.
SURFACE TOOL CLEANING: before application of release agent, tool surface must be cleaned removing oxidation, dirt and contamination, using clean clothes or if necessary, Scotch-Brite Type A or S, soaked in solvent.
APPLICATION OF LIQUID RELEASE AGENTS: the application and curing shall be made following the procedure indicated in the corresponding Work Order, taking into account the indicated in this Process Instruction.
APPLICATION AND CURING: the liquid release agent shall be applied using clean brush or clean and lint-free cotton cloths or by spraying.
The following Table 7 has been extracted from AIPI 03-02-018 [Ref.1], For our case is marked in yellow.
5) LAY UP:
For manual lay-up, once the prepreg materials have been thawed and the corresponding patterns cut, we remove the release film or protection paper from one face of the
prepreg,
performing this operation with extreme care so as not to detach strands, alter their alignment or produce damages. The prepreg plies shall be placed one on top of another,
Table 7. Parameters for application of release agents/mold sealers
fulfilling the orientations called out in the applicable drawing and minimizing the amount of air occluded below the ply.
For manual lay-up, prepregs with protection film on both sides, we place the ply keeping the protection film on its external face, subsequently removing it just before application of the next prepreg ply.
During the lay-up process, special attention shall be paid to prevent leaving any rest of protection film or backing paper incorporated inside the part.
Now that we know the process according to normative reference AIPI 03-02-018 it is the moment of explaining how to install material PS TAPE in order to eliminate the Pinholes and interlaminar porosity.
1) After laminating all the part, we install the release film and start to install material PS TAPE all around the special radius. First of all, we install a cylindrical tube for all the contour as we would like to increase the pressure during the cure cycle and after that we install two planar tapes on the cylindrical shape.
2) Install a second ply of release film in order to avoid the direct contact of PS TAPE with breather and vacuum bag.
First ply of
Release film Breather
Vacuum Bag Tool
3) After the cure cycle we can appreciate in FIGURE 3.4.2 the material PS TAPE has completely taken the shape of the corner.
As we can see in the FIGURE 3.4.4 shown below, the quality of the part after cure cycle is perfect. No pin-holes appeared in the special radius.
FIGURE 3.4.2 Detail of how to use PS TAPE.
Second ply of Release film
FIGURE 3.4.3 Detail PS TAPE after cure cycle Fibre Carbon
Material PS TAPE
Now we should check if between the laminate it doesn’t exist porosity. In our case, we are going to use a C-SCAN inspection but before that we will explain what it is.
The high frequency ultrasonic C-SCAN is a non-destructive technique to examine defects inside a material. This apparatus permits researchers to identify the depth of the observed defect in the sample, but the size of the deviation is recommended measure with the technique pulse-echo that after we will be explained.
In the following picture, we show a Robot Ultrasonic Inspection System:
This system presents high flexibility, allowing the inspection of CFRP components. The main advantages of this configuration are:
FIGURE 3.4.4 Results after cure cycle. External view
FIGURE 3.4.5 Robot Ultrasonic Inspection System
o Machine simplicity o High productivity o Cost effectiveness
o Versatility and flexibility, thanks to modular design o System upgrades possible
All the Robot System works always inside a controlled room like that shown in the following picture:
For this type of system, it is not necessary to perform any civil work for the installation of the track and the robot. In particular, only some metallic plates have to be installed on the floor, by means of an anchoring system (“Hilti” type or similar), for tracking fixation. The track-motion is fixed on the floor and constructed as a steel structure with embedded linear guides and pinions. In addition, it includes cable chains and an
automatic lubrication system.
Robot Ultrasonic Inspection System works with local immersion. Local immersion applies to large parts without resorting to total immersion. In this case, Ultrasonic
FIGURE 3.4.6 Lay out of Robot System
coupling occurs through a jet or column of water. See example below in FIGURE 3.4.7
The following picture of CATIA 3D Model show the critical area that we are going to inspected by ultrasonic C-SCAN (non-destructive technique).
Always the Part is inspected completely but in this part of the project we are analyzing only the special shapes areas.
FIGURE 3.4.7 Real pic (left side) and Sketch (right side) of local immersion C-Scan
Critical AREAS to be inspectioned
FIGURE 3.4.8 Screenshot CATIA 3D Model
After performing the local immersion completely for all the part, in our computer will appear a FIGURE like that:
ADMISIBLE POROSITY DETECTED ADMISIBLE POROSITY DETECTED
SANDWICH AREA
HOLE OR MONOLITIC AREA WITHOUT POROSITY
In case that a deviation appears, it is recommended to perform the manual inspection pulse-echo. This technique is based on the study of the phenomena of reflection that the ultrasonic waves undergo at the interfaces of the inspected pieces and on the
discontinuities that they may present. The following definitions are taken from AITM6-4005 “Ultrasonic pulse-echo inspection of carbon fibre plastics” [Ref.6]
FIGURE 3.4.9 Part inspectioned by C-Scan
Volume porosity area:
Volume porosity area is detected by a clear reduction of the back-wall echo and the absence of a clear intermediate echo unless a different cause for the back-wall echo loss can be found, as we can see in FIGURE 3.4.10
Volume porosity indications shall be sized using the back-wall echo drop in dB, equal to or greater than the attenuation level defined in the drawing or specific engineering document.
If the sizing criterion defined is not indicated in the drawing or specific engineering document, the sizing criterion in AITM6-0011 shall be used.
FIGURE 3.4.10 Detection/sizing of a volume porosity area
Layer porosity area:
Layer porosity area is detected by an intermediate echo exceeding the applicable threshold varying amplitude and a back-wall echo of at least 6 dB above the noise level (varying amplitude), see FIGURE 3.4.11. Layer porosity shall be sized using the amplitude of the intermediate echo(es).
FIGURE 3.4.11 Detection/sizing of a layer porosity area