ATLÂNTICA - Escola Universitária de Ciências Empresariais, Saúde, Tecnologias e Engenharia
SPECIAL MATERIALS FOR SOLVE DEVIATIONS APPEARED IN MANUFACTURING PARTS OF CFRP AND GFRP
Francisco Coro Leveque Mestrado em Engenharia de Materiais, 2020
ATLÂNTICA - Escola Universitária de Ciências Empresariais, Saúde, Tecnologias e Engenharia
SPECIAL MATERIALS FOR SOLVE DEVIATIONS APPEARED IN MANUFACTURING PARTS OF CFRP AND GFRP
Francisco Coro Leveque Mestrado em Engenharia de Materiais, 2020 Dissertação orientada pelo Professor Doutor Manuel Freitas
MASTER´S DEGREE IN MATERIALS ENGINEERING
SPECIAL MATERIALS FOR SOLVE DEVIATIONS APPEARED IN MANUFACTURING PARTS OF CFRP AND GFRP
Author: Francisco Coro Leveque
Advisor: Professor Manuel José Moreira de Freitas
ACKNOWLEDGMENT
First and foremost, I would like to express the deepest gratitude to my supervisor, Prof. Manuel Freitas, for his excellent guidance and for providing me with an exceptional atmosphere for doing my research.
Special thanks to ATLANTICA UNIVERSITY and to all the university professors who have helped me during these last two years.
I also would like to thank to CARBURES, now AIRTIFICIAL, the bet to increase the knowledge of its workers through this master.
Last but not least, I would like to thank my partner, Marina, for her love, kindness and support she has shown during the past two years
INDEX
0. RESUMO ... 13
1. INTRODUCTION...………... 17
1.1 WHAT’S ABOUT THE PROJECT? ..………. 17
1.1 .1 COMMON BASIC INFORMATION IN HOLLOW PARTS AND PLANAR PARTS WITH SPECIAL RADIUS ………18
1.1 .2 MANUFACTURE OF STRUCTURAL SANDWICH PARTS WITH THERMOSETING FIBER REINFORCED SKINS ………. 20
1.1 .3 MANUFACTURE OF STRUCTURAL PARTS WITH THERMOSETING FIBER REINFORCED SKINS ………. 30
2. HOLLOW PARTS ... 41
2.1 DEFINITION AND PROCESS FOR MANUFACTURE A HOLLOW PART ………... 41
2.2 TYPICAL DEVIATIONS ... 42
2.3 CHARACTERISTICS OF MATERIAL SELECTED ... 43
2.4 DEVELOPMENT OF THE PROOFS ... 45
3. PLANAR PARTS WITH SPECIAL RADIOUS ... 61
3.1 DEFINITION AND PROCESS FOR MANUFACTURE P.P WITH SPECIAL RADIOUS ... 61
3.2 TYPICAL DEVIATIONS ... 62
3.3 CHARACTERISTICS OF MATERIAL SELECTED ... 65
3.4 DEVELOPMENT OF THE PROOFS ... 66
4. ANALYSYS OF FINAL RESULTS AND BUSINESS CASE ... 81
4.1 HOLLOW PARTS ... 81
4.1 .1 ANALISYS OF THE FINAL RESULTS ... 81
4.1 .2 BUSINESS CASE ... 82
4.2 PLANAR PARTS WITH SPECIAL RADIOUS ... 85
4.2 .1 ANALISYS OF THE FINAL RESULTS ... 85
4.2 .2 BUSINESS CASE ... 86
5. CONCLUSSION ... 89
6. REFERENCES ... 91
FIGURES INDEX
FIGURE 1.1.1.1 PANEL SANDWICH ... 21
FIGURE 1.1.1.2 EXAMPLE PANEL SANDWICH SECTION ... 22
FIGURE 1.1.2.2 EXAMPLE OF LACK OF RESIN ... 28
FIGURE 1.1.2.3 EXAMPLE OF PIN HOLES ... 28
FIGURE 1.1.2.4 TEMPORARY VACUUM BAG SCHEME ... 30
FIGURE 1.1.2.5 EXAMPLE APPLYING MANUAL PRESSURE ... 30
FIGURE 1.1.3.1 MONOLITIC STRUCTURE EXAMPLE ... 31
FIGURE 1.1.3.2 MONOLITIC TUBE MADE WITH GLASS FIBRE ... 31
FIGURE 2.1.1 PART 1 & PART 2 JOINED ... 41
FIGURE 2.1.2 PART 2 LAMINATED ... 41
FIGURE 2.2.1 EXAMPLE OF LACK OF RESIN ... 42
FIGURE 2.2.2 EXAMPLE OF EXCESS OF RESIN ... 42
FIGURE 2.2.3 EXAMPLE OF DELAMINATION ... 42
FIGURE 2.3.1.1 BAGGING FILM ... 43
FIGURE 2.3.1.2 RELEASE FILM ... 43
FIGURE 2.3.1.3 BREATHER ... 43
FIGURE 2.3.1.4 TYPICAL VACUUM BAG SCHEME... 44
FIGURE 2.4.1 DATE OF INTEREST ABOUT AIMS 05-10-008... 45
FIGURE 2.4.1.1 GLASS FIBRE LAMINATED WITHOUT BAG RB 460 INSTALLED ... 48
FIGURE 2.4.1.2 BAG RG 460 INSTALLATION IN PROCESS ... 48
FIGURE 2.4.1.3 VACUUM APPLIED IN BAG RB 460 ... 49
FIGURE 2.4.1.4 WRINKLES IN BAG RB 460 AFTER VACUUM ... 49
FIGURE 2.4.1.5 PART0001 DEMOULDED AFTER CURE CYCLE ... 50
FIGURE 2.4.2.1 VACUUM APPLIED IN SECOND TEST ... 51
FIGURE 2.4.2.2 RESULT USING RB BAG ... 52
FIGURE 2.4.2.3 RESULT WITH CONVENTIONAL HAND LAY UP PROCESS ... 52
FIGURE 2.4.2.3.1 DETAIL ZOOM OF PIN HOLES ... 52
FIGURE 2.4.3.1 INSTALLATION OF BAG RB370 IN PROCESS ... 53
FIGURE 2.4.3.2 MANUFACTURING TOOL USED IN FIRST TEST WITH BAG RB370 ... 54
FIGURE 2.4.3.3 SKETCH SIMULATION OF INNER TOOL WITH BAG RB 370 ... 54
FIGURE 2.4.3.3A SKETCH INNER SIMULATION WITH BAG RB370. PRE & POST VACUUM ... 55
FIGURE 2.4.3.3B VIEW FROM A. REAL PICTURE ... 55
FIGURE 2.4.3.4 VIEW FROM INSIDE WITH BAG RB370 ADAPTED AFTER APPLY VACUUM ... 56
FIGURE 2.4.3.5 VIEW FROM INSIDE TOOL AFTER CURE CYCLE ... 56
FIGURE 2.4.3.6 VIEW FROM INIDE PART AFTER DEMOULD ... 57
FIGURE 2.4.3.7 COMPARISON RESULT BETWEEN CONVENTIONAL
HAND LAY UP AND WITH BAG 370 ... 57
FIGURE 2.4.4.1 INNER VIEW FOR SECOND TEST WITH RB370 ... 58
FIGURE 2.4.4.2 EXCESS OF RESIN APPEAR AFTER CURE CYCLE ... 58
FIGURE 2.4.5.1 OUTSIDE VIEW OF MANUFACTURING TOOL AND SECTION OF PART DRAWING ... 59
FIGURE 2.4.5.2 INNER VIEW OF MANUFACTURING TOOL WITH BAG RB500 POSITIONED (LEFT) AND BAG RB500 WITH VACUUM APPLIED (RIGHT) ... 60
FIGURE 2.4.5.3 OUTSIDE VIEW AFTER CURE CYCLE ... 60
FIGURE 2.4.5.4 INSIDE VIEW AFTER CURE CYCLE ... 60
FIGURE 3.1.1 PLANAR PART WITH SPECIAL RADIUS ... 61
FIGURE 3.1.2 SECTION OF SPECIAL RAIUS ... 62
FIGURE 3.2.1 PINHOLES AFTER PAINT ... 63
FIGURE 3.2.2 CRATERS IN RADIUS ... 63
FIGURE 3.2.3 POROSITY INTERLAMINAR ... 64
FIGURE 3.3.1. TECHNICAL DATA OF PS TAPE ... 65
FIGURE 3.4.1A DATA OF INTEREST ABOUT AIMS 05-01-005 ... 66
FIGURE 3.4.2 DETAIL OF HOW TO USE PS TAPE ... 74
FIGURE 3.4.3 DETAIL OF PS TAPE AFER CURE CYCLE ... 74
FIGURE 3.4.4 RESULT AFTER CURE CYCLE. EXTERNAL VIEW ... 75
FIGURE 3.4.5 ROBOT ULTRASONIC INSPECTION SYSTEM... 75
FIGURE 3.4.6 LAY OUT OF ROBOT SYSTEM ... 76
FIGURE 3.4.7 REAL PIC (LEFT SIDE) AND SKETCH (RIGHT SIDE) OF LOCAL INMERSION C.SCAN ... 77
FIGURE 3.4.8 SCREENSHOT CATIA 3D MODEL ... 77
FIGURE 3.4.9 PART INSPECTION BY C-SCAN... 78
FIGURE 3.4.10 DETECTION/SIZING OF VOLUME POROSITY AREA... 79
FIGURE 3.4.11 DETECTION/SIZING OF LAYER POROSITY AREA ... 80
FIGURE 4.2.1A SPECIAL RADIUS WITH CONVENCIONAL PROCESS ... 85
FIGURE 4.2.1B SPECIAL RADIUS WITH PS TAPE ... 85
FIGURE 4.2.2A SIZES OF PS TAPE ... 86
FIGURE 4.2.2B DIMENSION OF SPECIAL RADIUS ... 86
FIGURE 4.2.2C QUANTITY OF TAPE PER RADIUS ... 86
TABLES INDEX.
TABLE 1. GENERAL ACCEPTANCE CRITERIA FOR SANDWICH
PARTS ... 28
TABLE 2. GENERAL ACCEPTANCE CRITERIA FOR MONOLITIC PARTS ... 40
TABLE 3. THAWING TIMES FOR FABRICS ... 46
TABLE 4. PARAMETERS FOR APPLICATION OF RELEASE AGENTS .... 47
TABLE 5. THAWING TIMES FOR FABRICS ... 67
TABLE 6. GENERAL ACCEPTANCE CRITERIA FOR HONEYCOMB CORES ... 71
TABLE 7. PARAMETERS FOR APPLICATION OF RELEASE AGENTS ... 72
TABLE 8. BUSINESS CASE ... 83
TABLE 9. BUSINESS CASE ... 84
TABLE 10. BUSINESS CASE ... 87
TABLE 11. BUSINESS CASE ... 87
TABLE 12. BUSINESS CASE ... 88
TABLE 13. BUSINESS CASE ...88
LIST OF ACRONYMS -HLU: Hand Lay Up.
-R&D: Research and development.
-CFRP: Carbon Fiber Reinforced Plastic -GFRP: Glass Fiber Reinforced Plastic
-AIPI 03-02-018: Manufacture of Structural Sandwich Parts with Thermosetting Fiber Reinforced Skins.
-AIPI 03-02-019: Manufacture of Monolithic Parts with Thermoset Prepreg Materials.
-GF: Glass Fibre
-NDT: nondestructive test.
-AIPI: Airbus Process Instruction -RB: Release Bag
-AIMS: Airbus Industry Material Specification -R: Radius of the tube
-PS: Pressure Sensitive -P/N: Part Number
-AITM: Airbus Industrial Testing Methods
SUMMARY
Composites are materials increasingly used due to their characteristics and properties and the process Hand Lay Up is one of the most common process used in the word because it is a process that doesn’t need a high investment in machines as in other processes but it is mandatory to expend resources in research and development (R&D).
When a part of composites is manufactured, typical deviations normally appear depending on the manufacturing process, geometry of the part, human factors, materials, etc...
The process Hand Lay Up is a very slow process because the manual sheet placement stage consume about half of the total process time, and for this reason, the corrective actions to solve the deviations which appear during the cure cycle, should be taken in this stage, during the Hand Lay Up.
As the name of the thesis shows: “SPECIAL MATERIALS FOR SOLVE DEVIATIONS APPEARED IN MANUFACTURING PARTS OF CFRP AND GFRP”
the approach is showing how with some special materials it is possible to solve typical deviations that appear during the manufacturing process of a part of composites, and demonstrating how it is possible to decrease total cost by adding or modifying the typical material used in the process Hand Lau UP. The special materials used for eradicating the defects are ancillary materials. Ancillary materials are used only during the manufacturing process, but they do not remain incorporated to the part and are divided by two types: Material Type A and Material Type B.
During the thesis, on one hand, we will analyze how is possible to solve defects of Lack of resin, surface porosity, delamination and excess of resin appeared during the manufacturing of Hollow Parts of GFRP using ancillary materials Type A, and on the other hand, defects of Porosity between layers, lack of resin and surface porosity appeared during the manufacturing of Planar Parts with special radius of CFRP using ancillary materials Type B.
Finally, with a business case will be demonstrate how is possible to decrease total costs using these ancillary materials. In one case replacing conventional materials used during the performing of the vacuum bag and in other case adding a new material.
RESUMO
Os compósitos são materiais cada vez mais utilizados devido às suas características e propriedades e o processo Hand Lay Up é um dos processos mais comuns utilizados no mundo porque é um processo que não precisa de um alto investimento em máquinas como em outros processos, mas é obrigatório gastar recursos em pesquisa e desenvolvimento (P&D).
Quando uma parte dos compósitos é fabricada, normalmente aparecem desvios típicos dependendo do processo de fabricação, geometria da peça, fatores humanos, materiais, etc...
O processo de Hand Lay Up é um processo muito lento porque a fase de colocação manual da chapa consome cerca de metade do tempo total do processo e, por este motivo, as ações corretivas para resolver os desvios que aparecem durante o ciclo de cura, devem ser tomadas nesta fase, durante o Hand Lay Up.
Como o nome da tese mostra: "MATERIAIS ESPECIAIS PARA DISPOSIÇÕES SOLVADAS APELADAS EM PEÇAS FABRICANTES DE CFRP E GFRP" a abordagem está mostrando como com alguns materiais especiais é possível resolver desvios típicos que aparecem durante o processo de fabricação de uma parte de compósitos, e demonstrando como é possível diminuir o custo total através da adição ou modificação do material típico utilizado no processo de Hand Lau Up. Os materiais especiais utilizados para a erradicação dos defeitos são materiais auxiliares. Os materiais auxiliares são utilizados apenas durante o processo de fabricação, mas não permanecem incorporados à peça e são divididos por dois tipos: Material Tipo A e Material Tipo B.
Durante a tese, por um lado, vamos analisar como é possível resolver defeitos de Falta de resina, porosidade superficial, delaminação e excesso de resina surgidos durante a fabricação de Peças ocas de PRFVF usando materiais auxiliares Tipo A, e por outro lado, defeitos de Porosidade entre camadas, falta de resina e porosidade superficial
surgiram durante a fabricação de Peças planas com raio especial de PRFVFV usando materiais auxiliares Tipo B.
Finalmente, com um business case será demonstrado como é possível diminuir os custos totais usando estes materiais auxiliares. Num caso, substituindo os materiais convencionais utilizados durante a realização do saco de vácuo e no outro caso adicionando um novo material.
1. INTRODUCTION
When we manufacture parts of composites we should know that some defects can appear. For this reason, the aim of this work is focused on eradicate all these defects using materials Type A and materials Type B:
- Material Type A for Hollow Parts which the defects to solve are:
Lack of resin Surface porosity Delamination Excess of resin
- Material Type B for Parts with special shapes.
Porosity between layers Lack of resin
Surface porosity
This general objective will be finalized with a Business Case in order to show all the associated cost before and after making the improvements with both materials.
1.1 What’s about the project?
When a part of CFRP or GFRP is manufactured, sometimes typical appear deviations depending on the manufacturing process, geometry of the part, human factors,
materials, etc...
Always, when we talk about manufacturing process during this thesis we are going to talk about HAND LAY UP that is the process that I have more KNOW HOW.
Also, when we talk about manufacturing process during this thesis, we will be based in normative aeronautics.
According to the normative rules, we must separate the family of the parts that are going to be analyzed in two groups:
Manufacture of Structural Sandwich Parts with Thermosetting Fiber Reinforced Skins AIPI 03-02-018 [Ref.1]
Manufacture of Structural Parts with Thermosetting Fiber Reinforced Skins AIPI 03-02-019 [Ref.2]
In this project, I am analyzing some deviations which appear when we manufacture a hollow part like tubes (normative reference AIPI 03-02-019) and planar parts with special radius (normative reference AIPI 03-02-018) always manufacturing with the process Hand Lay UP.
1.1.1 Common basic information in Hollow Parts and Planar Parts with special radius.
When we manufacture a Part, we must classify two types of materials:
Structural materials: from a Manufacturing point of view, structural materials are those incorporated in the final part manufactured. Structural materials shall be indicated in the drawing and in accordance with the corresponding AIRBUS Material Specification. Any change during the manufacturing will be cause of rejection and establishment of the corresponding discrepancy. Only qualified materials can be used in production.
Ancillary materials: Ancillary materials are used only during manufacturing, but they do not remain incorporated to the part. All ancillary materials to be placed in direct contact with any non-cured material must be stored in sealed polyethylene bags and handled using qualified gloves.
Such ancillary materials must be classified in two types of material. Each of the consumables showed below is extracted from AIPI 03-02-018 [Ref.1]:
Type A materials:
Materials that are in direct contact with structural materials during previous
operations, lay-up or curing, or which can affect the structural behaviour.
Typical materials are:
- Peel plies for structural bonding.
- Peel plies for general use.
- Release films.
- Liquid release agents.
- Adhesive tapes.
- Spatulas and gloves.
- Protection materials for cutting tables.
- Polyethylene films for plies cutting & bagging - Doubled faced self-adhesive tapes.
- Marking pencils.
- Tacking promoter for fixing prepreg layers on tool surface
Type B materials:
Materials that are not in direct contact with the structural materials during previous operations, lay-up or curing.
For example:
- Bagging films.
- Breather and bleeder fabrics.
- Sealant tapes.
- Pressure sensitive tapes.
- Rubber pad.
- Silicone rubber.
- Compactation film and verifilm - Cotton cloths and hand creams.
- Antihumidity barriers and temporary protections.
The objective of the project is showing how we can solve deviations appeared in Hollow Parts and Planar Parts with special radius with non-typical ancillary materials Type A and B.
1.1.2 Manufacture of Structural Sandwich Parts with Thermosetting Fiber Reinforced Skins (AIPI 03-02-018):
This Process Instruction establishes the requirements and defines the procedures for manufacturing of sandwich parts with metallic and non-metallic cores and
thermosetting fiber reinforced skins, made of carbon fiber/organic matrix and glass fiber/organic matrix or hybrids, giving complete detailed in-house process instructions.
The structure of panels sandwich can be seen in the FIGURE 1.1.1.1 extract from ASM Handbook, Volume 21. Composites [Ref.3].
FIGURE 1.1.1.1 Panel Sandwich. Picture of an assembled composite sandwich (A), and its constituent face sheets of CFRP (B), honeycomb core (C) and adhesives (D)
(A) (B)
(B)
(C)
(D)
In our case, the panel sandwich that we manufacture in our plant is made with
honeycomb cores made of phenolic resin bonded glass fiber for light density structures, to be used specifically for sandwich structural parts.
When we manufacture panels sandwich we should know that some typical deviations can appear.
The following Table 1 have been extracted from AIPI 03-02-018 [Ref.1] and shows the typical discrepancies and the corrective methods after cure cycle in Manufacture of Structural Sandwich Parts. In order to explain the discrepancies, I have divided this Table 1 per 18 type of defects.
The table is composed of 4 columns:
TYPICAL DISCREPANCIES: is the name of the deviation appearing after the cure cycle.
ACCEPTABLE VALUES WITHOUT REWORK: some deviations are acceptable without necessity of rework, due to the discrepancy which doesn’t affect structurally the final part.
ACCEPTABLE WITH REWORK: when it’s necessary to rework the discrepancy even when this affects structurally the final part.
REWORK METHOD: this column indicates how we must rework the discrepancies.
FIGURE 1.1.1.2 Example Panel Sandwich section [Ref.7]
No.1: Superficial Scratches: scratches that only affect the first ply.
No.2: Surface depression: an indentation or low spot in a surface. It can be in tool face side or bag face side.
No.3: Delamination or voids:
Delamination: Separation of plies from each other and/or facing plies from core.
Voids: Empty space within the fiber-resin system not on the surface.
Table1. General acceptance criteria for finished parts and definitions.
No.4: Bridging: lack of contact between upper and lower skin in the core / monolithic transition area, typically caused by core displacement.
No.5: Resin ridges: a sharp build-up of resin on the surface.
No.6: Inclusion of Foreing materials: physical object (prepreg or film adhesive
protector, auxiliary material such as peel ply, release film or other material) that can be visually detected when it is on the composite surface or by NDT inspection, when it is inside the composite structure
No.7: Ply wrinkles: A ridge or fold-over of a ply.
No.8: Depresion in the core contour: A collapse, distortion or deformation by compression of the core.
No.9: Lack of flatness on coupling surfaces:
No.10: Part warping: when the part manufactured, at rest, after demould suffers springback. Normally concave or convex.
No.11: Discrepances on Tedlar: some deviations that we have seen before can appear on Tedlar.
No.12: Delamination’s on contours: are delaminations that appear after machined contours. They normally affect only the lasts plies.
No.13: Defects on the core in sandwich structures:
Partial node bond separation: lack of contact between upper or lower skin with the core.
Contour waviness: A collapse, distortion or deformation by compression of the core.
No.14: Lack of resin: incomplete resin filling of the surface in a composite structure.
No.15: Telegraphing: depression in skin corresponding to underlying honeycomb core cells.
No.16: Delaminations visible from exterior: separation of the first/second ply and can be visible from exterior (No NDT needed)
No.17: Lack of material in laminate edges: during the machining process after cure cycle the final part has some areas with lack of material according to drawing.
No.18: Absence or displacement of GF: when during the Hand Lay Up the layer of GF has been laminated in the incorrect position.
As we can see in the Table 1. the deviations can be divided in two types:
Acceptable values without rework.
Acceptable values with rework
In case that the values of deviation are higher than the values indicated “with rework”
the deviation should be analyzed by a specialist according to AIPI03-08-003 “Rework of Structures Manufactured from Composite Materials”
The deviations that we are going to analyze for Planar Parts with special radius are the deviations mentioned in Table 1. Points 3 (internal Porosity between layers) and 14 (Lack of resin or pinholes) and shown in FIGURE 1.1.2.2 and 1.1.2.3.
Point 3: this kind of deviation is possible to be detected by visual inspection.
These two kinds of deviations are tied to the quality or status of the tool and the correct lamination of the first layer.
Point 14: this kind of deviation is only possible to be detected by inspection NDT (non- destruction test). We have used the technique ultrasonic pulse-echo inspection and ultrasonic through transmission inspection.
Both methods are analyzed in the chapter 4 of the project.
Ultrasonic through transmission inspection. (Automatic) page 75 Ultrasonic pulse-echo inspection (manual) page 79
Typical corrective actions in order to avoid porosity deviation:
FIGURE 1.1.2.2 Example of Lack of resin
FIGURE 1.1.2.3 Example of Pin Holes
Compact in all the layers: as we know, according to AIPI, in order to avoid air entrapment between plies, compaction between plies shall be adequate. On automatic processes, this can be achieved by a roll pressure and on hand processes the following procedures may be used for compaction or lay-up adaptation purposes, provided that it shall be required by the documentation associated to the drawing or by the Manufacturing Work Orders.
The specific parameters used in the process shall be indicated in documentation associated to the drawing or in the associated component related process
instruction, as they depend on the material and form of element to manufacture.
In our case, we use cold compactation.
Cold compaction:
o Cover the lay-up with temporary vacuum bag.
o Apply vacuum until a manometric pressure inside the vacuum bag ≤ - 66kPa for plies previously incorporated to the core and ≤ -33 kPa for the later plies when the core density is ≥ 48 kg/m3 or ≤ -16 kPa when the core density is < 48 kg/m3.
o As a general rule, the compactation time shall be between 5 and 6 minutes.
o Take off the vacuum and remove the vacuum bag.
o Continue the manufacturing
FIGURE 1.1.2.4 Temporary vacuum bag scheme
Specific manual pressure in the special radius: when we perform the compact in all the layers, also apply a manually pressure with a spatula.
These two corrective actions improve the quality of the manufactured part but sometimes they are not enough to avoid internals porosities of laminate.
FIGURE 1.1.2.5 Example applying manual pressure
1.1.3 Manufacture of Structural Parts with thermosetting Fiber Reinforced Skins (AIPI 03-02-019):
This Process Instruction establishes the requirements and defines the necessary procedures for the manufacture of monolithic structures with pre-impregnated
thermosetting material reinforced with carbon, glass, ceramic or hybrid fiber providing the process instructions completely detailed.
The structure of monolithic structures can be seen in the picture 1.1.3.1 extract from ASM Handbook, Volume 21. Composites [Ref.3].
In our case, the hollow part that we manufacture in our plant is made with glass fibre:
FIGURE 1.1.3.1 Monolithic structure example
FIGURE 1.1.3.2 Monolithic tube made with glass fibre
When we manufacture hollow parts, we should know that some typical deviations can appear.
The following Table 2 has been extracted from AIPI 03-02-019 [Ref.2] and show the typicals discrepancies and the corrective methods after cure cycle in Manufacture of Hollow Parts. In order to explain the discrepancies, I have divided this Table per 14 type of defects. The table is composed of 4 columns:
TYPICAL DISCREPANCIES: it is the name of the deviation appear after the cure cycle.
ACCEPTABLE VALUES WITHOUT REWORK: some deviations are acceptable without necessity of rework due to the discrepancy which doesn’t affect structurally to the final part.
ACCEPTABLE WITH REWORK: when rework is necessary, even when the discrepancy affects structurally the final part.
REWORK METHOD: this column indicate how we must rework the discrepancies.
No.1: Not covered fibers: this deviation appears when the resin doesn’t flow correctly between fibers or due to some impacts/scratches.
Table2. General acceptance criteria for monolithic parts
No.2: Superficial depressions: an indentation or low spot in the part surface. For example, it can appear due to an excess of pressure apply during the cure cycle, as a consequence of an incorrect vacuum bag performed.
No.3: Superficial protuberances: a protuberance in the part surface. They normally appear below Tedlar, in bag side and are excess of resin.
No.4: Surface ondulations / wrinkles:
Wrinkle: ridge or fold-over of a ply. This Kind of deviation may cause the scrapped part.
Surface ondulations: low and tall spot togethers in the part surface. Also called waves.
No.5: Internal defects: defects that only can be detected by NDT.
Delaminations: Separation of plies from each other.
Porosity: Accumulation of small voids in a composite structure.
Voids: Empty space within the fiber-resin system not on the surface.
No.6: Resin ridges: a build-up of resin on the surface. Depending on the side we have some acceptance tolerance, but always with the same rework method.
No.7: Foreing materials inlaid in the surface: physical object (prepreg or film adhesive protector, auxiliary material such as peel ply, release film or other material) that can be visually detected when it is on the composite surface or by NDT inspection, when it is inside the composite structure.
No.8: Lack of flatness on coupling surfaces: when the flatness is not according to drawing.
No.9: Part wraping: when the part manufactured, at rest, after demould suffers springback. It is normally concave or convex.
No.10: Burrs on contours: the generation of burrs is one of the most common problems affecting carbon fiber reinforced plastic (CFRP) machining processes.
No.11: Resin starvation: an incomplete resin filling on the surface in a composite.
structure.
No.12: Delaminations visible from exterior: are delaminations that can be detected without inspection NDT. They normally affect only the lasts plies and can appear
during the demoulding of the part after cure cycle, after machining the part in contour or in holes, etc...
No.13: Lack of material in the edges: it is normally produced during machining process.
As the name of deviation said, it is a lack of material in the contour of the part.
No.14: Absence or displacement of GF: during the Hand Lay Up, the layer of GF has been laminated in the incorrect position.
As we can see in the Table 2. the deviations can be divided in two types:
Acceptable values without rework.
Acceptable values with rework
In case that the values of deviation are higher than the values indicated “with rework”, the deviation should be analyzed by a specialist according to AIPI03-08-003.
The deviations that we are going to analyze for Hollow Parts are the deviations mentioned in “Table2”, points 6 (excess resin), point 11 (resin starvation or surface porosity) and point 12 (delaminations visible from the exterior). All these deviations we will be seen later in chapter 2.2 of the thesis.
2. HOLLOW PARTS
2.1 Definition and process manufacture.
Normally, when we manufacture Hollow Parts with the process HLU (Hand Lay Up) our tool is composed of two parts and before cure cycle, we have to flip one of these parts and perform the vacuum bag together, so the plies of these two parts are in contact before cure cycle, and then the part in only one piece can be obtained. If we perform the manufacture of these two-part separately, with individual vacuum bags, after cure cycle is needed to join then with adhesive or fasteners.
In the following pictures we can see on the left side Tool Part1 and Tool Part2 joined, and on the right-side Tool Part 2 with all the plies laminated before joint.
Tool Parts are made of steel.
We must always laminate in each part of the tool according to the manual created by the engineer based on the laminate drawings. After that, when all the plies are
laminated, we have to flip one part and join the second part as we said before in order to create one.
FIGURE 2.1.1 Tool Part1 & Tool Part 2 joined after flip Tool Part 1.
FIGURE 2.1.2 Part 2 laminated
Tool Part 1 Tool Part 2
Tool Part 2
Plies GFRP laminated
2.2 TYPICAL DEVIATIONS:
Lack of Resin: this deviation appears when the resin doesn’t flow correctly during the cure cycle. The resin doesn’t flow correctly when the pressure is not applyied
homogeneously during the cure cycle, and one of the main causes is the incorrect vacuum bag performed.
Excess of resin: this deviation appears when there is a GAP between the GFRP and bagging during the cure cycle. The main cause is the incorrect vacuum bag performed.
Delamination: this deviation appears when two layers of GFRP are separated during the cure cycle. Normally, in hollow parts, it appears during the cure cycle as the pressure is not applied uniformly or due to a human error during the Lay Up.
FIGURE 2.2.1 Example of lack of resin
FIGURE 2.2.2 Example of excess of resin
FIGURE 2.2.3 Example of delamination
2.3 CHARACTERISTIC OF THE MATERIAL SELECTED
2.3.1 What are we looking for?
The material selected for the production of the proofs is a bagging film with high elasticity that has an exceptional conformability characteristic, permits molding of complex forms and has release properties. A very important handicap that must withstand is high temperatures due to cure cycle.
The objective is using this material instead of the other 3 materials normally used in HLU:
Bagging films1
Breather and bleeder fabrics2
Release Film3
In the following typical vacuum bag scheme, we can appreciate where these 3 materials are located.
FIGURE 2.3.1.1 Bagging film
FIGURE 2.3.1.2 Release film
FIGURE 2.3.1.3 Breather
2.3.2 Variabilities and properties of material selected:
Once we have selected the kind of material that we have already used in our proofs, we have to make some tests with the material selected.
In the case of the material that we have selected there are three variabilities:
Material RB 460
Elongation max 250%.
Work Temperature resistance 193 ºC.
Material RB 375
Elongation max 500%.
Work Temperature resistance 155 ºC.
Material RB 500
Elongation max 350%.
Work Temperature resistance 260 ºC.
BAGGING FILM (1) BREATHER(2) RELEASE FILM (3) COMPOSITE MATERIAL
RELEASE AGENT
CONTOUR BREATHER FABRIC SEALANT TAPE
TOOL
FIGURE 2.3.1.4 Typical vacuum Bag scheme
Each of them has different properties of elongation and tensile strength, but all of them have in common the property of being able to be in direct contact with the pre-
impregnated.
2.4 DEVELOPMENT OF THE PROOFS
All the proofs that I manufactured are with glass fiber reinforced plastic AIMS 05-10- 008.
The following FIGURE 2.4.1 has been extracted from I+D-N-19 [Ref.4]
Until installing the Material RB we are going to realize the following process based on AIPI 03-02-019 [Ref.2]
1) PREPREG AND ADHESIVE PREPARATION
During cutting, placing and shaping work operations, materials shall be always handled with clean gloves Type A.
2) PREPREG AND ADHESIVE HANDLING
FIGURE 2.4.1 Date of interest about AIMS 05-10-008
Materials shall be thawed before the waterproof seals are opened. Thawing must be performed in an area with controlled temperature between 15 and 27ºC; it is not allowed to accelerate the thawing applying higher temperature.
The following Table 3 was extracted from AIPI 03-02-019 [Ref.2], For our case is marked in yellow.
3) PREPREG AND FILM ADHESIVE CUTTING.
The prepregs or film adhesives, after cutting (manual or automatic), must not show:
Contamination (dirt, moisture, materials or products from the cutting machine…)
Shears.
Cuts or geometry other than the one indicated in the drawing set.
Discrepancies exceeding the requirements of its applicable material
4) TOOLING PREPARATION (RELEASE AGENT APPLICATION)
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.
Table 3. Thawing times for Fabrics
The following Table 4 has been extracted from AIPI 03-02-019 [Ref.2], For our case it is marked in yellow.
5) LAY UP:
For manual lay-up, once the prepreg materials have been thawed and the corresponding patterns cut, the release film must be released as well as the protection paper from one face of the prepreg, performing this operation with extreme care so as not to detach strands that alter their alignment or produce damages. The prepreg plies shall be placed one on top of another, 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, the ply keeping must be placed 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.
Table 4. Parameters for application of release agents/mold sealers
2.4.1 First Test. Material RB 460.
The first Test was executed with Bag RB 460. The main characteristics of the RB and the piece are the followings:
Ø bag tubular 12” = 194mm = Ø inner tube
As we can see in the FIGURE 2.4.1, the piece that we are going to manufacture doesn’t have installed the release film or the breather
In the picture 2.4.2 we can see the RB460 partially installed. RB has only a part with release agent, the part in contact with de GFRP.
FIGURE 2.4.1.1 Glass fibre laminated without Bag RB 460 installed
FIGURE 2.4.1.2. Bag RB460 Installation in process
AIMS 05-010-008
Vacuum intakes Vacuum tape
After performing the complete vacuum bag, we can see that inside the tube (our hollow part is a tube) the Bag RB is completely adapted to the internal GFRP face. This is possible due to the characteristics of elongation of the RB Bag, and because the diameter of the RB Bag is litter than the internal diameter of the tube.
If we don’t adjust correctly the RB Bag to the inner face of the tube, during the cure cycle the resin of the GFRP will flow looking the GAP that we have left.
FIGURE 2.4.1.3. Vacuum applied in Bag RB460
FIGURE 2.4.1.4. wrinkles in bag RB 460 after vacuum
Retenedor of cork RB 460
The aspect of the part after cure cycle is the following:
As we can see in the picture, the aspect of the part is very good. Only there are some little excess of resin that are not a high deviation because with a little sanding it will be solved. This excess of resin, as we saw in the page previous, can be avoid if we brace well the RB Bag.
FIGURE 2.4.1.5. PART0001 demould after cure cycle.
Excess of resin AIMS 05-010-008 cure
2.4.2 Second Test. Material RB 460.
After checking that the RB bag 460 Works well, we took another test in order to compare the same part but manufactured with the process stablished with the
conventional HLU process (Bagging films, Release film, Breather and bleeder fabrics,) The main characteristics of the RB Bag and piece that we manufactured in the second proof were the followings:
Ø bag tubular 12” = 194mm = Ø inner tube Tube without curves
As we can see in the FIGURE 2.4.2.1, the Bag RB is completely adapted to the internal GFRP face of the inner tube.
FIGURE 2.4.2.1Vacuum applied in second test
In the following picture we can see the difference between the proof manufacturing using RB 460 FIGURE 2.4.2.2 and a part manufactured with the conventional HLU process FIGURE 2.4.2.3.
The deviation that we can appreciate in FIGURE 2.4.2.3 is called “Pin Holes” and the kind of rework has been indicated in Point 11 of FIGURE 1.1.3.
FIGURE 2.4.2.2. Result using RB BAG
FIGURE 2.4.2.3 Result with conventional Hand Lay Up process
FIGURE 2.4.2.3.1 Detail zoom of pin holes
AIMS 05-010-008 cure
2.4.3 First Test. Material RB 370.
After performing the first two tests with RB 460, now it is the moment to try with the RB Bag 375. Firstly, let me remind you the characteristics of this bag:
RB 375
Elongation max 500%.
Work Temperature resistance 155 ºC.
Comparing it to the previous bag, this one has a higher limit of elongation (RB 460 Elongation max 250%) but the work temperature resistance is lower (RB 460 193 ºC).
RB Bag 375 can be better for parts with a more complicated shape.
The main characteristics of the RB Bag and piece that we are going to manufacture in the second test are the following:
Ø tubular bag 12” = 194mm = Ø inner tube
Like in the cases before, the diameter of the inner tube is more or the same that the tubular bag.
Knowing that the characteristics of elongation are very high, we will realize the test in a tube with curves. The Bag RB 375, when starting to elongate, it deforms differently inside the tube due to the shape. It is very important to leave a little of excess of Bag in order to help the material in the elongation to R1 and R2.
FIGURE 2.4.3.1 Installation of Bag RB370 in process.
FIGURE 2.4.3.2 Manufacturing tool used in first Test with bag RB370
AIMS 05-10-008
Contour breather fabric
R1 and R2 are the radius of the tube. The area is indicated in blue color and has to expand the RB 375 when vacuum is applied.
After applying vacuum in our RB375 bag, the material will be elongated until arriving to R1 and R2. For this reason, it is very important to leave an excess of bag in the inner radius. In the following sketches the status of RB 375 has been simulated before and after apply vacuum.
FIGURE 2.4.3.3 Sketch simulation of inner tool with bag RB370.
FIGURE 2.4.3.3a Sketch inner simulation with Bag RB370. PRE-& POST Vacuum
PRE-Vacuum POST-Vacuum
External shape of the tooling.
A
In the following picture we can appreciate how the RB Bag has expanded until being in contact with the pre-preg glass fibre.
In the FIGURE 2.4.3.4 we can see how the RB375 has been adapted fully to the inner shape of the tool. Also we can see the exceess of Bag.
After cure cycle, we can appreciate that the RB 375 Bag has been more elongated during the curing of the Part, as we can see in the FIGURE 2.4.3.5 . We think that this has been caused due to the excess of capacity of elongation of the RB 375 bag. As we
FIGURE 2.4.3.4 View from Inside with Bag RB 370 adapted after vacuum.
FIGURE 2.4.3.3b View from A. Real picture
Excess of bag
R2
can see in the FIGURE 2.4.3.6, all the piece has excess of resin in all the inner part of the tube.
In the following FIGURE 2.4.3.6 we can appreciate how is the RB Bag has little wrinkles during the cure cycle, the resin flow and how it fills these Gaps.
Now, we are going to compare a conventional manufacturing HLU vs manufacture with RB 375. As we can see in the pictures below, the delamination doesn’t exist with RB 375 but the deviation of excess of resin exists.
FIGURE 2.4.3.5 View from Inside Tool After Cure Cycle
FIGURE 2.4.3.6 View from Inside Part After demould
Both views are from outside of the part.
2.4.4 Second Test. Material RB 370.
After seeing the problems that we have had in the first test, lets show another sample with another piece (Part004) in order to see if the problem is the excess of capacity of elongation of RB 375 Bag. The main characteristics of the RB Bag and piece that we are going to manufacture in the second test are the followings:
Ø tubular bag 12” = 194mm = Ø inner tube
Only one radius.
FIGURE 2.4.3.7 Comparison result between conventional HLU and with bag RB370.
FIGURE 2.4.4.1 Inner view for Second Test with bag RB370.
After manufacturing and curing cycle of the second test with RB 375 bag we can appreciate that we have had the same problem than in the first test. We see excess of resin induced by the elongation of the bag during the cure cycle.
2.4.5 First Test. Material RB 500.
After performing the first four tests with RB 375 & 460, we tried with the RB Bag 500.
First of all, lets me remind you the characteristics of this bag:
RB 500
Elongation max 350%.
Work Temperature resistance 260 ºC
Comparing this one to the previous two bags, this one has the limit of elongation between RB 460 and RB 375, but the work temperature resistance is the biggest (260 ºC). Although the limit of elongation is higher than the limit of RB 375 we are going to do the test with a tube without curves because we observed that the bag is too rigid.
The main characteristics of the RB Bag and piece that manufactured in the second test are the followings:
Ø tubular bag 65mm < 80mm = Ø inner tube
FIGURE 2.4.4.2 Excess of resin appear after cure cycle
In this case, the diameter of the inner tube is bigger than the tubular bag:
Although the diameter of the tubular RB500 is quite bigger than the diameter of the inner tube, after applying the vacuum the RB 500 bag have been adapted completely to the tool face as we can see in the picture POST-VACUUM.
As it is shown below this, is the best bag adapted of all the test performed.
As we can see in the pictures below, the quality of the part after cure cycle is perfect:
No excess of resin
FIGURE 2.4.5.1 Outside view of manufacturing tool and section of part drawing
View Pre-Vacuum View Post-Vacuum
FIGURE 2.4.5.2 Inner view of manufacturing tool with bag RB500 positioned (left) and bag RB500 with vacuum applied (right).
No lack of resin
No delamination appears
3. PLANAR PARTS WITH ESPECIAL RADIUS
3.1 Definition and process for manufacture planar parts with special radius.
Normally, when we manufacture Planar Parts with pre-preg materials we use the process HLU (Hand Lay UP).
For this kind of Parts, the process is like when we laminate a planar part, but in this case in a mold with a special shape. The objective is the same, obtaining a part according to the Handbook created by the engineer based on the laminate drawings.
Normally these kinds of parts are manufactured by operators with more than 3 years of experience, due to the deviations that can appear after cure cycle which can scrap the parts.
In the Point 3.2 Typical deviations, we will see which these deviations that can appear are.
The FIGURE 3.1.1 show a typical planar part with special radius that we are going to analyze in order to solve the deviations and improve the process.
FIGURE 2.4.5.3 Outside view after cure cycle FIGURE 2.4.5.4 inside view after cure cycle
During this part of the project, when we talk about Special Radius we will be talking about Parts with the following shape in some areas:
3.2 Typical deviations:
When we manufacture a planar part with special radius, we must know that it is very probably that after cure cycle some deviations may appear. The deviations that we are going to analyze are pinholes and internal porosities between layers.
What is a porosity: little bubbles that appear during the cure cycle of the part.
There are two kind of porosities. Depending on the zone of the part where the porosity appeared, there can be a high deviation or little deviation.
FIGURE 3.1.1 Planar Part with Special Radius
FIGURE 3.1.2 Section of Special Radius
Little deviation: when the bubbles appear in the superficial part they are
denominated pinholes. They normally affect to the resin. Depending on the size it is necessary to make a reparation or not.
NO Repair: if the bubble is ≤ 0,5mm and the number of bubbles is <
15cm2 in all the surface.
Repair: if the bubbles are ≤ 0,5mm and the number of bubbles is ≥ 15cm2 in all the surface.
The method of reparation is applying resinAIMS 08-02-001 in the porosity appeared, or if the Part will be painted in the next process before delivery to the customer, the
pinholes can be filled with epoxy pore filler prior to paint. But sometimes, when there are too many pinholes it is mandatory apply resin, and after that we start with the process of painting.
In the following FIGURE 3.2.1 we can appreciate a part painted and after that the pinholes remain. For this reason, I mentioned before that sometimes it is mandatory to apply resin.
FIGURE 3.2.1 Pinholes after paint
Also, sometimes when too many pinholes are accumulated in the same area, craters like showed in the FIGURE 3.2.2. appear. In this case we must apply resin.
Bigger deviation: when the bubbles appear between the layers of CFRP it is denominated internal porosity of laminated. This kind of deviation is only possible to be detected by ultrasonic test and it was always is necessary to make a reparation replacing layer of CFRP until eliminating the bubbles.
Depending on the number of layers affected the part can be repaired or the part is scrapped:
Scrap: if the layers affected are more than 50% of total laminate.
Repair: if the layers affected are less than 50% of total laminate.
FIGURE 3.2.2 Craters in radius.
Porosity/internal bubbles.
Resin
3.3 CHARACTERISTIC OF THE MATERIAL SELECTED
The material Type B that we have selected to solve the problem of porosity between layers and pinholes is called PS TAPE. The following information has been extracted from https://catalog.airtechintl.com/ [Ref.5]
The objective to use this material is applying an extra pressure during the cure cycle just in the affected area with pin-holes or internal porosity of laminate. The extra pressure will pushes out the bubbles.
PS TAPE is a rubber tape used as an intensifier in corners where pressure is difficult to apply only with a vacuum bag. PS TAPE is easily applied uncured on the pre-preg Layup and moulds to Part Shape during cure cycle.
PS TAPE works from 120ºC up to 230ºC in autoclave or oven.
CFRP Layers
FIGURE 3.2.3 Porosity interlaminar.
This material doesn’t substitute a conventional material used during the process hand lay up with pre-preg materials.
3.4 DEVELOPMENTS OF THE PROOFs:
All the proofs that were produced are with carbon fiber reinforced plastic AIMS 05-01- 005.
The following FIGURE 3.4.1a has been extracted from I+D-N-19 [Ref.4]
FIGURE 3.3.1 Technical Data of PS TAPE
Until we install the Material PS TAPE pressure intensifier we must realize the following process based on AIPI 03-02-018 [Ref.1]
1) PREPREG AND ADHESIVE PREPARATION
During cutting, placing and shaping work operations, materials shall be always handled with clean gloves Type A.
2) PREPREG AND ADHESIVE HANDLING
Materials shall be thawed before the waterproof seals are opened. Thawing must be performed in an area with controlled temperature between 15 and 27ºC; it is not allowed to accelerate the thawing applying higher temperature.
The following Table 5 have been extracted from AIPI 03-02-018 [Ref.1], For our case is marked in yellow.
3) CORES HANDLING:
Handling of cores shall be performed in such a way that no damage, contamination (greases, oils, dirt, etc…) or other circumstances degrades the physical and/or mechanical properties of the core to be produced.
Table 5. Thawing times for Fabrics
4) PREPREG AND FILM ADHESIVE CUTTING.
The prepregs or film adhesives, after cutting (manual or automatic), must not show:
Contamination (dirt, moisture, materials or products from the cutting machine…)
Shears.
Cuts or geometry, no others, than the ones indicated in the drawing set.
Discrepancies exceeding the requirements of its applicable material
5) CORE PREPARATION:
Non-metallic honeycomb cores are prone to take-up moisture in a short time. If not otherwise indicated in the associated drawing documentation, non-metallic honeycomb cores must not be dried, but held for a minimum of 12 hours at clean-room conditions prior to processing.
During cutting and machining, avoid any contamination or tear in the core; any discrepancy shall be evaluated according to Table 6.
This table has been extracted from AIPI 03-02-018 [Ref.1] and show the typical discrepancies and the corrective methods during the core preparation (before cycle in Manufacture of Structural Sandwich Parts).
The table is composed of 4 columns, distributed according with 8 types of defects:
TYPICAL DISCREPANCIES: is the name of the deviation appeared after the cure cycle.
ACCEPTABLE VALUES WITHOUT REWORK: some deviations are acceptable without necessity of rework as the discrepancy doesn’t affect structurally to the final part.
ACCEPTABLE WITH REWORK: when it’s necessary to rework the discrepancy due it affects structurally the final part.
REWORK METHOD: this column indicates how we must rework the discrepancies.
No.1: Contour
Cell tear out: broken cells
Waviness: non planar cuts, generating irregularities.
Machining Burrs: cut not clean, generating burrs
Table 6. “General acceptance criteria for honeycomb cores”
No.2: Interior
Partial node bond separation: when two cells are separated.
“Total” node bond separation: when more than two cells are separated.
No.3: Splices
Partially unbonded areas: when a splice is separated after it has been bonded Step in the splice line: difference in height between both cores bonded.
Depression of the bonding line: depression that appear between both cores bonded. Just in the splice line.
Excessive separation in the core splice: when the cores have been bonded with excess of GAP between them.
No.4: Surface depressions: deformations generated normally by human errors during the manipulation of the core.
No.5: Cell collapsed: cell crushing. Normally generated by human errors and it is a deformation that generate cell crushed
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.
6) TOOLING PREPARATION (RELEASE AGENT APPLICATION)
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
4. ANALYSIS OF THE FINAL RESULTS AND BUSINES CASE:
4.1 HOLLOW PARTS
4.1.1 ANALISYS OF THE FINAL RESULTS:
After realizing the different tests with the same kind of bagging but with different properties, we can see that all of them have worked well except the RB375 (color red) because of the excessive capacity of elongation (500%). During the cure cycle the bag continue to deform and it causes deviations in the part manufactured due to the resin flow to the GAPs generated between the bag and the GFRP. In case of RB 460 and RB 500 this didn’t happen.
We can see that for both types of bags (460 & 500) it is very important that the diameter of the RB Bag should be less than the diameter of the inner tube so when the vacuum will be applied, the RB Bag will expand until the tool face is laminated.
For both cases, (460 & 500) the quality aspect of the parts manufactured are very good for the tubes without curves as we have seen in the pictures presented in the thesis but in the parts with curves we always found excess of resin. This kind of excess of resin is not a serious problem due to the fact that is not very large and with a smooth sanding are solved.
4.1.2 BUSINESS CASE:
After Checking that the RB bagging works well, we have to analyze if it is profitable to change the material in our company replacing the conventional materials used in HLU.
For this reason, we must analyze the price of materials and process affected.
Analysis of materials:
Materials used during the process HLU in Hollow parts:
Bagging film:
Cost per m2 1,1 €/m2
Release film:
Cost per m2 4,5 €/m2
Breather:
Cost per m2 3,1 €/m2
Material used in the proofs:
RB 460:
Cost per m2 of 8” 0,93 €/m2 Cost per m2 of 11” 1,18 €/m2 Cost per m2 of 12” 1,35 €/m2
RB 500:
Cost per m2 of 4” 1,06 €/m2 Cost per m2 of 6” 1,17 €/m2
