Honeycomb Core Fabrication PDF

HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION LEARNING OBJECTIVES: IDENTIFY TYPES OF CORE DEMONSTRATE ABILITY TO TRIM CORE DEMONSTRATE ABILITY TO CHAMFER CORE UNDERSTAND HOW TO STABILIZE CORE UNDERSTAND THE USE OF POTTING COMPOUNDS UNDERSTAND HOW TO POT OR...

HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION LEARNING OBJECTIVES: IDENTIFY TYPES OF CORE DEMONSTRATE ABILITY TO TRIM CORE DEMONSTRATE ABILITY TO CHAMFER CORE UNDERSTAND HOW TO STABILIZE CORE UNDERSTAND THE USE OF POTTING COMPOUNDS UNDERSTAND HOW TO POT OR BOND CORE SPLICES DEMONSTRATE ABILITY TO COMPLETE ALL REQUIRED PAPERWORK (NEAT, ACCURATE AND LEGIBLE) LEARNING OUTCOME: DEMONSTRATE THE “BASIC” KNOWLEDGE AND SKILLS TO FABRICATE CORE DETAILS FOR COMPOSITE FABRICATION HONEYCOMB CORE FABRICATION EVALUATION WRITTEN TEST: MULTIPLE CHOICE WITH TRUE/FALSE QUESTIONS AND A 70% PASS MARK PRACTICAL EVALUATION OF THE 115W4533-3TR/-5TR CORE DETAILS WHICH MUST MEET MINIMUM PROCESS SPEC REQUIREMENTS AND A 70% PASS MARK 50% OF THE MARK ACHIEVED ON THE WRITTEN TEST ADDED TO 50% OF THE MARK OBTAINED FOR THE PRACTICAL TO CALCULATE THE MODULE FINAL MARK *NOTE: BOTH THE WRITTEN AND PRACTICAL TEST MUST ACHIEVE A MINIMUM OF 70% TO PASS THE MODULE HONEYCOMB CORE FABRICATION CORE MATERIALS GENERAL: Core material is the central member of a composite structure When bonded between plies of composite material, it produces a rigid, lightweight component referred to as a sandwich panel The core material provides a great deal of compressive strength to a composite structure HONEYCOMB CORE FABRICATION Two popular core materials are foam and honeycomb Honeycomb has the greatest strength-to-weight ratio but has very little resiliency when damaged If a foam core is damaged, it has a memory and will return to about 80% of its original strength Core is used in composites because of: Strength to weight advantage Reduces the number of composite plies required Makes the panel stiffer HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION HONEYCOMB CORE MATERIAL: Has the shape of natural honeycomb and a very high strength-to-weight ratio May be constructed of aluminum, Kevlar, carbon, fiberglass, paper, Nomex or steel Nomex is a trade name of DuPont and is widely used as an advanced composite core material Nomex is an aramid-fiber paper reinforced in a phenolic resin (a composite resin system) HONEYCOMB CORE FABRICATION Made by stacking sheets of material with adhesive patterns printed on the sheets and cured into place The cured block of material is expanded and dipped in the phenolic resin The pattern of the bond line is known as the core ribbon direction The ribbon direction can be found by tearing along one side of the honeycomb The honeycomb will not tear except in the ribbon direction HONEYCOMB CORE FABRICATION EXPANSION PROCESS OF HONEYCOMB CORE MANUFACTURE HONEYCOMB CORE FABRICATION IDENTIFYING CORE RIBBON DIRECTION: Core ribbon direction is parallel to the double cell wall direction. The core material will tear easily along the ribbon direction. A ruler can be used to help identify the double wall bond line or ribbon direction. HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION ACRONYMS: PAR PROCESS AND ASSEMBLY RECORD BOM BILL OF MATERIALS BAC BOEING AIRPLANE COMPANY BMS BOEING MATERIAL SPECIFICATION EB EDGE BAND EBT EDGE BAND THICKNESS EBW EDGE BAND WIDTH MIR MATERIAL INSPECTION RECORD HONEYCOMB CORE FABRICATION CTT CORE TRIM TEMPLATE T/S TOOLSIDE B/S BAGSIDE TY TYPE P/N PART NUMBER S/N SERIAL NUMBER CL CLASS GR GRADE HONEYCOMB CORE FABRICATION DEFINITIONS: Block - Thin sheets of pressed or woven nonmetallic materials coated with a specific resin, bonded with an adhesive or compatible resin and expanded into specific cell sizes or shapes Buckle Line - A line of collapsed cells, two or three cells wide with undistorted cells on either side. Buckle lines generally appear on the inner radius of formed core Cell Tear Out – See Fig. 5 of SSM Compaction - The application of a temporary vacuum bag and vacuum to remove trapped air and compact the part Core Bay – The top flat portion of the core not including the core chamfer HONEYCOMB CORE FABRICATION Core Crush - A collapse, distortion, or compression of the core Core Depression - A localized indentation or gouge in the core Core Movement - Sideways movement of the core resulting in distorted cells, or the core detail shape is no longer within Engineering tolerances Core Orientation – See Fig. 3 of SSM Core Stabilization - Process of supporting or reinforcing the core to prevent movement during cure cycle Cell Size - Distance between two parallel and opposite cell walls at node bonds, measured in W Direction HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION Flexible Core - Core that has bell shaped open cells when viewed in the W direction and is specifically designed for formability into compound curvatures HONEYCOMB CORE FABRICATION Core Splicing - The joining of segments of core by: (1) Overlapping each segment two to four cells and driving them together (crush splice). (2) Pegging with a third piece, or (3) by bonding them together Nodes - Bonded area between cells Over-expanded Core - Core that has a rectangular cell configuration, rather than hexagonal, in which the W opening of the cell is approximately twice the L opening HONEYCOMB CORE FABRICATION Precut Sheet - A slice taken from a block having a constant thickness Thickness- (T) Distance between core faces, Fig. 2 of SSM Batch – A unit of finished material manufactured under controlled conditions at one time Gel Time - The amount of time from the start of mixing of the compound components to the point at which the material becomes non-fluid or gels Work Life - The amount of time from the point at which a material has been thawed to the point at which the material is no longer usable as intended. Work life is sometimes called pot life HONEYCOMB CORE FABRICATION CORE IDENTIFICATION: Core is identified by Class, Type and Grade Class identifies the material type: Class 1 - Fiberglass Fabric Reinforced Core Class 2 / 3 - Obsolete Class 4 - Aramid Paper Core Class 4A - Aramid Paper Core, Heat Forming Grade Class 5 – Bias Weave Fiberglass – Reinforced Core Class 6 – High Modulus (Stiffness) Aramid Paper Core *Most Commonly Used Classes HONEYCOMB CORE FABRICATION Type identifies the size and shape of core cells: Type I - 3/16 inch hexagonal shaped core Type II - 1/4 inch hexagonal shaped core Type III - 3/8 inch hexagonal shaped core Type IV - 1/4-inch hexagonal core over- expanded in the W direction Type V - 1/8 inch hexagonal shaped core Type VI - 3/16 hexagonal core, over- expanded in the W direction Type VII - Flexible core with 35 bell shaped open cells per 12 inches *Most commonly used types HONEYCOMB CORE FABRICATION Grade identifies the honeycomb core nominal density in pounds per cubic foot: 8-124 NOMINAL DENSITY LB/CUBIC FOOT IDENTIFICATION GRADE LB/CUBIC FOOT COLOR 1.5 1.5 1.3 to 1.7 Green – White 1.8 1.8 1.6 to 2.0 Black – White 2.0 2.0 1.8 to 2.2 Purple – White 2.5 2.5 2.2 to 2.8 Brown 3.0 3.0 2.7 to 3.3 Orange 3.5 3.5 3.15 to 3.85 Blue 4.0 4.0 3.7 to 4.3 Red – Green 4.5 4.5 4.05 to 4.95 Black 5.0 5.0 4.6 to 5.4 Yellow – White 5.5 5.5 5.0 to 6.0 Yellow 6.0 6.0 5.5 to 6.5 Red – White 6.5 6.5 6.0 to 7.0 Purple 8.0 8.0 7.3 to 8.7 Green 9.0 9.0 8.2 to 9.8 White 12.0 12.0 11.0 to 13.0 Pink HONEYCOMB CORE FABRICATION CORE MATERIAL FORMS: Core may be supplied in one of the following forms: Block Form – delivered from the manufacturer in an approximately 4 ft thick by 3ft wide by 10 ft long solid block Precut Sheet – cut to a specific thickness and size Preformed Sheet – heat formed for a specific part The core block is set on a horizontal band saw and sliced into sheets. The saw maintains a thickness tolerance of + 0.006” (per BAC 5317) Core Core Block Saw Roughly 4’ x 3’ x 10’ $10,000 HONEYCOMB CORE FABRICATION EQUIPMENT / MACHINES: Block Saw - slices incoming core blocks to the required thickness Band Saw - cuts the desired chamfer as indicated on the CTT N/C Milling Machine - mills core material and/or potting locations to the required depth indicated in the plan and/or CTT Oven - used to mold non-flexible core at high temperatures, cure splices and stabilizations Environmental Booth – special booth for dust collection Scale - used to measure compounds as identified by manufacturer's product data sheet  Back plate supports the core Blade guard 20 degree chamfer applied to edge of core Blade Adjustable table set at 20 degrees Band Saw 20 degree chamfer HONEYCOMB CORE FABRICATION HAND TOOLS: Disc Grinder - used to grind off core material to desired form and/or thickness Dial Caliper – instrument used to verify thickness of core Core Trim Template – used as a guide for trimming honeycomb core to size. Typically built with a set back of up to 0.100” to help maintain the edge band width. The template may also show chamfer information, core ribbon direction and potting locations where applicable HONEYCOMB CORE FABRICATION CORE MACHINING AREAS: Food and drinks are not allowed in this area Contaminants detrimental to adhesion are prohibited eg: dirt, grease or liquid release agents Use of waxes or compounds containing uncured silicone HONEYCOMB CORE FABRICATION CORE CHAMFERING: Defined as applying an angle cut to the core periphery and any core cutouts Typical chamfer is 20˚± 3˚ but can range from 7˚ to 45˚ depending on application Cores are chamfered to: Reduce weight Prevent core crush Provide a smooth transition from the core body to the edge band to aid in transfer of stress loads HONEYCOMB CORE FABRICATION Chamfer intersections and corner radius are rounded off. Specifically: Lower edge of core chamfer sharp to within 0.000” to +0.050” Top of chamfer rounded off 0.500” to 2.000” Chamfer intersections rounded off “Fuzz” from die grinders removed by sanding *Finished core chamfers shall meet the requirements of BAC5317 table 3 HONEYCOMB CORE FABRICATION Rounded off to approximate radius of 0.5 to 2.0 Flat to within ± 3 Degree +/- 0.050 Tolerance Section A - A +0.050 Sharp to within 0.000 -0.00 Detail B HONEYCOMB CORE FABRICATION Point C Sharp corner radius Point D Chamfer intersections may be rounded off, tapering from Point D (0.5 to 2.0R) to Point c (0.0 to 0.15R) Rounded off to approximate radius 0f 0.5 to 2.0 HONEYCOMB CORE FABRICATION Cut out in core Core chamfer Point C Point D Chamfer intersections may be Rounded off, tapering from Point D (0.5 to 2.0 inch R) to Point C (0.0 to 1.5 inch R) Lower edge of chamfer must be sharp (0.00 to + 0.050 inch) HONEYCOMB CORE FABRICATION DETERMINING TOP OF CHAMFER LOCATION: There are 2 methods: By drawing out the chamfer or By mathematical calculation HONEYCOMB CORE FABRICATION By drawing: First draw two lines, parallel to each other, spaced apart equal to the thickness of the core: 0.500 HONEYCOMB CORE FABRICATION Determining the top of the chamfer – by drawing Second, set your protractor at the correct chamfer angle (Eg. 20⁰) HONEYCOMB CORE FABRICATION Determining the top of the chamfer – by drawing Next, pick a spot on the top line, position the protractor on it and draw a line from the top line to the bottom line following the protractor HONEYCOMB CORE FABRICATION Determining the top of the chamfer – by drawing From the point on the top line draw a line perpendicular to it to cross the second line HONEYCOMB CORE FABRICATION Determining the top of the chamfer – by drawing Measure the distance between the two lines. This is the distance from the edge of the core to the top of the chamfer. HONEYCOMB CORE FABRICATION By calculation: This is done by using the required angle, the thickness of the core and the formula for Tan Tan = Opposite Adjacent Opposite Adjacent Required Angle HONEYCOMB CORE FABRICATION If the required angle is 20⁰ and the core thickness is 0.500” rewrite the formula: Adjacent (Width) = Opposite (Height) Tan of Angle.500 =.500 = 1.37 (1.4 on previous slide) Tan 20⁰.364 KNOWN MATH CONVERSIONS: 20 deg =.36 27 deg =.51 23 deg =.42 30 deg =.58 25 deg =.47 HONEYCOMB CORE FABRICATION CORE ASSEMBLY IDENTIFICATION: Mark each completed core assembly IAW the applicable specification. Identify with the following information: Part number as listed on drawing Unit serial number if required by engineering drawing Date of manufacture Manufacturers identification Use the Core tags as required to identify core HONEYCOMB CORE FABRICATION CORE TRIM TEMPLATE WILL PROVIDE: CTT149A7255-3-4 Part Number OPP UNIT Unit Number 5 Top of Chamfer line CORE RIBBON Chamfer angle Core Ribbon Direction DIRECTION Stock core thickness POTTING Core class, type LOC. and grade May provide potting CORE THICKNESS PER SHOP ORDER locations CORE CL. TY. & GR. PER SHOP ORDER HONEYCOMB CORE FABRICATION MATERIAL INSPECTION RECORD DATE:___________________PART NUMBER:______________________SERIAL NUMBER__________________  CORE MATERIAL IDENTIFICATION  BLOCK NUMBER: ___________________ BLOCK NUMBER: ____________________ CLASS: ___________________ CLASS: ____________________ TYPE: ___________________ TYPE: ____________________ GRADE: ___________________ GRADE: ____________________ PRODUCT LOT NO.: ___________________ PRODUCT LOT NO.: ____________________ MANUFACTURER NAME: ___________________ MANUFACTURER NAME: ____________________ _____________________________________________________________________________________________ BLOCK NUMBER: ___________________ BLOCK NUMBER: ____________________ HONEYCOMB CORE FABRICATION CORE IDENTIFICATION TAG POTTING IDENTIFICATION TAG HONEYCOMB CORE FABRICATION MATERIAL INSPECTION RECORD Date Kit Cut ________ Part Number _______________________________ Serial Number ________________ Mir Done By ________ Operated By _______________________________ Collated By ________________ Machine No. ________ LAY UP MATERIAL IDENTIFICATION BMS/TY/CL/GR: _________________________ BMS/TY/CL/GR: _________________________ Batch Number: _________________________ Batch Number: _________________________ Roll Number: ________Plus Hours________ Roll Number: ________Plus Hours________ Manufacture Name: _________________________ Manufacture Name: _________________________ Test Date: _________________________ Test Date: _________________________ Exposed Out Date/Time: _________________________ Exposed Out Date/Time: _________________________ Freezer In Date/Time(Kit) _________________________ Freezer In Date/Time(Kit) _________________________ Freezer Out Date/Time(Kit)_______________ID________ Freezer Out Date/Time(Kit)_______________ID________ Total Exposed Date/Time _______________Date______ Total Exposed Date/Time _______________Date______ HONEYCOMB CORE FABRICATION MATERIAL INSPECTION RECORD DATE:___________________PART NUMBER:______________________SERIAL NUMBER___________________  POTTING / SEALANT / LIQUID ADHESIVE INFORMATION  BMS & TYPE: ________________________ BMS & TYPE: ________________________ BATCH/LOT NO: ________________________ BATCH/LOT NO: ________________________ MANUFACTURER NAME: ________________________ MANUFACTURER NAME: ________________________ TEST DATE: ________________________ TEST DATE: ________________________ RETEST/SCRAP DATE: ____________ID:__________ RETEST/SCRAP DATE: ____________ID:__________ DATE USED ON: ____________DATE:_______ DATE USED ON: ____________DATE:_______ _______________________________________________________________________________________________ BMS & TYPE: ________________________ BMS & TYPE: ________________________ HONEYCOMB CORE FABRICATION STORAGE, HANDLING, PACKAGING OF HONEYCOMB CORE: Store, fabricate and package core so that it does not become damaged or contaminated Clearly ID core and/or subassemblies with its drawing number using a core ID label Ink pens (sharpie) are used to mark core for machining only not to label core All core fabrication using uncured prepreg, film or foaming adhesive shall be carried out in a controlled contamination area HONEYCOMB CORE FABRICATION Table 3 Discrepancy Acceptance and Rework Criteria for Honeycomb Core Discrepan Acceptable Limits Rework Rework Procedures cy Limits Complete Less than 1 % of the 1. A linear 1. Splice separation Node total separation IAW applicable spec. Bond nodes of a core detail of Separation and unlimited Fill damaged core less than 3 of the nodes length. cells IAW applicable in 2. 0.75 in. spec. any 3 in. diameter dia. circle. area. 3. Replace damaged core 3. Unlimited IAW applicable spec. Core 0.02inch deep, 0.50 inch 1. 1. Fill depression IAW Surface long Depression applicable spec. As an Depressio less than or option core may be ns equal to 1 replaced or spliced HONEYCOMB CORE FABRICATION REWORK: Rework shall be documented as required by quality assurance and performed IAW the appropriate specification GENERAL REWORK MATERIALS: BMS 5-28 Type 7 Class 1 and Class 2 potting compounds Mix IAW manufactures instructions. Class 1 may add up to 10 percent by weight of inert filler to thicken (Class 2 already contains microballons and milled glass fibers). Cure IAW the appropriate specifications HONEYCOMB CORE FABRICATION REWORK: Allowable rework during fabrication to bring detail into compliance with acceptable limits is referenced in BAC5317 acceptance/rework tables All in-process rework is to be documented on an In Process Repair Tag including a sketch of the repair All In Process Repair Tags completed by core technicians shall be attached to affected core and subsequently attached to the lay up paperwork HONEYCOMB CORE FABRICATION REWORK IN PROCESS REPAIR TAG THIS PAGE TO ACCOMPANY BUILD SHEET THROUGHOUT SYSTEM.(ATTACH TO COMPLETED CORE DETAIL) PART #_____________________________ SERIAL #_________________________________ MATERIAL USED IN REPAIR:BMS MANUF: MATL. TEST DATE: MATL. RETEST DATE: BATCH# ESTIMATED PERCENT OF SURFACE AREA REPAIRED: % DIAGRAM SHOWING APPROXIMATE LOCATION OF REPAIR(S) LEAD HAND VERFICATION: DATE: EMP#: NOTE: If potting is required for repair only then the potting tag is not required when this form is used. HONEYCOMB CORE FABRICATION CORE VIDEOS 001 - 006 DO WORKSHOPS: #1 - #3: CHAMFER CORES in Shop ensure students have PPE. ANY QUESTIONS TO THIS POINT? $1,500,000.00 HONEYCOMB CORE FABRICATION CORE SPLICING: Core is spliced for the following reasons: To join segments of core to facilitate production of core details To have ribbon direction going in different directions To bond different core thicknesses together To bond different classes, types, and grades of core together There are 2 methods of splicing core: Mechanical Bond HONEYCOMB CORE FABRICATION Mechanical Splicing Applies to Fiberglass core only (BMS 8-124 Class 1) There are 2 methods of mechanical splicing Crush splice Peg splice HONEYCOMB CORE FABRICATION Mechanical Splicing – Crush Splice Overlap core sections 2 to 4 cells Crush together with modified hammer For core 1 inch or thicker, overlap may be chamfered HONEYCOMB CORE FABRICATION Mechanical Splicing – Peg Splice Core may be spliced together by overlapping a third piece (peg) of the same core material across the splice joint. Use a modified hammer to drive core pieces together An overlap of 2 to 4 cell widths is required Use BMS 8-201 or BMS 8-301 epoxy resin after splicing to keep splice from separating. Apply resin a maximum of 1 inch past spliced edge HONEYCOMB CORE FABRICATION Mechanical Splicing – Peg Splice HONEYCOMB CORE FABRICATION CORE SPLICING Mechanical Splicing – Modified Hammer HONEYCOMB CORE FABRICATION CORE SPLICING: Bond Splice using: Foaming Adhesive Film Adhesive Potting Compounds Foaming Adhesive: Prepare and clean core pieces to be bonded Using BMS 5-90 Ty. 2, any Class and Grades 25 – 100 foaming adhesive; apply to core edges to be bonded Ensure maximum gap “T Max” is not exceeded per BAC5317 HONEYCOMB CORE FABRICATION Position core segments and hold core together using a vacuum bag during cure to prevent core movement To prevent core crush or adhesive foaming, vacuum pressure may be limited to 8 to 10 inches Cure IAW the appropriate specification Prepare the bonded surface for subsequent processing steps IAW the appropriate specification HONEYCOMB CORE FABRICATION CORE SPLICING WITH FOAMING ADHESIVE HONEYCOMB CORE FABRICATION VACUUM BAGGING A FOAMING ADHESIVE SPLICE FOR CURE HONEYCOMB CORE FABRICATION PARTING FILM VACUUM BAGGING A FOAMING ADHESIVE SPLICE FOR CURE HONEYCOMB CORE FABRICATION BREATHER BLANKET VACUUM BAGGING A FOAMING ADHESIVE SPLICE FOR CURE HONEYCOMB CORE FABRICATION VACUUM BAG MATERIAL VACUUM PROBE BASE VACUUM BAGGING A FOAMING ADHESIVE SPLICE FOR CURE HONEYCOMB CORE FABRICATION FOAMING ADHESIVE SPLICE UNDER VACUUM AND READY FOR CURE HONEYCOMB CORE FABRICATION Film Adhesive: Clean core IAW applicable specifications Apply film adhesive to core edge segments and position together using a vacuum bag during cure to prevent core movement Ensure maximum gap “T Max” is not exceeded per BAC5317 To prevent core crush or adhesive foaming, vacuum pressure may be limited to 8 to 10 inches Cure IAW the appropriate specification Prepare the bonded surface for subsequent processing steps IAW the appropriate specification HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION Potting Compound: Clean core IAW applicable specifications Using BMS 5-28, Type 7, Class 1 or 2, Type 12, or Type 13, apply potting to both core edges Position core segments together and hold core together securely during cure Ensure maximum gap “T Max” is not exceeded per BAC5317 Prepare the bonded surface for subsequent processing steps IAW applicable specifications HONEYCOMB CORE FABRICATION CORE SPLICING WITH POTTING (BACK SIDE) HONEYCOMB CORE FABRICATION NOTE: MASKING TO PREVENT SQUEEZED OUT POTTING FROM FILLING CELLS CORE SPLICING WITH POTTING (FRONT SIDE) HONEYCOMB CORE FABRICATION NOTE: MASKING TO PREVENT SQUEEZED OUT POTTING FROM FILLING CELLS CORE SPLICING WITH POTTING HONEYCOMB CORE FABRICATION CORE SPLICING WITH POTTING HONEYCOMB CORE FABRICATION Discrepancy Acceptance and Rework Criteria for Spliced and Potted Honeycomb Core Table IV Discrepancy Acceptable Limits Rework Rework Limits Procedures a. Incorrect Overlap of Unlimited Cut out Mechanical mechanically discrepant area Bond-line spliced pieces of and Overlap core shall be a re-splice minimum of 2 cells b. Thickness Shall not exceed Unlimited Mismatch 0.008 inch 1. High 1. Sand with 150 in Bond-lines core grit or finer and 2. Low adhesive Potted Areas core 2. Replace core 3. Offset 3. Sand with 150 grit or finer abrasive or re- splice core HONEYCOMB CORE FABRICATION Discrepancy Acceptance and Rework Criteria for Spliced and Potted Honeycomb Core Table IV Discrepancy Acceptable Limits Rework Rework Procedures Limits c. Bubbles in Surface Bubbles shall not Unlimited Fill surface bubbles Potting Compound exceed 1 core cell size in using applicable material and the longest surface or cut out and re-splice. Foaming Adhesive dimension d.Bond line Depressions 1. No depressions allowed Unlimited Fill depression using 1. On tool side 2. No depressions allowed applicable material surfaces 3. Maximum size 0.02 inch 2. On bag side deep and 0.50 inch long surfaces to be subsequently bonded to a pre-cured skin 3.On bag-side surfaces not subsequently bonded to a HONEYCOMB CORE FABRICATION Discrepancy Acceptance and Rework Criteria for Spliced and Potted Honeycomb Core Table IV Discrepancy Acceptable Limits Rework Rework Procedures Limits e. Potted area Maximum size 0.03 inch Unlimited Fill with additional depressions deep measured from core potting compound surface f. Excessive core Maximum core splice gap Unlimited Fill splice gap using splice gap varies with cell size applicable material or re-splice g. Partial unbonded Cumulative length of un- Unlimited Fill un-bonded area using area bonded areas in any 12 in. applicable material shall not exceed 3 times cell size HONEYCOMB CORE FABRICATION Discrepancy Acceptance and Rework Criteria for Spliced and Potted Honeycomb Core Table IV Discrepancy Acceptable Limits Rework Rework Procedures Limits h. Full depth gap Maximum size 0.1 inch Unlimited Fill splice gap using across the splice long (parallel to bond line) applicable material or No gap greater than or re-splice equal to 0.02 inch long shall be closer than 6 inches to another gap I. Excessive Maximum size 2 cells or Unlimited Remove and replace with Adhesive 0.375 inch (whichever is acceptable core. or Potting larger) beyond the core compounds edge of a splice or beyond the designated area to be bonded HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION CORE POTTING: Core is potted for the following reasons: Edge filler for exposed honeycomb in a part (Net Trim is within core) Strengthen areas of attachment points for hinges, fasteners, stiffeners, etc In extreme cases to prevent core crush Core is potted by one (1) of the following methods: Prior to lay-up - pre-potted at core detail stage Precured Potting Insert – A fabricated insert is bonded into the core detail cavity with either film or foam adhesive or BMS 5-28 potting compound. Usually installed and co-cured at the lay-up stage Potting after lay-up and cure - drilling a hole through the bagside facing, “Hogging" out core cells, and injecting BMS 5-28 potting compound into cavity HONEYCOMB CORE FABRICATION POTTING PRIOR TO LAYUP: Mask core with pressure sensitive tape to define the dimensions of the potted area Mask off opposite side using a piece of peel ply slightly larger than the area to be potted and masking tape Apply potting compound to completely fill core cells Remove masking tape and cover exposed potting with peel ply and masking tape HONEYCOMB CORE FABRICATION AREA TO BE POTTED HONEYCOMB CORE FABRICATION PEEL PLY ON OPPOSITE SIDE HONEYCOMB CORE FABRICATION PEEL PLY MASKED IN PLACE HONEYCOMB CORE FABRICATION PEEL PLY OVER POTTED AREA HONEYCOMB CORE FABRICATION PEEL PLY MASKED IN PLACE HONEYCOMB CORE FABRICATION PRECURED POTTED INSERTS: Bond pre-cured potted inserts in place with one of the following: BMS 5-129 film adhesive BMS 5-90 foaming adhesive BMS 5-28 potting compound Cure IAW the applicable specification HONEYCOMB CORE FABRICATION PRECURED POTTED INSERT HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION POTTING AFTER LAYUP AND CURE: Drill a hole through the bagside the same size as the fastener diameter Drill a 0.063” maximum diameter vent hole within 0.250” of the potted area to ensure evacuation of entrapped air Tear out the walls of the core (hog out) Inject BMS 5-28 potting material through the hole until the area is completely filled (as evidenced by the potting material extruding from the vent hole) Cure IAW the appropriate specification HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION SHOP WORKSHOPS: #4: POTTING CORE LOCATIONS #5: POTTING CORE BONDLINE #6: CHAMFER CORE #7: BOND LINE WITH FOAM ADHESIVE HONEYCOMB CORE FABRICATION CORE FORMING: A process whereby non-flexible core is heated in an oven and "formed" to a contoured fixture Does not apply to over-expanded or flexible core material Nomex core may require pre-drying to prevent resin blistering and cell wall or node bond damage caused by water vaporization during heat up Heat Forming Oven Core fitted into heat resistant bag & placed in 600 degree oven for several minutes Core placed in 2 piece forming tool HONEYCOMB CORE FABRICATION Table V Discrepancy Acceptance and Rework Criteria for Formed and Chamfered Honeycomb Core Discrepancy Acceptable Limits Rework Rework Procedures Limits a. Formed core Core shall hold in place Nomex core Reform Nomex core IAW Contour in lay-up tool or check may be applicable irregularities fixture when tacked in reformed once. specification place with prepreg or Fiberglass core film adhesive No rework allowed b. Buckle lines No buckle lines Unlimited Remove and replace with exceeding 20 inches in acceptable core length No more than 3 buckle lines in any formed radius  HONEYCOMB CORE FABRICATION Table V Discrepancy Acceptance and Rework Criteria for Formed and Chamfered Honeycomb Core Discrepancy Acceptable Limits Rework Rework Procedures Limits c. Core chamfer ` 1. Waviness 1. Core chamfered face 1. Unlimited 1. Sand with 150 grit or finer shall be flat or for abrasive contoured surfaces smooth within ± 0.050 inch in any 3 inch 2. Blunt core 2. Sharp, with lower edge 1. a. Unlimited 2. a. Splice core IAW applicable Chamfer Height 0.000 to 0.050 specification inch b. Max. 0.025 b. Butt drawing specified filler inch wide plies in this local area (perpendicular to core edge) by 3 inch long 3. Oversized 3. Core edge location 3. Unlimited 3. Trim with scissor or a knife Chamfered shall meet the and a rigid cutting surface. core requirements of the Rework blunt trimmed edge. Engineering drawing HONEYCOMB CORE FABRICATION CORE STABILIZATION: six different methods of stabilizing a core detail to prevent core movement during cure Methods 1 and 6 are optional to manufacturing during composite fabrication (tiedowns) Methods 2, 3, 4, and 5 are called by the engineering drawing prior to use and are carried out in the core department. They are: Resin Dip: Method 2 (Info Only) Adhesive Film: Method 3 (Shop Practical) Core Chamfer Pegging: Method 4 (Info Only) Septum: Method 5 (Info Only) HONEYCOMB CORE FABRICATION Method 2 – Resin Dip: Apply the applicable resin to the core chamfer area. Do not coat more than 2 inches beyond the chamfer Within 2 hours cure resin IAW the appropriate specification Method 3 – Adhesive Film: Stabilize with adhesive film on the bag side, tool side, or both sides Use film adhesive, heat up rates, cure temperatures and times IAW the appropriate specification To prevent core crush or adhesive foaming vacuum pressure may be limited to 8 to 10 inches. HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION Method 4 – Core Chamfer Pegging: (F/G core only) An additional piece of core of the same density as the part may be pegged into the chamfer area Method 5 – Septum: Use pre-impregnated fiberglass and film adhesive called out in the applicable specification Septum stabilize using one ply of pre- impregnated fiberglass between two plies of film adhesive Cure per the applicable specification HONEYCOMB CORE FABRICATION HONEYCOMB CORE FABRICATION SHOP WORKSHOPS: #8 or #9: STABILIZATION HONEYCOMB CORE FABRICATION PRACTICAL EVALUATION CORE RIBBON DIRECTION CORE THICKNESS NET SIZE, TRIMMED TO CTT CHAMFER ANGLES / WAVINESS BLUNT EDGE OF CORE CELL TEAR OUT CORE “FUZZ” REMOVAL (PART QUALITY) PART IDENTIFICATION COMPLETION OF PAPERWORK