WFIRST-IC-SPEC-0035-.pdf

Effective Date: June 20, 2019 Expiration Date: June 20, 2024

CHECK https://ipdtdms.gsfc.nasa.gov

TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.

National Aeronautics and Space Administration

Goddard Space Flight Center Greenbelt, Maryland

WFIRST-IC-SPEC-0035, Revision -

Wide Field Infrared Survey Telescope (WFIRST), Code 448

Specification for Machining, Drilling and Trimming of Composite Structures

GSFC WFIRST CMO

June 21, 2019

Released https://ipdtdms.gsfc.nasa.gov/

SPEC for MDT of CS WFIRST-IC-SPEC-0035, Revision -ii

Specification for Machining, Drilling and Trimming of Composite Structures

Review/Signature/Approval Page

Prepared by:

Wes Alexander

Approving Signature Authority:

Christopher Tolman

Electronic Approval available on-line at: https://ipdtdms.gsfc.nasa.gov iii

Preface This document is a Wide Field Infrared Survey Telescope (WFIRST) Configuration Management (CM)-controlled document. Changes to this document require prior approval of the applicable Signature Authority or designee. Proposed changes shall be submitted to the WFIRST CM Office (CMO), along with supportive material justifying the proposed change.

In this document, a requirement is identified by “shall,” a good practice by “should,” permission by “may” or “can,” expectation by “will,” and descriptive material by “is.”

Questions or comments concerning this document should be addressed to:

WFIRST Configuration Management Office Mail Stop 448 Goddard Space Flight Center Greenbelt, Maryland 20771 iv

Change History Log

Revision Effective Date Description of Changes (Reference the Signature Authority Approval Date)

Revision - June 20, 2019 This was approved by the WFIRST Signature Authority via WFIRST-SCoRe-0137 on the effective date shown.

v

Table of TBDs/TBRs/TBSs

Item No. Location Summary Individual/ Organization

Actionee

Due Date vi

Table of Contents

1 INTRODUCTION

1.1 Purpose

1.2 Scope

1.3 Related Documentation

1.3.1 Applicable Documents [and Forms]

1.3.2 Reference Documents

2 REQUIREMENTS

2.1 Material Requirements

2.2 Process Requirements

2.3 Contamination Control Requirements

2.1 Material Handling and Packaging

2.2 Backup Material

2.3 Process Development

2.4 Tooling

2.5 Fixtures

2.6 Speed and Feed Rates

2.7 Finishing

3 WORKMANSHIP REQUIREMENTS

3.1 Appearance

3.2 Edge Finish

3.3 Hole Finish

3.4 Edge Coating of Edges and Cutouts

3.5 Tow Removal after Cutting of Fabric Laminates

4 QUALITY ASSURANCE PROVISONS AND TESTING METHODS

4.1 General

4.2 Cutting Edge Inspection

4.3 Non Destructive Inspections

4.4 Edge Coating Inspection

5 REFERENCE INFORMATION

5.1 Suggested Cutting Equipment, Tools, Speeds and Feeds

5.2 Mix Record Sheet (Reference)

APPENDIX C ABBREVIATIONS AND ACRONYMS

1 INTRODUCTION

1.1 Purpose

This specification covers performance measures for machining, drilling, and trimming of composite structures for the Wide Field Infrared Survey Telescope (WFIRST). The contractor is responsible for compliance with all requirements within this specification.

1.2 Scope

This specification describes requirements and sets limits of acceptance for machining, drilling and trimming of composite material details and assembled structures for the IC Flight and development program.

1.3 Related Documentation

The latest versions of all documents below should be used. WFIRST documents can be obtained from URL: https://ipdtdms.gsfc.nasa.gov.

1.3.1 Applicable Documents [and Forms]

The following documents are referenced within this document and are directly applicable or contain policies or other directive matters that are binding for the contents of this document. In the event of conflict between an Applicable Document and the content of this document, the applicable Signature Authority has the final authority for conflict resolution.

In case of conflicting requirements between the requirements of this specification and those noted on the engineering drawing, the drawing requirements shall take precedence.

Document Number Title WFIRST-IC-SPEC-0046 Instrument Carrier Flight Structure Fabrication Specification

1.3.2 Reference Documents

The following documents are referenced herein and amplify or clarify the information presented in this document. These documents are not binding on the content of this document.

Document Number Title WFIRST-IC-SPEC-0056 WFIRST Non-Destructive Examination Specification and

Defect Acceptance Criteria for Non Metallics

WFIRST-SYS-PLAN-0051 WFIRST Contamination Control Plan

2 REQUIREMENTS

2.1 Material Requirements

Composite material to be machined shall be, at a minimum, visually inspected prior to machining operations. Any defective areas shall be clearly marked. These areas shall be removed during the machining operations if the removal results in an acceptable condition per the appropriate engineering drawing. Otherwise, disposition of the defective areas shall be directed by GSFC Material Review Board.

2.2 Process Requirements

Carbon fiber composites are sensitive to the machining tools and processes used. Care shall be taken during all steps to prevent damage such as breakout around a hole, splitting, and delamination. Specific limits for damage due to machining operations are presented herein.

*CAUTION: Carbon fiber composites are electrically conductive and will generate conductive machining debris that can damage electrical equipment. Air-driven tools are recommended for hand operations. Electrically driven tools such as drills, routers, etc.

shall be protected to prevent intrusion of carbon particles.

Machining of carbon composites will generate particles and splinters that can irritate and penetrate skin.

Vacuum systems are recommended for debris removal during machining operations.

Vacuum systems shall be equipped with microspore filters capable of trapping particles of 20 microns and larger if the vacuum is exhausted into the work area.

Personal protective equipment shall include gloves and dust mask or respirator.

2.3 Contamination Control Requirements

Contamination control implementation shall conform to WFIRST-SYS-PLAN-0051, WFIRST Contamination Plan.

Machining and drilling operations inherently generate debris. To the extent possible, machining debris shall be removed during machining and drilling operations at the assembly level. After completion of machining operations, parts shall be thoroughly cleaned by vacuuming, followed by wiping with isopropyl alcohol or acetone, until the part is visibly clean and a moistened wipe does not remove further machining debris.

Non-contaminating gloves shall be worn during wiping operations. Nitrile gloves are required for operations other than acetone wiping. For acetone wiping, polyethylene gloves shall be worn.

Acetone will dissolve nitrile gloves and contaminate the surface.

Non-contaminating lint-free wipes shall be used for cleaning. The specific type(s) used shall be approved by the WFIRST Materials Engineering Board.

When parts, particularly cleaned parts, are to be left for an extended period of time, they shall be covered with a non-contaminating material.

Use of cutting lubricants shall be restricted to isopropyl alcohol. Use of any other cutting fluids is subject to approval by the GSFC Materials Engineering Branch. Use of cutting fluids containing oils, silicones or other contaminating agents is strictly prohibited.

2.1 Material Handling and Packaging

Material shall be protected from handling damage at all times. Laminates shall be wrapped in protective material, such as non-contaminating plastic film, during storage. Laminates and other parts shall be well supported and shall not be stacked unless previously wrapped or covered in protective material. Laminates shall be transported using appropriate non-contaminating backing materials, to prevent bending and cracking during transport.

Laminates and other composite parts shall be labeled to maintain traceability to the original raw material, manufacturing processes and cure process. If a permanent label or marking are used, the label material, marking method, and location shall be per the appropriate engineering drawing.

Material shall be protected from knocks, kicks, dropped objects, and other potential damage.

Any material that is subjected to any percussive, excessive bending or dropping event shall be tagged for NDE inspection.

2.2 Backup Material

A solid non-contaminating backup material, such as plastic, spoil board, or aluminum, shall be used to prevent splintering of the back surface of the work piece during drilling and cutting operations which penetrate the back surface. All backup materials shall be debris free. The backup material must cover the area where the cutting tool will penetrate the material over the entire length of the cut.

The backup material shall be contoured if necessary to ensure intimate contact. The backup material shall be firmly clamped or otherwise held to the work piece to ensure intimate contact.

Care shall be taken not to entrap debris between the work piece and the backup material that could scratch the work piece or interfere with intimate contact. It is recommended that all surfaces be thoroughly cleaned and inspected prior to clamping.

*Caution: Care shall be taken during any operation involving clamping of composites as clamp pressure can delaminate the matrix. There should be a compliant layer of material between any composite and clamp face (such as tongue depressor). All clamped areas within the final part should have NDE inspection after machining operations.

2.3 Process Development

Tryout cuts shall be made using scrap material representing the configuration to be cut prior to machining of any flight or critical development parts. Parts used in process development shall be inspected per Section 3.

2.4 Tooling

Drilling, routing and milling shall be performed with solid carbide, diamond, or carbide coated cutting tools. Sawing shall be performed with carbide grit or diamond impregnated cutting blades. Alternate tool types shall be reviewed and approved by WFIRST.

The cutting tool shall be kept sharp at all times and shall be changed frequently. Drilling with a dull bit or cutter, particularly a high-speed steel bit, will result in damage to the part.

For cutting of thin materials, such as face sheets, axial reciprocation or frequent adjustment of tool depth is recommended to extend tool life and avoid localized wear.

When a circular cutting wheel is used, it shall extend through the part such that the cut edges are not shaped by the circular cross-section at the edge of the wheel. Thin circular cutting wheels shall be stiffened to prevent excessive blade deflection.

2.5 Fixtures

The cutting tool shall be secured with fixtures or other means to maintain position and perpendicularity of the hole or feature being machined. Freehand cutting is not permitted for flight and critical features of development test hardware unless approved by WFIRST.

2.6 Speed and Feed Rates

Cutting speeds and feed rates shall be determined by process development machining cuts using scrap material and the tools and cutting bits that are intended to be used. Cutting speeds and feed rates for specific laminate and cutting tool combinations will be documented in work orders or procedures.

2.7 Finishing

Tools used to perform hand finishing operations shall be chosen with care to avoid damage to the composite. Use of metal deburring tools for holes or other scraping device is not recommended.

In most cases, minimal or no hand finishing should be required if the machining operation is properly performed. Final end edge finish cuts may be performed, with approved from WFIRST, using a cutoff saw and water or alcohol flushing the saw blade. This method will be evaluated and approved by WFIRST. This method should insure that there are no cracks visible under 30X magnification. If necessary, finishing of tube and gusset edges by sanding is allowed as follows:

The process is defined as removal of .020 to .040 per edge, which is performed by sanding with 240 grit followed by 320 grit and finished with 500 grit aluminum oxide paper only without approval from WFIRST.

3 WORKMANSHIP REQUIREMENTS

3.1 Appearance

Laminated parts and assemblies shall be 100% visually inspected after machining and shall show no signs of fractured fibers, delaminated plies, missing or loose fibers, or dents, except as specified herein. Tube and Gusset machined end edges shall not show any cracks inspected under 30X magnification around any area too be used for bonding. After the machining process has been proven, a sampling plan with less than 100% article inspection may be approved by WFIRST. For all cut areas, the material shall be free of dirt and other foreign material. There shall be no visible cracks or delamination. Visible scorching or discoloration of the composite material due to machining is not permitted. Surface scratches or gouges shall not be greater than

0.05 inch long, .010 inch wide and 0.003 inch deep. There shall be no scratches or gouges penetrating the surface resin layer in face-sheets or detail parts within 2 inches of areas where parts will subsequently be bonded.

3.2 Edge Finish

Finish of edges and cutouts that will not be in direct contact with other hardware, such as, lightening holes, outside edges, etc., shall not be greater than 125 microinches rms. For edges which are coated per 3.4, the allowable surface finish prior to coating is 250 microinches rms.

Allowable breakout of fibers at the edge of a part and around holes shall be .030 inches maximum. Ragged edges or projecting fibers are not permitted. Cuts shall be made perpendicular to the surface within 1 degree.

3.3 Hole Finish

Finish of holes for fasteners shall be 63 microinches rms maximum. Minor discontinuities around the cylindrical surface of the hole are acceptable provided the surface finish requirement is met. There shall be no visible scorching of the hole. There shall be no evidence of delamination, with the exception that allowable breakout around the surface of the hole is .010 inches maximum. Breakout shall be limited to the outer ply only, and shall not exceed 25% of the circumference of the hole. Burrs, dust or fiber particles that would prevent proper insertion of the fastener shall be removed.

3.4 Edge Coating of Edges and Cutouts

When specified on the engineering drawing, edges of laminates and cutouts shall be coated with EA956 or EA9396 epoxy adhesive to prevent splintering damage. The application shall be a thin coat and shall not cause the part or assembly to exceed the applicable drawing tolerances. The edge coating shall extend approximately .01 to .06 inches onto the part surface adjacent to the edge unless otherwise specified by the engineering drawing. The application shall not interfere with the bonding or installation of parts at higher levels of assembly.

A mix record and hardness sample shall be prepared for each adhesive mix used. Adhesive preparation shall be per the adhesive manufacturer’s specification or supplier process specification approved by WFIRST.

The adhesive shall be traceable to the vendor lot control number. The mix record shall meet the requirements of the mix sheet in Section 5.2 (reference GSFC specification 548-WI-8072.1.10).

The measured hardness of the adhesive sample shall be 65 Shore D minimum for EA956 and 75 Shore D minimum for EA9396. Full cure is 5 days at room temperature for EA956 and EA9396.

Processing of the parts may continue after a minimum adhesive cure of 24 hours.

3.5 Tow Removal after Cutting of Fabric Laminates

For fabric laminates that have been face cut to a final thickness, such as thick (>.12 inch) laminates, it is permissible for localized portions of fabric tow that have been severed by the machining operation to be removed. The depth of the missing portions of a tow shall not exceed the ply thickness of the material. The maximum individual length of a missing portion of tow is .25 inch. The surrounding tows shall not be distorted or otherwise damaged.

4 QUALITY ASSURANCE PROVISONS AND TESTING METHODS

4.1 General

Inspection shall be performed by trained personnel. The contractor shall present the training process and a list of names of individuals that have passed the training and how it relates to the WFIRST instrument carrier work. The process shall include the duration of certification and definition of the re-training process.

4.2 Cutting Edge Inspection

Parts and machined features, such as edges, shall be, as a minimum, inspected visually. All areas identified to be bonded surface shall be inspected under 30X and have no cracks. A sampling inspection can be established after the machining process has been proven. The sampling shall identify parameters for the machining inspection process such as intervals, change of cutters etc.

4.3 Non Destructive Inspections

NDI shall be used to evaluate features initially found using visual inspection. NDI procedures shall be in accordance with WFIRST-IC-SPEC-0056. In particular, areas of suspected delamination shall be evaluated as required using A-scan or other suitable techniques to define the extent of the damaged area.

4.4 Edge Coating Inspection

Adhesive sample hardness shall be measured by a Shore D scale durometer, which is within calibration limits. Mix records shall be inspected for completeness of recorded data and to confirm completion of cure.

5 REFERENCE INFORMATION

5.1 Suggested Cutting Equipment, Tools, Speeds and Feeds

5.2 Mix Record Sheet (Reference)

Appendix C Abbreviations and Acronyms

Abbreviation/ Acronym

DEFINITION

GSFC Goddard Space Flight Center TBD To Be Determined TBR To Be Revised TBS To Be Scheduled NDE Non-Destructive Examination MEB Materials Engineering Branch (Here at GSFC)