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Material and Process Spec Review

Material and Process Spec Review. Cindy Cole Certification and Materials Engineer The Lancair Company. Material Specification - Methodology. In general, I found the document difficult to follow because I didn’t think the two material specifications were clearly discussed and separated

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Material and Process Spec Review

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  1. Material and Process Spec Review Cindy Cole Certification and Materials Engineer The Lancair Company

  2. Material Specification - Methodology • In general, I found the document difficult to follow because I didn’t think the two material specifications were clearly discussed and separated • Industry material specification and/or • A ‘standard’ end-user material specification

  3. Material Specification - Methodology • Industry Specification should include: • Test requirements (properties, methods, replicates) • Test frequency for IMQ and Supplier required testing and schedule for reducing Supplier testing • Slash sheet with properties and cure cycle to obtain them

  4. Material Specification - Methodology • End-User Specification should include: • Receiving Inspection test requirements • In-process test requirements • Address any changes in cure cycle and/or panel manufacturing • Need to decide if there will be standard criteria the Suppliers can count on in the industry spec, or will the end-user specification have overriding requirements

  5. Material Specification - Comments • Include Table of Standard Tolerances • A TSO is discussed in Section 2.4, what about PMA? • What about TSOA issuance? What oversight (if any) does the end-user have to perform? Is an end-user material specification even required if the Supplier has a TSO & TSOA? • How does the data generated from periodic batch testing get incorporated into the end-user specification / type design?

  6. Material Specification - Comments • An example of a Process Control Document would be very beneficial (Section 6) • By combining ‘minimal thermal history’ with the shortest cure cycle and the ‘max thermal history’ with the longest cure cycle, is that the worst-case scenario? Or are you tailoring the cure cycle / material to what works best together? (Methodology should be explained) (Section 6.1)

  7. Material Specification - Comments • I would disagree with requiring actual tests for kinetics, rheology, moisture diffusion, moisture absorption and thermally induced microcracking, as long as other macro properties are checked and as long as the prepreg manufacturing materials, processes, and environment are controlled (Table 1) • Should there be a requirement on number of splices and tracers in Section 6.2.1?

  8. Material Specification - Comments • Material test methods require better definition than just referencing the ASTM standard (e.g. describe how ‘chemical reactivity and degree of advancement’ will be measured via the DSC) (Table 3) • Section 6.2.3 could have more defects and limits such as incomplete wet out, foreign material, yarn twists and crossovers, broken yarns, gaps, open spaces, distortion, crushed yarns, or bowed fibers.

  9. Material Specification - Comments • Most venders certify their material from the date of shipment. If that is the case, do we need to track storage/outlife of material from the date of manufacture to the arrival on the dock at the purchaser? (Section 6.2.4) • It was not clear to me in Section 6.3.1 if there is one cure cycle, or different ones – say one used for panels vs. one used in production, or one used by the supplier vs. one used by the end-user

  10. Material Specification - Comments • We have seen large variations in cured ply thickness and would be reluctant to put a pass/fail criteria on it. Fiber properties are being normalized by the thickness. • Do we really want an open-hole test for batch acceptance? (Table 5b) • Will there be an upper limit for strengths? • What sort of third party would certify the test laboratories? Is this the FAA? (Section 10)

  11. Process Specification • In general, I was confused as to whether this was supposed to be a specification for making panels and/or full scale parts. • Should allow the use of a full-scale test article or sub-component in addition to the ‘demonstrator panel’ defined in Section 3.1. • Table 1 holds the kind of information that I believe our MIDO would prefer to see defined in a Quality document, rather than a type design document.

  12. Process Specification • Table 3 should mention an oven in addition to an autoclave • AC 21-26 already defines an acceptable processing environment, should Section 5.3.4 reference that? • What is a ‘warp clock’ in Table 5? (There should have been a section for definitions and abbreviations in the beginning of the spec, plus list of standard tolerances)

  13. Process Specification • Table 5 should include approved tooling materials, if it isn’t defined elsewhere in type design (e.g. Teflon, aluminum, glass/epoxy, carbon/epoxy). What about insert materials or mold repair materials? (For example, is it acceptable to cover small blemished with clear tape?) • Section 5.3.6.4 should identify the reference edge on the panel

  14. Process Specification • Again, not sure if we would support having pass/fail on ply thickness in Section 5.3.6.7

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