REG NASA-LLIS-6616-2012 Lessons Learned Undocumented Process Steps And Process Drift Is Root Cause For Scrap Of High Value Part.pdf

1、Public Lessons Learned Entry: 6616 Lesson Info: Lesson Number: 6616 Lesson Date: 2012-05-29 Submitting Organization: MSFC Submitted by: Michael Haynes Subject: Undocumented Process Steps And Process Drift Is Root Cause For Scrap Of High Value Part Abstract: An Orion composite structural part was scr

2、apped due to loss of vacuum during cure. The failure investigation revealed that loss of vacuum was caused by a leak in the vacuum bag due to excessive bleed of resin all the way to this bag. Description of Driving Event: To cure a large laminate structural part, the part is wrapped in layers of mat

3、erial that maintain a vacuum on the part and allow a portion of the resin to bleed away from the part. For this part, the stack up of bag layers is: peel ply, perforated release film, bleeder, solid release film, breather, and then vacuum bag. The function of these layers is: Peel ply Layer of no-st

4、icking material that allows the bagging to be removed after cure; Provides flow path for the applied vacuum Perforated release film Allows for the appropriate volume of resin bleed by having the specified bleed holes at the specified spacing Bleeder cloth Soaks up resin as the vacuum process pulls i

5、t from the composite structure to permit part cure Solid release film (non perforated) Protect the vacuum bag from the resin Breather Polyester material allows a vacuum to be maintained throughout the entire part without pinching off in any area Vacuum bag Provide the pressure barrier between the hi

6、gh pressure in the curing chamber and the vacuum drawn on the part Vacuum Sealer Tape Seals the joints in the bagging material to complete the bags. The scrapped part was the third unit of this part to be built. The part is conical in shape, so flat sheets of bagging material did not drape nicely ov

7、er the part. During the original two builds, the manufacturing crew cut the bagging materials into gore sections and taped them together to achieve a good fit to the part. The criticality of cutting bagging materials into gore sections was unknown and un-documented. On the third build of this part,

8、the manufacturing crew wrapped the flat sheets around the part then taped the one joint. During the cure of the third part, wrinkles formed when vacuum was applied to the bags. At the wrinkles areas, additional holes formed in the perforated release film and holes formed in the solid release film. T

9、hese new holes in the bagging material allowed excessive resin to bleed through the perforated release film and also to bleed through the solid release film. The resin in contact with the vacuum bag cured, permitting stress concentrations to form on the vacuum bag. The vacuum bag failed at 231 minut

10、es into the cure and at 329 deg F, causing the part to be nonconforming. Lesson(s) Learned: During the design development and manufacturing process development phase, establish configuration controlled manufacturing processes. These manufacturing processes should establish the critical steps and pro

11、vide detailed work instructions for the critical steps. Changes to the build process require a configuration controlled revision to these manufacturing processes. If significant time has elapsed or a new manufacturing crew is used, require them to hold a process walk thru of the manufacturing proces

12、s to assure they understand the steps in the process, the equipment required, condition of the equipment, and materials required. The fit of the vacuum curing bag materials is a critical parameter for the curing of a composite structural part. The perforated release film and solid release film are s

13、usceptible to having unintended holes when the materials do not lay flat. The process step of cutting the materials into gore sections was not documented within the bagging process instructions. These steps need to be documented to assure that these steps performed consistently. Provided by IHSNot f

14、or ResaleNo reproduction or networking permitted without license from IHS-,-,-Recommendation(s): The following are the corrective actions from the failure investigation. 1. Provide the manufacturing crew with an approved and controlled manufacturing process 2. Pre-cut all bagging materials into cont

15、rolled kits to assure right size and shape is used 3. Work instructions will link specific gore patterns 4. Close visual inspection by Production to ensure no wrinkles in bagging material 5. Use either two layers of solid release or thicker solid release material Evidence of Recurrence Control Effec

16、tiveness: Recurrence control will be per the contractors nonconformance system. Documents Related to Lesson: N/A Mission Directorate(s): Exploration Systems Additional Key Phrase(s): Manufacturing and Assembly Additional Categories.Parts, Materials, & Processes Additional Categories.Hardware Safety and Mission Assurance.Product Assurance Additional Info: Project: Multi-Purpose Crew Vehicle (MPCV) Approval Info: Approval Date: 2012-11-28 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-