AC 33.70-5 APPENDIX E. DEF INITION OF AN AXIAL BLADE SLOT FOR MANUFACTURING ANOMALY
ASSESSMENT E.1 Definition and Description of Axial Blade Slots.
E.1.1 General Description of Axial Blade Slots.
Axial blade slots are a set of nominally identical features within the same component, typically one per blade root, located at the same nominal radius, usually in the rim of a disk.
• Each blade slot is positioned radially along the disk rim, providing a mechanical constraint.
• Blade slots are typically located at the same nominal radius for uniformity.
• Figure E-1 provides an example of a component with two axial blade slot features.
Each feature consists of a set of axial blade slots.
E.1.2 Common Manufacturing Methods.
Axial blade slots are manufactured using a common method and can have the following configurations:
• Dovetail Root Form: Blades with a dovetail root form, as shown in figure E-2, have a single pair of contact faces.
• Firtree Root Form: Blades with a firtree root form, as shown in figure E-3, have multiple pairs of contact faces.
The blades are assembled into the slots predominantly parallel to the engine’s axis of rotation.
E.1.3 Edge and Surface Features for Assessment.
Edge features extend between the points on either side of the blade slot, associated with the minimum disk post thickness, located radially inboard of the lowest blade-disk contact point.
• Edges to Assess: Assess the edges on both the front and rear faces of the disk.
• Surface for Assessment: The surface within the slot is defined by connecting the extreme points of the edge features.
E–1
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Figure E-1. Example of Axial Blade Slot Component Features
Slot surface Edge Figure E-2. Example Dovetail Axial Blade Slot Geometry and Definition of the Features Covered by this AC E–2
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Edge Slot surface Figure E-3. Example Firtree Axial Blade Slot Geometry and Definition of the Features Covered by this AC E.2 [Reserved.] E–3
AC 33.70-5 APPENDIX F. MA NUFACTURING CREDITS F.1 Overview of Manufacturing Credits.
F.1.1 This appendix contains the approach for taking credit for enhanced axial blade slot manufacturing processes in the POF calculations to meet the axial blade slots feature DTR. A process and rationale were developed by the AIA Rotor Integrity Steering Committee to establish the manufacturing credits promoting enhanced manufacturing of axial blade slots.
F.1.2 The manufacturing credits are applied in two ways:
• the application of a defined credit specific to the manufacturing process to reduce the actual risk calculated for the part, and
• a reduction in the number of “effective” slots used in the risk calculation.
The manufacturing credits are defined in tables F-1 and F-2. The process for determining the number of effective slots to use in the risk calculation is described below. Tables F-1 and F-2 outline the manufacturing credits.
F.1.3 The approach for calculating the number of effective slots centers on the concept that an automated means of manufacturing should reduce the risk associated with producing a poorly manufactured slot compared to a purely manual process and that the risk associated with manufacturing multiple slots in a disk is further reduced significantly with an automated process.
F.1.4 An expression has been derived that defines an “effective number of slots” (Neff) based on the ratio of the manufacturing credits being claimed for automation compared to the maximum possible credit for automation. If a purely manual process is used to manufacture the axial blade slots, then the effective number of slots is equal to the actual number of slots. Conversely, if a purely automated process is used with full process monitoring, then the effective number of slots can be reduced significantly.
F.2 Calculation of Effective Number of Slots.
F.2.1 The expression for Neff is as follows:
𝑑𝑑𝐾𝐾𝐾𝐾𝐾𝐾 = 𝑑𝑑 𝐾𝐾𝐾𝐾 𝑑𝑑 <= 90 𝑑𝑑𝐾𝐾𝐾𝐾𝐾𝐾 = 90 + (1 − 𝑑𝑑) ∗ (𝑑𝑑 − 90) 𝐾𝐾𝐾𝐾 𝑑𝑑 > 90 Where:
• N = actual number of slots.
• a = (Automated manufacturing credits being applied) / (Maximum value of automated manufacturing credits available (15 for edges, 20 for surfaces)) F–1
F–2 AC 33.70-5 F.2.2 Specifically for edges.
• a = 0 for a manual process
• a = 5/15 = 1/3 for Semi-Automated (Manual Deburr) (table F-2)
• a = 8/15 for Semi-Automated (Manual Finish) (table F-2)
• a = 0.9 for Fully Automated F.2.3 Specifically for surfaces.
• a = 0 for a manual process
• a = 5/20 = 1/4 for Machine Condition (table F-1)
• a = 10/20 = 1/2 for Machine Condition & Fluid Monitoring (table F-1)
• a = 0.9 for Machine Condition and Fluid Monitoring Process Monitoring The relationship between Neff and N for this approach is shown in figure F-1. Note that Neff is always rounded up to the nearest integer.
Table F-1. Slot Surfaces – Process Controls, Control Definitions, and Credit Factor Process control Definition Credit Factor Used for:
Process Validation The most recent revi sion of the 5 Risk reduction and Control Plan DOT/FAA/TC-23/8 report (see paragraph 1.3.3) should be used to define an appropriate means of process validation and associated manufacturing control plan. A successful process validation and control plan means the manufacturing intent is met throughout the component production run.
Machine Condition, The machine condition is periodically 5 Number of Fluid & Fluid evaluated to validate it is capable of effective slots (see Condition, Tooling, delivering product meeting the Paragraph F.2) and Setup Validation manufacturing intent. The fluid is directed to the cutting zone during the machining operation. The fluid condition is maintained. Cutting tool design, material properties, fabrication (new & resharpened) and geometry are controlled. Cutting tool condition is Risk reduction
AC 33.70-5
Process control Definition Credit Factor Used for:
monitored to preclude excessively worn or broken cutting tools. A cutting trial is used to validate the setup produces acceptable component geometry and prescribed material removal.
Fluid Monitoring A real time, automated monitoring strategy which has the capability to ensure the fluid volume and flow to the cutting zone are maintained within validated process limit(s) and can interrupt the process when the established limit(s) are violated. This includes directional control of the fluid without human intervention and maintaining the fluid condition.
5 Number of effective slots (see Paragraph F.2) Risk reduction Process Monitoring A real time, automated monitoring strategy which has the capability to identify when the process varies outside the established validated process limit(s) and can interrupt the process when the established validated process limit(s) are violated. Feedback from the monitoring should be used to ensure the process remains within the acceptable validated range. Credit for process monitoring requires the use of fluid monitoring.
10 Number of effective slots (see Paragraph F.2) Risk reduction Geometry Inspection Axial Blade Slot Geometry inspection:
The credit applies only to the axial blade slot surface and not the edge.
2 Risk reduction F–3
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Process control Definition Credit Factor Used for:
Surface Condition Inspection Note: Only one of these credits may be claimed.
Non-Destructive Method: A quantitative non-destructive evaluation method(s) to ensure the surface condition (that is, metallography, finish and residual stress) of the axial slot or slot edge remains within the acceptable range to meet the manufacturing intent.
The credit applies only to the location where the inspection is applied.
5 Risk reduction Cutup: A representative periodic test sample cutup to ensure the surface metallography of the axial slot or slot edge remains within the acceptable range to meet the manufacturing intent.
2 Risk reduction Etch: Etchants able to detect distorted surface metallography when combined with an appropriate visual standard reference. Caution: An etched surface can reduce the fatigue capability of the material and should be evaluated as part of the approved lifing method of the component.
2 Risk reduction
Table F-2. Slot Edges – Process Controls, Control Definitions, and Credit Factor Process control Definition Credit Factor Used for:
Edge Processing Process Validation and Control plan Process validation of edge processing method(s) shall include upstream operations to ensure incoming edge conditions are not detrimental to the edge processing method(s). A successful process validation and control plan means the manufacturing intent is met throughout the component production run.
5 Risk reduction F–4
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Process control Definition Credit Factor Used for:
Edge Processing:
Semi-Automated Method of Manufacturing Manual Deburr and Pre-Form: A manual process is used to deburr and pre-form the edge geometry prior to final edge geometry generation and finishing by automated method(s). The automated method(s) at time of process validation should demonstrate the ability to remove any damage caused by the prior manual preparation method.
5 Number of effective slots (see Paragraph F.2) Risk reduction Note: Only one of these credits may be claimed.
Edge Processing: Manual Finishing: An automated 8 Manual Finishing deburring and edge break method(s) is (are) used to form the edge geometry and produce a nearly finished edge condition. Final finishing is completed by manual method(s) involving soft tooling such as paper or cloth, without the use of power tools.
Edge Processing:
Automated Method of Manufacturing Automated method(s) is (are) used for deburring, edge geometry generation, and finishing.
15 Geometry Inspection Edge Geometry inspection: The credit applies only to the edge and not the axial blade slot surface.
5 Risk reduction Edge Condition Non-Destructive Method: A 5 Risk reduction Inspection quantitative non-destructive Note: Only one of these credits may be claimed.
evaluation method(s) to ensure the surface condition (that is, metallography, finish and residual stress) of the axial slot or slot edge remains within the acceptable range to meet the manufacturing intent. The credit applies only to the location where the inspection is applied.
F–5
AC 33.70-5 Process control Definition Credit Used for:
Factor Cutup: A representative periodic test 2 Risk reduction sample cutup to ensure the surface metallography of the axial slot or slot edge remains within the acceptable range to meet the manufacturing intent.
Etch: Etchants able to detect distorted 2 Risk reduction surface metallography when combined with an appropriate visual standard reference. Caution: An etched surface can reduce the fatigue capability of the material and should be evaluated as part of the approved lifing method of the component.
F–6
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Figure F-1. Number of Effective Slots as a Function of Automated Manufacturing Credits for Axial Blade Slot (Edges and Surfaces) F.3 Rules for Applying Credits.
F.3.1 Rules.
• Process validation is considered mandatory on machining processes on all future products when using the methods provided by this AC. Use of process validation provides a 5X manufacturing credit as specified in tables F-1 and F-2.
• Use of manufacturing credits including process validation should be part of the certification data submittal.
• Process monitoring should be used in both roughing and finishing operations.
• Surface Credit for Fluid Monitoring cannot be claimed unless Machine Condition, Fluid & Fluid Condition, Tooling, and Setup Validation are also in use.
F–7
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• Surface Credit for Process Monitoring cannot be claimed unless Fluid Monitoring and Machine Condition, Fluid & Fluid Condition, Tooling, and Setup Validation are also in use.
F.3.2 Restrictions.
• Use of Surface Credits requires a Process Validation and Control Plan.
• Use of Edge Credits requires a Process Validation and Control Plan.
• Surface Credits cannot be used for edges.
• Edge Credits cannot be used for surfaces.
• Non-destructive inspection(s) at manufacture cannot be accounted for in the analysis to lower the POF value before application of manufacturing credits.
F.4 Credit Application Process.
1. Decide which controls are to be applied.
2. Sum the credit values for the combination of controls.
3. Calculate the number of effective slots.
4. Calculate the probability of fracture for the axial slot feature in the disk.
5. Divide the probability of fracture by the sum of the credit values.
6. This reduced probability of fracture should be compared to the DTR.
F.5 Slot Surface Credit Examples.
F.5.1 An axial slot feature with 100 slots, N:
a. Applicable Credits:
Process Validation and Control Plan 5 Total Credit 5 Number of Effective Slots: a = 0, Neff = 90 + (1-0)*(N-90) = N = 100 Initial design POF using Neff: 5.0E-4 events per service life POF with controls is now: 5.0E-4 / 5 = 1.0E-4 events per service life This is not adequate against Axial Blade Slot DTR.
b. Applicable Credits:
Process Validation and Control Plan 5 Machine Condition, Fluid & Fluid condition, Tooling and Setup validation 5 F–8
AC 33.70-5 Fluid Monitoring 5 Surface Condition inspection – nondestructive 5 Total credit 20 Number of Effective Slots: a = 10/20=0.5, Neff = 90 – (1-0.5)*(N-90) = 95 Initial design POF using Neff: 4.5E-4 events per service life POF with controls is now: 4.5E-4 / 20 = 2.25E-5 events per service life This is not adequate against Axial Blade Slot DTR
c. Applicable Credits:
Process Validation and Control Plan 5 Machine Condition, Fluid & Fluid condition, Tooling and Setup validation 5 Fluid Monitoring 5 Process Monitoring 10 Surface Condition inspection – nondestructive 5 Total credit 30 Number of Effective Slots: a = 0.9, Neff = 90 – (1-0.9)*(N-90) = 91 Initial design POF using Neff: 4.0E-4 events per service life POF with controls is now: 4.0E-4 / 30 = 1.3E-5 events per service life This is acceptable to Axial Blade Slot DTR.
F.6 Slot Edge Credit Examples.
F.6.1 An axial slot feature with 100 slots, N:
a. Applicable Credits:
Process Validation and Control Plan 5 Total Credit 5 Number of Effective Slots: a = 0, Neff = 90 + (1-0)*(N-90) = N = 100 Initial design POF using Neff: 2.5E-4 events per service life F–9