TASK 70-31-04-220-001
1 . General.
This standard practice defines the allowable acceptability limits for as-manufactured, open-face honeycomb only. After the open-faced honeycomb is brazed to the inseparable assembly, the limits in the Engine/Shop manual apply.
2 . Classification.
Subtask 70-31-04-220-051
A.This standard practice provides for the identification and requirements for the following classes.
CLASS A: Recommended for 0.125 in. (3.18 mm) honeycomb cell size.
CLASS B: Recommended for 0.062 in. (1.59 mm) honeycomb cell size.
CLASS C: Recommended for 0.031 in. (0.79 mm) honeycomb cell size.
3 . Honeycomb Definitions.
Subtask 70-31-04-220-052
A.The following definitions apply to this standard practice.
 
Nomenclature
Definition
 
Cell
A single enclosed opening in a honeycomb core formed by attaching rows of ribbons at positioned nodes.
 
Cell Height
The dimension from the cell bottom to the top of the cell (see Figure 3).
 
Cell Size
The inside distance between the two opposite and parallel sides of a cell. Nodes flats shall not be considered cell sides when measuring for cell size.
Cell size is measured with the raw honeycomb in a flat state before the formation into a ring (see Figure 2).
 
Honeycomb Core
A pattern of metal ribbons formed and joined that results in multiple open adjacent cells.
 
Honeycomb Core Width
A point-to-point dimension of the honeycomb core measured transverse to the ribbon direction (see Figure 3).
 
Honeycomb Core Splice
Any area in which two edges of honeycomb core are joined (see Figure 1).
 
Node
The ribbon surface that contacts an adjacent ribbon surface area.
 
Open Cell
A cell not completely enclosed resulting from a machining operation.
 
Partial Cell
A cell not completely enclosed by the honeycomb ribbon by its position at the outer edge of the formed structure.
 
Pin Holes
Holes less than 0.015 in. (0.38 mm) in diameter.
 
Ribbon
A single strip of metal that forms the cell wall. The joining of multiple ribbons in rows result in a honeycomb core.
 
Ribbon Connection
The connection (tack welding) of two formed ribbons at points of contact.
 
Ribbon Direction
The direction parallel to the ribbon node as assembled in the honeycomb core.
Figure 1   Honeycomb Core Splice
Figure 2   Honeycomb Cell
Figure 3   Honeycomb Core
4 . Honeycomb Cell Requirements.
Subtask 70-31-04-220-053
NOTE:
The following tolerances shall apply unless otherwise noted in the engine shop manual.
A.Honeycomb Cell Size.
NOTE:
Honeycomb cell size is the dimension as measured between the cell inside surfaces across the flats (see Figure 2).
(1)The average cell size shall be within plus or minus 6 percent (±6%) from nominal cell size as specified per table 1.
 
Average Cell Size Variation (±6% from nominal) - Table 1
 
Class-Cell Size (across flats)
Variation (across flats)
 
A 0.125 in. (3.175 mm)
0.118 to 0.133 in. - (2.997 to 3.378 mm)
 
B 0.062 in. (1.575 mm)
0.058 to 0.066 in. - (1.473 to 1.680 mm)
 
C 0.031 in. (0.787 mm)
0.029 to 0.033 in. - (0.736 to 0.838 mm)
(2)No single cell shall vary from the nominal cell size by more than plus or minus 12 percent (±12%) as specified per table 2.
 
Single Cell Size Variation (±12% from nominal) - Table 2
 
Class-Cell Size (across flats)
Variation (across flats)
 
A 0.125 in. (3.175 mm)
0.110 to 0.140 in. - (2.794 to 3.556 mm)
 
B 0.062 in. (1.575 mm)
0.055 to 0.069 in. - (1.397 to 1.752 mm)
 
C 0.031 in. (0.787 mm)
0.027 to 0.035 in. - (0.686 to 0.889 mm)
B.Ribbon Connections.
(1)The following limits shall not be exceeded when ribbons are tack welded at the nodes.
(a)Each 0.25 in. (6.35 mm) of cell height in one node shall contain not more than two tack welds.
(b)Pin holes (holes less than 0.015 in. (0.38 mm) in diameter) through nuggets in more than 10 percent of the nodes. Any hole larger than 0.015 in. (0.38 mm) in diameter through any one nugget is not allowed.
(c)Inspect the ribbon ends for mismatch at the core splice. A maximum mismatch of 0.003 in. (0.076 mm) is allowed (see Figure 1).
C.Open Cells for Class A, B, and C.
(1)Open cells at either edge of the honeycomb core resulting from machining or other processing shall not be allowed.
(2)Open cells at either end of the honeycomb core segment is allowed (see Figure 3).
D.Finished Dimensions.
(1)Finished dimensions of open faced honeycomb shall apply to the total core configuration. Width measurements shall be taken at the extreme edges of the honeycomb core.
E.Honeycomb Core Splices.
(1)Core splices shall conform to the following:
(a)Splices shall be joined on a diagonal.
(b)Splices shall not be closer than 2 inches (51 mm) to another splice (no point in the diagonal line).
(c)Specific splice geometry/configuration shall be defined in the shop manual.
F.Non-Conventional Machining.
(1)Non-conventional machining of the honeycomb core is permitted if the surfaces meet the requirements of Class H in TASK 70-31-05-220-001, Engine Part Surface Integrity Acceptability Limits for Nontraditional Machined Surfaces.