Test_Spur_Gears_SOW.pdf

Solicitation

XXXXXXXXXX

Test Spur Gears

Specification / SOW

1. Quantity of parts and Delivery Date – The vendor shall deliver 64 test gears meeting this specification and meeting the requirements of NASA GRC drawing CD851944–5. The 64 gears delivered will NOT all have the same tooth thickness.

The tooth thicknesses, and quantity of gears with each tooth thickness to be delivered, are listed in paragraph 3.5. The gears shall be delivered on or before September 12,

2. Material

2.1. The test gears shall be made from steel alloy meeting Aerospace Material

Specification (AMS) 6308E

2.2. The vendor shall make the gears using forged bars provided by NASA. NASA has acquired two forged bars of material. The size of each bar is 4.25 inches diameter (as forged - unfinished) and 30 inches long. The two bars will be delivered by NASA to the vendor for purposes of making the gears.

2.3. The bars to be delivered by NASA to the vendor for making gears have been certified to meet AMS6308E material specification. Copies of certification data are provided in Appendix A.

2.4. Any excess bar stock material not needed by the vendor for gear manufacture shall be returned to NASA. Excess bar stock, if any, shall be delivered together with the test gears.

3. Gear geometry

3.1. The gears shall be made per NASA drawing 851944–5 for “Pitting Test Gear –

High Torque”. The following numbered sections provide the details of the required part geometry.

3.2. The gears shall have flanks and roots ground. There shall be a smooth transition of profile to root radius. A 0.005 inch max. undercut to 0.001 inch max. step is permissible at the blend of profile and root radius, undercut or step must be below the start of active profile (true involute form) that is to start at or below

10.2 degree of roll. Radius at step must comply with minimum fillet radius.

3.3. The gear tooth profile shall include involute modification. The nominal desired profile shall be as defined in chart 3.3 below. The final involute profile shall be a smooth curve. After final grinding the tooth profile shall meet the nominal desired profile to within tolerance for AGMA class 13, or better, as defined by AGMA 2002-A88, “Gear Classification and Inspection Handbook”

Chart 3.3 – Involute profile modification data and plot

Nominal profile modification to be 0.0025inch magnitude at tip, parabolic shaped profile modification starting at 21.0 degree roll ending at 31.202 degree roll

3.4. The gear tooth lead profile shall include a circular crown lead profile with nominal drop of 0.0005 inch. The nominal desired lead profile shall be as defined in chart 3.4 below. After final grinding the tooth profile shall meet the nominal desired profile to within tolerance for AGMA class 13, or better, as defined by AGMA 2002-A88, “Gear Classification and Inspection Handbook”.

The lead profile shall be free of lead hollow to within 0.0001 inch max. local irregularity.

Chart 3.4 – Lead crown plot

3.5. The gears shall be manufactured with 3 tooth thicknesses as defined by the measurement over pin dimensions as defined in chart 3.5. Also in the chart, for

SAP (deg) 10.506

LPSTC (deg) 18.345

Oper Pitch (deg) 20.854

Theo Pitch (deg) 20.854

HPSTC (deg) 23.363

Tip (deg) 31.202 roll angle (degree roll)

10 12 14 16 18 20 22 24 26 28 30 32 m o d if ic a ti o n (i n c h

-0.0030

-0.0025

-0.0020

-0.0015

-0.0010

-0.0005

0.0000 reference, are the chordal tooth thickness and backlash when gears of like thickness are mated together. The contractor shall deliver the required number of gears for each design “A”, “B”, and “C” corresponding to the 3 required tooth thickness values as specified in Chart 3.5. A pin diameter of 0.216” shall be used for measurement over pins.

Chart 3.5 – Specifications for gear tooth thickness as defined by measurement over pins (using 0.216 inch diameter pin).

Design

Quantity of Gears to

Be

Delivered

Measurement Over Pins

Min. / Max. ;

inch

Chordal

Tooth

Thickness;

inch

(Ref.)

Backlash;

inch

(Ref.)

A 10 3.7926 / 3.7973 0.19375 0.005

B 44 3.7878 / 3.7926 0.19175 0.009

C 10 3.7829 / 3.7878 0.18975 0.013

3.6. After final grinding, the gears shall meet AGMA Class 13 or better as defined by

AGMA 2002-A88, “Gear Classification and Inspection Handbook” for index and tooth spacing errors.

3.7. The surface roughness on the active profiles of the ground gears shall be 14 microinch roughness R.M.S maximum.

3.8. The gear teeth shall have tip and edge rounds per the drawing. Note that the tip and edge rounding are required even though but such features are not depicted in the involute modification and lead crown plots, chart 3.3 and chart 3.4.

3.9. Keyway detail. The keyway corner radius shall be 0.012 – 0.025 inch.

4. Heat treatment, hardness, and case requirements

4.1. The gears shall be case-carburized and heat treated to aerospace quality. Table

4.1 below provides a heat treatment cycle that is proposed. The process defined in Table 4.1 is based on NASA’s experience with this gear geometry and AMS material specification. The manufacturer is responsible to meet final requirements for surface hardness, case depth, case properties, and core properties. NASA recognizes that the manufacturer might desire to deviate from the process based on manufacturing experience. The manufacturer may deviate from the guideline only with approval from NASA.

TABLE 4.1 —Required heat treatment process for AMS 6308E NASA test gears. A deviation from this heat treatment process requires approval from

NASA. Application and removal of copper plating are also required processes but are not included in the table.

Table 4.1 – Heat Treatment Process for AMS6308E test gears

Pre-oxidize 1500 °F for 30 minutes air atmosphere

Gas Carburize 1700 °F target, [1625 – 1725] for 5 hours

Temper within 5 hours

1200-1315 °F for 4 hours minimum

Austentize / Harden 1700 °F target, [1650 – 1715 °F] for 30 minutes

Oil quench within 30 seconds

75-140 °F

Subzero cool treatment within 30 minutes, -110 °F or less, for 3 hours minimum

Double temper 450°F, 2 + 2 hours

Final grind

Stress relief after final grind

450°F, 2 hours

4.2. The drawing includes a note for masking of surfaces from carburization. All surfaces except the gear teeth profiles and roots are to be masked. The masking shall be by copper plating. Stop off paint may be used to supplement copper plating in areas where adequacy of plating coverage is difficult, for example internal diameter surfaces. Stop off paint is not to be used as a substitute for copper plating but only as a supplement if judged as needed.

4.3. Surface hardness. Parts shall be checked for hardness after the quenching operation and before the subzero cool operation. Parts shall have a minimum hardness of Rc 58 and maximum hardness of Rc 64, parts not meeting this requirement shall be rejected as unacceptable.

4.4. Core Hardness. The core hardness shall be Rc 30-45, parts not meeting this requirement shall be rejected as unacceptable.

4.5. Case depth. The gears shall have a finished case depth of 0.040 inch minimum to

0.056 inch maximum. The case depth shall be verified by witness coupons of appropriate geometry or by using sectors of gears. If witness coupons are used the vendor must account for the grinding stock. The case depth requirement is for the mid-height of the gear tooth, and it represents the depth to an equivalent hardness of HRC 50 as obtained by Vickers hardness check. Results of quality checks for case depth requirements (including consideration of final grinding stock) shall be provided.

4.6. Recarburizing: In the event that carburized parts do not meet the case depth requirements, a maximum one (1) recarburizing cycle will be permitted.

4.7. Reheat treatment: In the event that carburized and/ or recarburized parts do not meet the hardness requirements, a maximum one (1) reheat treat cycle will be permitted.

4.8. Case microstructure - Witness coupons of appropriate geometry or sectors of gears shall be inspected to verify aircraft quality microstructure was produced by the heat treatment. The test samples shall be etched and examined for free carbides and retained austenite. Parts with heavy continuous carbide networks are not acceptable. Visual retained austenite (maximum amount) uniformly distributed is 10%, localized areas with a higher amount is acceptable so long as the overall average is less than 10%. The manufacturer shall provide results of the quality check procedures.

4.9. Gears shall be free of grinding burns per aircraft standards. All delivered gears shall be checked for grinding burns by nital etch inspection.

4.10. The gears shall be free of cracks. All delivered gears shall be checked for cracks using magnetic particle inspection. Indications on gear teeth shall meet the acceptance criteria of ANSI/AGMA 2001-C95 for grade 3 carburized gears.

5. Parts marking. Gears shall be provided serial numbers via permanent marking. The serial numbers shall follow the format “16-P53-(A,B or C)-XXX”. The “A”, “B”, or

“C” marking will designate the tooth thickness as defined in paragraph 3.5. The

“XXX’ shall be a unique 3-digit numeral. The serial number and any other permanent marking shall be on the side of the gear within the region falling between diameters 2.00 inch to 2.80 inch.

6. Protection from corrosion and handling damage. After final grind the gears shall be protected using good industry practice to maintain the gears free of dings, scratches, and corrosion. Gears delivered with corrosion or handling damage will not be accepted.

7. Documentation of compliance. Documents showing compliance with this specification shall be delivered with the gears as follows.

7.1. The vendor shall supply legible copies of quality control checks and measurements made to make certain the delivered gears meet the part geometry specified on the drawing.

7.2. The vendor shall supply a legible copy of certification and quality controls of the heat treatment process. Actual process steps, time, and temperatures used shall be documented. Copies of certification of case depth and surface hardness requirements shall be provided

7.3. The vendor shall supply legible copies of results of nital etch and magnetic particle inspection checks.

7.4. The vendor shall supply legible copies of results of check for surface roughness requirements for the active gear profile and the gear serial number shall be noted on the roughness inspection data. Surface roughness checks shall be provided for

2 gears each of the differing tooth thicknesses, that, is for 2 each of designs “A”, “B”, and “C” as defined in paragraph 3.5.

7.5. The vendor shall supply legible copies of gear tooth involute, lead, and tooth spacing inspections for each gear delivered. The inspection documents shall be labeled with the individual serial number as was provided on the gear in accordance with Section 5 above. The gear inspection chart shall indicate the

AGMA quality number actually achieved as defined per ANSI/AGMA 2001-

C95.

7.6. The inspections for grinding burns by nital etch and for crack by magnetic particle inspections shall be for 100 percent of the delivered gears.

Appendix A – Certifications data from the material to be provided by NASA for making gears under this solicitation