(a) Furnace pressure and leak rate prior to power on.
(b) Furnace pressure, voltage, and curr ent profile during start up and transient to steady state conditions.
(c) Furnace pressure, current, voltage melt rate, melt rate excursions, and the frequency and duration of transient over voltage pulses or transient arc short circuits (pulse rate/drip short) during the quasi-steady state or main segment of the melting program.
(d) Electrode weight or length at the start of the hot top sequence.
(e) Furnace pressure, voltage and the current profile during the transient from quasi-steady state to the end of the melt.
(f) Inert gas (i.e. helium) cooling gas pressure and flow.
(g) Water flow rate and inlet and exit temperatures.
(h) Drip short control parameters.
(11) Ingot cooling. The VAR source must develop procedures to uniformly and consistently cool the solidifying ingot. Limits should be established for inlet and outlet crucible water temperature, water flow rate, inert gas type, and pressure or flow rate.
9. Billet/Bar Conversion, Disk Forgin g, and Nondestructive Testing (NDT).
a. Control of Bill et/Bar Manufacture.
(1) Conversion Process. Specific detaile d procedures must exist for the conversion of ingot to billet and bar products. These must include, but are not necessarily limited to:
(a) Billet/Bar Conversion. Perfor m ingot to billet/bar conversion using controlled, consistent, and detailed procedures.
1 Ingot Conditioning. Establish documented procedures for conditioning the ingot surface prior to heating for forging.
2 Forge Parameter Control. Develop and use documented procedures to control ingot and billet/bar products. These procedures must include, but are not limited to:
Homogenization time and temperature and cooling procedure for preforge soaking Forge furnace temperatures/atmospheres Soak times Amount of draft Reduction schedules/sequences Quench time, media, and methods 13
Die type Single or double end procedures Off-die procedures
3 Forge Practice. Develop forge practices which preclude formation of strain induced porosity (SIP) or clean voids.
4 Records. Maintain reduction sizes, sequences, and temperature records.
(b) Traceability. Billet must be traceable to location and orientation in the VAR ingot. Bar must be traceable to the final VAR ingot and at least to the top, or bottom half of the cropped ingot, and to a section of the original ingot not to exceed 3000 pounds.
(2) Cropping. Any ingot conversion must incorporate a minimum crop of the ingot extremities. Limits for crop lengths should be established to account for the bottom charge and hot topping procedures used for the final melting.
b. Control of Disk/Component Manufacture.
(1) Forging/Heat Treatment Process. Specific detailed procedures must exist for the production of finished rotating components from billet product. These should include but are not necessarily limited to:
(a) Forging Controls. Controlled, cons istent, and detailed procedures must be established for the control of the forging process. These must include but are not limited to:
Furnace loading diagram for each operation;
Strain profile for each part made; strain may be defined through controlled ram speeds and load/stroke parameters;
Standard die designation for each forging operation;
Forging mult weight and diameter; and To die and off-die transfer times from furnace and to cooling station respectively.
(b) Thermal Controls. Documented procedures must be es tablished for control of forge/soaking furnace temperature and times.
(c) Heat Treatment Controls. Docume nted procedures must be established for the control of heat treatment furnaces, atmospheres, times and temperatures.
(d) Quenching. Quench practice and coo ling rates must be controlled to ensure freedom from quench related cracking.
(e) Traceability. Traceability of forgi ngs and bar products to billet location must be maintained.
(f) Records. Reduction sizes, sequences, and temperature records must be maintained.
c. Nondestructive Testing and Criteria.
(1) To obtain further confidence that nick el-base alloy rotating parts are free from potentially detrimental anomalies, NDT must be performed at appropriate stages throughout billet/bar and component manufacture. These inspections must be chosen based on melting, billet conversion, heat treatment, and forging processes used and part requirements.
Controlled procedures must define the inspection processes and acceptance criteria. Consider the following NDT inspections:
(a) Billet/Bar.
1 Immersion ultrasonic testing.
2 Macroetch inspection of billet/bar ends and slices adjacent to ultrasonic crops.
(b) Forging.
1 Immersion ultrasonic testing.
2 Macroetch of sonic or intermediate machined forgings.
(c) Finish Machined Component.
1 Fluorescent Penetrant Inspection.
(2) Ultrasonic Testing (UT) Criteria. The criteria for UT of billet/bar and forgings should consider the operational and control requirements that materials/ultrasonic inspection systems must achieve. The criteria should include but are not necessarily limited to:
(a) System Variability. Materials sy stems from billet/bar through forging, heat treatment, and machining should be engineered so that materials-generated ultrasonic noise or boundary (surface finish) ultrasound transmission characteristics do not interfere with detectability of potentially detrimental anomalies. Conduct periodic system reliability/repeatability studies to ensure instrumentation and standards are functioning properly and within calibration.
(b) Test Blocks. Test blocks must be manufactured using material with fabrication and ultrasonic characteristics similar to those of the billet or forging being tested.
Document calibration procedures adequately to verify the proper operation of the ultrasonic inspection system.
(3) Acceptance Limit. When using scanning systems, set the acceptance limit appropriately (at least 3 db) above the noise level to minimize false calls while maintaining detection sensitivity consistent with design requirements.
(4) Records. Retain electronic data (p referred) or equivalent strip charts according to the engine manufacturer's FAA-approved records retention schedule.
d. Actions Following Indication Detection.
(1) Ultrasonic Indication Characteriza tion of unacceptable indications should be conducted on billet/bar, forgings or finished parts, as appropriate. Report unacceptable indications found in the forging and finished parts to the JETQC (Jet Engine Titanium Committee) in accordance with JETQC practices. At a minimum, report the following information for all indications:
(a) Defect type;
(b) Cross-section defect size;
(c) Cross-section void/crack size, if any;
(d) Ultrasonic inspection calibration and test procedures;
(e) Ultrasonic amplitude;
(f) Ultrasonic signal-to-noise ratio (SNR), if available; and
(g) Indication location in the billet/forging.
(2) For metallic inclusions, report the following additional information:
(a) Microhardness; and
(b) Scanning electron microscope a nd/or microprobe evaluation: nature of constituents, fractography of void/crack.
(3) Indications Detected In Billet/Bar.
(a) Freckle after all Crops. Review any heat which is shown by billet/bar inspection and indication characterization to contain a freckle. Consider rejecting any heat containing a freckle for a critical rotating part application unless a special cause can be determined which would allow only partial rejection of the heat.
(b) Other Anomalies. Evaluate use of heats with any other anomalies on an individual basis.
(4) Indications Detected in Forgings and Finished Parts. The Production Approval Holder should take appropriate action upon finding and characterizing unacceptable indications in forgings and finished parts. Action regarding suspect material should be based on historical experience with the process and may include, but is not necessarily limited to, over-inspections of parts from heats, lots, batches, etc., that contain the forging or part with the anomaly.
(5) Associated Heats. Associated heat s must be identified and investigated for potentially similar defects as appropriate.
Peter A. White Acting Manager, Engine and Propeller Directorate