1、 AEROSPACE MATERIAL SPECIFICATION Grinding of HVOF Sprayed Tungsten Carbide Coatings Applied to High Strength Steels AMS 24491. SCOPE: 1.1 Purpose: This specification covers engineering requirements for the grinding of tungsten carbide High Velocity Oxygen/Fuel (HVOF) thermal spray coatings applied
2、to high strength steels (220 ksi and above). 1.2 Application: This process has been used typically to grind tungsten carbide HVOF coatings applied in accordance with AMS 2447 or AMS 2448 to high strength steels for applications requiring wear, heat, and corrosion resistance or dimensional restoratio
3、n, such as aircraft landing gear components. However, usage is not limited to such applications. This process specification does not cover superfinishing of HVOF applied coatings. 1.3 Safety - Hazardous Materials: While the materials, methods, applications, and processes described or referenced in t
4、his specification may involve the use of hazardous materials, this specification does not address the hazards which may be involved in such use. It is the sole responsibility of the user to ensure familiarity with the safe and proper use of any hazardous materials and to take necessary precautionary
5、 measures to ensure the health and safety of all personnel involved. 2. APPLICABLE DOCUMENTS: The issue of the following documents in effect on the date of the purchase order forms a part of this specification to the extent specified herein. The supplier may work to a subsequent revision of a docume
6、nt unless a specific document issue is specified. When the referenced document has been cancelled and no superseding document has been specified, the last published issue of that document shall apply. Reaffirmed 2010-03 Issued 2004-07 SAE Technical Standards Board Rules provide that: “This report is
7、 published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each tec
8、hnical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2010 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in a
9、ny form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS
10、: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AMS2449 SAE - 2 - AMS 2449 AMS 24492.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001 or www.sae.org. AMS 2447 Coating,
11、 Thermal Spray High Velocity Oxygen/Fuel Process AMS 2448 Coating, Thermal Spray High Velocity Oxygen/Fuel Process 2.2 ASTM Publications: Available from ASTM, 100 Barr Harbor Drive, PO Box C700, West Conshocken, PA 19428-2959 or www.astm.org. ASTM E 1417 Fluorescent Penetrant Inspection Methods 2.3
12、ANSI Publications: Available from ANSI, 25 West 43rdStreet, New York, NY 10036 or www.ansi.org. ANSI B7.1 Safety Requirements for the Use, Care and Protection of Abrasive Wheels ANSI B74.13 Markings for Identifying Grinding Wheels and Other Bonded Abrasives 3. TECHNICAL REQUIREMENTS: 3.1 Parts to be
13、 ground shall have been coated with tungsten carbide coating in accordance with AMS 2447 or AMS 2448. 3.2 Specific surface finish requirements shall be specified by the cognizant engineering authority. Unless otherwise specified, the surface finish shall be 8 Ra maximum. Note: Superfinishing of surf
14、aces is generally indicated by measured surface finishes less than 8 Ra. Grit sizes used in the ranges above are not capable of producing super finished surfaces. Superfinished surfaces typically have higher bearing area ratios than as-ground surfaces. Ra = Arithmetic Average (Micro-inch) surface fi
15、nish. 3.3 Equipment: 3.3.1 Grinding Equipment: Grinding equipment shall be capable of maintaining grinding wheel speed, workpiece speed, traverse or cross feed speed, and (down feed) infeed in increments necessary to avoid surface degradation of the part. Provisions shall be made to supply a constan
16、t application of cutting fluid (coolant) to the working surface of the wheel at the grinding zone interface. SAE - 3 - AMS 2449 AMS 24493.4 Materials: 3.4.1 Grinding Wheels: Diamond abrasive resin bonded grinding wheels shall be used. Grinding wheels shall be labeled with the complete grinding wheel
17、 specification including abrasive type, grit size, grade, bond type and maximum operating speed in accordance with ANSI B74.13. Care and protection of grinding wheels, including proper storage, handling and mounting, shall be in accordance with ANSI B7.1. 3.4.1.1 Each of the following parameters sha
18、ll be met when selecting a grinding wheel. Abrasive - Diamond. Bond - Resin Grit or Grain Size - 100 to 400 grit Hardness or Grade of resin bonded portion of wheel - H, L, M, N, P, or R Concentration - 75 to 125 3.4.2 Cutting Fluids (Coolants): A suitable cutting fluid shall be used which does not h
19、ave an adverse effect on the part being ground. Recirculating cutting fluids shall be continuously filtered to minimize recycling grinding residue and swarf. A coolant nozzle sufficiently wide to flood the entire width of the grinding wheel shall be used. For proper application of the cutting fluid,
20、 the cutting fluid nozzle should be designed to deliver cutting fluid at a speed equal to or slightly faster than the peripheral grinding wheel speed. (See Appendix A). 3.5 Cleaning: Protective coatings and other foreign materials shall be removed from parts prior to grinding to preclude contaminati
21、on of coolant and wheels. Coolants and grinding residuals that have a deleterious effect on the part shall be removed after grinding. Cleaning materials shall not corrode or otherwise degrade the surfaces of the part. 3.6 Grinding Process Control: The grinding process shall be performed in accordanc
22、e with 3.7 to result in metallurgically sound parts. All speeds, feeds, and stock removal parameters are actual and not necessarily machine or indicator readings. Prior to grinding, clean all surfaces to be ground as stated in 3.5. 3.6.1 Balance the grinding wheel assembly at the time the wheel is m
23、ounted. If the grinding wheel remains on the machine arbor it will not need to be balanced again. If the grinding wheel is removed from the machine/arbor it should be re-balanced at the next mounting. True the wheel face so that it is geometrically correct for the application and runs concentric wit
24、h the centerline of the arbor assembly (see Appendix B). Dress the grinding wheel frequently during use to keep the wheel open with sharp grit exposed to freely cut the work material. 3.6.2 Flood the entire width of the grinding wheel at the wheel-work interface with a filtered continuous flow of cu
25、tting fluid. SAE - 4 - AMS 2449 AMS 24493.7 Grinding Parameters: 3.7.1 Use a peripheral grinding wheel speed of 4800 to 6500 surface feet per minute (SFPM). 3.7.2 Use cross feeds/traverse rate and infeeds as follows: 3.7.2.1 Cylindrical and Internal Grinding: 3.7.2.1.1 Roughing Infeeds: The roughing
26、 infeed (on the diameter) shall not exceed a maximum of 0.002 inch for 100 or 120 grit, 0.0015 inch for 150 grit, 0.001 inch for 180 grit, 0.0008 inch for 220 grit, 0.0006 inch for 320 grit, or 0.0004 inch for 400 grit for each pass. Incremental infeed shall be done at each end of the traverse or cr
27、ossfeed to maintain wheel face flatness. Use a roughing cross feed or traverse rate of 1/4 to 1/8 wheel width per workpiece revolution. 3.7.2.1.2 Finishing Infeeds: A minimum of 0.002 inch stock removal per side (0.004 inch on diameter) is required for finish grinding. The finishing infeeds (on the
28、diameter) shall not exceed a maximum of 0.0005 inch for 100 or 120 grit, 0.0004 inch for 150 grit, 0.0003 inch for 180 grit, 0.0002 inch for 220 grit, or 0.0001 inch for 320 or 400 grit for each pass. Incremental infeed shall be done at each end of the traverse or crossfeed to maintain wheel face fl
29、atness. Use a finishing cross feed or traverse rate of 1/8 to 1/12 wheel width per workpiece revolution. 3.7.2.2 Surface Grinding: 3.7.2.2.1 Roughing Infeeds: The roughing infeed (depth of cut) shall not exceed a maximum of 0.001 inch for 100 or 120 grit, 0.0008 inch for 150 grit, 0.0005 inch for 18
30、0 grit, 0.0004 inch for 220 grit, 0.0003 inch for 320 grit, or 0.0002 inch for 400 grit for each pass. The cross feeds shall not exceed 0.080 inch per pass. Table speeds shall be 50 to 75 feet per minute. 3.7.2.2.2 Finishing Infeeds: A minimum of 0.002 inch stock removal is required for finish grind
31、ing. The finishing infeeds (depth of cut) shall not exceed a maximum of 0.0005 inch for 100 or 120 grit, 0.0004 inch for 150 grit, 0.0003 inch for 180 grit, 0.0002 inch for 220 grit, or 0.0001 inch for 320 or 400 grit. The cross feeds shall not exceed 0.080 inch per pass. Table speeds shall be 50 to
32、 75 feet per minute. 3.7.3 When grinding OD surfaces, the work should have a speed of 60 to 100 surface feet per minute. When grinding ID surfaces, the work should have a speed of 75 to 200 surface feet per minute. 3.7.4 Table 1 contains general guidelines for surface finish generation for the grit
33、sizes indicated above. Traverse grinding with spark-out or dead passes (i.e. passes with no infeed) may produce finer finishes than shown here. SAE - 5 - AMS 2449 AMS 2449Table 1. Surface Finish vs. Grit Size Grit Size Roughing Mode Finishing Mode 100-120 32-36 Ra 18-32 Ra 150 22-26 Ra 12-20 Ra 180
34、18-22 Ra 8-14 Ra 220 12-16 Ra 6-12 Ra 320-400 8-11 Ra 4-10 Ra 3.8 Inspection Requirements: All ground surfaces shall be visually inspected without magnification for evidence of overheating (discoloration), cracks, flaking or peeling. Ground surfaces shall be checked for surface finish. 3.9 Fluoresce
35、nt Penetrant Inspection: All ground surfaces shall be inspected by fluorescent penetrant inspection in accordance with ASTM E 1417 or approved alternate procedure. 4. QUALITY ASSURANCE: 4.1 Monitoring of the process and examination of the finished items shall be in compliance with local quality assu
36、rance provisions which ensure that the requirements of this specification are met. 4.2 The coated surface shall be free from heat checks, pull-outs, cracks, and separation from the base metal. Penetrant inspection, in accordance with ASTM E 1417, Type I, Level 2, or higher, shall be used to check fo
37、r cracking caused by, or revealed by, grinding; and separation of the thermal spray coating from the base metal along the periphery of the coating. Examine for heat checks and pull-outs visually using up to 40X magnification. Etching prior to penetrant inspection is not required. 4.3 The process des
38、cription and control factors shall be documented on a Grinding Process Control sheet in accordance with Figure 1 prior to commencement of production grinding. 4.4 The processor of parts ground in accordance with this specification shall make no significant change to the process description, or to th
39、e materials, processes, or controls referenced in the process description (see Figure 1) unless the change is approved by the cognizant engineering organization. A significant change is one which deviates more than plus or minus ten percent of the approved baseline. 4.5 If the results of any inspect
40、ion fail to meet the specified requirements, the process is nonconforming. No additional parts shall be processed until the process is corrected and new specimens are coated and ground. Results of all tests shall be recorded and when requested, reported. Purchaser shall be notified of all parts grou
41、nd since the last successful inspection. SAE - 6 - AMS 2449 AMS 24495. PREPARATION FOR DELIVERY: 5.1 Finish ground parts shall be handled and preserved and packaged to ensure that the required physical characteristics and properties of the ground coating are preserved. 5.2 Packages of parts shall be
42、 prepared for shipment in accordance with commercial practice and in compliance with applicable rules and regulations pertaining to the handling, packaging, and transportation of the parts to ensure carrier acceptance and safe delivery. 6. ACKNOWLEDGMENT: Processor shall mention this specification n
43、umber and its revision letter in all quotations and when acknowledging purchase orders. 7. REJECTIONS: Parts, which have non-compliant surface finish coating that does not conform to this specification, or to modifications authorized by purchaser, will be subject to rejection. 8. NOTES: 8.1 Dimensio
44、ns are in inches. 8.2 Terms used in AMS are clarified in ARP1917 and as follows: 8.2.1 Balance (Dynamic): Dynamic balance is the balancing of the complete rotating assembly; grinding wheel, mounting arbor, and the machine spindle. Depending on the balancing machine, the balance condition is measured
45、 and corrected at wheel speed. 8.2.2 Balance (Static): Static balance is the balance of the grinding wheel mounted on an arbor, typically balanced on a pair of knife-edges. 8.2.3 Bearing Ratio: The ratio of material to air in a horizontal slice through the surface profile expressed as a percentage.
46、The zero percent or reference line for the bearing ratio is located at the top of the highest peak within the evaluated profile. The bearing ratio is measured at different depths through the profile and varies with slice depth. SAE - 7 - AMS 2449 AMS 24498.2.4 Concentration: The amount of superabras
47、ive material contained in a unit volume of the grinding wheel. The measurement is based on the number of carats of superabrasive material per unit volume. Typical concentration numbers are in the range of 30 to 175. A concentration of 100 does not mean 100 percent and therefore is not the maximum co
48、ncentration. A concentration of 100 means that there are 4.4 carats of abrasive per cm3(or 72 carats/cu. in. or 25 volume percent). The abrasive concentration of the selected grinding wheel, for grinding HVOF applied tungsten carbide coatings, is based upon the area of contact between the wheel and
49、workpiece. A large contact area may dictate a low concentration and a small area of contact may dictate a higher concentration so the wheel can hold form and resist premature wear. Since OD grinding generally has smaller contact areas than ID grinding, the concentration of the abrasive in the grinding wheel should generally be higher for OD grinding and lower for most ID applications. 8.2.5 Coolant: Coolant is the misnomer for cutting fluid. The cutting fluid not only cools; it also lubricates and washes away chips and debris. The better term is cutting fluid. 8.2.6 Cutting F
