1、 WORLDWIDE FASTENER STANDARD WD 956 Date: 2010 07 20 Printed copies are uncontrolled Copyright 2010 Ford Global Technologies, Inc. Page 1 of 4 Mechanical and Performance Requirements of Through Hardened and Carbon Restored Thread Rolling Screws for Use in Aluminum Applications. 1. SCOPE This standar
2、d specifies the requirements for high performance through hardened and carbon restored TAPTITE 2000“SP” thread rolling screws which have performance capabilities beyond those normally expected of other types of tapping screws. The standard relates to screws with Radius Profile screw thread form, ran
3、ging from sizes M3 to M14 and for use in applications where fastener toughness is a prime consideration. As partial or complete decarburization of the thread of thread forming screws seriously impairs the thread rolling properties of the screw, this condition is not permitted. Decarburization as per
4、mitted by ISO 898/1 is replaced in this standard by a requirement for carbon restoration as detailed in Clause 3.2. Fasteners produced to this standard possess mechanical properties in line with ISO 898/1 property class 8.8 except surface hardness. Clause 3.4 defines thread forming capability in alu
5、minum up to a hardness of 150 HV and thickness equal to 2x the nominal screw diameter. The parameters of material hardness and thread engagement may be varied by analysis of joint requirements and it is therefore recommended that the specific application be investigated to determine joint criteria.
6、1.1 REFERENCES ISO 262 ISO General Purpose Metric Screw Threads - Selected Sizes for Screws, Bolts and Nuts. ISO 898/1 Mechanical Properties of Fasteners - Part 1: Bolts, Screws and Studs. ISO 6507-1 Metallic Materials Vickers Hardness, Part 1: Test Method ISO 6157-3 Fasteners-Surface Discontinuitie
7、s SAE/USCAR-8 Grain Flow Pattern for Bolts and Screws WSS-M99A3-A Embrittlement Avoidance 2. MATERIALS Screws shall be made from cold heading quality fully killed, fine grain, spherodized annealed steel wire. Material shall meet the chemical composition limits for PC8.8 per ISO 898 Part 1. Table 1.
8、Marking Symbol Property Class and Marking Symbol ISO 898/1 Equivalent Property Class 8N 8.8 WORLDWIDE FASTENER STANDARD WD 956 Date: 2010 07 20 Printed copies are uncontrolled Copyright 2010 Ford Global Technologies, Inc. Page 2 of 4 3. MECHANICAL PROPERTIES ISO898/1 Mechanical properties apply exce
9、pt as detailed in Table 2. Table 2. Mechanical Properties Criteria Clause Test Reference Wedge Tensile Strength 3.1 ISO 898/1 Decarburization 3.2 4.1 Surface Hardness 3.3 and Table 3. 4.2 Thread Forming Capability 3.4 4.3 3.1 WEDGE TENSILE Finished screws shall be hardened and tempered to achieve th
10、e minimum tensile strength for the applicable equivalent property class detailed in ISO 898/1 (see Table 1). 3.2 DECARBURIZATION During the hardening process, the carbon potential of the atmosphere shall be maintained at a level slightly in excess of the carbon content of the screws being processed.
11、 This process of carbon restoration is designed to eliminate partial and total decarburization of the screw thread form. Partial or complete decarburization of the screw thread form would seriously impair the thread rolling properties of the screw. Carbon enrichment up to 0.1mm (.004”) maximum from
12、the surface of the screw is permitted as a result of the carbon restoration process when tested in accordance with Clause 4.1. 3.3 SURFACE HARDNESS The minimum tempering temperatures specified in paragraph 2 shall apply. When tested in accordance with Clause 4.2, the hardness levels as given in Tabl
13、e 3 shall be achieved. Table 3. Surface Hardness Property Class Surface Hardness (HV) 8N 280-370 1)1)Surface hardness shall not be more than 30 Vickers points above the measured core hardness on the product when the readings of both surface and core are carried out at HV 0.3. 3.4 THREAD FORMING CAPA
14、BILITY The screw shall, without permanent deformation of its own thread when viewed at 10x magnification, form a mating thread in an aluminum test plate in accordance with Clause 4.3. The thread formed by the screw in the test plate shall be capable of accepting a fastener threaded in accordance wit
15、h ISO 262 tolerance class 6g. 3.5 EMBRITTLEMENT All through hardened and carbon restored thread rolling screws shall meet the requirements of WSS-M99A3-A. WORLDWIDE FASTENER STANDARD WD 956 Date: 2010 07 20 Printed copies are uncontrolled Copyright 2010 Ford Global Technologies, Inc. Page 3 of 4 3.6
16、 GRAIN FLOW Grain flow shall be verified in accordance with SAE/USCAR-8. This verification should be conducted at job setup, or whenever tooling or raw material changes are made that affect grain flow. The sample size and frequency should be identified in the manufacturers Control Plan. All records,
17、 test specimens or photographs for this requirement shall conform to QS9000 record retention requirements. 3.7 SURFACE INTEGRITY Acceptability of thread discontinuities per ISO 6157-3, except not applicable to thread forming threads and lead area. 4. TEST METHODS 4.1 DECARBURIZATION Longitudinal sec
18、tions shall be taken through the thread axis approximately one nominal diameter from the end of the screw. The specimen shall be suitably mounted and prepared for metallographic examination at not less than 100 x magnification. Prior to examination the sample shall be etched in 2% Nital solution. 4.
19、2 SURFACE HARDNESS TEST The surface hardness shall be measured using the Vickers Hardness Testing Procedure in accordance with ISO 6507. The surface hardness shall be performed on the head after removal of any finish and suitable preparation (1200 grit grinding or better). Care should be taken to re
20、move as little material as possible. For referee purposes, a micro-hardness instrument with a Vickers indenter and a 300g load shall be used. In such cases, measurements shall be made on the thread profile of a suitably prepared longitudinal metallographic specimen. 4.3 THREAD FORMING CAPABILITY. A
21、mating thread must be formed by driving the sample screw into the test plate until a minimum of one pitch of the screw, excluding the tapered lead threads, extends beyond the plate. The axial load to ensure commencement of the thread forming process shall not exceed 90N. The test plate must be alumi
22、num with a hardness of HB30-75. The plate thickness must be 2x the nominal diameter of the fastener. The pilot holes are given in Table 4. 4.4 TORQUE WRENCHES Torque sensing power devices used in all tests shall be accurate within 3% of the specified torques. Alternatively, a torque wrench of equiva
23、lent accuracy may be used. For referee purposes a torque sensing power device shall be used. 5. MARKING 5.1 IDENTIFICATION Through hardened and carbon restored TAPTITE 2000“SP” thread rolling screws shall be marked by indenting or embossing with the marking symbol 8N as defined in Table 1. Marking i
24、s obligatory for hexagon screws with nominal diameters of 5mm (#12) or greater and for other products where the shape permits, preferable on the head. WORLDWIDE FASTENER STANDARD WD 956 Date: 2010 07 20 Printed copies are uncontrolled Copyright 2010 Ford Global Technologies, Inc. Page 4 of 4 5.2 TRA
25、DE (IDENTIFICATION) MARKING The trade (identification) marking of the manufacturer is mandatory on all products which are required to be marked with the marking symbol. Table 4. Test Plate Thickness and Hole Sizes 6. SUMMARY OF REVISIONS 2010 07 20 Para 2 Delete reference to minimum tempering temper
26、ature 2009 12 08 Para 1 Expanded scope to include M3 M14 Para 1.1 Added new references Para 2 Added direct reference to ISO 898/1 and increased minimum tempering temperature. Para 3.3 (note 1) Revised surface hardness from 50 to 30 Added 3.6 & 3.7 2005 11 Updated the test plate thickness and hole si
27、zes were added to Table 4 for 3mm, 4mm and 14mm.( Nominal Thread Size 3mm 4mm 5mm 6mm 8mm 10mm 12mm 14mm Min. 2.76 3.66 4.61 5.51 7.39 9.27 11.15 13.03 Hole Dia Max. 2.79 3.70 4.66 5.58 7.47 9.37 11.26 13.16 Plate Thickness 6.0 8.0 10.0 12.0 16.0 20.0 24.0 28.0 NOTE: Plate thickness tolerance in accordance with ISO 5954 (for rolled plate)
