1、 WORLDWIDE FASTENER STANDARD Date: 2008-12-01 Printed copies are uncontrolled Copyright 2008, Ford Global Technologies, LLC. Page 1 of 4 WZ 200 GUIDELINES FOR THE SELECTION OF TORQUE VALUES BY FASTENER SIZE AND GRADE 1. SCOPE The purpose of this standard is to give guidelines for the selection of ti
2、ghtening torques with assembly joints for property class (grade) 8.8 and 10.9 fasteners, and for spaced thread forming screws. This torque standard may be used to initially set the tightening torque, but testing is recommended to verify the final torque specification. 2. REFERENCES ISO 261 General p
3、urpose metric screw threads - General Plan ISO 273 Fasteners - Clearance holes for bolts and screws ISO 898-1 Mechanical properties of fasteners made of carbon steel and alloy steel ISO 965 General purpose metric screw threads - Tolerances ISO 1478 Tapping screws thread WX100 Finish Specification PT
4、-3 Global Torque Standard FST-10 Torque-Angle-Failure 3. FIELD OF APPLICATION The recommended torque values apply only for tools with a process capability, Cpk of 1.67 or better, based on the 15% variance and the specified working range of the particular tool. The recommendations given for grade 8.8
5、 and 10.9 fasteners are based on the following assumptions: ISO coarse pitch metric threads. A hex flange bolt geometry and performance in accordance with WA900, or a hex flange nut geometry in accordance with WE900. An associated bolt and nut property class where an 8.8 bolt is used with an 8 nut o
6、r higher, or a 10.9 bolt is used with a 10 nut or higher, as well as the minimum thread engagement so that the failure mode results in the fracture of the bolt. Surface treatments and a thread tolerance class in accordance with WX100. Clearance holes in accordance with ISO 273, so that the effective
7、 bearing diameter is defined as (dw+da)/2 with a hex flange geometry. Joints should withstand the clamp load so that the ultimate fracture is with the fastener. Joints should have a tightening angle of 20 to 800, taken from the threshold torque. 4. TIGHTENING TORQUE DEFINITIONS The torque specificat
8、ions shall consist of a recommended nominal tightening torque and a symmetrical tolerance (15% variance). Fastener Standard Test, FST-10, will establish the process capability as shown in Figure 1. Manufacturing will need to establish the following: A mean tightening torque or assembly torque that s
9、upports PT-3, and the affects of joint relaxation. The specific residual torque or inspection torque shall be determined for each particular joint. The total torque deviation should be contained within a 6 tolerance zone. WORLDWIDE FASTENER STANDARD Date: 2008-12-01 Printed copies are uncontrolled C
10、opyright 2008, Ford Global Technologies, LLC. Page 3 of 4 Figure 1: The process capability, Cpk = (Process Average - LSL)/3 = X/Y for this example. 5. FACTORS AFFECTING TORQUE SELECTION The nominal tightening torque and tolerance shall be selected with respect to the following: The Torque-Tension re
11、lationship of a joint, which relates the tightening torque and clamp force. Variation can be reduced by using standard fasteners in accordance with WA900 and WE900, surface treatments in accordance with WX100, and torque tension ratios in accordance with WZ101. Standard torque values for a specific
12、size and property class shown in Table I, are based on an average 0.14 0.03 coefficient of friction. If the average value of the assembly coefficient of friction is lower than 0.11 or higher than 0.17, alternatives torque values given in the Global Torque Standard PT-3 can be used. The assembly prop
13、erties of the joint and the resulting tolerance limits will affect or restrict the selection of assembly tools. As a general rule, the highest torque allowed by the assembly torque distribution and the ultimate torque limits should be used. The +3 Sigma limit must be less than the ultimate torque to
14、 reliability prevent fracturing of the fastener. Alternative torques can be used for both static and dynamic high strength joints with the proper analysis of both the joint and the assembly tooling. The ultimate failure torque of the joint. The design engineer will determine the load requirements of
15、 the joint, based on the intended function, and verify the load against the nominal tightening torque. Minimum thread engagement and bearing surface area. The utilization level of the fastener. -3 +3 Target value X Y LSL (-15%) USL (+15%) WORLDWIDE FASTENER STANDARD Date: 2008-12-01 Printed copies a
16、re uncontrolled Copyright 2008, Ford Global Technologies, LLC. Page 3 of 4 6. STANDARD TORQUE VALUES FOR METRIC THREADED FASTENERS Torques normally used with metric threaded fasteners tightened with DC tools or pneumatic tools (with a process capability, Cpk above 1.67 with 15% as specification limi
17、t) are contained in Table I. These torque values can be applied to Standard joints using hex flange bolts in accordance with WA900, hex flange nuts in accordance with WE900, and with an assembly coefficient of friction between 0.11 and 0.17. For clamp load critical joints, the values must be verifie
18、d with additional detailed joint analysis. Table I Dimension mm Property Class or Grade Assembly Torque Target Value Nm Tool Variance Nm Corresponding Clamping Force kN M5 M5 8.8 10.9 6.2 7.0 1.0 1.1 4.2 -8.4 4.9-10 M6 M6 8.8 10.9 10.5 12.0 1.6 1.8 5.5-11 6.5-13 M8 M8 8.8 10.9 25 30 3.8 4.5 10-20 12
19、-24 M10 M10 8.8 10.9 47.5 62.5 7.2 9.4 16-32 21-42 M12 M12 8.8 10.9 80.0 110 12 16.5 22-44 30-60 M14 M14 8.8 10.9 133 175 20 26.3 33-66 40-80 M16 M16 8.8 10.9 200 275 30 41.3 41-82 54-108 7. STANDARD TORQUE VALUES FOR SPACED THREADED FASTENERS Torques normally used with space threaded fasteners (e.g
20、. Delta PT), typically tightened with pneumatic or battery tools, are contained in Table II. Table II 0,80.2 0.90.2 1.00.2 1.10.2 1.30.20 1.50.3 1.70.3 1.90.3 2.20.4 2.50.4 2.80.5 3.20.5 3.70.6 4.10.7 4.80.8 8. STANDARD TORQUE GROSS LIST Tables I & II stipulates the assembly torques that can be used
21、 with Standard joints in FMC plants, in common platform projects and with standard tools. For additional torque values see Global Torque Standard PT-3 via: https:/ WORLDWIDE FASTENER STANDARD Date: 2008-12-01 Printed copies are uncontrolled Copyright 2008, Ford Global Technologies, LLC. Page 3 of 4 9. SUMMARY OF REVISIONS SUMMARY OF REVISIONS Date Revisions 2008-12-01 Initial Release
