1、 WORLDWIDE FASTENER STANDARD Date: 2001-01-04 WD951 MECHANICAL AND PERFORMANCE REQUIREMENTS OF CASE HARDENED THREAD ROLLING SCREWS Printed copies are uncontrolled. Page 1 of 5 Copyright 2001, Ford Global Technologies, Inc. 1. SCOPE. This standard specifies the requirements for high performance case
2、hardened and tempered thread rolling screws that have performance capabilities beyond those normally expected of other types of tapping screws. It relates to screws with basic 60oscrew thread form, metric series, intended for parts up to and including 5mm nominal thread diameter only. For parts abov
3、e 5mm, WD 952 is recommended. Clause 3.4 defines thread-forming capability in steel up to a hardness of 150 HV and thickness equal to the screw diameter. The parameters of material hardness and thread engagement may be varied by analysis of joint requirements and it is therefore recommended that spe
4、cific applications be investigated to determine joint criteria. NOTE: Lubrication approved by Ford is permitted on parts to which this specification is applied unless otherwise specified. 1.1 REFERENCES. ISO 262 - ISO general purpose metric screw threads - Selected sizes for screws, bolts and nuts.
5、ISO 898/2 - Mechanical properties of fasteners - Part 2: Nuts with specified proof load values. ISO 5954 - Cold reduced carbon steel sheet to hardness requirements. ISO 6507 - Metallic materials - Hardness test - Vickers test. WSS-M99A3-A - Embrittlement Avoidance 2. MATERIALS. Screws shall be made
6、from cold heading quality fully killed steel wire; the following chemical composition is given for guidance only. Table 1. Chemical composition Analysis Composition Limits (% by Weight) Carbon Manganese Ladle 0.18 to 0.28 0.60 to 1.75 Check 0.16 to 0.30 0.54 to 1.81 3. MECHANICAL PROPERTIES. 3.1 HEA
7、T TREATMENT. Finished screws shall be case hardened and tempered in order to meet all the mechanical and performance requirements of this standard as detailed in Table 3. The case depth shall be as given in Table 4. The core hardness shall be 370 HV maximum, and the case hardness shall be 450 HV min
8、imum. However, the main criterion for acceptance is that the screws meet all the performance tests specified in this standard. WORLDWIDE FASTENER STANDARD Date: 2001-01-04 WD951 MECHANICAL AND PERFORMANCE REQUIREMENTS OF CASE HARDENED THREAD ROLLING SCREWS Printed copies are uncontrolled. Page 2 of
9、5 Copyright 2001, Ford Global Technologies, Inc. Table 2. Mechanical properties to be determined Criteria Clause Test Reference Referee Tests Case Hardness 3.1 4.2 Core Hardness 3.1 4.1 Case Depth 3.1 and Table 4 4.3 Torsional Strength 3.2 and Table 3 4.4 * Thread Forming Capability 3.4 4.5 Drive Te
10、st 3.4 4.6 * Table 3. Mechanical and performance requirements Nominal Screw Diameter (mm) Torsional Test Torque Nm Minimum 2 0.6 2.5 1.2 3 2.2 (3.5) 3.5 4 5.2 5 10.5 Table 4. Case depth Nominal Screw Case Depth (mm) Diameter (mm) Minimum Maximum 2 and 2.5 0.04 0.12 3 and (3.5) 0.05 0.18 4 and 5 0.10
11、 0.25 WORLDWIDE FASTENER STANDARD Date: 2001-01-04 WD951 MECHANICAL AND PERFORMANCE REQUIREMENTS OF CASE HARDENED THREAD ROLLING SCREWS Printed copies are uncontrolled. Page 3 of 5 Copyright 2001, Ford Global Technologies, Inc. 3.2 TORSIONAL TEST TORQUE. Minimum torsional test torque is specified in
12、 Table 3, when tested in accordance with Clause 4.4. Failure must not occur in the clamped threads. 3.3 DUCTILITY. There shall be no fracture at the head/shank intersection when a permanent deformation of 10ois induced between the plane of the underhead bearing face and a plane normal to the axis of
13、 the screw, when tested in accordance with Clause 4.5. The test shall be regarded as satisfactory even if a crack should appear in the first thread, provided that the head does not snap off. This test does not apply to countersunk head screws. 3.4 THREAD FORMING CAPABILITY. The screw shall, without
14、permanent deformation of its own thread when viewed at 10 x magnification, form a mating thread in a test plate in accordance with Clause 4.6. The thread formed by the screw in the test plate shall be capable of accepting a fastener threaded in accordance with ISO 262 tolerance class 6g and shall re
15、sist a proof load test in accordance with ISO 898/2 Property Class 8. 3.5 EMBRITTLEMENT. All case hardened thread rolling screws shall meet the requirements of WSS-M99A3-A. 4. TEST METHODS. 4.1 CORE HARDNESS TEST. Core hardness shall be determined at the mid-radius of a transverse section through th
16、e screw taken at a distance sufficiently behind the point of the screw to be through the full minor diameter. The test shall comply with ISO 6507. 4.2 CASE HARDNESS TEST. For routine control purposes (where case depth and geometry of the screw permit), case hardness may be measured on end, shank, or
17、 head using the Vickers Hardness Procedure in accordance with ISO 6507. Hardness tests shall be made on plated screws after the removal of the plated finish. For referee purposes, a micro-hardness instrument with a Vickers indenter and a 300g load shall be used. In such cases, measurements shall be
18、made on the thread profile of a suitably prepared longitudinal metallographic specimen. 4.3 CASE DEPTH TEST. Case depth shall be measured at the mid-point between crest and root on the thread flank. For referee purposes, a micro-hardness plot shall be made using a Vickers indenter and a 300g load on
19、 the thread profile of a properly prepared metallographic specimen. The case depth shall be the point at which the hardness recorded in 30 HV above the actual core hardness. WORLDWIDE FASTENER STANDARD Date: 2001-01-04 WD951 MECHANICAL AND PERFORMANCE REQUIREMENTS OF CASE HARDENED THREAD ROLLING SCR
20、EWS Printed copies are uncontrolled. Page 4 of 5 Copyright 2001, Ford Global Technologies, Inc. 4.4 TORSIONAL TEST. The sample screw shall be securely clamped by suitable means (See Figure 1) with at least two full threads projecting above the clamping device, and at least two full threads exclusive
21、 of point, held within the clamping device. By means of a suitably calibrated measuring device, torque shall be applied to the screw until failure of the screw occurs. The torque required to cause failure shall be recorded as the torsional test torque and must equal or exceed the minimum torsional t
22、est torque specified in Table 3. 4.5 DUCTILITY TEST. The sample screw shall be inserted into a drilled hole of a diameter equal to the maximum major thread diameter + 0.05mm in a hardened wedge block, or other suitable device and an axial compressive load applied against the top of the screw. Loadin
23、g shall be continued until the plane of the underhead bearing face is bent permanently through 10owith respect to a plane normal to the axis of the screw. NOTE: It is normal procedure to induce the 10opermanent deformation by a blow or blows from a suitable hand held hammer. Figure 1. Typical test d
24、evice for the torsional and thread forming capability tests WORLDWIDE FASTENER STANDARD Date: 2001-01-04 WD951 MECHANICAL AND PERFORMANCE REQUIREMENTS OF CASE HARDENED THREAD ROLLING SCREWS Printed copies are uncontrolled. Page 5 of 5 Copyright 2001, Ford Global Technologies, Inc. 4.6 THREAD FORMING
25、 CAPABILITY TEST. A 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 test plate. The axial load to ensure commencement of the thread forming process shall not exceed 20N. 4.6
26、.1 TEST PLATE. The test plate shall be of low carbon rolled steel having a hardness of 115 to 150 HV30. Plate thickness shall be equivalent to the nominal screw diameter. Hole sizes shall be as given in Table 5. Table 5. Test plate thickness and hole sizes Nominal Thread Size and Plate Thickness (mm
27、) 2 2.5 3 (3.5) 4 5 Hole Dia. (mm) Min. 1.8 2.25 2.75 3.15 3.65 4.5 Max. 1.825 2.275 2.775 3.18 3.68 4.53 NOTE: Plate thickness tolerance in accordance with ISO 5954 (for rolled plate) 4.7 TORQUE WRENCHES. Torque sensing power devices used in all tests shall be accurate within 3% of the specified to
28、rques. Alternatively, a torque wrench of equivalent accuracy may be used. For referee purposes a torque sensing power device shall be used. 5. MARKING. 5.1 SYMBOL. The marking symbol for case hardened thread rolling screws is “-0-“. 5.2 IDENTIFICATION. Marking for case hardened thread rolling screws M5 and below is not mandatory. 5.3 TRADE (IDENTIFICATION) MARKING. The trade (identification) marking of the manufacturer is mandatory on all products which are required to be marked with the marking symbol.
