FI58819B - FOER FARING FOER FRAMSTAELLNING AV EN SJAELVGAENGANDE SKRUV OCH ETT VALSNINGSBACKPAR FOER UTFOERANDE AV FOERFARANDET - Google Patents

Description

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^ STa CbJ (11) utlAggningsskrift 5881 9 C Patent granted 10 04 1931 (45) Patent aeddelat ^ T ^ (51) Kv.lk?/lntci.3 F 16 B 25/00 FINLAND —FINLAND (21) P »U« ttlh »Lumu« —P «* ntw» aknlrit 1 ^ 98/73 (22) HakemltpUvi - AiMÖknlnsfdag 09 · 05 · 73 (23) AlkupiM —Glkljh * t »d» | 09.05.73 (41) Become public - Blivlt offwwllf 25.11.73 P.tonttf-). reki.terih.mtu. NlhUvIkslp ™ kuL | ulk * un pvm- rUMt · och reglrterrtyrWMfl '' Ansaiten utlagd och utl.skrlften pubikerad 31.12.80 (32) (33) (31) Pyydetty etuoikeus — 8 «| lrd priority 2k. 05.72 USA (US) 256370 (71) USM Corporation, lHO Federal Street, Boston, Massachusetts, USA (US) (72) Edvin John Skierski, Stratford, Connecticut, USA (US) (7U) Oy Kolster Ab (5 ^) Method The present invention relates to a method for manufacturing a self-tapping screw and a pair of rolling jaws for carrying out the method.

A wide variety of self-tapping connectors are available. Most of these connectors fall into one of two classes of principles in terms of thread forming activity: cutting or molding. Although both basic shapes are effective in forming an internal thread in a receiving body, the molding shape is the most common today. One of the illuminating connectors of the molded types is disclosed in U.S. Patent No. 3 ^ + 26 61 + 2, issued February 11, 1969. The thread-forming means in this type of forming screw is a cam structure (number 21 in Figures 1, 2 and 3 of the above-mentioned patent) which is placed substantially through the tip through a continuously continuous screw thread of the mandrel.

Although the connector described above is effective as a low torque demanding thread former, it is hampered by the same characteristics that are characteristic of its previously known mass fabrication methods. Today, 2 58819, these connectors are rolled between two helical rolling jaws, both individual jaws of which are provided with a plurality of parallel thread-forming brushes, threaded ridge-forming grooves and cam-forming pockets, whereby the material of the screw mandrel changes a screw thread is formed. When forming self-tapping screws with thread-forming cams, the grooves forming the thread-ridge of the jaws are provided with a group of pockets, which pockets are cavities. These pockets are filled with plastic metal and form a reinforced part that is substantially on top of the thread. Since the cam-forming jaw portions are in fact bumps in the grooves forming the thread ridge, the cam sheath naturally extends to the other side of the screw thread sheath in an area near the junction of the connector mandrel and conical portions where the cone portion diameter approaches the mandrel diameter (see Figure 3 above). · Where a screw thread formed in the connector having a substantially constant cross-section begins, the thread-forming cams in the vicinity of the joint form an internal thread in the receiving part of the connector which is larger than the actual thread in the spindle part of said connector. Thus, when the connector is inserted into the receiving part, there is no prevailing torque between the internal thread of the receiving part and the thread of the connector stem. On the contrary, it has a relatively loose fit between the connector and the receiving part. It should be noted at the outset that this feature must in some cases be considered a deficiency that limits the overall, utilization of the connector.

This deficiency has been identified and an attempt has been made to remedy the described deficiency.

Figures 2k-26 of the above patent show an attempt to provide a self-tapping screw which also provides a controlled prevailing torque (zero clearance or positive anxiety between the connector and the internal thread formed). As described, previous connectors of this nature comprised a threaded portion projecting into a workpiece with a conical threaded formation having a decreasing outer and split diameter of the thread but a constant core diameter. Although the described connector may provide the prevailing torque because the height and thickness of the threaded cams per head penetrating the workpiece decreased from a value less than the corresponding value of the threaded formation on the mandrel, its overall efficiency and desirability as a self-tapping screw was impaired.

The efficiency of a self-tapping screw depends to a large extent on the thread structure of the part penetrating the workpiece. The structure of the thread therein should not only form the internal thread on the approaching spindle part but also move the connector to the receiving part. If the thread does not "bite" deep enough into the material of the sides of the receiving part to "drill in", the connector will not move forward and will not form the desired thread. On the contrary, it crushes the thread, leaving the receiving part without threads or leaving an enlarged hole in it.

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The object of the invention is to provide a method for manufacturing a self-tapping screw which does not have the disadvantages of known manufacturing methods and which can be used to manufacture a self-tapping screw in a very simple manner.

The present invention comprises a method of manufacturing a self-tapping screw having a conically decreasing diameter of the threaded rod shank towards the tip of the shank and having cams arranged for threading preferably in axial rows, the method comprising producing a blank having a conically decreasing shank and rolling from the earthy stem end to the cylindrical stem portion is unchanged, as well as cams fitted to the conical stem end.

This method is characterized in that the cams in the first stage are rolled higher than the imaginary extension of the threaded surface of the cylindrical shank part and that the cams are then compressed so far below this imaginary threading surface.

The pair of rolling jaws according to the present invention have parallel helical grooves which in both jaws move from a flat area to an edge area rising towards the rear edge running in the rolling direction, in which edge area they are transversely recessed in at least one jaw by pocket-forming pockets. This pair of rolling jaws is characterized in that the pockets are recessed deeper than the depth of the grooves in the flat rear area and that a post-rolling area is connected to the pocket edge area in the rolling direction, where the grooves are a certain amount less above the flat area than in the edge area.

Figure 1 shows a screw made by the method according to the invention.

Figure 2 is a partial sectional view of the connector of Figure 1 prior to the post-rolling step.

Figure 2a is a front view of the connector of Figure 2.

Fig. 3 is a partial sectional view of the connector of Fig. 2 after post-rolling.

Figure 3a is a front view of the connector of Figure 3.

Figure H shows the jaws used to carry out the method according to the invention.

Fig. 5 is a view showing a partial section of the jaws of Fig. 1+ in the rolling step.

Figure 6 is a phase view of the jaws of Figure k during rolling.

Figure T is a vertical section of the post-rolling step performed by the jaws.

Fig. 8 is a sectional view of the alternative embodiment of Fig. 6.

Reference is now made to the drawings, and in particular to Figure 1, in which a self-tapping screw illustrating an embodiment of the invention is designated 10. The screw 10 comprises a cylindrical mandrel portion 12 having a base 1U at one end and a conical workpiece portion 16 terminating at the other end. the tip 18. The tip 18 may be pointed or blunt, as described. A means, e.g. a transverse groove 20, is suitably provided in the base 1 to which a tool (not shown), e.g. a conventional screwdriver, engages. Position 1 * + does not necessarily have to be extended.

The screw 10 has a thread 22 starting from the tip 18, which extends as a helical screw thread 2h to the conical part 16 projecting into the workpiece and extends as a cylindrical screw thread 26 to at least a part of the mandrel 12.

As can be seen from the cross section (see Figure 2a), the thread 26 on the mandrel 12 is cylindrical along its entire length. Each thread shape comprises, a base r, sides f and a brush c, which are indicated together with the thread reference number, for example 22r, 2äf, 26c.

The screw thread 2h on the workpiece penetrating the workpiece 16 (Fig. 1) comprises thread-forming cams 30 extending from 2Ur along the sides 2 ^ f to the ridge 2 ^ c and appearing as protrusions on the thread 2bc and appearing on the thread 2b. The cams 30 are shown in cross-section as a jacket 32 (Fig. 2), generally parallel to the sides 2hf and the brush 2l + c and which, except for the area of the joint 12 of the mandrel 12 and the workpiece penetrating part 16, as will be explained later, appear as a cam brush 30c projecting from the threaded brush 2Uc.

The cams 30 are boldly placed peripherally at the distances, along the screw thread, in axially arranged rows (see Figures 1, 2 and 3) extending from the tip 18 along the workpiece penetrating portion 16 to the spindle portion 12, but not thereto.

Further, the cam 30 is described as having front surfaces 30a and back surfaces 30t on both sides (Fig. 2), which gradually curve outwards from the sides 2bf and thus round. However, it will be appreciated that helical cams may take a variety of shapes in addition to those shown herein, however, there are three basic shape requirements. The first requirement is that the profile of the cam is larger than the profile of the thread, in order to have the screw supported in this area so as to achieve a reduction in the friction between the screw and the workpiece when the internal thread is molded. Another requirement for the shape of the cam is that it gradually rises above the sides 2b f and the brush 2bc so that it does not cause the receiving body to cut. A third structural consideration of the cam is that successive cams in the workpiece-penetrating portion further progressively extend outwardly from the screw axis so that the last spindle-side cam in said workpiece-penetrating portion and the projection of certain predetermined cams . As will be immediately explained, the new jaws and the method of manufacturing the self-tapping connector allow for the novel structure of this invention.

5 5881 9

The self-tapping connector shown in Figures 1, 2 and 3 is made by keenly rolling a spindle thread, a workpiece penetrating thread and cams on a conventional cylindrical karate frame with the device shown in Figures U-8. The rolling jaws comprise a pre-rolling jaw 1 + 2 and a secondary rolling jaw hk. These two jaws comprise a flat spindle rolling section U6 extending longitudinally from the connector inlet ends 1 + 3 and l + 3a towards the connector outlet ends 1 + 5 and l + 5a. The mandrel rolling section 1 + 6 comprises threaded groove rolling grooves 1 + 8 and threaded bottom forming brushes 50. Each jaw is also fitted with an inclined cone rolling section 52 which is generally the same size as and forms a boundary for said mandrel rolling section 1 + 6. Said rolling part of the mandrel also comprises grooves 1 * 8 and brushes 50. The primary jaw 1 + 2 comprises in particular recesses in the grooves 1 + 8 in the inclined rolling part 1 + 6, i.e. pockets 5 ^ · »which form the cams shown in Figures 2 and 2a. Said recesses are arranged in rows (A, B and C), cf. Figures U-6 and 8.

The screw blank 1 + 0 is fed in a conventional manner between the threaded jaws 1 + 2 and 1 + 1 +, as shown in Fig. 1+. The threaded ridge rolling grooves 1 + 8 in the mandrel rolling section 1 + 6 and the threaded bottom forming brushes 50 roll a cylindrical screw thread 26 into the mandrel section 12 (as shown in Figs. 1-3). Cone rolling sections 52 having brushes 50 and grooves are tightly fitted to the same jaw sections. 1 + 8. Thus, the conical part 16 penetrating the workpiece is rolled into the connector simultaneously with the mandrel, and the connector 10 is thus provided with a helical screw thread 21 + extending substantially to the tip 18. Jaws 1 + 2 and 1 + 1 + and the described rolling method have long been generally known.

The cams 30a and 30 'can be preliminarily formed simultaneously with the rolling of the thread 21 + by providing the ridge-forming grooves 1 + 8 with pockets 5 + + shaped to correspond to the cams 30, i.e. the cams 30a and 30' shown in more detail in Figures 2 and 2a. During the rolling step of the screw blank 1 + 0, the metal of the blank 1 + 0 is forced to press into the pockets so that over the thread 2l + the cams 30a and 30 'on the sides 2l + f of this thread and the brush 2l + c are formed. As previously mentioned, a preliminary molding of the cams 30a and 31 has been described above, as shown at 30 'in Figure 2. As can be seen, the recesses 5 in the described rolling jaw structure and method extend deeper than the grooves 1 + 8 forming the thread ridge in which they are placed. The method described so far has resulted in providing a base cam 30 and 30 '(Figures 2, 2a, 5, 6 and 8) to the outer portions of the workpiece penetrating portion 16, a cam extending radially toward the tip of the cylindrical screw thread 26 to the other side of the extended sheath 27. These protrusions of the cams 30 'on the other side of the spindle thread sheath result in a self-tapping connector having the desired zero clearance or adjusted torque with its internally threaded counterpart.

Certain cams 30 '(projecting onto the other side of the thread sheath 27) are preliminarily formed simultaneously with the helical screw thread 2h (see

5881 9 6 Figures 2 and 2a). These cams 30a, including the cams 30 ', are substantially equal (in the preferred embodiment) from the tip 18 to the mandrel 12. After initial molding, the pre-rolled cams 30a and in particular the cams 30' are finally rolled into the shape of the cams 30 (see Figures 3, 6 and 6). a precisely calibrated thread-forming surface is obtained, in particular in the vicinity of the junction 25 of the part 16 projecting into the workpiece and the spindle 12. The jaw structure with which this post-rolling is performed is described in the description of details below. Thus, the cams 30 ', which would otherwise protrude to the other side of the threaded sheath, are accurately rolled back into the desired sheath. By this post-rolling, the cams 30 are shaped so that each cam sheath enters the inside of the sheath projecting towards the tip from the junction 25 of the imaginary cylindrical screw thread of the mandrel 12 and the workpiece penetrating the workpiece, see Figures 3 and 3a. It should also be noted that this post-rolling occurs simultaneously on the ridges 30c and sides 30s of the cam 30 'so that the entire cross-sectional sheath of the cam 30 is within the actual dimensions of the mandrel thread 22 which in this embodiment results in a screw 10 with adjusted torque when the connector 10 is placed on the receiving body after it has been molded with an internal thread.

In the embodiment shown in Figures 1 and 3, in which all the cams 30 in the rows (A, B and C) are post-rolled (Figure 3) very precisely, thread forming takes place in the last cams. This is due in part to the controlled calibration during post-rolling in the formation of these final molded cams and in part to the low compression loads present in these cams during post-rolling, as their function is to perform small final thread inspections of the thread formed by the nip during initial rolling. The main purpose of certain post-rolling cams during the molding operation is to equalize the torque load on the thread-forming cams. The balancing of the cam loads avoids harmful stresses when forming the internal thread, which in turn dramatically increases the ratio of torque to torque. The ratio present in connectors made by conventional methods is approximately 3: 1, while the connectors of the present invention give a ratio of approximately 10: 1.

According to the previous paragraph, the molded screw also provides another significant threading feature. It is known that many substances in which the self-tapping screws are placed have a "memory". That is, the material has some elasticity, and after it has been brought into the exact shape of the mandrel thread by the connector during molding, there is a slight tendency in the internal thread to return to its original or "filled" shape. Thus, there is little anxiety between the molded internal thread and the mandrel thread 26 when the screw is inserted into the threaded hole. This anxiety ensures a “zero clearance” and, in fact, a locking effect. The degree of locking, i.e. the amount of anxiety, can be adjusted directly in the post-rolling section 60 of the jaw UU by the amount of reduction rolling performed on each cam row. The thinner the brush 1 5881 9 30c and the sides 30s are rolled, the smaller the internal thread and the greater the anxiety or prevailing torque in the screw.

The jaws 42 and UU, which are suitable for the production of the new connector according to the invention described above, have a post-rolling or calibration part 6θ, the thread-forming surface 62 of which is shaped to the desired final shape and size of the cams 30. Correspondingly, the jaw k2 has a post-rolling support portion 61 having a thread-forming surface 63. In the illustrated embodiment, these molding surfaces are provided with brushes 50 and grooves 48 comparable to corresponding portions in the thread rolling portion 46 in which the cylindrical screw thread is rolled. These post-rolling parts 60 and 6l are located in the jaws 42 and 44, after said spindle rolling part 46 and cone rolling part 52. In the preferred embodiment, the post-rolling portions 60 and 6l are only a short addition to the jaws 42 and 44 adjacent the outlet ends 45 and 45a. The length of these parts in the rolling direction is approximately equal to the circumferential length of the connector 10. This ensures post-rolling on the entire circumference of the connector 10 and thus on a portion of all cam rows (especially those cam rows 30 'of rows A, B and C that would otherwise protrude on the other side of the sheath 27 extending in the direction of the mandrel thread).

In one embodiment of the jaws, the rolling length of the post-rolling support portion 6l of the jaw 44 may be substantially shorter than the circumferential length of the connector. In such an embodiment, post-rolling can affect only a portion of the soot 30 '. In the jaws shown in Fig. 8, the cams 30 'formed by the recesses 54 of rows A and B are rolled back to a predetermined shape (cylindrical spindle thread) and the cams 30' of row C remain rolled once. This is because the length of the thread forming surface 62 of this embodiment is limited so that it no longer supports or works the connector after the first two-thirds of post-rolling. Of course, the primary jaw 42 supports the screw during this post-rolling and the amount of post-rolling can also be adjusted by the length of the support part 63.

The product of the jaws described above, i. the product of the second embodiment, is a self-tapping screw in which the threaded cams 30 'are all the same size in the tip 18 side portion of the workpiece penetrating portion 16, however, the region near the spindle junction 25 has one oversized row of cams (row C in the figure) which protrudes radially past the thread 26 of the mandrel 12. Thus, the cams 30 of rows A and B can accurately shape the internal thread of the receiving body to fit the cylindrical screw thread of the mandrel 26, and the oversized cams 30 'of the row C tend to shape the larger internal thread. The torque required to form this screw is much smaller than the torque required to form the thread of the first embodiment, and the screw forms an internal thread in the receiving body with zero torque or very low prevailing torque between it and the mandrel thread 8 in the receiving body. screw continuous product uniformity.

In conventional practice, the cams are rolled on both jaws, which requires a careful alignment method when the jaws are placed on a rolling machine. As previously mentioned, the circumferential alignment of the cams is confused if the screw blank slips slightly on the other jaw during the pre-rolling stages. In conventional practice, very often the entire row of cams may be wiped or rolled off the screw (or significantly damaged) due to adjustment or sliding problems.

In contrast to previous practice, the cam forming recesses 5 of the present invention are located only in the second thread forming jaw (see Figure U). By locating all the cam-forming recesses in the second jaw, such as the jaw k2, the correct circumferential position of the cams can be ensured, which contributes to the accurate rolling of the thread-forming cam 30.

This arrangement of the cam-forming recesses 51 * and the construction of the jaw result in a connector with cams which are absolutely correctly positioned and not subsequently wiped or rolled out uncontrollably. All the cams 30 are placed on the thread 2h by means of a single jaw and the relative position or change of position of the contributing jaw has no effect on the position of the cam.

Claims (3)

9,58819 A method of making a self-tapping screw having a tapered pin shank diameter tapering toward the shank tip (18) and the shank having cams (30) adapted to be threaded into preferably axial rows, the method comprising producing a blank having a tapered shank end (16). ) and a thread is rolled therefrom, the rise of which from the conical shank end (16) to the cylindrical shank part (12) is constant, and cams (30) fitted to the conical shank end (16), characterized in that the cams (30) are rolled in a first step. higher than the imaginary extension of the threaded surface (27) of the shank part (12) and that the cams (30) are then compressed so far below this imaginary threaded surface (27) in the same operation that they preferably delimit the conical threaded end (16) of the evenly spaced threaded surface 27) with respect to. A pair of rolling jaws for carrying out the method according to claim 1, wherein the pair of rolling jaws (1 + 2, 1 + 1 +) has parallel helical grooves (1 * 8) which in both jaws move from a flat area (1 + 6) to an edge area (52) rising towards the rear edge running in the rolling direction, in which edge region (52) they are transversely recessed in at least one jaw by means of pocket-forming pockets (5 ^), characterized in that the pockets (5l *) are recessed in grooves in a flat rear area (1 + 6) (1 + 8) deeper and that a post-rolling area (60, 6l) is connected to the edge area (52) with pockets (5 * +) in the rolling direction, where the grooves (62, 63) are located a certain amount less above the flat area (1 + 6). ) than in the edge region (52) where the pockets (5I +) are. A pair of rolling jaws according to claim 2, characterized in that the longitudinal dimension of the post-rolling area (60) of the jaw (1 + 1 +) of the at least second threaded roller is at least equal to the circumference of the screw rolled on said jaw of the threaded roller. 1+. A pair of rolling jaws according to claim 2, characterized in that the longitudinal dimension of the post-rolling region (60) of the jaw (1 + 1 +) of the at least second threaded roller is at least equal to half the circumference of the screw rolled by this jaw of the threaded roller.