GB2197236A - Lead clinching tools - Google Patents

Abstract

A lead clinching tool 10' comprises a pair of bases 12A ,12B and a fixed cutter 18' which is secured in place between the bases and has a pair of cutting edges 20'. The tool 10' further comprises a pair of movable cutters (24'-Fig. 11, not shown) which have respective cutting edges (26') and which are movable such that the cutting edges (26') thereof approach the cutting edges 20' of the fixed cutter 18' and cooperate therewith to cut a pair of leads L of a component C that extend, in a use position of the anvil 10', downwardly into the anvil, after which the cut leads are bent by movement of the movable cutters (24'). The positions of both the fixed cutter 18' and the movable cutters (24') can be adjusted in vertical directions. The cutting edges 20' and (26') are formed on tungsten carbide inserts (42 and 44, Figs. 10, 11, not shown) respectively and the cutter (18') can be reversed to bring a further pair of cutting edges 20' into a working position. <IMAGE>

Description

SPECIFICATION Lead clinching tools This invention relates to lead clinching tools.

In the course of assembling electrical circuit units, it is known to form a pair of leads of a component (for example, a resistor, capacitor, diode or jumper wire) so that the leads extend parallel to one another with a predetermined pitch or spacing between them, and to insert the leads into a pair of holes in a printed circuit board, which holes have the same pitch or spacing, so that the component rests on top of the board and the leads extend substantially vertically downwardly from the under-surface of the board. The components may, for example, be formed in this manner by a rotating head that cuts a component from a bandolier, bends the leads of the component, and then inserts the leads into the holes.

In a relatively simple manufacturing process, the leads may then be soldered to printed circuit tracks on the under-surface of the board. However, in a more complex manufacturing process, in which the board is passed through several component insertion stages before soldering, there is a risk of the components becoming dislodged, upon movement of the board, if the leads are cut to the desired final length before insertion and are left hanging vertically downwardly through the holes in the board. To overcome this problem, the practice of clinching the leads has developed.

To this end, the leads are longer than desired when inserted through the holes in the board.

The leads then are clinched, from below the board, that is they are cut to a final desired length and are bent, usually towards one another. The clinching serves to hold the components in place, that is to prevent them from being dislodged, until the clinched leads eventually are permanently secured by soldering.

Both the angle of clinch (the angle between the bent leads and the under-surface of the board after clinching) and the clinch length (the length of the portions (also known as "legs") of the leads extending below the board after clinching) are to some extent critical. If the clinch angle and/or clinch length depart significantly from acceptable ranges of values, problems can occur.

Fig. 1 of the accompanying drawings shows components C1 to C6 (for example resistors) that have had leads thereof formed and inserted into pairs of holes, spaced by a pitch P, in a printed circuit board B. The leads of all of the components C1 to C6 have thereafter been clinched.

The leads of the component C1 have been correctly clinched. That is, the clinch length and the clinch angle of the leg of each lead protruding below the board B lie within ac ceptable ranges of values. By way of example, if the pitch P is 5 mm, the ranges of acceptable values of the clinch length and clinch angle may be 1.5 to 2.0 mm and 150 to 30 , respectively.

The component C2 is clinched too loosely, that is the clinch angle is too great. There is a risk of the component C2 falling out when the board B is moved during further assembly operations prior to the legs being soldered to printed circuit tracks on the under-surface of the board.

The component C3 is clinched too tightly, that is the clinch angle is too small. There is a risk that the legs of the component C2 will cut into a printed circuit track that may extend between the legs.

The component C4 is clinched unevenly, that is the clinch angles of the legs thereof differ from one another. There is a risk that the component C4 may fall out and/or that the legs may become soldered together, thereby short circuiting the component C4, when soldering eventually takes place.

The component C5 has been clinched such that the clinch length is too great. There is a risk that the legs of the component C5 may become soldered together.

The component C6 has been clinched such that the clinch length is too small. There is a risk that the component C6 will fall out.

The clinching of the legs of the components can be effected by a lead clinching tool, which is generally known in the art as an anvil. A form of lead clinching tool or anvil 10 previously proposed for this purpose is shown in part, and somewhat schematically, in Figs. 2 to 4 of the accompanying drawings, in which: Fig. 2 is a partial side view of the anvil 10 positioned below a component C whose leads L have been inserted through holes (spaced at a pitch P) in a printed circuit board B, prior to clinching of the leads; Fig. 3 is a sectional view taken along a line Ill-Ill in Fig. 2, again prior to clinching; and Fig. 4 corresponds to Fig. 3, but shows the situation after clinching has been effected.

The anvil 10 comprises a pair of substantially identical steel anvil bases 12 which are mounted by screws or bolts (not shown) which extend through holes 14 in the anvil bases into tapped holes in a chassis or main body portion (not shown) of the anvil so that the anvil bases are positioned to confront one another as shown in Fig. 2. Formed integrally with the confronting faces of the anvil bases 12 are a pair of members 16 which, when the anvil bases are positioned as shown in Fig. 2, cooperate to form a fixed cutter 18 having a pair of cutting edges 20. Small board sup ports 22 are formed integrally with upper edges of the anvil bases 12.Since the upper surfaces of the board supports 22 may come into contact with the undersurface of the board B during clinching of the leads L of the component C, the upper surfaces of the board supports are made as small as possible to minimise the possibility of their causing damage to printed circuit tracks on the under-surface of the board and/or of their disturbing leads of adjacent components that already have been clinched.

The anvil 10 further comprises a pair of like movable cutters 24 (omitted from Fig. 2 for the sake of clarity) that can be moved inwardly towards one another by actuator means (not shown) from the positions shown in Fig. 3 to those shown in Fig. 4. The movable cutters 24 have respective cutting edges 26.

The operation of mounting the component C and clinching its leads L will now be described. The leads L of the component C are formed into the configuration shown in Fig. 3 and inserted into the holes in the board B.

Though this operation could be performed manually, it generally is performed by an autoinsertion machine which cuts the component C from a bandolier, bends the leads L to the configuration shown in Fig. 3, and inserts the leads into the holes in the board B. The anvil 10 then is moved upwardly from a position below the leads 10 until it is disposed as shown in Figs. 2 and 3, in which position each lead L is disposed between a respective pair of the cutting edges 20, 26. The movable cutters 24 then are moved inwardly towards one another. During the course of such movement, the cutting edges 20 of the fixed cutter 18 and the cutting edges of the movable cutters 24 cooperate to cut the leads L to a desired clinch length.As the movement thereafter continues, the cut ends of the leads L ride up over the upper surfaces of the movable cutters until, at the end of the movement, as shown in Fig. 4, the cut leads L have been bent to a desired clinch angle. The movable cutters 24 then are retracted to their original positions and the anvil 10 is moved away from the component C.

To maintain a good clinch, that is to keep both the clinch length and clinch angle within their ranges of acceptable values, it is important to preserve desired geometrical relationships between the components of the anvil 10 and between the anvil 10 and the board B. In particular, it is desirable to keep constant both the distance or spacing a (see Fig. 3) between the upper surfaces of the board supports 22 and the under-surface of the board B and the distance or spacing b (see Fig. 3) between the tops of the movable cutters 24 and the cutting edges 20, 26. In fact, with the previously proposed anvil 10 as described above, it is difficult to maintain a good clinch. One reason for this is that, after a few weeks of use, the upper surfaces of the board supports 22 wear away.The reason for this is believed to be that the board supports 22 come into contact with the under-surface of the board B by virtue of the board B being pulled slightly downwardly during each clinching operation. Even though this contact is only momentary and, in principle, is not of an abrasive nature, in that it should not involve relative sliding movement (rubbing) between the board supports 22 and the board while they are in contact, it is believed that rubbing does in practice occur because significant wear does in practice take place. Another reason why it is difficult to maintain a good clinch is that the upper surfaces of the movable cutters 24 wear away as they cut and bend the component leads.

The foregoing problems are so severe that the anvil 10 can become so badly worn as to be unusable within a matter of only a few weeks.

As a consequence, the anvil 10 must be stripped down and at least the clinch bases 12 (and possibly also the movable cutters 24) must be replaced. This involves not only the loss of valuable production time, but the considerable cost of replacing the clinch bases and movable cutters.

A temporary expedient has been proposed in an attempt to lengthen the short usable lifetimes of the clinch bases 12. As shown in Fig. 5 of the accompanying drawings, which is a simplified representation of part of Fig. 2 on a reduced scale, and in Fig. 6, which is a view taken in the direction of an arrow VI in Fig. 5, a thin plate 28 whose upper portion has the same profile as the board support 22 (before it was worn) can be fitted (e.g. by brazing) to the side of one of the two anvil bases 12 of the anvil 10. This expedient has, however, been found to be unsatisfactory.

This is because the plate 28 will, like the worn board support 22 whose function it takes over, also wear away quickly. Further, when components of 5 mm pitch are mounted close together on a printed circuit board, whereas no difficulty is experienced when the plate 28 is not fitted, when the plate 28 is fitted it can crush the legs of a component closely adjacent the component whose legs are being clinched. This can result not only in an unacceptable tightening of the clinch of the adjacent component, but can cause damage to printed circuit tracks on the under-surface of the board as well as a poor clinch of the component then being clinched.

According to the present invention there is provided a lead clinching tool comprising: a pair of bases; a fixed cutter which is secured in place between the bases and which has a pair of cutting edges; and a pair of movable cutters which have respective cutting edges and which are movable such that the cutting edges thereof approach the cutting edges of the fixed cutter and cooperate therewith to cut a pair of leads that, in use, extend into the tool in predetermined directions, after which the cut leads are bent by movement of the movable cutters; wherein the positions of both the fixed cut ter and the movable cutters can be adjusted in directions substantially parallel to said predetermined directions.

By adjusting the positions of the cutters, the clinch can be adjusted to an optimum value from time to time, thereby permitting at least partial compensation for the effects of wear and increasing the useful lifetime of the tool.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which like references designate like items throughout, and in which: Figure 1 shows components that have had leads thereof inserted into holes in a printed circuit board, after which the leads have been clinched; Figure 2 is a side view of part of a previously proposed anvil (lead clinching tool), shown positioned ready to clinch the leads of a component; Figure 3 is a sectional view taken along a line Ill-Ill in Fig. 2; Figure 4 is a view corresponding to Fig. 3, but after clinching has taken place; Figure 5 is a simplified representation of Fig.

2 on a reduced scale, showing a plate fitted to one of a pair of #anvil bases of the anvil of Fig. 2 in an attempt to compensate for degradation of clinch quality caused by wear; Figure 6 is a view taken in the direction of an arrow VI in Fig. 5; Figure 7 is a side view of part of an anvil (lead clinching tool) embodying the present invention; Figures 8 and 9 show interior faces of respective ones of a pair of anvil bases of the anvil of Fig. 7; Figure 10 shows an adjustable fixed cutter of the anvil of Fig. 7; Figure 11 shows one of a pair of movable cutters of the anvil of Fig. 7; and Figure 12 is a view of the movable cutter of Fig. 11 in the direction of an arrow XII in Fig.

11.

An anvil 10' embodying the present invention will now be described with reference to Figs. 7 to 12 of the accompanying drawings.

The anvil 10' depicted in Figs. 7 to 12 resembles in many respects the previously proposed anvil 10 depicted in Figs. 1 to 4 and therefore will be described only in so far as it differs therefrom. In Figs. 7 to 12, items which correspond to items depicted in Figs. 1 to 4 are designated in most cases by the same references with prime superscripts.

The anvil 10' comprises a pair of steel anvil bases 12A, 12B which are mounted by screws or bolts (not shown) which extend through holes 14' in the anvil bases into tapped holes in a chassis or main body portion (not shown) of the anvil so that the anvil bases are positioned to confront one another as shown in Fig. 7. In contrast to the anvil bases 12 of the previously proposed anvil 10, the anvil bases 12A, 12B of the anvil 10' are not substantially identical.

The anvil base 12A of the anvil 10', like the anvil bases 12 of the anvil 10, has a board support 22' which may be dimensioned similarly to the board supports 22 of the anvil bases 12 of the anvil 10. However, the board support 22' is not formed integrally with the anvil 12A. Instead, it comprises part of a tungsten carbide insert 30 which is secured (for example by brazing or soldering) into the anvil 12A.

In contrast to the anvil bases 12 of the anvil 10, the confronting faces 32, 34 of the anvil bases 12A, 12B of the anvil 10' do not have the members 16, which cooperate to form the fixed cutter, formed integrally therewith. Instead, the fixed cutter 18' is formed entirely separately and is demountably attached to the face 34 of the anvil 12B. More specifically, the fixed cutter 18' fits into a groove 36 (Fig. 9) in the face 34 of the anvil 1 2B and is secured in place by bolts or screws 38 (Fig. 7) that extend through a slot 38 (Fig. 9) into tapped holes 40 (Fig. 10) in the fixed cutter 18'.The fixed cutter 18' is a sliding fit in the groove 38, whereby its position can be adjusted, by loosening the bolts or screws 38 and moving the fixed cutter, in a direction paerallel to that in which the leads L extend, in use, into the anvil 10': namely, in the usual condition of use, in a vertical direction.

As can be seen from Fig. 10, the fixed cutter 18' has a pair of cutting edges 20' which are formed on a tungsten carbide insert 42 (shown cross-hatched) which is secured (for example by brazing or soldering) to a main body portion of the fixed cutter. At its other end, the fixed cutter 18' comprises a like tungsten carbide insert 42 which has formed thereon another pair of cutting edges 20'. The fixed cutter 18' thus can be installed either way up in the groove 26 in the face 34 of the anvil 12B whereby, at any one time, either one of the pairs of cutting edges 20' can be used in cutting the leads L of a component C.

The anvil 10' further comprises a pair of like movable cutters 24', one of which is shown in Figs. 11 and 12. The movable cutters 24' of the anvil 10' can be constructed and operated in like manner to the movable cutters 24 of the anvil 10, though they differ therefrom as follows. First, an upper portion 44 (shown cross-hatched) of each movable cutter 24', which portion defines both the cutting edge 26' and the upper surface which is contacted by the component leads as they are bent, comprises a tungsten carbide insert which is secured (for example by brazing or soldering) to a main body portion of the movable cutter.

Second, apertures 46, by way of which each movable cutter 24' is secured by bolts or screws (not shown) to the actuator means (not shown) for moving the movable cutters 24', are in the form of slots so as to enable the positions of the movable cutters 24' to be adjusted, by loosening the bolts or screws and moving the cutters, in directions parallel to that in which the leads L extend, in use, into the anvil 10': namely, in the usual condition of use, in vertical directions.

The anvil 10' preferably is provided with an electrical continuity test facility, which also is provided in the previously proposed anvil 10.

Accordingly to this facility, the fixed cutter and the movable cutters are electrically isolated from one another and are connected to external circuitry which checks that a short circuit is established between each moveable cutter and the fixed cutter, via the leads L, as the leads are cut. Failure to pass this test indicates that there has been an operating error in that the presence of both leads is necessary if the test is to be passed.To accomplish the necessary electrical isolation, in the anvil 10', between the movable cutters 24' and the fixed cutter 18, those surface portions of the anvils 12A, 128 which contact the fixed and movable cutters (and the bolts or screws 38) directly, and also the under-surfaces of the anvil bases, which may electrically contact the movable cutters indirectly via the chassis or main body portion of the anvil, are coated with an electrically insulative coating, which may be formed by spraying on aluminium oxide. In the case of the anvil 12A, the coating is effected after the tungsten carbide insert 30 has been secured in place.

The anvil 10' is operated and used in the same manner as described above for the previously proposed anvil 10 in order to clinch the leads L of the components. However, by virtue of the advantageous features described below, the anvil 10' has a much greater useful lifetime, thereby reducing lost production time and reducing the cost of frequently replacing expensive parts thereof.

Since the board support 22' of the anvil is of a highly abrasion-resistant material, namely tungsten carbide, the problem of degradation of clinch quality experienced with the anvil 10 due to wearing away of the board supports 22 is greatly reduced. Similarly, the problem of degradation of clinch quality due to wearing away of the upper surfaces of the movable supports that are contacted by the leads as they are bent also is reduced, in the anvil 10', by virtue of the upper surfaces being defined by the tungsten carbide inserts 44 of the movable cutters 24'. These measures alone greatly increase the useful lifetimes of the anvil bases and movable cutters, respectively.

However, when significant wear eventually does take place, the degradation in clinch quality can be compensated for by adjusting the positions of the fixed cutters 18' and the movable cutters 24' as described above, thereby even further increasing the lifetime of the anvil. Such adjustment can be carried out from time to time to optimise the clinch. Raising the cutters reduces the clinch length and lowering them increases the clinch length.

It is anticipated that the use of the tungsten carbide board support 22', together with the above-described feature of adjustability of the fixed cutter 18' and movable cutters 24', may provide a useful lifetime of maybe six months or more for the anvil base 12A of the anvil 10', which contrasts with a useful lifetime of only a few weeks for the anvil bases 12 of the anvil 10. Clearly, the need for much less frequent replacement of the anvil bases can save a lot of expense. Further, it is to be noted that, in the anvil 10', the anvil base 12B is not subject to the board support wear problem. The anvil base 12B has an indefinitely long lifetime and does not need to be replaced when the anvil base 1 2A eventually has to be replaced due to wearing away of the board support 22'.

In this connection, the tungsten carbide board support 22' provides such good wear resistance that, in the anvil 10', in contrast to the anvil 10, only one of the anvil bases (the anvil base 12A) need be provided with a board support. It is, however, possible for each of the anvil bases 12A, 12B to be provided, if desired, with a tungsten carbide board support.

The degradation of clinch quality due to wear, in the case of the previously proposed anvil 10, produces such a short lifetime of the anvil bases 12 and movable cutters 24 that blunting of the cutting edges 20 of the fixed cutter 18 formed integrally with the anvil bases and the cutting edges 26 of the movable cutters is not a significant problem in that the cutting edges are removed when these components are replaced due to clinch quality degradation. (However, should blunting of the cutting edges 20 take place before the short lifetime of the anvil bases 12 has expired, both anvil bases will, nonetheless, have to be replaced). The great increase in lifetime of the corresponding components in the case of the anvil 10' means that the problem of blunting of the cutting edges deserves more consideration.

The fact that, in the anvil 10', the fixed cutter 18' is demountably secured in place enables the cutting edges 20' to be removed, by replacement of the fixed cutter, without at the same time having to scrap the anvil bases 12A, 12B. Further, the fact that all of the cutting edges 20' and 26' of the anvil 10' are formed on tungsten carbide inserts will considerably increase their lifetimes, probably by a factor of at least about 4 as compared to high speed cutting steel as used for the cutting edges 20 and 26 of the anvil 10.Still further, the fact that the fixed cutter 18' of the anvil 10' is provided with two sets of cutting edges 20', whereby its lifetime can be doubled when one of the pairs of cutting edges is worn out simply by positioning the fixed cutter the other way up and using the other pair of cutting edges, means that the fixed cutter 18' should have a useful cutting lifetime which is at least about eight times that of the cutting edges 20 of the fixed cutter 18 formed integrally with the two anvil bases 12 in the anvil 10. Furthermore, it may be possible to regrind the cutting edges 20' of the fixed cutter 18' so that it can be reused at least once.

As indicated above, the anvil 10' is believed to be much cheaper to operate than the anvil 10 in that it is not necessary to replace both the anvil bases and the movable cutters frequently: in particular, it is not necessary to replace the rather expensive anvil bases every few weeks. Furthermore, it is expected that use of the anvil 10' should substantially reduce lost production time, thereby increasing production, and should lead to an overall improvement in clinch quality.

Claims (10)

1. A lead clinching tool comprising: a pair of bases; a fixed cutter which is secured in place between the bases and which has a pair of cutting edges; and a pair of movable cutters which have respective cutting edges and which are movable such that the cutting edges thereof approach the cutting edges of the fixed cutter and cooperate therewith to cut a pair of leads that, in use, extend into the tool in predetermined directions, after which the cut leads are bent by movement of the movable cutters; wherein the positions of both the fixed cutter and the movable cutters can be adjusted in directions substantially parallel to said predetermined directions.

2. A tool according to claim 1, wherein a part of at least one of said bases which, in use, may contact a board from which the leads extend, comprises an insert of tungsten carbide.

3. A tool according to claim 2, wherein one only of said bases has a said part which, in use, may contact said board.

4. A tool according to claim 1, claim 2 or claim 3, wherein the fixed cutter comprises two pairs of cutting edges and can be secured in place in either of two positions, in each of which a respective one of said two pairs of cutting edges can cooperate with the cutting edges of the movable cutters.

5. A tool according to any one of the preceding claims, wherein the cutting edges of the fixed cutter are formed on at least one tungsten carbide insert.

6. A tool according to any one of the preceding claims, wherein upper surfaces of the movable cutters which are contacted by the leads as the leads are bent comprise surfaces of tungsten carbide inserts.

7. A tool according to claim 6, wherein the cutting edges of the movable cutters are formed on the tungsten carbide inserts.

8. A tool according to any one of the preceding claims, wherein the fixed cutter comprises a unitary member which is demountably secured in place.

9. A tool according to claim 8, wherein the fixed cutter is demountably secured to one only of said bases.

10. A lead clinching tool substantially as herein described with reference to Figs. 7 to 12 of the accompanying drawings.