GB2055648A - Apparatus for applying a nut to a workpiece - Google Patents

Abstract

A nut-installation head for self- piercing clinch nuts 28 in a panel 36 is provided with a relatively stiff resilient block 37 of urethane material, between the head housing 11 and the mounting plate 17. The block surrounds a nut punch 13 which passes through an aperture 38 in the block. When the mounting plate 17 is lowered towards the panel 36, the bottom face 31 of the housing first meets and rests on the panel 36, supported by the opposing die 34. When the descending plate 17 meets the urethane block 37, it compresses the block so as to apply sufficient force to the panel to cause it to deform around the top 35 of the die 34. This deformation or embossing of the panel is completed before the bottom nut 30 pierces the panel. <IMAGE>

Description

SPECIFICATION Apparatus for applying a nut to a workpiece Apparatus and methods for applying a nut to a workpiece are well known. Such nuts are commonly known as clinch nuts, since the nut is secured to the workpiece (which is typicaily a sheet metal panel) by clinching the corners or sides of the rectangular nut body to the panel. Clinch nuts are usually applied to panels by installation in preformed holes. A specialised form of clinch nut is the pierce nut, which pierces its own hole in the panel on, or just before, installation.

The metal panel is usually thinner than the nut, so that the nut projects from the panel on at least one side thereof and usually on both sides, and indeed this is necessary for the installed nut to adequately resist removal from the panel. For certain purposes it is necessary that one face of the nut should be flush with the panel face. Consequently the practice has arisen of making a local deformation in the panel, around the portion occupied by the nut, so that the local part of the panel in which the nut is installed is displaced away from the body of the panel but parallel thereto, so that the installed nut has one face flush with the body of the panel. Such a deformation process is known in the art as embossing.

Where the hole in the panel is preformed, it may not involve much more work to also preform the emboss. However, with a pierce nut which is installed in one stroke of an installation head which both pierces the hole and applies the nut to the panel, it is desirable in practice to be able to form the emboss as well, in the same stroke of the installation head.

One apparatus which does this operates so as to first secure the nut in the flat panel and thereafter form the emboss. It has been found, however, that the bending of the panel when the emboss is formed tends to pull the panel out of engagement with the installed nut, and thereby weaken the resistance of the nut to removal from the panel. Consequently it is desirable to provide apparatus for applying a nut to a workpiece, in which the emboss of the panel is completed before the nut is applied to the panel.

Accordingly, the present invention provides apparatus for applying a nut to a workpiece, which apparatus comprises: a housing having a passage therethrough; a punch reciprocable in the passage, one end (the leading end) of the punch being adapted, on movement through the passage in the appropriate direction, to apply a nut from within the passage to a workpiece adjacent one end of the passage; the other end of the punch protruding from the housing and being secured to a mounting member; a surround portion on the housing surrounding the aforesaid one end of the passage:: and a resilient member positioned between the mounting member and the housing and surrounding the protruding portion of the punch; whereby when the mounting member and punch are advanced towards a workpiece positioned between the surround portion and a co-operating die opposite thereto, the surround portion on the housing first meets the workpiece and deforms it in co-operation with the die under the resilient urging of the resilient member which applies force to the housing whilst allowing relative movement between the housing and the punch as the mounting member advances; and the leading end of the punch thereafter applies the nut to the workpiece after deformation thereof by the surround portion is substantially complete.

In a preferred embodiment of the invention, the resilient member is accommodated within the common, overlying lateral extent of the mounting member and the adjacent face of the housing. Preferably the resilient member comprises a body of elastomeric material with an aperture therethrough, through which the protruding portion of the punch passes.

A specific embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, which: Figures 1 to 5 are similar side elevations and partial sections through a nut installation head embodying the invention, showing respectively successive stages in the formation of the emboss and the placing of a nut; Figure 6 is a plan view of the head; and Figures 7A and 7B are respectively a plan and elevation of the resilient member.

The nut installation head of this example is for placing pierce nuts which are supplied in strip form, and in this example is arranged for placing nuts in a vertically downwards direction into a horizontally positioned metal panel.

The head comprises a strong rigid housing 11 having a straight vertical passage 1 2 of rectangular cross-section extending completely through it. A steel punch 1 3 of rectangular cross-section is a sliding fit in the passage 11.

The punch is reciprocable in the passage and has its lower end portion 1 4 of reduced crosssectional dimensions, terminating in a lower end face 15.

The installation head of this particular example also has a vertical ram 1 6 which is also reciprocable with respect to the housing 11.

The upper ends of the punch 1 3 and ram 1 6 are secured to a steel mounting plate 1 7 which overlies the top face 1 8 of the housing, and as shown in ghost in Fig. 6, is of greater width and length than the housing 11.

A helical compression spring 20 is provided between the mounting plate 1 7 and the housing 11. It is positioned intermediate the punch 1 3 and ram 16, and its upper end is received in a shallow recess in the mounting plate 1 7 and its lower end in a rather deeper recess in the top of the housing 11. The effect af the spring 20 is to resiliently urge the housing downwardly away from the mounting plate 1 7 and thus to urge the punch 1 3 and ram 1 6 upwardly with respect to the housing 11. The limits of travel of the housing 11 with respect to the punch 1 3 and ram 1 6 are determined by stop means (not shown).

Nuts in the form of a strip 1 9 (best seen in Fig. 2) are fed into the head and through a horizontal guideway 21 which opens into the passage near the bottom end thereof. Mechanism for feeding the nut strip one nut at a time towards the passage includes a nut feed pawl 22 operated by means (not shown) actuated by the downwards movement of ram 1 6 in housing 11.

A pivoting safety stop 23 is provided in a slot 24 on the opposite side of the passage 12 to the opening of guideway 21. When the punch 1 3 is in its uppermost position, clear of guideway 21, the lower end of the stop is moved across the passage 1 2 towards guideway 21 to prevent undesired feed of the nut strip across the passage 1 2. As the punch descends, the upper end of the stop 23 can move into a groove (not shown) ;n the side of the punch 1 3 thereby retracting the lower end of the stop and allowing feed of the :?ading nut 26 of the strip 1 9 into the passage.

The lowermost part 27 of the passage 1 3 is of somewhat reduced cross-section dimensions, in order to accommodate a stack 28 of nuts, below the bottom face 1 5 of the punch.

This stack is prevented from falling out of the passage under the urging of gravity by suitable restraining means (not shown), e.g. knifeedge ribs, spring-ball catches or sprung runners. The lowermost part 27 of the passage is provided in a downwardly-projecting extension or nose 29 of the housing which nose is, in this particular example head, provided as a separate part detachable from the remainder of the housing. The lower end of passage 1 2 opens into the lower face 31 of the nose 29 in a shallow recess 32 which surrounds the end of the passage and has sloping sides 33.

The head is installed in a press by securing the mounting plate 1 7 to the upper movable part of the press (not shown). Secured to the bottom fixed part of the press (not shown) is a die 34. This die is aligned with the housing and has a top flange 35 which is substantially complementary in shape to the nose recess 32. It also has an interior throat (not shown) and clinching means (not shown), the functions which will be described later.

Ignoring for the moment the application of the present invention to the installation head of this example, the head functions as fol lows: A metal panel 36, in which a nut is to be installed, is placed on top of the die 34, as shown in Fig. 1, which also shows the head in its uppermost or starting position. The housing is held at its lowermost position with respect to the punch 1 3 and nut strip feed actuating ram 1 6 by the urging of the spring 20. The press is actuated, to progressively advance the head towards the panel 36 and die 34.

The first thing that happens is that the underface 31 of the nose 29 contacts the top of the panel 36. The stiffness of the panel, supported by the die 34, is sufficient to overcome the urging of spring 20, and the downward movement of the housing is arrested whilst the punch 1 3 and ram 1 6 continue to advance. The relative advance of the ram 1 6 into the housing actuates the nut strip advance mechanism to feed the nut strip 1 9 forwards, the stop 23 being withdrawn as the punch 1 3 advances.By the time the bottom face 1 5 of the punch 1 3 approaches the top of the nut strip, the leading nut 26 is correctly positioned in the passage 1 2. The punch continues to advance, and severs the leading nut 26 from the strip. The nut is carried down to the top of the stack 28 of nuts below it.

The punch continues to advance downwardly, and contacts the top of the augmented stack of nuts. It pushes the stack downwards through the lowermost part 27 of the passage 12, ejecting the lowermost nut 40 from the bottom end of the passage and forcing it against and into the panel 36. The panel is supported by the die 34, and the leading part of the nut, in co-operation with the die, punches out a slug from the panel, the slug failing out through the interior throat in the die. As th nut advances through the panel, the clinching means in the die deform parts of the nut (and maybe parts of the panel adjacent thereto) to secure the nut to the panel. The movement of the press then stops and reverses. The mounting plate 1 7 is raised, allowing spring 20 to expand to urge the punch 1 3 and ram 1 6 upwardly through the housing 11, to return to their initial positions. Towards the end of the upwards press stroke the housing nose 29 separates from the panel 36 on the die 34, allowing removal of the panel and installed nut.

The pierce nut installation head and its operation, so far as described above, are well known in the art. Such a system is commer cialiy available in the United Kingdom under the trade nark SYSTEM MF.

The combination of the recess 32 under the nose 29 and the complementary configuration of the top 35 of the die, as described above, has been used on prior art nut installation apparatus to produce embossing, as previ ously mentioned. However, in the applicants' experience such embossing weakens the resistance of the nut to removal from the panel. It seems that this is due to the emboss being formed while the nut is punching its hole in the panel and/or while the nut is being clinched into locking engagement with the panel. The embossing action stretches the panel and pulls the part of the panel immediately adjacent the nut away from the nut, during and/or after the punching and/or clinching operations.

The nut installation apparatus embodying the present invention provides for the emboss ing action to be completed before the nut starts punching its hole in the panel. It incorporates a resilient member, positioned between the mounting member 1 7 and the housing 11 and surrounding the punch 1 3. In this example, the resilient member is provided in the form of a rectangular block 37 of polyurethane elastomeric material, having through it a rectangular section aperture 38 in which the punch 1 3 is a sliding fit. The polyurethane block rests on the top face 1 8 of the housing 11, and on its top face is provided with a steel backing plate 39. The polyurethane block is resilient but is very much stiffer than the spring 20.The thickness of the block 37 is about one third of the maximum distance between the bottom of the mounting plate 1 7 and the top face 1 8 of the housing 11. The function of the elastomeric block 37 will be apparent from the following description.

The function of the installation head is generally the same as has been already described, and the differences due to the presence of the block 37 will be pointed out.

The head starts from the initial or uppermost position illustrated in Fig. 1. The underface of the nose 29 contacts the top of the panel 36. The panel arrests movement of the head, relative to the punch 1 3 and ram 16, causing feeding of the nut strip. On continued advance of the mounting plate 1 7 downwards, the underface of the mounting plate contacts the washer 39 on top of the elastomeric block 37, as illustrated in Fig. 2. At this position, the bottom end 1 5 of the punch has not quite reached the leading nut 26 which it is about to shear from the strip 1 9.

As the mounting plate 1 7 continues to descend, it is now applying force to the housing 11 and nose 29 through the elastomeric block 37, which is very much stiffer than the spring 20. The block is sufficiently stiff to transmit enough force to cause the panel 36 to deform and emboss, as illustrated at 41 in Fig. 3, moulded between the faces of the recess 32 under the nose and the top flange 35 of the die. The embossing is completed when the panel can deform no more, and the underface 31 of the nose 29 has sandwiched the part of the panel 36 surrounding the emboss 41 against the part of the die 42 surrounding the die top 35. As illustrated in Fig. 3, the force required to complete the emboss may be sufficient to cause deformation of the elastomeric block 37.

However, as also illustrated in Fig. 3, at the completion of the embossing process, the bottom nut 40 of the stack has not reached the panel 36. In this particular example, when the emboss is complete there is a finite gap between the bottom nut 40 and the panel, and this gap has been measured at 0.5 mm.

(i.e. 20 thousandths of an inch). This gap is shown at 43 in Fig. 3 (slightly exagerated for clarity of illustration).

Thereafter the housing 11 does not descend any further, but the punch 1 3 does, bringing the bottom nut 40 into contact with the panel 36, as illustrated in Fig. 4. This relative movement between the punch 1 3 and housing 11 further corn presses the elastomeric block 37 (and the weaker spring 20). It is only now that punching of the sheet 36 by the nut 40 starts, on further descent of the punch 1 3. The clinching of the nut 40 to the panel 36 follows, and the clinching process is finally completed with the apparatus in the position shown in Fig. 5.

Thus the nut installation head of the foregoing example operates in such a way that the emboss of the panel is completed before the nut is applied to the panel.

The provision of the resilient block 37 between the mounting plate 1 7 and the top of the housing 11, and surrounding the punch 13, has the benefit that the force transmitted by the block to the housing is directly in line with the surround portion i.e. the recess 32 including faces 33 and the immediately surrounding face 31 of the nosepiece, thereby minimising forces which might tend to tilt the head. As illustrated in Fig. 6, the elastomeric block is accommodated entirely within the common, overlying lateral extent of the mounting plate 1 7 and the adjacent face 1 8 of the housing. This means that the lateral dimensions of the housing are not increased due to the provision of the elastomeric block.

One example of a suitable polyurethane elastomeric material for the resilient member is that which is commercially available under the designation FLEX-I-CAST formula No.

1017, and is manufactured from Du Pont ADIPRENE material.

The invention is not restricted to the details of the foreging example. For instance, there need not necessarily be a positive gap left between the bottom nut 40, and the panel 36, at the completion of the emboss. In other words, the nut could be in contact with the panel, provided that deformation due to the embossing action is substantially completed before the nut starts to punch its hole in the panel, so that deformation movement of the panel due to the embossing does not draw panel material away from contact with the nut and thereby reduce its resistance to removal from the panel.

Claims (4)

1. Apparatus for applying a nut to a workpiece, which apparatus comprises: a housing having a passage therethrough; a punch reciprocable in the passage, one end (the leading end) of the punch being adapted, on movement through the passage in the appropriate direction, to apply a nut from within the passage to a workpiece adjacent one end of the passage; the other end of the punch protruding from the housing and being secured to a mounting member; a surround portion on the housing surrounding the aforesaid one end of the passage; and a resilient member positioned between the mounting member and the housing and surrounding the protruding portion of the punch;; whereby when the mounting member and punch are advanced towards a workpiece positioned between the surround portion and cooperating die opposite thereto, the surround portion on the housing first meets the workpiece and deforms it in co-operation with the die under the resilient urging of the resilient member which applies force to the housing whilst allowing lost motion between the housing and the punch as the mounting member advances; and the leading end of the punch .hereafter applies the nut to the workpiece after deformation thereof by the surround portion is substantially complete.

2. Apparatus as claimed in claim 1, in which the resilient member is accommodated within the common, overlying lateral extent of the mounting member and the adjacent face of the housing.

3. Apparatus as claimed in claim 1 or claim 2, in which the resilient member comprises a body of elastomeric material with an aperture therethrough, through which the protruding portion of the punch passes.

4. Apparatus for applying a nut to a workpiece, substantially as hereinbefore described with reference to, and illustrated in, the accompanying drawings.