GB2174627A - A method of reducing stress in metallic articles having a bend therein and metallic articles produced using such a method - Google Patents

Abstract

A through slit or slot (10) is formed in the article (2) in an area stressed by the bending operation prior to at least the last bending operation forming the bend, the slit or slot (10) extending, parallel to the bend, to an edge of the material forming the article so that the slit or slot is open ended. The article is a yoke or lever of a windscreen wiper blade and arm assembly. <IMAGE>

Description

SPECIFICATION A method of reducing stress in metallic articles having a bend therein and metallic articles produced using such a method This invention relates to a method of reducing stress in metallic articles having a bend therein and to merallic articles produced using a such a method.

The yokes and levers of windscreen wiper blades, particularly primary yokes and levers, are usually formed from flat stock using piercing, blanking and forming operations. Thus the yoke or lever has the form of an inverted channel and is provided with articulation points at its ends, often in the form of depending ears. The yoke or lever is initially formed such that the ear portions, which will eventually lie substantially parallel to each other, take up an outwardly inclined position to enable assembly of the joints. In assembling the joints, the ears are again bent towards each other so as to encompass knuckle joint trunnions, secondary yokes or levers etc.

Considerable use is made of low cost materials such as that known as "Galvatite" which comprises a mild steel with a zinc coating applied by hot dipping. Other such materials include electroplated materials, painted materials and materials with a surface treatment such as an anodising treatment. The use of such a material is generally satisfactory providing that the coating or finish remains intact. Otherwise, as is generally appreciated, corrosion problems can occur under extreme environmental conditions as a result of moisture penetrating the surface coating or finish and attacking the mild steel or other material therebeneath.

The amount of bending and other forming which can be carried out on these low cost metals without sufficient stress being set up to cause some disruption of the coating or finish is limited. Thus, in the case of the articulation points of yokes or levers subject to two bending or forming operations, difficulties can arise as a result of disruption of the coating and corrosion has been shown to occur, under extreme environmental conditions.

The present invention seeks to provide a method of reducing the stress in metallic articles having bend therein to the extent that corrosion problems are significantly reduced and to provide an article having increased corrosion resistance.

According to a first aspect of the invention there is provided a method of reducing the stress in a metallic article having a bend therein comprising forming a through slit or slot in the article in an area stressed by the bending prior to at least the last bending operation forming the bend, the slit or slot extending, parallel to the bend, to an edge of the material forming the article so that the slit or slot is open ended.

Preferably the slit or slot is formed in the article prior to any bending operation used to form the bend.

The slit or slot may be spaced from the line of the bend.

According to a second aspect of the invention there is provided a method of producing a yoke or lever for a windscreen wiper blade comprising, taking a flat metal strip, forming a through slit or slot in the strip parallel to the longitudinal axis of the strip at a position or positions corresponding to the end or ends of the completed yoke or lever such that the slit or slot extends to the end of the completed yoke or lever so as to be open ended, bending the strip into inverted channel shape with the end or ends of the channel having the slit or slot therein splayed apart and thereafter further bending the splayed apart end or ends towards each other about a knuckle element, secondary yoke or lever or other element to which the yoke or lever is to be articulated.

According to a third aspect of the invention, there is provided a metallic article having a bend therein wherein the article has a through slit or slot therein in an area of the article stressed by the formation of the bend the slit or slot extending, parallel to the bend, to an edge of the material forming the article so that the slit or slot is open ended.

According to a fourth aspect of the invention, there is provided a yoke or lever for a windscreen wiper blade comprising an element of inverted channel shape having articulation points at one or both ends at which it is to be articulated to a knuckle element, secondary yoke or lever or other element wherein the base of the channel has, at the said end or ends, and open ended through slit or slot extending from the said end or ends longitudinally of the channel.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which:~ Figure 1 is a perspective view of the connection between a primary yoke or lever and a secondary yoke or lever of a windscreen wiper blade showing the corrosion problem which can exist with current methods; Figure 2 is a perspective view similar to Fig.

1 in which a slit or slot has been formed in the end of the primary yoke or lever in accordance with the invention; Figure 3 is a sectional view of the end of the primary yoke or lever after initial forming and painting; Figure 4 is a sectional view similar to Fig. 3, but showing the end of the primary yoke or lever after postforming, the secondary lever and connector being omitted for clarity; Figure 5 is a perspective view similar to Fig.

2 showing the invention applied to a primary yoke with a direct articulation to a secondary yoke; Figure 6 is a perspective view similar to Fig.

5, but showing the use of a stabilising rib, and Figure 7 is an exploded view of the parts of the joint of Fig. 6 showing the parts ready for assembly.

Referring firstly to Fig. 1, there is shown a joint 1 between a primary yoke or lever 2 and a secondary yoke or lever 3 of the blade of a windscreen wiper. This figure shows the known form of joint. In the version shown, both the primary yoke or lever 2 and the secondary yoke or lever 3 are made of metal and a knuckle element 4 is provided between the yokes or levers to prevent contact between them and to provide for pivotting between them. To this end the knuckle element 4 is provided with exterior trunnions 5 which cooperate with apertures 6 in the primary yoke or lever 2 and interior trunnions (not shown) cooperating with apertures in the secondary yoke or lever 3. Both the primary and secondary yokes or levers have depending ears (those of the primary yoke or lever being shown at 7) which provide an additional surface areas for accommodating the apertures for the trunnions.

In the construction of the primary yoke or lever 2, a flat strip of metal is used. This, in the present instance, is formed of Galvatite.

The strip is pierced and blanked into the requisite flat blank and then the blank is formed into a channel section of generally inverted "U" shape with the portions of the yoke or lever carrying the ears 7 being splayed. This stage is shown, in the case of the present invention, at Fig. 3. The yoke or lever 2 is then subjected to phosphate pretreatment and is painted using an anodic electrophoretic process. The secondary yoke or lever is also produced in the same way.

In order to assemble the blade harness and, in particular, the joint 1, the knuckle element 4 is placed arround the secondary yoke or lever so as to engage its inner trunnions in the apertures of the secondary yoke or lever. The end of the primary yoke or lever 2 is then placed over the knuckle element 4 and the ears 7 are bent towards each other to engage the exterior trunnions 5 in the apertures 6.

This is the position of the ears 7 shown in Fig. 4.

Tests carried out on this form of construction have shown that corrosion problems can occur in the dotted area marked 8 in Fig. 1. In order to overcome this problem, it is proposed to provide a slit or slot 10 in the end of the primary yoke or lever as shown in Fig.

2. This slit or slot is formed in the original strip when producing the blank and, in the finished joint as shown in Fig. 3, extends to the edge of the material so that the slit or slot 10 is open ended. The effect of the slit or slot 10s is is to reduce the stress in the material and its surface coating or finish, which is caused by the dual bending operation of the ears 7 and thus reduce any damage to the zinc coating of the material and to the paint covering thereof.

Tests on the completed blade have shown that any corrosion problems associated with the dual bending operation are substantially reduced.

Fig. 5 shows the invention applied to the end of a primary yoke where the secondary yoke is constructed from plastics material. In this case, the trunnions are formed directly on the secondary yoke and no knuckle element is provided. It is also to be noted that the yoke or lever 3 is not of substantially the same dimensions throughout its length but is formed with a larger dimensioned portion 9 outside the yoke or lever 2. In this way, a shoulder is provided facing the end of the yoke or lever 2 which effectively protects the end in the same way as the knuckle element 4. The assembly operation is otherwise indentical to that previously described in connection with Figs. 2 to 4.

Figs. 6 and 7 show an embodiment of the invention similar to Fig. 5. The difference from Fig. 5 consists in the provision of a rib 12 on the upper surface 14 of the reduced dimension part 15 of the yoke or lever 3. The construction of the yoke or lever 3 can clearly be seen from the exploded view of Fig. 7. As can be seen from Fig. 6, the rib 12 fits into the slit or slot 10 in the yoke or lever 2 and is a fairly close fit therein. However, there must be sufficient play to enable the pivot to operate.

By careful selection of the inner dimensions of the slit or slot 10 and the external dimensions of the rib 12, a satisfactory pivoting action can be obtained while at the same time the arrangement provides a stiffening up of the joint in the transverse direction, preventing any significant lateral flexing between the two yokes or levers. In addition, the presence of the rib 12 occupies the major part of the slit or slot 10 and thus increases the aesthetic appearance of the joint while at the same time reducing the ingress of dirt into the joint.

It is also to be noted that the exploded view of Fig. 7 shows the parts in their preassembly condition. Thus the final bending of the yoke or lever 2 has still to be carried out.

For the best results, the slit or slot 10 should extend to beyond the region of the ears 7. Suitable dimensions or the slit or slot include a width of about twice the thickness of the material used. However, a compromise is required in that while the slit or slot should be of sufficient dimensions to ensure stress relief, these dimensions should not so large that the strength of the structure is impaired.

It will be appreciated that modifications may be made to the above described embodiment without departing from the scope of the invention. For example, more than one slit or slot may be provided in a single stress area.

The shape of the slits or slots may be varied.

For example, they could be tapered either towards or away from the edge of the material.

While the provision of a rib 12 has only been shown in Figs. 6 and 7, it will be understood that the rib could equally well be applied to the plastics knuckle element 4 shown in Fig. 2.

The creation of the slits or slots does not necessarily take place in the formation of the original blank although this is believed to be desirable. Where the problem occurs with two bending operations, the slits or slots could be formed in the material between the two bending operations. In any event, even with more than two bending operations, the slit or slot must be formed prior to the last bending operation.

It is to be understood that while the invention as shown has been applied to the joint between a primary yoke or lever of a windscreen wiper blade and a secondary yoke or lever, it could equally be applied to the joints betwen secondary levers and secondary yokes for example.

It will also be understood that the invention is not limited to windscreen wiper applications but is applicable to any situtation in which bending causes undesirable stress in the metal being bent.

Claims (13)

1. A method of reducing the stress in a metallic article having a bend therein comprising forming a through slit or slot in the article in an area stressed by the bending operation prior to at least the last bending operation forming the bend, the slit or slot extending, parallel to the bend, to an edge of the material formiag the article so that the slit or slot is open ended.

2. A method as claimed in claim 1, wherein the slit or slot is formed in the article prior to any bending operation to form the bend.

3. A method as claimed in claim 1 or 2, wherein the slit or slot is spaced from the line of the bend.

4. A method of producing a yoke or lever for a windscreen wiper blade comprising taking a flat metal strip, forming a through slit or slot in the strip parallel to the longitudinal axis of the strip at a position or positions corresponding to the end or ends of the completed yoke or lever such that the slit or slot extends to the end of the completed yoke or lever so as to be open ended, bending the strip into inverted channel shape with the end or ends of the channel having the slit or slot therein splayed apart and thereafter further bending the splayed out end or ends towards each other about a knuckle element, secondary yoke or lever or other element to which the yoke or lever is to be articulated.

5. A method as claimed in claim 4, wherein the slit or slot is formed at both ends of the yoke or lever.

6. A metallic article having a bend therein wherein the article has a through slit or slot therein an area of the article stressed by the formation of the bend, the slit or slot extending, parallel to the bend, to an edge of the material forming the article so that the slit or slot is open ended.

7. An article as claimed in claim 6, wherein the slit or slot is spaced from the line of the bend.

8. A yoke or lever for a windscreen wiper blade comprising an element of innverted channel shape having articulation points at one or both ends at which it is to be articulated to a knuckle element, secondary yoke or lever or other element wherein the base of the channel has, at the said end or ends, an open ended through slit or slot extending from the said end or ends longitudinally of the channel.

9. A yoke or lever as claimed in claim 8, wherein the slit or slot is spaced from the side walls of the channel.

10. A method of reducing the stress in a metallic article having a bend therein substantially as described herein with reference to any of Figs. 2 to 7 of the drawings.

11. A method of producing a yoke or lever for a windscreen wiper blade substantially as described herein with reference to any of Figs.

2 to 7 of the drawings.

12. A metallic article having a bend therein substantially as described herein with reference to any of Figs. 2 to 7 of the drawings.

13. A yoke or lever for a windscreen wiper blade substantially as described herein with reference to any of Figs. 2 to 7 of the drawings.