GB2280392A - Laminated pressings - Google Patents

Abstract

A laminar article such as a catalyst heat shield for vehicle exhausts or body panels is formed by placing two sheets of steel 10, 12 of dissimilar thickness in contact, spot welding them together, and pressing them together in a standard transfer press. The resulting laminar article is less susceptible to vibration than standard pressed articles of a single layer. <IMAGE>

Description

LAMINATED PRESSINGS The present invention relates to the production of articles by pressing sheets of material into desired shapes, and to articles made in this way.

A wide variety of articles are made by pressing sheets of material, usually metal. These include many parts of vehicles such as boay panels and silencer and catalyst casings. In applications such as this there is a requirement to prevent the pressed components from vibrating to reduce noise and fatigue. This is conventionally done by attaching stiffening ribs or vibration damping masses to the pressed components.

However these methods are time consuming and costly and add to the weight of the complete component.

Accordingly the present invention provides a method of forming a pressed article comprising the steps of providing at least two sheets of material having different vibration characteristics, placing the sheets in contact with one another and deforming the sheets together to form a laminar pressed article.

Preferably the method further includes the step of fastening the sheets together at at least one point prior to the deforming step. This helps to ensure that the sheets are deformed in substantially the same way as each other.

Preferably the sheets are of dissimilar thickness, and they may be of different material.

The present invention also provides an article made according to the method of the invention.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sequence illustrating a method according to the invention, Figures 2 is a top view of an article made according to the method of the invention, and Figures 3 and 4 are sections on lines III-III and IV-IV through the article of Figure 2 Referring to Figure 1, in an example of the method of the invention two sheets of steel 10, 12 are placed incontact, one on top of the other on the transfer equipment of a standard transfer press, and spot welded together at the points indicated by the arrows A and B. The positions of the spot welds is not critical as they only serve to ensure that the two sheets do not slide relative to one another during the pressing process.They are then passed to the first pressing stage 13 as shown in Figure lb where they are deformed between the upper and lower parts 14, 16 of a press tool 14,16 to a shape part way towards the final required shape. They are then passed on to second and third pressing stages 15, 17, as shown in Figures lc and ld where they are progressively deformed until they reach the desired shape of the catalyst heat shield.

As shown in Figures 2 to 4, the heat shield in this example is of a standard shape comprising a single pressing 20, formed from the two sheets 10, 12, of approximately semi-circular cross section with strengthening ribs 22 formed in it, and is 350mm in length. The thickness of the sheets of steel used are 0.4 and 0.6mm. The pressing operations used are therefore substantially the same as would be used to obtain a single layer pressed heat shield using a sheet of lmm thickness.

There are two factors which reduce vibrations in the laminar structure of the invention compared to a single layer structure. Firstly, as the layers have different vibration characteristics, they will have different resonant frequencies of vibration and so, at the resonant frequency of one layer, the other will act to dampen vibration. Also vibrations in the laminar structure cause the two layers to move slightly against each other and the friction between the two layers therefore dampens the vibrations.

For the best results it is therefore preferable to use two layers with substantially different vibration characteristics, in particular resonant frequencies. This can be achieved by using different thicknesses, as described above, or by using different materials for the two layers, or a combination of the two.

The method of the invention can vary from that described above. For example, instead of using spot welding to fasten the two sheets together, a layer or one or more beads of adhesive can be used. This adhesive can act to further reduce vibration of the laminar pressing, and it can be advantageous to include a layer of elastomeric or other resilient material between the other layers of material for its damping effects alone.

Claims (6)

Claims

1. A method of forming a pressed article comprising the steps of providing at least two sheets of material, placing the sheets having different vibration characteristics in contact with one another and deforming the sheets together to form a laminar pressed article.

2. A method according to claim 1 further comprising the step of fastening the sheets together at at least one point prior to the deforming step.

3. A method according to claim 1 or claim 2 wherein the sheets are of dissimilar thickness.

4. A method according to any foregoing claim wherein the sheets are of different material.

5. A method substantially as herein described with reference to the accompanying drawings.

6. A pressed article formed using the method of any foregoing claim.