METHOD OF MANUFACTURING A PRESS-FORMED SHEET-METAL PRODUCT

Technical field

This invention relates to a method of manufacturing a formed sheet-metal product according to the pre-characterising part of claim 1. The invention also relates to a product manufactured by the method.

Background of the invention

In what are referred to as press-hardened sheet-metal products, subsequent cutting or subsequent punching is sometimes necessary in order to meet prescribed tolerance requirements. It is important that the dimensional accuracy of the product is retained during subsequent finishing. Subsequent welding operations, such as, e.g. spot welding, also have to be carried out without compromising the strength of the respective final product.

Aim of the invention

One aim of this invention is to provide a method allowing for the advantageous subsequent finishing of press-hardened products without compromising the form tolerances of the products.

One aim is to produce a soft edge zone with good tolerances while simultaneously reducing tool wear and minimising punching burrs.

One aim of this invention is to facilitate welding, such as spot welding, while minimising, e.g. the risk of crack formation, etc..

Another aim is to achieve an increase in quality compared to the prior art.

The aim of the invention is achieved in that the method of manufacture and the press-hardened sheet-metal product have the features specified in the claims.

Brief description of the drawings

Figure 1 is a perspective view of a press-hardened sheet-metal product in the form of what is referred to as a B-pillar for a passenger car prior to subsequent cutting/subsequent punching.

Figure 2 is a perspective view of a press-hardened sheet-metal product in the form of what is referred to as a B-pillar for a passenger car after subsequent cutting/subsequent punching.

Figure 3 is a cross section through a forming tool along the line 3-3 of the sheet-metal product according to Figure 1 manufactured in the forming tool.

Figure 4 is a partial enlarged view of the forming tool according to Figure 3.

Detailed description of the illustrated embodiment

Figure 1 shows what is referred to as a B-pillar 10 for a passenger car, the said pillar/product/component being formed by press hardening. Figure 2 shows the component 10 after subsequent finishing.

The component 10 is manufactured from a flat sheet-metal blank which is heated, then formed in a forming tool and cooled while being held in the pressing tool/forming tool so as to obtain the desired hardness. The aforementioned method of manufacture is referred to as press hardening and results in dimensionally accurate products of high strength since the sheet-metal component is pressed during the hardening process.

The component 10 shown has a central part in the form of a hat-shaped section with a central flange 15, two web parts 16,17 and side flanges 18,19. The component 10 is provided at its upper and lower ends with parts 25,26 for connection to a vehicle chassis.

Figure 3 is a cross section through a central part of a press-hardening tool/forming tool 50 used to form and harden the component 10. The press-hardening tool includes an upper 51 and a lower 52 tool half.

Figure 4 shows part of the press-hardening tool 50 serving for forming and hardening of the side flange 18 on a larger scale. According to the invention, an elongated soft zone A is arranged at a distance L from the free edge of the side flange 18, as a result of which the edge part 18a of the side flange acquires a degree of hardness that increases the dimensional accuracy of the component 10 when the component 10 leaves the tool 50. The soft zone A is obtained in that recesses 55,56 are arranged in the upper 51 and lower 52 tool halves. This results in the formation of an air gap resulting in reduced cooling of the zone part A during the cooling process of the tool 50 and therefore in a lower degree of hardness. As an alternative to the abovementioned recesses 55,56, insulating plates can be arranged in the tool so as to obtain the zone part A. Another alternative is to arrange local heating coils in the cooling tool in order to obtain the zone part A.

When the component 10 as shown in Figure 1 has been produced by the method described hereinabove, subsequent finishing then follows. The aforementioned subsequent finishing is illustrated in Figure 2. The subsequent finishing in the example shown is carried out by edge trimming or edge punching, such that a sheet-metal strip/waste edge 60 is removed from the component 10, as will be clear from Figure 2. A new free edge 18b which is now soft is thus formed since the cutting/punching is carried out in the soft zone A, resulting in advantages from the point of view of the tool, the hard edge 18a having performed its shape-retaining role from the forming and hardening operation.

The soft zone A is also suitable for various subsequent welding operations, such as, e.g. spot welding, thereby making it possible to minimise the risk of crack formation.

It will be clear that the elongated or oblong soft zone A positioned close to the outer edge according to the invention can be arranged around the entire periphery of a component or along parts thereof depending on the respective desired aim. One field of application is when subsequent finishing is required in order to observe close tolerances. The soft edge zone may be made narrow.

According to the invention, curved or bowed/bent edge trimming is made possible in that the elongated or oblong soft zone A is designed to be curved so as to correspond to the desired configuration of the curved edge trimming. A bowed cutting line of the aforementioned type is illustrated in Figure 2.

It will thus be clear that the invention can be applied to components and profiles of any desired configuration. The invention is thus not limited to what is illustrated and described here, and amendments and modifications are possible within the scope of the following claims.