Method for making structural automotive components and the like

Abstract

A method for making structural automotive components and the like provides a strip of high strength steel having a selected thickness. A predetermined thickness of a metal coating, such as nickel, is applied to the opposite faces of the steel strip. The coated steel strip is cut to form a blank. The blank is heated in a generally open atmosphere to a temperature in the range of 800° C. to 1000° C. within less than ten minutes, thereby diffusing at least a portion of the metal coating a predetermined distance into the faces of the steel strip portion of the blank to alleviate scale formation, and simultaneously raise the temperature of the blank for hot forming the same. The heated blank is hot formed in a pressing tool, and cooled therein to heat treat the formed component through microstructure phase change, without substantial scale formation, such that the component need not be descaled prior to post-form processing and / or assembly in a vehicle.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to structural automotive components and the like, and in particular to a method for making heat treated structural automotive components with reduced surface oxides and / or scale. [0002] Structural automotive components and parts, such as door pillars or beams, frame rails, frame components, bumpers, bumper beams, and related bumper components, side impact beams, instrument panel reinforcements, and the like, are well known in the art, and improve vehicle safety and performance in impact situations. Many such structural components have a specially contoured shape, and are heat treated to meet exacting safety specifications. [0003] Some types of structural automotive components are manufactured using a hot press method, such as that disclosed in U.S. Pat. No. 5,972,134, which is assigned to Benteler AG, related company to the assignee of the present application. In the method disclosed in the Benteler AG U.S. Pat. No. 5,...

AI Technical Summary

Benefits of technology

[0011] Another aspect of the present invention is a method for making a vehicle having at least one contoured structural door beam comprising providing an elongate strip of high strength steel having a thickness in the range of 0.5-5.0 millimeters. The steel strip is electroplated with a metal comprising primarily nickel to form on at least the opposite faces of the steel strip a nickel coating having a thickness in the range of 1.0-5.0 microns. The nickel coated steel strip is cut to length to form a flat, plate-shaped blank. The plate-shaped blank is heated in a generally open atmosphere comprising primarily ambient air to a temperature in the range of 800° C. to 1000° C. within less than ten minutes, thereby diffusing at least a portion of the nickel coating a predetermined distance into the opposite faces of the steel strip portion of the plate-shaped blank to alleviate scale formation, and simultaneously raising the temperature of the plate-shaped blank for hot forming the same. The heated plate-shaped blank is transported into a pressing tool, and formed in the pressing tool into a predetermined contoured shape to define a selected structural door beam. The formed structural door beam is then cooled in the pressing tool to heat treat the same through microstructure phase change without substantial scale formation. The heat treated structural door beam is removed from the pressing tool, and welded in the vehicle without cleaning the same between the removing step and the welding step.

[0014] Yet another aspect of the present invention is a method for making structural automotive components and the like with greatly reduced scale and decarburization to overcome those problems experienced with prior art processes, while retaining and / or improving upon the important performance characteristics of the parts, such as mechanical strength, formability, surface hardness, ductility, weldability and the like. Furthermore, the method has the ability to achieve such results, while reducing overall manufacturing and / or assembly costs. The method is efficient in use and particularly well adapted for the proposed use.

Problems solved by technology

Exemplary problems experienced with such prior art processes include the formation of surface oxides and / or scale (collectively referred to herein as “scale”) on the steel during heating, and decarburization of the steel.

In many applications, however, a protective atmosphere is impractical due to cost or technical constraints.

This layer of scale is generally less desirable from a mechanical strength aspect, and also creates difficulties for secondary processing operations, such as welding and painting.

There is currently no known practical advantage in the presence of the scale.

When scale must be prevented on an uncoated base steel during heating, the furnace atmosphere must contain no water vapor, oxygen or carbon dioxide, and complete prevention can only be completed in a fully enclosed furnace that is quite costly, and may not be economical for most high volume vehicle part processing.

Further, oil coating on incoming parts to alleviate oxide formation can add undesirable elements to the furnace atmosphere, and result in environmental concerns.

In addition, reduced scale processing typically requires a furnace that does not allow the combustion gases to mix with the heating atmosphere, which again is more costly than an open air furnace.

Furthermore, since hot press forming techniques require transporting the heated blank to a pressing tool, exposure to ambient air during transport can still result in some amount of scale formation, even when an enclosed furnace is used.

The scaling of vehicle components manufactured using prior art technologies cause several serious problems.

One such problem is the deposition of scale in the hot forming tools, and related part handling equipment.

The loosened scale then becomes lodged in the handling and / or pressing portions of the tooling.

Because the scale is relatively abrasive, galling and other tool wear results.

While the die can be cleaned and polished to temporarily correct such problems, the wear caused by scale abrasion is sufficiently severe that the tool must eventually be replaced.

This regular cleaning and replacement of the pressing and handling portions of the tooling adds substantial cost to the process, and results in expensive machine downtime.

As noted above, another serious problem resulting from scale formed on the components relates to secondary operations on the formed vehicle part, such as welding, painting, rust-proofing and the like.

The existence of scale adversely impacts the quality of spot welds, and also shortens the life of the welder tips.

Similarly, scale adversely impacts the adherence of paint and / or rust-proofing, such that most scale must be eliminated from the components prior to these post-form operations as well.

While abrasive blasting is generally effective, it adds additional cost to the manufacturing process.

Further, since abrasive blasting processes are normally conducted in a separate building from fabrication or stamping, due to noise and cleanliness concerns, additional material handling and / or shipping costs are incurred.

Even when sophisticated abrasive blasting processes are used to control dimensional characteristics of the vehicle components by accurately monitoring the flow and pressure rates of the cleaning particles and accurate placement of the blasting nozzles, any slight deviations from process parameters may result in a component that is out of specification dimensionally, resulting in possible warping or distortion.

However, such processes are relatively slow, and not particularly effective in making structural components for vehicles, and other similar applications, which use a high strength steel that must be heated relatively quickly to very high temperatures in the range of 800° C. to 1000° C., hot formed and then quenched to heat treat the part.

The aluminum coating tends to soften and / or melt under such high temperatures, and can become detached from the steel, particularly during handling, thereby fouling the furnace and / or oven, transport devices, forming presses, and other such equipment.

Also, the aluminum coating is not effective when pre-form notches, apertures or other such formations are desired in the part, since the coating tends to crack during the forming or pressing operations.

Aluminum coatings also tend to adversely impact the weldability of the finished component, which renders post-form operations and vehicle assembly more expensive.

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