EP1755805B1

EP1755805B1 - Method for cold pressing of a metal plate without wrinkling, for making an axle housing.

Info

Publication number: EP1755805B1
Application number: EP05745518A
Authority: EP
Inventors: Michael Tanskanen
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2004-06-02
Filing date: 2005-05-27
Publication date: 2011-03-09
Anticipated expiration: 2025-05-27
Also published as: WO2005118178A1; BRPI0510795A; ES2361199T3; SE527277C2; ATE500909T1; SE0401406D0; DE602005026806D1; SE0401406L; EP1755805A1

Abstract

The invention relates to a method for preventing the occurrence of wrinkling in a metal plate due to compressive stresses in the metal plate during cold pressing of the latter, and a method for manufacture of an object, starting from a metal plate (10), whereby the object is formed by cold pressing of the metal plate. The cold pressing of the metal plate (10) is preceded by providing slits (12) in the portions (11) of the metal plate where compressive stresses occur as a result of the cold pressing and where wrinkling in the metal plate due to these compressive stresses is to be prevented, said slits (12) being adapted so that the compressive stresses which occur in these portions (11) of the metal plate as a result of the cold pressing of the metal plate cause local thickening (22) of the metal plate in a region around the bottom (15) of each slit (12).

Description

FIELD OF THE INVENTION AND STATE OF THE ART

The present invention relates to a method according to the preamble of claim 1 for manufacture of an axle housing half intended to form part of an axle housing for a rear axle assembly of a vehicle (see for example DE-A-2030086 ).
An axle housing for a rear axle assembly of a vehicle normally comprises two axle housing halves welded together. Each axle housing half takes the form of a profile with a U-shaped cross-section. In the middle portion of the profile as seen in a side view of the profile, the profile extends in a substantially semicircular bulge. Axle housing halves may for example be manufactured by hot pressing of a suitably cut-to-size metal plate as described, for example, in US 2 674 783 A , whereby the metal plate is heated to a very high temperature before being formed by pressing between a punch and a die of a forming tool.
Another example of a method of manufacturing an axle housing is shown in US 2 370 641 A . This document teaches that the arms of the axle housing are made from tubular material, separate from the central "banjo" section. The arms are later welded or otherwise attached to the "banjo" section.
To simplify the manufacture of axle housing halves and reduce the time which the manufacturing process takes, there has been a changeover to the manufacture of axle housing halves by cold pressing of metal plates made of steel. A problem in relation to this cold pressing is the occurrence of wrinkling in the portions of the metal plate which are subjected to compressive stresses during cold pressing. The wrinkles are caused by steel being difficult to compress, which leads to the compressive stresses causing the metal plate to wrinkle instead of being compressed. This wrinkling occurs more specifically in the portions of the metal plate which, after the cold pressing, constitute longitudinal flanges of the substantially semicircular bulge of axle housing halves. This wrinkling problem increases with increasing width of the area of the metal plate in which these portions liable to wrinkling are situated. A method which has been used for reducing this problem is therefore to make the metal plate which is to be cold-pressed to form an axle housing half as narrow as possible in the area of the metal plate where these portions liable to wrinkling are situated. This is illustrated in Figs. 1 and 2. Fig. 1 depicts a metal plate 1 in its spread state, i.e. before it is cold-pressed to form an axle housing half. This metal plate 1 has been subjected to cutting or stamping to give it a basic shape suitable for it to be formed as an axle housing half. The area 2 of the metal plate 1 which is subject to compressive stresses during cold pressing, i.e. the middle portion of the metal plate, has here been made as narrow as possible in order to reduce wrinkling of the metal plate due to the cold pressing. As illustrated in Fig. 2, however, wrinkles in the axle housing half 3 due to the cold pressing of the metal plate 1 cannot be entirely eliminated by this method. Cold pressing still results in wrinkles 4 in the aforesaid flanges 5 of the axle housing half 3. Removing these wrinkles entails machining the lateral surfaces of these flanges, thereby leading to higher manufacturing costs.

OBJECT OF THE INVENTION

The object of the present invention is to solve the aforesaid wrinkling problem in the cold pressing of metal plates and thereby, for example, to make it possible to manufacture wrinkle-free axle housing halves without having to machine lateral surfaces of the axle housing halves.

SUMMARY OF THE INVENTION

According to the present invention, said object is achieved by means of a method exhibiting the features indicated in claim 1. According to the invention, before the cold pressing of the metal plate, slits are provided in the portions of the metal plate where compressive stresses occur as a result of cold pressing and where wrinkling in the metal plate due to compressive stresses is to be prevented, said slits being adapted so that the compressive stresses which occur in these portions of the metal plate as a result of cold pressing of the metal plate cause local thickening of the metal plate in a region around the bottom of the respective slits instead of causing wrinkling of the metal plate. The aforesaid wrinkling of the metal plate due to cold pressing is thereby prevented. The slits concerned are easy to provide in the flat metal plate by stamping or cutting.
According to a preferred embodiment of the invention, said slits and the locally thickened regions around the bottom of the slits are removed after the cold pressing by removing, preferably by cutting, areas of metal plate around the respective slits. The result is a simple way of making an object, e.g. an axle housing half, which is free from wrinkles and thickenings.
Further preferred embodiments of the methods according to the invention are indicated by the dependent claims and the description set out below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail below on the basis of examples of embodiments with reference to the attached drawings, in which:

Fig. 1: depicts a metal plate which in accordance with a previously known method has been prepared for cold pressing to form an axle housing half,
Fig. 2: depicts part of an axle housing half made by cold pressing of the metal plate according to Fig. 1,
Fig. 3: depicts a metal plate which in accordance with the method according to the present invention has been prepared for cold pressing,
Fig. 4: depicts part of an object made by cold pressing of the metal plate according to Fig. 3,
Fig. 5: is a schematic illustration of a metal plate placed between a punch and a die of a cold pressing tool before cold pressing of the metal plate,
Fig. 6: depicts the punch and die according to Fig. 5 during the cold pressing of the metal plate,
Fig. 7: depicts a side view of an object formed by the cold pressing illustrated in Figs. 5 and 6, and
Fig. 8: depicts an axle housing for a rear axle assembly comprising two axle housing halves manufactured by a method according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The method according to the invention are exemplified below in an application for manufacture of an axle housing half intended to form part of an axle housing for a rear axle assembly of a vehicle. It does however constitute only one of many possible applications for the methods according to the invention, which can of course also be used for the manufacture of objects with shapes other than as here illustrated.
Fig. 1 depicts in plan view a metal plate 10, e.g. made of steel, which by cutting and/or stamping has been given a shape adapted to the manufacture of an axle housing half. In the subsequent cold pressing of this metal plate 10, compressive stresses occur in the middle area of the metal plate. These compressive stresses are mainly concentrated in the portions 11 of the metal plate which are denoted by broken lines in Fig. 3. These portions 11 form part of the areas of the metal plate which as a result of the cold pressing are shaped as longitudinal flanges 21 of the axle housing, and more specifically in the areas of the metal plate which as a result of the cold pressing are shaped as flange portions of the substantially semicircular bulge 43 of the axle housing (see Fig. 7). Before the cold pressing of the metal plate 10, slits 12 are provided in said portions 11 of the metal plate. The respective slits 12 are provided in one edge of the metal plate so that they each present an aperture 13 facing towards the edge. In the application illustrated, the respective slits 12 are provided in a longitudinal edge 14 of the metal plate so that they extend from the relating edge a short distance into the metal plate 10 towards the centreline of the metal plate. The respective slits 12 are preferably formed with a depth which is greater than their width, i.e. the extent of each slit into the metal plate from the relating edge 14 is preferably greater than its extent along said edge 14. The respective slits 12 are also with advantage each provided with a rounded bottom 15. It has in fact been found that a slit with a rounded bottom has in this context a more advantageous effect than a corresponding slit with a pointed bottom.
The metal plate illustrated in Fig. 3 is also provided in a known manner with a guide hole 17, a so-called pilot hole, for cooperation with a corresponding guide pin, a so-called pilot, of the cold pressing tool's punch in order to ensure correct positioning of the metal plate in the cold pressing tool.
Fig. 4 depicts part of the metal plate 10 according to Fig. 3 after the metal plate's cold pressing in a cold pressing tool. In this case the cold pressing has resulted in the metal plate 10 having a U-shaped cross-section with a web 20 and two longitudinal flanges 21 which each protrude upwards in the same direction on their respective side of the web 20. As may be seen in Fig. 4, the aforesaid slits 12 will be situated in the area of the respective longitudinal flange 21 where the latter's upper edge 21 a has a concave extent. It is precisely in this area of the respective longitudinal flange 21 that the greatest compressive stresses occur as a result of the metal plate 10 being cold-pressed to the shape illustrated in Fig. 4. The slits 12 are adapted so that the compressive stresses which occur in the aforesaid portions 11 of the metal plate as a result of the cold pressing of the metal plate cause local thickenings 22 of the metal plate in the region around the bottom 15 of the respective slits 12 instead of causing wrinkles in the metal plate. The respective thickenings 22 each exhibit a substantially circular or oval shape on the surface of the metal plate. It has been found that by suitable adaptation of the positioning and configuration of the slits 12 it is possible to achieve local thickenings of relatively limited extent around the bottom of the respective slits. The positioning and configuration of the slits 12 is adapted from case to case according to the shape imparted to the metal plate by the cold pressing and the associated compressive stresses in the metal plate. The respective slits 12 need to be wide enough not to be squeezed fully together by the cold pressing. The shape of each slit 12 also needs to be adapted so that the slit is not squeezed fully together at its bottom 15 during the cold pressing, since it is advantageous that the plate material be allowed to flow into the bottom of the slit instead of merely becoming thickened. For the sake of maximum thickening effect, the depth of the respective slits 12 needs to be as large as possible relative to their width. The slits 12 have also to be positioned not too close to one another, since a certain amount of plate material between the slits is necessary for counteracting the formation of wrinkles in the regions between them. The slits 12 are with advantage arranged in such a way that there is between two mutually adjacent slits an area of plate 16 with a width which is at least twice the thickness of the metal plate 10.
During the cold pressing, the slit bottoms 15 will act as "hinges" or articulation points where it is permissible for the metal plate to become thickened, instead of becoming wrinkled, by the compressive stresses occurring during the cold pressing.
After the cold pressing, said slits 12 are with advantage removed by removal of the respective area of metal plate around each slit. Said areas of metal plate are advantageously removed by cutting. The regions 22 of the metal plate which exhibit said local thickenings, or at least the major part of each of these regions, are preferably also removed.
Figs. 5 and 6 illustrate a process for cold pressing of a metal plate 10 which in accordance with the method according to the invention has been provided with slits 12. The metal plate 10 is here intended for the manufacture of an axle housing and has two protrusions 18 on the respective longitudinal edge 14 for adaptation to the final shape of the axle housing half. The slits 12 are here arranged in the area of said edge 14 which extends in an arcuate shape between the two edge protrusions 18. The metal plate 10 is shaped by means of a cold pressing tool which comprises a punch 30 and a die 31. The metal plate 10 is placed between the punch 30 and the die 31 and brought, on the basis of the aforesaid guide hole 17 and guide pin (not depicted), to a correct position relative to the punch and the die (see Fig. 5). Thereafter the punch 30 is pressed towards the die 31, whereby the metal plate 10 is pressed down in the die 31 by the punch 30 until the punch, via the metal plate 10, comes into contact with the die (see Fig. 6). The metal plate 10 will thus be pressed to desired shape. This pressing is effected without preheating of the metal plate 10.
Fig. 7 illustrates in side view an object 40 formed by the cold pressing illustrated in Figs. 5 and 6. In this case the cold pressing has resulted in the object 40 having a U-shaped cross-section with a web 20 and two longitudinal flanges 21 which each protrude upwards in the same direction on their respective side of the web 20. The object 40 comprises in its longitudinal direction two substantially straight portions 41, 42 each situated at its respective end of the object, and a middle portion 43 which extends between these substantially straight portions 41, 42 and forms a substantially semicircular bulge of the object. As may be seen in Figs. 7, the slits 12 will be situated in the area of the respective longitudinal flanges 21 where the flange's upper edge 2 1 a has a concave extent, i.e. in the area of the respective longitudinal flanges 21 which extend along the bulging middle portion 43 of the object 40. The slits 12 are so adapted that the compressive stresses which occur as a result of the cold pressing of the metal plate 10 cause local thickenings 22 of the metal plate in the region around the respective bottoms 15 of the slits 12 instead of causing wrinkles of the metal plate. After the cold pressing, the object 40 is given its final form by the upper area of the respective longitudinal flanges 21 being removed, preferably by cutting. The cut line 45 is represented by a broken line in Fig. 7. The slits 12 and the local thickenings 22 in the example illustrated are situated in the upper area 44 of the respective longitudinal flanges 21 which is removed, with the result that after these areas 44 have been removed the object 40 is free both from slits 12 and from thickenings 22. After the removal of said areas in the example concerned, the object 40 has the shape of an axle housing half. Fig. 8 illustrates an axle housing 50 formed by joining together, e.g. by welding, two such axle housing halves 40. The axle housing 50 illustrated is intended for a rear axle assembly of a motor vehicle, e.g. a truck. This axle housing 50 is intended to accommodate inter alia a differential gear and a rear axle.
The method according to the invention is particularly advantageous in the cold pressing of metal plates which have a thickness of the order of 6 mm or more.
The invention is of course in no way limited to the embodiments described above, since a multiplicity of possibilities for modifications thereof are likely to be obvious to a specialist in the field without thereby deviating from the basic concept of the invention as defined in the attached claims.

Claims

A method for manufacture of an axle housing half intended to form part of an axle housing for a rear axle assembly of a vehicle, starting from a metal plate (10), whereby the object (40) is formed by cold pressing of the metal plate (10), characterised in that the cold pressing of the metal plate is preceded by providing slits (12) in at least some of the portions (11) of the metal plate where compressive stresses occur as a result of cold pressing, said slits (12) being adapted so that the compressive stresses which occur in these portions (11) of the metal plate as a result of cold pressing of the metal plate (10) cause local thickening (22) of the metal plate in a region around the bottom (15) of the respective slits (12) in order thereby substantially to prevent wrinkling in these portions (11) of the metal plate due to said compressive stresses.
A method according to claim 1, characterised in that said slits (12) are removed after the cold pressing by removal of areas of metal plate around the respective slits.
A method according to claim 2, characterised in that the regions of the metal plate which exhibit said local thickenings (22) are substantially removed after the cold pressing.
A method according to claim 2 or 3, characterised in that said removal is effected by cutting.
A method according to any one of claims 2-4, characterised in that at least some of said slits (12) are provided in an area of the metal plate which as a result of the cold pressing is shaped to form a flange (21) of the object (40).
A method according to any one of the foregoing claims, characterised in that the respective slits (12) are arranged in an edge (14) of the metal plate so that they present an aperture (13) facing towards the edge.
A method according to any one of the foregoing claims, characterised in that the respective slits (12) are provided with a depth which is greater than their width.
A method according to any one of the foregoing claims, characterised in that the shape of each of the respective slits (12) is adapted so that its bottom (15) is not squeezed fully together during the cold pressing.
A method according to any one of the foregoing claims, characterised in that the slits (12) are arranged so that there is between two mutually adjacent slits an area of plate (16) whose width is at least double the thickness of the metal plate (10).
A method according to any one of the foregoing claims, characterised in that each of the respective slits (12) is provided with a rounded bottom (15).