EP0393250A1

EP0393250A1 - Method for manufacturing welded sheet metal wheels for motor vehicles, the plant for its implementation and the wheels obtained

Info

Publication number: EP0393250A1
Application number: EP89200984A
Authority: EP
Inventors: Renato Colombo
Original assignee: MAXNOVO ITALIA Srl
Current assignee: MAXNOVO ITALIA Srl
Priority date: 1989-04-18
Filing date: 1989-04-18
Publication date: 1990-10-24

Abstract

A method for manufacturing shaped and welded sheet metal wheels comprises the following operations relative to the manufacture of the rim:
- forming and sizing a continuous tube (13) from a roll of sheet (3) metal by roller-shaping (7) and high frequency welding (8)
- eliminating the external weld seam by chipping with a fixed tool during the advancement of the tube
- cutting the tube into cylindrical segments (15, 16)
- rolling the cylindrical segments to shape the rim (20);
a plant for implementing the method comprises:
- a clamp for clamping and locking the tube and arranged to move in the direction of the tube axis between two end positions,
- a circular frame rotating in front of said clamp and carrying peripherally in equidistant positions at least two idle circular cutters each supported at the end of a rod of a cylinder-piston unit located on the frame in a radial position,
- a plug coaxial to the clamp and shaped to provide a shoulder able to act as a backing blade for said idle circular cutters, and a slightly tapered portion of diameter substantially equal to the inner diameter of the tube and provided with electromagnets,
- means for moving said clamp in the forward and rearward directions,
- means for moving said plug in the forward and rearward directions;
the sheet metal wheels for motor vehicles have their rim welded along a generating line by high-frequency welding.

Description

Welded sheet metal wheels for motor vehicles are composed of a central part known as the disc and provided with means for fixing the wheel to the hub, and a peripheral rim of channel shape which is fixed to the disc by welding, for the purpose of receiving the tyre.
The disc is commonly formed by deep-drawing and punching a metal sheet.
The rim is commonly formed from a sheet metal strip which is firstly calendered into a cylindrical shape, then welded along its mating edges, and then, after finishing operations, subjected to one or more rolling passes to give the rim the required shape.
Said method gives rise to a series of drawbacks which have so far not been obviated and which seriously affect costs.
A first series of drawbacks derives from the fact that that the circular band, ie the cylindrical element which is to be subsequently shaped by rolling, has substantial formation defects.
Generally the two edges of the sheet metal strip do not mate perfectly and therefore the circular band obtained on welding has frontal steps at the ends of the weld seams which it is not always possible to eliminate by mechanical grinding, and which are a very large source of rejects (an average of between 3 and 6 percent of the circular bands produced).
In addition the type of welding most commonly used, ie flash welding, often results in porosity which means that the wheels cannot be used with tubeless tyres.
The welding operation requires a very lengthy time, of between 6 and 8 seconds per circular band, and uses about 400-500 kW of power, the welding method used resulting in the creation along the welding line of considerable material crests which have to be removed mechanically, with considerable effect on costs. A further cost increase is due to the wastage of material, which can be estimated at about 15 mm of the length of sheet metal strip from which the circular band is to be formed.
In additon the formed circular band has sharp edges which can hinder its subsequent painting.
Experiments carried out using roll welding machines operating side by side (so-called forge welding) have shown improved weld quality but have created subordinate problems in terms of the need to hot-roll the obtained circular band to give it a perfect cylindrical shape with a continuous stepless surface.
From the aforegoing it is apparent that the crucial step in the rim manufacture is to obtain circular bands of perfect dimensional characteristics and surface finish.
The object of the present patent is to provide and protect a complete method for the manufacture of welded sheet metal wheels and in particular for the manufacture of the necessary sheet metal circular bands having perfect dimensional characteristics.
The object of the patent is attained according to the invention by operations particularly but not exclusively concerning that stage of the circular band manufacture by which the peripheral tyre holding rim is obtained.
According to the invention the circular bands are welded by a high frequency or HF induction process which allows very short welding times but provides very efficient welds able to ensure the air-tightness required for using tubeless tyres.
More specifically, the invention provides for forming a continuous tube from a portion of strip using a roll forming machine. This procedure not only ensures perfect shape and dimension characteristics but also makes it possible to eliminate both the external and internal weld seam during tube construction.
The method then provides for cutting the tube into segments forming the circular bands.
The cutting process is one of the most delicate stages of the method in that it must take place without any deformation of the circular band edge.
For this purpose the invention provides a particular cutting device, the characteristics of which are defined in claim 4. When the circular bands have been formed they are subjected to the usual channel-shaping by rolling, possibly preceded by a spinning operation to eliminate sharp edges.
By this means the tyre holding rims are formed and are welded to the respective discs which are formed from sheet metal by punching and deep-drawing.
According to the invention, before cutting the tube into segments to form the circular bands, it is annealed to eliminate the work hardening adjacent to the welding line.
The annealing operation is carried out along the tube formation line by induction heating followed by slow cooling in an insulated environment at controlled temperature.
This operation greatly facilitates the subsequent operations involved in shaping the rim.
The most apparent advantage of the invention is the enormous energy saving.
Currently, the welding of a circular band takes 7-10 seconds and uses a power of 450 kW, which means that each circular band consumes 0.80 kWh of energy for the weld alone.
In the worst possible case, the welding of the tube of the invention requires a maximum power of 250 kW at a formation speed of about 25 m/min.
Calculating an average of 5 circular bands per metre of tube, 7500 circular bands per hour can be produced with an energy consumption of the order of 0.035 kWh per circular band.
The energy saving on the welding alone is therefore of the order of 95%.
Although the advantage of the welding energy saving is the most striking it is certainly not the most important.
In this respect the ability to obtain circular bands of absolute dimensional precision without surface or shape defects and practically without rejects, and with a weld providing perfect air-tightness, represents progress in the motor vehicle wheel field which would have been unthinkable up to the present time.
The operational and constructional merits and characteristics of the invention will be apparent from the detailed description given hereinafter of a preferred embodiment of the plant, which is illustrated by way of non-limiting example on the accompanying drawings.

Figure 1 is a diagrammatic view of the tube forming plant.
Figure 2 is a diagrammatic view of the plant for forming rims from the tube.
Figure 3 is a partly sectional side view of the devices for separating the circular bands from the tube.
Figure 4 is a section on the line IV-IV of Figure 3.
Figure 5 is a partial view in the direction V of Figure 3.
Figure 6 is a partial section on the line VI-VI of Figure 3.

The figures show a line 1 for forming welded tube of the desired diameter, for example 13 inches.
Said line comprises a reel 2 supporting a roll 3 of sheet metal of the desired width.
After being unwound from the roll 3, the sheet metal passes through a butt-welding unit 4 which joins the rear end of a consumed roll to the front end of a new roll.
Downstream of the butt-welding unit there is a buffer stock of sheet metal 5 in the form of looping which ensures operational continuity of the downstream units during the butt-welding operation.
Said units consist substantially of a roller flattening unit 6, a forming unit 7 comprising seven seven stands with horizontal rolls and six intermediate stands with vertical rolls, a welding unit 8 having a power of between 100 and 200 kW, an annealing and controlled cooling device 9 which heats the material to a temperature exceeding 800°C and then cools it to about 80-100°C within a time of 1-1.5 minutes, this device occupying a length of about 40-50 metres, a sizing unit 10 and a cutting unit 11 with mobile shears 12.
From the cutting unit 13 tubes leave having a length which is a minimum of 4 metres and preferably exceeds 10 metres, they being collected on a pallet 4 and sent to store.
With reference to Figure 2, the tubes 13 are withdrawn from store and fed to a sectioning device 15 described in detail hereinafter.
The circular bands 16 are discharged from said device perfectly cylindrical and with very precise dimensions, and are then subjected to three consecutive rolling operations by the machines 17, 18 and 19. The shapes gradually assumed by the rim are indicated by 16a, 16b and 20.
The device for sectioning the tube into circular bands will now be described with reference to Figures 3 to 6.
Said device comprises a robust bed 21, on the left hand side of which there are positioned various guide supports for the tube 13, these not being visible in the figure. The most downstream of said supports is a clamp 22 with two semi-cylindrical jaws, namely upper 221, and lower 222.
The lower jaw 222 comprises two downwardly-extending lateral appendices 23, each of which slides on a rod 24 rigid with the bed 21.
The two jaws 221 and 222 are made to move to and fro by a pneumatic cylinder-piston unit 25, the body of which is rigid with the bed.
The upper jaw 221 is connected by the symmetrical lateral appendices 26 to the body of two cylinder-piston units 27, the rods 28 of which, suitably guided in a bush 29, are rigid with the symmetrical lateral plates 23 which are rigid with the lower jaw 222. The two jaws are guided relative to each other by the pins 30. Each jaw is coated with antislip material 131.
It can be seen in Figure 3 that immediately downstream of the clamp 22 there is a portal structure 31 rigid with the base.
The structure 31 comprises a circular guide 32 within which a circular frame 33 rotates. The frame 33 is made to rotate relative to the guide 32 by a helical gear-worm coupling 34. In positions spaced apart by 120° the circular frame 33 supports three cylinder-piston units 35, to the rod of each of which there is fixed an idle circular cutter 36.
Coaxial to the tube there is a rod 37 driven with to-and-fro movement and carrying a cylindrical plug 38 at its end. Said plug comprises a ledge 39 of diameter substantially equal to the inner diameter of the tube 13 and acting as a backing blade for the circular cutters 36.
The plug also comprises a slightly tapered portion provided with electromagnets 40, its purpose being to guide, support and lock the tube 13 when its residual part is to be extracted after the last circular band has been cut.
The circular bands gradually separated by the cutters 36 have a length equal to the stroke of travel of the clamp 22 along the guides 24.
After the circular bands have been separated they remain resting and retained on a cradle 41 also provided with electromagnets, not shown, which by withdrawing along the guides 42 under the action of the cylinder-piston unit 43 positions the circular bands 16 for subsequent final removal.
The rod 37 is moved by a cylinder-piston unit 44 and is guided with great accuracy between two pairs of rollers 45, as can be seen in Figure 4.
The invention is not limited to the single embodiment described heretofore and illustrated on the accompanying drawings, and modifications and improvements can be made thereto but without leaving the scope of the invention, the basic characteristics of which are summarised in the following claims.

Claims

1. A method for manufacturing shaped and welded sheet metal wheels consisting of a central disc provided with means for its fixing to the vehicle hub, and a peripheral shaped rim for retaining the tyre, characterised by comprising the following operations relative to the manufacture of the rim:
- forming and sizing a continuous tube from a roll of sheet metal by roller-shaping and high frequency welding
- eliminating the external weld seam by chipping with a fixed tool during the advancement of the tube
- cutting the tube into cylindrical segments
- rolling the cylindrical segments to shape the rim.

2. A method as claimed in claim 1, characterised by comprising an operation for eliminating the internal weld seam by roller-forging immediately downstream of the high frequency welding operation.

3. A method as claimed in claim 1, characterised by comprising, upstream of the sizing operation, the annealing of the material by heating to a temperature exceeding 800°C followed by controlled cooling over a period of 1-1.5 minutes to 80-100°C.

4. A plant for implementing the method claimed in claims 1 to 3, characterised by comprising a device for cutting the tube into segments which comprises in combination:
- a clamp for clamping and locking the tube and arranged to move in the direction of the tube axis between two end positions,
- a circular frame rotating in front of said clamp and carrying peripherally in equidistant positions at least two idle circular cutters each supported at the end of a rod of a cylinder-piston unit located on the frame in a radial position,
- a plug coaxial to the clamp and shaped to provide a shoulder able to act as a backing blade for said idle circular cutters, and a slightly tapered portion of diameter substantially equal to the inner diameter of the tube and provided with electromagnets,
- means for moving said clamp in the forward and rearward directions,
- means for moving said plug in the forward and rearward directions.

5. A plant as claimed in claim 4, characterised in that said plug is supported by a rod guided between two pairs of shaped rollers and coupled to a cylinder-piston unit.

6. A plant as claimed in claim 4, characterised in that downstream of the idle circular cutters in a position below the tube there is a cradle provided with electromagnetic means and arranged to move in the direction of the tube axis to remove the circular band after its cutting.

7. Welded sheet metal wheels for motor vehicles, of the type comprising a central disc and a peripheral rim, characterised in that the rim is welded along a generating line by high-frequency welding.