FR2464761A1 - APPARATUS FOR PLANING DEFORMED SHEETS BY ELECTRIC HEATING, PARTICULARLY FOR BODYWORK OF VEHICLE BODY ELEMENTS - Google Patents

Abstract

THIS APPARATUS INCLUDES A TRANSFORMER AND TWO ELECTRODES 18B, 24 PRESENTING CONTACT FACES 20B, 33A WHICH ARE INTENDED TO BE APPLIED AGAINST THE BODY SHEET 2. AT LEAST ONE OF THE ELECTRODES IS CHARGED BY A SPRING, SO THAT ONE FORCE MAY BE EXERCISED BY IT ON THE SHEET 2. THIS ELECTRODE 18B IS A DEFORMATION ELECTRODE, WHILE THE OTHER IS A RETURN ELECTRODE 24. THE RETURN ELECTRODE SURROUNDED THE DEFORMATION ELECTRODE; THIS LATTER EXCEEDS IN THE REST STATE OF THE RETURN ELECTRODE AND MAY BE PUSHED AGAINST THE INCREASING FORCE OF THE SPRING BEHIND THE CONTACT FACE OF THE RETURN ELECTRODE AND THE MUTUAL DISTANCE OF THE CONTACT FACES IN THE STATE REST OF THE DEFORMATION ELECTRODE 18B MAY BE VARIED IN A DEFINED WAY.

Description

The invention relates to an apparatus for planing deformed sheets, in

  particular of bodywork elements, by heating

electric localized of the tle by direct passage of an electric current

  sheet through the sheet, comprising a transformer supplying a high intensity electric current and two electrodes connected to this transformer, which have contact faces with the sheet, at least one of which is a deformation electrode intended to be

  pressed against the deformed area of the tale and the other is an elect

current return trode.

  The deformations likely to be treated by such an apparatus are bumps, that is to say protuberances with respect to the general shape of the bodywork element considered, such as those produced frequently by the forced closing of hoods or covers. baggage compartments against angular transported objects, as well as sheet metal instabilities, i.e. parts of

that can be pushed in and out with the thumb

laughing and making a noise each time they jump elastically from one position to the other. These instabilities are the consequence of over-stretching of the sheet, caused by minor contact or impact with external objects or by dent removal with a mallet and counter-support. The sheet has been partially extended and can no longer return to its original middle position but passes each

  times through it, sometimes towards one side sometimes towards the other.

  Electrothermal leveling or dent removal by an appliance

reil as described above has gained in importance lately,

  since it was found that an electric current from the elec-

deformation and substantially radial trode in the sheet makes it possible to eliminate bumps as well, in particular small bumps

  accentuated or "pustules", than the instabilities described above.

At the point of contact of the deformation electrode with the tCle, there is a noticeable rise in temperature, with a maximum in the middle, so that the bumps, especially the small accentuated bumps, can be eliminated by a medium to strong pressure which deforms the heated sheet in the opposite direction. In the case of instabilities, it has been observed that - apparently under the effect of specific thermal stresses created in the sheet - a cooling process occurs during cooling - which tends the sheet and withdraws it in its position

stable original.

  For this electrothermal leveling of deformed tCles, an apparatus is known which consists of a transformer which resembles a welding transformer and two electrodes connected to it by cables and movable independently of one another, including the one can be attached to practically any point on the

  t8le, while the other, held in the hand, serves as a deformation electrode

  mation. It is also already known to produce the deformation electrode.

  mation as a percussion tool so that the simultaneous work of the t8le does not require an additional tool (patent application DE-AS 23 62 103 of the Federal Republic of Germany). Known devices require great experience and a lot of dexterity to eliminate bumps. Instabilities can hardly be

  suppressed by known devices due to the fact that the force is diffi-

cilately dosable.

  There is also known an apparatus comprising concentric electrodes, one of which can be moved longitudinally against the force of a spring, but these electrodes are only used for supplying current, the actual work of the sheet being done by

  additional tools (patent 22 617 of the Democratic Republic

German tick).

The invention aims to create an apparatus of the type indicated at the beginning, by which can be eliminated, without additional tools,

  both bumps and instabilities, and which allows handling

problem-free and quick learning of handling.

According to an essential characteristic of the invention a) the return electrode surrounds the deformation electrode,

  b) the deformation electrode protrudes in the rest state of the elect

  return electrode and can be moved against the increasing force of a spring and on an elastic path or stroke as far as behind the contact face of the return electrode, and c) the mutual spacing of the contact faces in the direction of the elastic travel in the resting state of the deformation electrode can

be modified in a defined way.

  The invention firstly combines the advantages of the prior art by the provision of a deformation electrode

  capable of being handled with sensitivity in an electrified device

  coaxial trodes. In addition, by the defined variation in the spacing of the electrode faces in the direction of the elastic stroke, the invention

  tion allows knowingly to use different parts of the characteris-

  elastic tick according to the size of this spacing. Apart from a pre-

  stress, which may be low, the spring is in the rest state, i.e. practically relaxed when the deformation electrode is extended to the maximum, the rest position being the same for all applications and being fixed by a stop which is preferably easily adjustable. The maximum possible elastic stroke and therefore the restoring force of the deformation electrode can be

  obtained at the end of this race are now determined by pre-

best place by the possible relative displacement of the contact faces when the device is pressed against the blade. It should be noted in this regard that the two electrode faces must be applied against the blade so that a current can flow. The selective or defined variation of the spacing of the electrode faces therefore makes it possible to fix the maximum force of the spring within narrow limits, the nature and the magnitude of the deformation of the sheet playing of course also

  a certain rûle but which is secondary.

  If the distance between the electrode faces is large, the elastic stroke is also large and the maximum force produced by the spring is high. Such an adjustment of the spacing of the electrodes is used in particular for the elimination of small accentuated or pointed bumps. If, on the contrary, it is a matter of tensioning the sheet to eliminate instability, it is advantageous to choose an axial spacing more

  weak electrodes, which consequently decreases the elas-

  therefore also ticks the maximum force exerted on the sheet until the return electrode also applies against the sheet. It should be noted here that the elastic force of the deformation electrode when

  the tale is contracted or stretched is necessarily opposed to this

  cessation of contraction or tension. Depending on the prior setting of the mutual spacing of the electrode faces, the device can therefore be used for very specific shaping purposes, without the operator being able to make large errors. To remove instabilities by contraction, you can slide the device on the sheet in certain patterns, so as to remove the

  instabilities step by step under a weak pressing force of the elect

  deformation rod against the sheet. The axial spacing of the electrode faces can be varied

  in different ways. In particular, it is possible to extend the elect

  return tripod in the direction of the elastic stroke, which can be achieved, for example, by a ring which can be plugged onto an electrode

hollow cylindrical return. A removable ring has the additional advantage

  keep silent that it can be discarded, without this representing a significant loss, if, after a certain period of service, its front face, which is in this case the electrode face of the return electrode, shows traces of bralure. However, it is also possible to fix the deformation electrode removably in a support

mounted on a spring and replace it as necessary with an electric

  shorter or longer deformation trode. The longer electrode also produces a longer elastic stroke and is therefore suitable for dent removal, especially small accentuated bumps. Such an electrode advantageously has a front face or substantially planar contact face. The shorter deformation electrode

  also produces an elastic stroke which is also shorter and therefore serves mainly

  cipale to the contraction of the sheet to eliminate instabilities.

Since this work is most often performed step by step over a relatively large area, as described above, the contact face of this shorter electrode is preferably curved, this

  which facilitates its sliding on the sheet and prevents burns

  lures too strong by a point contact or by an edge of the elect

  trode when the device is tilted. The interchangeable deformation electrodes can of course also be replaced by

new electrodes if they have too many burn marks.

According to another advantageous improvement of the invention, the two electrodes can be disposed on the body of a portable tool in the form of a pistol, it being particularly advantageous for the body of the tool also to contain the high-intensity transformer. A compact device is thus obtained which is easy to handle and transport and which can also be used without problems on parts of the body which are difficult to access. Such a device can '

  be handled like a hand drill.

  Other characteristics and advantages of the invention

will emerge more clearly from the following description of a

non-limiting example of embodiment and of various possibilities of variation of the axial spacing of the electrodes, as well as of the appended drawings, in which: FIG. 1 is an axial section of a complete apparatus in the form of a gun; FIG. 2 is an axial section of a ring which can be attached to the return electrode;

  FIG. 3 represents an interformation deformation electrode

  changeable, Figures 4 to 6 correspond to the part of Figure 1 containing the electrodes, but on a larger scale, and show different variants for varying the axial spacing of the electrode faces; and

FIG. 7 is a stroke-force graph (characteristics

  elastic tick) of the apparatus of FIGS. 1 to 6.

  Figure 1 shows an apparatus 1 which is specially suitable for

  Lement to the dressing of body panels 2. The device has a body or fairing 3 which is composed of two half-shells, shown open along its joint plane and takes the form of a pistol comprising a handle 4 which is only shown. in part. Through the handle 4 passes a current supply conductor 5 which

leads to the primary winding of a high current transformer 6.

Switching on and off is produced by a switch

push button 7 incorporated in the handle 4 but whose branches-

  not shown. An overload circuit breaker 8 connected

  in the electrical circuit is used to protect the transformer 6.

  In an end wall 9 of the fairing 3 is mounted, by an annular groove 10, an insulating piece II of plastic and with symmetry of revolution, which has a longitudinal bore

  coaxial 12. At the inner end of this bore is a collar

  let 13 which serves as a support for a pressure spring 14 having a characteristic

  progressive teristics. The other end of the spring 14 rests on a shoulder 15 of a pin-shaped support 16, which can be moved against the force of the spring 14 in the bore 12. The support 16 has a cavity at its outer end conical 17 in which a deformation electrode 18 is fixed by a complementary cone 19. A contact surface 20 serves for the transmission of current to the bodywork t8le 2. The other end of the support 16 carries a thread and two nuts 21 which serve for the axial adjustment of the support 16 and for fixing the preload of the spring 14 The support 16 is connected by two conductive bars 22 and 23 articulated one to

  the other to one of the secondary output terminals of transformer 6.

  In the insulating part It is mounted, concentrically with respect to this and to the deformation electrode 18, a return electrode 24 in the form of a hollow cylinder. This is connected by

a conductive strip 25 at the other output terminal of the winding-

  secondary transformer 6, the connection of the bar 25 on the return electrode 24 being on the side not visible on the

drawing. The parts traversed by the current, in particular the elect

  trodes 18 and 24 are made of copper. An indicator light 26 indicates, when it is on, that the transformer 6 is energized. The device

can be suspended by an eye 27 at the work station.

FIG. 2 represents a ring 28 having a bore 29 and a narrower bore 30 which are connected to each other by a radial shoulder 31. Slots 32 distributed circumferentially

and of which only the one located at the rear is visible on the drawing

  give the ring 28 a certain elasticity in the region of the

  sage 29, so that the ring can be rolled up to the shoulder

31 on the return electrode 24 (FIG. 1), thereby extending this electrode by the axial length of the bore 30. The surface of

contact 33 of the return electrode 24, against which is applied

  quer the shoulder 31, is thus thus replaced by the surface of con-

tact 33a of the ring 28, also made of copper.

  FIG. 3 represents a deformation electrode 18a

  having a curved contact surface 20a and the cone 19a of which

  corresponds to the cone 19 of FIG. 1. The deformation electrode 18a

  can thus be placed in the support 16 4 instead of the elect

deformation trode 18. However, the electrode 18a is much shorter than the electrode 18 as regards the protruding part of the support 16, so that the elastic stroke available until the return electrode 24 comes abutting against the body plate 2 is also much shorter. The use of the electrodes shown in Figures 2 and 3 in combination with the tool in Figure 1 will be explained in more detail with respect to Figures 4, 5 and 6. The representation being the same, except for an enlargement with the 2: 1 ratio, some

only references are shown in Figures 4 to 6.

  The bodywork tDle 2 visible in FIG. 4 carries a small accentuated hump 34 which is typical for those produced on the luggage compartment covers. The support 16 in this case contains the relatively long deformation electrode 18 of FIG. 1, of which

  the contact surface 20 is flat. In the example shown, we say

  fitting at least the elastic stroke S2 for the deformation of the spring 14.

When pressure is exerted on the device in the direction of the arrow, the return electrode 24 moves to the left until the electrode face 33 is pressed against the sheet 2. This occurs after a stroke which is slightly larger than the stroke S2 * From this moment, an electric current can flow from the electrode. deformation 18 through the plate 2 to the return electrode 24, which produces a heating function of the intensity of the current - of the sheet in the region of the boss 34. The deformation electrode 18 being pressed against the t8le by the great force of the spring 14, the hump 34

is eliminated.

In the example of Figure 5, the body sheet 2 has an instability not visible in the drawing. The return electrode 24 is in this case extended by a length X, corresponding to the length of the bore 30, by the fitting thereon of the ring 28 according to FIG. 2. The deformation electrode 18b used here has the same free length as the deformation electrode 18 in the

  Figure 4 but its contact face 20b is curved. If the device trans-

  formed according to Figure 5 is pushed against the sheet in the direction of arrow 35, the contact face 33a of the ring 28 is applied against the sheet after a much shorter stroke. From this instant, an electric current can also flow from the deformation electrode 18 through the t6le 2 to the ring 28 then from there to the return electrode 24, which produces a corresponding heating of the t8le 2 in the region instability. As the spring 14 is compressed less, it exerts a much weaker force on the sheet, the pressure being just

sufficient for the correct flow of current to be ensured. The ins-

The stability is eliminated by the heat developed by the electric current.

  stick and by subsequent cooling. This process can if necessary be supported by a transverse displacement of the device on

the sheet 2. The contact face 20b is curved to facilitate this displacement

transverse cement.

Figure 6 shows an inversion of the arrangement by

  compared to that of figure 5. The nature of the deformation (insta-

  bility) is the same as in the previous example. The length of-

  the return electrode 24, used here without a ring, is the same as in the example in FIG. 4. In the support 16 has been fixed a deformation electrode 18a like that of FIG. 3, the free length of which is considerably reduced compared to that of the deformation electrodes 18 and 18b of FIGS. 4 and 5. The contact face 20a is also curved. The race and force ratios are essentially the same as in the example in FIG. 5 in

  this sense that the contact face 33 of the return electrode 24 applies

only against sheet 2 after a short stroke similar to that of

figure 5, so that the contraction process takes place equally

the same way.

FIG. 7 represents the characteristic of the spring 14.

  Its prestress is produced by compression of approximately 6 mm by the nuts 21 (Figure 1) up to point S0. The pre-stress P0 thus obtained is approximately 1.3 kg. The available elastic stroke is essentially determined by the maximum spacing between the contact faces and is located between S and S The maximum spring force

0 2V

  obtainable corresponds to P2 and is approximately 8 kg. This force is reached when, in the arrangement of FIG. 4, the contact faces 20 and 33 are located in the same plane. Since, due to the bump, the deformation electrode 18 penetrates a little more into the return electrode 24, the elastic characteristic is extended a little further, by the dotted part. The maximum force can therefore vary. The available force domain is represented by the

  hatched area in the upper part of figure 7.

  When the device is transformed as shown in FIG. 5 or FIG. 6, an average elastic stroke S is obtained which is smaller and which gives an average spring force P1. The

spring force obtainable at the start of the con-

traction in this case also depends on the dimensions of the deformation of the tCle. The spring force P1 can therefore also vary here in

the hatched area in the middle of Figure 7. However> despite the dis-

possible persions in the hatched areas, it can be seen that the defined variation of the spacings between the contact faces, with the use of the elastic characteristic, makes it possible to obtain a defined adjustment of the deformation or contact forces, which favors obtaining the desired leveling effect, following the direction from

which the leveling must be carried out.

The extension ring 28 (figure 2) can be produced

with different lengths of bore 30, i.e. with different

  rents distances between the contact face 33a and the shoulder 31.

The device can in this case be used in combination with two or more rings 28, the ring having the shortest distance between the contact face 33a and the shoulder 31 being always used, also for dent removal, to collect the - burns, this ring being discarded after a certain period of service to be replaced by a new one. The length of the return electrode 24 is in this case

  reduced by the distance between the contact face 33a and the shoulder 31.

The distance between the contact face 33a and the shoulder 31 on the ring to be used for the contraction process must in this case be increased by the shortening length of the return electrode 24, in order to restore the starting conditions. . The defined variation of the spacing of the contact face 20, 20a or 20b and the contact face 33a is then carried out by simply replacing the rings.

Claims (8)

R E V E N D I C A T I 0 N S ___________________________ 1. Apparatus for leveling deformed sheets, in particular bodywork elements, by localized electric heating of the sheet   by direct passage of an electric current through the sheet,   nant a transformer providing a strong electric current   sity and two electrodes connected to this transformer, which have   contact faces with the sheet, at least one of which is an electro   deformation trode intended to be pressed against the deformed area   of the tale and the other is a current return electrode,   in that: a) the return electrode (24) surrounds the deformation electrode (18, 18a, 18b),   b) the deformation electrode protrudes in the rest state of the elect return electrode and can be moved against the increasing force of a spring (14) and on an elastic path or stroke as far as behind the contact face (33, 33a) of the return electrode, and c) mutual spacing contact faces (20, 20a, 20b, 33,   33a) in the direction of the elastic stroke in the state of rest of the elect deformation trode can be modified in a defined way. 2. Apparatus according to claim 1, characterized in that the return electrode (24) can be extended in the direction of the elastic stroke. 3. Apparatus according to claim 2, characterized in that the return electrode (24) takes the form of a hollow cylinder and can   be extended by a ring (28) which can be fitted thereon.   4. Apparatus according to claim 1, characterized in that the deformation electrode (18, 18a, 18b) is fixed in an inter- changeable in a spring-mounted support (16) and can be replaced   created by a shorter or longer deformation electrode. 5. Apparatus according to claim 1, characterized in that   the spring (14) has a progressive characteristic.   6. Apparatus according to claim 1, characterized in that the deformation electrode (18, 18a 18b) and the return electrode (24) are arranged concentrically in an insulating part (11) which surrounds   at the same time the spring (14) for the deformation electrode. he   7. Apparatus according to any one of the pre- claims   cedents, characterized in that the electrodes (18, 24) are provided mounted on the body (3) of a portable pistol-shaped tool.   8. Apparatus according to claim 7, characterized in that the high intensity transformer (6) is also arranged in the body (3).