A method of bending metal objects

Abstract

 This present invention solves the problem of bending objects, particularly flat parallel ones, without employing an external force.
The method according to this present invention involves subjecting the material of the object bent to a repe­titive, two-phase heating and cooling process.
During the first phase, the material undergoes heating with a concentrated stream of energy causing a thermal effect along the predetermined bending line and a partial plasticising, melting and flowing out in the region of the bending line.
On the other hand, the material is subjected in the second phase to being cooled at ambient temperature or, additionally, in a stream of a blown air, thereby causing the previously heated material to shrink along fibres in the direction perpendicular to the bending line due to the internal stresses created by the thermal shrinkage of the material in the heated region, and thus the deformation of the material to be permanently changed.
The method is suitable for bending metal objects.

Description

[0001] The subject of this present invention is a method of bending metal objects, such as plates, bars, etc., along straight lines. By this method it is possible to bend objects with constant and varying thickness, and also objects made of brittle materials and of materials with high hardness.

[0002] The hitherto known methods of bending objects of such type, being made of metals, involve the plastic deformation of the material of the object being bent by applying external forces appropriate as to size and direction. The bending is effected by means of the bending machines, bending dies and bending presses adapted to that purpose, frequently very powerful.

[0003] Elastic compressive and tensile stresses appear in the material bent and they cause the shape to be changed after the operation of the force has ceased. This affects the accuracy of the intended deformation and makes it difficult to control that process.

[0004] In addition to the above these stresses cause a decrease in the service life of the bent objects during their operation. The known methods cannot be used for bending brittle as well as high-strength and high-hardness materials.

[0005] The purpose of this present invention has been to develop a method of changing the curvature of metal objects, in the way that would not require the appli­cation of heavy equipment and, simultaneously, should make it possible to apply a controlled bending process with a high accuracy of deformation. The essence of this present invention involves sub­jecting the objects to the repetitive, two-phase process of heating and cooling the material along a selected line.

[0006] In the first phase, the material is subjected to heating with a concentrated stream of energy causing a thermal effect. The heating either takes place simultaneously along the entire line, or the stream of energy is moving along the line at a predetermined speed.

[0007] Consequently, the material is locally plasticised and partially melted in the region of the heating line.

[0008] The local nature of the action of the stream of energy together with the heating speed cause the material undergo plastic deformation in that region due to the phenomenon of thermal expansion. The heating mentioned is conducted in such a way that the zone of the material in which the deformation occurs reaches a depth smaller than the thickness of the object.

[0009] Next, during the second phase, the object is cooled at ambient temperature or, additionally, in a stream of blown gas, so as to reach the condition in which the material ceases to be plastic throughout the entire region. During cooling the previously deformed zone of the material becomes shorter along the fibres perpendicular to the heating lines due to the thermal shrinkage of the material. Since the shrinking fibres of the material form the zone which does not cover the entire thickness of the object, the object bends at an angle along the line of the original heating.

[0010] By repeating the above-mentioned operation many times, the object is given the required curvature.

[0011] It is recommended that the heating and cooling process take place under a protective gas atmosphere for the purpose of eliminating the harmful effect of air on the heated area. It is advantageous to carry out the heating process by means of a layer of a substance increasing the coefficient of absorption of the stream of energy.

[0012] A high-power laser or electron beam is used as the source of energy.

[0013] The method as per this present invention makes it possible to bend metal objects without the need of employing external forces. By this method, the curvature of objects can be changed from a distance under the conditions in which the access to that object is impossible. Besides, the same method allows bending of objects made of brittle and high-hardness materials, for which the previously known methods could not be employed.

[0014] The subject of this present invention is shown in the drawing where Fig. 1 shows the method of bending a flat parallel plate object whose side view is shown, Fig. 2 shows the front view of the same plate, Fig. 3 shows a fragment of a section of the plate being heated, Fig. 4 shows the same fragment of the section of the plate when being cooled, Fig. 5 shows the diagram of the material heating temperature distribution vs. the thickness of the object within the heating phase, and Fig. 6 shows a stress distribution diagram of the cooling phase.

[0015] During the first phase, the material of the object being bent is subject to heating with concentrated stream of energy SE of laser radiation. Application of the stream of energy SE of laser radiation, moving at speed V along the bending line AA entails a local change in the condition of the material cha­racterised by different properties at depth G.

[0016] Within that region, two zones can be observed, the material being liquid in the first zone S1 and plasticised in the second zone S2 with the boundary of the area encompassing the melting and plasticising zones shown with the line U.

[0017] The temperature distribution of the heated material, as shown schematically in Fig. 5 as a function of thicknessL of the object indicates additionally the material melting temperature T_m. In the heating stage the material of the first, S1, and the second, S2, zones, flows out to occupy an increased volume as a result of the stresses caused by the effect of thermal expansion. This temperature distribution related to melting temperature T_m determines the size of the first, S1, and the second, S2 zones relative to material thickness L.

[0018] During the second phase the material is cooled at ambient temperature or, additionally, in the stream of a blown gas. The material within the region of the bending line, i. e. the liquid in first zone S1 and the plasticised material in the second zone, S2, is transformed into solid state. The boundary of the region encompassing the plasticising and melting zone in the heating phase has been marked with line U in Fig. 4.

[0019] Due to internal stressesσ_t caused by the shrinkage of the cooled material, it becomes shorter along the fibres marked with arrow, which is shown through the stress distribution along the thickness L of the object in Fig. 6.

[0020] In this diagram, the values of limit compression σ_s and of limit tensile stress σ_r are marked. Should the limit tensile stress, σ_r, for example, be exceeded, the brittle materials may crack.

[0021] The heating and cooling conditions are selected so that the tensile and compressive stresses created in the material should be much smaller than are their limit stresses. By changing the heating and cooling parameters, such as the stream movement speed, the stream power, the absence or presence, and nature of a layer absorbing the stream of energy, etc., one may affect the temperature distribution in the heating phase (Fig. 5) and the stress distributon in the cooling phase (Fig. 6). In the above-mentioned manner, control is exercised on the magnitude of the stresses created in the material in order to obtain the desired angle of bending (Figs. 1 and 4) during one cycle of heating and cooling along the bending line. In one of the possible embodiments, a flat parallel slab shown in Figs. 1 and 2 has been subjected to a process of bending according to this present invention. The slab, 0.7 mm thick and 20 mm wide, is made of 50HSA steel and heated with a radiation beam of a continuously operating 300 W CO₂ laser, the source of energy moving along line AA (Fig. 2) at the speed of 2,5 cm/sec. The beam is directed perpendicu­larly to the surface of the slab.

[0022] The heating takes place under a protective argon atmosphere. The slab was cooled in the ambient atmos­phere within about 1 second. With such conditions of the method employed and after a single heating and cooling cycle, the slab was bent at the angle of 2,8°.

[0023] The method of bending objects according to this present invention, can be used for shaping objects of brittle or high-strength materials. Besides, this method can be employed for shaping objects when access to them is difficult, e. g. under vacuum or under hazardous conditions (high-tension, harmful radiation, etc.).

Claims

1. A method of bending metal objects along straight lines, involving deformation of the objects, cha­racterised in that the material of the object being bent is subjected to a repetitive, two-­phase heating and cooling process where during its first phase the material is subjected to heating with a concentrated stream of energy causing a thermal effect along the predermined bending line and brought to being partially plasticised, melted and flowed out within the region of the bending line, whereas during the second phase the material is subjected to being cooled at ambient temperature or, additionally, in a stream of a blown gas causing the material to shrink along the fibres perpendicular to the bending line due to the internal stresses originated by the thermal shrinkage of the material in the heated region and the deformation of the object to be permanently changed.

2. A method according to Claim 1, characteri­sed in that the heating is performed with a focussed laser radiation beam or a concentrated high-power electron beam.

3. A method according to Claim 1, characte­rised in that the material is brought up to the plasticising and melting state to a depth G smaller than the thickness L of the object.

4. A method according to Claim 1, characte­rised in that the heating takes place under a protective atmosphere, thereby preventing the access of air to the region being heated.

5. A method according to Claim 1, characte­rised in that the surface of the heated material is covered with a substance increasing the coefficient of absorption of the stream of energy.

Drawing