DE10212400C1 - Production of molded components comprises cold forming and induction heating of molding to produce recrystallization along seam and lower resistance to further working and cooling - Google Patents

Abstract

Production of molded components (2) comprises cold forming and induction heating of the molding to produce recrystallization along the seam and lower resistance to further working and cooling. The heating is only partial in those areas (a,b) on which further working is to be carried out.

Description

The invention relates to a method for producing a molded component by cold reshape with an annealing of the reshaped molded component for the purpose of recrystallization sation of the structure to reduce the deformation resistance for one further forming process with subsequent cooling.

Metallic components such as circuit boards or preformed components made of unalloyed or low-alloy steels, alloyed or high-alloyed stainless steels such as austeniti usually, ferritic or duplex steels or made of light metal good formability, so that all common cold forming processes such as Example bending, upsetting, expanding and hydroforming for forming men of these materials can be used. Since there is a metal if there is is plastically deformed above the yield point in the deformed areas solidified, this strain is a strain hardening of the material bound by which the hardness, the yield strength and the tensile strength of the work increase, while the elongation at break and the impact strength decrease takes.

Strain hardening is positive, on the one hand, because it also has a higher material strength leads to a longer service life under dynamic load. It ever prepares but problems if the molded component is formed in several steps and due to the remaining residual elongation, the resistance to deformation in the cold solidified area is so large that there is further plastic deformation would otherwise lead to breakage of the material in this area. To the cold to be able to reshape the solidified area is a recrystallization in this area in the direction of the starting structure of the material prior to the work hardening tion so that the original forming capacity and the ent  speaking ductility of the material is restored. A full or partial structural transformation can be carried out using a suitable annealing process and a temperature adapted to the material, which also depends on the degree of deformation can be agreed, achieved. The molded component is converted temperature such as austenitization temperature or recrystallization temperature warmed and cooled after a transformation of the structure, so that the At least partially restores the initial structure. That way, at for example a molded component made of suitable steels on austenitizing temp temperature warmed up and after a transformation of the structure into austenite slowly decreased be cooled so that the austenite converts to a ferrite / pearlite structure converts. This is the recrystallization to reduce the shape change wi carried out for another forming process.

According to the prior art, the heat treatment is carried out in a continuous furnace performed with a temperature control adapted to the material, whereby at this process the entire component slowly to transition temperature warms and is held until sufficient conversion. In connection there is a slow cooling with the aim of using the ge to restore at least part of the lower deformation resistance. because is always annealed the entire component in the furnace, so that in some Effect of the work hardening for all areas of the Component is reversed by recrystallization. Consequently, in Be range, which are not reshaped, the potential of the material is not fully exploited.

In addition, such a continuous furnace with a length of up to 30 meters and up Appropriate space and time for 90 minutes process time sprucht. In mass production, the production chain is through this glow pro process is also interrupted because it is transported from the forming tool to the furnace and thus often to external service providers with additional handling and correspond appropriate logistics is required. This is associated with considerable costs.  

DE 31 27 327 A1 describes a method for producing bellows Metal alloys in which a piece of pipe is deformed by rolling onto a Temperature above the recrystallization temperature heated, cooled, locally is cross-deformed and axially compressed. The heating of the pipe section is made by means of electric current. However, here too the whole Component heated, so that the work hardening effect for the entire component undone.

The present invention is therefore based on the object of a generic to demonstrate a process that is simple, reliable and inexpensive classifies an existing mass production process.

The invention solves this problem with the method mentioned in claim 1. Accordingly, annealing is only carried out partially in the areas where another forming process follows. This will in the annealed Be the work hardening by recrystallization of the structure is sufficient The structure of the material was removed before another cold forming step or reduced. As a result, you save energy and time because not all of it Molded component is heated to transition temperature.

According to a special embodiment, remain in the formed molded component in addition to annealed and further formed areas by the first forming Strain hardened areas, which in the work hardened areas Advantages of work hardening such as a longer service life with dynamic loading load is retained due to the higher material strength. By the Bei retention of these already generated local strength increases in the component make better use of the potential of the material.

The partial annealing is preferably carried out by means of induction heating. The areas with existing work hardening can be specifically annealed, which is followed by a further forming process. In addition, the In production heating within seconds with compact systems conditions, which enables a closed process chain forming / annealing. The Continuous furnace can be substituted, so that a transport to the furnace, eventu ell also to external service providers with appropriate logistics and compliance the expenditure of time is eliminated.

According to this particular embodiment of the method according to the invention can in particular to carry out the partial induction heating Molded component and an induction heating device moved relative to each other become. For example, the molded component is gripped in a defined manner by a robot fen and passed through a stationary induction coil. Accordingly, too  the coil robot-controlled the contour of the area to be annealed on the molded component depart. Depending on the molded component, it is also possible to use other control elements such as for example a linear control, in which the coil the component or vice versa the component travels the coil on a predetermined linear path. Component tolerances and changes in the geometry and wall thickness of the molded component can via a temperature-controlled power adjustment and / or egg ner appropriate alignment of the positions of induction coil and component be balanced.

The partial induction heating can be adapted to the contour of the component be performed. This can additionally or alternatively to a relative move happen. In addition to a relative movement, the coil can do the component or vice versa the component the coil for example on one of the component geometry Follow the simulated path, whereby the coil or the component also smelled perform a feed movement in the direction of the component or the coil can. As an alternative to a relative movement, one of the cones Form inductor adapted to the area to be annealed is used. in this connection For example, the component can be inserted into a form inductor, so that without further relative movement, a uniform heating on conversion can be generated over the desired range.

The are particularly advantageous for achieving uniform heating Induction heating device and the molded component rotating against each other or oscillating up and down.

Cooling by means of still or slightly flowing air is preferred carried out. For example, unalloyed and low-alloy steels as well certain stainless steels after annealing in still or slightly flowing air cooled to the desired structure with less deformation resistance and to get the corresponding grain sizes.

In a further embodiment, the cooling is carried out by means of one of the inductors ring heating device downstream for water cooling carried out. Such an immediate cooling serves, for example, at austeni  stainless steel containing chromium, a loss of corrosion-resistant Chromium content in the surface, which is responsible for the corrosion resistance Lich, and to counteract a formation of chromium carbide.

About surface oxidation and the formation of scale layers when heated to avoid the area, the glow can take place in a protective atmosphere.

In a preferred embodiment of the method according to the invention for the production of an exhaust pipe for motor vehicle construction in a first Cold forming of a pipe, a central bellows as well as on the bellows adjacent pipe bends are formed, then only these pipe bends are partial annealed and then in a subsequent forming process Pipe bends expanded, in particular by internal high pressure forming. Possible further applications of the method according to the invention relate, for example se pipe components with multi-stage hydroforming processes, where local Solidifications are desired, as are preformed pipe components a consolidation in the first forming area to increase the service life is such.

The method according to the invention is based on some embodiments examples described in more detail in the drawings. Show

Fig. 1 in top view of a straight tube (1),

Fig. 2, the tube (1) of FIG. 1 after a first forming step,

Fig. 3, the tube (1) of Fig. 2 after a widening in the formed region (a),

Fig. 4, in top view, a straight exhaust pipe (2)

Fig. 5, the exhaust pipe (2) of Fig. 4 after the shaping of a central folding bellows (3),

Fig. 6, the exhaust pipe (2) of Fig. 5 after the forming of each one Rohrbo gen (4, 5) left and right of the bellows (3),

Fig. 7, the exhaust pipe (2) of FIG. 6 for a widening of the tube sheets (4, 5) in the previously-formed region (b, c),

Fig. 8 schematically shows a robot ( 6 ) which guides the tube ( 1 ) from Fig. 2 through an induction coil ( 7 ) with a downstream ring shower ( 8 ).

Fig. 1 shows a top view of a pipe ( 1 ) which has not yet been formed.

In Fig. 2, the straight tube ( 1 ) was bent in the middle by means of cold forming by bending. As a result, the material of the tube ( 1 ) has been strain-hardened in the deformed area (a). A further cold forming in the already formed area of the curvature (a) would possibly lead to a breakage of the tube ( 1 ) in the already formed area (a) due to the higher deformation resistance resulting from the cold forming. By means of the method according to the invention, the tube ( 1 ) is therefore partially annealed in the region of the bend (a) in which it is to be further formed. With the help of an induction heating device, the annealing can be accomplished in seconds and exactly in the area of the curvature. The respective pipe ends, which have not undergone forming, are not heated to the transition temperature. This can save time and energy. The tube ( 1 ) is then cooled so that the desired recrystallization takes place in the curved region (a) in the direction of the initial structure and the resistance to deformation decreases.

In Fig. 3 the tube ( 1 ) in the curved area (a) has subsequently been expanded by means of internal high-pressure forming. As a result, it has hardened again in this area (a). At the respective pipe ends, the material is still in the initial structure without strain hardening, since no forming process took place in the area of the pipe ends.

Fig. 4 shows in plan view a straight exhaust pipe (2), for example, from an austenitic stainless steel with the material names X15CrNiSi 20-12.

In FIG. 5, in the middle of this straight exhaust pipe (2) is a bellows (3) has been formed by hydroforming. As a result, the material of the exhaust pipe ( 2 ) has hardened in the area of the bellows ( 3 ). This Kaltver consolidation of the bellows ( 3 ) increases its life, it is therefore desirable and should be retained in a further shaping of the exhaust pipe ( 2 ).

In Fig. 6, a pipe bend ( 4 , 5 ) has been formed from the exhaust pipe ( 2 ) left and right of the bellows ( 3 ) by bending. As a result, the exhaust pipe ( 2 ) in the two curved areas (b, c) of the pipe bends ( 4 , 5 ) has been strain hardened by the cold forming. The work hardening of the bellows ( 3 ) has remained unaffected. A further deformation of the pipe bends ( 4 , 5 ) is not possible due to the work hardening in the already curved areas (b, c) without the risk of cracking or breaking of the exhaust pipe ( 2 ) in these areas (b, c). Therefore, the exhaust pipe ( 2 ) in the curved areas (b, c) of the pipe bends ( 4 , 5 ) is preferably inductively partially annealed. With this annealing, the exhaust pipe ( 2 ) made of the material X15CrNiSi 20-12 is heated in the curved areas (b, c) to 1050 ° to 1100 ° C, whereby the material structure in these areas (b, c) is converted, by which the initial structure of the material before cold work hardening with the lower resistance to deformation resets itself after a subsequent cooling. This eliminates strain hardening in the curved areas (b, c). In the bellows ( 3 ), which did not take part in the annealing due to the precise control option of the induction heating device, the work hardening is retained as desired despite the annealing process by using the method according to the invention.

In Fig. 7, the pipe bends ( 4 , 5 ) of the exhaust pipe ( 2 ) in the already formed and annealed area (b, c) have been expanded by means of hydroforming. As a result, the material structure in the widened areas (b, c) has hardened again. Thus, both the widened pipe bends ( 4 , 5 ) and the bellows ( 3 ) are strain hardened on this exhaust pipe ( 2 ), which increases the life of the exhaust pipe ( 2 ). Especially in the bellows ( 3 ), which was annealed in a manufac turing of the exhaust pipe ( 2 ) using a conventional method and would therefore be more ductile, this life-increasing strain hardening can only be achieved by means of the partial annealing method according to the invention.

Fig. 8 shows schematically a robot ( 6 ), which has gripped the tube ( 1 ) from Fig. 2 after forming the curve in the middle of the tube ( 1 ) and for annealing the strain hardened area (a) of the curve in downward movement through an induction heating device ( 7 ) or a stationary induction coil. Exactly the area of the curvature (a) is annealed by induction. The induction coil ( 7 ) is connected downstream of a ring shower ( 8 ) for water cooling. For example, in the case of austenitic chromium-containing stainless steels, a loss of corrosion-resistant chromium contents in the surface, which are responsible for the corrosion resistance, and a formation of chromium carbide are counteracted. In the case of suitable steels which do not harden due to the immediate cooling, the cooling process can also be accelerated in this way.

Claims (11)

1. A method for producing a molded component ( 1 , 2 ) by cold forming with an annealing of the molded component ( 1 , 2 ) for the purpose of recrystallization of the structure to reduce the resistance to deformation for a further forming process with subsequent cooling, characterized in that annealing only is partially carried out in the areas (a, b, c) in which a further forming process follows. 2. The method according to claim 1, characterized in that in the molded component ( 1 , 2 ) in addition to annealed and further formed areas (a, b, c) remain work hardened areas ( 3 ) by the first forming step. 3. The method according to claim 1 or 2, characterized, that the partial annealing is carried out by induction heating. 4. The method according to claim 3, characterized in that the partial component ( 1 , 2 ) and an induction heating device ( 7 ) are moved relative to each other for partial induction heating. 5. The method according to any one of claims 3 and 4, characterized in that the partial induction heating is carried out adapted to the contour of the molded component ( 1 , 2 ). 6. The method according to any one of claims 3 to 5, characterized in that the induction heating device ( 7 ) and molded component ( 1 , 2 ) are moved up and down against each other in a circular or oscillating manner. 7. The method according to any one of claims 1 to 6, characterized, that the cooling is carried out by means of still or slightly flowing air leads. 8. The method according to any one of claims 1 to 6, characterized in that the cooling is carried out by means of a ring shower ( 8 ) connected downstream of the induction heating device ( 7 ) for water cooling. 9. The method according to any one of the preceding claims, characterized, that the glow takes place in a protective atmosphere.   10. The method according to any one of the preceding claims, characterized in that for the production of an exhaust pipe ( 2 ) for motor vehicle construction in a first cold forming of a pipe ( 2 ) a central bellows ( 3 ) and the bellow ( 3 ) adjacent pipe bends ( 4 , 5 ) are formed so that only these pipe bends ( 4 , 5 ) are partially annealed, and then these pipe bends ( 4 , 5 ) are expanded in a subsequent forming process. 11. The method according to claim 10, characterized in that the pipe bends ( 4 , 5 ) are expanded by internal high pressure forming.