DE102014001806A1 - Manufacturing piston useful for an internal combustion engine, comprises welding at least two components with each other by a weld seam, in which at least one of components to be welded, is formed from steel having specific carbon content - Google Patents

Abstract

Manufacturing piston (1) for an internal combustion engine, comprises welding at least two components (2, 3) with each other by at least one weld seam (5). At least one of the components to be welded, is formed from steel having a carbon content of not > 0.3 wt.%, preferably not > 0.25 wt.%. An independent claim is also included for the piston for the internal combustion engine, manufactured by the above method.

Description

The invention relates to a method for producing a piston for an internal combustion engine according to the features of the preamble of claim 1 and a piston for an internal combustion engine according to the features of the preamble of claim 5.

From the prior art, as in the DE 40 24 381 C2 described a piston for internal combustion engines with forged steel areas known. The piston has forged areas of precipitation-hardening ferritic-pearlitic steel and areas of light metal.

In the DE 10 2007 021 101 A1 an alloyed steel is described. The steel is used for a component for internal combustion engines, in particular for pistons or piston parts.

From the EP 1 640 105 A1 a method for laser welding is known. In the process of laser welding carbon steel components, a weld is produced by a first laser beam. A second laser beam is provided for tracing the weld for a heat treatment of the weld.

In the DE 10 2004 001 166 B4 a method for laser welding with preheating and / or reheating in the region of the weld is described. The welding and the heat treatment are carried out by means of a single laser beam with substantially equal power. The welding and the heat treatment are spaced in time such that the temperature decrease of the respective irradiation surface from the time of the first irradiation to the time of the subsequent irradiation is less than 50 percent. During the heat treatment, the laser energy input related to the irradiation surface and the time unit is adjusted by increasing the feed rate such that the side of the already existing or future weld seam facing away from the laser beam is heated by at least 10 ° C.

The invention is based on the object to provide a comparison with the prior art improved piston for an internal combustion engine and an improved method for its production.

The object is achieved by a method for producing a piston for an internal combustion engine having the features of claim 1 and a piston for an internal combustion engine having the features of claim 5.

Advantageous embodiments of the invention are the subject of the dependent claims.

In a method according to the invention for producing a piston for an internal combustion engine, at least two components are welded to one another by means of at least one weld seam, wherein at least one of the components to be welded together is formed from a steel having a carbon content of at most 0.3 percent by weight, in particular a maximum carbon content of 0.25% by weight.

Pistons for internal combustion engines are made to reduce carbon dioxide emissions from steel. In this case, individual components, for example a bottom and a shaft of the piston, are welded together to form optimized component shapes. Prior art piston manufacturing processes, particularly for commercial vehicle pistons, use steels having a carbon content greater than 0.3 percent by weight, such as 42CrMo4 steel. However, due to this relatively high carbon content when using fusion welding methods, these steels are only of limited weldability due to strong hardening and a high risk of cracking. Therefore, in these known from the prior art piston manufacturing process, a high manufacturing and quality assurance effort is required. For example, the components must be preheated before welding and reheated after welding. Furthermore, in order to eliminate the swelling-related hardening and tensile residual stresses in the weld seam area, additional compensation of the entire piston is additionally carried out. Such a process sequence, which provides several of the steps preheating, reheating, quenching and one hundred percent crack detection is very complex and very costly.

This effort is significantly reduced by the inventive method in which at least one of the components to be welded together is formed from a much better weldable due to the lower carbon content steel. The use of a weldable steel for at least one of the components to be welded together, ie the formation of at least one of these components of such a weldable steel, which has a maximum carbon content of 0.3 weight percent, in particular of at most 0.25 weight percent, leads to significant less hardening due to welding than, for example, when using 42CrMo4 steel or other steel with a carbon content greater than 0.3% by weight. This is a Vickers hardness of the piston produced by the method in the weld area and adjacent to the weld heat-affected zones advantageously less than 500 HV 1. In this way, the risk of cracking is significantly reduced and robustness of the piston is significantly increased.

By means of the method according to the invention, a strength of the piston can already be achieved without additional pretreatment and after-treatment, which corresponds to the strength of aluminum pistons hitherto used in the automobile sector. These aluminum pistons have a strength of less than 400 MPa. This value is determined by the steels which are suitable for the formation of at least one of the components to be welded, ie. H. which have a carbon content of at most 0.3 percent by weight, in particular of at most 0.25 percent by weight, already achieved in the unmolded state. A tempering to increase the strength can thus be omitted in the process of the invention. The steel used in each case with the carbon content of at most 0.3 percent by weight, in particular not more than 0.25 percent by weight, for forming at least one of the components to be welded can by appropriate alloying elements, such as chromium, silicon and / or aluminum, with respect to its oxidation resistance and / or its physical-thermal properties such as thermal conductivity, thermal expansion and heat capacity can be optimized.

By using a weldable steel, i. H. by the formation of at least one of the components to be welded together from such a weldable steel, which has a maximum carbon content of 0.3 weight percent, in particular of at most 0.25 weight percent, thus in the process according to the invention, the steps required for steels with a higher carbon content Preheating before welding and / or postheating after welding is eliminated. Furthermore, can be dispensed with a tempering for relaxation of the welded piston. If such a remuneration is required for reasons of strength due to predetermined strength values which the piston must reach, then such a remuneration can continue to be carried out. In addition, the 100% non-destructive testing can account for cracks, since the cracking risk is considerably reduced by the method according to the invention. The inventive method for the production of pistons offers by the described use of weldable steel for at least one of the components to be welded together with comparable component robustness of the piston cost savings through the described elimination of individual process steps.

Embodiments of the invention are explained in more detail below with reference to drawings.

Showing:

1 2 is a schematic sectional view of two components to be welded together to form a piston;

2 schematically a sectional view of a piston of two welded together components with holders of the components, and

3 schematically a sectional view of a piston of two welded together components showing heat affected zones.

Corresponding parts are provided in all figures with the same reference numerals.

1 shows a longitudinal sectional view of two components 2 . 3 made of steel, which in a process for the production of a piston 1 for an internal combustion engine to be welded together. In the example shown here is the one component 2 around a bottom of the piston 1 and the other component 3 around a shaft of the piston 1 , The piston shown here 1 is an example of two components 2 . 3 built up. Likewise, more than two components can become a piston 1 be welded. For welding, the two components 2 . 3 clamped in a holding device and held, as in 2 shown greatly simplified, with holding means 4 the holding device are shown schematically as arrows. A clamping force of the respective holding means 4 for clamping the respective component 2 . 3 acts in the direction of the arrow. 3 shows the piston 1 with a weld formed by the welding 5 and heat affected zones 6 , which is the side of the weld 5 be formed by welding. These heat affected zones 6 are areas in which the material of the piston 1 influenced by the introduction of heat during welding and thereby changed in its structure.

The two components 2 . 3 be welded together by means of at least one welding unit not shown here in a welding process, in particular a fusion welding process. For this, the two components 2 . 3 and / or the welding unit moves, so that a relative movement between the two components 2 . 3 and the welding unit takes place, whereby the formation of the weld 5 , in this example, completely or in sections, around a circumference of the two components 2 . 3 around, is made possible. Be the two components 2 . 3 moved, this is synchronous to a relative movement between the two components 2 . 3 to avoid and exact and constant alignment of the two components 2 . 3 to ensure each other. For example, the two components 2 . 3 about an axis of rotation, which is a longitudinal axis of the piston 1 , ie its axis of rotation, corresponds, turned and the welding unit stands still. Alternatively or additionally, a movement of the welding unit is possible.

The at least one welding unit can be designed, for example, as a laser beam welding unit, as a laser hybrid welding unit, as an electron beam welding unit, as a capacitor discharge welding unit or as a metal inert gas welding unit, so that the two components 2 . 3 Accordingly, by laser welding, laser hybrid welding, electron beam welding, capacitor discharge welding (KE) or gas metal arc welding, ie by metal welding with inert gases (MIG welding) or with active, ie reactive gases (MAG welding) welded. The welding process can be carried out with or without filler metal. This depends, for example, on the particular welding process. It is also possible to use several identical or different welding units.

In principle, the welding process can also be carried out by means of a friction welding process.

By means of this chosen welding process, the components become 2 . 3 made of steel welded together. In this case, at least one of the two components to be welded has 2 . 3 , ie their steel, a carbon content of at most 0.3 percent by weight, advantageously a maximum carbon content of 0.25 percent by weight. Ie. In the process, at least one of the two components to be welded is first of all 2 . 3 formed of such a steel having a carbon content of at most 0.3 weight percent, advantageously at most 0.25 weight percent, and thereafter the two components 2 . 3 welded together. It can also be both components to be welded together 2 . 3 such a low carbon content of at most 0.3 weight percent, advantageously at most 0.25 weight percent, ie, be formed in the process of a steel having this carbon content.

Preferably, this steel, from which at least one of the components 2 . 3 or both components 2 . 3 be formed, a manganese content of up to 2.5 weight percent and / or a chromium content of up to three percent by weight and / or a molybdenum content of up to one percent by weight. The steel may, alternatively or additionally, be optimized by appropriate alloying elements, for example chromium, silicon and / or aluminum, in terms of its oxidation resistance and / or its physical-thermal properties such as thermal conductivity, thermal expansion and heat capacity. A suitable steel is for example 18MnCr5-3 or 18MoCr4 or 18CrMo4. In a steel with such a low carbon content of at most 0.3 weight percent, in particular at most 0.25 weight percent, it is a particularly good weldable steel, so no costly pretreatment of the components 2 . 3 before welding and no time-consuming post-treatment of the piston 1 after welding is required.

piston 1 for internal combustion engines are made to reduce carbon dioxide emissions from steel. In piston manufacturing processes according to the prior art, steel pistons, in particular in the commercial vehicle sector, are usually made of steel with a significantly higher carbon content, ie with a carbon content above 0.3 percent by weight, for example with a carbon content of about 0.4 percent by weight, for example made of 42CrMo4 steel.

Because of this high carbon content, this steel or the piston components made of this steel are only partially suitable for welding. The problem is when welding such steels in the high degree of hardening and the risk of cracking. Therefore, a cost-intensive and complex process for producing the known from the prior art steel pistons made of steel with the carbon content of greater than 0.3 weight percent is required, in particular a high production and quality assurance effort. This process sequence requires the process steps of preheating the piston components before welding and / or reheating the steel piston after welding, tempering and crack testing. In this process, for example, the piston components are preheated, welded together and reheated. Subsequently, a crack test in the form of a non-destructive test is carried out. Thereafter, the tempering of the steel piston and then a new crack test in the form of a non-destructive test are performed.

By using a steel with a lower carbon content, ie with one Carbon content of at most 0.3 percent by weight, in particular at most 0.25 percent by weight, for at least one of the components 2 . 3 , this risk of hardening and cracking in the area of the weld 5 prevented or at least significantly reduced. In addition, this steel has a high robustness. By using this steel with the described low carbon content are the above-mentioned process steps, ie the preheating of the components 2 . 3 before welding and / or reheating the piston 1 after welding, tempering and crack testing, no longer required. If necessary, however, individual of the process steps can still be used in the process, for example, for a given strength level of the components 2 . 3 before welding and / or the piston 1 after welding the components 2 . 3 adjust. The process steps mentioned are thus in the method described here, in which at least one of the components 2 . 3 is formed from a low carbon steel of not more than 0.3% by weight, in particular not more than 0.25% by weight, an optional component of this process and no longer an obligatory constituent.

In particular, the preheating of the components 2 . 3 completely eliminated before welding. The reheating of the piston 1 after welding can be optionally retained. The crack test, ie the non-destructive testing after welding, can be omitted or at least significantly reduced. For example, only random samples are performed.

The tempering of the piston 1 if this is only intended to serve the stress situation in the area of the weld 5 and the adjacent heat affected zone 6 it is not necessary to calm down. However, it may be a compensation of the piston 1 be performed to the strength of the piston 1 to set specifically, ie to set a predetermined strength level.

In the simplest variant of the method thus become the components 2 . 3 of which at least one, as described, from a steel having a carbon content of at most 0.3 weight percent, in particular at most 0.25 weight percent, is welded together and the process is completed. In this simplest variant of the method, there is no preheating of the components 2 . 3 before welding, no reheating of the piston 1 after welding, no tempering and no crack testing required. As a result, the production costs and costs are considerably reduced.

To set a predetermined strength level, in a further variant of the method after the welding of the components 2 . 3 hardening, tempering and / or reheating are performed. For example, to adjust the predetermined strength levels after welding the components 2 . 3 a heat treatment process, in particular a tempering over martensite and / or bainite, are performed.

In a further variant of the method, to adjust the predetermined strength level, as an alternative or in addition to the described hardening, tempering, reheating and / or heat treatment process, such components 2 . 3 be welded together, of which at least one component 2 . 3 already has an increased basic strength before welding, preferably both components 2 . 3 , Ie. at least one of the components 2 . 3 already has a predetermined level of strength before welding. Preferably, both components 2 . 3 this high level of strength. This is done, for example, by an appropriate pretreatment of the at least one component 2 . 3 , preferably both components 2 . 3 , achieved before welding. This pretreatment may include, for example, a pre-tempering via martensite and / or bainite and / or a work hardening process and / or a natural or controlled cooling after a forming process, in particular after a hot forming process, or a combination of said processes.

The method thus provides by the use of the steel with the low carbon content of at most 0.3 weight percent, in particular at most 0.25 weight percent, compared to the steel pistons from the steel with a higher carbon content comparable component robustness cost savings through the elimination of individual process steps.

A Vickers hardness of the process by welding two components 2 . 3 made of steel pistons 1 this good weldable steel with the low carbon content described above is in the weld area and in the weld 5 adjacent heat-affected zones 6 advantageously less than 500 HV 1.

The method enables an economical and safe overall process management of the piston production, by the use of a weldable steel, ie a steel having a carbon content of at most 0.3 weight percent, in particular at most 0.25 weight percent, for at least one of the components 2 . 3 the risk of hardening and hardening cracks, reduced or avoided while improving the impact resistance and fatigue strength. Furthermore, this improved by the method properties of the piston 1 Reduction of quality assurance efforts, especially in mass production, guarantee and goodwill costs are reduced and customer satisfaction is increased. The trained with the process piston 1 contribute to the reduction of carbon dioxide emissions from internal combustion engines.

In prior art steel pistons having the above-described high carbon content of greater than 0.3 weight percent and having at least one welded joint, without the preheat and heat treatment after welding, the weld produced by the joining process is often 5 Weak point under dynamic load, which is why in the method known from the prior art, these process steps can not be omitted. When welding material is the two components to be joined 2 . 3 melted. After solidification, in addition to the unavoidable notch at the weld root, a hardened, not relaxed weld structure is created. Practice shows that under dynamic stress exactly this weld 5 or the weld root area can be the starting point for vibration cracks and thus life-limiting. Under motor conditions exactly this weld can be 5 represent the weak point.

To increase the dynamic piston strength or the service life of the piston 1 It is precisely this area that needs to be optimized. This is achieved by the use of the weldable steel having a carbon content of at most 0.3 percent by weight, in particular at most 0.25 percent by weight, wherein the preheating, reheating and tempering are no longer strictly necessary, as described. In this way, with a much lower manufacturing and cost an increase in the component toughness of the piston 1 and a reduction of harmful component residual stresses of the piston 1 achieved in comparison to the steel piston known from the prior art. This leads to improved dynamic strength values.

Basically, the described piston 1 be designed in the ready for the engine state with or without surface coating. In the case of a surface coating, this can be present completely or in sections on the component.

The process is very economical and cost-effective, since significantly fewer process steps are required. By means of the method is a life of the piston 1 increases, a dynamic component strength of the piston 1 is increased and constructive degrees of freedom are increased, for example, a reduction in wall thickness and thus a reduction in weight is possible. These aspects play in particular with a piston 1 for a combustion engine of a vehicle a significant role. The method thus also makes a contribution to lightweight construction possible and engine damage by a destroyed piston 1 are avoided or at least reduced to a minimum.

The invention is not limited to the described embodiments. In principle, it is also conceivable that the piston 1 not from at least two components 2 . 3 is formed, but in one piece and that by means of the method according to the invention at least one point of the integral or joined piston 1 a component opening, not shown, is closed by a fusion welding process.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4024381 C2 [0002]
• DE 102007021101 A1 [0003]
• EP 1640105 A1 [0004]
• DE 102004001166 B4 [0005]

Claims (6)

Method for producing a piston ( 1 ) for an internal combustion engine, characterized in that for the formation of the piston ( 1 ) at least two components ( 2 . 3 ) by means of at least one weld ( 5 ) are welded together, wherein at least one of the components to be welded together ( 2 . 3 ) is formed of a steel which has a carbon content of at most 0.3 percent by weight, in particular a maximum carbon content of 0.25 percent by weight. A method according to claim 1, characterized in that at least one of the components to be welded together ( 2 . 3 ) is formed from a steel having a manganese content of up to 2.5 percent by weight and / or having a chromium content of up to three percent by weight and / or with a molybdenum content of up to one percent by weight. Method according to claim 1 or 2, characterized in that before the welding of the components ( 2 . 3 ) in at least one of the components ( 2 . 3 ) is set by pretreatment a predetermined strength level. Method according to one of claims 1 to 3, characterized in that after the welding of the components ( 2 . 3 ) a heat treatment process of the piston ( 1 ) is performed to set a predetermined strength level. Piston ( 1 ) for an internal combustion engine, produced by a method according to one of claims 1 to 4, which by welding at least two components ( 2 . 3 ), wherein at least one of the components ( 2 . 3 ) is formed of a steel which has a carbon content of at most 0.3 percent by weight, in particular a maximum carbon content of 0.25 percent by weight. Piston ( 1 ) for an internal combustion engine according to claim 5, wherein at least one of the components to be welded together ( 2 . 3 ) is made of a steel having a manganese content of up to 25 percent by weight and / or having a chromium content of up to three percent by weight and / or having a molybdenum content of up to one percent by weight.

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