DE102020210036B4 - Method of manufacturing a piston for an internal combustion engine and Pistons for an internal combustion engine - Google Patents

Abstract

Method for producing a piston for an internal combustion engine, characterized in that a piston blank is provided, a region of the piston blank is remelted by means of tungsten inert gas welding and then the first annular groove is machined into the remelted area, characterized in that the depth of the remelted area is in Circumferential direction of the piston blank is varied.

Description

TECHNICAL AREA

The invention relates to a method for producing a piston for an internal combustion engine and a piston produced in this way.

STATE OF THE ART

Due to increasing loads in internal combustion engines, in particular due to high ignition pressures and changed combustion strategies, which promote the occurrence of pre-ignition with locally limited ignition pressure loads, modern gasoline engine pistons have to be reinforced in the first ring groove. As a result, piston damage, such as ring land fractures, starting from the groove base of the first ring groove, can be largely prevented.

Diesel engine pistons in particular are known as prior-use objects, in which the first ring groove is reinforced by casting in a so-called ring carrier made of an iron material (Niresist). More recently, this principle has also been applied to petrol engine pistons. However, this procedure is associated with additional costs due to the need for a ring carrier as a purchased part, the increased process complexity during casting, the increased effort involved in machining the piston and an increased risk of rejects due to a poor material connection between the base material and the ring carrier. In addition, the weight of the piston is disadvantageously increased.

US 2005/0 132 569 A1 discloses the strengthening of an annular groove by applying a coating material and subsequent heating using a laser beam.

US 2008/0 053 384 A1 relates to hardening of the groove flanks using a similar method.

According to the DE 28 35 332 C2 an annular groove is remelted by means of an energy beam, in particular an electron beam.

the DE 10 2008 048 978 A1 relates to a method for reinforcing at least one annular groove of a piston for an internal combustion engine, with an inhomogeneous structure in the area of the annular groove to be introduced being homogenized by a remelting process after the production of a piston blank, and in this first processing step of the remelting process alloying additives are melted with the aid of a heat source and thus in be added to the reinforcing area, with the invention providing that the already partially homogenized structure is superficially melted again in a further processing step, but now without the addition of alloying additives, with the aid of the heat source.

In the EP 0 284 118 A2 discloses a method of reducing wear between the radial faces of a piston ring and the radial faces of the cooperating piston ring groove in an aluminum alloy piston, the method comprising the step of locally alloying at least a portion.

the DE 29 26 699 A1 relates to a method for hardening an annular groove in a piston made of an aluminum alloy, in which an annular wear-resistant weld seam is made in the piston and the annular groove is then turned out in it, the weld seam being melted through a predetermined ring zone of the piston with simultaneous addition of an alloy material to the molten aluminum alloy of the piston is generated.

In the DE 24 25 358 A1 describes a method of applying a wear-resistant copper-based reinforcement layer to one or more areas of an aluminum alloy piston by preheating and arc spraying, the piston being preheated to 75 to 125 °C and the spraying of the alloy particles initially with a gas pressure of 3, 10 bar and subsequently with a gas pressure of 4.80 bar and at an arc voltage of 27 or 28 volts throughout spraying or initially with a gas pressure of 2.80 bar and an arc voltage of 42 volts and subsequently with a gas pressure of 4.50 bar and an arc voltage of 30 volts.

1. a) Anordnen des Kolbens mit der zu beschichtenden Kolbennut in einer Beschichtungseinrichtung,
2. b) Fluiddichtes Abdichten eines Zwischenraums, der im Bereich der zu beschichtenden Kolbennut zwischen dem Kolben und der Beschichtungseinrichtung ausgebildet wird, mittels eines mit einem Fluid befüllbaren und expandierbaren Dichtungselements,
3. c) Aufbringen der Schutzbeschichtung durch Einbringen eines Beschichtungsmaterials in den Zwischenraum, so dass eine Oberfläche der Kolbennut mit dem Beschichtungsmaterial beschichtet wird.

the DE 10 2015 222 862 A1 relates to a method for coating at least one piston groove provided on a piston with a protective coating, comprising the following steps:

1. a) arranging the piston with the piston groove to be coated in a coating device,
2. b) Fluid-tight sealing of an intermediate space, which is formed in the area of the piston groove to be coated between the piston and the coating device, by means of a sealing element that can be filled and expanded with a fluid,
3. c) applying the protective coating by introducing a coating material into the gap so that a surface of the piston groove is coated with the coating material.

In the DE 10 37 201 B describes a light metal piston intended for internal combustion engines with partial reinforcement of the flanks of the ring groove by cast-in flat inserts made of a material that has a lower coefficient of thermal expansion and greater hardness than the piston material, in which the inserts in the area of the flanks of the ring groove represent separate segment parts and in which the individual segment part is assigned to only one of the two flanks of the same annular groove as a reinforcement element.

the DE 24 05 389 A1 describes light-metal pistons for internal combustion engines with ring carriers cast in the ring zone, preferably in the region of the uppermost ring groove, which meander in the radial direction and are made of ordinary gray cast iron and into which the ring grooves are incorporated.

PRESENTATION OF THE INVENTION

Against this background, the object of the invention is to create an efficient method for producing a piston for an internal combustion engine, in which the susceptibility to cracking in the area of the piston ring grooves is reduced. Furthermore, a piston produced in this way is to be provided.

This problem is solved on the one hand by the method described in patent claim 1 . Accordingly, in the course of manufacturing a piston for an internal combustion engine, a piston blank is first provided, then a region of the piston blank is remelted using tungsten inert gas welding (WIG/TIG) and then the first annular groove is machined into the remelted region. The first annular groove is the annular groove closest to the combustion chamber. In other words, the piston material itself is remelted and no cast-in part with the associated disadvantages is required.

The invention is based on the finding that rapid solidification occurs after the local melting by means of tungsten inert gas welding, which leads to a solidification structure that is very much finer compared to the original cast structure. These significantly finer phases have a significant positive influence on strength, ductility and crack susceptibility. In particular, the inventors have found that cracks often start from the comparatively small radius of curvature between the bottom and flank of the groove. These areas are also referred to as groove base radii and benefit particularly from the extremely fine structure, as the initiation of cracks in this area can be significantly reduced. According to the invention, the first annular groove is worked into the remelted area.

Due to the preferred use of the tungsten inert gas welding process for the remelting treatment, comparatively little thermal energy is introduced, so that the heat-affected zone is locally extremely limited and there is no risk of thermal damage to the piston, for example due to distortion and the like.

The remelting depth is advantageously changed over the circumference of the piston blank, so that in other words a different remelting depth is produced in different areas of the piston circumference. As a result, on the one hand the process time can be optimized and on the other hand the technical effectiveness of the remelting can be improved in individual areas.

Due to the positive properties described above, use of the method according to the invention is suitable for the production of Otto pistons as well as diesel pistons.

Preferred developments of the method according to the invention are described in the further claims.

According to an advantageous embodiment of the invention, the first annular groove lies entirely in the remelted area. Preferably, the remelted area also includes at least part of the second ring land present in the resulting piston below the first ring groove. All ring grooves are particularly preferably in the remelted area. The refined microstructure advantageously leads to improved material properties in terms of strength, ductility and susceptibility to cracking in the relevant sections of the piston.

Advantageously, the remelted area is deeper than the first annular groove machined subsequently, preferably 1 mm deeper than the first annular groove machined. Furthermore, it is preferred that the remelted area has a depth of 0.5 mm to 3 mm, preferably a depth of 1 to 2 mm, based on the bottom of the groove. In this way it can be ensured that the fine structure is present in the groove base and in the groove flank of the first annular groove. In this area, the microstructure has a particularly significant positive effect on the material properties.

According to an advantageous embodiment of the invention, the welding parameters are varied in the circumferential direction during tungsten inert gas welding. In this way, on the one hand, the different remelting depths discussed in the previous paragraph can be controlled in the circumferential direction. On the other hand, however, it is also possible to produce a constant remelting depth in the circumferential direction by varying the welding parameters. This can be necessary if, for example, there are local differences in the heat dissipation during welding that are due to the design of the piston. In this context, amperage, voltage, feed speed, angle of attack of the torch, electrode shape, shielding gas flow and/or shielding gas mixing ratio (e.g. He/Ar) are particularly suitable welding parameters for tungsten inert gas welding. A suitable setting of the aforementioned parameters can result in undesirable changes in the shape of the Piston and too wide a heat-affected zone, which represents an undesirable influence on the piston base material, can be avoided. The specific setting of the parameters is in accordance with the usual value ranges for tungsten inert gas welding.

An electrolytically applied oxidation layer or a chemically or galvanically applied nickel coating is advantageously applied to part of the piston surface, which comprises at least part of the first annular groove. Such layers benefit in a synergistic way from the preceding remelting according to the invention: In particular, the layers mentioned, which are applied for the purpose of wear protection, grow on the remelted area in a finer-grained, smoother, more homogeneous manner and with fewer pores and thus inhibit the crack formation process in the groove base area pre-ignition events.

The tungsten inert gas welding is preferably carried out in one step. In this way, the desired fine structure can be produced particularly efficiently.

In an advantageous manner, a welding filler can be used in tungsten inert gas welding, which is then found at least partially in the remelted area. In this way, the alloy of the piston can be locally adapted to the individual requirements in the remelted area, i.e. in the area of the ring grooves, by adding suitable alloying elements.

According to an advantageous embodiment of the invention, the WIG/TIG remelting takes place on a piston blank that has been pre-machined with a slight allowance in diameter, before the ring grooves are cut and the finished diameter and the skirt profile are machined. In particular, before the tungsten inert gas welding, the piston blank has an oversize of 0.5 mm to 2.0 mm, preferably at least 1.0 mm, at least in the area to be remelted. In this way, a weld sink point that exceeds the size of the oversize can be avoided.

The piston blank is preferably heated to a temperature of at least 180° C. before the tungsten inert gas welding. This process step can be used in particular to avoid welding cracks in tungsten inert gas welding.

character list

• 1 shows a piston blank for an internal combustion engine after tungsten inert gas welding.
• 2 shows a schematic cross section of the piston blank after tungsten inert gas welding with a schematically drawn course of the ring lands and ring grooves in the finished piston.
• 3 shows a micrograph of the microstructure of the piston blank after tungsten inert gas welding, which illustrates the differences in the fineness of the structure between the remelted material (“remelted material”) and the base material (“base material”).

Claims (15)

Method for producing a piston for an internal combustion engine, characterized in that a piston blank is provided, a region of the piston blank is remelted by means of tungsten inert gas welding and then the first annular groove is machined into the remelted region, characterized in that the depth of the remelted Area is varied in the circumferential direction of the piston blank. According to a method for producing a piston for an internal combustion engine claim 1 , whereby the first ring groove lies completely in the remelted area. According to a method for producing a piston for an internal combustion engine claim 1 or 2 , wherein the remelted area also includes a portion of the second ring land present in the resulting piston below the first ring groove. Method for producing a piston for an internal combustion engine according to one of the preceding claims, wherein the remelted area is deeper than the subsequently machined first annular groove, preferably by 1 mm deeper than the machined first annular groove. Method for producing a piston for an internal combustion engine according to one of the preceding claims, wherein the piston blank consists at least partially of an aluminum alloy and/or the first ring groove is pierced in the remelted area. Method of manufacturing a piston for an internal combustion engine according to any one of the preceding claims, wherein the welding parameters of the tungsten inert gas welding are varied in the circumferential direction during the welding. Method for producing a piston for an internal combustion engine according to one of the preceding claims, wherein the remelted area has a depth of 0.5 mm to 3 mm, preferably a depth of 1 to 2 mm, based on the groove base. Method for manufacturing a piston for an internal combustion engine according to any one of the preceding claims, wherein an electrolytically applied oxidation layer or a chemically or galvanically applied nickel coating is applied to at least a part of the piston surface, which comprises at least part of the first annular groove. Method for manufacturing a piston for an internal combustion engine according to any one of the preceding claims, wherein the tungsten inert gas welding is carried out in one step. Method for producing a piston for an internal combustion engine according to one of the preceding claims, wherein a filler metal is used in tungsten inert gas welding, which is then at least partially found in the remelted area. Method for producing a piston for an internal combustion engine according to one of the preceding claims, wherein the piston blank before the tungsten inert gas welding has an oversize of at least 0.5 to 2.0 mm, preferably at least 1.0 mm, at least in the area to be remelted. Method for producing a piston for an internal combustion engine according to one of the preceding claims, wherein the tungsten inert gas welding and the incorporation of the ring grooves takes place in such a way that all ring grooves lie in the remelted area. A method of manufacturing a piston for an internal combustion engine as claimed in any preceding claim, wherein the piston blank is heated to a temperature of at least 180°C prior to tungsten inert gas welding. Pistons for an internal combustion engine, obtainable by a method according to any one of Claims 1 until 13 . Using a piston according to Claim 14 for a petrol engine or a diesel engine.

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