DE102014211350A1 - Casting method for producing a piston and pistons for internal combustion engines - Google Patents

Abstract

The invention relates to one or multi-part pistons made of metal or a metal alloy for an internal combustion engine, the piston or at least one piston part being manufactured in a casting process based on a lost mold or in a casting process based on a permanent mold, and a process for its manufacture.

Description

The invention relates to a method for producing pistons for internal combustion engines and a piston produced by this method, according to the features of the respective preamble of the independent claims.

The DE 10 2010 052 579 A1 relates to a piston for an internal combustion engine, comprising a piston upper part and a piston lower part, which are made of different materials, wherein at least one of the piston parts is formed as a cast component, wherein the at least one piston member designed as a cast component is cast on the other piston part. The casting of a piston part to another piston part is very complicated and expensive, since an accurate positioning of the piston part to be cast around in the mold must be done.

The DE 102 97 060 T5 discloses a forged piston for an aluminum-silicon alloy internal combustion engine and a method of manufacturing the piston.

The DE 85 01 763 U1 relates to a one-piece forged piston for an internal combustion engine with piston crown and piston skirt, wherein the piston crown has at least one land and a circumferential collar surrounding the piston skirt, wherein the piston skirt consists of two pendulum shank ears.

The DE 38 11 200 A1 relates to a piston blank for a forged piston for an internal combustion engine with piston crown with heat-restricting annular gap and to the piston crown underside integrally formed pendulum ears, which consist of a crown-side portion and a Pendelschaftaugenteilstück and in Pendelschaftaugenteilstück Pendelschaftaugen for receiving a pendulum shank bolt. The pendulum shaft suction sections of the pendulum shaft have in the upper part of the pendulum shaft eyes a greater wall thickness than the crown-side sections. The crown side sections connect to the pendulum shaft suction sections via an undercut.

The DE 1 525 895 A refers to forged one-piece engine pistons with a long oil passage and a single weld and to the process of making same.

Until now, swage forges were used for the production of the piston lower part and the piston upper part. Drop forged are elaborate, inflexible and expensive tools. Each change in shape on the piston lower part or upper piston part requires a new tool.

The object of the invention is to increase the freedom of design and material selection for pistons with a reduction of manufacturing costs for pistons. This object is achieved by a method and a piston with the features of the independent claims.

According to the invention, a forged lower part of a piston is preferably replaced by a cast lower part produced at least partially in the particular horizontal lost-mold casting process. This casting lower part can be assembled with a forging upper part of a piston to form a piston. A production of the piston upper part in the casting process is also conceivable. The production of a lower piston part, at least partially, in the horizontal lost-mold casting increases the flexibility for the design, material selection and design changes for the piston lower part according to the invention. Furthermore, a cost reduction for steel pistons is achieved for use in HD and HSDI engines. Preferably, several piston parts are produced in a primary molding with a low cycle time.

According to the invention, the cast part, in particular a lower piston part is arranged horizontally with respect to the piston axis for carrying out the method. The gate occurs laterally on the circumference of the piston or the piston lower part. The filling of the casting paths is vertical. The separation of the molds is vertical. The casting takes place in lost-mold casting or die-casting. The method described above is not limited to piston bottoms but can be applied to any components, including the piston top. Preferably, more than one casting, at least two castings, are manufactured in one casting.

Cast metals are metals, preferably iron materials. The use of aluminum alloys is conceivable.

The advantages are a cost reduction in the finished part, during development and short prototype times.

Furthermore, by the method according to the invention for producing a piston for internal combustion engines or internal combustion engines, a selection of material for the piston lower part, piston upper part or for the entire piston can be made.

For the purposes of this document, lost-mold casting methods are understood to mean processes in which so-called lost forms are used.

Lost forms are divided into permanent models and lost models. A procedure at The Lost Foam Process is used for lost models. The Lost Foam process is also known as Lost Foam Casting (LFGV).

Lost Foam is a casting process, which is suitable for the production of complex component geometries of pistons or piston parts from a single casting. Characteristic of the process is the use of "lost" models of organic foams. The foam models are embedded under vibration compaction in a binder-free molding material. During casting, the foam model is then thermally decomposed by the melt of the casting material, wherein the melt simultaneously fills the resulting cavity. The result is an exact image of the foam model as a metallic casting. The pistons or piston parts produced by the lost-foam process are distinguished not only by the possible geometric complexity but also by their outstanding surface and dimensional stability.

The used models of polystyrene foams are embedded in a casting container in molding sand and decomposed by supplied, liquid metal. The resulting mold cavity is filled by the molten metal, the geometry of the model is replicated exactly.

The raw material used for the lost foam models is, for example, expanded polystyrene (EPS), expanded polymethylmethacrylate (EPMMA) or a copolymer. The production of model segments consists of three process steps. When prefoaming raw particles are expanded by supplying thermal energy, which is realized by means of embedded propellant, such as pentane. During the subsequent conditioning, the particles are subjected to a compensation process with the ambient air for stabilization. The last stage of the process is followed by ready-foaming. The prefoamed and conditioned EPS beads are placed in the split mold of a foam tool and subsequently subjected to thermal energy, thereby causing the molding to form the finished model segment. A model segment may represent a portion of a piston or piston member. For example, the shaft, the formation of the subsequent combustion chamber, the cooling channel, the refrigerator or the ring section.

For the subsequent joining of model segments to a piston or piston part model, for example, mating, gluing and heating element welding are suitable. These piston or piston submodels form the lost models for use in the lost foam process.

Several piston or piston submodels can be assembled to form model screws.

In the subsequent finishing of the model grapes, the assembled casting screws are coated with size, a thin refractory coating. The sizing consists of an aqueous suspension of ceramic particles; it must fulfill a wide variety of requirements and tasks in the lost-foam process. The sizing serves to stabilize the piston or piston part model or the model screw consisting of connected piston or piston submodels during the molding process in binder-free quartz sand, since during casting a cushion of gas and plastic melt between the model and molten metal would be created without the sizing as a barrier The binder-free quartz sand inevitably break and make the casting useless. Furthermore, the size, through its gas permeability, influences the removal of the resulting gases and liquids into the surrounding binder-free quartz sand and thus determines the pressure which builds up in the gas cushion between the piston or piston submodel or the model grape consisting of connected piston or piston submodels and molten metal can. The size therefore controls the speed of the mold filling to a decisive extent and thus has a direct influence on the casting result.

After drying the piston or piston part models or the model screws consisting of connected piston or piston part models, they are placed in a casting container and wrapped with binder-free sand and molded therein. By applying vibration, the sand is fluidized, runs into the cavities and undercuts of the models and is compacted.

In the subsequent casting of the piston or piston submodels or the model grape consisting of connected piston or piston submodels, the present foam model is reproduced exactly in metal. The molten metal is poured into the casting mold after gravity casting to the finished part. The foam material is decomposed by the high temperature of the melt and enters the binder-free sand surrounding the model via the sizing layer. The resulting gases can be fed directly to a filter system via a suction system installed on the tank. After solidification of the melt, the sand can be separated by simply emptying the mold container from the Gusstraube. This process is called demolding. Since the sand contains no binder, it trickles out of holes and cooling channels directly without further help. The cleaning and blasting work at the Lost Foam process is very low. Since the mold is not split, no burr is produced when pouring.

The Lost-Foam process enables the production of pistons or piston parts with complex casting geometries of the highest quality. The lost-foam process enables the production of pistons or piston parts with high dimensional accuracy and low tolerances. The use of the Lost-Foam process enables the production of thin-walled, filigree piston castings. This can lead to lower masses for the finished piston. The lost-foam process eliminates the need for reworking because it works coreless and without burrs. Therefore, there is almost no Nachputzaufwand. This leads to a high surface quality of the piston or piston parts produced in the lost foam process. The Lost-Foam process is environmentally friendly as it is an energy-efficient casting process with low emissions and closed molding cycle. The lost-foam process is an economically efficient casting process for piston or piston part prototypes and piston or piston part series castings.

• 1 Modellherstellung
• 1a Vorschäumen
• 1b Fertigschäumen
• 2 Modellmontage
• 3 Schlichten
• 4 Einformen und Gießen
• 5 Entnahme der Kolben oder Kolbenteile

The production of pistons or piston components by the lost-foam process is divided into the following process steps:

• 1 model production
• 1a pre-foaming
• 1b ready foams
• 2 model assembly
• 3 finishing
• 4 molding and casting
• 5 Removal of pistons or piston parts

Methods in the permanent models are used, for example, Sandgießverfahren. Also in Sandgießverfahren pistons or piston parts can be produced.

After the binder used in each case, the process variants are differentiated in the sand casting process. Clay (bentonite) is used together with water or organic resins, for example polyurethane or furan resin. In addition, other inorganic binder systems are used. As molding material, apart from exceptions, quartz sand is used.

As Grunsandverfahren the casting process is referred to, in which bentonite is used as a binder. Lost molds are produced by applying the molding sand (clay mineral-clad quartz sand) to a model plate in a box or boxless and then compacting. The compaction of the foundry sand can be done manually (hand molding) or mechanically (machine casting). By merging the mold halves of the cavity is generated, in which the metal can be poured.

As an alternative to clay-bonded molding sand can also be worked with resin-bonded sand. The pourable strength of the molding sand is thereby achieved above a chemical reaction.

Another way to make sand molds is that several resin-bonded sand cores are produced and assembled into a package. The case is referred to as the core packet or core block method. The production of sand cores will be described below.

With the help of inserted into the mold cores, such as cooling channels, breakthroughs and undercuts in pistons or piston parts can be produced by casting. Cores are used only if required for molding purposes. Secure positioning of the cores in the mold is required.

The molding material used is preferably quartz sand. Inorganic processes are characterized by a lower workplace and environmental impact. In addition, there may be other technical advantages such as lower gas evolution during casting. Thermosetting inorganic processes for the production of cores for the production of pistons or piston parts sometimes require alternative molding materials (synthetic sands) to achieve optimum surface quality. In combination with cores, the sand casting processes offer very wide-ranging design possibilities. In terms of quantities, the bandwidth ranges from single-piece production to series in the largest number of units.

The degree of mechanization of the molding process and the quality of the models can be used to control the dimensional accuracy of the castings. By using particularly fine sands or special sizing a high surface quality can be achieved.

Due to the lower solidification rate in sand casting, not quite as high strength values can be achieved in comparison to chill casting. The local use of heat sinks or casting parts allows targeted high strength values to be achieved in certain regions of the piston or of the piston part. These heat sinks are specifically positioned in areas where higher demands are placed on the mechanical properties of the piston or piston part. As an alternative to gravity filling, higher pressure can be achieved by filling the mold with a low-pressure application Strengths are achieved under cyclic loading.

In a further embodiment, the production of the piston or at least one piston part takes place in Kokillengießverfahren. Mold casting are based on permanent molds.

A variant is the gravity die casting process, with it can be produced dimensionally accurate castings with good surface finish. The relatively rapid solidification in Kokillengießverfahren results in favorable mechanical material properties. The molds (molds) are made of steels, for example hot-work steels or cast iron with lamellar graphite. In a so-called full mold, the entire mold is made of metal. In a half-mold, the lower part of a mold and the upper part of a sand mold.

Chill castings, as well as sand castings, are fully heat-treatable, weldable and decorative anodically oxidizable, if the alloys suitable for this purpose are chosen.

In the standard Kokillengießverfahren the mold filling takes place by gravity and predominantly in the rising cast, that is, the melt is filled through a sprue, then flows through a run, which is located below and possibly laterally of the actual casting over the gate or the gates in the mold cavity. This will fill the mold rising from bottom to top.

To optimize the filling process, alternative process variants were developed as an alternative to the standard gravity die casting process. In one variant, the mold is filled via a rotational movement about the mold longitudinal axis. This variant is called tilting mold casting. Depending on the casting geometry, the filling takes place directly through so-called inlet feeders or through laterally arranged pouring runs. Harmful turbulence is avoided by the inclination of the mold at the beginning of mold filling. The directed solidification is conveyed in parallel, as is usually filled by those casting-technical elements from which the saturation (feed) takes place during solidification. With the tilt mold casting, an improvement of the casting quality is achieved since there are fewer fillings and pores due to filling in the casting, for example a piston or piston part.

Another variant of the Kokillengießverfahrens represents the low-pressure Kokillengießverfahren. While in the previously described Kokillengießverfahren the mold filling by gravity, this is done in the low-pressure Kokillengießverfahren by a slight overpressure of about 0.3 to 0.7 bar. For this purpose, a pressure-tight casting furnace is connected via a riser pipe with the mold arranged above. By increasing the pressure, the metal mirror rises through the riser from below into the mold cavity. Thus, a quiet mold filling and a suitable casting shape ensures a good feed. Advantageous are associated with the low-pressure Kokillengießverfahren quiet metal feed and the low cycle content. With appropriate castings and series sizes, the low-pressure die casting process can also be largely automated. Preferably, rotationally symmetric parts are produced in the low-pressure Kokillengießverfahren, for example, pistons or piston parts.

Another variant of Kokillengießverfahrens represents the counter-pressure Kokillengießverfahren (also CPC method - Counter Pressure Casting). The main difference to the low-pressure Kokillengießverfahren consists in the pressure-tight design of the mold. The mold is pressurized before mold filling (about 4-5 bar) and then filled with a correspondingly higher differential pressure. The advantage of the method is that the feed pressure is increased compared to the low-pressure Kokillengießverfahren, which can produce a pore-poorer structure and thus better mechanical properties. However, the procedural effort is higher and therefore also the casting costs.

In the case of multi-part pistons, all piston parts produced in a casting process can be positively, positively and / or materially joined with a piston part produced in a forging process. Casting methods include, in particular, lost mold based casting processes and permanent casting methods.

Lost-Form methods include Lost-Foam and investment casting based on lost models as well as continuous casting sand casting methods.

In particular, all variants of the mold casting process and all variants of the die casting process are among the casting molds based on permanent molds.

Also piston parts can be produced with different casting process force, form and / or cohesively joined together to form a piston for internal combustion engines.

According to the invention is provided one or more parts piston made of metal or a A metal alloy for an internal combustion engine, wherein the piston or at least one piston part is produced in a casting process based on a lost mold or in a casting process based on a permanent mold.

The use of casting processes enables the flexible response to market or customer requirements. Even small batches can thus be produced economically. Changes in the series are possible in a timely manner and with reasonable effort. Depending on the casting process, a batch size of one is possible.

Furthermore, it is provided according to the invention that at least one piston part produced in the casting process is positively, positively and / or materially joined with at least one piston part produced in a forging process.

When combining piston parts produced by the casting process with piston components produced by forging processes, the advantages of both methods can be utilized for a piston. A base part on which few changes can be expected within a series can be produced, for example, in the forging process.

Furthermore, it is provided according to the invention that the piston or at least one piston part is produced in the lost-mold process.

Lost-form methods offer a high degree of flexibility in shaping the shape. They therefore offer great advantages in the production of pistons for small series and experiments.

Furthermore, it is provided according to the invention that it piston or at least one piston part is manufactured by Kokillengießverfahren.

Die casting methods enable larger quantities to be cast with high precision.

Furthermore, it is provided according to the invention that the lost-mold method is a lost-foam method.

The preferred based on polystyrene foams Lost Foam method allows cost to manufacture individual pistons or piston parts.

Furthermore, it is provided according to the invention that the lost-mold method is a sand casting method.

Also Sandgießverfahren allow the production of small quantities or the production of small batches.

Furthermore, it is provided according to the invention that a casting lower part with a forging upper part is positively, positively and / or materially joined together.

Furthermore, it is provided according to the invention that a forged lower part base with a cast shell is force, form and / or materially joined together.

The combination of forgings and castings on pistons allows to take advantage of the particular manufacturing process. Forging processes are suitable for the piston parts which are preferably subject to no change within a series. Also, the post-processing of forgings is often more expensive.

Furthermore, it is provided according to the invention that the piston or a piston part, in particular the casting lower part or the casting shell, at least partially produced in the horizontal lost-mold casting process.

The use of the horizontal lost-mold casting process offers advantages due to the geometry of the pistons or piston parts.

• a) Herstellung eines verloren Modells oder Dauermodells des Kolbens oder Kolbenteils
• b) Einformen des verloren Modells oder Dauermodells eines Kolbens oder Kolbenteils
• c) Füllen der Form mit Metallschmelze
• d) Entnahme der Kolben oder Kolbenteile

According to the invention, a method is provided for producing a piston or piston part for a piston for internal combustion engines, comprising the following steps:

• a) Preparation of a lost model or permanent model of the piston or piston part
• b) molding the lost model or permanent model of a piston or piston part
• c) filling the mold with molten metal
• d) removal of the pistons or piston parts

The cost of producing a single mold or model is low in lost-mold processes over other casting processes. In the sense of a continuous improvement process, changes to the piston design can be transferred to the series at short notice.

• a) Modellherstellung mit den Teilschritten
• a1) Vorschäumen und
• a2) Fertigschäumen
• b) optionale Modellmontage
• c) Schlichten
• d) Einformen und Gießen
• e) Entnahme der Kolben oder Kolbenteile

Furthermore, according to the invention, a lost-foam method is provided with the following steps:

• a) Modeling with the sub-steps
• a1) Prefoaming and
• a2) ready foaming
• b) optional model assembly
• c) sizing
• d) molding and casting
• e) Removing the pistons or piston parts

The Lost-Foam process offers the possibility to create precise models or shapes cost-effectively. Changes to the piston design can be taken over at short notice in series production.

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 102010052579 A1 [0002]
• DE 10297060 T5 [0003]
• DE 8501763 U1 [0004]
• DE 3811200 A1 [0005]
• DE 1525895 A [0006]

Claims (9)

Method for producing a piston made of metal or a metal alloy for an internal combustion engine, characterized in that at least one piston part, in particular the entire piston, is produced in a lost-mold process. Method for producing a piston according to claim 1, characterized in that at least one piston part produced in the casting process, in particular a piston lower part, with at least one piston part produced in a forging process, in particular a piston upper part, is positively, positively and / or materially joined. A method for producing a piston according to claim 1 or 2, characterized in that the piston or at least one piston part is manufactured by Kokillengießverfahren. A method of manufacturing a piston according to claim 1, 2 or 3, characterized in that the lost-mold method is a lost-foam method. Method for producing a piston according to one of the preceding claims, in particular according to claim 5, characterized in that the lost-mold method is carried out as a horizontal lost-mold or lost-foam casting method. Method for producing a piston according to one of the preceding claims, characterized in that the lost-mold method is a sand casting method. Method for producing a piston according to one of the preceding claims, characterized in that the piston or a piston part, in particular the cast base or the cast shell, at least partially made in the horizontal lost-cast casting process. Method for producing a piston or piston part for a piston for internal combustion engines, characterized by the following steps: a) Preparation of a lost model or permanent model of the piston or piston part b) molding the lost model or permanent model of a piston or piston part c) filling the mold with molten metal d) removal of the pistons or piston parts A method for producing a piston or piston part according to claim 8, characterized by a lost foam method comprising the following steps: a) Modeling with the sub-steps a1) Prefoaming and a2) ready foaming b) optional model assembly c) sizing d) molding and casting e) Removing the pistons or piston parts