DE102019106209A1 - Process for the production of a hollow valve for internal combustion engines - Google Patents

Abstract

A manufacturing method for a valve body of a hollow valve is provided, the method comprising: providing a preform with a valve head / valve disc and with a tubular wall which surrounds a hollow space; and axial-feed cross-rolling of the tubular wall with at least one pinch roll to increase a length of the tubular wall by moving the preform relative to the at least one pinch roll. A hollow valve produced by means of this method is also provided.

Description

Field of invention

The present invention relates to a method for producing hollow valves, or hollow space valves, for internal combustion engines and hollow valves produced therewith.

State of the art

In combustion engines, inlet and outlet valves are components that are subject to high thermal and mechanical loads. Sufficient cooling is therefore necessary to ensure the long-term functionality of the valves. Here, hollow disk valves are advantageous over full stem valves and hollow stem valves (i.e. a hollow valve in which a hollow space is only provided in the shaft), since a hollow space is present both in the shaft and in the valve head, whereby improved internal cooling - by means of a cooling medium, e.g. Sodium - can be achieved. Further advantages are a lower weight, the avoidance of hot spots (in the combustion engine) and a reduction in CO2.

Hollow valves are usually manufactured by a combination of different processes, such as forging, turning and welding. Turning or milling the cavity is particularly costly. Welding points on the plate surface or other critical points for operational reasons should also be avoided. Another disadvantage of known methods is that a large number of process steps are often necessary, such as B. in EP 2325446 A1 . However, fast forming processes are advantageous for the cost-effective production of large quantities.

For example, describe the EP 0898055 A1 and the US 006006713 A a hollow disk valve that is produced by closing a hollow blank by means of welding (friction welding, laser welding) or armoring. Other publications dealing with the manufacture of cavity valves CN 104791040 A and JP 1995102917 .

The object of the present invention is therefore to provide a manufacturing method for hollow valves or for a valve body for hollow valves which does not have the disadvantages mentioned and at the same time has high productivity, good material utilization and fast forming processes.

Summary of the invention

According to the invention, the problem is solved by a method for producing a valve body of a hollow valve according to the features of the appended claim 1.

The method of manufacturing a valve body of a hollow valve comprises the steps of providing a preform having a valve head and a tubular wall surrounding a cylindrical cavity, and axial-feed transverse rolling of the tubular wall with at least one pinch roll to a length of the tubular wall increase and / or reduce their thickness by moving the preform relative to the at least one pressure roller.

This invention advantageously avoids weld seams on the valve disk surface, and enables a continuous forming process, a short cycle time, high productivity, time savings and good material utilization.

An alternative method of manufacturing a valve body of a hollow valve comprises the steps of providing a preform with a valve head and a tubular wall surrounding a cylindrical cavity, and spinning the tubular wall over a spinning mandrel inserted into the cavity by a length of the to enlarge tubular wall.

According to one aspect of the present invention, the axial feed transverse rolling or spinning of the tubular wall can take place over a spinning mandrel inserted into the cavity and a compressive force of the spinning mandrel moves the preform.

In accordance with one aspect of the present invention, a chuck can hold the valve head and apply a pulling force to move the preform.

According to one aspect of the present invention, the restraint can hold the valve head by means of at least one projection and form a form-fitting connection between them.

According to one aspect of the present invention, providing the preform can include: providing a cup-shaped semifinished product, the semifinished product having the tubular wall which surrounds the cylindrical cavity of the semifinished product and a bottom section; and molding the valve head from the bottom portion.

According to a further aspect, the provision of the cup-shaped semi-finished product can include: provision of an at least partially cylindrical blank; and shaping the cup-shaped semi-finished product from the blank.

According to a further aspect, the cup-shaped semi-finished product can be shaped by extrusion or forging.

According to a further aspect, the valve head can be formed by extrusion or forging.

According to a further aspect, a plurality of pressure rollers can be used in the case of the axial feed transverse rollers or pressure rollers, three pressure rollers preferably being used.

According to a further aspect, the plurality of spinning rollers can be offset from one another radially and axially during spinning.

According to a further aspect, at least two sets of spinning rollers can be provided. The spinning rollers of a set are not axially (and radially) offset, but the sets are axially spaced apart.

According to a further aspect, the method can further comprise: a further flow-forming of the tubular wall without a flow-forming mandrel.

According to a further aspect, the method can further comprise: reducing an outer diameter of the tubular wall after the axial-feed cross-rolling or spinning.

According to a further aspect, the outer diameter of the tubular wall can be reduced by swaging or drawing in.

According to a further aspect, the reduction of the outer diameter of the tubular wall can take place without a mandrel.

According to a further aspect, the reduction of the outer diameter of the tubular wall can take place with a mandrel inserted into the cavity.

According to a further aspect, the method can further comprise: filling a cooling medium, in particular sodium, into the cavity; and closing the cavity.

According to the invention, the problem is further solved by a hollow valve which comprises a valve body which was produced using the above method.

Figure list

• 1A - 1F verschiedene Zwischenschritte der erfindungsgemäßen Herstellung eines Ventilkörpers eines Hohlventils (dargestellt in 1D bzw. 1F) aus einem Rohling (dargestellt in 1A) zeigen;
• 2 eine Schnittansicht während des Drückwalzens zeigt; und
• 3 eine Schnittansicht während des Axial-Vorschub-Querwalzen zeigt.

Exemplary embodiments of the invention are described in more detail below with reference to the figures, wherein

• 1A - 1F various intermediate steps in the production of a valve body of a hollow valve according to the invention (shown in FIG 1D or. 1F) from a blank (shown in 1A) demonstrate;
• 2 Fig. 3 shows a sectional view during spin forming; and
• 3 Figure 9 shows a sectional view during axial-feed cross-rolling.

In the following, the same reference symbols are used for the same or similar elements or components both in the description and in the drawing. A list of reference symbols is also given which is valid for all figures. The designs shown in the figures are only schematic and do not necessarily represent the actual size relationships.

Detailed description of the invention

In the 1A to 1F various intermediate stages of the production method according to the invention are shown in sectional views, with optional or preferred production steps / intermediate stages also being shown.

Preferably used as a starting point, see 1A , a blank 2 from a valve steel known to the person skilled in the art. The blank has an at least partially cylindrical shape, preferably a circular cylindrical shape, corresponding to the circular shape of the valve body or valve to be produced.

The blank 2 is turned into an in 1B shown cup-shaped semi-finished product (or workpiece) 4th reshaped. The semi-finished product 4th in the form of a cup comprises a bottom portion 10 , from which a valve head (or valve disk) 12 is formed, and a tubular wall (or annular wall) 14th that have a cylindrical, preferably circular-cylindrical, cavity 8th of the cup-shaped semi-finished product 4th surrounds and from which later a valve stem 20th is formed. In this case, material can possibly be placed between the bottom section during the subsequent forming steps 10 and tubular wall 14th flow. According to the invention, the cup-shaped semi-finished product is more general 4th directly provided; the process then starts with the provision of the in 1B shown cup-shaped semi-finished product 4th .

In a subsequent forming step, the bottom section becomes 10 the valve head 12 shaped. A preform obtained thereby 6th of the valve body is in 1C shown.

Both the forming of the blank 2 into a cup-shaped workpiece 4th as well as shaping the valve head 12 from the bottom section 10 can be carried out, for example, by a hot or cold forming process. Extrusion or forging is preferably used. During extrusion, a punch is inserted into the blank 2 or the semi-finished product 4th pressed to the cavity 8th or the valve head 12 to form, ie it is essentially a (cup) reverse extrusion or cross extrusion. The preform 6th can also be produced directly from the blank in a single forming step, e.g. forging or extrusion 2 be shaped.

In the next processing step, from 1C to 1D , becomes an axial length of the tubular wall 14th enlarged. 'Axial' here refers to that through the tubular wall 14th (ie the later shaft) defined direction, ie on the (central) axis of the tubular wall; "Radial" is correspondingly a direction orthogonal to the axial direction. A length of the tubular wall 6th is therefore measured in the axial direction.

For this purpose, pressure rollers or cylinder pressure rollers are used according to the invention over a pressure-rolling mandrel 22nd carried out; see. 2 . During spinning, the preform rotates and there is at least one spinning roll that rotates with it by frictional engagement 24 , 26th pressed against the outside of the tubular wall and moved in the axial direction, so that there is a plastic change in shape. The associated incremental deformation leads to an advantageous strain hardening of the processed steel. Overall, the wall thickness of the tubular wall is reduced while the axial length of the tubular wall increases at the same time. The at least one pressure roller is moved several times in the axial direction, if necessary, until the desired increase in length or reduction in wall thickness is achieved. The radial distance between the at least one pressure roller and the axis of the tubular wall is successively reduced during successive passes.

The flow-forming therefore leads, due to the flow-forming mandrel used 22nd , essentially to an elongation of the tubular wall 14th , whereby their outside diameter decreases a little (corresponding to the decrease in wall thickness). If a larger reduction in the outer diameter is desired, spinning can also be carried out with several spinning rolls without a spinning mandrel.

If dimensions of the preform 6th and parameters of the flow-forming are selected so that the length of the tubular wall achieved by the flow-forming 14th , the outside diameter achieved by the spinning and an inside diameter of the tubular wall 14th the preform (which corresponds to a diameter of the flow forming mandrel) correspond to the desired dimensions of the hollow valve to be produced, a valve body can in this way 16 can be obtained for a hollow shaft valve (cf. 1D , whereby it should be noted that the relative dimensions shown in the figures do not have to correspond to the actual relative dimensions, in particular in 1D the diameter of the valve disk / head in relation to the stem diameter is smaller than in the case of a conventional actual valve, likewise the stem diameter is in relation to the length of the stem 20th larger than usual).

Finally (from 1D over 1E to 1F) becomes, optionally, the outside diameter of the tubular wall 14th reduced to a finished valve body 18th for a hollow disk valve, its valve stem 20th has a predetermined outer diameter, ie has a desired target diameter; see. 1F . This forming step is preferably carried out without a mandrel inserted, so that the diameter can be effectively reduced. In addition to reducing the outside diameter, this step also leads to a further elongation of the tubular wall 14th and, if done without a mandrel, an increase in the wall thickness of the tubular wall 14th . The wall thickness would therefore have to be set somewhat smaller in the previous flow-forming step in order to obtain a specific wall thickness, and thus a specific inside diameter for a given outside diameter D, taking into account the increase in thickness in the final step.

Reducing the outside diameter of the tubular wall 14th can be done by swaging or drawing in ("necking", diameter reduction by constricting), with swaging being preferred. With rotary swaging it is important that after rotary swaging to reduce the outside diameter of the tubular wall 14th no further deformation step of the valve body 18th takes place for a hollow disk valve, as this would worsen the positive material properties obtained by rotary kneading. In this case, rotary swaging is the final forming step.

Rotary swaging is an incremental pressure forming process in which the workpiece to be machined is hammered in rapid succession from different sides in the radial direction. Due to the resulting pressure, the material flows, so to speak, and the material structure is not distorted by tensile stresses. Rotary swaging is preferably carried out as a cold forming process, ie below the recrystallization temperature of the processed material. The main advantage of using rotary swaging as the final forming step is that compressive stresses are induced during rotary swaging due to the radial introduction of force, which leads to the occurrence of tensile stresses, which make it susceptible to Increasing cracks is prevented, in particular this applies to the edge layers of the hollow shaft. The rotary swaging thus interacts in an advantageous manner with the preceding, likewise incremental forming process of flow-forming, so that optimal material properties, such as strength, are achieved.

Further advantages of rotary swaging as a final forming step - compared to the drawing process or "necking" - are given by a better surface quality that can be achieved and by a relatively higher diameter reduction of the shank per step. Due to the high surface quality that can be achieved and the fact that the tolerances that can be maintained with rotary swaging are very small, post-processing of the valve stem is usually not necessary. With freeform processes or upsetting processes - e.g. Necking - in general, only a poorer surface quality or tolerance compliance can be achieved. Accordingly, no further process step by means of a drawing process or necking should take place after the rotary kneading to reduce the outer diameter of the tubular wall.

To complete the manufacturing process of the hollow valve, a cooling medium, e.g. Sodium, via the end of the valve stem which is open to the outside, can be filled into the cavity of the valve body and then this end of the valve stem is closed, e.g. by a valve stem end piece, which is attached, for example by means of friction welding or another welding process (not shown in the figures).

The outer diameter can be reduced in several sub-steps (an intermediate step is, for example, in 1E shown), whereby the individual sub-steps can optionally be carried out with or without a mandrel (at the beginning of a sub-step, the diameter of a mandrel can be smaller than the diameter of the cavity); a diameter of the mandrels of successive substeps can also be reduced.

2 represents the process step of flow forming, which is between 1C and 1D takes place, in a sectional view. This is in the cavity of the preform 6th a flow mandrel 22nd used. The mandrel rotates together with the preform 6th and a tailstock 28 , which supports the preform on the valve base. Against the tubular wall 14th are two opposite pressure rollers 24 , 26th pressed, which also rotate by means of frictional engagement. The pressure rollers 24 , 26th are moved in the axial direction relative to the preform, resulting in a plastic deformation of the tubular wall 14th , being the outer radius of the tubular wall 14th decreases and at the same time the length of the tubular wall 14th increases (in the axial direction). The material of the tubular wall "flows" here 14th in the direction of movement of the pressure rollers 24 , 26th (Synchronous pressure rollers). The directions of rotation of the preform (together with the spinning mandrel and tailstock) and the spinning rollers, the direction of movement of the spinning rollers 24 , 26th and the direction of flow of the material of the tubular wall 14th are indicated in the figure by arrows.

In 2 are an example of two pressure rollers 24 , 26th (partially) shown, the use of only one or more than two pressure rollers is also possible, the use of two or three pressure rollers being preferred. If several pressure rollers are used, they are preferably distributed regularly over the circumference; ie with two spinning rollers the angle (in the circumferential direction) between the spinning rollers is approximately 180 °, with three spinning rollers it is approximately 120 °, etc. As a result, the preform is supported in all directions.

Alternatively, there is a radial and an axial offset between the spinning rollers, as in FIG 2 shown. Radial offset means that the radial distance between the pressure rollers 24 , 26th is different from the central axis. The axial offset of the pressure rollers 24 , 26th leads to the pressure roller closer to the workpiece 24 first hits the workpiece and processes it, while pressure rollers are further away 26th later process the workpiece, i.e. the places that have already been processed by the previous pressure roller 24 was edited. So can the thickness of the tubular wall 14th are gradually quenched. As a result, the pressure roller closest to the workpiece must 24 have the greatest radial distance from the central axis, for the first ironing step, followed by the one with the second largest radial distance, etc. In this way the process can be accelerated, since several radius or wall thickness reduction steps can be carried out in one pass. Instead of a radial offset of spinning rollers of the same diameter, it is also possible to use spinning rollers with different diameters.

The waiver of an axial offset of the pressure rollers 24 , 26th (In this case, a radial offset would be pointless), but it reduces transverse and torsional forces on the workpiece that would result from axially offset pressing rollers.

Alternatively, multiple sets (not shown) of spinning rollers can be arranged. The pressure rollers of each set 24 , 26th are arranged without offset. The sets are axially spaced and each set provides partial ironing of the workpiece 6th . This causes lateral and torsional forces on the workpiece in the Reduced / avoided compared to spinning with radial / axial offset, and yet the advantage of gradual ironing and lower flow forces in the material of the workpiece is realized.

3 represents a process step of axial feed cross rolling, which is used as an alternative forming method between the 1C and 1D takes place in a sectional view. As in 2 in the case of "spinning with roller feed" into the cavity of the preform 6th a flow mandrel 22nd used. The mandrel rotates together with the preform 6th and a restraint 29 that supports the preform on the valve base or by means of projections 30th on the valve base or valve head 12 , which form a positive connection, can pull in the axial direction.

Against the tubular wall 14th are two opposite pressure rollers 24 , 26th pressed, which also rotate by means of frictional engagement. Unlike in 2 not the tools, ie the pressure rollers 24 , 26th moved relative to the preform in the axial direction or translationally, but it is the workpiece, ie the preform 6th relative to the pressure rollers 24 , 26th moved translationally. The pressure rollers are fixed in position and rotate. This also leads to a plastic deformation of the tubular wall 14th , being the outer radius of the tubular wall 14th decreases and at the same time the length of the tubular wall 14th increases (in the axial direction). The preform 6th is pulled axially through the two rollers.

The material of the tubular wall "flows" here 14th against the direction of movement of the preform 6th or accumulates in front of the pressure rollers 24 , 26th . The directions of rotation of the preform (together with the spinning mandrel and clamping) and the spinning rolls, the direction of movement of the preform 6th and restraint 29 with mandrel 22nd and the direction of flow of the material of the tubular wall 14th are indicated in the figure by arrows. The flow rate of the material of the tubular wall 14th is less when the workpiece is pulled through the tool than when the tool is pressed over the workpiece, because in the former part of the material flows off as a finished ironed pipe as the workpiece moves in the direction of movement, while in the latter the rollers 24 , 26th push all the excess material in front of you and thus the flow speed increases.

Axial feed transverse rolling offers the advantage that the material is moved less during the forming process and is therefore less stressed. This also reduces the development of heat. The process can be done both warm and cold.

With the workpiece, of course, its fixation, ie the clamping 29 and the mandrel 22nd that are friction-locked with the preform 6th connected are moves. The force required to move the workpiece can either be supplied via the flow forming mandrel 22nd or the protrusions or noses 30th the restraint. In the former case, the workpiece is pushed through the spinning rollers 24 , 26th pushed through, pulled through in the second. If there is only one compressive force via the mandrel 22nd is exercised so can on the ledge 30th can be dispensed with, or alternatively a tailstock 28 instead of restraint 29 be used. It is also possible to exert force by both variants at the same time, in particular to avoid a peak force load in some places, e.g. B. the valve head / valve disc 12 to reduce.

In 3 are the pressure rollers 24 and 26th axially (and radially) offset. This applies to the number and arrangement of the pressure rollers to one another 2 mentioned accordingly. As a result, the spinning rollers 24 and 26th can be arranged just as well without offset.

List of reference symbols

2

blank

4th

cup-shaped semi-finished product

6th

Preform

8th

cavity

10

Floor section

12

Valve head / valve disc

14th

tubular wall

16

finished valve body for hollow shaft valve

18th

finished valve body for hollow disk valve

20th

Valve stem

22nd

Flow mandrel

24

Pressure roller

26th

Pressure roller

28

Tailstock

29

Restraint

30th

Projection / nose

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• EP 2325446 A1 [0003]
• EP 0898055 A1 [0004]
• US 006006713 A [0004]
• CN 104791040 A [0004]
• JP 1995102917 [0004]

Claims (18)

A method for producing a valve body (16, 18) of a hollow valve, comprising the following steps: Providing a preform (6) having a valve head (12) and a tubular wall (14) surrounding a cylindrical cavity (8); Axial feed transverse rollers of the tubular wall (14) with at least one pressure roller (24) in order to increase a length of the tubular wall (14) and / or to reduce its thickness, in that the preform (6) opposite the at least one pressure roller ( 24) is moved. Procedure according to Claim 1 wherein the axial feed cross-rolling of the tubular wall takes place over a pressure-rolling mandrel (22) inserted into the cavity (8) and a compressive force of the pressure-rolling mandrel (22) moves the preform (6). Procedure according to Claim 1 or 2 wherein a clamp (29) holds the valve head (12) and exerts a tensile force to move the preform (6). Procedure according to Claim 3 , wherein the clamp (29) holds the valve head (12) by means of at least one projection (30) and forms a positive connection between them. Method according to one of the preceding claims, wherein providing the preform comprises: Providing a cup-shaped semifinished product (4), the semifinished product having the tubular wall (14) which surrounds the cylindrical cavity (8) of the semifinished product, and a base section (10); and Forming the valve head (12) from the base section (10). Procedure according to Claim 5 wherein the provision of the cup-shaped semi-finished product (4) comprises: provision of an at least partially cylindrical blank (2); and forming the cup-shaped semi-finished product (4) from the blank (2). Procedure according to Claim 6 , wherein the shaping of the cup-shaped semi-finished product (4) takes place by extrusion or forging. Procedure according to Claim 5 , wherein the shaping of the valve head (12) takes place by extrusion or forging. Method according to one of the preceding claims, wherein a plurality of pressure rollers (24, 26) are used in the axial feed transverse rolling, three pressure rollers preferably being used. Procedure according to Claim 9 wherein the plurality of spinning rolls are radially and axially offset from one another during spinning. Procedure according to Claim 9 wherein at least two sets of spinning rollers (24, 26) are provided, the spinning rollers (24, 26) of one set having no axial (and radial) offset but the sets being axially spaced from one another. Method according to one of the preceding claims, further comprising: a further spinning of the tubular wall (14) without a spinning mandrel. Method according to one of the preceding claims, further comprising: Reducing an outside diameter of the tubular wall (14) after the axial-feed cross-rolling. Procedure according to Claim 13 , wherein the reduction of the outer diameter of the tubular wall (14) is carried out by rotary swaging, necking or drawing in. Method according to one of the Claims 13 or 14th wherein the reducing of the outer diameter of the tubular wall (14) takes place without a mandrel. Method according to one of the Claims 13 or 14th wherein the reduction of the outer diameter of the tubular wall (14) takes place with a mandrel inserted into the cavity. Method according to one of the preceding claims, further comprising: Filling a cooling medium, in particular sodium, into the cavity; and Closing the cavity. A hollow valve comprising a valve body produced using the method according to one of the Claims 1 to 17th .

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