Electric sheet metal for an electric machine, comprising an improved closure structure for an open recess, and method for producing same

Abstract

The invention relates to an electric sheet metal (11, 11a, 11b, 14) for an electric machine (1), having a basic shape (15, 15a, 15b) made of a first metal material. The basic shape (15, 15a, 15b) has a ring structure with recesses (16) therein which are open towards an inner edge (B) or an outer edge (C) of the ring structure. The electric sheet metal (11, 11a, 11b, 14) additionally comprises a closure structure (17a, 17b) made of a second metal material which differs from the first metal material, wherein the closure structure (17a, 17b) is provided on an opening (D) of the recess (16) and closes same. The closure structure (17a, 17b) is produced using a metal printing method. The invention also relates to a laminated core (10, 13) comprising such an electric sheet metal (11, 11a, 11b, 14), to an electric machine (1) comprising such a laminated core (10, 13), to a vehicle (18) comprising such an electric machine (1), and to a method for producing such an electric sheet metal (11, 11a, 11b, 14).

Description

[0001] Electrical sheet for an electrical machine with improved closure structure of an open recess and manufacturing method thereof

[0002] TECHNICAL FIELD

[0003] The invention relates to an electrical steel sheet for an electrical machine, which comprises a basic shape made of a first metallic material, wherein the basic shape has a ring structure with recesses arranged therein, which are open towards an inner edge or outer edge of the ring structure. Furthermore, the electrical machine comprises a closure structure made of a second metallic material that differs from the first metallic material, wherein the closure structure is arranged at an opening in the recess and closes it. This means that the closure structure connects the basic shape of the electrical steel sheet in the region of the opening. Furthermore, the invention relates to a laminated core for a stator or rotor of an electrical machine, which has a plurality of electrical steel sheets of the type mentioned above stacked on top of one another along an axis, to an electrical machine having such a laminated core, and to a vehicle having such an electrical machine.Finally, the invention also relates to a method for producing an electrical sheet of the type mentioned.

[0004] STATE OF THE ART

[0005] The above-mentioned electrical steel sheet, a laminated core, an electrical machine, a vehicle, and a manufacturing method of the aforementioned type are generally known from the prior art. The individual electrical steel sheets are first produced, which are then stacked on top of each other to form a laminated core for a stator or rotor. The basic shape of the electrical steel sheets gives rise to the following problems: The mechanical rigidity of the electrical steel sheet or the laminated core is relatively low due to the recesses, which can lead to vibrations and noise problems during operation of the electrical machine.

[0006] The recesses generate harmonics in the magnetic conductivity. This causes magnetic losses, which reduce the efficiency of the electric machine. Furthermore, the harmonics in the magnetic conductivity also cause harmonics in the torque generated by the electric machine. This also results in suboptimal running behavior of the electric machine.

[0007] The shaft voltage in the rotor shaft caused by the capacitance of the stator winding is comparatively high.

[0008] Strong air turbulence is created by the recesses, which causes aerodynamic friction losses.

[0009] DISCLOSURE OF THE INVENTION

[0010] An object of the invention is therefore to provide an improved electrical steel sheet, an improved laminated core, an improved electrical machine, an improved vehicle, and an improved manufacturing method for an electrical steel sheet. In particular, the above-mentioned disadvantages are to be overcome.

[0011] The object of the invention is achieved with an electrical steel sheet of the type mentioned above, in which the closure structure is produced using a metal printing process. The electrical steel sheet can be designed as a stator steel sheet or a rotor steel sheet.

[0012] Furthermore, the object of the invention is achieved by a laminated core for a stator or rotor of an electrical machine, wherein the laminated core has a plurality of electrical sheets of the aforementioned type stacked on top of one another along an axis. In addition, the object of the invention is achieved by an electrical machine with a stator and a rotor rotatably arranged therein, wherein the stator has a laminated core with stator sheets of the above-mentioned type stacked on top of one another and / or the rotor has a laminated core with rotor sheets of the above-mentioned type stacked on top of one another. Stator windings can be arranged in slots which are formed in a laminated core for a stator by the recesses lying one above the other. Furthermore, rotor windings can be arranged in slots which are formed in a laminated core for a rotor by the recesses lying one above the other.

[0013] In addition, the object of the invention is achieved by a vehicle which has an electric machine of the above-mentioned type which is intended to drive the vehicle.

[0014] Finally, the object of the invention is achieved by a method for producing an electrical sheet for an electrical machine, which comprises the following steps:

[0015] Providing a basic shape made of a first metallic material, wherein the basic shape has a ring structure with recesses arranged therein, which are open towards an inner edge or outer edge of the ring structure, and

[0016] Producing a closure structure from a second metallic material that is different from the first metallic material, wherein the closure structure is produced at an opening of the recess by means of a metal printing process and wherein the closure structure closes the opening after printing.

[0017] The proposed measures overcome the disadvantages mentioned above and achieve the following advantages, among others:

[0018] The mechanical rigidity of the electrical sheet or the laminated core is significantly increased by the closure structure, which significantly reduces vibrations and noise during operation of the electrical machine.

[0019] The closure structure reduces magnetic losses. This improves the efficiency of the electric machine compared to the state of the art. Furthermore, during operation of the electric machine, comparatively few harmonics are generated in the magnetic conductivity and thus also fewer harmonics in the torque generated by the electric machine. This also improves the running behavior of the electric machine compared to the state of the art.

[0020] Compared to the conventional design, the shaft voltage in the rotor shaft is reduced. This is because the capacitance of the stator winding to the rotor is shielded by a closed, metallic surface.

[0021] The smooth inner surface of the laminated core reduces air turbulence, thus reducing aerodynamic friction losses. Overall, the efficiency and running behavior of the electric machine can be significantly improved by the proposed closure structure.

[0022] Using the metal printing process, particularly fine closure structures can be produced without deforming the basic shape of the electrical steel sheet, because virtually no internal mechanical stresses are induced in the basic shape during the printing process. Furthermore, the metal printing process allows different metallic materials to be applied in a confined space and mechanically bonded together. Consequently, the closure structure can be designed with great diversity in terms of shape and material to achieve the aforementioned advantages.

[0023] It should be noted here that the term "ring structure" does not mean that its outer or inner contour must be circular. It is sufficient if the outer or inner contour forms a ring with a general shape, or if the outer or inner contour forms a circular shape on average. Furthermore, it should be noted that the proposed measures are equally suitable for internal rotor machines and external rotor machines. Therefore, the following embodiments are particularly conceivable:

[0024] In the case of an internal rotor machine, the closure structure is arranged radially inward on the stator.

[0025] In the case of an internal rotor machine, the closure structure is arranged radially outward on the rotor.

[0026] In the case of an external rotor machine, the closure structure is arranged radially outward on the stator.

[0027] In the case of an external rotor machine, the closure structure is arranged radially inward on the rotor.

[0028] Further advantageous embodiments and developments of the invention emerge from the subclaims and from the description in conjunction with the figures.

[0029] It is advantageous if the first metallic material has a magnetic conductivity of .R > 20 (and is therefore magnetic) and the second metallic material has a magnetic conductivity in a range of 1 .1 < .R < 10 (weakly magnetic) or a magnetic conductivity of 1 .0 < |IR < 1 .1 (non-magnetic).

[0030] This allows the above-mentioned advantages to be achieved particularly effectively, particularly with regard to magnetic losses and the resulting efficiency and operating behavior of the electric machine. The magnetic conductivity of a weakly magnetic material can preferably be in a range of 1.1 < .R < 5.

[0031] By shaping the electrical steel sheet in the area towards the opening of the recess and by selecting a suitable second metallic material for the closing structure, the magnetic conductivity curve or air gap conductance can be advantageously influenced. It is particularly advantageous in this context if the contour of the electrical steel sheet tapers towards the opening of the recess and the second metallic material has a magnetic conductivity of 1.0 < pR < 1.1 (non-magnetic). The magnetic conductivity curve then essentially corresponds to that of the prior art, but the closed openings are mechanically stiffer. This results in improved vibration behavior and a reduction in disruptive noise.

[0032] Alternatively, it is also particularly advantageous if a contour of the electrical steel sheet is wide (or blunt) towards the opening of the recess and the second metallic material has a magnetic conductivity in a range of 1.1 < .R < 10 (weakly magnetic). Preferably, the magnetic conductivity of a weakly magnetic material can in turn be in a range of 1.1 < .R < 5. The magnetic conductivity profile is thereby superimposed with wide but flat gaps. The mechanical stability is again improved compared to the prior art. The mean value of the air gap conductance essentially corresponds to that of the previously mentioned solution, and particularly few harmonics are generated.As a result, the advantages mentioned above, particularly with regard to magnetic losses and the resulting efficiency and running behavior of the electrical machine, become very apparent again.

[0033] The basic shape of the electrical steel sheet can, for example, be punched or cut with a laser. However, it is also advantageous if the basic shape is produced using a metal printing process, in particular using the same metal printing process as the closure structure. The metal printing process allows particularly fine structures to be produced in the basic shape of the electrical steel sheet without causing deformation or the buildup of internal mechanical stresses. Consequently, the basic structure can also be designed with highly differentiated shapes and materials in order to achieve the aforementioned advantages. In a preferred embodiment, a metal screen printing process can be provided as the metal printing process. This process has proven particularly suitable for the production of an electrical steel sheet.

[0034] The metal printing process can be carried out using a homogeneous base material that only contains grains of the same metal alloy. However, it is also conceivable for the metal printing process to be carried out using an inhomogeneous base material that contains grains of different metals and / or metal alloys. Accordingly, the closure structure of the electrical sheet and, if applicable, the basic shape of the electrical sheet can consist of a homogeneous base material that only contains grains of the same metal alloy, or of an inhomogeneous base material that contains grains of different metals and / or metal alloys.

[0035] The non-magnetic material can, in particular, be stainless steel. The slightly magnetic material can, for example, be a mixture of stainless steel and a powder containing predominantly iron and some phosphorus. This can increase the rigidity of the electrical steel sheet.

[0036] In general, the electrical steel sheet can be heated after printing for a sintering process to permanently bond the printed components and to ensure the stability of the electrical steel sheet.

[0037] At this point, it is noted that the design variants mentioned for electrical steel and the resulting advantages are also applicable to the process presented and vice versa.

[0038] SHORT DESCRIPTION OF THE CHARACTERS

[0039] Embodiments of the invention are illustrated by way of example in the accompanying schematic figures. They show: Fig. 1 shows an exemplary electrical machine, schematically illustrated in half section;

[0040] Fig. 2 shows an exemplary basic shape of a stator lamination in front view;

[0041] Fig. 3 shows a first exemplary embodiment of a closure structure in detailed view;

[0042] Fig. 4 shows a second exemplary embodiment of a closure structure in detailed view and

[0043] Fig. 5 shows an exemplary vehicle with an electric machine of the proposed type.

[0044] DETAILED DESCRIPTION OF THE INVENTION

[0045] By way of introduction, it should be noted that identical parts in the different embodiments are provided with the same reference symbols or component designations, possibly with different indices. The disclosure of a component contained in the description can be applied analogously to another component with the same reference symbol or component designation. Furthermore, the positional information chosen in the description, such as "top," "bottom," "rear," "front," "side," and so on, refers to the directly described and illustrated figure and, in the event of a change in position, is to be applied analogously to the new position.

[0046] Fig. 1 shows a half-section through a schematically illustrated electrical machine 1. The electrical machine 1 comprises a rotor shaft 2 and a rotor 3 mounted thereon, wherein the rotor shaft 2 is rotatably mounted about a rotor axis or stator axis A by means of (rolling) bearings 4a, 4b. The electrical machine 1 also comprises a stator 5 in which the rotor 3 is arranged. In addition, the electrical machine 1 comprises a (first or front) bearing plate 6, a (second or rear) bearing plate 7 and a stator housing 8, which together form the machine housing 9 or are at least enclosed by it. The bearing plate 6 accommodates the bearing 4a, the bearing plate 7 accommodates the bearing 5b, and the stator housing 8 accommodates the stator 5.

[0047] The stator 5 comprises in detail a stator laminated core 10 with a plurality of axially stacked stator laminates 11 and optional stator windings 12 arranged in the stator laminated core 10. However, stator magnets could also be provided instead of the stator windings 12. The rotor 5 comprises in detail a rotor laminated core 13 with a plurality of axially stacked rotor laminates 14 and optional rotor windings or rotor magnets arranged in the rotor laminated core 13 (not shown in Fig. 1). In general, the stator laminates 11 and the rotor laminates 14 are electrical laminates 11, 14, and the stator laminated core 10 and the rotor laminated core 13 are generally laminated cores 10, 13.

[0048] Fig. 2 shows an electrical steel sheet or stator steel sheet 11, now in a front view. The stator steel sheet 11 comprises a basic shape made of a first metallic material, wherein the basic shape 15 has a ring structure with recesses 16 arranged therein, which, in this example, are open toward an inner edge B of the ring structure. The recesses 16 are closed with a closure structure 17a, 17b made of a second metallic material that differs from the first metallic material. Specifically, the closure structure 17a, 17b is arranged at the opening D of the recess 16 and closes it (see Figs. 3 and 4).

[0049] In general, the closure structure 17a, 17b is produced using a metal printing process, wherein the first metallic material in particular has a magnetic conductivity of .R > 20 and is therefore magnetic, and wherein the second metallic material in particular has a magnetic conductivity in a range of 1.1 < .R < 10 and is therefore weakly magnetic, or in particular has a magnetic conductivity of 1.0 < pR < 1.1 and is therefore non-magnetic. In the case of weakly magnetic materials, a value for the magnetic conductivity in a range of 1.1 < .R < 5 can be provided.

[0050] Fig. 3 now shows a detailed view of a first example of an electrical steel sheet or stator steel sheet 11a in front view. A contour of the electrical steel sheet 11a is wide or blunt toward the opening D of the recess 16, and the second metallic material of the closure structure 17a has a magnetic conductivity in a range of 1.1 < .R < 10 (weakly magnetic). Preferably, a value for the magnetic conductivity in a range of 1.1 < .R < 5 can also be provided.

[0051] Fig. 3 also shows the curve of the magnetic conductivity P over the rotation angle αp. As can be seen from Fig. 3, this embodiment results in a substantially trapezoidal curve of the magnetic conductivity P. The provision of the closure structure 17a offers several advantages, including:

[0052] The mechanical rigidity of the stator lamination 11a or the stator lamination stack 10 is significantly increased.

[0053] Vibrations and noise during operation of the electrical machine 1 are significantly reduced.

[0054] The weakly magnetic material causes lower losses than without the closure structure 17a. The mean value of the air gap conductance is high, and comparatively few harmonics are caused in the magnetic conductivity P and thus in the currents absorbed by the electrical machine 1.

[0055] The shaft voltage is reduced compared to stator laminations 11a or stator lamination stacks 10 without the closure structure 17a. The reason for this is that the capacitance of the stator winding 12 to the rotor 3 is shielded by a closed, metallic surface. The smooth inner surface of the stator lamination stack 10 reduces air turbulence, thereby reducing aerodynamic friction losses.

[0056] Overall, the efficiency and running behavior of the electric machine 1 can be significantly improved by the closure structure 17a.

[0057] Fig. 4 shows an alternative embodiment of an electrical steel sheet or stator steel sheet 11b, in which a contour of the electrical steel sheet 11 tapers towards the opening D of the recess 16 and in which the second metallic material of the closure structure 17b has a magnetic conductivity of 1.0 < |IR < 1.1 (non-magnetic). The profile of the magnetic conductivity P essentially corresponds to that of the prior art. Compared to Fig. 3, the gaps in the profile of the magnetic conductivity P are narrower but deeper. The mean value of the air gap conductance, which is shown in dashed lines in Figs. 3 and 4, is essentially the same, but more harmonics are generated in the magnetic conductivity P, and there are more harmonics in the torque generated by the electrical machine.The advantages mentioned above regarding stiffness, bearing currents and air turbulence apply accordingly; the magnetic losses are not or only slightly improved compared to the state of the art.

[0058] In the examples shown so far, the electric machine 1 is designed as an internal rotor machine, and the closure structure 17a, 17b is arranged internally on the stator lamination 11, 11a, 11b. However, this is by no means the only possible application of the closure structure 17a, 17b. Rather, the basic shape 15, 15a, 15b can have a ring structure with recesses 16 arranged therein, which are open toward the outer edge C of the ring structure. In summary, the following embodiments are particularly conceivable:

[0059] In the case of an internal rotor machine, the closure structure 17a, 17b is arranged radially inward on the stator 5 (as shown in the figures).

[0060] In the case of an internal rotor machine, the closure structure 17a, 17b is arranged radially outward on the rotor 3. In the case of an external rotor machine, the closure structure 17a, 17b is arranged radially outward on the stator 5.

[0061] In the case of an external rotor machine, the closure structure 17a, 17b is arranged radially inward on the rotor 3 (similar to that shown in Figures 2 to 4).

[0062] The proposed measures can also be provided within an electrical machine 1 both on the rotor 3 and on the stator 5.

[0063] Stator windings 12 can be arranged in the slots formed by the superimposed recesses 16 in a laminated core 10 for a stator 5. Alternatively or additionally, rotor windings can be arranged in the slots formed by the superimposed recesses 16 in a laminated core 13 for a rotor 3.

[0064] A method for producing an electrical sheet 1 1 , 1 1 a, 1 1 b, 14 for an electrical machine 1 can now comprise the following steps:

[0065] Providing the basic shape 15, 15a, 15b from a first metallic material, wherein the basic shape 15, 15a, 15b has a ring structure with recesses 16 arranged therein, which are open towards an inner edge B or outer edge C of the ring structure,

[0066] Producing the closure structure 17a, 17b from a second metallic material which differs from the first metallic material, wherein the closure structure 17a, 17b is produced by means of a metal printing process at an opening D of the recess 16 and wherein the closure structure 17a, 17b closes the opening D after printing.

[0067] The basic shape 15, 15a, 15b can, for example, be punched or cut out with a laser. However, it is also conceivable, in particular, for the basic shape 15, 15a, 15b to be produced using a metal printing process, in particular using the same metal printing process as the closure structure 17a, 17b. In a preferred embodiment, a metal screen printing process can be provided as the metal printing process. This process has proven particularly suitable for the production of an electrical steel sheet 11, 11a, 11b, 14.

[0068] The metal printing process can be carried out using a homogeneous base material that contains only grains of the same metal alloy. However, it is also conceivable that the metal printing process is carried out using an inhomogeneous base material that contains grains of different metals and / or metal alloys.

[0069] The non-magnetic material can, in particular, be stainless steel. The slightly magnetic material can, for example, be a mixture of stainless steel and a powder containing predominantly iron and some phosphorus. This can increase the rigidity of the electrical steel sheet 11, 11a, 11b, 14.

[0070] In general, the electrical steel sheet 1 1 , 1 1 a, 1 1 b, 14 can be heated after printing for a sintering process in order to permanently bond the printed components together and to ensure the stability of the electrical steel sheet 1 1 , 1 1 a, 1 1 b, 14.

[0071] Finally, Fig. 5 shows the electric machine 1 installed in a vehicle 18. The vehicle 18 has two axles, one of which is driven. Specifically, the electric machine 1 is connected to the half-axles 20 of the rear axle or front axle via an optional transmission 19. The driven wheels 21 are mounted on the half-axles 20. The electric machine 1, the transmission 19 and the half-axles 20 are part of the drive train of the vehicle 18. The vehicle 18 is driven at least partially or temporarily by the electric machine 1. This means that the electric machine 1 can serve to drive the vehicle 18 alone or, for example, be provided in conjunction with an internal combustion engine (hybrid drive). Finally, it is noted that the scope of protection is determined by the patent claims. However, the description and the drawings must be used to interpret the claims.The features contained in the figures can be interchanged and combined with one another as desired. In particular, it is also noted that the devices depicted may in reality comprise more or fewer components than shown. In some cases, the depicted devices or their components may also be shown not to scale and / or enlarged and / or reduced in size.

[0072] List of reference symbols

[0073] 1 electric machine

[0074] 2 rotor shaft

[0075] 3 Rotor

[0076] 4a, 4b camp

[0077] 5 Stator

[0078] 6 first bearing plate

[0079] 7 second bearing plate

[0080] 8 Stator housing

[0081] 9 Machine housing

[0082] 10 laminated core (stator laminated core)

[0083] 11, 1 1 a, 1 1 b electrical sheet metal (stator sheet)

[0084] 12 Stator winding

[0085] 13 Laminated core (rotor laminated core)

[0086] 14 Electrical steel (rotor sheet)

[0087] 15, 15a, 15b basic form

[0088] 16 Recess

[0089] 17a, 17b Closure structure

[0090] 18 vehicles

[0091] 19 gearboxes

[0092] 20 semi-axle

[0093] 21 wheels

[0094] A axis (rotor axis / stator axis)

[0095] B inner edge of the ring structure

[0096] C outer edge of the ring structure

[0097] D Opening

[0098] P magnetic conductivity cp rotation angle

Claims

Patent claims 1. An electrical sheet (11, 11a, 11b, 14) for an electrical machine (1), comprising a basic shape (15, 15a, 15b) made of a first metallic material, wherein the basic shape (15, 15a, 15b) has a ring structure with recesses (16) arranged therein, which are open towards an inner edge (B) or outer edge (C) of the ring structure, and a closure structure (17a, 17b) made of a second metallic material which is different from the first metallic material, wherein the closure structure (17a, 17b) is arranged at an opening (D) of the recess (16) and closes it, characterized in that the closure structure (17a, 17b) is produced using a metal printing process.

2. Electrical steel sheet (11, 11a, 11b, 14) according to claim 1, characterized in that the first metallic material has a magnetic conductivity of .R > 20 and the second metallic material has a magnetic conductivity in a range of 1.1 < .R < 10 or a magnetic conductivity of 1.0 < pR < 1.

1.

3. Electrical sheet (1 1 , 1 1 a, 1 1 b, 14) according to claim 1 or 2, characterized in that a contour of the electrical sheet (1 1 , 1 1 a, 1 1 b, 14) tapers to a point towards the opening (D) of the recess (16) and the second metallic material has a magnetic conductivity of 1.0 < pR < 1.

1.

4. Electrical sheet (1 1 , 1 1 a, 1 1 b, 14) according to claim 1 or 2, characterized in that a contour of the electrical sheet (1 1 , 1 1 a, 1 1 b, 14) to the opening (D) the recess (16) is wide and the second metallic material has a magnetic conductivity in a range of 1 .1 < .R < 10.

5. Electrical sheet (11, 11a, 11b, 14) according to one of claims 1 to 4, characterized in that it is designed as a stator sheet (11) or as a rotor sheet (14).

6. Laminated core (10, 13) for a stator (5) or rotor (3) of an electrical machine (1), characterized by a plurality of electrical sheets (11, 11a, 11b, 14) stacked one on top of the other along an axis (A) according to one of claims 1 to 5.

7. Laminated core (10, 13) according to claim 6, characterized in that stator windings (12) are arranged in slots which are formed in a laminated core (10) for a stator (5) by the recesses (16) lying one above the other, or rotor windings are arranged in slots which are formed in a laminated core (13) for a rotor (3) by the recesses (16) lying one above the other.

8. Electrical machine (1) with a stator (5) and a rotor (3) rotatably arranged therein, characterized in that the stator (5) has a laminated core (10) according to claim 6 or 7 with stacked stator laminations (11) according to claim 5 and / or the rotor (3) has a laminated core (13) according to claim 6 or 7 with stacked rotor laminations (14) according to claim 5.

9. Vehicle (18), characterized by an electric machine (1) according to claim 8, which is provided for driving the vehicle (18).

10. A method for producing an electrical sheet (11, 11a, 11b, 14) for an electrical machine (1), comprising the steps Providing a basic shape (15, 15a, 15b) made of a first metallic material, wherein the basic shape (15, 15a, 15b) has a ring structure with recesses (16) arranged therein, which are open towards an inner edge (B) or outer edge (C) of the ring structure, Producing a closure structure (17a, 17b) from a second metallic material which is different from the first metallic material, wherein the closure structure (17a, 17b) is produced by means of a metal printing process at an opening (D) of the recess (16), and wherein the closure structure (17a, 17b) closes the opening (D) after printing.

11. Method according to claim 10, characterized in that the provision of the basic mold (15, 15a, 15b) comprises the production thereof by a metal printing process.

12. The method according to claim 10 or 11, characterized in that a metal screen printing process is provided as the metal printing process.

13. Method according to one of claims 10 to 12, characterized in that the basic shape (15, 15a, 15b) is produced by the same metal printing process as the closure structure (17a, 17b).

14. Method according to one of claims 10 to 13, characterized in that the metal printing process is carried out with a homogeneous base material which only has grains of the same metal alloy, or with an inhomogeneous base material which has grains of different metals and / or metal alloys.

15. Method according to one of claims 10 to 14, characterized in that the electrical steel sheet (11, 11a, 11b, 14) is heated for a sintering process after printing.

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