Method for manufacturing hybrid impact mechanism body for hand-held power tool

Abstract

The invention relates to a method for producing a hybrid percussion mechanism body (1) of a percussion mechanism of a hand-held power tool, consisting of at least one core element (2) and a sheath element (3) at least partially surrounding the core element, the method comprises the following manufacturing steps: providing a core element blank (2 ') inserted into a sheath element blank (3'), wherein at least one of the two parts is made of a steel material; the sheathing element blank (3 ') and the core element blank (2') are solid-formed by at least a single-stage combined extrusion in such a way that the core element (2) is connected to the surrounding sheathing element (3) in a forcibly locked and bound manner.

Description

Technical Field

[0001] The present invention relates to a method for producing a hybrid striking mechanism body of a striking mechanism for a handheld power tool, the hybrid striking mechanism body consisting of at least one core element and a jacket element at least partially surrounding the core element. The present invention also relates to various embodiments of the hybrid striking mechanism body that can be produced using this method, as well as a pneumatic striking mechanism for a handheld power tool, the pneumatic striking mechanism comprising the hybrid striking mechanism body according to the invention and the handheld power tool itself.

[0002] The field of application of the present invention extends primarily to rotary hammers and percussion hammers. Handheld power tools of the type in question are capable of transmitting pulsed impacts to a tool, such as, in particular, a hammer drill or chisel, at a suitable repetition rate. To this end, the impact mechanism is operated by means of a motor drive, which acts on a movable impact mechanism body (such as a striker or a striker pin) of a per se known impact mechanism in an accelerating manner. The drive of the impact mechanism can, for example, be formed by an eccentric mounted on a drive wheel, which causes a piston to move in a lifting manner in the manner of a crank drive. This piston then pneumatically drives the striker back and forth, for example, and this in turn stimulates the striker pin. The pulsed impact is thus first transmitted from the directly driven striker of the impact mechanism to the striker pin, and then from the striker pin to the tool shaft of the tool.

[0003] The impact mechanism body typically has side surfaces and a stop surface. The impulse impact of the impact mechanism body is typically transferred to a pulse absorbing component on the stop side. The pulse absorbing component is a tool component of a handheld power tool that absorbs the impulse impact at one end surface of the tool. The pulse-transmitting stop surface primarily serves to transfer the impulse between the impact mechanism body (e.g., the striker and the striker pin) within the impact mechanism. The impact mechanism components of the impact mechanism must be able to withstand relatively high loads, particularly on the stop surface and / or side surfaces. Background Art

[0004] According to the generally known prior art, the striking mechanism body usually consists of case-hardened or tempered steel that is heat-treated throughout, for example, by case hardening, tempering, etc., and therefore has uniform material properties throughout the entire striking mechanism body, particularly also on the stop surfaces and side surfaces. However, it has been found that the striking mechanism body is exposed to different stresses in different areas, which place different demands on the material.

[0005] These requirements become more stringent with increasing energy density in the striking mechanism, i.e. with increasing ratio of energy input to component size of the striking mechanism body, and with uncertain energy control, which can lead to so-called "bounce" of the one-piece striking mechanism body.

[0006] The decisive factor is the pulse to be transmitted by the striking mechanism body, which is determined by the speed and the resistance of the moving mass and the material of the striking mechanism body, in particular on the stop surface and / or side surfaces of the striking mechanism body.

[0007] Furthermore, the large striking mass of the striking mechanism body always means that the striking mechanism has a larger installation space in terms of diameter and length within the handheld power tool, resulting in a larger and possibly disproportionately heavy machine.

[0008] JP 10169385 A discloses a technical solution for increasing the energy density in a striking mechanism by increasing the specific density of the striking mechanism body. Even when using very high-quality materials and conventional heat treatment methods for the striking mechanism body, the increased energy density ultimately leads to excessive stresses and premature material failure, and also makes economical production impossible.

[0009] JP 2006 123025 A discloses technical measures for adjusting the mass of the striking mechanism body using different material densities. However, these measures are insufficient because, on the one hand, they only achieve an inadequate connection of the masses of the different parts of the striking mechanism. On the other hand, the areas of the striking mechanism body that are subject to the greatest stress, particularly the stop and side surfaces, consistently prove to be insufficiently resistant.

[0010] For example, JP 8197458 A and DE 103 044 07 A1 disclose various hybrid striking mechanism bodies having a cavity as a jacket element, which is filled with a plastic material or individual particles as a core element and has a damping effect on the movement of the striking mechanism body. The purpose is to counteract rebound. However, continuous production of these has proven to be technically quite complex.

[0011] Therefore, it has not been possible to eliminate negative effects such as rebound or the generation of excessive tensile stresses in the insertion tool or insufficient impact energy in a small handheld device using the measures known in the prior art.

[0012] The object of the present invention is to further develop a striking mechanism body of a striking mechanism of a handheld electric machine tool so that it can be produced in a simple manner, effectively avoids rebound and, for this purpose, has sufficient stability, compactness and weight. Summary of the Invention

[0013] This object is achieved with reference to the manufacturing method described in claim 1. Various embodiments of the striking mechanism body manufactured in this manner are indicated in claims 6 to 10. Claim 11 relates to a pneumatic striking mechanism having a striking mechanism body according to the invention, while claim 12 relates to a handheld power tool having such a pneumatic striking mechanism. The remaining dependent claims describe further advantageous embodiments of the invention.

[0014] The present invention includes a method for producing a hybrid striking mechanism body of a striking mechanism of a handheld power tool, the hybrid striking mechanism body consisting of at least one core element and a sheath element at least partially surrounding the core element, by performing the following production steps: - Providing a core element blank which is inserted into the sheathing element blank, wherein at least one of the two components is made of a steel material.

[0015] - Solidly shaping the sheathing element blank together with the core element blank by at least a single-stage co-extrusion, such that the core element is connected to the surrounding sheathing element in a positively locked and captive manner.

[0016] Therefore, the solution according to the present invention utilizes solid forming technology to manufacture the hybrid impact mechanism body according to the present invention. Solid forming is commonly used in the automotive industry as part of so-called "solid lightweight construction" to reduce component weight, either structurally or by combining multiple materials and subsequently molding them together. An example of this is the use of co-extrusion, a subcategory of solid forming, to reduce the weight of a gear shaft. The shaft typically consists of a light metal core surrounded by a stainless steel sheath. However, the present invention reverses this principle of solid lightweight construction, increasing the weight of the impact mechanism body while optimizing additional static and dynamic requirements.

[0017] The advantages of using the molding technology according to the present invention are particularly significant in that heat treatment and mechanical finishing of the components can be completely eliminated. Hybrid impact mechanism bodies manufactured according to the present invention have higher impact energy than conventional impact mechanism bodies. Consequently, impact mechanisms equipped with these hybrid impact mechanism bodies can provide greater impact power within the same installation space, or the impact mechanism can provide the same impact power within a smaller installation space. Compared to conventional, single-piece impact mechanism bodies, hybrid impact mechanism bodies manufactured according to the present invention cause less rebound.

[0018] The positively locked captive connection between the core element of the hybrid impact mechanism body and the jacket body is preferably produced by forming an undercut profile on the core element in the axial joint region, the undercut profile being at least partially filled with material from the jacket element. Suitable undercut profiles are, for example, a constriction or at least one shoulder on the preferably rotationally symmetrical core element.

[0019] Additionally or alternatively, a locally increased surface roughness can be generated on the core element and / or the corresponding sheath element in the region of the axial joining zone, which surface roughness is higher than the surface roughness on other surface regions of the components to be joined. This surface roughness can be produced mechanically or chemically, for example by chemical etching, mechanical knurling, etc.

[0020] According to a preferred embodiment, both the core element and the jacket element are made of steel. The core element is preferably made of a hard metal material to provide the impact mechanism body with a high material density and, therefore, a high energy density. In contrast, the jacket element is preferably made of conventional carbon steel, which has a higher toughness than hard metal, to ensure suitable side and stop surfaces for the impact mechanism body.

[0021] In its initial state, the sheath element blank can be preformed into a can or cylinder shape using a forming technique. The interior space formed in this way is preferably cylindrical so as to at least partially accommodate a corresponding, preferably also cylindrical core element before solidification. Alternatively, the sheath element blank can also be preformed into a non-cylindrical or non-axially symmetrical shape on the inside. For example, a polygonal shape or the like can be provided, or the cross section can be a polygon, such as a rectangle, or the cross section can have, for example, a plurality of curves with different radii.

[0022] According to a first preferred embodiment, the hybrid impact mechanism body is manufactured by solid molding. The jacket element of the hybrid impact mechanism body is designed in the shape of a cylindrical sleeve, wherein the axial length of the jacket element is shorter than the axial length of the core element enclosed by the jacket element, so that the end surfaces are formed on both sides of the core element. This forms a continuous core element, and the two metal components are joined by co-extrusion using a molding technique in a positively locked manner. The materials of the core and jacket elements are selected to maximize the material density of the core element. Therefore, during subsequent use in the impact mechanism, the maximum impact energy is generated due to the corresponding increase in component weight. The core element has the aforementioned undercut profile, which is filled with the material of the plastically molded jacket element by molding. Therefore, at the moment of impact, the jacket element cannot be displaced axially relative to the core element. In terms of functional integration, the joining area thus also has the function of transmitting force in the axial direction and / or radial direction.

[0023] In contrast, the sheath element is made of a metal with favorable properties using forming technology. This ensures that the sheath surface, which also functions as a sealing surface in the pneumatic impact mechanism, can be produced to a so-called "net shape" through the forming process, i.e., a surface that is ready for installation. This eliminates the need for time-consuming post-processing processes such as grinding the surface. The sheath element can be made of, for example, carbon steel 16MnCr5. This steel material can also be hardened after forming as required. However, residual deformation in the hardness of the aforementioned functional surface must be taken into account. The sheath element, which is geometrically described as a cylindrical sleeve in this embodiment, can be prefabricated by forming. Since the core element protrudes in front of the sheath element on the end face, the sheath element is not part of the impact surface of the impact mechanism body.

[0024] According to a second preferred embodiment of the hybrid impact mechanism body designed according to the present invention, its jacket element is cylindrically pot-shaped, wherein the core element enclosed by the jacket element forms a first end surface, and the base surface of the jacket element forms a second end surface, these two end surfaces being securely connected to each other by joining using a forming technique. Unlike the above-described embodiment, in this embodiment, one of the end surfaces is composed of the material of the pot-shaped jacket element. Preferably, one end surface of the impact mechanism body is composed of the jacket element material, and the other end surface of the impact mechanism body is composed of the core element material.

[0025] Alternatively, according to a third preferred embodiment, it is also possible to consider using the jacket element material to form the two end faces of the impact mechanism body. For this purpose, the jacket element encloses the core element from four sides or at least mostly from four sides.

[0026] According to a fourth preferred embodiment of the hybrid impact mechanism body manufactured according to the present invention, the sheath element is designed in the shape of a cylindrical can, wherein the core element is enclosed by the sheath element, so that the core element is designed to form a piston-cylinder arrangement that is axially movable relative to the sheath element. The protruding portion of the core element serves as the first end surface of the impact mechanism body, while the base surface of the sheath element forms the second end surface of the impact mechanism body. Unlike the aforementioned preferred embodiments of the hybrid impact mechanism body, in this fourth embodiment, the two components are axially displaceable relative to each other. This feature further minimizes the rebound behavior of the impact mechanism body during an impact.

[0027] According to a preferred embodiment of the hybrid impact mechanism body produced according to the invention, an anti-rotation lock is provided, which at least limits and in particular completely prevents a rotation of the core element relative to the jacket element. The anti-rotation lock can be achieved in particular by shaping the core element relative to the jacket element, wherein the core element is not rotationally symmetrical for this purpose.

[0028] The hybrid striking mechanism body of the above-described embodiment is preferably used as part of a pneumatic striking mechanism of a handheld power tool, which also comprises a striking mechanism cylinder, a so-called "riveting pin" for axially impacting the tool, and a striking mechanism piston designed as a striking mechanism body according to one of the preceding claims. The striking mechanism piston is part of a crank drive on the drive side, which is known per se. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further measures for improving the invention are explained in more detail below together with the description of preferred exemplary embodiments of the invention with reference to the accompanying drawings. In the drawings: Figure 1 is a schematic flow chart of a method for manufacturing a hybrid striking mechanism body according to the present invention, Figure 2 is a schematic diagram of an impact mechanism of a handheld power tool having a hybrid impact mechanism body designed according to the present invention, Figure 3 It is the first embodiment of the hybrid impact mechanism body, Figure 4 is the second embodiment of the hybrid impact mechanism body, Figure 5 is a third embodiment of the hybrid impact mechanism body, and Figure 6 This is the fourth embodiment of the hybrid impact mechanism body. DETAILED DESCRIPTION

[0030] according to Figure 1 The method for manufacturing a hybrid striking mechanism body according to the present invention is based on providing (I) a core element blank 2', which is inserted into a sleeve-shaped jacket element blank 3', the core element blank and the jacket element blank consisting of steel materials of different hardness. The cylindrical core element blank 2' consists of a hard metal, while the jacket element blank 3' is preformed from an extrudable carbon steel.

[0031] Subsequently, solid forming of the sheathing element blank 3 ′ and the core element blank 2 ′ is achieved by co-extrusion in a suitable forming tool (II), which ensures that the resulting core element 2 is connected to the surrounding sheathing element 3 in a positively locked and captive manner.

[0032] according to Figure 2 The pneumatic impact mechanism of the handheld power tool shown here is provided with a hybrid impact mechanism body 1 manufactured in this manner, which is arranged in a displaceable and dynamically sealed manner in an impact mechanism cylinder 4. The impact mechanism body 1 serves to apply axial impact loading to a tool 5, which in this case is intended to be a percussion chisel.

[0033] In contrast, the exciter piston 6, which is also arranged in a dynamically sealed, axially displaceable manner in the impact mechanism cylinder 4, can be moved axially back and forth via a crank drive 7. The crank drive 7 thus converts the rotary drive movement into an alternating reciprocating movement of the exciter piston 6, which transmits the movement to the impact mechanism body 1 via a pneumatic transmission path to dampen the impact loading of the tool 5.

[0034] according to Figure 3 In a first embodiment, a positively locked and captive connection between the core element 2 and the sheath element 3 is produced by forming an undercut profile 9 on the core element 2 in the axial joining region 8 in the form of a constriction of the core element 2, which is otherwise cylindrical, and which is filled with the material of the sheath element 3 after solid forming. The sheath element 3 is designed in the shape of a cylindrical sleeve and has a smaller axial length than the core element 2 enclosed by the sheath element. Therefore, the end faces 10 and 11 on both sides are formed by the core element 2.

[0035] according to Figure 4 The second embodiment of the hybrid impact mechanism body differs from the above-described embodiments in that the sheath element 3 is designed in the shape of a cylindrical pot. The core element 2, enclosed by the sheath element, protrudes from this, forming a first end surface 10. Conversely, the base surface of the sheath element 3 forms a second end surface 11.

[0036] exist Figure 5 In the third embodiment of the striking mechanism body illustrated in FIG, the jacket element 3 surrounds the core element 2 from all sides. This forms the two end faces 10 and 11 of the jacket element 3.

[0037] according to Figure 6 In the fourth embodiment of the impact mechanism body, the sheath element 3 is also designed in the shape of a cylindrical pot. The core element 2 is enclosed by the sheath element so that the core element forms a piston-cylinder arrangement and is designed to be able to move axially relative to the sheath element 3. The axial joint area 8 is basically formed by the piston cover part of the sheath element 3, and the piston rod part of the core element 2 passes through the piston cover part in an axially movable manner. This is in the path s H Axial adjustability is achieved on both sides in the direction of rotation, thereby minimizing rebound effects.

[0038] The present invention is not limited to the exemplary embodiments described above. Modifications thereof are also conceivable and are covered by the scope of protection of the following claims. For example, it is also possible for the hybrid impact mechanism body to consist of more than three components. It should also be noted that the joining of the jacket element 3 and the core element 2 using forming techniques can be verified in cross-section by flow lines through the components. Forming can be achieved by combining standardized solid forming methods according to DIN 8583.

[0039] List of Reference Numerals 1 Impact mechanism body 2-core components 2' core element blank 3 sheath components 3' sheath element blank 4 Impact mechanism cylinder 5 Tools 6 actuator piston 7 Crank drive 8 Junction area 9 Undercut Profile 10 first end surface 11 Second end face s H Improvement Path

Claims

1. A method for producing a hybrid striking mechanism body (1) of a striking mechanism of a handheld power tool, the hybrid striking mechanism body consisting of at least one core element (2) and a sheath element (3) at least partially surrounding the core element, It is characterized by The following manufacturing steps: - providing a core element blank (2') to be inserted into a sheath element blank (3'), wherein at least one of the two components is made of a steel material; - solid forming of the sheathing element blank (3') and the core element blank (2') by at least a single-stage co-extrusion, such that the core element (2) is connected to the surrounding sheathing element (3) in a positively locked and captive manner.

2. The method according to claim 1, It is characterized by A positively locking captive connection between the core element (2) and the sheath element (3) is produced by forming an undercut profile (9) on the core element (2) in the axial joining region (8), the undercut profile being at least partially filled with material from the sheath element (3).

3. The method according to claim 1 or 2, It is characterized by A locally increased surface roughness is generated on the core element (2) and / or the corresponding sheath element (3) in the axial joining zone (8), said roughness being higher than the surface roughness on other surface areas of the components to be joined.

4. The method according to claim 1 , It is characterized by The core element (2) and the jacket element (3) are in each case made of different steel materials, wherein the core element (2), which is preferably made of a hard metal material, has a higher material density than the jacket element (3).

5. The method according to claim 1 , It is characterized by The sheathing element blank (3') is made of a metal material, preferably composed of carbon steel, and is preformed into a can or cylinder shape using forming technology.

6. A hybrid striking mechanism body manufactured by the method according to one of the preceding claims, It is characterized by The sheath element (3) is designed in a cylindrical sleeve shape, wherein the axial length of the sheath element is smaller than the axial length of the core element (2) enclosed by the sheath element, so that end surfaces (10, 11) are formed on both sides of the core element (2).

7. A hybrid striking mechanism body manufactured by the method according to one of the preceding claims, It is characterized by The sheath element (3) is designed in a cylindrical pot shape, wherein the core element (2) enclosed by the sheath element forms a first end surface (10) protruding from the core element, and the base surface of the sheath element (3) forms a second end surface (11).

8. A hybrid striking mechanism body manufactured by the method according to one of the preceding claims, It is characterized by The sheathing element (3) encloses the core element (2) from all sides, so that the end faces (10, 11) on both sides are formed by the sheathing element (3).

9. A hybrid striking mechanism body manufactured by the method according to one of the preceding claims, It is characterized by The sheath element (3) is designed in the shape of a cylindrical pot, wherein the core element (2) is enclosed by the sheath element so that the core element is designed to form a piston-cylinder arrangement that can move axially relative to the sheath element (3), wherein the protruding portion of the core element (2) forms the first end surface (10) and the base surface of the sheath element (3) forms the second end surface (11).

10. Hybrid striking mechanism body according to one of claims 6 to 9, It is characterized by An anti-rotation lock is provided, which at least limits and in particular prevents a rotation of the core element (2) relative to the sheath element (3).

11. A pneumatic impact mechanism for a handheld power tool, comprising an impact mechanism cylinder (4) having an exciter piston (6) driven by a crank drive (7) and an axially opposed impact mechanism piston (1) for axial impact loading of a tool (5) according to one of the preceding claims.

12. A handheld power tool, in particular a rotary hammer or an impact hammer, having a pneumatic impact mechanism according to claim 10.

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