Method for manufacturing a hybrid striking mechanism body for a handheld power tool

Abstract

The present invention relates to a method for manufacturing a hybrid striking mechanism body (1) for a striking mechanism of a handheld power tool, the hybrid striking mechanism body (1) consisting of at least one core element (2) and a sheath element (3) at least partially surrounding the core element (2), the manufacturing method comprising the following manufacturing steps: providing a core element blank (2') inserted into a sheath element blank (3'), at least one of the two components being made of a steel material; solid-molding the sheath element blank (3') together with the core element blank (2') by at least one composite extrusion stage, so that the core element (2) is securely connected to the surrounding sheath element (3) in a locked and fixed manner.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a hybrid striking mechanism body for a striking mechanism of a hand-held power tool, the hybrid striking mechanism body comprising at least one core element and a sheath element at least partially surrounding the core element. The present invention also relates to several embodiments of the hybrid striking mechanism body that can be manufactured by such a method, as well as to a pneumatic striking mechanism for a hand-held power tool that includes a hybrid striking mechanism body according to the invention and the hand-held power tool itself.

[0002] The field of application of the present invention primarily encompasses rotary hammers and striking hammers. Handheld power tools of the type of interest here are capable of transmitting impacts at a suitable repetition rate, particularly to tools such as striking drills or chisels. For this purpose, the striking mechanism is operated by an electric motor drive that acts in an accelerating manner on a movable striking mechanism body, e.g., a striking body or striking pin, of a striking mechanism known per se. The striking mechanism drive can be formed, for example, by an eccentric wheel attached to a drive wheel, which causes a piston to move up and down like a crank drive. The striking body is then moved back and forth, for example, by air pressure, which stimulates the striking pin. Thus, the impact is first transmitted from the striking body, which is driven directly by the striking mechanism, to the striking pin, and then from the striking pin to the tool shank of the tool.

[0003] The striking mechanism body typically has a side surface and a stop surface. Impact from the striking mechanism body is periodically transmitted to a shock-absorbing component on the stop side. The shock-absorbing component is a part of the handheld power tool and absorbs the impact at one end surface of the tool. The shock-transmitting stop surface is primarily used to transmit impact between the striking mechanism body within the striking mechanism, e.g., between the striking body and the striking pin. The striking mechanism portion of the striking mechanism must be able to withstand relatively high loads, particularly at the stop surface and / or side surface. [Background technology]

[0004] According to the known prior art, the striking mechanism body is usually made of hardened or tempered steel, which is heat-treated throughout, for example by hardening, tempering, etc., and has the same material properties throughout the entire striking mechanism body, especially on the stop face and on the side faces. However, it has been shown that the striking mechanism body is subjected to different stresses in different regions, which place different demands on the material.

[0005] These requirements become more stringent as the energy density of the striking mechanism increases, i.e., the ratio of energy input to the size of the components of the striking mechanism body increases, which can lead to so-called "rebound" of the integral striking mechanism body if energy control is not provided for.

[0006] The determining factor is the impulse transmitted by the striking mechanism body resulting from the velocity and moving mass against the resistance of the material of the striking mechanism body, in particular the resistance at the stop faces and / or sides of the striking mechanism body.

[0007] Furthermore, as the striking mass of the striking mechanism body increases, the installation space required for the diameter and length of the striking mechanism within the handheld power tool increases, making the machine larger and, in some cases, unduly heavy.

[0008] Japanese Patent Application Laid-Open No. 10-169385 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 very high-quality materials and conventional heat treatment methods are used for the striking mechanism body, the increased energy density eventually leads to excessive stress and premature material failure, making economical manufacturing unachievable.

[0009] Technical measures for adjusting the mass of the striking mechanism body using different material densities are known from JP 2006-123025 A. However, these measures are insufficient because, on the one hand, they only achieve an insufficient connection of the different parts of the striking mechanism. On the other hand, the most highly stressed areas of the striking mechanism body, in particular the stop faces and flanks, always prove to be insufficiently resistant.

[0010] For example, JP 8197458 A1 and DE 10304407 A1 disclose various hybrid striking mechanism bodies, each of which has a cavity as a sheath element, filled with a plastic material or individual particles as a core element, which has a damping effect on the movement of the striking mechanism body. The purpose is to counteract recoil. However, continuous production has proven to be technically very complex.

[0011] Therefore, using the means known in the prior art, it is not yet possible to eliminate adverse effects such as rebound and the generation of excessive tensile stresses in insertion tools, or insufficient impact energy in small handheld devices. Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to further improve a striking mechanism body for a striking mechanism of a handheld electric machine tool so that it can be easily manufactured, can effectively avoid rebound, and has sufficient stability, compactness, and weight for this purpose. [Means for solving the problem]

[0013] This object is achieved by the manufacturing method of claim 1. Various embodiments of the striking mechanism body manufactured in this way are shown in claims 6 to 10. Claim 11 relates to a pneumatic striking mechanism comprising a striking mechanism body according to the invention, while claim 12 relates to a hand-held power tool comprising such a pneumatic striking mechanism. The remaining dependent claims describe advantageous further embodiments of the invention.

[0014] The present invention includes teachings of a method for manufacturing a hybrid striking mechanism body for a striking mechanism of a hand-held power tool, the hybrid striking mechanism body comprising at least one core element and a sheath element at least partially surrounding the core element, by carrying out the following manufacturing steps: - Providing a core element blank inserted into a sheath element blank, at least one of the two components being made from a steel material. - solid-molding the sheath element blank together with the core element blank by at least one composite extrusion stage, so that the core element is connected to the surrounding sheath element in a securely locked and fixed manner.

[0015] The solution according to the invention therefore utilizes the technology of solid-state molding to manufacture the hybrid striking mechanism body according to the invention. Solid-state molding is typically used in the automotive industry as part of so-called "solid lightweight construction" to reduce the weight of components structurally or by combining multiple materials and then molding them together. One example is the lightweighting of gear shafts, which uses composite extrusion as a subcategory of solid-state molding. The shaft typically consists of a light metal core surrounded by a stainless steel sheath. However, in the present invention, this principle of solid-state lightweight construction is reversed, increasing the weight of the striking mechanism body while still optimizing static and dynamic requirements.

[0016] The advantages of the solution using molding technology according to the invention are, in particular, that heat treatment and mechanical finishing of the parts can be completely omitted. The hybrid striking mechanism body produced according to the invention has a higher striking energy than conventional striking mechanism bodies, so that a striking mechanism equipped with this hybrid striking mechanism body can provide a higher striking force in the same installation space, or the same striking force in a smaller installation space. The hybrid striking mechanism body produced according to the invention has a lower recoil effect than conventional one-piece striking mechanism bodies.

[0017] The securely locked, fixed connection between the core element and the sheath body of the hybrid striking mechanism body is preferably produced by creating an undercut contour in the core element within the axial coupling zone, which undercut contour is at least partially filled with the material of the sheath element. Suitable undercut contours are, for example, a constriction or at least one shoulder on the core element, which is preferably rotationally symmetrical.

[0018] Additionally or alternatively, a locally increased surface roughness can be created on the core element and / or the corresponding sheath element in the region of the axial bonding zone, which roughness is greater than the surface roughness on other surface regions of the components to be joined. Such a surface roughness can be created by mechanical or chemical methods, for example by chemical etching, mechanical knurling, etc.

[0019] According to a preferred embodiment, both the core element and the sheath element are made from a steel material, the core element preferably being made from a hard metal material in order to provide a high material density and therefore energy density to the striking mechanism body, whereas the sheath element is preferably made from a conventional carbon steel having a higher hardness than the hard metal in order to ensure adequate flank and stop surfaces for the striking mechanism body.

[0020] In its initial state, the sheath element blank can be preformed into a pot-shaped or cylindrical shape using a molding technique. The interior space thus formed is preferably cylindrical in order to at least partially accommodate the corresponding core element, which is preferably cylindrical, before solid molding. Alternatively, the sheath element blank can be preformed internally in a cylindrical or non-axially symmetrical shape. For example, it may have a polygonal shape or a cross section that is polygonal, rectangular, or has multiple curves with different radii.

[0021] According to a first preferred embodiment, the hybrid striking mechanism body is manufactured by solid molding. The sheath element is designed in the shape of a cylindrical sleeve, with an axial length smaller than that of the core element it surrounds, resulting in end faces on both sides of the core element. This creates a continuous core element, and the two metal components are securely joined by combined extrusion using molding techniques. The materials of the core and sheath elements are selected to maximize the material density of the core element. As a result, during subsequent use in the striking mechanism, the correspondingly increased component weight generates maximum striking energy. The core element has the aforementioned undercut contour, which is filled with the plastically formed sheath element material by joining using molding techniques. Therefore, at the moment of striking, the sheath element cannot be displaced axially relative to the core element. From the perspective of functional integration, the coupling zone also has the function of transmitting forces in the axial and / or radial directions.

[0022] In contrast, the sheath element is fabricated from a metal with desirable properties using forming techniques. This ensures that the sheath surface, which also serves as a sealing surface in the pneumatic striking mechanism, can be manufactured as a so-called "net shape," i.e., a ready-to-install surface, through the forming process. This eliminates the need for time-consuming post-processing processes such as surface grinding. The sheath element can be made, for example, from carbon steel 16MnCr5. This steel material can also be quenched after forming, if necessary. However, the residual strain in the hardness of the functional surface mentioned above must be taken into account. In this embodiment, the sheath element is geometrically cylindrical and can be prefabricated by forming. Due to the protrusion of the core element forward at the end face of the sheath element, the sheath element is not part of the striking surface of the striking mechanism body.

[0023] According to a second preferred embodiment of the hybrid striking mechanism body designed in accordance with the present invention, the sheath element has a cylindrical pot shape, whereby the enclosed core element forms a first end face, and the base surface of the sheath element forms a second end face, both of which are firmly connected to each other by joining using molding techniques. In contrast to the above-mentioned embodiment, here, at least one of the end faces is made of the material of the pot-shaped sheath element. Preferably, one end face of the striking mechanism body is made of the sheath element material, and the other end face of the striking mechanism body is made of the core element material.

[0024] Alternatively, according to a third preferred embodiment, it is also conceivable that both end faces of the striking mechanism body are formed by the sheath element material, for which purpose the sheath element surrounds the core element on all sides, or at least on a large part of all sides.

[0025] According to a fourth preferred embodiment of the hybrid striking mechanism body manufactured according to the present invention, the sheath element is designed to be cylindrical and pot-shaped, and the core element is surrounded by the sheath element so as to form an axially movable piston-cylinder arrangement relative to the sheath element. The protruding portion of the core element serves as the first end face of the striking mechanism body, and the base surface of the sheath element forms the second end face of the striking mechanism body. In contrast to the above-described preferred embodiments of the hybrid striking mechanism body, in the fourth embodiment, the two components can be displaced axially relative to each other. This feature serves the purpose of further minimizing the rebound behavior of the striking mechanism body during striking.

[0026] According to a preferred embodiment of the hybrid striking mechanism body manufactured according to the invention, an anti-rotation lock is provided which at least limits, and in particular completely prevents, the core element from rotating relative to the sheath element, which can in particular be achieved by molding the core element relative to the sheath element, the core element not being rotationally symmetric for this purpose.

[0027] The hybrid striking mechanism body of the above-described embodiment is preferably used as part of a pneumatic striking mechanism for a hand-held power tool, which also comprises a striking mechanism cylinder and a so-called "rivet pin" for the axial impact load of the tool, and a striking mechanism piston, which is designed as a striking mechanism body according to one of the preceding claims and which is part of a drive-side crank drive known per se.

[0028] Further means for improving the invention will be explained in more detail below in conjunction with the description of preferred exemplary embodiments of the invention with reference to the drawings, in which: [Brief explanation of the drawings]

[0029] [Figure 1] 4 is a schematic flow chart of a method for manufacturing a hybrid striking mechanism body according to the present invention. [Figure 2]1 is a schematic diagram of a striking mechanism of a handheld power tool having a hybrid striking mechanism body designed in accordance with the present invention; [Figure 3] 1A and 1B are diagrams showing a first embodiment of a hybrid striking mechanism body. [Figure 4] FIG. 10 is a diagram showing a second embodiment of a hybrid striking mechanism body. [Figure 5] FIG. 10 is a diagram showing a third embodiment of a hybrid striking mechanism body. [Figure 6] FIG. 10 is a view showing a fourth embodiment of a hybrid striking mechanism body. DETAILED DESCRIPTION OF THE INVENTION

[0030] 1, the method for manufacturing the hybrid striking mechanism body according to the invention is based on (I) providing a core element blank 2' inserted into a sleeve-shaped sheath element blank 3', both made of steel materials with different hardnesses: the cylindrical core element blank 2' is made of hard metal, while the sheath element blank 3' is preformed from extrudable carbon steel.

[0031] Subsequently, (II) solid molding of the sheath element blank 3' with the core element blank 2' is carried out by compound extrusion in a suitable molding tool, which ensures that the resulting core element 2 is securely connected to the surrounding sheath element 3 in a locked and fixed manner.

[0032] 2, the hybrid striking mechanism body 1 thus produced is provided in the pneumatic striking mechanism of the hand-held power tool shown here, and is slidably and dynamically sealed within the striking mechanism cylinder 4. The striking mechanism body 1 is used to apply an axial impact load to a tool 5, which in this case is intended to represent a striking chisel.

[0033] Opposite this is an excitation piston 6 dynamically sealed within the striking mechanism cylinder 4 and arranged so as to be able to reciprocate axially, and can move back and forth via a crank drive 7. Thus, the crank drive 7 converts the rotary drive motion into alternating back and forth motion of the excitation piston 6, which transmits the motion to the striking mechanism body 1 via a pneumatic transmission path, thereby damping the impact load on the tool 5.

[0034] 3, in a first embodiment, the securely locked and fixed connection between the core element 2 and the sheath element 3 is produced by creating an undercut contour 9 in the form of a constriction of the otherwise cylindrical core element 2 in the axial coupling zone 8 of the core element 2, which undercut contour is filled by the material of the sheath element 3 after solid molding. The sheath element 3 is designed to be cylindrical and sleeve-shaped and has a shorter axial length than the core element 2 that it surrounds. Thereby, both end faces 10, 11 are formed by the core element 2.

[0035] 4, the second embodiment of the hybrid percussion mechanism body differs from the above-described embodiment in that the sheath element 3 is designed in the shape of a cylindrical pot, from which the enclosed core element 2 protrudes and forms a first end face 10. In contrast, the base surface of the sheath element 3 forms a second end face 11.

[0036] In the third embodiment of the striking mechanism body shown in Figure 5, the sheath element 3 surrounds the core element 2 on all sides, thereby forming two end faces 10 and 11 of the sheath element 3.

[0037] According to Fig. 6, in the fourth embodiment of the striking mechanism body, the sheath element 3 is also designed cylindrically and pot-shaped. The core element 2 is surrounded by the sheath element 3 to form a piston-cylinder arrangement and is designed to be axially movable relative to the sheath element 3. The axial coupling zone 8 is substantially formed by the piston cover part of the sheath element 3, which is axially movably penetrated by the piston rod part of the core element 2. This allows the path s to be narrowed to minimize the rebound effect. H The axial adjustment is possible on both sides of the direction of the arrow.

[0038] The present invention is not limited to the above-described exemplary embodiments. On the contrary, modifications thereof are also conceivable, which are within the scope of protection of the following claims. For example, it is also possible for the hybrid striking mechanism body to consist of more than two components. It should also be noted that the joining of the sheath element 3 to the core element 2 using molding techniques can be seen in cross section by flow lines on the components. Molding can be performed as a combination of standardized solid molding methods according to DIN 8583. [Explanation of symbols]

[0039] 1. Striking mechanism body 2 Core Elements 2' core element blank 3 Sheath elements 3' sheath element blank 4. Impact mechanism cylinder 5 Tools 6 Excitation piston 7 Crank drive unit 8. Bonding Zone 9 Undercut Contour 10 first end face 11 Second end face s H Lift route

Claims

1. A method for manufacturing a hybrid striking mechanism body (1) for a striking mechanism of a hand-held power tool, the hybrid striking mechanism body (1) comprising at least one core element (2) and a sheath element (3) at least partially surrounding the core element (2), the method comprising: - providing a core element blank (2') inserted in a sheath element blank (3'), at least one of said two components being made of steel material; - solid-molding, by at least one composite extrusion stage, of said core element blank (2') together with said sheath element blank (3') so that said core element (2) is securely connected to the surrounding sheath element (3) in a locked and fixed manner.

2. 2. The method according to claim 1, characterized in that the securely locked and fixed connection between the core element (2) and the sheath element (3) is produced by creating an undercut contour (9) in the core element (2) within an axial bonding zone (8), the undercut contour being at least partially filled by the material of the sheath element (3).

3. 3. The method according to claim 1 or 2, characterized in that within an axial bonding zone (8) a locally increased surface roughness is created on the core element (2) and / or the corresponding sheath element (3), said surface roughness being greater than the surface roughness on other surface areas of the components to be joined.

4. 4. The method according to claim 1, wherein both the core element (2) and the sheath element (3) are made in each case from different steel materials, the core element (2), preferably made from a hard metal material, having a higher material density than the sheath element (3).

5. The method according to any one of claims 1 to 4, characterized in that the sheath element blank (3') is manufactured from a metal material, preferably carbon steel, and is preformed into a pot-shaped or cylindrical shape using a forming technique.

6. A hybrid striking mechanism body manufactured by the method according to any one of claims 1 to 5, 1. A hybrid striking mechanism body, characterized in that the sheath element (3) is designed in the shape of a cylindrical sleeve, the axial length of the sheath element being smaller than the axial length of the core element (2) surrounded by the sheath element, so that end faces (10, 11) are formed on both sides of the core element (2).

7. A hybrid striking mechanism body manufactured by the method according to any one of claims 1 to 5, 1. A hybrid striking mechanism body, characterized in that the sheath element (3) is designed in the shape of a cylindrical pot, the core element (2) surrounded by the sheath element (3) forms a first end face (10) protruding from the core element (2), and the base surface of the sheath element (3) forms a second end face (11).

8. A hybrid striking mechanism body manufactured by the method according to any one of claims 1 to 5, The hybrid striking mechanism body is characterized in that the sheath element (3) surrounds the core element (2) on all sides, and both end faces (10, 11) are formed by the sheath element (3).

9. A hybrid striking mechanism body manufactured by the method according to any one of claims 1 to 5, 1. A hybrid striking mechanism body, characterized in that the sheath element (3) is designed in the shape of a cylindrical pot, the core element (2) is surrounded by the sheath element (3) to form a piston-cylinder arrangement and is designed to be axially movable relative to the sheath element (3), a protruding portion of the core element (2) forming a first end face (10) and a base surface of the sheath element (3) forming a second end face (11).

10. The hybrid impact mechanism body according to any one of claims 6 to 9, A hybrid striking mechanism body, characterized in that it is provided with an anti-rotation lock which at least limits, and in particular prevents, the core element (2) from rotating relative to the sheath element (3).

11. A pneumatic striking mechanism for a hand-held power tool, comprising a striking mechanism cylinder (4) with an exciter piston (6) driven by a crank drive (7) together with axially opposed striking mechanism pistons (1) according to any one of claims 1 to 10 for axial impact loading of the tool (5).

12. A hand-held power tool, in particular a rotary hammer or a striking hammer, equipped with a pneumatic striking mechanism according to claim 10.

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