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

Abstract

The invention relates to a method for producing a hybrid striking mechanism body (1) for a striking mechanism of a handheld power tool, the hybrid striking mechanism body being composed of at least a core element (2) and a casing element (3) which at least partially surrounds the core element, the method comprising the following manufacturing steps: providing a core element blank (2') which is inserted into a casing element blank (3'), at least one of the two components consisting of a steel material; and solid forming the casing element blank (3') containing the core element blank (2') by means of at least one-stage composite extrusion in such a way that the core element (2) is interlockingly non-releasably connected to the surrounding casing element (3).

Description

[0001] METHOD FOR PRODUCING A HYBRID IMPACT BODY FOR AN ELECTRIC HAND TOOL

[0002] DESCRIPTION

[0003] The present invention relates to a method for producing a hybrid impact mechanism body for an impact mechanism of a power hand tool, which is composed of at least one core element and a casing element that at least partially surrounds the core element. Furthermore, the invention also relates to several embodiments of hybrid impact mechanism bodies that can be produced using such a method, as well as to a pneumatic impact mechanism for a power hand tool, comprising an inventive hybrid impact mechanism body and an power hand tool itself.

[0004] The field of application of the invention extends primarily to hammer drills and impact hammers. Power tools of the type of interest here are capable of transmitting a pulsed impact to a tool, such as, in particular, a percussion drill or chisel, at a suitable repetition rate. For this purpose, the impact mechanism is driven by an electric motor, which accelerates a movable impact mechanism body, such as a striker or firing pin, of a known impact mechanism. The drive of the impact mechanism can, for example, be formed by an eccentric wheel mounted on a drive wheel, which causes a piston, similar to a crank drive, to perform a reciprocating movement. This piston then, for example pneumatically, drives the striker to reciprocate, which in turn activates the firing pin.A pulse is therefore transmitted from the directly driven striker of the percussion mechanism first to the firing pin and then from the firing pin to the tool shank of the tool. The percussion mechanism body usually has a side surface and a stop surface. The pulse from the percussion mechanism body is usually transmitted on the stop side to a pulse-absorbing component. The pulse-absorbing component is the tool of the power hand tool, which absorbs the pulse on a front surface of the tool. Pulse-transmitting stop surfaces are primarily used to transmit pulses between percussion mechanism bodies within the percussion mechanism, for example a striker and a firing pin. Percussion mechanism components of the percussion mechanism have to withstand comparatively high loads, particularly on a stop surface and / or side surface.

[0005] State of the art

[0006] According to the generally known state of the art, a percussion mechanism body is usually made of case-hardened or tempered steel, which is heat-treated as a whole, for example, by case hardening, tempering, or the like, and as such has identical material properties throughout the entire percussion mechanism body, particularly on the impact surface and side surfaces. However, it has been shown that a percussion mechanism body is exposed to different stresses in different areas, which place different demands on the material.

[0007] The requirements become more severe with increasing energy density in a percussion mechanism, i.e. with increasing ratio of energy input to component size of a percussion mechanism body, and can cause a so-called rebound of the one-piece percussion mechanism body in the case of undefined energy controls.

[0008] What is decisive is the impulse to be transmitted by a percussion body resulting from the speed and moving mass in relation to the resistance of the material of the percussion body, in particular on its stop surface and / or side surface.

[0009] In addition, larger impact masses of an impact mechanism body always mean a larger installation space for the impact mechanism in terms of diameter and length within the power hand tool, which leads to larger and possibly disproportionately heavy machines.

[0010] JP 10169385 A discloses a technical solution in which the energy density in a percussion mechanism is increased by increasing the specific density of the percussion mechanism body. Even with the use of very high-quality materials and conventional heat treatment processes for the percussion mechanism body, excessive stress and premature material fatigue can ultimately no longer be avoided at increased energy densities, making cost-effective production impossible.

[0011] JP 2006 123025 A discloses technical measures for adjusting the mass of a percussion mechanism body using different material densities. However, these measures are insufficient because, on the one hand, they only achieve an inadequate bond between the different percussion mechanism component masses. On the other hand, the most stressed areas of a percussion mechanism body, namely the impact surfaces and side surfaces, always prove to be insufficiently resilient.

[0012] For example, JP 8197458 A and DE 103 044 07 A1 describe various hybrid percussion bodies with hollow spaces as shell elements. These hollow spaces, filled with plastic materials or individual particles as core elements, dampen the movement of the percussion body. This is intended to counteract rebound. However, serial production proves to be quite complex from a technological perspective.

[0013] It is therefore not yet possible to eliminate negative effects such as impact or the generation of excessive tensile stresses in an insert tool or insufficient impact energy in small hand tools using measures known in the state of the art.

[0014] It is the object of the present invention to further improve a percussion mechanism body for a percussion mechanism of an electric hand-held power tool in such a way that it can be produced easily, effectively prevents re-impacting and is designed to be sufficiently stable, compact and heavy.

[0015] Disclosure of the invention

[0016] The problem is solved with regard to a manufacturing method by claim 1. Various embodiments of a percussion mechanism body produced thereby are specified in claims 6 to 10. While claim 11 is directed to a pneumatic percussion mechanism with a percussion mechanism body according to the invention, claim 12 is directed to an electric hand tool with such a pneumatic percussion mechanism. The remaining dependent claims represent advantageous developments of the invention.

[0017] The invention includes the process engineering teaching that for the production of a hybrid impact mechanism body for an impact mechanism of an electric hand tool, which is composed of at least one core element and a casing element at least partially surrounding it, the following manufacturing steps are carried out:

[0018] Providing a core element blank inserted in a shell element blank, wherein at least one of the two components consists of a steel material.

[0019] Massive forming of the shell element blank together with the core element blank by means of at least one-stage compound extrusion, such that the core element is positively and captively connected to the surrounding shell element.

[0020] The inventive solution thus utilizes forging technology to produce the hybrid impact mechanism body according to the invention. Typically, forging is used in the automotive industry as part of so-called forging lightweight construction to reduce the weight of components, either structurally or by combining multiple materials and subsequently forming them together. One example is the weight reduction of a transmission shaft through compound extrusion, a subcategory of forging. The shaft usually consists of a light metal core surrounded by a stainless steel shell. In the present invention, however, this principle of forging lightweight construction is reversed, and the weight of an impact mechanism body is increased, while other static and dynamic requirements are optimized.

[0021] The advantage of the inventive forming solution lies in the fact that heat treatment and mechanical finishing of the component can be completely eliminated. The hybrid impact mechanism body produced according to the invention exhibits higher impact energy than conventional impact mechanism bodies, so that an impact mechanism equipped with it can deliver more impact power in the same installation space, or an impact mechanism can deliver the same impact power in a smaller installation space. The hybrid impact mechanism body produced according to the invention causes a lower impact effect than conventional single-piece impact mechanism bodies.

[0022] The positive, captive connection between the core element and the shell body of the hybrid impact mechanism body is preferably created by creating an undercut contour on the core element within an axial joining zone, which is at least partially filled by material from the shell element. A constriction or at least one shoulder on a preferably rotationally symmetrical core element is suitable as an undercut contour, for example.

[0023] Additionally or alternatively, a locally increased surface roughness can be created on the core element and / or the corresponding shell element in the area of ​​the axial joining zone, which is higher than the surface roughness on the remaining surface areas of the components to be joined. Such surface roughness can be created using mechanical or chemical processes, for example by chemical etching, mechanical knurling and the like. According to a preferred embodiment, both the core element and the shell element are made of a steel material, with the core element preferably consisting of a hard metal material in order to impart a high material and thus energy density to the impact mechanism body. In contrast, the shell element is preferably made of a conventional carbon steel, which has a higher toughness than a hard metal in order to ensure suitable side and stop surfaces of the impact mechanism body.

[0024] In its initial state, the shell element blank can be preformed in a pot-shaped or cylindrical manner. The resulting interior is preferably cylindrical in order to at least partially accommodate the corresponding, preferably also cylindrical, core element therein prior to bulk forming. Alternatively, the shell element blank can also be preformed on the inside in a non-cylindrical or non-axially symmetrical manner. For example, a polygonal shape or the like can be provided, or a cross-section can be polygonal, for example, rectangular, or have multiple curves with, for example, different radii.

[0025] According to a first preferred embodiment, a hybrid impact mechanism body is produced by bulk forming, the shell element of which is cylindrically sleeve-shaped, the axial length of which is smaller than the axial length of the core element enclosed thereby, such that the core element forms end faces on both sides. This creates a continuous core element and both metallic components are positively connected by forming and joining using composite extrusion. The materials of the core element and shell element are selected such that the core element has a maximum material density. This is intended to generate maximum impact energy during later use in the impact mechanism through a correspondingly increased component weight. The core element has the aforementioned undercut contour, which is filled with the material of the plastically formed shell element by forming and joining.This prevents the shell element from being axially displaced relative to the core element at the moment of impact. With regard to functional integration, the joining zone also serves the function of transmitting force in the axial and / or radial directions.

[0026] The shell element, on the other hand, is made of a metal that has favorable forming properties. This ensures that the shell surface, which also functions as a sealing surface in the pneumatic impact mechanism, can be produced as a so-called net-shape, i.e., a ready-to-install surface, through the forming process. This eliminates the need for costly post-processing processes such as surface grinding. The shell element can, for example, be made of 16MnCr5 carbon steel. This steel material can also be hardened after forming, if necessary. However, allowance must be made for the hardening distortion of the aforementioned functional surfaces. The shell element, which in this embodiment has a cylindrical sleeve shape, can be prefabricated by forming.Due to the frontal protrusion of the core element in front of the shell element, the latter is not part of the impact surfaces of the impact mechanism body.

[0027] According to a second preferred embodiment of a hybrid percussion mechanism body constructed according to the invention, its casing element is cylindrically cup-shaped, with the core element enclosed thereby protruding therefrom to form the first end face, and the base surface of the casing element forming the second end face, the two being firmly connected to one another by the forming joining process. In contrast to the embodiment described above, here at least one of the end faces consists of the material of the cup-shaped casing element. Thus, one end face of the percussion mechanism body preferably consists of the casing element material, and the other end face of the percussion mechanism body consists of the core element material.

[0028] Alternatively, according to a third preferred embodiment, it is also conceivable to form both end faces of the percussion body from the casing element material. For this purpose, the casing element encloses the core element on all sides, or at least largely on all sides. According to a fourth preferred embodiment of a hybrid percussion body produced according to the invention, the casing element is cylindrically pot-shaped, wherein the core element is enclosed thereby in such a way that it is designed to form a piston-cylinder arrangement and is axially movable relative to the casing element. A protruding part of the core element functions as the first end face of the percussion body, whereas the bottom surface of the casing element forms the second end face of the percussion body.In contrast to the previously described preferred embodiments of a hybrid impact mechanism body, the two components in the fourth embodiment are axially displaceable relative to each other. This function serves the purpose of further minimizing the impact behavior of the impact mechanism body upon impact.

[0029] According to a preferred embodiment of a hybrid impact mechanism body manufactured according to the invention, an anti-rotation device is provided, which at least limits and, in particular, completely prevents the core element from rotating relative to the casing element. The anti-rotation device can be achieved, in particular, by appropriately shaping the core element relative to the casing element, with the core element being designed, in particular, to be non-rotationally symmetrical.

[0030] A hybrid impact mechanism body of the embodiments described above is preferably used in a pneumatic impact mechanism for a power hand tool, which also comprises an impact mechanism cylinder, a so-called striker for axially impacting a tool, and an impact mechanism piston designed as an impact mechanism body according to one of the preceding claims. The impact mechanism piston is a component of a known drive-side crank drive.

[0031] Detailed description of the drawing

[0032] Further measures improving the invention are described in more detail below, together with the description of preferred embodiments of the invention, with reference to the figures. Therein: Fig. 1 shows a schematic flow chart of the inventive method for producing a hybrid impact mechanism body,

[0033] Fig. 2 is a schematic representation of a percussion mechanism of an electric hand tool with a hybrid percussion mechanism body designed according to the invention,

[0034] Fig. 3 shows a first embodiment of a hybrid impact body,

[0035] Fig. 4 shows a second embodiment of a hybrid impact mechanism body,

[0036] Fig. 5 shows a third embodiment of a hybrid impact body, and

[0037] Fig. 6 a fourth embodiment of a hybrid impact body.

[0038] According to Fig. 1, a manufacturing method for a hybrid impact mechanism body according to the invention is based on the provision (I) of a core element blank 2' inserted into a sleeve-shaped shell element blank 3', both made of a steel material of different hardness. While the cylindrical core element blank 2' is made of a hard metal, the shell element blank 3' is preformed from an extrudable carbon steel.

[0039] Subsequently, a massive forming (II) of the shell element blank 3' with the core element blank 2' takes place by means of compound extrusion in a suitable forming tool, which ensures that the resulting core element 2 is positively and captively connected to the surrounding shell element 3.

[0040] According to Fig. 2, a hybrid impact mechanism body 1 manufactured in this way is provided for the pneumatic impact mechanism of an electric hand tool shown here, 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 to a tool 5, which in this case is intended to represent a striking chisel.

[0041] Opposite, an exciter piston 6, also arranged in the percussion cylinder 4 with a dynamic seal and axially movable, is axially reciprocating via a crank drive 7. Thus, the crank drive 7 converts a rotating drive movement into an alternating reciprocating movement of the exciter piston 6, which transmits the movement to the percussion body 1 via a pneumatic transmission line for the dampened impact application of the tool 5.

[0042] According to Fig. 3, according to the first embodiment, the positively locking, captive connection between the core element 2 and the shell element 3 is created by creating an undercut contour 9 on the core element 2 within an axial joining zone 8, similar to a constriction of the otherwise cylindrical core element 2, which is filled by the material of the shell element 3 after bulk forming. The shell element 3 is cylindrically sleeve-shaped and has a smaller axial length than the core element 2 enclosed by it. Thus, the end faces 10 and 11 on both sides are formed by the core element 2.

[0043] According to Fig. 4, the second embodiment of a hybrid impact mechanism body differs from the previously described embodiment in that the casing element 3 is cylindrically cup-shaped. The core element 2 enclosed by it protrudes from it, forming the first end face 10. In contrast, the bottom surface of the casing element 3 forms the second end face 11.

[0044] In the third embodiment of a percussion mechanism body illustrated in Fig. 5, the casing element 3 surrounds the kernel element 2 on all sides. As a result, the two end faces 10 and 11 are formed by the casing element 3.

[0045] According to Fig. 6, in the fourth embodiment of a percussion mechanism body, the casing element 3 is also cylindrically pot-shaped. The core element 2 is enclosed by it in such a way that it forms a piston-cylinder arrangement and is designed to be axially movable relative to the casing element 3. The axial joining zone 8 is essentially formed by the piston cover section of the casing element 3, which is penetrated in an axially movable manner by a piston rod section of the core element 2. This results in axial adjustability on both sides in the direction of the travel SH to minimize a rebound effect.

[0046] The invention is not limited to the exemplary embodiments described above. Rather, modifications thereof are also conceivable, which are also encompassed by the scope of the following claims. For example, it is also possible for the hybrid impact mechanism body to be composed of more than three components. Furthermore, it should be noted that the joining of the shell element 3 to the core element 2 by forming can be verified in cross-section by flow lines on the component. The forming can be realized as a combination of standardized bulk forming processes according to DIN 8583.

[0047] List of reference symbols

[0048] 1 percussion body

[0049] 2 core element 2' core element blank

[0050] 3 Sheath element

[0051] 3' sheath element blank

[0052] 4 percussion cylinders

[0053] 5 Tool 6 Excitation piston

[0054] 7 Crank drive

[0055] 8 Joining zone

[0056] 9 Undercut contour

[0057] 10 first end face 11 second end face

[0058] SH stroke

Claims

CLAIMS 1. A method for producing a hybrid impact mechanism body (1) for an impact mechanism of an electric hand tool, which is composed of at least one core element (2) and a casing element (3) at least partially surrounding said core element, characterized by the following manufacturing steps: Providing a core element blank (2') inserted into a shell element blank (3'), wherein at least one of the two components consists of a steel material; Massive forming of the shell element blank (3') with the core element blank (2') by means of at least one-stage compound extrusion, such that the core element (2) is positively and captively connected to the surrounding shell element (3).

2. Method according to claim 1, characterized in that the positively locking, captive connection between the core element (2) and the sheath element (3) is produced by creating an undercut contour (9) on the core element (2) within an axial joining zone (8), which undercut contour is at least partially filled by material of the sheath element (3).

3. Method according to claim 1 or 2, characterized in that on the core element (2) and / or the corresponding shell element (3) within an axial joining zone (8) a locally increased surface roughness is produced, which is higher than the surface roughness on the remaining surface areas of the components to be joined.

4. Method according to one of the preceding claims, characterized in that both the core element (2) and the casing element (3) are made of a different steel material, wherein the core element (2), which preferably consists of a hard metal material, has a higher material density than the casing element (3).

5. Method according to one of the preceding claims, characterized in that the casing element blank (3') is produced from a metal material, preferably consisting of a carbon steel, which is pre-formed in a pot-shaped or cylindrical shape by forming technology.

6. Hybrid impact mechanism body, manufactured by a method according to one of the preceding claims, characterized in that the casing element (3) is cylindrically sleeve-shaped, the axial length of which is smaller than the axial length of the core element (2) enclosed thereby, so that end faces (10, 11) on both sides of the core element (2) are formed.

7. Hybrid impact mechanism body, manufactured by a method according to one of the preceding claims, characterized in that the casing element (3) is cylindrically pot-shaped, the core element (2) enclosed thereby protruding therefrom forming the first end face (10) and the bottom surface of the casing element (3) forming the second end face (11).

8. Hybrid impact mechanism body, manufactured by a method according to one of the preceding claims, characterized in that the casing element (3) encloses the core element (2) on all sides, so that the end faces (10, 11) on both sides are formed by the casing element (3).

9. Hybrid percussion body, produced by a method according to one of the preceding claims, characterized in that the casing element (3) is cylindrically pot-shaped, the core element (2) being enclosed thereby in such a way that it is designed to form a piston-cylinder arrangement and is axially movable relative to the casing element (3), a protruding part of the core element (2) forming the first end face (10) and the bottom surface of the casing element (3) forming the second end face (11).

10. Hybrid impact mechanism body according to one of claims 6 to 9, characterized in that an anti-twist device is provided which at least limits and in particular prevents the core element (2) from twisting relative to the casing element (3).

11. Pneumatic impact mechanism for an electric hand tool, comprising an impact mechanism cylinder (4) with an excitation piston (6) driven by a crank mechanism (7) and an axially opposite impact mechanism piston (1) according to one of the preceding claims for axially impacting a tool (5).

12. Electric hand tool, in particular a hammer drill or percussion hammer, with a pneumatic percussion mechanism according to claim 10.

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