Abstract:
A production method for a tool socket includes forming a hollow spindle An elongated recess is provided in the wall. The spindle includes unalloyed or low-alloyed steel grades. An insert includes a high-alloyed tool steel. The insert has a pedestal that is complementary to the recess and it also has a rib. The insert is placed into the hollow spindle in such a way that the pedestal rests in the recess and the rib projects into the interior of the spindle. The pedestal is soldered into the recess at a temperature that is above the Ac3 temperatures of the steel grades employed. The combined structure is cooled and then undergoes a heat treatment in an atmosphere containing sufficient carbon to carburize the hollow spindle but not sufficient to carburize the insert. The heat treatment of the combined structure is carried out at a temperature between 800° C. and 950° C. The combined structure is cooled down in a salt bath or liquid bath subsequent to the heat treatment.

Description:
[0001]    The present invention relates to a production method for a tool socket, especially for a handheld rotating and chiseling power tool. 
       BACKGROUND 
       [0002]    U.S. Pat. No. 7,338,051 describes a tool socket for a combination hammer drill. The tool socket has a tubular main body in whose interior the drill bit is accommodated so that it can be moved along its axis. Locking elements engage in the interior and secure the drill bit against falling out. Moreover, the tool socket has ribs that engage with corresponding grooves of the drill bit in order to transfer a torque from the tool socket to the drill bit. The ribs are made of a sintered hard metal and are inserted into the main body as inserts. The sintered hard metal is very abrasion-resistant. The ribs are secured in overlapping holes drilled in the main body. Adhesives, a press fit, soldering or welding as well as laser welding can all be employed to achieve a durable fixation. 
       SUMMARY OF THE INVENTION 
       [0003]    The rib is subject to very high mechanical loads. Peak loads of the torque occur, among other things, when the drill bit gets caught on a piece of rebar during the drilling procedure. Moreover, the insert and the main body are subject to vibrations caused by the striking mechanism. High requirements are made of the durability of the connection between the rib and the main body. The process of soldering and welding sintered hard metals is laborious, while adhesives and a press fit do not appear to be suitable measures. 
         [0004]    The rib should have a high abrasion resistance and nevertheless be easy to process during the production of the tool socket. 
         [0005]    The second material is preferably a cold work tool steel or a high-speed tool steel; hot work tool steels prove to be relatively soft after the soldering and heating treatment. 
         [0006]    The production method according to the invention for a tool socket comprises the following steps: a hollow spindle (main body) is formed. At least one elongated recess is provided in the wall. The spindle is made of a first material comprising unalloyed or low-alloyed steel grades. An insert is formed from a second material comprising a high-alloyed tool steel. The insert has a pedestal that is complementary to the recess and it also has a rib. The insert is placed into the hollow spindle in such a way that the pedestal rests in the recess and the rib projects into the interior of the spindle. The pedestal is soldered into the recess at a temperature that is above the Ac3 temperatures of the steel grades employed. The combined structure consisting of the hollow spindle and the insert is cooled off. The combined structure undergoes a heat treatment in an atmosphere containing sufficient carbon to carburize the hollow spindle but not sufficient to carburize the insert. The heat treatment of the combined structure is carried out at a temperature between 800° C. and 950° C. The combined structure is cooled down in a salt bath or liquid bath subsequent to the heat treatment. 
         [0007]    Surprisingly, this production method yields an abrasion-resistant rib. A tool steel acquires its hardness from a very specific multi-stage hardening process whose temperature profile is indicated by the steel suppliers. The hardening process entails at least heating the steel up to a temperature at which carbides dissolve as well as a tempering procedure repeated three times at a temperature between 500° C. and 600° C. The third tempering procedure is described in the literature as being essential in order to eliminate residual austenite from the second material as well as to remove the vitreous martensite formed during cooling off, thus resulting in the desired strength of the tool steel. The tool steel loses its hardness when it is heated to considerably above 600° C., while soft annealing can be expected at approximately 800° C. According to conventional teaching, the temperature during soldering as well as during the subsequent heat treatment step speaks against the use of tool steel for the rib. 
         [0008]    The heat treatment of the combined structure can be followed by tempering at 180° C. to 210° C., which eliminates stresses, especially in the hollow spindle. 
         [0009]    The insert is advantageously formed by means of a forging process or an investment cast process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The description below explains the invention on the basis of embodiments and figures provided by way of an example. The figures show the following: 
           [0011]      FIG. 1 : a combination hammer drill; 
           [0012]      FIG. 2 : a tool socket; 
           [0013]      FIG. 3 : the tool socket in a cross-sectional view along plane III; 
           [0014]      FIG. 4 : an insert in a top view. 
       
    
    
       [0015]    Unless otherwise indicated, identical or functionally equivalent elements are designated in the figures by the same reference numerals. 
       DETAILED DESCRIPTION 
       [0016]      FIG. 1  schematically shows a combination hammer drill  1  as an example of a handheld chiseling power tool. The combination hammer drill  1  has a tool socket  2  into which one shank end  3  of a tool, for example, a hammer drill bit  4 , can be inserted. The primary drive of the combination hammer drill  1  is in the form of a motor  5  which drives a striking mechanism  6  as well as a driven shaft  7 . The user can guide the combination hammer drill  1  by means of a handle  8  and can start up the combination hammer drill  1  by means of a system switch  9 . During operation, the combination hammer drill  1  continuously rotates the hammer drill bit  4  around the working axis  10  and, in this process, it can strike the hammer drill bit  4  into a substrate in the striking direction  11  along the working axis  10 . The striking mechanism  6  is preferably a motor-driven pneumatic striking mechanism  6 . A striker  12  is coupled via an air spring  13  to a piston  14  that is moved back and forth along a working axis  10  by the motor  5 . The striker  12  strikes the shank end  3  either directly or else indirectly via a striking pin  15 . 
         [0017]    The tool socket  2  is shown in detail in a longitudinal sectional view in  FIG. 2 , and in a cross-sectional view in  FIG. 3 . The tool socket  2  has a hollow spindle  16  (main body) that is driven by the driven shaft  7  and it has a receptacle  17  for the tool  4 . The hammer drill bit  4  can be inserted in the insertion direction (counter to the striking direction  11 ) into the receptacle  17  through an opening  18  located on the driven side. The receptacle  17  is preferably configured so as to be complementary to the shank end  3 , for example, cylindrically. 
         [0018]    The hammer drill bit  4 , which is provided with locking grooves, can be reversibly locked in the receptacle  17  by means of locking elements, here, for instance, pawls  19 . The pawls  19  are inserted into elongated holes  20  situated in a wall of the hollow spindle  16 . Radial blocking of the pawls  19  is effectuated by a locking ring  21  on which the pawls  19  partially protrude into the receptacle  17  radially from the inside. The part of the pawls  19  that protrudes into the receptacle  17  can engage with the locking groove of the tool  4 . A spring-loaded slide  22  holds the pawls  19  inside the locking ring  21 , that is to say, so as to overlap axially with the locking ring  21 . When the hammer drill bit  4  is inserted, the pawls  19  are moved counter to the spring-loaded slide  22  and they are disengaged from the locking ring  21 . The pawls  19  can deflect radially and give access to the receptacle  17 . The pawls  19  can be moved counter to the spring-loaded slide  22  by an actuating sleeve  23 , as a result of which the radial blocking of the pawls  19  is eliminated and the hammer drill bit  4  can be removed. 
         [0019]    The rotational movement of the hollow spindle  16  is transferred to the hammer drill bit  4  via ribs  24  that protrude into the receptacle  17 . The tool socket  2  configuration given by way of an example has a rib  24 . Alternative tool sockets  4 , especially for hammer drill bits having a large diameter, can have two or more ribs  24 . Along the working axis  10 , the rib  24  is at the height of the elongated holes  20  for the pawls  19 . 
         [0020]    The rib  24  is the part of an insert  25  that extends beyond the receptacle  17 . The insert  25  has the rib  24  and a pedestal  26 . For each rib  24 , the hollow spindle  16  has a recess  27  into which the pedestal  26  is inserted in the radial direction  28 . The recess  27  is complementary to the pedestal  26 . The pedestal  26  is permanently affixed in the recess  27  by soldering. The entire insert  25  is preferably monolithic, that is to say, made contiguously of one material, without joining zones. The insert  25  can be made of a tool steel. The hollow spindle  16  is made of a different material, for instance, of an unalloyed or low-alloyed steel. 
         [0021]    The rib  24  has a main section  29 . The main section  29  transmits essentially the entire torque to the combination hammer drill  1 . The exposed outer surfaces—especially a top surface  30  and two side surfaces  31 —of the main section  29  are parallel to the working axis  10 . The outer surfaces delimit a trapezoidal cross section that is constant along the working axis  10  over the entire length of the main section  29 . The top surface  30  is situated perpendicular to a radial direction  28  (vertical direction). The side surfaces  31  preferably adjoin the opposite lengthwise edges of the top surface  30 . The side surfaces  31  are preferably slanted relative to each other by between 20° and 40°. Therefore, the rib  24  is preferably wider at its bottom surface, that is to say, at the pedestal  26 , than at the top surface  30 . The center width  32  of the rib  24  is approximately the same as the height  33  of the rib  24 , differing, for example, by less than 20%. The length  34  of the main section  29  is at least three times the value of the height  33 . The rib  24  has to be sufficiently long to transfer the torque to the drill bit  4 . 
         [0022]    The rib  24  has a rear section  35  that is arranged behind the main section  29  in the striking direction  11 . The rear section  35  has a front face  36  that faces in the striking direction  11 . The front face  36  is preferably trapezoidal. The normal of the front face  36  lies in a plane formed by the working axis  10  and the vertical direction  28 . The front face  36  given by way of an example is not perpendicular to the working axis  10  but rather, it is slanted by between 70° and 80°. The front face  36  is preferably flat. The front face  36  is somewhat narrower than the main section  29 , that is to say, smaller than the trapezoidal cross section. The width  37  of the front face  36  at the pedestal  26  is between 80% and 90% of the width  32  of the cross section at the pedestal  26 . 
         [0023]    Two opposite inlet surfaces  38  laterally adjoin the front face  36 . The inlet surfaces  38  connect the front face  36  to the side surfaces  31 . The flat inlet surfaces  38  are somewhat slanted relative to the side surfaces  31 , preferably by between 2° and 10°. The inlet surfaces  38  preferably extend from the pedestal  26  all the way to the top surface  30 . The length  39  of the inlet surfaces  38  corresponds approximately to the distance of the two inlet surfaces  38 , that is to say, the width  37  of the rib  24 . 
         [0024]    The pedestal  26  is longer and wider than the rib  2 . The pedestal  26  is closed off at its lengthwise ends by semi-cylindrical end pieces. The pedestal  26  is essentially cuboidal between the two end pieces. The recess  27  correspondingly has likewise semi-cylindrical ends with a cuboidal intermediate area. 
         [0025]    The hollow spindle  16  is made, for instance, out of a tubular blank. The tubular blank can be cold-expanded to give it the desired inner profile. Subsequently, the inner and outer surfaces are machined. Moreover, the elongated holes  29  for the pawls  19  and also the recess  27  for the insert  25  are machined, for instance, with a grinding head. Bearing sections can be trimmed and polished to the target diameter. 
         [0026]    The steel of the tubular blank is preferably a low-alloyed steel, for instance, 16MnCr5. The carbon content is less than 0.4% by weight, preferably more than 0.1% by weight. The steel is low-alloyed; the total admixture of alloy elements is less than 5% by weight. Here, chromium can make up the largest amount, for instance, between 1.0% and 2.2% by weight. The steel can also be unalloyed. The carbon content in this case is likewise less than 0.4% by weight. 
         [0027]    The insert  25  is preferably made without involving machining work. The insert  25  is forged, for example, from a steel blank. The shaping is done using, for example, a die into which the blank is placed. The die can consist of multiple parts and it has a shape that is complementary to the insert  25 , that is to say, the rib  24  with the pedestal  26 . The blank is forged at a temperature between 950° C. and 1150° C. In this process, the Ac3 temperature of the steel is exceeded, as a result of which austenite is formed. After the shaping procedure, the insert  25  cools down, preferably in the air, to room temperature. As an alternative, the insert  25  can be produced by means of an investment cast process. 
         [0028]    The blank for the insert  25  is a tool steel, for instance, X155CrVMo12-1. The carbon content is more than 0.8% by weight, preferably less than 2.2% by weight. The blank is high-alloyed, the percentage of the totality of alloy elements is more than 7% by weight. 
         [0029]    The insert  25  is placed into the recess  27  of the hollow spindle  16 . A soldering agent, preferably a solder containing copper, is inserted between the insert  25  and the hollow spindle  16 . The insert  25  is soldered to the hollow spindle  16 , for example, in a soldering oven, at a temperature within the range from 1030° C. and 1070° C. The soldering operation takes between 20 and 60 minutes. During the soldering, the steels of the hollow spindle  16  and of the insert  25  are heated up to above their re-crystallization temperature. The tool steel loses hardness in this process. After the soldering, the combined structure consisting of the hollow spindle  16  and the insert  25  cools down in air or in some other gas atmosphere. 
         [0030]    The combined structure undergoes heat treatment in the immediately following step. The combined structure is heated up to a temperature between 800° C. and 950° C. The temperature can be raised in two or more steps in order to minimize thermomechanical stresses in the combined structure. The combined structure is kept at this temperature for 30 minutes to 2 hours. This temperature is considerably lower than the temperature that is suitable for hardening the tool steel. In the case of the tool steel X155CrVMo12-1 given by way of an example, this temperature is indicated as being 1160° C. to 1190° C. This temperature is likewise atypical for the heat treatments that are repeated three times for tool steel and that are carried out at a temperature between 400° C. and 600° C. in order to yield the typical hardness and strength of a tool steel. 
         [0031]    The heat treatment is carried out in an atmosphere containing carbon, for example, in a gas carburizing furnace. The carbon level is raised by admixing, for instance, methanol and propane. Regulation of the carbon level serves to keep the carbon level preferably constant during the heat treatment. The carbon level is selected in such a way that the hollow spindle  16  is carburized. The carbon level for the selected steel can be obtained from tables or simulations, or else it can be ascertained with just a few experiments. The carbon level is measured in a known manner, indirectly on the basis of the partial pressure of oxygen. The carbon level is also set in such a manner that the tool steel of the insert  25  is not carburized. For instance, the carbon level is between 0.7 and 0.75. The carbon in the insert  25  can be reduced or kept at the same level. 
         [0032]    The heat treatment is ended by means of rapid quenching, for example, in oil. The combined structure is hardened. Advantageously, the heat treatment is followed by a one-time tempering procedure at a low temperature between 180° C. and 210° C. in order to relieve internal stresses. 
         [0033]    In one embodiment, the quenching of the combined structure to room temperature can be followed by cooling to a temperature between −60° C. and −120° C. Low-temperature cooling is conducive to the hardening of the combined structure. The low-temperature cooling is followed by the one-time tempering procedure.