Abstract:
A machining head ( 36 ) is drivable along a vertical axis and two horizontal axes with respect to a workpiece held on a workpiece-holding device, and has, at progressively lower levels along said vertical axis, one or two high-speed spindles ( 44 ), one or two low-speed spindles ( 46 ) and one or two feed-out spindles ( 48 ), all arranged at right angles to said vertical axis and driven by one or more motors ( 42 ) mounted on the head. The machining head can bring the high-speed spindles to cooperate with a tool-changing magazine ( 52 ). The workpiece-holding device ( 54; 154 ) is adapted to carry two sets of workpieces on respective supports ( 56, 58; 170 ), and to shift said supports in succession between a working position near the head and a tool-changing position remote from the head.

Description:
BACKGROUND OF THE INVENTION 
     This invention is concerned with an apparatus for machining caliper blocks and brackets of motorcar disk brakes. 
     As well known in the art, production of disk brake caliper blocks and brackets starts from a blank generally consisting of a workpiece cast in iron or aluminum, which undergoes a set of machining steps comprising milling, facing, boring, drilling and tapping, which operations may be made along different axes. 
     An approach that is often adopted nowadays in the mass production of caliper blocks and brackets is to set up a highly automated machining line, which is typically capable of a cycle time of about 20 sec/cycle, giving rise to a production of the order of a few thousands pieces/day (i.e., a few hundreds of pieces/hour). The drawback of such approach is the high rigidity of the dedicated line, which makes the line obsolete as soon as the production is changed. If such a change takes place prematurely with respect to the initial forecast, e.g. where a motorcar model has not been successful, this may cause a serious economic damage, since not always the line can be equipped for another production, and the investment in the equipment is then lost. 
     A highly flexible approach is, on the other hand, to perform machining in a machining center. This, however, requires a few minutes for one work cycle, and consequently this approach is economically viable only where the production required is less than 20 pieces/hour, as in the case of caliper blocks and brackets for lorries, or for deluxe cars. 
     When the production required is of the order of 50 to 100 pieces/hour, or when the lifetime of a model is uncertain, neither of the above approaches is clearly satisfactory, in the former case, because the risk that the investment in the equipment is not recovered is high, in the latter case, because the cost of the part turns out to be excessively high. 
     The main object of this invention is now to provide an apparatus for machining motorcar disk brake caliper blocks and brackets which provides a production that is definitely higher than a machining center, while being capable of being re-equipped in case of a production change. 
     SUMMARY OF THE INVENTION 
     The invention achieves the above and other objects and advantages, such as will appear from the following disclosure, with an apparatus for machining motorcar disk brake caliper blocks and brackets, having the feutures set out in claim  1 . 
     The dependent claims define other advantageous features of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described with reference to a few preferred embodiments, disclosed in the following disclosure and shown by way of non-limiting example, in the attached drawings, wherein: 
     FIGS. 1,  2  are  3  are, respectively, a lateral view, a front view and a rear view, partly in cross-section, of an example of a brake caliper block, which is intended to be machined with the apparatus of the invention; 
     FIG. 4 is a view in side elevation of a first preferred embodiment of the apparatus of the invention; 
     FIG. 5 is a plan view of the apparatus of FIG. 4; 
     FIG. 6 is a view in front elevation of the apparatus of FIG. 4; 
     FIG. 7 is a view in transverse cross-section, on an enlarged scale, of a machining head belonging to the apparatus of FIGS. 4 to  6 ; 
     FIG. 8 is a plan view of a swapping device for workpiece-holding supports, which is a part of the apparatus of FIGS. 4 to  6 ; 
     FIG. 9 is a view in transverse cross-section of the swapping device of FIG. 8; 
     FIG. 10 is a partially driagrammatical view, in vertical cross-section and on a further enlarged scale, of a tipping cradle having a workpiece-retaining member, belonging to the apparatus of FIGS. 8 and 9; 
     FIG. 11 is a view in side elevation of a second preferred embodiment of the apparatus of the invention; 
     FIG. 12 is a plan view of the apparatus of FIG.  11 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1,  2  and  3  show a typical caliper block of a disk brake, as known to those skilled in the art, which it is intended to machine by the apparatus of the invention. The brake caliper block typically requires facing in  10 , large-gauge milling in  12 , boring and profiling in a cylindrical chamber  14 , drilling and/or tapping, as well as milling and spot-facing, in  16 ,  18 , and other that may change in different cases. The special function of the part generally requires that, for instance, the axes of facing in  10  and of milling in  12  sometimes form a small angle, and it often turns out that the axes of holes  18  are not parallel to each other and/or to the axis of the chamber. Similar operations and like peculiarities are also found in the brake bracket, which is not shown here for simplicity. 
     With reference to FIGS. 4,  5  and  6 , a bedplate  20  bears horizontal roller guides  22 , which slidably support a truck  24 . The truck is drivable along a horizontal axis of motion X by motor means not shown, through a ball screw  26 . Truck  24  is also provided with horizontal guides  28 , crossing guides  22 . Guides  28  also slidably support a column  30 , which is driven by motor means  32  for moving along a horizontal axis Z, also by means of a screw  34 . Finally, column  30  slidably supports a machining head  36  on vertical guides  38  (axis Y). Machining head  36  is moved by motor means  40 , carried by column  30  by means of a ball screw not shown, and is further provided with an electric motor  42  for driving tool-holding spindles  44 ,  46 ,  48 , further described below, as well as with an electric motor  43  for controlling the feed-out of one of the spindles, also as disclosed below. 
     Having now reference to FIG. 7, the two upper spindles  44  of machining head  36  derive their motion, via a gearing  45 , from a shaft  41  that is driven by a driving motor  42 , with an appropriate driving ratio, so that a high speed (e.g. 4500 rev/min) is imparted to spindles  44 . Hydraulic actuators  47  lock and unlock spindles  44  when changing the tool, as further explained below. High-speed spindles  44  are intended mainly for drilling, tapping, milling or spot-facing and the like, on small areas of a workpiece, also as will best appear below. 
     A further gearing  49 , provided with a clutch  51 , is also dependent from motor shaft  41 . Gearing  49  drives a spindle  46 , which is in a lower and more backward position, with a gear ratio such that will provide a low speed (e.g. 500 rev/min). Spindle  46  is of a size and geometry that will carry a large-size, for large-diameter milling. 
     Finally, spindle  48  is also driven through a gearing  49 . This spindle is provided with a tool feed-out capability, and, accordingly, it is provided with a mechanism  53  for feeding out the tool, as known in the art, under control of electric motor  43 . Spindle  48  is especially intended for outside and inside profiling (say, for milling grooves within the cylinder of the caliper), as will also be explained below in more detail. 
     With further reference to FIGS. 4 to  6 , a frame  50  rising from bedplate  20  carries a mechanized tool-changing magazine  52  (only visible on FIG.  4 ), known per se, for instance of the type using a drum (although it could be of another kind, such as using a chain, a plurality of arms, etc.), and capable of bringing different tools in an appropriate position for selective grasping by spindles  44  of machining head  36 . 
     Finally, bedplate  20  supports a workpiece-holding support swapping device  54 , placed in front of machining head  36 . Device  54 , shown in more detail on FIGS. 8 and 9, is a drum rotating around a horizontal axis that is parallel to axis x, and provided with hydraulic motor means  55 , capable of driving the drum through tipping strokes between the position shown in the drawing and a position that is tipped by 180° around its axis. 
     Drum  54  has two opposite bays, accommodating respective workpiece-holding supports in form of cradles  56 ,  58 , which are rotatable around respective axes A 1 , A 2 , parallel to the tipping axis of the swapping device, and acting as supports for respective sets of four workpieces  60 ,  62 , which are aligned parallelly to axis X. Two electric motors  64 ,  65 , are mounted on swapping device  54  and drive, through respective worm screws, worm gears  67 ,  69 , which are integral with their respective cradles  56 ,  58 . Means are provided for taking up slacks and for locking during stops, as known in the art, and not shown here for simplicity. 
     Finally, cradle  58  carries an electric motor  71 , which drives a worm screw  73  engaging worm gears  75 . Worm gears  75  are integral with respective retaining members for respective workpieces, so that the workpieces can be rotated around respective axes B, at right angles to the cradle axis. Means may be provided, also in this case, for taking up slacks and for locking during stops, not shown here because they are known in the art. 
     All the motor means of the apparatus are obviously capable of being controlled by numeric control, and particularly, the the motors of the spindles can be controlled both as to speed and as to stop position, according to techniques that are known in the art of automated machining. 
     FIG. 10 shows a preferred workpiece-retaining member for a single caliper block, and which is a part of cradle support  56 . A reference template  76  is mounted on cradle  56 , preferably designed according to EP 0 689 898. A caliper block  78  rests on template  76  and is locked by retaining members  80 ,  82 , which are operated by hydraulic cylinders  84 ,  86 . Cradle  56  comprises four workpiece-retaining members as described and as illustrated on FIG.  10 . 
     Cradle  58  may also be provided with workpiece-retaining members similar to the one shown on FIG. 10, although the templates (as it may be seen on FIG. 8) should in this case be mounted on respective rotating platforms. However, since cradle  58  is intended for supporting workpieces that have already undergone a first cycle of heavy operations on cradle  56 , it is generally preferable to use a conventional retaining device, where the references used are one or more of the surfaces that were machined in the first cycle of operations. 
     Cradles  56  and  58  could of course be designed to support only two workpieces, rather than four workpieces each. 
     Alternatively, according to a different implementation of the invention, spindle  46  is installed with an inclination to axis y by a small angle, typically less than 1°, so that it is capable of performing an inclined milling along surface  10  of a caliper block mounted on the device with horizontal cylinder, the feeding motion being obtained by interpolation of axes Z and Y. 
     In the operation of the apparatus as described above, while the machining head performs a set of operations on the workpieces supported on one of the cradles, say cradle  56 , a workman  68  loads four workpieces on crdale  58 , after unloading the workpieces that were machined previously. Unloading may be manual, or may be made by dropping the workpieces from the cradle while it points downward, to be subsequently overturned for loading. Device  54  is then tipped, and during tipping the cradle rotates typically by 180°, so that it will eventually place the workpieces in the proper position with respect to the machining head. Machining head  36  executes its work program on the workpieces, while the workpieces on cradle  56  are unloaded and replaced with other workpieces requiring machining. 
     The workpieces will typically undergo two machining cycles: in a first cycle, they are mounted on cradle  56 , which lacks an axis B and on which the heavier operations are preferably performed, such as milling, boring or facing over wide surfaces; in a second cycle, they are mounted on cradle  58 , where the availability of the two axes of rotation A and B allows the workpiece to be presented to the tools with arbitrary angles, in order to execute operations, usually less heavy, such as drilling, tapping, milling, profiling, etc. with practically arbitrary orientations. 
     The less stressful operations, such as drilling and tapping, will generally be performed by spindles  44 , which are capable of working in parallel to perform the same operations simultaneously upon two side-by-side workpieces, provided that the machining head has been designed with a distance between spindles  44  that is equal to the distance between two adjacent (or alternate) workpiece retaining members. 
     The structure of the apparatus allows most motions and operations that are accessory to the actual machining to be overlapped. For instance, as far as the machining times are concerned, the cradle tipping operations around axes A 1  and A 2 , as well as some of the rotations around axes B, might be masked by the tipping motion of drum  54  for cradle swapping. Also, loading and unloading the workpieces could take place with ease on one of the cradles during the machining operations of the spindles on the workpieces of the other cradle. 
     In a second preferred embodiment, shown on FIGS. 9 and 10, the machining head and the control members for its motion and for tool changing are substantially identical to the corresponding members in the first embodiment. However, the swapping device  54  is replaced by a turning table  154  with a vertical axis. Table  154  has a cradle  170  which is rotatable around a horizontal axis A 2 , similarly to cradle  58  of the first embodiment. The rotation arc of cradle  170  may extend over a full turn, but, alternatively, may be restricted to an arc of a few degrees. 
     Turning table  154  has a first pair of workpiece-retaining members  190 , preferably of the kind shown on FIG.  10 . In an opposite position, cradle  170  carries a second pair of workpiece-retaining members  192 , also similar to FIG. 10, although they could be conventional. Workpiece-retaining members  192  are also capable of rotation around respective axes at right angles to the cradle tipping axis A 2 , for instance as described with reference to FIG. 8, or of another known type. If required, of course, workpiece-retaining members  190  could also be provided with similar rotation capability. 
     It will be understood that the second embodiment of the invention is capable of performing the same operations as the first, the operating positions being swapped by rotation of the table by 180°, and by using axes A 2  and B similarly to the corresponding axes in the first embodiment. 
     Obviously, the preferred embodiments of the invention as described above are susceptible to modifications and changes, which are evident for the person skilled in the art. For instance, the structure driving the head might have a different design, according to any of the mechanisms known in the art, using one or more motors, and with or without clutch, while one or more of the axes of motion might be transferred to the workpiece-holding device, in a way to provide the same relative movements. The number of spindles on the head might also be different from the preferred embodiment shown and described above: for instance, the feed-out spindles might be two in number rather than one, while the milling spindle might also be duplicated in certain cases. These and other modifications should be regarded as falling within the scope of the invention.