The present invention relates to a toolhead for multi-axis machine tools.
A toolhead embodied according to the invention is able to perform drilling, countersinking or other machining operations automatically and to extremely close tolerances, given an approximate knowledge of the surface being machined. In particular, the toolhead disclosed will countersink to a controlled depth on surfaces lying at any height relative to the feed direction of the tool.
The invention can be associated to advantage with numerically controlled multi-axis machine tools as used especially in the aircraft-building industry for drilling and countersinking holes in the outer panels of wing structures and fuselage sections, destined to accommodate rivets. In practice, the heads of the inserted rivets must remain perfectly flush with the outer skin of the aircraft in order to ensure they will not generate turbulence, which would occasion a marked increase in aerodynamic resistance. The present invention finds application nonetheless, and to similar advantage, in other sectors of industry such as that of motor vehicle manufacturing.
The prior art embraces devices able to control drilling or countersinking depth, as disclosed in patent IT 1220732, for instance, which are set up by performing a mechanical adjustment before each machining job, also devices by which machining depth can be monitored continuously and controlled entirely in automatic mode, as disclosed by way of example in application BO2003A 000043 for Italian patent, both of the references mentioned being filed in the name of the present applicant.
Disadvantageously, devices of the prior art type noted above are integrated into the tool-holder mounted to the spindle of a toolhead.
In the case of patent IT 1220732, more exactly, the device in question comprises a tool-holder with a shank that can be attached to the spindle of a machine tool, also a stop cage mechanism associated with the tool-holder by way of a pair of bearings and presenting a pair of cylinders with piston rods that project from both ends. Each rod is connected at one end to a collar, through which the tool is insertable when penetrating the work, and at the opposite end to a mounting plate. The collar is translatable relative to the tool-holder, in a direction parallel to the tool axis. The mounting plate associated with the ends of the rods remote from the tool carries respective micrometer screws that can be locked fast in a selected position by means of stops. Two microswitches are fixed to the toolhead, near the spindle, their axes coinciding with those of the two micrometer screws. The two microswitches are also wired to suitable devices piloting the tool feed movement of the spindle. To control the depth of the countersink, the position of the screws is adjusted in such a way that the distance between the tip of the screw and the corresponding microswitch is equal to the distance between the face of the collar and the tool, plus the countersink depth. During operation, the spindle of the machine continues to advance until the screws engage and trip the microswitches. At this point, the devices piloting the movement of the spindle will cause the tool to retract.
The applicant finds that prior art devices as outlined above are improvable in a number of ways.
More particularly, in the case of fully automatic multi-axis machines with numerical control, the integration of a drilling depth control device into a tool-holder will dictate the use, conventionally, of a number of single tool-holders corresponding to the number of operations carried out on the piece, given that after each operation the tool-holder is released from the spindle, by appropriate means, and replaced with a tool-holder carrying the tool for the next operation. A machine therefore has to be equipped with a plurality of tool-holders, each incorporating the depth-control device, which in comparison to standard tool-holders are much more expensive, and much heavier.
Moreover, given that the sensor serving to detect the displacement of the stop cage device in prior art embodiments is installed on the toolhead, near to the spindle, the setting of the sensor needs to be checked after every tool change, and this has the effect of slowing down operations even if the check is run automatically.
Also, the bearings coupling the stop cage to the tool-holder operate in a dust-laden environment and must therefore be shielded; consequently, spindle speeds must not exceed 16000 rev/min or thereabouts otherwise these components could overheat.
Given the situation outlined, the main object of the present invention is to provide a toolhead for a multi-axis machine tool substantially capable of overcoming the above noted drawbacks.
In particular, the object of the invention is to set forth a toolhead for multi-axis machine tools such as will perform depth-controlled machining operations on surfaces located at whatever height relative to the feed direction of the tool.
It is also an object of the invention to provide a toolhead for multi-axis machine tools that will allow such depth-controlled machining operations to be performed using standard tool-holders.
A further object of the invention is to provide a toolhead on which tool changes can be effected automatically, swiftly and reliably.