GB1558918A - Apparatus in a multi-spindle automatic lathe for cutting internal and external screwthreads on workpieces - Google Patents

Description

(54) APPARATUS ON A MULTI-SPINDLE AUTOMATIC LATHE FOR CUTTING INTERNAL AND EXTERNAL SCREWTHREADS ON WORKPIECES (71) We, GILDEMEISTER AKTIENGESELLSCHAFT, a body corporate oganised and existing under the laws of the Federal Republic of Germany of Am Hauptbahnhof, 4800 Bielefeld 1, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The invention relates to apparatus on a multi-spindle automatic lathe for cutting internal and external screwthreads on workpieces.

Apparatus have been previously proposed for this purpose having a thread chaser as a cutting tool. In thread chasing, a chaser having a profile in the form of the screwthread to be cut is employed. The chaser does not rotate but is fed radially inwardly and then moved in a pass longitudinally of the workpiece while the workpiece rotates.

After an average ten to twenty passes of the chaser, the screwthread is finished. However, extremely strict limitations are placed on thread chasing on multi-spindle automatic lathes, particularly in the working of long chip materials, such as occur in cold extruded parts, deep drawn workpieces, and the like. In the case of such materials, it is impossible to achieve satisfactory and uninterrupted production even when observing the best possible cutting values and the best posible cutting geometry. In fact, the automatic lathe must be run continuously to remove the chips and splinters. and the chaser is frequently broken. While the production of an external thread is difficult, the production of an internal thread is often not even possible, since the long snarled chips cannot be removed from the tapped hole.

Milling of screwthreads on multi-spindle automatic lathes is however also beset by problems. In short-thread milling a thread milling cutter is used the grooves of which have no pitch and which has a length equal to the length of the screwthread to be cut.

The thread milling cutter is rotated and is fed transversely into the workpiece which, in order to achieve the pitch of the screwthread, executes a screw-like forward feed movement. The screwthread is thus produced in full depth in about 1l/6 to 11/3 revolutions of the workpiece.

Although long-chip materials can be worked in this way, short-thread milling can be carried out on multi-spindle automatic lathes only at considerable and usually uneconomical cost, since the main spindles in such automatic lathes usually all rotate with the same velocity and the rotational velocity required for the machining operations on the workpieces at the other spindle positions is usually much too high for the short-thread milling operation. For the short-thread milling, the relevant workpiece spindle must in practice be driven at creep speed. which results in a long cycle time and consequent high expenditure as regards the machinery.

In the case of screwthread milling in the plunge-cut milling process, a milling cutter the grooves of which do have a pitch is driven throughout the whole screwthread length. radially to the workpiece, to the screwthread depth. In this connection the rotational velocities of the workpiece and tool must be the same. Large milling cutters having as large a number of teeth as possible must be used in order to obtain a good thread profile in the produced workpiece.

However, this results in extremely large cutting velocities at the "active" site, with the result that quite apart from the fact that this kind of screwthread manufacture can only be used for external threads, only non-ferrous metals can in practice successfully be cut by the plunge-cut milling process on multi-spindle automatic lathes since the cutting velocities generated are much too high for steels and for example steel workpieces would in practice cause burning of the tool.

According to the invention there is provided apparatus mounted on a side carriage of a multi-spindle automatic lathe for cutting internal or external screw threads on a workpiece mounted on a rotatable spindle of the lathe, the apparatus comprising a rotatably driven tool having spaced successive cutting edges which are disposed in the manner of a short-thread milling cutter, in circumferentially extending rows, and cam control means driven by the drive of the lathe to effect a cycle of movement of the tool in the manner of thread chasing apparatus and including a plurality of passes of the tool longitudinally of the workpiece, each pass comprising advance movement of the tool towards the workpiece, movement of the tool along the workpiece while effecting a cut and retraction of the tool from the workpiece, the depth of cut made by the tool being controlled by movement of said side carriage of the lathe.

The advance movement along the workpiece and retraction movements are carried out as in thread chasing. In this case also, screwthreads are produced by a rotational movement of the workpiece, but now with a tool which has spaced apart, successive cutting edges around its circumference and which is rotatably driven. Spacing the cutting edges apart results in gaps between the cutting edges, the cutting edges thus successively come out of engagement and accordingly the chips are of only short length even in the case of so called long-chip materials, with the result that the chips can be satisfactorily removed even when cutting internal screwthreads. It is thus possible to produce internal screwthreads economically since the short chips can be removed from the threaded holes in the normal manner, for example by normal flushing out and also by reverse movements of the tool.

Since the individual cutting edges remain in engagement for only a relatively short time, they are always able to cool down, so tllat, compared for example with the speed of rotation of the workpiece for normal thread chasing, higher cutting outputs can be achieved and/or materials which are normally only machinable with difficulty can be more easily machined. The operation can easily be effected by existing multi-spindle automatic lathes without special expenditure or effort, and without additional gearings in the machine tool.

According to a preferred embodiment, a drive shaft to cause the rotational motion of the tool is supported on a saddle of the automatic lathe by way of a housing, whereupon the forces of inertia can be kept very low when setting and lifting the tool.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 is a sectional view of apparatus according to the invention; Figure 2 shows a section taken on line II-II of Figure 1; Figure 3 is a diagrammatic representation of the apparatus within the tool space of a multi-spindle automatic lathe; and Figure 4 shows a tool of the apparatus according to the invention.

Referring to the drawings a housing 1 is mounted on a guide 2 for movement parallel to the axis of rotation of the spindles (Figure 2) on a side-carriage 3 of a multi-spindle automatic lathe. This arrangement enables a tool 4 of the apparatus, when producing internal screwthreads to be withdrawn from the region of the workpieces during indexing movement of a spindle drum 5. To this end, a lever system 6, controlled by a cam track 7 is coupled to an auxiliary drive 12, securely connected to the housing 1, and effects movement of the tool 4 in a direction parallel to the axes of the spindles of the spindle drum 5.

As can be seen from Figure 3, a changegear train 9 which takes the rotational movement of a central shaft 10 of the automatic lathe, converts it, and transmits it via a cardan shaft 11 and the auxiliary drive 12 to a control shaft 13 of the apparatus, is disposed in the tool space of the multispindle automatic lathe on the wall of its stand 8. The conversion ratio between a spindle 14, of the spindle drum 5 of the automatic lathe, which carries the workpiece, and the control shaft 13 must be an integer, in the case of single-start screwthreads, so that the tool 4 always comes into engagement again at the same point of the circumference of the workpiece at each of a plurality of successive passes.

A drum cam 15 and a peripheral cam 16 are disposed on the control shaft 13. The longitudinal movements for the cutting passes and for the return to the starting point of the screwthread are transmitted from the drum cam 15 via a cam follower roller 17 and a roller bolt 18 to a sliding coupler device 19. A tool holder 20 is disposed in the coupler device 19, and is mounted so as to swivel about an axis 21 and is moved by the peripheral cam 16 against springs 22 so that the tool 4, during its return movement, is lifted from the workpiece 23 before again being set against it.

A spindle 24 which mounts the tool 4 is itself mounted in the tool holder 20. The spindle 24 is rotatably driven in such a way that the tool 4 is rotatably driven in a direction contrary to the direction of rotation of the workpiece when producing internal screwthreads, and is rotatably driven in the same direction of rotation as the workpiece when producing external screwthreads.

The rotational movement for this drive is likewise taken from the central shaft 10 of the automatic lathe, and is transmitted to the spindle 24 via a change-gear train 25, a drive shaft 26, a sleeve 27 and a cardan shaft 28. In this connection, the sleeve 27 is mounted in a housing 29, which is movably mounted on a guide 30 on the saddle 31 of the automatic lathe.

In the embodiment described above, the feed of the tool 4 which produces and determines the depth of cut is effected by a continuous feed movement of the sidecarriage 3, on which the apparatus is mounted. Alternatively it is possible to displace the side-carriage 3 in steps radially after each pass to effect the desired increase in depth of cut.

As can be seen from Figure 4, the tool 4 is provided with longitudinally extending grooves to form cutting edges 4a of which there are several rows. with the cutting edges of each row circumferentially spaced apart. The tool is thus similar to a shortthread milling cutter.

WHAT WE CLAIM IS: 1. Apparatus mounted on a side carriage of a multi-spindle automatic lathe for cutting internal or external screw threads on a workpiece mounted on a rotatable spindle of the lathe, the apparatus comprising a rotatably driven tool having spaced successive cutting edges which are disposed in the manner of a short-thread milling cutter, in circumferentially extending rows. and cam control means driven by the drive of the lathe to effect a cycle of movement of the tool in the manner of thread chasing apparatus and including a plurality of passes of the tool longitudinally of the workpiece, movement of the tool along the workpiece while effecting a cut and retraction of the tool from the workpiece, the depth of cut made by the tool being controlled by movement of said side carriage of the lathe.

2. Apparatus according to claim 1. in which said rotatably driven tool is rotated by a shaft movably supported on a saddle of the lathe by way of a housing.

3. Apparatus on a multi-spindle automatic lathe for cutting internal or external screwthreads on workpieces substantially as hereinbefore described and illustrated with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. swivel about an axis 21 and is moved by the peripheral cam 16 against springs 22 so that the tool 4, during its return movement, is lifted from the workpiece 23 before again being set against it. A spindle 24 which mounts the tool 4 is itself mounted in the tool holder 20. The spindle 24 is rotatably driven in such a way that the tool 4 is rotatably driven in a direction contrary to the direction of rotation of the workpiece when producing internal screwthreads, and is rotatably driven in the same direction of rotation as the workpiece when producing external screwthreads. The rotational movement for this drive is likewise taken from the central shaft 10 of the automatic lathe, and is transmitted to the spindle 24 via a change-gear train 25, a drive shaft 26, a sleeve 27 and a cardan shaft 28. In this connection, the sleeve 27 is mounted in a housing 29, which is movably mounted on a guide 30 on the saddle 31 of the automatic lathe. In the embodiment described above, the feed of the tool 4 which produces and determines the depth of cut is effected by a continuous feed movement of the sidecarriage 3, on which the apparatus is mounted. Alternatively it is possible to displace the side-carriage 3 in steps radially after each pass to effect the desired increase in depth of cut. As can be seen from Figure 4, the tool 4 is provided with longitudinally extending grooves to form cutting edges 4a of which there are several rows. with the cutting edges of each row circumferentially spaced apart. The tool is thus similar to a shortthread milling cutter. WHAT WE CLAIM IS:

1. Apparatus mounted on a side carriage of a multi-spindle automatic lathe for cutting internal or external screw threads on a workpiece mounted on a rotatable spindle of the lathe, the apparatus comprising a rotatably driven tool having spaced successive cutting edges which are disposed in the manner of a short-thread milling cutter, in circumferentially extending rows. and cam control means driven by the drive of the lathe to effect a cycle of movement of the tool in the manner of thread chasing apparatus and including a plurality of passes of the tool longitudinally of the workpiece, movement of the tool along the workpiece while effecting a cut and retraction of the tool from the workpiece, the depth of cut made by the tool being controlled by movement of said side carriage of the lathe.

2. Apparatus according to claim 1. in which said rotatably driven tool is rotated by a shaft movably supported on a saddle of the lathe by way of a housing.

3. Apparatus on a multi-spindle automatic lathe for cutting internal or external screwthreads on workpieces substantially as hereinbefore described and illustrated with reference to the accompanying drawings.