This invention is attributed to manufacturing engineering and may be used in the metalworking, furniture, automotive, construction and consumer goods industries for hole forming and tapping in thin metal sheets, hollow pipes of various cross-sections and other thin walled parts.

An economic effect is achieved by forming and tapping holes using the proposed combined tool, because the inter-operational time related to the tool changing and setting new forming regimes, furthermore, after the tapping, the sharp-edged collar, which occurs on the top of the workpiece after the drilling, is compressed, therefore an additional mechanical operation for its removal is avoided.

From US 7552610 B2 a method and a tool are known for hole forming an tapping in a thin walled part using a special tool and device. The device is placed at a predetermined position by a robot, thread portion processing position is formed with a weld overlay by generating an arc by the filler and melting the filler, and then a threaded hole is formed by the special tool. The tool is comprised of a pilot hole forming portion having a tapered shape, the pilot hole forming portion having a first spiral groove, and a thread forming portion having a second spiral groove.

The main disadvantages of the method and the tool: limited usability, the complex and expensive design of the device, separate drives for rotating and transition the tool, a mechanism for feeding the filler as well as a device for arc generation are needed. The proposed tool is not versatile, it is intended to use only with the proposed device, besides it does not compress the sharp-edged collar, therefore an additional machining operation is required to remove the metal excess from the upper surface of the hole.

From US 8827615 B2 a method and a tool is known for forming a nut with a female thread with a sufficient strength in a metallic plate. The design of the device and tool is similar to the device with a combined tool proposed in US 7552610 B2, but differs in that it contains a heating unit which heats a region where a female thread is to be formed in a metallic plate and a cooling unit which cools the machining tool. By providing these heating unit and cooling unit, the machining tool is inserted into a heated machined point, the machined point is abruptly cooled to be hardened in the metallographic structure, thereby forming a female thread with a high strength.

The main disadvantages of the method and the tool: limited usability, the complex and expensive design of the device, devices for heating the workpiece and cooling the tool are needed. The proposed tool is not versatile, it is intended to use only with the proposed device, besides it does not compress the sharp-edged collar, therefore an additional machining operation is required to remove the metal excess from the upper surface of the hole.

From DE 19653394 Al a tool for chipless forming a hole with an internal thread in sheets, hollow profiles in one operation is known. The tool comprises of three phases. The first phase comprises of a conical shaping tip, with a polygonal shaped cross- section. The second phase comprises of a following cylindrical transition piece with a polygonal shaped cross-section and a groove at the rise of the thread being cut. The third phase comprises of a thread a non-cylindrical polygonal shaped cross- section.

The main disadvantages of the tool is that it does not contain a part for hole calibration which is required to form a neck for threading completely at the bottom surface of the hole, besides, a sharp-edged collar is formed after the operation of hole forming and tapping, therefore an additional machining operation is required to remove the sharp-edged collar.

The aim of the invention is to form a hole with a neck, calibrate and the hole and neck, tap a thread and achieve an economic effect due to an increase in the efficiency of manufacturing, as an additional machining operation is not required to remove the metal excess from the upper surface of the hole.

The aim of the invention is achieved by using the proposed combined tool comprising of 7 parts, which gradually transit from one to another. The tool forms and calibrates a hole with a neck, taps and calibrates a thread, furthermore, at the end of the operation, compresses the sharp-edged collar, which occurs on the top of the hole.

The essence of the invention is shown in the figures.

Fig. 1 shows the design of the combined drilling-taping tool comprising of seven parts.

Fig. 2 shows the cross-section shapes of the first, the second and the third part of the tool.

Fig. 3 shows the cross-section shapes of the fourth and the fifth part of the tool.

The essence of the invention consists of the created combined drilling-taping tool for chipless thermoplastic forming, calibration and tapping of a hole with a neck in thin metal sheets, hollow pipes of various cross-sections and other thin walled parts and compression of the sharp-edged collar, which forms on the top of the workpiece after the drilling due to the excess of the metal.

The tool (Fig. 1) comprises of 7 parts, which gradually transit from one to another: the first part is a cone 1 of a rounded polygonal cross-section for forming a centring hole in the workpiece; the second part is a conical frustum 2 of a rounded polygonal cross-section for hole forming by gradually penetrating the metal and pushing the excess of the metal downwards and, in this manner, forming an additional molten flange (a neck) on the underneath side of the workpiece; the third part is a cylinder 3 of a rounded polygonal cross-section for hole and neck calibration until the required diameter for tapping is achieved; the fourth part is a conical tap 4 of a rounded polygonal cross-section and having not less than 2-3 turns for gradual pilot tapping until the nominal thread diameter is achieved; the fifth part is a cylindrical thread 5 of a polygonal cross-section for finishing the thread; the sixth part is a cylindrical shoulder 6 of a circular cross-section with a diameter not less than the compressed sharp-edged collar for compressing the sharp-edged collar; the seventh part is a shank 7 for mounting the tool in a collet (not shown in the figures). When the tool is plunging downwards, the rounded polygonal cross-sections of the tool (Fig 2 and 3) are needed because the heated metal not only would be extruded downwards and to the sides, but countercurrent as well, in this manner forming a hole of the required diameter and threadform.

The combined drilling-taping tool operates as follows: due to the friction between the tool and the workpiece, the temperature in the contact zone rises over 600 °C, the first part of the tool 1 forms a centring hole in the workpiece, the second part 2 penetrates the metal and pushes the metal excess downwards and, in this manner, a neck is formed on the underneath side of the workpiece. The third part forms and calibrates the hole with the neck until the required diameter for tapping is achieved. After the forming, the thickness of the workpiece at the hole zone is increased about 3-4 times compared to the initial thickness, however, during the tool plunging into the workpiece, some portion of the metal is pushed upwards, thus on the top of the workpiece a sharp- edged collar is formed. After reducing the spindle speed and feed rate to the values required for tapping, the fourth part 4 gradually performs pilot tapping until the nominal thread diameter is achieved and, after that, the fifth part 5 completely forms the thread of the required shape and dimensions. At the end of the tapping, the shoulder 6 compresses the sharp-edged collar and the tapping feed is turned off. After that, the spindle speed is reversed and the tool is withdrawn from the hole.

Compared to the prototype, the third part of the tool enables to form the size and shape of the neck as well as the hole dimension more precisely for the tapping operation and, at the end of the tapping, the shoulder compresses the sharp-edged collar formed around the hole on the top of the workpiece, therefore, an additional mechanical operation for its removal is not required.