GB2043511A

GB2043511A - Drawing dies

Info

Publication number: GB2043511A
Application number: GB7944199A
Authority: GB
Original assignee: EDELSTAHLWERKE 8 MAI 1945 FREI
Current assignee: EDELSTAHLWERKE 8 MAI 1945 FREI
Priority date: 1978-12-27
Filing date: 1979-12-21
Publication date: 1980-10-08
Also published as: BE880806A; DD143872A1; FR2445188A1; JPS55125926A; SE7910655L; YU302679A; GB2043511B; DE2951056A1

Abstract

An interchangeable die for drawing and drawing-and-shaving comprises a body member 1 which has a frusto-conical bore 1' which receives a frusto-conical clamping sleeve 3. The sleeve 3 has a cylindrical bore in which an annular shoulder 3' is provided for locating a cylindrical cemented carbide die member 4 in the clamping sleeve 3. The clamping sleeve has a plurality of axially extending slots 5. The sleeve 3, and with it the die member 4, is clamped in position by means of a cylindrical externally screwthreaded thrust ring 2 which is screwed into a cylindrical bore portion of the body member 1. <IMAGE>

Description

SPECIFICATION An interchangeable socket for drawing and drawing-and-shaving tools This invention relates to the second processing stage in metallurgy. Articles to which it can conveniently be applied are drawing and drawing-and-shaving dies in which a known cemented carbide slug is received in a multiply re-usable socket.

The known process of drawing predominates in the cold processing of wires, rods, tubes or the like. The material to be deformed is drawn through a die aperture, the material being deformed mainly by the radial forces produced in dependence on the geometry of the die. It is also found to be advantageous to remove contaminations and surface faults by chip-removing machining before cold working.

In addition to the known process of turning, the less well-known drawing-and-shaving process can be used. In this process, the material is drawn through a shaving nozzle, the dimensions of the material to be machined being larger than those of the shaving aperture. As it is being drawn through the nozzle, the material is given the shape of the shaving aperture and the surface of the material is subjected to chip removal.

For drawing and drawing-and-shaving mainly dies are used which consist of a cemented carbide slug and a tempered steel socket. The cemented carbide slug and the steel socket are intimately connected to one another by heat shrinkage. During heat shrinkage the cemented carbide slug is inserted into the heated and therefore expanded socket. When the socket cools it contracts and therefore stresses the cemented carbide slug radially. The durability of the drawing and drawing-and-shaping die depends substantially on the value of the radial stressing, since the forces produced during deformation or chip removal must be compensated by the stressing. With inadequate stressing the radial deformation or chip-removing forces may subject the cemented carbide slugs to heavy alternating stressing or burst them.Due to the relatively slight machining tolerances, with heat shrinkage it is difficult to apply welldefined stressings. As a result durability varies greatly, or rejects occur even during heat shrinkage. The technology of heat shrinkage is expensive, since the cemented carbide slug must be adapted to the material of the socket or vice versa.

In drawing and drawing-and-shaving the durability of the die is influenced by the cooling conditions. The maximum processing temperatures occurring must be kept as low as possible, to limit to a minimum the alternate thermal stressing of the cemented carbide. At present drawing dies are mainly used without and drawing-and-shaving dies with cooling. Certain hints in the literature indicate that research is going on concerning the use of water-cooled drawing dies. A substantial proportion of the heat evolved in the cemented carbide slug during drawing and shaving must be dissipated via the material of the socket, so that a relatively high temperature level is set up in such material and in the cemented carbide slug. The lower the temperature level can be kept adjacent the cemented carbide slug, the better the dissipation of the heat.

To avoid the afore-described disadvantages of heat shrinkage and rationalise the expensive technology of manufacture, tests have already been carried out to discover some other way of retaining the cemented carbide slug. Drawing dies are known whose axissymmetrical slug has a smaller diameter at its ends than in the centre and is stressed by a two-part socket. This drawing die has the disadvantage that the cemented carbide slug takes the form of a double frustum the manufacture of which uses more material and is more complicated than the conventional cylindrical cemented carbide slugs. A further disadvantage of this construction is that due to the axial forces, during drawing one frusto-conical part of the cemented carbide slug is drawn into the conical socket and the other part out of the conical socket.As a result the radial stressing is so changed that stressing is relieved in the zones of maximum deformation, whereas further stressing occurs in those zones where no deforming forces are produced. These relationships represent an inconvenient distribution of force. The disadvantage of the additional radial stressing in dependence on the drawing forces also occurs in another design of drawing dies. The face that such a proportion is not insufficient is shown by the following example: about 2000 kp of drawing force is required to draw a wire 8 mm in diameter. With a conical angle of about 10 this drawing force produces a radial force component of about 10,000 kp.

These 10,000 kp are superimposed on the elastic stressing. The static stressing of drawing dies is about 30 kp/mm2 in the case of heat-shrunk dies. With a cemented carbide slug generated surface of 1 ,000 mm2, therefore, 30,000 kp are required. As a result the processing pressure can influence the radial stressing by about one third.

It is also known for the material of the socket to be formed with slots adjacent the generated surface of the cemented carbide slug for the purpose of more intensive cooling. The slots have only a small contact surface with the cemented carbide slug, so that nevertheless a large proportion of the heat must be removed via the material of the socket. A disadvantage is that socket materials of poor thermal conductivity are used. Since the drawing die proposed is made up of two parts, the manufacture of the socket from material having good thermal conductivity raises economic problems. The existing cooling slots are disposed in the peripheral direction of the cemented carbide slug, so that elastic deformation is prevented and the coolant passage is too small.

There are other forms of slot which exclusively increase elastic deformability. They are disposed radially and cannot be used as a coolant passage.

It is an object of the invention to provide for practical use a reliable, uncomplicated method of producing drawing and drawing-and-shaving dies of improved storability and to reduce the high costs of material and manufacture.

Another object of the invention is to avoid the expensive technology of the heat shrinkage of cemented carbide slugs into the socket, by substituting mechanical stressing for the radial stressing of the cemented carbide slug hitherto produced by the thermal properties of the material of the socket. The dies must be exchangeable in a very simple manner and the multiple re-use of the constructional parts of the socket must be ensured. Moreover, an exchangeable socket for drawing and drawing-and-shaving dies is to be provided whose static stressing can be produced in an always well-defined manner and whose size is not influenced by the processing forces. The cooling of the die is to be improved.

Accordingly, the present invention consists in an interchangeable socket for drawing and drawing-and-shaving tools having a cylindrical cemented carbide slug, comprising a body member having a frusto-conical bore, the imaginary apex of which points opposite to the direction of processing of the material to be drawn, frusto-conical, multiply-slotted or multiple-part clamping sleeve received in the frusto-conical bore of said body member and radially enclosing the cylindrical cemented carbide slug by its inner surfaces, said sleeve being clamped in position by a cylindrical screwthreaded thrust ring the screwthread of which engages in the body member. The geometrical ratios of the pitch of the thrust ring and the inclination of the frusto-conical clamping sleeve enable the cemented carbide slug to be stressed in an always well-defined manner.To meet the practical requirements for drawing and drawing-and-shaving tools in a range of dimensions from 1.5 to 14.0 mm.

in diameter, the pitch of the screwthread of the ring is preferably 1.5 mm. and the inclination of the frusto-conical clamping sleeve 1:5.

The purpose of the axially disposed slots in the clamping sleeve is to increase elastic deformability while at the same time possibly acting as a coolant passage. Preferably, to improve the heat transfer from the cemented carbide slug via the clamping sleeve to the coolant, the clamping sleeve is made of a material of good thermal conductivity, for example brass.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example embodiments thereof, and in which: Figure 1 is an axial section through an exchangeable drawing die socket according to the invention, Figure 2 is an axial section through an exchangeable shaving die socket according to the invention, Figure 3 is an elevation of the frusto-conical, axially slotted clamping sleeve acting as a coolant passage, and Figure 4 is an end view of Fig. 3.

A cylindrical cemented carbide slug 4 is received in a frusto-conical clamping sleeve 3 which has, adjacent the major diameter, a shoulder 3' which locates the slug 4 in the processing direction. The periphery of the clamping sleeve 3 is formed in the axial direction with continuous slots 5 which are constructed to increase the deformability of the clamping sleeve 3 while at the same time acting as a coolant passage means. The clamping sleeve 3 is made of a material of good thermal conductivity, for example brass, and is received in a body member 1 having a frusto-conical bore 1'. The frusto-conical bore 1' in the body member 1 and the associated frust-conical clamping sleeve 3 are so disposed that the imaginary apex of the cone points against the direction of processing of the material to be drawn.The frusto-conical clamping sleeve 3 is pressed into the frustoconical bore 1' in the body member 1 by means of a screwthreaded thrust ring 2, as a result the cemented carbide slug 4 is radially stressed with the clamping sleeve 3 and the body member 1. The thrust ring 2 has a cylindrical screwthreaded outer periphery and is formed with axial bores or a polygonal section for receiving a tightening lever. The tightening torque M of the thrust ring 2 required to produce a necessary radial stressing depends on the pitch P of the thrust ring 2, the angle of inclination a of the frustoconical clamping sleeve 3, and the peripheral surface area A of the cemented carbide slug 4.

These stand in the following mathematical relationship to one another: P A N = tan a Perf 10m77 where: M is tightening torque (kpcm) P is pitch of the thrust ring (mm) A is peripheral surface of the cemented carbide slug (mm2) a is angle of inclination (degrees) Perf is necessary radial stressing (kp/mm2) 17 is mechanical efficiency (-) Test showed for drawing dies produced by heat shrinkage a radial stressing of 30 to 40 kp/mm2, a value for drawing-and-shaving tools being 20 to 25 kp/mm2. As a result it is possible to calculate the tightening torque required to produce the same radial stressing as with heat shrinkage. The predetermined tightening torque can be applied by a known torque wrench.The mechanical efficiency with the stated transmission ratios of the pitch of the screwthreading and the inclination of the frusto-conical clamping sleeve 3 is assumed to be about a1 = 0.5. The advantages of the interchangeable socket according to the invention in comparison with the comparable prior art drawing dies consist more particularly in the possibility of producing a constantly welldefined radial stressing of the cemented carbide slug which is not influenced by the processing forces. As a result it becomes possible to produce optimum stressings in accordance with the processing conditions, for example, application for high-quality steels or non-ferrous metals. The possibility of mechanical stressing permits the use of titanium carbide coated cemented carbide metals.

The shape of the slots in the clamping sleeve not only increases the deformability of the clamping sleeve but can also be used as a coolant passage permitting a high rate of flow.

The interchangeable socket of the invention substantially reduces the labour required for the manufacture of drawing and drawing-andshaving dies and their storage. The multiple re-usability of the interchangeable socket produces an appreciable saving of socket material.

The shaving die socket illustrated in Fig. 2 is constructed in similar manner to the drawing die socket of Fig. 1.

Claims

1. An interchangeable socket for drawing and drawing-and-shaving tools having a cylindrical cemented carbide slug, comprising a body member having a frusto-conical bore, the imaginary apex of which points opposite to the direction of processing of the material to be drawn, a frusto-conical, multiply-slotted or multiple-part clamping sleeve received in the frusto-conical bore of said body member and radially enclosing the cylindrical cemented carbide slug by its inner surfaces, said sleeve being clamped in position by a cylindrical, screwthreaded thrust ring the screwthread of which engages in the body member.

2. An interchangeable socket according to claim 1, wherein the clamping sleeve is formed with axial slots which increase the deformability of the clamping sleeve and at the same time act as a coolant passage.

3. An interchangeable socket according to claim 1 or 2, wherein unlike the body member and thrust ring, the clamping sleeve is made from a material of good thermal conductivity, for example brass.

4. An interchangeable socket according to any of claims 1 to 3, wherein the geometrical ratios of the pitch of the thrust ring and the inclination of the conical clamping sleeve correspond to a predetermined radial stressing between the body member, clamping sleeve and the cemented carbide slug, in dependence on the tightening torque of the thrust ring and the peripheral surface area of the cemented carbide slug.

5. An interchangeable socket according to claims 1 to 4, wherein the pitch of the screwthread of the thrust ring is preferably 1.5 mm and the inclination of the frustoconical clamping sleeve has a ratio of 1:5.

6. An interchangeable socket for drawing and drawing-and-shaving tools, substantially as herein described with reference to and as shown in the accompanying drawings.