WO2004020132A1

WO2004020132A1 - Process for the roughing of moulds, tools to achieve such process and moulds obtained with such process and such means

Info

Publication number: WO2004020132A1
Application number: PCT/EP2003/009182
Authority: WO
Inventors: Donatella Assali
Original assignee: Ctm Di Assali Donatella
Priority date: 2002-08-27
Filing date: 2003-08-19
Publication date: 2004-03-11
Also published as: ITVA20020044A1; AU2003255462A1

Abstract

The mould (1) is fixed on the table of the machine tool moving forwards in the direction of the arrow against a cutter (6) that is turning quickly. The teeth (8) of the cutter are sharp at a 10° leading angle (7).

Description

PROCESS AND TOOLS FOR THE ROUGHING OF MOULDS

The subject of the present invention is a process for carrying out the roughing of moulds, the tools able to carry out this process and the obtained moulds following this process or by employing such means. The present invention relates to the construction of injection moulds for plastics for the manufacturing of accessories for the transportation industry; injection moulds for plastics for the manufacturing of electric and electronic goods; injection moulds for plastics for the manufacturing of various products, packaging and alike; extrusion moulds of every type of material suitable to be extruded for the manufacturing of profiles of any type and any section; blowing moulds; vacuum moulds; compression mould; moulds for the manufacturing of rubber objects for the footwear industry; moulds for the manufacturing of tyres; moulds for the industrial manufacturing of rubber objects of every type and for any use; moulds for the manufacturing of glass objects by means of pressure; moulds for the manufacturing of glass objects by means of glass- blowing; moulds for the manufacturing of object pieces by means of melting; moulds for the manufacturing of object pieces by means of shell melting; moulds for the production of pieces or objects, in which the molten materials fall inside them due to gravity; melting moulds without heating pre-chamber; melting moulds with heating pre-chamber; moulds for hot forging; moulds for cold forging; transfer shearing moulds for the manufacturing of pieces or objects for the transportation industry; transfer shearing moulds for the manufacturing of electric and electronic goods; transfer shearing moulds for the manufacturing of goods not included in the preceding types; graduated or step shearing moulds for the manufacturing of accessories for the transportation industry; graduated or step shearing moulds for the production of electric and electronic goods; graduated or step shearing moulds for the production of goods not included in the preceding types; shearing moulds for multi-moulding; shearing moulds for sintering; moulds for injection or for deformation not included in the preceding list. It is known that in the past the moulds were obtained from steel that had been exposed beforehand to annealing and soaking treatments. This was done in order to make it as least hard as possible, in order to make its chip removal working easier. The hardening of the mould used to be carried out once the workings with the tools had completed. This process created heat distortion problems in the metal of the mould and it was then necessary to expose the mould itself to a further manufacturing process. In order to avoid this draw-back, for some time, pre- hardened steel is employed for the manufacturing of the moulds. That is to say, steel is used that has previously been subjected to hardening treatment, so as to obtain the desired hardness, and once the steel has such hardness, the steel pieces are worked by chip removal tools until the same pieces have the shape of the desired mould. Accordingly, machine tools and tools suitable for working steel, having a superior hardness at 60 HRC (Rockwell hardness) , were manufactured. Generally the proto-mould steel pieces, before being transformed in the final mould, undergo three successive processes, one after another: I Roughing; II Semi-finishing; III Finishing. The present invention relates only to the first and second steps: that of the roughing and that of the semi-finishing. Despite the noteworthy technical progress contributed from the above said machine tool and from the processes, they, especially the tools and the processes, still present draw-backs. In particular such draw-backs are to be found in the manufacturing processes and the cutters. There are two types of these, as far as the frontal leading angle is concerned. There are cutters with leading angles of 90°, and there are the so called "toric" cutters with interlinked leading edge, precisely forming a "torus", a "toroidal circle", which work at 40° frontal leading angle. In fact with the above said known cutters, for carrying out the so called "terrace-like" roughing of the mould it is necessary to maintain low the feed speed of the machine tool table that carries the mould. This is implies a long working time and therefore high manufacturing costs of the mould.

The inventor, with ingenious intuition, has understood that the origin of the draw-backs resides in the fact that, with the processes known to date, the cutters, for detaching the chip, cut the metal of the mould only with their vertical cutting edges, i.e. only with the cutting edge drawn into the cylindrical surface of the cutter bars. From here the strong radial stresses manifest themselves in vibrations and strong flexo-torsion stresses and then in the failure of the cutter. Still maintaining small the feeding of the machine tool table, on which the piece to be transform in the mould is fixed, the cutter has always free ends which bears radial loads which are at the thresholds of its strength. By consequence the cutter failures are frequent. Therefore the fabrication of the moulds according to the processes known to date and by employing the cutters known to date, requires an operator to always attend the machine, ready to stop the machine tool immediately when a cutter breaks. It deals with very complicated, very delicate and very expensive machines and, if are not stopped immediately when the smallest imperfection happens, very extensive damages occur. Furthermore, the continuous presence of the operator also carries high costs. Besides this, with the processes known to date, the contact times between the cutter and the metal of the mould are short because, with this mode of removal the chip in no time the sharpening deteriorates, the machine tools need to be stopped frequently and the cutter needs to be replaced. If this is not done straightaway, the cutter, having lost even if only partially the edge, is found to be exposed to a continuously enlarging radial loading, so much as to bring it quickly to failure; with the above described consequences.

The objective of the present invention is to eliminate all the draw-backs related to the known processes and applied and deriving from the employment of the cutter known to date and used for the manufacturing of the moulds. The inventor, as a result of her ingenious intuition, has thought-up a new process and a new cutter able to carry out the same process, so that the said cutter is exposed to a loading for the most part coaxial to the axis of the bar, i.e. in the direction of its maximum stress resistance. That is the resistance to the compression.

Such process and cutter also allow the radial loading on the cutter to be very small, negligible, i.e. in the way of its minimum stress resistance that is to the flexo-torsion. In this way, in respect to the processes known to date and in respect to the cutters known to date for the roughing of the moulds, the diameter of the cutters employed being the same, they can double both the number of turns of the new cutter, and the feed speed of the table, of the machine tool, which carries the mould afoot. Furthermore it is possible to increase both the pressure of the mould against the cutting edge of the cutter, and the cutting pitch.

Then, with the process and the cutter thought-up by the inventor, in respect to the processes and the cutters known to date, the diameter of the cutters being the same, doubles the weight of the produced chip, doubles the production, and furthermore the cutting machine can take place without the continuous presence of the operator. The cutting edges of the new cutter are in sintered tungsten carbide and are head sharpened, from the axis until the circumference of the bar, in order to also have a lower rake. The more acute the frontal leading angle of the cutting edge of the cutter, the greater the number of turns of the cutter itself, and the feed speed of the table of the machine tool, which carries the mould under construction. Experiments carried out by the inventor have shown that the optimum is achieved if the frontal leading angle is of 10°.

Another essential characteristic, both of the process according to the present invention and of the cutter according to the present invention that serves to achieve said new process, consists in that the teeth of the cutter are sharp and cutting along the whole of their length, i.e. from the axis of the bar until the circumference of the same bar. The cutter, according to the present invention, can be monolithic, or assembled with an insert in the shape of a spear, almost flattened, i.e. with two joined and sharp sides along the whole of their length, i.e. from the axis of the corner until the outer end at an acute leading angle. The process that forms object of the present invention can be carried out with the already known machine tools and equipments, mounting the cutter on the mandrel which also forms the object of the invention. Being the same diameter of the cutter it is possible to make the mandrel turn at a speed that is twice and it is possible to make the table carrying the mould to be machined to move at a feed rate which is double that is used up to now. Furthermore, the cutter that forms the object of the present invention can be used with an engagement along a 220° arch rather than along a 190° arch as is possible, as a maximum, with the known to date processes and cutters. Besides this, it is necessary to program the size of the pass so that it is the same or slightly smaller to the existing difference of level between the central bit of the cutting edge, i.e. its cutting edge bit coinciding with the axis of the bar of the cutter, of the tooth of the cutter and the cutting edges' circumferential rim of the cutting edge of the tooth itself, i.e. its cutting edge coinciding with the circumference of the bar of the cutter. That is to say, the size of the pass must be equal or lower to the existing difference of level between the lower internal end of the cutting rim of the cutter' s tooth and the higher outer end of the cutting edge of the cutter itself.

With the process and the cutters according to the present invention, not only are the draw-backs deriving from the processes already known and from the employment of the already known cutter, but, besides the advantages already described above, the great advantage of the possibility is achieved of making the machine tool carry automatically the roughing of the mould, also as heavy, i.e. without the assistance of the operator. In fact, by virtue of the present invention, the machine tools can be programmed for the roughing of the steel pieces for the night shift not attended working, with a noteworthy reduction of costs. With reference to the attached drawing, two of the possible forms of practical embodiment will be able to be described more minutely of the present finding, provided as a simple example only.

Figure 1 illustrates a schematic assembly of the already known roughing process of the so called 90° frontal leading angle type by means of so called "candle" cutter.

Figure 2 illustrates a schematic assembly of the already known roughing process of the so called 40° frontal leading angle by means of the so called "toric" cutter.

Figure 3 illustrates a schematic assembly of the roughing process according to present invention and of the cylindrical monolithic cutter, according to the present invention too, able to achieve the same process, i.e. at acute leading angle.

Figure 4 illustrates in greater scale and in greater detail the same assembly as illustrated in figure 3 for the roughing by means of acute leading angle. Figure 5 illustrates a plan taken from below the cylindrical monolithic cutter of figure 4, looking upwards .

Figure 6 illustrates again what has been illustrated in figure 4, however in a more schematic way, as to indicate the diagram of the forces operating on the toothed free end of the cylindrical monolithic cutter with acute leading angle according to the present invention.

Figure 7 illustrates in perspective the toothed end of the cylindrical monolithic cutter with teeth at acute leading angle.

Figure 8 illustrates, with a frontal view, an assembly of a cutter 17, also to carry out the process according to the present invention, however, unlike that of monolithic ones illustrated in the previous figures, it is of the so called "assembled" type, i.e. composed of one shank with a bracket shaped lower end in which, by means of a screw 18, an insert 19 is fixed. The insert 19 is composed of a slab of tungsten carbide with coverings that are suitable for the tools and having the corner in the shape of a spear with two sharp teeth in the same direction at an acute leading angle 20. The cutter 17 is unlike the monolithic cutter illustrated above mainly for its replaceability of the teeth-tools 19 in the form of a slab. Also the leading angle 20 is of 10°.

In figure 1 the mould 1 can be seen, fixed on the machine tool table, moving together with it in the direction of the arrow, whilst a candle cutter 2 turns and cuts off the chip at a 90° leading angle 3. In figure 2 the mould 1 can be seen again, fixed on the machine tool table, moving with it in the direction of the arrow, whilst a toric cutter 4 turns and cuts off the chip at a 40° leading angle 5. In figure 3 the mould 1 can again be seen, fixed on the machine tool table, moving with it in the direction of the arrow, whilst a cylindrical monolithic cutter 6, of the type that forms the objective of the present invention, is carrying out the process that also forms the objective of the present invention. The said cylindrical monolithic cutter 6 turns and cuts off the chip at a 10° leading angle 7. In the illustrated example the cylindrical monolithic cutter 6 has two teeth 8 and 9, however the number of the teeth could also be different and still remain within the scope of the present invention. The tooth 8 has the cutting edge 10 and the tooth 9 has the cutting edge 11. In figure 6 the force 12 can be seen that applies on the tooth of the cutter 6 whilst cutting off the chip at a 10° leading angle has as a resultant the force 13, applying on it a 10° inclined plane. The said resultant force 13 can be considered as decomposed in two orthogonal forces between them: the greater force 14 operating in a coaxial direction to the axis of the cutter 6 and the lesser force 15 operating in a radial direction to the cylindrical monolithic cutter 6 itself. Therefore it is demonstrated that the inventor has succeeded in achieving that which she ingeniously intuited: i.e. a process that makes the maximum load as a compression force in the axial direction of the cylindrical monolithic cutter 6 that is able of carry it out with absolute safety, whilst on the other side, as far as the flexo-torsion is concerned, on the cylindrical monolithic cutter 6 a very small force 15 is applied. Since the finding has been described and depicted with an indicative and not limiting purpose, it is quite clear that it will be possible to bear numerous modifications to its assembly and to its details, without however moving away from the basic principles on which the present invention is based.

Claims

1. Roughing process of moulds by means of terracelike chip removal, pass after pass, characterised in that while removing the chip the tool is moved along at an advancing arched inclined plane.

2. Roughing process of moulds by means of terracelike chip removal, pass after pass, as in claim 1, characterised in that while removing the chip the tool is moved along at an acute leading angle.

3. Roughing process of moulds by means of terracelike chip removal, pass after pass, as one or both the previous claims, characterised in that it is carried out by means of a cylindrical cutter whose sharp teeth remove the chip from the axis of the cutter itself until its circumference at an acute leading angle.

4. Roughing process of moulds by means of terracelike chip removal, pass after pass, as one or more of the preceding claims, characterised in that while removing the chip the tool is moved along at a 10° advancing arched inclined plane.

5. Roughing process of moulds by means of terracelike chip removal, pass after pass, as one or more of the preceding claims, characterised in that while removing the chip the tool is moved along at a 220° advancing arched inclined plane .

6. Cylindrical monolithic cutter for carrying out the process according to claims from 1 to 5, characterised in that it is cylindrical and monolithic, that its sharp teeth protrude from the circular frontal face, from the axis of the cutter itself to the circumference of the cutter itself and are able to remove the chip at an acute leading angle.

7. Cylindrical monolithic cutter for carrying out the process according to claims from 1 to 5 and as in claim 6 characterised by sharp teeth protruding on the frontal circular face with an inclination, from the axis to the circumference, of 80° in respect to the axis of the shank of the cutter itself.

8. Cylindrical monolithic cutter for carrying out the process according to claims from 1 to 5 and as in claims 6 and 7 characterised by at least one end having the shape of a conic point with sharp teeth from the axis to the circumference with an angular amplitude of 160° so to cut the moulds at an acute leading angle.

9. Cylindrical monolithic cutter for carrying out the process according to claims from 1 to 5 and as in one or more of claims 6 to 8 characterised in that it is sharpened to work on a 10° leading angle.

10. Assembled cutter for carrying out the process of claims from 1 to 5 characterised by an insert formed by a flat tool having the corner in the shape of a spear with two sharp teeth in the same direction at an acute leading angle.

11. Roughened mould according to the processes of claims from 1 to 5 and/or by employing cutters according to one or more of the claims from 6 to 10.

12. Roughing process of moulds, according to one or more of the claims from 1 to 5, cutters according to one or more of the claims from 6 to 10 and roughened machined mould as in claim 11, substantially conform to what is here described and depicted and for the specified purposes.