Patent Description:
More particularly, this invention relates to a method for manufacturing an ingot mold and a welding machine for an ingot mold.

In the iron and steel industry, it is known, e.g. from <CIT>, to make ingot molds out of copper by rolling a copper panel in such a way as to create a cylindrical cavity and a subsequent welding between two opposite flaps of the panel placed in close proximity to each other, so as to fully close the only longitudinal fissure remaining from the rolling process.

Said process of welding the two flaps is carried out by means of the known fusion welding of the two flaps, after having carefully heated the entire piece of copper.

Disadvantageously, this known welding process involves numerous issues. First of all, it is necessary to heat the entire copper piece, which requires high energy consumption and heating times; moreover, the aforementioned welding, performed manually, is highly dependent on the skills of the specific operator carrying out the welding, thus generating inhomogeneity both inside the single ingot mold and between ingot molds. Furthermore, precisely because of the way it is made, said weld often has internal defects which over time may lead to the failure of the welded region.

Furthermore, the welding carried out with the known art does not always succeed in satisfying the tolerance requirements required for the production of high-quality ingot molds.

The object of this invention is to eliminate the aforesaid drawbacks of the methods of the prior art for manufacturing ingot molds of copper. In particular, one object of this invention is to provide a method for manufacturing an ingot mold that is capable of reducing the time required to manufacture ingot molds and requires fewer resources.

According to the invention, these objects are achieved by a method for manufacturing an ingot mold and an ingot welding machine according to the attached independent claims.

The features and advantages of the method for manufacturing an ingot mold and a welding machine for ingot molds will be evident from the description below, given by way of non-limiting example, according to the attached figures, in which:.

According to the attached figures, a welding machine <NUM> for an ingot mold <NUM> for manufacturing an ingot mold <NUM> according to the method for manufacturing an ingot mold which will be described hereinafter has been indicated in its entirety with the reference number <NUM>.

The method for manufacturing an ingot mold <NUM> for casting comprises the steps of:.

Preferably, before step c), the method comprises the step of positioning a support structure <NUM> inside the inner cavity I. Said support structure <NUM> comprises a backing surface <NUM> which counteracts the mechanical pressing force exerted by the tool on the metal sheet when carrying out step c).

Preferably, the method provides for the step of cooling the tool holder head <NUM> by means of a cooling liquid during step c).

According to a particularly advantageous variant, during step c), the method includes dispensing an inert gas, for example argon, on the welding joint being formed between the right flap DX and the left flap SX, about the rotating tool <NUM>, so as to avoid the inclusion of other components in the weld.

According to a preferred embodiment of the method, step c) comprises the following steps, preferably carried out in the order indicated:.

Preferably, the predetermined force threshold is any value at least equal to 9000N and the predetermined temperature value is at least equal to <NUM> and lower than <NUM> and the number of revolutions of the tool <NUM> is at least equal to <NUM> rpm.

According to an aspect of this invention, it is clear that the method described above is also aimed at welding between a right flap DX and a left flap SX of two different metal sheets placed alongside each other. That is to say, in step a), instead of providing a metal sheet wrapped in such a way so that the two right and left flaps belong to the same sheet, a first and a second sheet may also be arranged next to each other so that the right flap DX of the first sheet is placed alongside the left flap SX of the second sheet.

According to a variant of the method, wherein a right flap DX and a left flap SX of one or more copper sheets having a plate thickness of at least <NUM> millimeters, preferably <NUM>-<NUM> millimeters, are to be welded, the method provides for maintaining an average temperature of the metal sheet in the vicinity of the tool <NUM> of about <NUM> with an advancement rate in the main extension direction X of about <NUM> millimeters per minute and a tool <NUM> speed of about <NUM> rpm. This results in a defect-free weld.

It is understood that a subject of this invention is a welding machine <NUM> for an ingot mold <NUM>.

The welding machine <NUM> for an ingot mold comprises a tool holder head <NUM> supporting a friction stir welding tool <NUM> and a tool holder head movement apparatus <NUM>, such as a three-axis numerical control machine, supporting the tool holder head <NUM> and comprising at least one translation assembly <NUM>, such as one or more carts, suitable for the controlled translation of the tool holder head <NUM> in a direction parallel to a main extension direction X of the ingot mold <NUM> and in a vertical direction Z incident or perpendicular to the main extension direction X.

Preferably, the tool <NUM> is made of a D2M W-Ni-Mo-Fe alloy (i.e., a tungsten, nickel, molybdenum, and iron alloy) or a tungsten-rhenium alloy <NUM>-<NUM> or a silicon nitride alloy.

Preferably, the welding machine <NUM> comprises a work plane P suitable to support the ingot mold <NUM> during welding and a locking frame <NUM> releasably fixed to the work plane P. The locking frame <NUM> comprises an upper frame portion <NUM> spaced from the work plane P in the vertical direction Z. Said upper frame portion <NUM> is suitable to exert a pressing force on the ingot mold <NUM> in the vertical direction P in the vicinity of a fissure <NUM> of the ingot frame <NUM> to be welded.

According to an embodiment, the locking frame <NUM> comprises a plurality of plates <NUM> spaced apart along the main extension direction X and having a concave surface <NUM> shaped to accommodate and hold the ingot mold <NUM> in place in at least one direction perpendicular to the main extension direction X.

According to a variant embodiment, the locking frame comprises at least two vertical uprights <NUM>, <NUM>, fixed to the work plane P each on the opposite side to the ingot mold <NUM>. On each of said vertical uprights <NUM>, <NUM>, a listel <NUM>, <NUM> is fixed in an upper region <NUM>', <NUM>' of the vertical upright, mainly extending in the main extension direction X and which is suitable for exerting a pressing force in the vertical direction Z.

Preferably, the welding machine <NUM> comprises lower fastening means <NUM>, <NUM> fixed in a lower region <NUM>", <NUM>" of the upright, closest to the work plane P with respect to the upper region <NUM>', <NUM>'. Spacer elements <NUM>, <NUM>' are fixed to said lower fastening means <NUM>, <NUM>, for example screws, suitable for laterally constraining the ingot mold to prevent it from moving along the transverse direction Y perpendicular to the main extension direction X and the vertical direction Z.

According to an advantageous embodiment, the welding machine <NUM> comprises a support structure <NUM> suitable for being positioned inside the inner cavity I of the ingot mold. Said support structure <NUM> comprises a backing surface <NUM> that counteracts the mechanical pressing force exerted by the tool <NUM> on the metal sheet while carrying out the welding.

Preferably, the tool holder head <NUM> comprises an internal liquid cooling circuit <NUM> and at least one inner welding gas conveyance circuit <NUM>. Said inner welding gas conveyance circuit <NUM> comprises a gas outlet mouth positioned about the tool and suitable for delivering a gas, preferably an inert gas, so as to ensure an inert atmosphere during welding to avoid inclusions of other substances in the weld.

According to an aspect of this invention, the tool <NUM> is made in one piece comprising a base portion <NUM> anchorable to the tool holder head <NUM> and a shank portion <NUM>, which extends from the base portion between a base end <NUM>' and a head end <NUM>" mainly along an axial direction K, parallel to or coincident with the rotation axis <NUM> of the tool when in use. The shank portion <NUM> has a tapered shape toward the head end <NUM>". Preferably, it has a substantially frustoconical shape with a smaller base near the head end <NUM>".

Additionally, the shank portion <NUM> comprises a lateral surface <NUM>, extending about and along the axial direction K, provided with protrusions <NUM> and depressions <NUM>. Preferably, said protrusions and depressions are the ridges and valleys of a threading obtained on said lateral surface <NUM>. In particular, said protrusions and depressions <NUM>, <NUM> are shaped to mix and convey the molten metal toward the surface of the metal sheet being welded during the welding operation, i.e., along the axial direction K and toward the base portion <NUM> of the tool <NUM>.

Additionally, according to an advantageous embodiment, the lateral surface <NUM> comprises one or more cuts or breaks in the tapered shape. Preferably, said cuts or breaks are flat lateral faces <NUM>, <NUM>' arranged about the axial direction K and each lying in a plane secant to the axial direction, i.e., said lateral faces are inclined so as to be convergent towards the head end <NUM>".

Preferably, in the variant with a frustoconically shaped shank portion <NUM>, the lateral faces <NUM>, <NUM>' are flat millings of the curvilinear conical side surface <NUM>. Preferably, this variant comprises three lateral faces <NUM>, <NUM>', <NUM>" arranged about the axial direction K and spaced angularly <NUM>° apart.

During the welding operation, i.e., while the tool <NUM> is rotating in the metal sheet, the shank portion <NUM> is subjected to a torque about the axial direction K, such as to induce a slight torsion of the shank portion <NUM>. This results in the lateral faces <NUM>, <NUM>' deforming to take on a curved or twisted or serpentine shape during the welding action. Said curved, serpentine, or twisted shape determines preferential channels for circulating the molten metal of the sheet subjected to welding, facilitating the mixing of the metal between the two right DX and left SX flaps of the sheet to be welded, for example, the transport of the molten material from the right flap to the left flap or vice versa. This ensures that the joint is properly and correctly welded.

Additionally, the curved or serpentine or twisted shape contributes to the conveyance of molten metal to the outermost surface of the sheet <NUM>.

According to an embodiment of the invention, the base portion <NUM> comprises a base surface <NUM> extending about the shank portion <NUM>, preferably completely about the shank portion <NUM>, in a plane perpendicular to the axial direction K. Said base surface <NUM> is suitable to come in contact with the outermost surface of the metal sheet <NUM> during the welding step. Preferably, one or more grooves <NUM> or reliefs shaped for determining the displacement of the fluid metal material toward the rotation axis <NUM> of the tool are made on said base surface <NUM>.

According to a preferred embodiment, the one or more grooves <NUM> or reliefs are shaped as a flat spiral, as for example shown in <FIG>.

According to a preferred embodiment of the invention, the welding step, i.e., for example during step c) or c5) of the method described above, occurs with an inclination of the rotation axis <NUM> of the tool <NUM> non-perpendicular to the tangent plane P' the left flap SX and the right flap DX of the metal sheet <NUM>. In other words, for example, the rotation axis <NUM> of the tool <NUM> is not perpendicular to the work plane P but is inclined with respect to the perpendicular to the work plane P by at least <NUM>°, preferably at least <NUM>° (for example as shown in <FIG>). This is the case, for example, because the work plane P of the welding machine <NUM> is tiltable at will, i.e., the welding machine comprises a device for tilting the work plane P. Alternatively or simultaneously, this occurs because the tool holder head movement apparatus <NUM> is configured to support the tool holder head <NUM> in such a way that the tool <NUM> is made to advance along the main extension direction X but with the rotation axis <NUM> inclined with respect to the perpendicular to the tangent plane P'.

Innovatively, the method for making an ingot mold and the welding machine for an ingot mold according to this invention enable the problems encountered in the prior art in making ingot molds to be successfully overcome.

In particular, the method for making an ingot mold according to this invention is able to reduce the time required to make ingot molds, requires fewer resources, and achieves improved weld quality with respect to the welds made using the techniques of the prior art.

Advantageously, the manufacturing method according to this invention does not require preheating the ingot mold for its welding, thus saving considerable time and energy resources.

In addition, the presence of a releasable locking frame makes it possible to secure ingot molds of different diameters and lengths to the work plane in a stable manner, thus ensuring flexibility in the use of the welding machine and an adequate locking to avoid possible displacements that could affect the quality of the weld.

Moreover, in an advantageous way, the presence of a support structure suitable for being positioned inside the inner cavity of the ingot mold allows the mechanical pressing force exerted by the tool <NUM> on the sheet during the execution of the weld to be counteracted and ensures an improved quality of the weld, since the sheet is less subject to localized bending during welding.

According to a further aspect, the tool <NUM> equipped with the shank portion <NUM> with a tapered shape and provided with protrusions <NUM> and depressions <NUM> for effectively conveying the fluid metal during welding, allows the welding operation to be optimized both from the point of view of the quality of the weld and from the point of view of the efficiency of the entire operation.

Claim 1:
A method for manufacturing an ingot mold (<NUM>), for example an ingot mold for casting, comprising the steps of:
a) providing a copper sheet (<NUM>) wrapped about a main extension direction (X) so as to encompass an inner cavity (I) and so that a left flap (SX) and a right flap (DX) of the metal sheet (<NUM>) are arranged close together in front of each other, said metal sheet (<NUM>) being arranged on a work plane (P);
b) providing a tool holder head (<NUM>), which is translatable at least along a direction parallel to the main extension direction (X), said tool holder head (<NUM>) supporting a tool (<NUM>) for friction stir welding;
c) rotating the tool (<NUM>) at the right flap (DX) and the left flap (SX) of the metal sheet (<NUM>) and proceeding with welding between the right flap (DX) and the left flap (SX) by friction stir welding until an ingot mold (<NUM>) is obtained.