WO2006008607A2

WO2006008607A2 - Automated method and plant for manufacturing pistons

Info

Publication number: WO2006008607A2
Application number: PCT/IB2005/001948
Authority: WO
Inventors: Roberto Gaddi; Giuseppe Zavattaro; Helmuth Althans
Original assignee: Global Foundry Systems S.R.L.; Mahle Pistoni S.P.A.
Priority date: 2004-07-09
Filing date: 2005-06-29
Publication date: 2006-01-26
Also published as: ITTO20040471A1; EP1776213A2; WO2006008607A3

Abstract

Plant and method for producing aluminium pistons of internal combustion engines having cast iron inserts, comprising: a first loading station (11) for loading the inserts (10) to be palced in a cast chill (43) for casting said pistons, a second station (21) wherein a molten metal bath is provided in which said inserts (10) are dipped for undergoing a coating treatment, a third exchange station (31) wherein said inserts (10) coming from said first station (11) or from said second station (21) are temporarily placed waiting for being transferred to said second station (21) or to said casting chill (43) respectively, a fourth casting station (41) wherein said inserts (10) are placed in said casting chill (43), a robot (51) for transferring said inserts (10) from one of said stations to another.

Description

" AUTOMATED METHOD AND PLANT FOR MANUF ACTUΪφWϊti^STQNS."

The invention relates to an automated method and plant for manufacturing pistons. More precisely the invention relates to an automated method and plant for treating by aluminizing ring-shaped inserts and for placing thereafter said rings in a chill for forming pistons, particularly of internal combustion engines, compressors, etc... The industrial production of pistons for internal-combustion engines is currently carried out with two processes quite different from each other: - by casting in a chill (the molten aluminum alloy is casted in a metallic die); -by hot-pressing (pistons are forged -it is also said that pistons are swaged- by approaching the lump of pre-heated material with a die and a half-die, then by pressing it with pressures of about some thousand of tons).

The molten pistons ("cast pistons") are normally used for mass-production of internal- combustion engines and the present invention relates to the first kind of process. In order to improve the performances of modern Diesel-cycle internal-combustion engines, aluminum alloy pistons are generally mounted which are reinforced with centrifuged cast iron inserts. Said inserts are incorporated near the first and/or second piston ring seat during the casting. Before being placed in the chill for cast forming the pistons, said inserts generally undergo an aluminizing process named "Alfin" process. The aluminizing consists in dipping the inserts in a molten aluminum bath for a time ranging from 2 to 4 minutes. The purpose of this operation is coating the rings with a thin aluminum layer before they are placed in the die or chill so as to provide a sure bond with the aluminum alloy of the piston. Currently, the operations of aluminizing and placing the inserts in a chill are carried out manually.

For obvious reasons, the manual working involves a number of disadvantages, first of all the hard working environment in which the personnel has to work and lastly a low production rate. In order to obviate to the aforesaid disadvantages and to increase the production rate, in the past some attempts have been made for providing automated plants for performing the operations of aluminizing and placing the rings on the pistons; however the attained results have been unsatisfactory due to the complexity and industrialization costs of the proposed solutions. Moreover, in the proposed solutions until now it has not been possible to place more than two rings at a time in the chill. An object of the present invention is providing an automated method and plant for manufacturing pistons, in particular for treating the ring-shaped inserts and for placing thereafter the rings in a chill, during the phase of preparing the die for casting the pistons.

Another object of the invention is providing an automated method and plant, for treating and placing thereafter the rings in a chill, that allows using the robot units currently used in several industrial assembling processes and that is therefore economically advantageously to be industrialized.

These and other objects are achieved with the plant and the method according to the invention as claimed in the appended claims. Advantageously, according to the invention it is possible carrying out at the same time the treatment and the successive placement in the chill of four or more rings at every working cycle.

Thanks to the plant and the method according to the invention it is possible carryng out a fast and fully automated production of pistons. Advantageously, in the plant and the method according to the invention at every cycle of picking up the rings from the aluminizing bath, a portion of the surface of said bath is freed from oxides so that the characteristics of the ring coating are not altered.

Moreover, to the same purpose, advantageously it is provided for periodically cleaning the surface of the molten metal bath from oxides and films that get formed during the cycle of coating rings.

The invention will be now described in greater detail with reference to a preferred, but not limiting embodiment, shown in the enclosed Figures, wherein:

Figure 1 is a plan top view of a plant according to the invention;

Figure 2 is a side view of the loading station; Figure 3 is a side view of the aluminizing station;

Figure 4 is a front view of the casting station;

Figure 5 is a side view of the aluminizing station during the bath cleaning;

Figure 6 is a view of a detail of the aluminizing station;

Figure 7 is a side view of the gripper assembly for picking the rings up; Figure 8 is a section view of a ring.

Referring first to Figure 8 a ring-like insert or ring 10 is shown in cross-section, the ring being made of pre- worked centrifuged cast iron that must be placed in the die or chill in which the pistons are formed by casting molten metal.

Referring to Figure 1 they are shown, counter-clockwise: -a first loading station 11 for loading rings 10;

-a second aluminizing station 21 wherein a molten metal bath is provided, typically aluminum or an alloy thereof, in which the rings 10 are dipped;

-a third exchange station 31 wherein said rings 10 are temporarily placed waiting for being sent to the aluminizing bath or to the casting chill; and

-a fourth casting station 41 wherein the rings are placed in a casting chill 43. Still referring to Figure 1 an anthropomorhic robot 51 is also shown for picking up and transferring the rings 10 from a station to another station in the plant. Said robot 51 is provided with a base 53 and an articulated revolving arm 55 and is able to reach all the stations of the plant with the end 57 of said arm 55.

Moreover the end 57 of said arm 55 is provided with a pair of pneumatically driven pick¬ up devices. More precisely, said devices comprise a first pneumatically driven pick-up device 59 provided with a plurality of grippers 61 and a second pneumatically driven pick¬ up device 63 provided with a single gripper; the purpose of said pick-up devices will become more evident from the following description.

Considering now Figure 2, the first loading station 11 is shown in better detail. Said station 11 comprises a pair of stores 13 comprising two cylindrical vertical parallel columns inside of which unfinished rings 10 - that is, rings that did not undergo the aluminizing treatment yet- are arranged in a stack. A pneumatic extraction device 15 horizontally arranged below stores 13 and provided with a pick-up head 17 allows extracting rings 10 one by one from the lower part of the stores 13 with a guillotine mechanism and putting them on a loading platform 19 arranged at the left of stores 13 in the Figure. Due to the thrust of the pick-up head 17, a pair of rings 10, extracted from the two stores 13, are simultaneously put on the loading platform 19 and can be removed from the loading station 11, as it will appear more evident from the description of the working cycle of the plant according to the invention.

Moreover said station 11 is provided with a chute 12 where rings 10 can be unloaded if the picking up operation has to be interrupted for any reason. Said chute 12 ends in a collecting basin (not shown) from which said not treated rings 10 can be recovered with known means.

A basin 14 containing a bath of liquid graphite is also provided at the front relative to said loading platform 19, between said platform 19 and the top of chute 12. The purpose of said graphite bath will become clearer from the following description. Considering now Figure 3 the second aluminizing station 21 is shown in which a molten metal bath is provided, preferably aluminum or an alloy thereof. Said station 21 comprises a crucible 23 containing the molten aluminum in which rings 10 are dipped for undergoing the aluminizing treatment.

Said rings 10 are arranged on a support 71 provided with four hooks 79, one for every ring 10.

It has to be noted that, even if the preferred embodiment presently described provides for using four rings 10, even a higher number of rings can be considered. More precisely, said support 71 cpmprises an upper suspension rod 73 the lower part of which ends with a crosspiece 75. To said crosspiece two parallel lower rods 77 are fixed, each of which provided with a pair of corresponding hooks 79 arranged at different levels along said lower rods 77.

Moreover on said upper rod 73 a cylindrical suspension metal ring 72 is provided by means of which said support 71 can advantageously be kept suspended on a suitable support. A rack bracket 81 mounted in a cantilever way on an arm 83 -preferably revolving so as to allow reaching the crucible 23- is provided at the second station 21 in order to allow a plurality of said supports 71 to be hung at such level that the lower part of said supports 71, to which said rings 10 are hung, is dipped in the molten aluminum bath. Generally the residence time of the rings in the aluminum bath is of approximately 180- 240 sec. therefore it is possible to use the same bath for treating some sets of four rings in fast sequence . Typically the bracket 81 is provided with four or five U-shaped seats 82 for a corresponding number of supports 71.

Still referring to Figure 3, the third exchange station 31 is shown comprising an upright 33 on the top of which an U-shaped seat 35 is provided for hanging, by means of said suspension metal ring 72, one of said supports 71 before and after the aluminizing treatment.

Referring to Figure 4 the fourth casting station 41 is shown in detail, wherein the rings 10 which previously underwent the aluminizing treatment are placed by groups of four in a chill 43 which will be subsequently covered for casting the piston bodies according to the prior art.

Advantageously, according to the invention, the placing time of the inserts in the chill, including even the step of covering the inserts with molten metal, is lower than 25 sec. Referring to Figure 5 the second aluminizing station 21 is partially shown again during the phase preceding the exit of the support 71 with the respective rings 10 from the molten aluminum bath. In this phase of the working cycle the arm 55 of the anthropomorhic robot 51, by means of the second pneumatic pick-up device 63 provided with a single gripper 64, picks a tool 91 up from one of the seats provided on the rack bracket 81. The tool 91 comprises a handle 93 -in the present description also referred to as "first handle 93" - at the lower part of which a shovel 95 is fixed, said handle 93 being provided with a cylindrical metal ring 97 for allowing said tool 91 to be hung to one of the seats in said rack bracket 81. Subsequently, the robot 51 dips partially the tool 91 in the molten aluminum bath and collects the oxide layer that formed on the surface by combining a translation and a rotation movement, creating thereby in said bath an "exit window" for one of the supports 71 that are dipped in the crucible 23.

At the end of the cleaning operation, the robot 51 arranges for the tool 91 to be placed again in the seat from which it has been picked up on the rack bracket 81. Referring to Figure 6 another side of the aluminizing station 21 is shown, in which a U- shaped support 92 is provided for a second tool 94 to be used for collecting and removing from the aluminum bath oxides and films that formed on the surface thereof. Said tool 94 comprises a handle 96 - also referred to as, in the present description, "second handle 96"- to the lower end of which a showel 98 is fixed, having a shape substantially rectangular and arched along a circumference parallel to said handle 96. Said handle 96 is also provided with a cylindrical metal ring 99 that allows the support tool 94 to be hung to said support 92.

Thanks to the tool 94 the oxides and films that are formed in the aluminum bath can be collected at the surface, removed from the crucible 23 and discharged in a container 100 arranged beside said crucible 23 in said aluminizing station 21. Referring to figure 7, the pneumatically driven pick-up device 59 is shown which is provided with a plurality of grippers 61 for picking up and transferring a set of four rings 10 at a time.

The pick-up device 59 comprises an aluminum support 65 fastened to the wrist of the end 57 of the arm 55 of the anthropomorhic robot 51, on which four pneumatic grippers 61 are mounted aligned. Each pneumatic gripper 61 is provided with three gripping teeth 67 arranged parallel and at angles of 120° relative to each other, and radially displaceable.

Said teeth 67 are suitable for engaging with the inner circumference of said ring 10, driven by the pneumatic control of the gripper 61.

The two central grippers 61 are not movable while the two external grippers 61 are movable, slidable on nitrided guides and driven by pneumatic cylinders; in particular two external grippers 61 can slide at least in a direction lateral to themselves relative to the support 65.

Advantageously, thanks to this solution it is possible reducing the overall dimensions of the supports 71 relative to the distances between the centers of the chills for casting the pistons, which are well-known fixed distances.

The driving of the grippers 61 is carried out by means of two electro valves arranged in the pneumatic circuit, a first of said electrovalves used for driving two of said grippers, the second electro valve used for driving the other grippers. Such separate handling is due to the fact that the steps of taking rings 10 from the first station 11 and from the support 71 when it is in the third exchange station is made by pairs.

Advantageously, according to the invention, each gripper 61 is provided with three telescopic pins 69 supported by springs and parallel to said teeth 67, they also arranged at angles of 120° and suitable for allowing an optimal positioning of the rings 10 in the chill thanks to the spring thrust in an axial direction relative to said rings 10. The operating cycle of the plant according to the invention and, consequently, the method according to the invention for treating and inserting the rings 10 in the chill will be now described in detail.

On request from the fourth casting station 41, that is when the chill 43 is free or is going to be free for receiving a new set of ring-shaped insert 10, the anthropomorhic robot 51 picks the tool 91 up with the pneumatic gripper 64 and cleans the surface of the aluminum bath in the crucible 23 with the corresponding shovel 95, removing the oxides and films and freeing therewith an exit zone for the rings 10.

Subsequently, after having put the tool 91 away, the robot 51 picks up one of the supports 71 that are hanging from the rack bracket 81 at the second aluminizing station 21, from which rack bracket four rings 10 are in turn hanging that underwent the aluminizing treatment. Said support 71 is picked up with the pneumatic membrane gripper 64 and by taking the support 71 out from the bath in the crucible 23 from the area previously freed from oxides. The support 71 is then laid on the seat 35 in the third exchange station 31. Now, by means of the four pneumatic grippers 61 the robots 51 pick four rings 10 up two by two from the support 71 that is in the third exchange station 31 and puts them immediately - that is, substantially without further waiting-, working- or handling steps - in the chill in the fourth casting station 41. After having put the rings 10 in the chill 43, the robot 51 reaches the first station 11 for picking up a new set of four unfinished rings 10.

The picking up of rings 10 from the station 11 is made two by two on the loading platform 19 by means of the pneumatic grippers 61.

This way two pairs of rings 10 are put in sequence on the corresponding four hooks 79 arranged on the support 71 that is in the third exchange station 31 and from which the rings 10 have been previously token away.

In a further step, the robot 51 picks the support 71 carrying the rings 10 up from the support 35 with the pneumatic gripper 63 and lays it down in the same position where it previously was in the rack support 81 at the second aluminizing station 21. When the robot 51 returns in waiting position, the cycle is over.

Moreover the operating cycle of the plant according to the invention may provide for carrying out several steps which are important for the good outcome of the whole process. Before picking up the ring-shaped insert 10 from the loading station 11 and after a complete cycle of placing the rings in the chill, the anthropomorhic robots 51 dips the gripping teeth 67 of grippers 61 in the basin 14 containing liquid graphite. This operation is important since facilitates separation of ring-like inserts 10 from the gripper 61 itself when said rings 10 are put on the support 71.

In case of unexpected anomaly on the fourth casting station 41 the robot 51, if it has already picked the rings 10 up, carries the "abort" operation out unloading said rings on the proper unload chute 12 provided in the station 11.

In order to remove the store of oxides and films that form in the aluminum bath, according to the invention it is also provided that robot 51 periodically - as an example after 8-10 complete cycles- picks the tool 94 up from the support 92 with the gripper 64 and carries out the operation of collecting the oxides and films from the bath discharging them in a suitable container 100.

Claims

1. Plant for manufacturing pistons, comprising:

- a first loading station (11) for loading inserts (10) to be arranged in a chill (43) for casting said pistons;

- a second station (21) wherein a molten metal bath is provided in which said inserts (10) are dipped for undergoing a coating treatment;

- a third exchange station (31) wherein said inserts (10) coming from said first station (11) or from said second station (21) are temporarily put waiting for being transferred to said second station (21) or said casting chill (43) respectively;

- a fourth casting station (41) wherein said inserts (10) are placed in said casting chill (43);

- a robot (51) for transferring said inserts (10) from one of said stations to another. 2.Plant according to claim 1, wherein said robot (51) is a anthropomorhic robot having an articulate arm (55) suitable for reaching, possibly with its end (57), any of the four stations (11, 21, 31, 41) of the plant.

3. Plant according to claim 2, wherein said arm (55), possibly at its end (57), is provided with a pair of pick-up devices (59,63), a first one of said pick-up devices (59) being provided with a plurality of grippers (61) for gripping a set of said inserts (10), and a second one of said pick-up devices being provided with a single gripper (64) for gripping one or more tools to be used in the production cycle of said pistons.

4. Plant according to claim 3 wherein, in the alternative or in combination:

- the pair of pick-up devices (59, 63) is a pair of pneumatically driven devices;

- at least one of said first (59) and second pick-up devices (63) is pneumatically driven.

5. Plant according to one or more preceding claims, wherein said first loading station (11) comprises a pair of stores (13) inside of which said unfinished inserts (10) and an extraction device (15) are arranged, said extraction device (15) being arranged below the stores (13) and being provided with a pick-up head (17) that allows extracting said inserts (10) to a loading platform (19) in such way that due to the thrust of said pick-up head (17) a pair of inserts (10) is put on the loading platform (19) and can be removed from the loading station ( 11 ) by means of said robot (51).

6. Plant according to claim 5, wherein, in the alternative or in combination:

-the pair of stores (13) comprises two columns inside of which said insert (10) are arranged in a stack;

-the pair of stores (13) comprises two cylindrical and/or vertical and/or parallel columns, inside of which said unfinished inserts (10) are arranged;

-the extraction device (15) is a pneumatic device and/or is horizontally arranged below the stores (13);

- the pick-up head (17) allows extracting said inserts (10) one by one from below said stores (13).

7.Plant according to one or more preceding claims, wherein the first loading station (11) is further provided with a chute (12) on which the inserts (10) can be put down if the picking operation of robot (51) needs to be interrupted before the inserts (10 ) are transferred to the next station. δ.Plant according to one or more preceding claims, wherein the second station (21) comprises a crucible (23) containing the molten metal in which said inserts (10) are dipped for undergoing the coating treatment.

9.Plant according to one or more preceding claims, comprising a support (71) provided with a plurality of hooks (79), one for each insert (10), to which the inserts (10) can be hung while they are immersed in the molten metal, where the support can be gripped and handled by the robot (51).

10. Plant according to claim 9, wherein the support (71) is provided with four hooks (79).

11. Plant according to claim 9 and/or 10, wherein the support (71) comprises an upper suspension rod (73) ending with a lower part provided with a crosspiece (75) to which a plurality of lower rods (77) is fixed, each of said lower rods being provided with corresponding hooks (79) arranged at different levels along said lower rods (77).

12. Plant according to claim 11, wherein in the alternative or in combination:

- two lower rods (77) are fixed to the crosspiece (75) at the lowed end of the the upper suspension rod (73); -the lower rods (77) are parallel;

-each parallel lower rod (77) is provided with a pair of the corresponding hooks (79);

- the upper rod (73) is suitable for being hung at its upper part;

-a suspension metal ring (72) is provided on the upper rod (73), said metal ring allowing to keep said support (71) suspended; - the suspension metal ring (72) is cylindrical.

13. Plant according to claim 8, wherein said second station (21) is provided with a rack bracket (81) which is provided with a series of seats (82) in order to allow suspending a plurality of said supports (71) by means of said suspension metal ring (72), said support (71) having its lower part, to which said inserts (10) are suspended, dipped in the molten metal bath.

14. Plant according to claim 13, wherein the seats (82) of the rack bracket (81) are U- shaped.

15. Plant according to claim 13 or 14, wherein said bracket (81) is provided with at least five seats (82) for corresponding supports (71). lό.Plant according to a claim from 13 to 15, comprising a first tool (91) comprising in its turn a first handle (93) to which a first shovel (95) is fixed, said first handle (93) being suitable for allowing said tool (91) to be suspended to a seat of said rack bracket (81), said first tool being suitable for being handled by said robot (51) for collecting the oxide layer that can form on the surface on said crucible (23) creating an exit "window" of escape for one of said supports (71) that are immersed in said molten metal bath.

17. Plant according to claim 16, wherein, in the alternative or in combination:

-the first shovel (95) is fixed at its lower part to the first handle (93);

-the first handle (93) is provided with a first cylindrical metal ring (97) suitable for allowing said tool (91) to be suspended to a seat of said rack bracket (81);

-the first tool is suitable for being handled by said robot (51) so as to collect, possibly combining a translation- and a rotation movement, the oxide layer that can form on the surface on said crucible (23).

18. Plant according to claim 16 or 17, wherein said second station (21) further comprises a support (92) for a second tool (94) provided for collecting and removing from the molten metal bath oxides and films that form on the surface thereof.

19.Plant according to claim 18, wherein said second tool (94) comprises a second handle

(96) to which a second shovel (98) is fixed and wherein, in the alternative or in combination: - the second shovel (98) is fixed to the lower end of the second handle (96);

- the second shovel (98) has a substantially rectangular shape;

- the second shovel (98) has a substantially arched shape along a circumference parallel to said second handle (96);

- said second handle (96) is suitable for allowing said second tool (94) to be hung to said support (92) provided for in said second station (21);

- said second handle (96) is provided with a second metal ring (99), possibly cylindrical, that allows said second tool (94) to be hung to said support (92) provided for in said second station (21). 2O.Plant at least according to claim 9, wherein said third exchange station (31) comprises a support (33) for suspending one of said supports (71) before and after the coating treatment.

21. Plant according to claim 20, in which, in the alternative or in combination: - the support (33) comprises an upright;

- on the support (33) an U-shaped seat (35) is provided for suspending one of said supports (71) before and after the coating treatment;

- the U-shaped seat (35) is arranged on the upright (33);

- the support (33) allows one of said supports (71) to be suspended by the suspension metal ring (72) before and after the coating treatment.

22.Plant according to one or more preceding claims, wherein said fourth casting station

(41) comprises a chill (43) in which said inserts (10) that previously underwent the coating treatment can be placed simultaneously by sets of four.

23.Plant according to one or more claims from 3 to 22, wherein said first pick-up device (59) is provided with a plurality of grippers (61) for picking up and transferring a set of four or more inserts (10) at a time.

24.Plant according to claim 23, suitable for handling ring-shaped inserts (10) and wherein said first pick-up device (59) comprises a support (65) on which at least four grippers (61) are mounted. 25. Plant according to claim 24 wherein, in the alternative or in combination:

- the support (65) is made of aluminum;

- the grippers (61) are mounted aligned on said support (65);

- each gripper (61) is provided with three parallel gripping teeth (67) arranged at angles of 120° suitable for engaging with the inner circumference of said ring-like inserts (10) driven by the pneumatic drive of said gripper (61).

26.Plant according to claim 24 or 25, wherein at least a central gripper (61) is fixed relative to the support (65), while at least one gripper is movable relative to the support

(65) at least in lateral direction of the same gripper.

27. Plant according to claim 26 wherein, in the alternative or in combination: - the two central grippers (61) are fixed;

- the two external grippers (61) are movable;

- at least a movable gripper is slidable on guides, and possibly the guides are drived by pneumatic cylinders.

28.Plant according to one or more claims from 24 to 27, wherein at least four grippers (61) are mounted on the support (65) and a pair of said four grippers (61) are driven independently from the other one.

29.Plant according to one or more claims from 3 to 28, wherein each gripper (61) is provided with three parallel telescopic pins (69) supported by springs and arranged at angles of 120°, suitable for allowing an optimal positioning of the inserts (10) in the chill (43).

3O.Plant according to one or more claims from 25 to 29, wherein said first station (11) further comprises a basin (14) containing a bath of liquid graphite in which it is possible to dip the gripping teeth (67) of grippers (61) at each cycle in order to facilitate the separation of inserts (10) from the gripper (61) itself.

31. Method for manufacturing pistons comprising the following steps:

- in a first loading station (11) loading a set of inserts (10) to be placed in a casting chill

(43) for forming said pistons by casting;

-transferring said inserts (10) in a third exchange station (31); - transferring said inserts (10) from said third exchange station (31) to a second station (21) in which a molten metal bath is provided in which said insert (10) can be dipped; -transferring said inserts (10) from said second station (21) to said third exchange station (31) in which said inserts (10) coming from said second station (21) are temporarily placed, waiting for being transferred to said casting chill (43); -transferring said inserts from said third station (31) to a fourth casting station (41) in which said inserts are placed in said casting chill (43); said operations of transferring said inserts (10) from one of said stations to the other being carried out by a robot (51). 32. Method according to claim 31, wherein said inserts (10) loaded in said loading station (11) are put two by two by said robot (51) on a support (71) suitable for taking at least four of said inserts (10).

33. Method according to claim 32, wherein said support (71) is placed at said third exchange station (31).

34.Method according to claim 33, comprising the step of picking up the support (71) that is at the third station (31) with said robot (51) and transferring the support to said second station (21) for coating said inserts (10).

35.Method according to one or more claims from 31 to 34 wherein, by means of a plant according to one or more claims from 16 to 30, before said inserts (10) are transferred from said second station (21) to said third station (31) a step is provided wherein said robot (51) picks a tool (91) up provided with said first shovel (95) and cleans the surface of the molten metal bath from oxides and films, freeing therefore the exit zone from said bath for said inserts (10).

36.Method according to or more claims from 32 to 35, comprising the step of picking four inserts (10) up two by two from said support (71) that is in the third exchange station (31) and to place said inserts in said casting chill (43) in the fourth casting station (41).

37. Method according to claim 36, comprising the step of picking four inserts (10) up two by two from said support (71) that is in the third exchange station (31) and immediately to place said inserts in said casting chill (43) in the fourth casting station (41). 38.Method according to one or more claims from 31 to 37, wherein said inserts (10) have a ring-like shape.

39. Method according to one or more claims from 31 to 38, wherein said robot (51) comprises a first pick-up device (59) on which a plurality of grippers (61) is mounted, each gripper being provided with a plurality of gripping teeth (67) suitable for engaging with the inner circumference of said ring-like inserts (10), said method comprising the step of dipping said gripping teeth (67) in a basin(14) containing liquid graphite before picking the ring-shaped inserts (10) up from the loading station (11) for facilitating the separation of said inserts (10) from said teeth (67).

40. Method according to claim 39 wherein, in the alternative or in combination: - said robot (51) comprises a first pick-up device (59) on which at least four pneumatic grippers (61) are mounted;

-each gripper is provided with three gripping teeth (67), possibly arranged parallel and/or at angles of 120°.

41.Method according to one or more claims from 31 to 40, wherein in case of anomaly on the casting station (41) the robot (51), if already picked the rings (10) up, carries out an "abort" operation unloading said rings in an unload chute (12) provided in the first station (11).

42.Method according to one or more claims from 31 to 41, further comprising the step of picking a tool (94) up by means of said robot (51) and of collecting with said tool oxides and films from the molten metal bath, evacuating them in a collection container (100). 43. Method according to one or more claims from 31 to 42, wherein said molten metal bath is an aluminum bath or a bath of alluminium alloys.

44. Method according to one or more claims from 31 to 43, wherein said inserts (10) are cast iron rings. 45.Method according to claim 44, wherein said rings are aluminated rings of "Alfm" kind, that is pre- worked centrifuged cast iron rings.

46.Method according to claims 43 and 44, or 43 and 45, wherein the residence time of the rings in the aluminum bath is approximately 120-240 seconds.

47.Method according to one or more claims from 31 to 46, wherein the time for placing inserts (10) in the chill, covering the chill included, is less than 25 seconds.

48. Method for manufacturing pistons for Diesel cycle internal combustion engines, comprising the steps according to one of the claims from 31 to 47.