Method and apparatus for production of aluminum alloy castings

Abstract: Method and simplified apparatus for manufacturing aluminum alloys castings, for example those cast aluminum parts utilized in the manufacture of automobile engines: cylinder heads, engine blocks and the like; whereby the castings are cast in a plurality of semi-permanent-type molds, said molds each being movable to a plurality of processing positions along one of a plurality of straight line paths (five in the preferred embodiment), wherein the operations of cleaning, core setting, casting, and casting extraction are performed on each mold at predetermined positions along its respective path and alternating said operations among the molds in order to permit minimization of the number of robot equipment and to increase the aggregate productivity of said molds, since any one processing operation is handled by only one robot arm moving between the plurality of lines seriatim, so that a given process step is performed at any one time only at one of the plurality of lines.

Description: FIELD OF THE INVENTION The present invention relates to an improved method and apparatus for the production of aluminum alloy castings, more particularly, to a production plant comprising a plurality of movable semi-permanent molds which are positioned in different stations corresponding to the activity being performed in the production cycle, thereby raising the productivity of the casting process and lowering the capital and maintenance costs of the currently used casting equipment. This is adaptable in simplified form to permanent molds also. BACKGROUND OF THE INVENTION Production of aluminum alloy castings, for example massive production of certain automobile engine parts, (such as cylinder heads), is usually made in permanent or semi-permanent type molds, in contrast with expendable molds made of sand which are used for only one casting. The semi-permanent molds are provided with means for heating, cooling, automatic opening and closing, etc. to complete a full casting cycle. Usually one operator serves several molds, and some operations such as core setting, mold filling, and extraction of the casting are made with the help of robot arms, programmed for performing these repetitive operations with accuracy in time and space. The production cycle of the casting process comprises the following operations, directly related to the mold: (A) mold cleaning; (B) core setting; (C) mold filling and cooling; and (D)extraction of casting, followed by breaking and elimination of external sand cores and removal of runners. The casting is then heat-treated, if necessary, finished and inspected. The production process currently in operation involves the use of fixed semi-permanent molds. One such process requires at least one operator and three robots per mold. An alternative process uses a revolving platform, typically with 4 to 6 molds mounted thereon, which are served by two or three operators and three robots for said five molds. The productivity of the revolving platforms has been relatively satisfactory but can be improved according to the present invention. The revolving platform also has some drawbacks, for example the mass of the revolving platform is on the order of 50 metric tons, which requires high capacity motors and equipment to rotate it from one station to the next. Also, if one of the molds breaks down and has to be repaired, most of the time, the whole platform has to be shut down with the consequent loss of production of the other molds thereon. The present invention overcomes the disadvantages of the presently utilized revolving platforms and allows for higher productivity of the casting process. This invention thus results in multimillion dollar savings in capital investment and upkeep costs of the revolving platforms and the maintenance costs of such equipment. The casting plants are therefore greatly simplified. There have been some proposals in the past addressed to upgrade the efficiency of foundries, where molds undergo a sequence of operations. All of prior art shows circular paths along which the molds circulate and are positioned at several stations for performing the required operations. Examples of the prior art are found in U.S. patents 3627028 to Carignan, 4747444 to Wasem et al, 4299629 to Friesen el al., 4422495 to Van Nette, 3530571 to Perry, 5056584 to Seaton and 38977461 to Pol et al. None of these patents however teach or suggest the arrangement proposed by the Applicants and its advantages in productivity. Some of these patents teach for example to synchronize the movement of the molds with the movement of ladles containing the liquid metal, but none suggest to have linear paths for the molds along which the molds can travel and meet the servicing robots for pouring the molten aluminum and extracting the casting one at a time and each one under wholly independent operation of the others. The prior art does not suggest to include one station where each mold can be positioned for maintenance, which is practical in the linear path arrangement and not in circular paths, where the molds can be positioned when needed without interfering in any way with the casting cycle of the other molds. OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a process of manufacturing aluminum alloy castings with improved productivity and at lower capital and operational costs. It is another object of the invention to provide a new lay-out of the equipment involved in the manufacturing of aluminum alloy castings with higher flexibility and productivity. Other objects of the invention will be in part obvious and in part pointed out hereinafter. According to the present invention the objects thereof are achieved by providing a method of manufacturing aluminum alloy castings with the features of claim 1, and further by providing an apparatus for producing aluminum alloy castings comprising the features of claim 8. Advantageous further embodiments of the inventive method and apparatus are defined in the respective dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS In this specification and in the accompanying drawings, some preferred embodiments of the invention are shown and described and various alternatives and modifications thereof have been suggested; but it is to be understood that these changes and modifications can be made within the scope of the invention. The suggestions herein are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will thus be enabled to modify it in a variety of forms, each as may be best suited to the conditions of a particular use. Figure 1 is a schematic plan view illustrating the lay-out of the casting system according to the present invention and particularly showing the sequence of positions A to E taken by each of a plurality of molds moving along a respective one of a plurality of parallel tracks to carry out the linearly staggered process steps A to D for producing aluminum castings. Figure 2 is a schematic side elevational view of the casting system shown in figure 1, illustrating mainly the sequence of operations A to E along one of the processing tracks, as well as the tracks of the robots for core setting, casting and extraction of the castings. Figure 3 is a schematic side elevational view of the casting system shown in figure 1, illustrating mainly the distribution of the mold cradles and the position of the aluminum holding furnace. Figure 4 is a schematic plan view of a casting system showing another embodiment of the invention wherein the number of moving molds is four and wherein the orientation of said molds is different as compared to the orientation of the molds in figure 1. Figure 5 is an elevational schematic view of the casting system shown in figure 4. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION The casting process of most aluminum alloy castings comprise the following steps: (A) Mold cleaning. This operation involves inspection by an operator of the mold in order to assure that the casting will be free of defects caused by inclusion of foreign elements, and cleaning of loose sand and other materials (B) Core setting. This operation is usually performed with the help of a first robot arm 38 for easing the operator's work and because of the repetitive nature of the operation. The robot arm is programmed for accurately placing at least one core in its position within the mold in a given line and to repeat the process for each other mold in the other lines. In the prior art revolving platform system, a similar robot arm serves the all molds, typically four to six, located on the platform. (C) Casting. The filling of molds 10, 12, 14, 16, and 18 with liquid aluminum is carried out by means of a second robot arm 66 having a small ladle 64, which is filled by immersion, by an autoladle, or the like, from a molten aluminum pool held nearby in a holding furnace 46. The ladle 64 pours the measured amount of liquid aluminum into one of the respective molds, each in its turn. One robot arm for this purpose is used in the prior art rotating platform systems. (D) Extraction. The casting 48, including the sand core(s) 36, is then withdrawn from the mold with the help of a third robot arm 52 as soon as the casting 48 has undergone sufficient cooling as to be sufficiently solidified to be handled outside of the mold. The mold is provided with a cooling system (not specifically described, many of which are commonly-known) in order to carry out the cooling process of the casting. The four steps A to D take place each at different times in the five or more adjoining lines 20, 22, 24, 26 and 28, so as to thereby be enabled to share a single respective robot device for each respective process step among the lines. Referring to figures 1, 2 and 3, numerals 10, 12, 14, 16 and 18 designate a set of five aluminum alloy casting semi-permanent molds, for example molds for producing automotive cylinder heads. Each mold, carried in a respective wheeled cradle 19 (typically in the art referred to as a "bench") , can be positioned at different operation positions: (A), (B), (C) or (D), along a plurality of linear paths, here illustrated and defined in the preferred embodiment by straight dual tracks 20, 22, 24, 26 and 28. Position (E) is an out-of-service maintenance position. A large linked chain 30 serves as a protective carrier in each line for wiring and hoses for compressed air, hydraulic power and cooling water. In the preferred embodiment, each mold cradle 19 is independently driven for example by an electric motor (not all being shown, to simplify the drawings). Any other effective motive device can be used to move and position each mold cradle 19 along its respective track. Position (A) is the first step in the casting cycle initiated for a given mold. This is the position nearest to the operator 32 and is where the mold is cleaned, usually by compressed air, e.g. from probe 34, which alternatively can be automated, and is also inspected and cleaned as necessary to prevent any defects due, for example, to the presence of extraneous matter in the mold. After this operation at position (A) is performed, the mold is moved to position (B) where the sand core(s) 36 is placed inside the mold by means of robot arm 38. By running along overhead rail 40, the robot arm 38, with its gripping device 42, places the core(s) 36 obtained from core baskets 44 in turn into each of the molds, 10, 12, 14 16 and 18. The mold is then closed and moved to casting position (C), where it is filled with liquid aluminum taken from holding furnace 46 by means of ladle 64 mounted on robot arm 66. Robot arm 66 similarly runs along its own overhead rail 68, enabling it also to serve each of the four molds in the system, one at a time. After the casting and cooling cycle, the mold is moved back to position (D), where the casting 48 is withdrawn from the mold by means of an extractor/holding device 50 mounted on robot arm 52 running along overhead rail 51. Fumes evolving during the casting and extraction operations are withdrawn through suitable conduits not shown, when casting is being carried out. Fume conduits 54 are suitably provided for each mold at the positions where fumes and vapors evolve. Once the casting 48 is extracted from the mold by robot arm 52, it can be further processed off-line, if required, typically as follows: the casting 48, initially delivered by robot arm 52 along rail 51 to station 56, where the bulk of the residuum of the sand cores 36 is removed, it is then moved along to station 58, where the excess aluminum alloy material solidified in the runners and top of the casting is cut and removed, then to quench tank 60 for quenching, then onto inspection table 62, and finally after inspection, it is placed in one of baskets 64 to continue any following heat treating and/or finishing processes. The casting system claimed herein provides a number of advantages over the prior art, for example the capital cost is considerably lower, on the order of 40% less than the cost of the systems comprising rotating tables with 5 molds on each table. The amount of equipment parts and installation time is lower too. Maintenance costs are reduced because the individual moving molds of this system according to the present invention have a smaller mass to be moved along the successive processing positions of each casting cycle. The overall productivity is increased, because if one of the molds is subject to failure or requires to be changed, the other molds respectively moving along the other parallel production lines can continue their production cycle. Conversely, with the rotating tables, when one mold stops the production of the other molds is also interrupted. Energy costs are also reduced, again because the moving equipment is lighter than the mass of the rotating tables. The productivity of the system is also increased by reason of the shorter cycle time for moving each mold to the different positions as compared to the cycle time taken for the rotating tables to accelerate, rotate (typically about 36° to 72°) and brake to stop a massive structure of about 50 metric tons at the respective production positions. The multiple in-line moving molds system provides also the capability of simultaneously producing two or more different products. Although the invention has been exemplified showing a system having five molds, it will be evident that at least two molds can be operated and that more than five molds can also provide the advantages of the invention, especially if the mold casting operation has more or less than 4 automatable processing steps. Also, the core setting can be done manually or combined with a robot arm in case products are being cast from two or more molds. Also, if applied to permanent molds, there would be no need for setting expendable cores, so step B could be eliminated. The thus simplified invention would still be advantageous over the current practices in this art. Although the invention has been described as a preferred embodiment comprising five molds, a second embodiment is also illustrated with reference to figures 4 and 5 wherein the casting system has only four molds oriented differently, so that the operator is given a wider access to the whole area of the mold. In these figures 4 and 5 the location of some other elements has been modified but preserving the essential feature of the invention, i.e. that each mold moves in a substantially straight line and that said molds are positioned in certain positions located in said linear tracks for carrying out the operations of the casting cycle for fabrication of aluminum castings. For convenience and simplification of this description, the same numerals used in figures 4 and 5 designate similar or equivalent elements as in figures 1, 2 and 3. The description of figures 1 to 3 also applies to the embodiment shown in figures 4 and 5, with the characteristic of having only four molds in a different orientation. Also, in figures 4 and 5 the positions of the molds have been shown with dotted lines on the same track to show the movement thereof without implying that several molds move on the same track. If it of course to be understood that the foregoing description is intended to be illustrative only and that numerous changes can be made in the structure of the system described and its operating conditions without departing from the spirit of the invention as ultimately defined in the claims.

Claims: Method of manufacturing aluminum alloy castings (48) comprising: using a system having a plurality of movable molds (10, 12, 14, 16, 18) and only one liquid aluminum holding furnace (46) in said system, said system including at least a casting position (C) and a casting extraction position (D) in a respective linear path of each movable mold, said method further comprising moving said molds along the respective linear path (20, 22, 24, 26, 28) for each mold, whereby each of said molds can be successively positioned at predetermined processing positions (A, B, C, D, E) in its respective mold path according to a scheduled order of process steps for manufacturing said aluminum alloy castings, cyclically positioning each of said molds at its respective predetermined processing positions (A, B, C, D) in its respective path at different times for each of said molds, so that an operation of filling said molds with liquid aluminum to form a casting can be done only on one of the molds at a given time and an operation of extracting said castings from the molds can be done only on one of the molds of said system at a given time. Method according to claim 1, wherein said operation of filling and said operation of extracting each are carried out only on one of the molds at a given time. Method according to any of claims 1 or 2, further comprising an operation of core setting. Method according to any of the preceding claims, further comprising an operation of mold cleaning. Method according to any of the preceding claims, wherein said operation of filling, said operation of extracting and/or said operation of core setting is carried out by robots (66, 52, 38). Method according to claim 5, wherein said robots (66, 52, 38) move along robot paths (68, 51, 40) crossing the linear paths (20, 22, 24, 26, 28) of the molds thus defining processing positions at the intersections of the crossing robot and mold paths. Method according to any of the preceding claims, wherein the processing positions (A, B, C, D) of said molds are linearly staggered. Apparatus for producing aluminum alloy castings (48) in a system comprising: a plurality of molds (10, 12, 14, 16, 18), only one liquid aluminum holding furnace (46) serving all molds in said system, a plurality of linear independent mold paths (20, 22, 24, 26, 28) along which each mold is respectively moved and positioned at predetermined processing positions (A, B, C, D, E) in its corresponding path, at least two linear robots: one (66) for filling said molds with said liquid aluminum and the other (52) for extracting the casting from the mold, said linear robots being movable along a respective robot path (68, 51) which intercepts the paths of the molds at the casting positions (C) and at the extracting positions (D), respectively; and means (19, 30) for cyclically positioning said molds at predetermined positions (A, B, C, D) in their respective paths at different times so that filling of said molds with liquid aluminum, and said casting extraction can be done only on one of the plurality of molds at a time. Apparatus according to claim 8, wherein further comprising a core setting position (B). Apparatus according to any of claims 8 or 9, further comprising a mold cleaning position (A). Apparatus according to any of claims 8 to 10, further comprising a robot (38) for carrying out said operation of core setting. Apparatus according to any of claims 8 to 11, wherein said robots (66, 52, 38) are movable along robot paths (68, 51, 40) crossing the linear paths (20, 22, 24, 26, 28) of the molds thus defining processing positions at the intersections of the crossing robot and mold paths. Apparatus according to any of claims 8 to 12, wherein the processing positions (A, B, C, D) of said molds are linearly staggered.

Inventors: CARRILLO-CANTU DAVID HUGO, GARZA-ONDARZA OSCAR, OCHOA-RODRIGUEZ OCTAVIO JUAN, SALINAS-PENA GERARDO, CARRILLO-CANTU, DAVID HUGO, GARZA-ONDARZA, OSCAR, OCHOA-RODRIGUEZ, OCTAVIO JUAN, SALINAS-PENA, GERARDO
Applicants: TENEDORA NEMAK S A DE C V, TENEDORA NEMAK, S.A. DE C.V.
Application year: 1996
Main classification: B22D47
IPC codes: B22D47