WO2003090951A1

WO2003090951A1 - Method for making a mould

Info

Publication number: WO2003090951A1
Application number: PCT/SE2003/000667
Authority: WO
Inventors: Dag Hersle
Original assignee: Koncentra Holding Ab
Priority date: 2002-04-26
Filing date: 2003-04-25
Publication date: 2003-11-06
Also published as: SE0201302D0; SE0201302L; AU2003224573A1

Abstract

This invention relates to a method of making a sand mould (1) for casting at least one piston ring blank. The method comprises the steps of: forming a mixture of sand and a hardening binder, filling a mould jacket (2) with a sufficient amount of said mixture, forming said mixture in said jacket (2) to a desired density and with at least one planar surface, allowing for said mixture to cure, applying an axially rotating cutting device (5) to the mixture in substantially normal direction relative to said planar surface, pressing said axially rotating cutting device (5) into the mixture, moving said axially rotating cutting device (5) in at least a generally cylindrical path, relative to said planar surface, within said jacket for providing a groove (3) between a wall (4a) and a core (4b) of said mixture.

Description

METHOD FOR MAKING A MOULD

Field of the Invention

The present invention relates to a method of making a sand mould for use in casting operations of a piston ring blank.

Technical Background

There exists various methods in the art for producing a sand mould for use in casting operations. A casting mould prepared from sand is widely used in making a casting with metallic material, such as cast iron.

Depending on the design of the sand mould, it may be used in casting articles not only with metallic material, but with ceramic material, plastic material, etc. The produced casting moulds, particularly those intended for metal casting normally have, apart from the compensation for shrinkage, the same kind of geometry as the desired castings .

One method for producing a sand mould is practised by the use of a master pattern which is replica of a desired casting. The master pattern may either be composed of a plurality of pattern construction parts or of a one-piece pattern construction part. Such pattern construction parts are typically made of wood, plastic or aluminium. The pattern construction is pressed down in a bed of sand and afterwards pulled out of the sand leaving a cavity of a desired casting shape in the mould. An unnecessary portion of sand is removed and the sand mould is left to harden before casting begins.

A second way is to arrange the pattern construction parts in jacket and fill the remaining space with a sand mixture. The sand mixture is allowed to harden and after the hardening the pattern construction part is pulled out. For preventing any collapses, when the pattern construction part or pattern construction parts are taken out of the sand, the pattern construction parts generally describe a draft angle of one or a couple of degrees.

For one-time moulding, prototype casting purposes or the like, a one-time pattern construction is often used. The pattern construction is preferably made of, for example, plastic foam or wax. The plastic foam or wax are cut or even machined to obtain the desired geometry. The one-time mould is typically covered with sand and the cast is being poured into the sand mould and the one-time mould melts. In this case it is possible to make the casting mould without any draft angles. There exist other methods for prototype casting, which are normally not considered by a man skilled in the art of making piston rings since the demands in production regarding precision and accuracy are such that these methods are not sufficient or even suitable for use in production.

The problems with these known techniques are that the casting moulds may result expensive and require a relatively long production and set-up time, which often involve steps that require a lot of labour.

An other issue is related to the use of pattern construction parts or insert moulds for a specific desired geometry of the resulting casting, but made with a different cast material with different material characteristics from occasion to occasion. The differences can be due to different solidification, absorption and shrinkage characteristics.

For piston rings and particularly for large piston rings intended for marine diesel engines, which piston rings have high demands on the material properties and are generally to be provided in a wide range of different sizes, the use of pattern construction parts is especially an issue. It is realized from the above mentioned issues that there is a need for many alternative pattern construction parts in today's moulding techniques for the manufacture of piston rings. Additionally, the draft angles of the moulds used in production methods more directed to series fabrication leads to an increased demand of cast material. Not only does this require more post treatment of the casting in order to enable a casting with the desired shape, but it also generates waste material. The constantly increased demands on material characteristics for piston rings sometimes makes it desirable to use more exclusive materials. When using more exclusive materials, there is risk for a highly increased cost due to the waste material generated during the manufacturing process.

Furthermore, there are limitations in such techniques for making adjustments and alterations and also on the durability of the mould. As a result the demand for storing space, for moulds and other pattern construction parts not currently in use, is often a significant problem for the manufacturer.

Quite often, such pattern construction parts are heavy and cumbersome to handle, which is especially an issue for workers having to deal with these parts during manufacture of a mould.

At present there is a strong need for resolving the above issues and provide an effective and flexible method for making sand moulds for casting of piston ring blanks. It is thus desirable for many reasons, bearing in mind the requirements for precision and quality to provide an improved method for making sand moulds for use in casting piston rings or piston ring blanks.

Summary of the Invention

The object of the present invention is to provide a method of making a mould that overcomes the above issues, and present a method which is fast, flexible and allow for proper accuracy during casting. A further object of the present invention is to provide a method for making a sand mould suitable for the casting of piston rings, which method is flexible and provides for effective use of cast material.

It is still a further object to reduce the need for a specific pattern construction part or parts for each type of casting geometry and material.

These and other objects are achieved by a method according to claim 1. Preferred embodiments of the invention are defined in the dependent claims.

According to the method of making a sand mould for casting at least one piston ring blank, comprising the steps of : forming a mixture of sand and a hardening binder, filling a mould jacket with a sufficient amount of said mixture, forming said mixture in said jacket to a desired density and with at least one planar surface, allowing for said mixture to cure, applying an axially rotating cutting device to the mixture in substantially normal direction relative to said planar surface, pressing said axially rotating cutting device into the mixture, moving said axially rotating cutting device in at least a generally cylindrical path, relative to said planar surface, within said jacket for providing a groove between a wall and a core of said mixture.

The method according to the invention provides for the making of a mould in a manner which is effective, flexible and allow for proper accuracy of the resulting casting. The groove is the generated cavity intended for said piston ring to be produced in said jacket. The inventive method also enables to reduce the need for a specific pattern construction part or parts for each type of casting geometry and material and hence an effective use of cast material is possible.

Preferably, said wall and said core of said mixture is being formed simultaneously by said axially rotating cutting device. This provides a method of making a sand mould which is fast and doe not involve the complex handling of pattern construction parts. Suitably, the diameter of said axially rotating cutting device correspond to the desired diameter of the groove. Preferably, a control unit is being used for controlling the movement of said axially rotating cutting device. Furthermore, said control unit is being used for controlling the movement of said axially rotating cutting device tri-axially. Thus, proper accuracy of the mould can be controlled in a rational and flexible manner.

According to a preferred method a control unit is being used for controlling the depth of said groove based on information on the number of piston rings to be made from the piston ring blank which is to be produced in said jacket. In addition a control unit is being used for controlling the shape of said groove based on information on the geometry of the piston ring blank to be produced in said jacket. Furthermore, said control unit is being used for controlling the shape of said groove based on information on the material characteristics of said piston ring blank to be produced in said jacket.

It is realized that by providing relevant data to the control unit the manufacturing of the mould can be controlled in a more automatized manner. Furthermore, a flexible manufacturing process is achieved since it enables, for example, the desired shape of the groove to be desired just before the making of the groove will take place. The information is preferably stored in a database which is connectable to the control unit. The result of the following casting is also preferably stored in said database together with the data for controlling the making of the mould in order to enable further control of the quality. The parameters in the database can easily be altered if it is desirable to make corrections for better results. It is also possible by the inventive method to account for the exact number of piston rings in a batch and adjust the groove shape in the necessary moulds so that not more material than necessary is used during casting.

Suitably, said method comprises the step of removing machined or residual mixture from said groove or said sand mould. This is desirable so that the machined sand will not interfere with the following casting operation.

According to a preferred method of the invention said mould jacket comprises a mould insert part for reducing the amount of said mixture for filling the jacket. Preferably, a control unit is being used for controlling said axially rotating cutting device for providing additional indentations in said mixture. This enables a smaller amount of mixture to be used or to generate a more complex form of the mould. Most commonly, indentations are made in order to facilitate the following handling of said piston ring blank, which is to be produced in said jacket.

Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention.

Brief Description of the Drawings

A currently preferred embodiment of the present method will now be described in more detail, with reference to the accompanying drawings .

Fig. 1 presents an example of a production system for performing the method according to the invention.

Fig. 2 presents an example of the production system in fig 1 during manufacture of a mould.

Detailed Description of Preferred Embodiments Referring now to Fig. 1, wherein the basic elements of a device for performing the inventive method is disclosed. A sand mould 1 comprising a mixture of sand and a hardening binder. Said sand mould is fitted in a mould jacket 2. The mould jacket is e.g. made of metal. The sand mixture suitably comprises at least one of the following sand material chosen from the group consisting of: silicate sand, green sand, black sand and furan sand. According to a preferred method, a processing machine 10, such as, a numerical controlled milling machine is used. Said processing machine 10 preferably comprises a control unit 9, which controls a movably fitted tri -axial apparatus 7 for moving an axially rotating cutting device 5. The axially rotating cutting device 5 is fitted in a subframe 8 of the tri-axial apparatus 7. The axially rotating cutting device 5 is preferably a milling device with a shank-end mill fitted with index able inserts. The index able inserts are preferably bare cutting edges made of hard metal and arranged axially spaced along a tool-shank of the milling device. For milling, a number of revolutions of the axially rotating cutting device of more than 1500 rpm is suitable.

In accordance with a preferred method for making a sand mould, for casting of a piston ring blank, the jacket 2 is now filled with the sand mixture. The mixture is preferably vibrated resulting in a substantially horizontally planar surface of the mixture in said jacket 2. The mixture is left for a time to cure and to become more solid. The axially rotating cutting device 5 fitted to the subframe 8 of the processing machine 10 is vertically immersed in the mixture. The axially rotating cutting device 5 is moved along a cylindrical path to mill a groove 3 in said mixture. The resulting groove is then surrounded by a sidewall 4a of mixture. The resulting groove further encompassing on the inner side a core 4b essentially consisting of the mixture. The milled sand or residual sand is preferably removed by a suction tube 6 or other kind of suitable remover device. The groove 3 now constitutes the geometrical form of the sand mould 1, which is to be filled with a casting.

The sand mould according to a preferred embodiment is suitably also provided with indentations 11, preferably by the upper part of the groove. The indentations 11 are made by controlled movement of the cutting device 5 . Such indentations 11 are used to enable better handling possibilities of the casting after the moulding step. The sides of the groove are conveniently blackened in order to enable a better and more uniform surface of the resulting casting.

The processing machine 10, although not disclosed in the drawings can of course be some kind of industrial robot provided with the axially rotating cutting device 5. The industrial robot can also be arranged on a track for moving the robot to different sand moulds and different operating positions for enabling flexible production.

For realizing a flexible production, the sand moulds waiting to be machined is suitably arranged in a pallet magazine system with conveyors.

The control unit 9 is suitably connected with a computer system, such as a CAD/CAM-system, for an effective operation. This kind of system also gives opportunities to consider parameters such as, solidification, absorption and shrink characteristics in more detail and with a high degree of flexibility. Alternatively, said jacket 2 is arranged to be moved in relation to said axially rotating cutting device 5 for providing said groove 3. The jacket 2 can, before being filled with mixture, be provided with different kinds of mould insert parts for reducing the necessary amount of said mixture . The insert parts can be located in said core 4b and/or in said wall 4a. The method can, for instance, be performed with the jacket upside-down when generating said groove 3 for an alternative removal of the machined or residual sand/mixture .

The processing machine 10 can also be provided with a plurality of axially rotating cutting devices 5.

Claims

1. A method of making a sand mould (1) , for casting of at least one piston ring blank, comprising the steps of: forming a mixture of sand and a hardening binder, filling a mould jacket (2) with a sufficient amount of said mixture, forming said mixture in said jacket (2) to a desired density and with at least one planar surface, allowing for said mixture to cure, applying an axially rotating cutting device (5) to the mixture in substantially normal direction relative to said planar surface, pressing said axially rotating cutting device (5) into the mixture, moving said axially rotating cutting device (5) in at least a generally cylindrical path, relative to said planar surface, within said jacket for providing a groove (3) between a wall (4a) and a core (4b) of said mixture.

2. The method according to claim 1, wherein said wall and said core of said mixture is being formed simultaneously by said axially rotating cutting device (5) .

3. The method according to any one of claims 1-2, wherein a control unit (9) is being used for controlling the movement of said axially rotating cutting device (5) .

4. The method according to claim3 , wherein said control unit (9) is being used for controlling the movement of said axially rotating cutting device (5) tri- axially .

5. The method according to any one of claims 3-4, wherein said control unit (9) is being used for controlling the depth of said groove (3) based on information on the number of piston rings to be made from the piston ring blank which is to be produced in said jacket (2) .

6. The method according to any one of claims 3-5, wherein said control unit (9) is being used for controlling the shape of said groove based on information on the geometry of the piston ring blank to be produced in said jacket (2) .

7. The method according to any one of claims 3-6, wherein said control unit (9) is being used for controlling the shape of said groove (3) based on information on the material characteristics of said piston ring blank to be produced in said jacket (2).

8. The method according to any one of claims 1-7, wherein said method comprises the step of removing machined or residual mixture from said groove (3) or said sand mould (1) .

9. The method according to any one of claims 1-8, wherein said mould jacket (2) comprises a mould insert part for reducing the amount of said mixture.

10. The method according to any one of claims 1-9, wherein said axially rotating cutting device (5) has a diameter exceeding the thickness of said piston ring to be produced from said piston ring blank.

11. The method according to any one of claims 3-10, wherein said control unit (9) is being used for controlling said axially rotating cutting device (5) for providing additional indentations (11) in said mixture.

12. The method according to any one of claims 1-11, wherein said jacket (2) is moved in relation to said axially rotating cutting device (5) for providing said groove (3) .