Gravity casting method in a chill mould pivotable by a robot-controlled hydraulic axis

Abstract

 The present invention relates to a gravity casting method by a robot, wherein a molten metal is cast by the robot into the chill while the latter carries out a pivoting on its axis by a hydraulic actuator, wherein the robot follows a previously set trajectory and detects the chill position by an encoder associated to the hydraulic pivoting axis, compares it to the casting cup position and, on the basis of the difference between said two values of position, acts on the flow rate of the fluid fed to the hydraulic actuator for accelerating or slowing down the rotation of said hydraulic axis. The invention also relates to a hydraulic axis for the rotation of the chill in the chilling process served by the robot, characterised in that it is controlled by a proportional valve controlled by the robot for adjusting the speed of rotation of the chill.

Description

Field of application

[0001] The present invention relates to the field of gravity casting systems and in particular, it refers to a new method for casting a molten material by a robot into a chill, whose horizontal pivoting motion is actuated by a hydraulic axis controlled by the robot.

Prior Art

[0002] As known, the chilling process provides for the molten material to be cast into the chill while the latter is rotating, generally by 90°, on a hydraulically controlled axis. The casting may be carried out either manually by an operator, or in automatic mode by a robot. In both cases, the cup containing the molten material must follow the rotation of the chill and rotate simultaneously. The speed of revolution of the chill is set on the basis of the type of metal used and of the piece to be obtained, but it can undergo alterations due to several factors, such as for example the room temperature, the features of the fluid used for the hydraulic actuator, etc., and it is therefore changeable according to the chilling process or even into a same chilling process. Then, in case a robot is used, the trajectory it must follow is divided into a multiplicity of intervals, and when the robot reaches each of them, it compares its own position with that of the chill, detected by an encoder, calculates any errors, and derives a new transfer function accordingly, to apply it to its driving axes for the next interval, so as to keep such error into account and cancel it.

[0003] In other words, the robot tracks the chill. Such tracking system is efficient when the chilling process takes place over relatively long periods, for example as it happens for aluminium alloys, but it has proved unsuitable for faster processes, as required for casting brass, since the time required by the robot to perform the complex computations mentioned above imply a discontinuous motion of the robot system that is not acceptable for the casting process.

Objects and summary of the invention

[0004] Object of the present invention is that of proposing a new method of chill casting where the chill is served by robots, which should allow a perfect synchronisation between the cup containing the molten material and the chill, also in fast casting processes.

[0005] Another object of the finding is that of providing a hydraulic axis for the rotation of the chill in chilling processes carried out by a robot, which should allow obtaining rotations of the chill and of the molten material cup perfectly synchronised with one another, without considerably altering the system structure and costs.

[0006] Such objects are achieved by a casting method according to claim 1 and by a relative hydraulic axis according to claim 3.

Brief description of the drawings

[0007] The present invention will be described hereinafter with reference to the attached indicative and non-limiting drawings, wherein:

• Fig. 1 shows a block diagram of the hydraulic axis;
• Fig. 2 shows the control ring of the hydraulic axis; and
• Fig. 3 shows an example of a gravity chilling system.

Detailed description of the invention

[0008] In said drawings, reference numeral 10 schematically indicates a chill pivoting around an axis X by a hydraulic actuator 11. An encoder 12 is associated to said hydraulic axis X for detecting the chill position. The chill is intended to receive a molten metal cast therein from a cup 13 moved by a multiple axis robot, globally and schematically indicated with reference numeral 14.

[0009] According to the finding, the hydraulic actuator 11 is controlled by a proportional valve 15 controlled by robot 14. The latter, moreover, is capable of detecting the position of chill 10 by encoder 12 and thereby calculate its speed.

[0010] The casting method proposed herein provides for robot 14 to follow a preset trajectory with a predetermined speed, according to the chilling process. The correction of the rotation speed of chill 10 occurs after comparing the position of said chill 10 to the position of cup 13. On the basis of the deviation detected, if any, the robot opens or closes the proportional valve 15 according to whether the chill is still back, and must therefore be accelerated, or has surpassed the cup, and must therefore be slowed down. The calculation of this error requires infinitesimal times, so the correction of the speed of rotation of the chill virtually occurs in real time, thereby meeting the strict requirements of very fast chilling processes.

[0011] In the practice, contrary to what occurs in current chilling processes wherein the robot tracks the chill, in this case the chill tracks the robot, as it can be seen in the control ring diagram shown in Fig. 2. The robot is therefore not forced to constantly recalculate the transfer function to apply to its driving axes, but it follows a preset trajectory.

Claims

1. Gravity casting method by a robot, wherein a metal is cast by the robot into the chill while the latter carries out a pivoting on its axis by a hydraulic actuator, characterised in that the robot

- follows a previously set trajectory; and

- detects the chill position by an encoder associated to the hydraulic pivoting axis, compares it to the casting cup position and, on the basis of the difference between said two values of position, acts on the flow rate of the fluid fed to the hydraulic actuator for accelerating or slowing down the rotation of said hydraulic axis.

2. Method according to claim 1, wherein for acting on the flow rate of the fluid fed to the hydraulic actuator, the robot controls a proportional valve associated to said actuator.

3. Hydraulic axis for the pivoting of a chill for a chilling process served by a robot according to the method of the previous claims, characterised in that it is controlled by a proportional valve controlled by the robot for adjusting the speed of rotation of the chill so as to allow the same to track the robot in real time with appropriate accuracy.

Drawing