Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1992-08-03
1993-10-26
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
425556, 425438, 425444, B29C 4540, B29C 4542
Patent
active
052563642
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for demolding a molded part from a mold of the type specified in the preamble of claim 1, as well as a device for carrying out the process.
In principle, the invention can be used in the case of all molding processes in which a molded part of any material is molded in a mold and is then removed from the opened mold; preferred area of application is the production of plastics molded parts by injection molding. The complete sequence of demolding a molded part comprises the opening of the mold, the moving-in of a gripping tool, which belongs to a handling unit, robot, manipulator or the like, between the opened mold halves, the ejection of the molded part by means of the ejector elements from the one mold half until gripping by the gripping tool, and the subsequent moving of the gripping tool with the gripped molded part out of the area of the mold. To be able to operate the molding machine, for example an injection-molding machine, with as high a number of cycles as possible, the said demolding operations should proceed at the greatest possible speed. The ejection speed at which the molded part is moved out of the mold half is, however, assigned limits, since an excessive ejection speed can result in the molded part being damaged. This applies in particular in the case of molded parts of large surface area, in the case of which great forces of adhesion and suction occur between the molded part and the corresponding mold walls. The risk of damage also depends on how thin-walled the workpiece is and at how many points it is gripped and supported by the ejector elements. The ejection of the molded part must be performed in such a way that it is not damaged, in particular by overcoming the adhesion between the molded part and the mold walls, and by accelerating the molded part. Here the ejection must be performed slowly enough to avoid an unacceptably high negative pressure between molded part and mold walls.
The invention is based on the object of specifying a process and a device by which the entire demolding operation can be carried out in a shorter time, but nevertheless without unacceptable stressing of the molded part.
This object is achieved according to the invention by the process specified in claim 1. The subclaims specify further advantageous features of the process according to the invention and a device for carrying out the process.
Since, in the case of the process according to the invention, the molded part is only moved into an intermediate position in the first partial stroke, in particular such a position in which it does not hinder the moving-in movement of the gripping tool, this first partial stroke can be commenced before the moving-in of the gripping tool and even before completion of the opening movement of the mold. Consequently, an adequate time is available for this first partial stroke, so that this first partial stroke can be carried out at low speed and therefore gently for the molded part. In this first partial stroke, it is essentially intended that a detaching and freeing of the main surfaces of the molded part from the corresponding mold walls take place, overcoming the forces of adhesion. After moving the gripping tool in, the second partial stroke of the ejecting movement can then be carried out in a very short time, because on the one hand only a remaining path distance still has to be covered and on the other hand the molded part already detached from the mold walls can be moved without risk at higher speed. By virtue of the gentle ejecting operation, it is also possible to work with relatively few ejector elements even in the case of sensitive and thin-walled molded parts.
An embodiment of the invention is explained in further detail with reference to the drawings, in which:
FIG. 1(a)-1(e) shows a diagrammatically simplified representation of the various phases of the demolding operation in the case of the process according to the invention;
FIG. 2 shows a section through the device according to the invention in the intermediate position o
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