Method for detecting insert objects in an injection-moulded part

A method for detecting an insert object in an injection-molded part pertains to an insert object that is fixedly connected to the injection-molded part during the injection molding by the insert object being placed in a cavity, which is surrounded by a mold wall of a mold, before the beginning of the injection-molding cycle. The mold wall includes at least one temperature or pressure sensor, which records and analyzes at least one measured value at at least one point in time during an injection-molding cycle. On the basis of the analysis, it is established whether an insert object was present at a specific location in the cavity during the injection-molding cycle. Finally, after it is ejected, the injection-molded part is sorted as an accepted part or a rejected part on the basis of the analysis of the measured value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application Serial No. PCT/CH2011/000114, filed May 18, 2011, which claims priority to Swiss Application No. CH 786/10 filed May 19, 2010. International Application Serial No. PCT/CH2011/000114 is hereby incorporated herein for all purposes by this reference.

FIELD OF THE INVENTION

The invention pertains to a method for detecting an insert object in an injection-moulded part, wherein the insert object is rigidly connected to the injection-moulded part during the injection moulding process due to the fact that the insert object was placed into a cavity that is surrounded by a mould wall of a mould before the beginning of the injection moulding cycle.

BACKGROUND

In injection moulding processes, insert objects are frequently placed into the cavity in order to provide the injection-moulded product with a certain surface, for example, by means of an externally arranged foil. Examples of such products are yogurt cups or insulin syringes. The surfaces of such insert objects feature, for example, product-specific information, advertising, an expiration date and/or a barcode.

During the manufacture of an injection-moulded part, an error may occur and no insert object or more than one insert object is inadvertently placed into the cavity. A thusly manufactured injection-moulded part needs to be sorted out as a reject part after the manufacture.

A quality control is nowadays carried out after the manufacturing process in order to detect such errors, i.e., in order to determine the presence of an insert object or exactly one insert object. This is realized with the aid of cameras that create images of the finished injection-moulded products. Elaborate analyses of these images ultimately make it possible to determine whether the injection-moulded part features a desired insert object such that the injection-moulded part can be accordingly sorted as an acceptable part or a reject part.

U.S. Pat. No. 5,582,845 discloses a system that optically detects inserts by means of a camera before the injection moulding process is carried out. If the insert is missing, an alarm is activated and the system backs up and obtains an insert in order to correct the error. In DE 202008014027U1, JP 60219017, JP 60068918 and JP 63220967, an insert part likewise is respectively detected prior to the injection moulding process and the process is stopped if it is determined that such an insert part is missing. In this way, the manufacture of defective parts is prevented.

All these methods indeed successfully prevent the manufacture of defective parts without inserts. However, it was determined that the process needs to be started up anew after a machine stop such that other complications may arise, particularly due to varied temperatures of the molten masses, to cite just one example.

In addition, optical methods proved to be problematic because different gray scales need to be reliably evaluated and a complicated evaluation system is required for this purpose.

BRIEF SUMMARY OF THE INVENTION

It is the objective of the present invention to disclose a method of the initially cited type for detecting an insert object in an injection-moulded part which is less elaborate and less costly than known methods. In addition, this method preferably should not disturb the injection moulding process.

This objective is attained with the characteristics described below.

According to the basic principle of the invention, it is initially proposed to arrange at least one temperature sensor or pressure sensor in the mould wall, wherein said sensor records at least one measured value in the form of a temperature or a pressure at least at one point in time during the injection moulding cycle. This measured value is ultimately analyzed. Based on this analysis, it is then determined whether or not an insert object was present at a certain location in the cavity during the injection moulding cycle. After the ejection of the injection-moulded part, it is sorted as an acceptable part or a reject part based on the analysis of the measured value.

The advantage of this method can be seen in that it is already certain whether or not the injection-moulded part is an acceptable part when it is ejected. Consequently, not only a camera and another elaborate analysis are eliminated, but also the required handling of the injection-moulded part after its ejection.

In addition, the manufacturing process is not interrupted for this detection, but the defective part rather is merely sorted out. In many instances, the damage caused by the production of rejects is much lower than an interruption of the process because it is not required to start up the process anew in this case.

Another advantage can be seen in that optical detection systems are replaced with temperature or pressure sensors, the measured values of which can be very easily evaluated. In the inventive method, it is also preferred to carry out the measurement during the injection moulding process. This provides the advantage that the thusly obtained measured values can also be used for the injection moulding process. This means that already existing sensors can be used or that the sensors used may simultaneously serve for controlling the system in certain instances.

Other advantageous methods are described below.

In this document, the terms “acceptable part” or “reject part” refer to the quality in connection with the insert object only. Manufactured injection-moulded parts that indeed correctly feature the insert object naturally may be defective for other reasons and therefore sorted out as reject parts. Acceptable parts ultimately are only the parts that fulfill all stipulated quality requirements.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

FIG. 1shows a cross section through a mould5of an injection moulding system. The mould5consists of two halves that jointly define a cavity3, wherein said cavity is surrounded by a mould wall4. The injection-moulded part2illustrated inFIG. 2is produced in this cavity3during the injection moulding process. For this purpose, a molten mass10in the form of liquid plastic is injected into the cavity3through a gate system9. After the molten mass10has solidified, the two mould halves5are opened in order to remove the finished injection-moulded part2. This concludes an injection moulding cycle.

An insert object1,8can be placed into the cavity3before the two mould halves5are once again joined at the beginning of a new cycle. During the injection of the molten mass10, this insert object1and the molten mass10are connected into an injection-moulded part2.

The inventive method for detecting an insert object1,8in an injection-moulded part2is described below.

According to the invention, at least one sensor6,7is arranged in the mould wall4, wherein said sensor records and analyzes at least one measured value in the form of a temperature or a pressure at least at one point in time during an injection moulding cycle. Based on this analysis, it is then determined whether or not an insert object1,8was present at a certain location in the cavity3during the injection moulding cycle. After the ejection of the injection-moulded part2, it is ultimately sorted as an acceptable part or a reject part based on the analysis of the measured value. However, if an acceptable part should be defective for other reasons such as, for example, insufficient dimensional accuracy, this acceptable part accordingly is also sorted out as reject part. The sorting described herein consequently should be interpreted as presorting.

The advantage of this inventive method is the early detection of an insert object1,8that still takes place during the injection moulding cycle. This eliminates the elaborate handling of the finished injection-moulded part2and the utilization of other recognition devices and analyses before the acceptable parts can ultimately be sorted.

The sensor6,7consists of a temperature sensor6,7or a pressure sensor6,7.

A temperature sensor6,7can determine the presence of the insert object1based on a decelerated increase in temperature at the time, at which the molten mass10arrives at the location of the sensor6,7, if this insert object directly adjoins the mould wall4at the sensor6,7. A pressure sensor6,7is also subjected to a lower increase in pressure and/or a lower maximum pressure during the injection moulding cycle if the insert object1directly adjoins the mould wall4at the sensor6,7. In this way, temperature and pressure sensors6,7can detect insert objects1.

As a general rule, the measured values are recorded during or no later than after the injection process, but always while the injection moulding cycle is still carried out, i.e., before the finished injection-moulded parts are ejected.

The sensors6,7can be installed into the mould wall4in different ways. Both aforementioned sensor types6,7may be installed in an opening toward the cavity3such that they actually define part of the cavity surface. However, they may also be installed in the mould wall4in the immediate vicinity of the cavity3such that they can still measure the pressures and/or heat flows transmitted through the remaining mould wall4with sufficient accuracy for determining the required variations.

It would naturally also be possible to arrange several sensors6,7in the mould wall4, for example, in order to determine if an insert object1,8is also correctly positioned. For example, it can be determined if an insert object1,8is positioned askew in the cavity3or was shifted from the desired position during the injection moulding process by carrying out the detection at key points such as, for example, at all four corners of a rectangular insert object1,8.

It can also be determined if no insert object1,8, exactly one insert object or more than one insert object was present at the respective location in the cavity3during the injection moulding cycle based on the analysis of the recorded measuring data.

Consequently, an injection-moulded part2can also be sorted out as a reject part if several insert objects1were inadvertently placed into the cavity. This can be determined, in particular, based on an excessively slow increase in temperature or an excessively low maximum pressure. This likewise can also be checked where no insert object1,8should be located.

It is frequently advisable to record and analyze several measured values, particularly a measured curve. In this way, it can always be determined which data of a data series needs to be evaluated, namely also if time delays occur during the injection moulding cycle. For example, the maximum pressure over the entire injection moulding cycle can be determined based on the measured curve and compared with reference values. On the other hand, the time, at which the molten mass10arrives, can be determined based on the measuring data by establishing the time, at which the increase in temperature occurs. At this time, an analysis of the measured values is informative with respect to the detection of an insert object1.

During the analysis, measured values or measured curves of all sensors6,7are compared with predetermined nominal ranges. The injection-moulded part2is sorted as an acceptable part if all recorded measured values or measured curves lie within these nominal ranges.

If several sensors6,7are arranged in the mould wall4, it is also possible to detect several insert objects1,8at different locations during the injection moulding cycle. The injection-moulded parts2ultimately are also sorted as acceptable parts or reject parts based on the analysis of these measured values. It is possible, in particular, to arrange identical and/or different sensors6,7in a mould5.

The insert object1may consist, in particular, of a foil on the outside of the injection-moulded part2. Examples of such injection-moulded parts2with foils on their surfaces are plastic packages for the food industry or medications, as well as consumer goods such as pens with advertising printed thereon. In order to obtain recyclable products, the insert objects1preferably consist of the same material as the molten mass for manufacturing the injection-moulded part. Alternative materials include cardboard, paper, aluminum, leather, plastic, metal and textile materials. Other materials naturally can also be used.

Other insert objects8are oversprayed with plastic material such that only a small portion lies on the edge of the cavity3. These insert objects may consist, in particular, of a chip, an LED, a battery, other electronic components and/or electrical lines. If a transparent molten mass10is used, oversprayed insert objects8may also be visible and used, for example, for decorative purposes.

Product-specific information such as the date and place of manufacture may be written on a chip contained in an injection-moulded part. The chip naturally may subsequently also be provided with other information such as, for example, the date of its installation into a machine. This may be important in order to draw conclusions with respect to the period of use, the period of storage, the manufacturer and/or the manufacture in case this injection-moulded part2subsequently fails.

It is preferred to utilize sensors6,7that are simultaneously used for controlling or managing the injection moulding process. This eliminates the need to add other sensors.

LIST OF REFERENCE SYMBOLS

1Insert object adjoining cavity wall2Injection-moulded part3Cavity4Mould wall5Mould6Temperature or pressure sensor, sensor7Temperature or pressure sensor, sensor8Insert object being spaced apart from cavity wall and with only a small portion adjoining the edge9Gate system10Molten mass, plastic mass