TEMPERATURE-DEPENDENT RELEASING FROM FORM

[0001] TEMPERATURE-DEPENDENT RELEASING FROM FORM

[0002] Technical area

[0003] The invention concerns a procedure and a control .zur determination of one point of mold release sequence with the injection moulding of amorphous and part-crystalline thermoplastics in accordance with generic term of the first patent claim.

[0004] Conditions of the technology

[0005] Amorphous and part-crystalline thermoplastics are used in many applications. Examples of products of such materials cover shaped parts such as housings for many devices such as mobile phones or computers as well as all kinds of plastic-good for household and hobby.

[0006] With the spraying casting process liquid thermoplastics are brought into a hollow tool, whose recess, also mentioned, exhibits cavity the form of a part which can be manufactured.

After the cavity is filled, follows the cooling period, which is necessary, in order to cool the part down form-stably on the necessary releasing from form temperature. Afterwards the forming tool is opened, which manufactures shaped part is taken and a new cycle can begun.

[0007] The shaped part may not be taken to early its forming tool, since it can itself otherwise afterwards forgiven. Further possible disadvantages of a too early withdrawal cover a possible unfavorable shrinking behavior, shaped part instabilities as well as a reduction in quality of the surface quality. If a before determined tolerance of the accuracy to size, which can be measured with teachings, one exceeds, the shaped part must be disposed of. This means that apart from the manufacturing costs still disposal costs result for a not salesable shaped part.

Therefore the shaped part is left longer during a so-called safety time, which is rather generously limited, in the forming tool than necessary. Thus the production time and the productivity of the manufacture process extend decrease.

[0008] The optimal point of mold release sequence is very difficult to determine. Most injection moulding machines possess a control, which introduces the releasing from form procedure after a freely selectable cooling period. This cooling period is entered before beginning of manufacturing and remains usually unchanged during the entire manufacturing. During a production disturbance, an interruption as well as with increased fluctuations of the processing parameters this can affect unfavorably the quality of the shaped part. Already a small variation of process parameters can change the necessary cooling period.

A degradation of the shaped part quality can be justified both in a change of the thermal household within the shaped part and in fluctuations of the form internal pressure.

[0009] Well-known methods are concerned with the determination of the point of mold release sequence by means of printing regulations. In the following the thermal conditions are examined. Representation of the invention

[0010] Task of the available invention is it to indicate a procedure which determines the point of optimal mold release sequence of shaped parts in forming tools by means of temperature measurements. This optimal time is, regardless of variances in the process parameters, which frühest in each case possible time of releasing from form its, which the necessary shaped part stability and the accuracy to size of a shaped part as well as other shaped part characteristics ensure.

Besides a control is to be indicated, by means of which the indicated procedure can be accomplished.

[0011] The task solved by the characteristics of the independent patent claim.

[0012] The procedure according to invention consists of the following steps: For the time being in at least one place at the shaped part due to the there wall thickness and geometry and due to the material parameters of the thermoplastic as well as the tool material and a releasing from form temperature is specified to the processing parameters. This releasing from form temperature corresponds to the temperature, which predominates to the optimal point of mold release sequence here, averaged over the wall thickness of the shaped part. During injecting with the spraying casting procedure the tool wall temperature is based on the appropriate place of the shaped part.

From the measured temperature leap during injecting with the spraying casting procedure at the beginning of the cooling one computes, at which time the releasing from form temperature is reached. As soon as this time enters, a signal is produced, which introduces releasing from form. A control according to invention knows the procedure described here would drive out. Short description of the designs

[0013] In the following the invention under Beizug of the designs is more near explained.

Show

[0014] Fig. 1 a schematic representation of a structure of a forming tool for the production of shaped parts;

[0015] Fig. 2 a graphic schematic representation of a measured wall temperature;

[0016] Fig. 3 a graphic schematic representation of temperature gradients in the cross section of the shaped part at different times;

[0017] Fig. 4 a graphic schematic representation of the process of a computed mass temperature.

[0018] Ways to the execution of the invention

[0019] The Fig. 1 shows two tool tools of 1, 1 ' of a spraying casting tool with an internal outline of the tool inner wall 3, whereby this 'outline defines a cavity 2, which the form of a shaped part which can be manufactured corresponds.

With the injection moulding the amorphous or part-crystalline thermoplastic fills out this cavity 2 to the outline of the tool inner wall 3 and solidifies afterwards slowly. In order to accelerate the cooling, the tool parts of 1, 1 are cooled '. During the cooling in the shaped part 2 the warmth is led slowly by the center of the shaped part to the external wall, thus to the tool inner wall 3. The necessary cooling down time therefore increases with the wall thickness s of the shaped part. The warmest places are in each case in the centers of local Verdickungen.

[0020] For the erfindungsgemasse procedure protecting injecting the thermoplastic into the Kavitat at a suitable place at the tool inner wall 3 the temperature is measured by means of a temperature sensor 4 attached for it.

In addition as temperature sensor 4 a tool wall temperature sensor is used, which exhibits a very fast response time, preferably within the range of milliseconds. Suitably for example sensors of the company are Kistler with the designation 6190, 6192, 6193 and 6194. The assembly place of the temperature sensor 4 should be selected in a place, in which the slowest cooling of the shaped part is to be expected 2. Also several temperature sensors 4 can be attached to different places of the outline of the tool inner wall 3.

[0021] The temperature sensor 4 measures the wall temperature powerplant at the measuring point protecting injection. Fig. a schematic process of a measured temperature curve in the period of injection ton shows 2.

As soon as the thermoplastic reached the place of the temperature sensor 4, the measured wall temperature powerplant rises precipitously from the cooled wall temperature ton to the contact temperature T. Afterwards drop this wall temperature by the cooling in the tool again slowly. The measured temperature leap is used for the further computation of the point of mold release sequence Te. Furthermore for this computation materials dates of the tool and materials dates of the thermoplastic are necessary.

[0022] Of the two materials in each case the Warmeeindringfahigkeit German Federal Armed Forces of the tool material and CBM of the injected thermoplastic must admits to be. A Warmeeindringfahigkeit b is calculated by the root of the product of the three factors heat conductivity, for density p and heat conductivity, density p and specific thermal capacity Cp.

Due to the formula

[0023] T = (TM, o <-> CBM + T0 <-> b ")/(CBM + German Federal Armed Forces)

[0024] leave yourself the only unknown quantity TM, o? the mass temperature of the thermoplastic, for the time of injection t0 intend.

[0025] The definition of the mass temperature TM of the thermoplastic leave yourself with the help of the Fig. 3 describe. In the shaped part 2 between the tool parts of 1 and 1 ' the cross section temperatures TQ, o TQ, i and TQ/2 are indicated to t2 as functions of the cross section process of the wall thickness s at different times tons, ti and.

The temperatures of these averaged over the cross section s run TQ, o, TQ/i and TQ, 2 are indicated as mass temperatures TM, 0, TM, i and TM, 2 at the respective times t0, ti and t2.

[0026] From the determined mass temperature of the thermoplastic at present injection TM, o let yourself in a further step the necessary Abkuhlzeit and thus the optimal point of mold release sequence Te determine. The materials dates benotigten for it cover zusatzlich to the already necessary Warmeeindringfahigkeit b and the wall thickness s the Temperaturleitfahigkeit A of the thermoplastic.

This Temperaturleitfahigkeit A let yourself from the quotient determine, which is formed divided by the warm line by the product of the density p with the specific thermal capacity cp.

[0027] The computed cooling of the mass temperature TM in the course is in schematic representation in the Fig. 4 represented. The mass temperature TM constantly cools down and falls finally to the value of the releasing from form temperature width unit. This Abkuhlkurve computational leave yourself with retained formulas he memo in. The point of mold release sequence Te is reached, as soon as the mass temperature is larger TM no longer than the releasing from form temperature width unit.

[0028] According to invention the descriptive procedure can be implemented by a control. Preferably this control is integrated into the process control of the injection moulding procedure.

This control preferably has a data base, in which the necessary material parameters are already stored by a multiplicity of possible thermoplastics as well as of tool materials. This data base can of course be also extended by the user. Under indication of the wall thickness and if necessary further process parameter can also the releasing from form temperature width unit be determined.

[0029] First a suitable measuring point at the tool is selected, at which a temperature sensor (4) one attaches. A place is selected, with which the slowest cooling is to be expected. In the case of doubt temperature sensors (4) can to be attached at several measuring points.

It is important that these temperature sensors have (4) a very fast response time.

[0030] Before with the production of the shaped parts one begins, the materials dates become as well as the wall thickness s into the control entered and the releasing from form temperature width unit determines and/or fixed.

[0031] The procedure according to invention measures now with each production cycle the temperature rise at or in the cavity wall during the injection of the thermoplastic T0, T into the tool at a representative place at or in the cavity wall and computes thereupon directly, under whom-fertilize the entered materials dates (CBM, German Federal Armed Forces, A, width unit) and the wall thickness s, the necessary point of mold release sequence Te.

As soon as this point of mold release sequence Te entered, a signal is produced for the introduction of releasing from form.

[0032] The advantage of this procedure consists of the fact that, independently of process disturbances and interruptions, which stays to shaped part not unnecessarily for a long time in the tool and thus the productivity of the plant reduces. On the other hand the danger does not exist that the shaped part suffers by a too short cooling down time quality A BUSEs.

Since the necessary cooling time is again determined with each cycle, both slow and small changes, for example changes of the ambient temperature, are always carried and sudden and substantial changes, for example caused by a process disturbance, for calculation.

[0033] Reference symbol list

[0034] s wall thickness of the shaped part with the measuring point t course ton time of the contact of the injection mass at the measuring point ti, t2 times during the cooling phase Te - point of mold release sequence

[0035] T temperature

[0036] Powerplant (t) measured wall temperature at the measuring point during injection

[0037] Ton of wall temperature directly before the contact that

[0038] Injection mass at the measuring point

[0039] T wall temperature immediately after the contact with the injection mass

[0040] TQ, ton of i TQ, ti, temperature gradients in the cross section of the shaped part

[0041] TQ, t2 at the times t0, ti and t

[0042] TM, o t TM, i, mass temperatures:

Middle cross section annealing at, 2 t TM (E turen, thus average values of the temperature gradients in the cross section of the shaped part at the times tons, ti, t2 and Te

[0043] TM (t) process of the mass temperature over the time

[0044] Width unit releasing from form temperature: Maximally certified middle cross section temperature of the thermoplastic with releasing b from form, German Federal Armed Forces, CBM heat penetrating ability of the tool respectable the injection mass A thermal diffusivity of the thermoplastic

[0045] 1, 1 ' tool parts

[0046] 2 recess for shaped part; Shaped part

[0047] 3 outline of the tool inner wall

[0048] 4 temperature sensor