JPH0618690B2 - Die element manufacturing method and die element - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to the attachment of die components such as bushings or mandrels. In one aspect, the invention relates to a die having a shaped element. In another aspect, the present invention is directed to a method for accurately determining a die element contour. In yet another aspect, the present invention is a blow molding apparatus.
pparatus). Yet another feature of the invention is a blow-expanded product. Yet another aspect of the present invention relates to a method of approximating the shaping required of a die for an accurately blow molded product.

[Prior Art] Blown expansion processing of plastic products is an advanced technology. The basic way of doing this is by using a blowout body or parison.
n) is extruded from a plastic tubular melt, and the extruded tubular parison is enclosed in a mold while in a semi-fluid state, creating a pressure difference between the inside of the parison and the outside of the parison. Inflating the parison to contact the mold. This allows the solidified parison to be blow-expanded into an expanded product and removed from the mold for further processing.

The uneven wall thickness distribution of blow blow molded products has been a difficult problem in such blow blow molding techniques. One way to solve this problem was to attach the die. The die attachment is made by cutting grooves or indentations (called molds) in one or more locations of the bushing and / or mandrel land (the portion of the die located upstream of the die opening). It includes producing a parison having an even distribution of wall thickness, and, prior to shaping, at a portion of the parison that corresponds to the portion of the molded product that has an undesired thin wall portion distribution. The thick material portion of the is located. As the mold becomes more complicated, that is, as the cross-sectional shape of the mold deviates from the circular cross-sectional shape, the nonuniformity of the wall thickness of the blow-expanded molded product becomes remarkable.

The known supplementary methods are basically empirical. While the molten parison is suspended between the two working mold halves, this molten parison is marked with a crayon to ensure that the exact shape of the shaped part required for the molded product relative to the parison is required. Trial and error technique for determining position (trial an
d error techniques) were used. Degree of attachment
In particular, the depth, width and length of the contours are also based on trial and error. These values have to be determined for each new mold and each new die, which is a time consuming, wasteful and costly method.

SUMMARY OF THE INVENTION One object of the present invention is to provide an affixed die based on predictable die ablation.

Another object of the invention is to determine the required shaping of the die prior to blow molding the product.

Another object of the present invention is to provide an extrusion die shaped to at least approximate the exact die gap required for the desired wall thickness distribution of a blow molded product in a given mold. is there.

[Means and Actions for Solving the Problems] The above-mentioned object according to the present invention is a method for manufacturing a die element, a die element, a blow-expansion molding method, and a blow-expansion method as defined in the claims. The solution is to provide a molded product.

Due to the features of the invention described above, it is possible to determine the required shaping of the die before blow molding the product, which is not only empirical as in the prior art, but also blow molded in the mold. The die components shaped to at least approximate the exact die gap required for the desired wall thickness distribution of the above can be manufactured based on a predictable die shaping method.

The present invention allows the die gap to be accurately calculated based on the cross-sectional shape of a given mold and the distribution of a given wall thickness within the mold, and based on such a calculation, the die can be at least It has been found that it can be shaped to approximate the die gap calculated as follows. It has been found that dies that can be blow-molded to approximate the desired wall thickness distribution, which has heretofore not been possible, with only a few contoured machining operations.

In other words, the present invention preferably automatically calculates the die gap width as a function of the position around the die gap from the desired wall thickness distribution in a given mold cross-section by a computer. Is included. Such calculations are preferably performed by determining a function of the parison wall thickness along the mold at a given mold cross section based on a circular cross-section parison having a uniform wall thickness. . However, within the scope of the present invention, such calculations can be made based on the cross-sectional shape and placement within the mold of other types of parisons when the blow-expansion process is initiated. Thus, before blow-expansion, the mold adheres to the parison causing partial solidification of the parison on the walls of the mold, after which blow-expansion takes place in the rest of the mold. It is possible. Yet another possibility for establishing a function of wall thickness (of a molded product formed using an unmodified die) with respect to die position (eg, the angle around a circular die) is in the cross section of the mold. The wall thickness of the molded product along is determined, thereby establishing a function of wall thickness versus length along the mold, and then the cross section of the parison between adjacent measuring points is taken from the previous point (or starting point). It is obtained by equating with an incremental parison cross section around the die gap to the next point, which establishes a functional functional relationship of actual wall thickness to die gap position.
In each case, one important feature of the invention is that the wall thickness of the given parison part as it comes into contact with the walls of the mold and solidifies in that position and the original parison. Both the azimuthal position of each part of the parison is determined, thus the actual wall thickness obtained in the mold by the part of the parison and the part of the parison at a particular position around the die gap. This is the point where the correlation with the original wall thickness of is obtained. In other words, the functional relationship between actual wall thickness and position along the die gap is established by the relative placement and shape of the mold and die gap. In this way, the actual wall thickness for a given point in the die gap is determined for at least a plurality of points.

The ideal die gap function or function for each die gap location is then determined by comparing the actual wall thickness calculated above to the desired wall thickness at each mold location. To be done. In order to establish the ideal die gap, the deviation of the desired wall thickness from the thus determined actual wall thickness is established for each of the points along the die gap. . In this way, an ideal die gap and a functional relationship between points along the die gap are established. Therefore, if the desired wall thickness at a given azimuthal position is greater than the actual wall thickness by x%, then the actual die gap at this position is increased by x%. At this position or point, an ideal die gap is created. Since this ideal die gap as a function of position on the die gap is often quite complex, an ideal die gap can be achieved by a limited number of machining operations in one or more parts of the die. It is desirable to approximate to the function of.
The die cannot be placed in any orientation with respect to the mold after it has been shaped according to the invention. Therefore, since such shaping is based on the orientation of the mold and the correlation between the dies, the die is directed to the machine so that the azimuth position of the shaped die is the same as calculated. Must be placed. In some symmetric cases, the die can be rotated, for example 180 °, with virtually no change in the resulting wall thickness distribution.

According to the preferred method of the invention, the following steps are performed in that order. That is, a. From a parison extruded with a given mold cross-section and a constant wall thickness, the distribution of the wall thickness of this parison blown into a mold with a given cross-section is calculated.

b. From this calculated wall thickness distribution, the deviation from the desired wall thickness distribution as a function of the position of the respective wall on the parison and thus on the die is calculated.

c. At least one of the die elements (eg, mandrel or bushing) is extruded from the die thus shaped to provide a desired wall thickness distribution in the mold after blow-expansion. It is shaped to have a wall thickness that is at least approximated at a given azimuthal position.

More specifically, the die gap width calculation is preferably performed according to the present invention as follows. That is, this calculation consists of the following given parameters defined by the shape to be molded and the machine containing the die and mold and their relative position and the mold separation line: a. An unmodified parison wall thickness distribution around the tubular parison as extruded, most preferably, this unmodified wall thickness distribution is a substantially constant wall thickness around the parison; b. The cross-sectional shape of a given mold perpendicular to the parison axis, the mold may have a cross-sectional shape that varies along the parison axis, but the most prominent cross-sectional shape must be chosen. This cross-sectional shape is preferably a cross-section located in the axial direction in the approximate center of the mold, c. The position of the parison in the mold, or correspondingly the position of the parting or pinching lines of the mold and the position of the axis of the parison in the mold, this latter parameter limiting the position where the parison first contacts the mold. It starts from.

The next step is to determine the distribution of wall thickness along the cross section of the selected mold and to determine the correlation of at least multiple wall thickness values to the position on the parison, i.e. the circumferential or azimuthal position on the parison. This determines the first point or points of contact of the parison with the mold, and how this parison contacts the walls of the mold during the blow-expansion process and thus the wall. This is done by determining whether the portion of the parison that is in contact with the part has solidified, which causes the plastic material to be immobilized along the wall of the mold so that it does not move further. Such calculations are shaped such that the parison encloses the maximum volume for a given surface area, or in other words has a minimum surface area for a given volume possible in the mold. It is based only on the geometrical consideration with the assumption. The correlation between the azimuthal or circumferential position on the extruded parison and any given point along the cross section of the mold is also a reference point on the part of the mold and on the part of the mold in question. The amount of plastic that has solidified in the wall of the mold between the given points of consideration is the amount of material between the reference point on the parison and the azimuthal or circumferential position on the parison to be determined. It is given by the fact that it is the same as.

After the calculated wall thicknesses for at least some of the points around the mold cross section and the corresponding positions of these points on the parison have been determined, the final die gap opening along the die gap is directly The die gap is modified or shaped to be related to the deviation of the desired wall thickness from the calculated wall thickness, which is done using a parison with a uniform wall thickness distribution. It is desirable to be told. Thus, if the desired wall thickness is greater than the wall thickness calculated at a given location by x%, the die gap is thus determined and the previous on the parison for the calculated wall thickness. Is corrected to at least approximate the x% increase in die clearance at the position of the die corresponding to the position determined in. Such ancillary steps are preferably performed only by approximation methods. In particular, it is desirable to shape the bushing and / or mandrel defining the die gap only by 6 to 20 "circular" cutting operations. If the given cross-sectional shape of the mold is defined by n straight line segments, it is generally sufficient to perform such shaping by 2n cuttings. Especially in the case of a rectangular mold cross section, it is desirable to utilize eight heavy weight circular cutting operations. The depth of these cutting operations (eg 2
5.4 mm (thousandths of a thousand) and width (for example in units of degrees)
Is determined mathematically accurately by the present invention.
Otherwise, the cutting process itself is performed by a normal tool, for example, a lathe, using a normal technique. In particular, the axial length of the cutting process depends on the plastic
It is determined based on the average width of the die gap, the overall die shape, and the like. The axial length of the auxiliary cutting process, which often tapers and converges in the upstream direction, is as large as the width of the cutting process.

The calculated cutting or shaping is preferably done at an axial position slightly upstream of the die opening with respect to the die. The particular axial location of the die for accurate or approximate shaping of the die gap is such that it allows lateral flow of plastic material in the critical asymmetric die gap. It is defined by the requirement of sufficient pressure gradient in The more viscous the extruded material, or the more die-formed (in the depth direction) the die, the more upstream this position must be. In general, positions having the above features are approximately 1 to 5 times, typically 2.5 to 3.0 times axially upstream from the opening and about 2.7 times the average die opening width. It is desirable to have.

According to a first embodiment of the present invention, there is provided a method of manufacturing a die element for an extrusion die that includes bushings and mandrels as the die element. By this method, the desired wall thickness distribution within a given, preferably non-circular cross-section shaped mold is selected. The ideal die gap width along the die gap is calculated from the desired wall thickness distribution. The die element is then shaped based on the width of the die gap thus calculated to obtain the die element shaped as a product of this method. The ideal die gap calculation is based on the desired wall thickness along the cross section when a parison extruded from a die having the aforementioned calculated width along the die gap is blown into this mold. To have a distribution of.

Another embodiment of the invention resides in a die element shaped to at least approximate the die gap width calculated as previously described.

Yet another embodiment of the present invention is an apparatus that includes a die that includes at least one element shaped as described above.

Yet another embodiment of the present invention is a method for blow molding a plastic product. This method comprises extruding a parison from a die according to the present invention and blow-expanding the thus extruded parison into a mold having a given cross-sectional shape to obtain at least approximately the desired wall thickness distribution. Forming a blow-molded product having.

The product blow-molded as described above constitutes still another embodiment of the present invention.

"Examples" The invention will be apparent from the following description and claims with reference to the drawings.

The details, features and various elements of the invention described below form preferred variants of the above-described embodiments of the invention in fields of applicability, either individually or in combination. Such details and examples are intended not to unduly limit the scope of the invention.

Die Gap The presently preferred method of shaping a die in accordance with the present invention involves shaping the bushing by fabrication. This operation can best be done by a lathe. However, it is within the scope of the invention to utilize other die shaping techniques and / or die mandrel shaping.

Numerical limits on how the die element can be shaped according to the present invention include the plastic material used, the shearing action associated with this method, the average width of the die gap,
Although significantly related to the degree of conicality of the die and other parameters, it has been found that the shaping process according to the present invention has been made easier to shape than was previously possible. Therefore, the following provides typical practical desirable ranges for the degree of shaping associated with the width of the die gap.

The above values indicate an approximate range or typical values,
It should be understood that it only gives the most recommended shaping depth features around the shaped die. The values actually used are of course related to the shape of the mold and the distribution of the calculated wall thickness of the product.

Materials The present invention is applicable to many plastic materials used in blow molding operations. Particularly desirable materials are ethylene polymers and copolymers, especially polyethylene and ethylene and 1 to 20 mol% of olefin copolymers having 4 to 10 carbon atoms per molecule, propylene polymers and especially polypropylene and propylene and small amounts. Other olefin copolymers are preferred.

Die Gap Calculation One of the most salient features of the present invention is the calculation of the die gap width at at least some points around the die gap.
According to the present invention, the die gap width around the die gap can be accurately calculated.

The first step of this calculation constitutes the determination of the distribution of wall thickness in a given mold, which is obtained with a parison of uniform wall thickness. This calculation is based on the paper “Floating Molding” by Etsch Fukase et al., Presented to ANTEC Journal of Society of Plastic Engineers at the 36th Annual Technical Meeting of April 24-27, 1978. Calculation method of wall thickness distribution in products "is described in some detail.

This calculation is based entirely, and preferably, on two dimensional considerations in a plane containing the cross section of the selected mold, perpendicular to the axis of the parison. This calculation is based on the shape of the parison at any given moment, which is the shape of a circle or part of a circle. When the cross section of the parison touches the two walls, this circle is defined solely by the tangential contact at selected points on these two walls. A slightly different consideration is required when the parison is in contact with only one wall or is blow molded around a corner. The calculations take different forms when the parison is blown into a mold having a cross-sectional shape that is not substantially polygonal or otherwise asymmetric. However, the search method and theory are the same in all of these calculations. In each calculation, the wall thickness is the residual material, i.e. the material remaining after subtracting the solidified material on the wall between the previous point and the currently observed point from the previously remaining material. Determined based on the wall thickness at the previous point by expanding into a substantially circular cross-sectional area having a radius and angle as determined by the cross-sectional shape of a given mold Of. This calculated wall thickness is related to the azimuthal or circumferential position on the extruded (or respectively around the die gap) parison, but at this position the problematic position And the total material between the reference points will be the same as the total material solidified between the reference points and the point in the mold where the wall thickness was just determined.

Such a calculation is done in a number of small steps so that the movement and solidification of the parison wall can be approximated and mimicked by a large number of small increments along the mold, with each increment being constant. It will be done. It is within the scope of the invention to establish the wall thickness of the blown wall as a function of position on the die opening by solving one or more differential equations.

The above calculation will be further clarified by the computer program given for the cross-sectional shape of the mold which is substantially rectangular shaped. This program is described below step by step.

A program to calculate the% increase in die clearance required to obtain a uniform wall thickness distribution in a rectangular blow-molding mold. 1 DIMENSION X (1000), T (1000), RX (10
00), FA (1000), DEG (1000) 2 Dimension (DIMENSION) PD (1000) 3 Read (READ) (5, ^* ) T1, XL, W, RC 4 R = W / 2 5 H = (XL- W) / 2. 6 TA = 3.1416 ^* R ^* R-3.1416 ^* (R-T1) ^* (R-
T1) 7 eye count (ICOUNT) = (XL / 2.-RC) ^* 100. 8 J-count (JCOUNT) = H ^* 100 9 Y = 0.0 10 XFA = 0.0 11 XT = T1 12 DO 10 I = 1, J-count 13 X (I) = Y + .01 14 DFA = 4. ^* .01 ^* XT 15 FA (I) = XFA + DFA 16 UFA = TA-FA (I) 17 DEG (I) = 90.-FA (I) ^* 90./TA 18 T (I) = R-SQRT (R ^* R-UFA / 3.1416) 19 PC (I) = ″ (T1-T (I)) / T (I) ^* 100. 20 Y = X (I) 21 XT = T (I) 22 XFA = FA (I ) 23 K = I + 1 24 10 Continue (CONTINUE) 25 DO 20I = K, eye count 26 X (I) = Y + .01 27 DFA = 8. ^* . 01 ^* XT 28 FA (I) = DFA + XFA 29 UFA = TA- FA (I) 30 DEG (I) = 90 .- (FA (I) + FA (K)) / 2 ^* 90. / TA 31 RX (I) XL / 2.-X (I) 32 XRX = RX (I ) 33 T (I) = XRX-SQRT (XRX ^* XRX--UFA / 3.1416) 34 PC (I) = (T1-T (I)) / T (I) ^* 100.35 Y = X (I) 36 XT = T (I) 37 XFA = FA (I) 38 20 Continue 39 Write (WRITE) (6, 100) 40 100 Format (FORMAT) (1X, 'distance from distance', 2X, 'thickness', 2X , And'angle from center ', 2X,'% increase ') 41 Write (6,200) (X (I), T (I), DEG (I), PC (I),
I = 10, eye count, 10) 42 200 format (11X, F8.2, 3X, F8.3, 13
X, F8.3, 10X, F8.3) 43 CFA = 3.1416 ^* XT / 2.0 ^* (2.0 ^* RC-XT)) 44 DEGC = 90.0-((XFA + FA (K)) / 2.0 + CFA) ^* 90.0 / TA 45 Write (6,300) XT, DEGC, PC (ICOUNT) 46 Format (13X, 'corner', F15.3, F21.3, F)
18.3) 47 STOP 48 END Use abbreviation T1 = Maximum wall thickness, ie initial wall thickness XL = Molded product or mold part length W = Molded product or mold part width RC = Molded product or mold Radius of the corner of R = radius of the parison at the moment the parison first contacts the mold wall H = length along the mold wall that moves while the parison is in a semi-circular shape TA = total break of the parison Area ICOUNT = number of increments (overall), starting at 0, 0.254 mm
(0.01in) each move along the wall from the first contact point to the origin of the corner radius JCOUNT = number of increments to move the parison along the quadrant, starting at 0, 0.254mm (0 .01in) each move along the wall to the point of contact with the corner Y = Intermediate position along the wall X (I) = Sizing position along the wall DFA = At each count (increment) Area of solidified parison XT = wall thickness of parison at each X (I), this value varies with I XFA = total solidified area of parison FA () at each X (I) FA ( I) = the total area of solidification of the parison in each X (I) UFA = the total area of the parison that remains unsolidified after the area of each X (I) is subtracted DEG (I) = Angle around parison at X (I) T (I) = wall thickness of parison at each X (I) PC (I) =% increase in wall thickness at each X (I) ,this is An increase of die gap to be required. This increase in die gap is the same as the% reduction in wall thickness at a given X (I) over the initial wall thickness of a product formed from a parison with constant wall thickness.

A counter at K = H (incremental change), which allows the next loop to start at the correct position FA (K) = solidified area of the parison to point H RX (I) = X Radius of the parison shape in (I) XRX = radius of transition to the next loop CFA = solidified area of the corner of the parison from the origin of the radius of the corner to the corner DEGC = separation line to the parison Angle to the corner position ゜ The above-mentioned Fortran language (Fortran Language)
The program proceeds as follows. The next number is the line number of the program shown above.

1. 2. A description of the dimension.

3. The maximum or desired thickness, thread length, width and corner radius of the molded product is read.

4. The parison radius R at the first wall contact is calculated and the width is the shorter dimension of the product.

Note: At this point, the parison now moves outward from the original parison extrusion position as two semicircles.

5. The length H of the parison moving in a semi-circle along the mold wall is calculated.

6. The initial total area (TA) of the parison cross section is calculated from the gasoline radius R and the width T1 of the parison ring cross section.

7. The total number of increments the parison moves is calculated. Because the rectangular mold and parison are placed symmetrically, the calculation only needs to be done for one quarter of the mold, the calculation along the half of the longer side, All that is required is for the parison to come into contact with all corner surfaces at once until the curvature of the corner radius begins. XL
And RC are read in (25.4 mm) and 100 times in the above equation is done because each step is chosen to be 0.254 mm (0.01 in).

8. The number of calculation process gage counts in which the parison is moved in a semi-circle along the wall is calculated.

9. 10. , 11. Initial values for the three parameters are set.

12. Beginning of a loop of calculations involving the movement of the parison from the first point of contact to the wall to the match H

13. The position X (I) along the wall is determined.

14. The incremental solidification area of the parison at X (I) is determined, 0.254 mm (0.01 in) is the length of this increment, XT is the wall thickness, and the parison is two walls. Factor 4 is used because four incrementally solidifying areas that have been contacted with and expanded in two directions must be used (only one quarter of the mold is tested).

15. The total solidified area of the parison at X (I) is calculated by adding the incremental solidified area to the previously determined total solidified area.

16. The total unsolidified area of the parison at X (I) is determined by subtracting the total solidified area calculated in step 15 from the total area already calculated in step 6.

17. This important step determines the azimuthal or circumferential position DEG (I) of the parison corresponding to the wall thickness part of X (I) in the mold from the 0 ° starting position (and hence in the die gap). To do. This calculation is based on the fact that the total solidified area / total area quotient in X (I) represents the 90 ° portion of the parison that remains unsolidified and was used in line 17. It should be noted that the formula changes the reference point from the center of the part to the separating line, but this is done for the benefit of the operator. This line calculates the angle on the parison corresponding to position X (I) on the mold.

18. Determine the wall thickness T (I) of the next parison part to be considered by solving the following equation. That is, for UFA = πr ² −π ^* (R−T (I)) ² T (I), 19. Calculate the% increase required to make the actual wall thickness T (I) the initial wall thickness T1.

20. 21. 22. Y, XT, for the next loop
Set the XFA values to those values just calculated.

23. Count the increment.

24. Return the program to line 1. The above loop is now repeated until the gage count reaches the value calculated on line 8.

25. Invokes a loop that calculates the wall thickness and azimuthal position for these incremental changes in contact with the next wall parison, which is 90 ° to the rectangular shape. Note that the radius and thickness change in this loop while the radius does not change in the previous loop.
This is because the two walls that the parison is moved along are parallel.

26. This is again a step of 0.254 mm (0.01 in). See line 13.

27. See line 14, the parison now moves from two directions to four corners, respectively, and is thus solidifying in eight different areas, so factor 8 must be used.

28. Calculation of solidified area. See line 15.

29. See line 16.

30. Same description as line 17, but note that FA (K), the total solidified area at the end of the previous loop (such as lines 13-24) must be added. . Instead of the formula shown in line 30, the calculation could also be based on DEG (I) = DEG (K) -FA (I) / 2 ^* TA ^* 90 °.

31. This line calculates the radius of the parison that moves to the corners and reduces each step by the momentum during this step. This occurs because the two walls of the mold are oriented perpendicular to each other.

32. Set the value XRX to the previously calculated radius value for the next calculation.

33. The same calculation as line 18 is made except for the new radius for each increment of the solidified area portion.

34. , 35. , 36. , 37. Same as 19, 20, 21, 22 respectively.

38. The loop continues by returning the program to line 26 until the eye count reaches the value already calculated on line 7.

39. -42. Write a description and format it (format
ting).

43. Calculate the solidified area of the parison at the corner.

44. Calculate the azimuthal or circumferential position of the point in question on the parison, from the parting line to the corner of the mold, or along the die gap as in step 17, respectively.

45. 46 Write the description and format it.

47. 48 Program ends.

Referring now to FIG. 1, blow molding of an object having a substantially rectangular cross section is shown. The parison is shown sandwiched between the two halves 1 and 2 of the mold.
This figure shows various parameters with the same abbreviations used for this program. Reference is made here to the above list of abbreviations. It should be noted that in FIG. 1 the abbreviations mentioned above are used for clarity only in one part, but some abbreviations indicate four or eight times their respective quantities. Must be understood.

The position B of the parison in FIG. 1 is shown at a position where the loop of the first program in the above program ends and the loop of the second program starts. Molded objects starting from a parison with a uniform wall thickness are shown in the right side of FIG. 1 to show a non-uniform wall thickness distribution in an exaggerated state.

In FIG. 2, the results of the above computer program are shown graphically. The percent increase in die gap is shown as a function of angular position around the die gap from the substantially circular die separation line. Curve 4 in Figure 2 resembling the shape of a volcano, except that the horizontal axis does not explain the angle in Figure 1, but shows the angle on a die or just an extruded parison. 1 shows the% change rate of the wall thickness along the wall portion 3 of the molded object of FIG.

It is necessary to completely compensate for the deviations in wall thickness caused by using an unshaped die, and thus a uniform wall thickness over the object molded in the mold as shown in FIG. In addition to curve 4 which defines the exact increase in die clearance required to obtain the distribution of, Figure 2 also shows an approximation of the curve obtained by the two circular cuts 5 and 6. . The exact calculation of these circular cuts 5 and 6 based on the volcanic curve of FIG. 2 is explained below in connection with FIGS. 3a and 3b.

For rounded or substantially rectangular cross-sections with rounded corners, it is desirable to approximate a corner with symmetrical portions of the die clearance increasing function on either side of the corner location. . In other words, the curve between 0 ° and 65 ° is symmetric with respect to the point of 32.5 °, which is the maximum ancillary angle and which is preferably approximated by a single machining operation. It is done. The next portion of the curve, that is, the portion between 65 ° and 90 °, is the second largest angulation angle, ie 40 ° to 9 °.
It can be approximated by a single cutting process symmetrical to the 65 ° position, which is one circular cutting process up to 0 °. However, it is also possible to change such cutting between two points 65 ° and 90 °. Because these two points alone do not define one circle. The difference between the 32.5 ° point and the 65 ° point is θ described in the program. However, for simplicity and ease of operation, use a symmetrical cutting operation in this state, i.e. give a single cutting operation that is symmetrical with respect to point B (65 °). It is also desirable to do so.

Reference is now made to FIGS. 3a and 3b, which show how the cutting radius and misalignment of the die forming process were calculated for a given value of die and the above program. Indicates whether the value is calculated.

The cutting radius r is found based on the following calculation,
Reference is made to the geometry in Figures and 3b. Third
Figure b is a more detailed version of Figure 3a and an expanded view of the additional symmetrical geometry.

Calculation of die cutting process DG = die gap (known) PC =% increase in corner (program), this is PC
(Eye count).

PH =% increase in separation line (program), this is PC
It is (F count) (PC (FCOUNT)).

θ ₁ = The angle (°) between the parting line and the corner line read on the parison (program), which is the first cut relative to the position of the cutting element corresponding to the parting line of the mold. It is an angle for processing.

θ ₂ = corresponding angle for the second cut R = radius of die bushing (known) r ₁ = first cut radius (found) S ₁ = position of the first cut Deviation (found) r ₂ = second cutting radius (found) S ₂ = positional deviation of second cutting (found) Y ₁ = R + (PC × DG) X ₁ = R + (PH × DG ) Z ₁ = (X ₁ ² + Y ₁ ² −2X ₁ Y ₁ cos θ ₁ ).
^1/2 The above values define the first cut (“corner cut”) as follows.

Similarly, the following values are obtained for the second cutting process (“separation line cutting”).

_{θ 2 = 90-2θ 1 Y 2 =} R + (PH × DG) X 2 = R Z 2 = (X 2 2 + Y 2 2 -2X 2 Y 2 cosθ 2)
^1/2 S ₂ = Y ₂ −r _{2 In} another embodiment shown in FIG. 7, the second cutting operation for shaping the die gap with respect to the cross-sectional shape of the rectangular mold is performed for this second cutting operation. The same position as for the first cutting can be used as the azimuthal cutting position, and in this example the following relationship applies (r ₁ ,
The values for S ₁ etc. of course remain the same as above). That is, θ ₂ = θ ₁ X ₂ = X ₁ (described above) r ₂ = (S ₂ ² + X ₂ ² −2S ₂ X ₂ cos θ ₂ )
The die angles (8 cuts) are defined using ^½ angles θ ₁ and θ ₂ , misalignments S ₁ and S ₂ and cutting radii r ₁ and r ₂ .

In FIG. 4, a slightly exaggerated cross section of the die gap at the die opening is shown, which corresponds to curve 4 shown in FIG. The four significant angles to the die gap and the respective% increase values are shown in FIG. The separation line is located at 0 ° in FIG.

Note that the desired die includes a bushing and mandrel such that the desired die forms a substantially frustoconical opening between the bushing and the mandrel, the frustoconical surface of which exits the die. It is adapted to taper outwardly in the direction of plastic material flow near the ends. This profiled cutting also begins at the upstream location and tapers outward near the opening in the face of the die to gradually increase to the final width in the direction of plastic material flow.

FIG. 5 illustrates such mold shapes to show how the corresponding calculations can be made in the context of complex mold shapes. This calculation is also based on a ring whose cross section is circular or a parison shaped to be a part of such a ring. Mold side (wall) AC
EG and BDFH are arbitrarily selected in terms of shape. The parison wall enters at 15 at the annex. Curve 10
Shows various positions relative to the center of the circular parison section as the parison contacts successive points along the wall of the mold.

In FIG. 5, the abbreviations have the following meanings.

WW: This is a parison touching two walls
It is the center of movement along the two walls.

PW: This is because the parison touches the corner on one side 1
It is the center of movement along the two walls.

PP: This is the position when the parison is inflated around the two corners.

WWP: This is the location where the parison is blown around the corner that contacts the two walls.

The suffixes in FIG. 5 indicate the respective walls and corners of the illustrated mold. Therefore, _{W D} represents a wall portion D, _{P e} represents the corners e, and so forth.

In FIG. 6, a contoured bushing of blow blow molding extrusion according to the above-described contoured contour is shown. This shaping takes the form of eight cuttings in this example. These cutting processes are those shown in FIG. 2 or 3a respectively.
It corresponds to that shown in the figure.

[Effects of the Invention] As described above, according to the present invention, it is possible to determine the required shape of the die before blow-expanding the product, as defined in the claims. Not only empirically, but also predictable die elements that are at least approximated to the exact die gap required for the desired wall thickness distribution of the product blown in the mold. A die having a shaped element having excellent characteristics which can be manufactured based on a die shaping method, a method for accurately determining the shaping of a die element, a blow expansion molding device, and a blow expansion molding Provided is a method capable of making the approximation of the shaping required for a die for molded and accurately blow molded products.

[Brief description of drawings]

FIG. 1 shows a mold with a uniform wall thickness parison at various stages of the blow molding process and the finished blow expanded product obtained with a uniform wall thickness parison inside the mold. Sectional schematic cross-sectional view showing the distribution of the wall thickness of the. Figure 2 shows the angle from the mold separation line (directional position)
% Increase in Die Gap Calculated from Preselected Die Gap as a Function of and Actual% of Die Gap Used to Approximate Calculated Value Utilizing Two Symmetrical Circular Machinings A schematic plot diagram showing the rate of increase, wherein the plot is shown for one quarter of the circumference of the die gap. 3a and 3b are drawings showing the geometry underlying the radius, width and misalignment calculations of the die geometry. FIG. 4 is an enlarged and exaggerated cross-sectional view of the die gap at the face of the die corresponding to the calculated representation of FIG. FIG. 5 is a drawing schematically showing the movement line of the center point of the parison when the parison is blow-expanded in a mold having a complicated shape, and the wall in a state where these center points are more complicated. Drawing designed to be used to calculate thickness distribution. FIG. 6 is an axial view of a die bushing with eight cuts, two of which are functionally shown in FIG. 2 to show an approximation of the calculated annex. The drawing shown in. FIG. 7 is a drawing showing the geometry of two cutting operations that approximate the calculated% increase in wall thickness, with these two cutting operations being performed in the same azimuthal position. Drawings. FIG. 8 is a flowchart showing a flow for schematically explaining the shaping method according to the present invention. 1, 2 ... Mold half 3 ... Wall 4 ... Curve 5, 6 ... Circular cutting

Claims (8)

[Claims] 1. A method of manufacturing a die element for an extrusion die, comprising a bushing as a die element and a mandrel forming a die gap for enabling tubular extrusion of a parison between the bushing and the bushing. , The method includes: (a) selecting a mold cross-sectional shape; (b) selecting a desired wall thickness distribution of the product along the cross-sectional shape; (c) a wall thickness distribution along the die gap. Calculating a width of the die gap, and (d) shaping the die element based on the calculated distribution of the width of the die gap to form the die element. Production method. 2. (a) calculating a calculated parison wall thickness distribution around the mold cross section from a given unmodified parison wall thickness distribution around the tubular parison; ) Shaping the bushing and / or the mandrel to approximate the die gap as calculated from the calculated wall thickness distribution deviation based on the desired wall thickness distribution deviation. The method according to claim 1, wherein 3. The distribution of the calculated wall thickness determines the wall thickness of the article along the cross section of the mold, and each point according to the calculated wall thickness determines a point around the parison to which it corresponds. The method of claim 2, wherein the method is adapted to be calculated by calculating. 4. The parison is based on a parison during blow-expansion that occupies the shape of the circular ring or the shape of the circular ring cross section tangentially contacting the wall within the cross section of the mold. , And so that the correlation between wall thickness and corresponding points on the parison and the die is calculated by equating the cross-section of the die and the total solidification area along the equivalent corresponding cross-section of the parison. The method of claim 3, wherein the method is performed. 5. The calculation advances the parison from the initial mold position in small increments, followed by the small increments to determine wall thickness, to determine the total solidified area, and The deviation of the determined wall thickness from the desired wall thickness is determined, the position on the parison is calculated from the total solidification area, and all the deviations thus determined are defined as the angle around the parison. Correlatively related and shaping the bushing and / or the mandrel to approximate the bias thus calculated at least at each angle to compensate for such a bias, and the die element Is performed by a series of separate steps including at least approximating a desired wall thickness distribution during use in blow molding by the mold.
The method described. 6. The mold has a non-circular cross-sectional shape that is substantially rectangular and the shape of the element is made by eight overlapping cuts, four of which are depth. And the shape is adapted to be manually the same, a method according to any one of the preceding claims. 7. A working surface such that the die element is a frustoconical surface in the direction of flow of the outwardly tapered, extruded plastic material that is rotationally symmetrical prior to said shaping. Method according to any one of the preceding claims, which is adapted to have. 8. A method of blow-expanding a product in a mold, which comprises: (a) blow-expanding at a blow-exposure temperature and pressure through a die gap formed by two die elements, a mandrel and a bushing. In extruding a tubular parison of a plastics material according to claim 1, wherein at least one of the die elements is manufactured by the method according to any one of claims 1 to 7, and (b) the extruding A blow-expandable parison is enclosed in the mold, (c) a pressure difference is generated between the inside and outside of the parison to expand the parison so as to contact the mold, and (d) Blowing an article having at least approximately the preselected wall thickness shaped from the mold from the mold.