HK1005085B - Extrusion die - Google Patents

Description

Extrusion die

The present invention relates to an extrusion die and a method of designing an extrusion die. The invention relates in particular to a method for designing and manufacturing an extrusion die with a higher extrusion speed. The invention relates specifically to an aluminum extrusion die with different lengths of continuous working belts and grooves that improve the flow of material into the die while allowing higher extrusion speeds.

Extrusion is a process in which a force forces a material through an extrusion die having an extrusion die orifice to produce a product having a cross-sectional shape that conforms to the extrusion die orifice. The length of the extruded product can be determined by the amount of material passing through the extrusion die. Conventional aluminum window frames can be made with extruded rails and mullions. Conventional crossbars and mullions have relatively complex cross-sectional shapes and include a plurality of ribs extending from a body. In addition, each rib may have a set of structural elements extending out. In the past, as the extrusion die holes became more complex, the rate of extrusion production had to be reduced to ensure high product quality.

Fig. 1 shows a known extrusion die. The prior art extrusion die, generally designated 210, includes a die body 212 having a feed side surface 214 and a discharge side surface 216 with a cavity 218 extending from the discharge side surface to the feed side surface. An extrusion die orifice 220 extends through the die body 212 from the feed side surface 214 to the cavity 218. A wall 222 parallel to the inlet side surface 214 and the outlet side surface 216 is attached between the extrusion die orifice and the cavity 218. The wall 222 may also be considered a relief 222 of the extrusion die 210. The depth of the extrusion die hole is technically referred to as the bearing or working band 224 of the die. The bearing or working band 224 of the mold is the portion of the embryonic ingot that the mold contacts as it is pressed through the mold 210. This contact causes friction. Friction causes heating and adversely affects the flow of the material.

The length of the working tape 224 and the length of the back-off blades 222 affect the strength of the mold 210. The strength of the die 210 is important, as the die 210 is subjected to high pressures and temperatures during the extrusion process. If the material around the extrusion die orifice 220 is not strong enough, product quality may be adversely affected. To increase the strength of the die 210, the length of the working tape 224 may be increased to reduce the size of the relief 222. But the operating speed of the die 210 is reduced due to the friction caused by the long work belt 224.

Therefore, it is desirable to minimize the length of the band to achieve maximum extrusion speed while maintaining sufficient die strength. For the extrusion industry, it is important to achieve maximum extrusion speed, since the die can only produce a product that is many miles long during its useful life. Even a small increase in extrusion speed can be of great benefit to the manufacturer.

Another feature of conventional molds is the groove 230 formed in the feed side surface 214 of the mold 210 to facilitate continuous feeding of the embryonic ingot. When the required product length exceeds the capacity of the extruder, continuous feeding is required. For continuous feeding, a groove 230 is machined in the feed side surface 214 of the die 210 around the extrusion die hole 220. As the extruder extrusion axis approaches the feed side surface 214 of the mold, the embryonic ingot is sheared and a portion of the extrudate remains in the groove 230. When the embryonic ingot is sheared, the shearing action creates a force tending to pull the material remaining in the groove 230 back out of the mold 210. To prevent material from being pulled completely out of groove 230, groove 230 should be relatively deep. The depth is typically determined such that the angle indicated by reference numeral 232 is less than 45 degrees. The depth of the groove 230 prevents shear forces from pulling the material completely out of the mold 210. Once the material is sheared, the extrusion shaft is pulled back and loaded into another embryonic ingot. The new ingot is welded to the material remaining in the groove and the extrusion process continues.

The depth of the groove 230 adversely affects the performance of the mold 210. Flow through the die 210 is restricted if the angle between a line drawn from the corner of the groove 230 perpendicular to the feed side surface 214 and a line drawn through the corner and the angle at which the extrusion die orifice 220 intersects the groove floor 234 is less than 45 degrees. Since the material is pressed against the die 210 in the extruder, the material extruded in the corners stays there substantially during the extrusion process. These portions are referred to as flow dead zones and are indicated at 236 in fig. 1. The dead zone 236 creates friction between the rest of the flow and itself. The deep groove 230 results in the formation of additional dead space, shown at 238. The deep groove 230 also serves as an extra length of the working tape because there is flow along the wall of the groove 230, as shown at 240. The additional friction caused by the dead zone 238 and the extra working band 240 is undesirable because it generates heat that degrades the surface quality of the finished product. To reduce the effect of friction, the extruder is run at a slower speed.

Mold designers typically use trial and error to design such conventional molds. The success of mold design often depends on the knowledge and experience of the designer. The die is typically manufactured by first determining the die orifice required for the final extruded product. And then processing a die hole on the die body. When the die designer initially forms the die orifice, he intentionally makes the working tape longer than necessary to adjust the length of the working tape as needed after the test run. The die may then be loaded into an extruder for a series of test runs. If the mold is working properly, it can be used to produce the finished product. One problem with this method is that the working belt of the mold is intentionally long and the mold must be run at a slow speed.

If the designer finds a problem with the die or requires a higher speed die band in a test run, he removes the die from the extruder and makes adjustments. The extent of these adjustments depends on the knowledge and experience of the designer. A common adjustment that may be made is to adjust or shorten the operating band. Known methods of adjusting the working band are to shorten the entire working band or to shorten part of the working band to form a stepped working band. After these adjustments were made, the mold was reinstalled and the test was performed. One problem with stepped working bands is that dies with stepped working bands produce products having surface linear marks at the working band steps which are undesirable and must be removed by further processing.

Modifications and testing were repeated until a satisfactory product and extrusion speed was obtained. It should be noted that the length of the working tape cannot be restored after it has been shortened, so that if the working tape is removed too much, the mold must be scrapped and the whole process restarted. For this reason the mold band is always left longer than necessary. The increased length allows for lower extrusion speeds than would be possible. Even a mold designer with a great deal of knowledge and experience typically goes through about three trials to make a satisfactory mold. The number of trial runs and labor costs required to complete the mold increase the manufacturing cost of the mold.

It is therefore a principal object of the present invention to provide a method for accurately designing and manufacturing an extrusion die capable of operating at higher speeds on an extruder.

It is a further object of the present invention to provide an extrusion die as described above which can be operated at higher speeds to produce products with acceptable surface quality.

It is a further object of the present invention to provide an extrusion die as described above with a continuous working belt specifically designed for the die extrusion orifice.

It is a further object of the present invention to provide an extrusion die as described above which avoids leaving mold marks on the extrusion surface.

It is a further object of the present invention to provide an extrusion die as described above with a recess shaped to improve the flow of material into the die.

It is a further object of the present invention to provide an extrusion die as described above with a groove that enables continuous ingot welding.

It is a further object of the present invention to provide an extrusion die as described above with relatively shallow recesses that improve the flow of material into the die.

A further object of the invention is to propose a strong extrusion die with a relatively small working band.

It is a further object of the present invention to provide an extrusion die as described above which is provided with a relief to increase the strength of the die.

It is a further object of the present invention to provide a method of designing an extrusion die having the above characteristics.

These and other objects and advantages of the present invention, as well as the advantages thereof over the prior art, which will become apparent from the detailed description to follow, are accomplished by the methods hereinafter described and claimed.

In general, extrusion dies embodying the concepts of the present invention utilize such extrusion dies. It comprises a body having a feed side surface and a discharge side surface; a groove made on the feed side surface; an extrusion die hole extending from the groove to the side surface of the discharge side on the main body, the depth of the die hole forming a working band; the shape of the recess is predetermined according to the shape of the die hole to improve the flow of material through the die. The method of manufacturing the mold includes these steps: determining an extrusion die hole required by a die; the shape of the groove around the extrusion orifice is determined according to the determined orifice to improve the flow of material through the die.

In order that those skilled in the art will best understand the invention, a preferred embodiment of a solid extrusion die and an embodiment of a hollow extrusion die are described herein by way of example and with reference to the accompanying drawings which form a part hereof, and which illustrate the best way in which the invention may be practiced. The detailed description of the exemplary extrusion die is not intended to list all of the various forms or modifications in which the present invention may be practiced. The embodiments illustrated and described herein are therefore illustrative and it will be apparent to those skilled in the art that they may be modified in various ways within the spirit and scope of the invention; the invention is defined by the following claims rather than by the detailed description in the specification.

FIG. 1 is a side cross-sectional view of a prior art extrusion die;

FIG. 2 is a side elevation, partially cross-sectional view of a conventional extruder equipped with an extrusion die according to the present invention;

FIG. 3 is a cross-section taken along line 3-3 of FIG. 2, and is a front view of an extrusion die according to the present invention;

FIG. 4 is a cross-section taken along line 4-4 of FIG. 3, and is a partial cross-sectional view of an extrusion die in accordance with the present invention;

FIG. 5 is a cross-sectional side view of the continuous working band of the extrusion die, taken along line 5-5 of FIG. 3;

FIG. 6 is an end view of a hollow extrusion die according to the present invention;

FIG. 7 is a cross-sectional view of the hollow extrusion die taken along line 7-7 of FIG. 6; and

FIG. 8 is a side cross-sectional view of the support column taken along line 8-8 of FIG. 6.

An exemplary extrusion die embodying the concepts of the present invention is shown generally at 10 in the drawings. In fig. 2, a typical extrusion die 10 is mounted on an extruder 12. The die 10 is secured to the extruder 12 by a set of weights 14, the weights 14 being bolted to the body 16. The extruder has an extrusion axis 18 that pushes an ingot 20 of extruded material toward the die 10. The force of the extrusion shaft 18 pushes the embryonic ingot 20 through the extrusion orifice 22 through the die 10. The embryonic ingot 20 emerges from the die 10 as an extruded product 24 having the same cross-sectional shape as the extrusion orifice 22. The product 24 exiting the die 10 may be supported by a set of rollers 26, as shown in FIG. 2.

The extrusion die 10 according to the present invention includes a body portion 30 having a feed side surface 32 and a discharge side surface 34 with an extrusion die orifice 22 therethrough. It should be noted that the extrusion orifices shown in the figures are exemplary only and that the concepts of the present invention are also applicable to dies 10 having other extrusion orifices, the extrusion orifices 22 being surrounded by a groove 40 to enable welding between successive billets and to improve the flow of material into the die 10. The tapered relief cavity 42 is recessed into the body portion 30 of the mold 10 from the discharge side surface 34. A relief knife 44 parallel to the infeed side surface 32 and the outfeed side surface 34 is attached between the relief cavity 42 and the extrusion die orifice 22.

The depth of the extrusion orifice 22 is technically referred to as the bearing or working band 46 of the die. In the past, the length 46 of the working tape was used only to control the flow of material through the die 10, so that a short working tape 46 would allow faster material flow through the die 10, and a long working tape would slow the material flow. The primary reason for this result is the friction that occurs between the flowing material and the working tape 46. To make a die that can operate at high extrusion speeds, the length of the working tape 46 must be limited as much as possible. In relatively complex extrusion die orifices, such as the one shown in the drawings, however, the flow of material through the orifice is not uniform. The limited open space limits the flow of material through the orifice 22 in that part of the section of the orifice 22 where the wall thickness is smaller. For clarity, it should be noted that the term wall thickness refers to the wall thickness of the extrusion die orifice 22, as indicated at 48 in FIG. 3. Thus, if a uniform length of working tape is used in such a die orifice 22, the material will flow through some sections of the orifice at a higher rate than other sections. This uneven flow results in product 24 being dimensionally unacceptable, such as twisted along the longitudinal axis of the product.

To control the flow of material, the present invention utilizes, in part, a continuous working belt 46 having a length determined by the wall thickness of the extrusion die orifice and the positional relationship of the wall thickness to the flow of material. It is known that the material flows with minimal friction at the center of the flow, as shown at 50, and with maximum friction at the edges, as shown at 52. The geometry is such that the material flow forms a dead zone 54 when in contact with the feed side surface 32 of the die 10. The work belt 46 of the present invention is designed to accommodate non-uniform material flow and to control the flow through the die 10.

To design the work belt 46, the die designer first determines the highest flow rate section and the lowest flow rate section of the extrusion orifice. The section of the orifice 22 where the flow rate is highest is typically the section with the greatest wall thickness closest to the center of the die 10. The skilled die designer can basically analyze the various factors that may cause the highest flow velocity zone to be offset from the center of the die. In the extrusion die orifice 22 shown in the drawings, the highest flow velocity zone is indicated at 56. The highest flow rate is in this section because it is located in the center of the mold 10 and has a wall thickness 57 that is approximately the same as the wall thickness of the rest of the mold shown at 48. The lowest flow rate section of the extrusion orifice is generally the section closest to the die edge 58. A tip 60 section or a section with a narrow wall thickness. In the illustrated extrusion die orifice 22, the lowest flow rate segment is indicated at 62.

To control the flow of material through the die 10, the working belt 46 should be adjusted to be the longest at 56 where the flow rate is highest and the shortest at 62 where the flow rate is lowest. As previously described, a short working band will increase the flow rate through the die 10, while a long working band will decrease the flow rate through the die 10. The designer next determines the minimum work band 46 that can actually be used in the designed mold 10. The length of the minimum working band 46 depends on a number of factors including the strength of the material from which the die is made, the pressure and temperature of the extrusion process, and the tooling available to the designer. The designer should place the minimum operating band 46 in the lowest flow rate section of the die orifice as shown in fig. 5.

The designer then determines the length of the working band 46 at the highest flow rate section 56 of the extrusion die orifice 22. If the wall thickness of the extrusion die orifice 22 at the highest flow velocity section 56 is approximately equal to the wall thickness of the extrusion die orifice 22 at the lowest flow velocity section 62, the length of the working band 46 at the highest flow velocity section 56 is equal to the length of the working band 46 at the lowest flow velocity section 62 multiplied by a factor, which factor generally ranges between 1.4 and 2.0. Thus, the length of the operating band 46 of the highest flow velocity section 56 is always longer than the length of the operating band 46 of the lowest flow velocity section 62.

In the following example, the coefficients selected for the length and different wall thicknesses of the working band 46 are exemplary in nature and are only used to illustrate how the method of determining the length of the working band 46 may be implemented. However, the inventors of the present invention have found that coefficients defining respective approximate ranges are useful for obtaining the results of the present invention.

The following is an example of a calculation of the working tape shown in the drawings with extrusion die holes 22 of the given exemplary dimensions. The designer first determines the minimum work band that is possible in the mold 10. If the length of the minimum operating band 46 is determined to be 0.4 units long, the operating band 46 for the highest flow rate zone 56 should be 0.4 times a factor in the range of approximately 1.4-2.0. If the coefficient is chosen to be 1.6, as desired, in this example, the length of the operating band 46 in the region of highest flow rate 56 should be 0.4 x 1.6 to 0.64 units.

If the wall thickness of the highest flow velocity zone 56 is greater than the lowest flow velocity zone, the range of 1.4-2.0 is increased by a first factor. The first factor is equal to the product of the ratio of the wall thickness of the highest flow velocity section 56 to the wall thickness of the lowest flow velocity section 62 and a factor in the range of 1.25-1.65. Thus, if the wall thickness of the lowest flow velocity section 62 is 1.4 units long, the wall thickness of the highest flow velocity section 56 is 1.6 units long, which is a ratio of 1.14(1.6 divided by 1.4). The first factor is the product of 1.14 and a factor in the range of 1.25-1.65. If the coefficient is chosen to be 1.45, the first factor is 1.14 × 1.45 — 1.65. The range of 1.4-2.0 is increased by a factor of 1.65. Further, the ratio of the length of the operating band in the highest flow velocity zone 56 to the length of the operating band in the lowest flow velocity zone 62 is approximately in the range of 2.31 to 3.3 (1.4X 1.65 to 2.0X 1.65). The land length of the highest flow rate section of the extrusion die orifice should be 0.4 units long (land length of the lowest flow rate section 62) multiplied by a factor in the range of 2.31-3.3. If the factor is chosen to be 2.7, the operating band length of the highest flow zone is 0.4 × 2.7 — 1.08.

If the wall thickness of the highest flow velocity section 56 is less than that of the lowest flow velocity section 62, the approximate range of 1.4-2.0 is reduced by a second factor. The second factor is equal to the product of the ratio of the wall thickness of the lowest flow velocity section 62 to the wall thickness of the highest flow velocity section 56 and a factor in the range 1.25-1.65. If the wall thickness of the lowest flow velocity section 62 is 1.4 units long, the wall thickness of the highest flow velocity section 56 is 1.2 units long, which is a ratio of 1.17(1.4 divided by 1.2). The second factor is the product of 1.17 and a factor in the range of 1.25-1.65. If the coefficient is chosen to be 1.45, the second factor is 1.17 × 1.45 — 1.70. Thus, the approximate range of 1.40-2.0 is reduced by a factor of 1.70. Further, the ratio of the length of the operating band of the highest flow velocity zone 56 to the length of the operating band of the lowest flow velocity zone 62 is approximately in the range of 0.82 to 1.18 (1.4/1.7 to 2.0/1.7). The land length of the highest flow rate section 56 of the extrusion die orifice should therefore be 0.4 units (land length of the lowest flow rate section 62) multiplied by a factor in the range of 0.82-1.18. If the factor is chosen to be 1.1, the operating band length of the highest flow rate zone is 0.4 units long × 1.1-0.44 units long.

For the points on the extrusion die orifice 22 between the highest flow velocity zone 56 and the lowest flow velocity zone 62, the operating band length can be interpolated from known data. If the wall thickness of the extrusion orifice 22 is maintained from the highest flow rate section 56 to the lowest flow rate section 62, the length of the working band can be simply calculated by linear interpolation. If such a method is used, the shape of the working tape is as shown in FIG. 5. In fig. 5, the operating band 46 is the shortest in the lowest flow rate section 62 and the longest in the highest flow rate section 56.

For points along the extrusion die orifice 22 having a different wall thickness than the highest flow velocity zone 56, the swath size calculated according to linear interpolation is also corrected by a third factor. If the wall thickness is greater than the wall thickness of the highest flow velocity section 56, the size of the operating band is increased by a factor of 1.25-1.65 multiplied by the ratio of the wall thickness at that point to the wall thickness of the highest flow velocity section 56. If the wall thickness at this point is less than the wall thickness of the highest flow velocity section 56, the length of the operating band is decreased by a fourth factor. The fourth factor is 1.25 to 1.65 times the ratio of the wall thickness of the highest flow velocity section 56 to the wall thickness at that point. After the adjustment of the active band length to account for the wall thickness, the active band 46 is again interpolated to take into account the new length.

Finally, the length of the band is adjusted according to the geometry of the extrusion die orifice 22. The length of the working tape is reduced by 30-50% for the point at the end 60 of the extrusion die orifice 22. Similarly, for the points at the corners, such as the corner shown at 64, the length of the working tape is reduced by 10-30%. After the adjustments made based on the geometric factors are complete, all length dimensions are re-interpolated to determine the final swath length for all points between the calculated unique points. Following these steps, the designer can calculate a continuous work band 46 for the selected extrusion die orifice 22. The continuous work belt 46 controls the flow of material through the die 10 and serves to equalize the frictional effects acting on the flow of material. In addition, the present method ensures that extruder 12 can be operated at the highest speed permitted for extrusion die 22, since the ribbon length of the lowest flow velocity section 62 of extrusion die 22 is minimized.

The above described working tape 46 will work best when used with the grooves 40 according to the present invention. The recess 40 in the drawings can be considered a cavity surrounding the extrusion orifice 22 on the feed side surface 32 of the die 10. The recess 40 may be formed as a recessed mold body 30 or may be formed in a plate (not shown) that is mounted against the feed side surface 32 of the mold 10. The groove 40 has a continuous tapered sidewall 70 which cooperates with the mold 10 to weld successive ingots together. The angle of inclination of the side walls 70 is between 0 and 30 degrees.

The tapered sidewalls 70 allow successive ingots to be welded together even though the depth 74 of the groove 40 is less than in the prior art. As described in the "background of the invention" section above, a welding sequence of ingots is often performed. To weld the two billets together, the first billet is sheared as the extrusion shaft 18 approaches the feed side surface 32 of the mold 10. The shearing action creates a force that drives the material remaining in the groove 40 back out of the groove 40. In the past, only the extended groove 40 sidewalls 70 were sized to prevent this force from pulling the material 20 completely out. In the present invention, the side walls 70 of the groove 40 are tapered to help retain the material 20 in the groove 40 as the ingot is sheared. The side walls 70 act to counteract this force as the shearing action creates force. The depth 74 of the groove 40 need not be as deep as in the prior art. Because the material is retained by the tapered side walls 70, the depth can be greatly reduced.

The shape of the recess 40 is designed to improve the flow of material into the mold 10 by changing the angle at which the material flows into the orifice 22. In the prior art, the material is pushed directly against the feed side surface 214 of the die 210 and under pressure is turned into the extrusion orifice 220 at a small radius of curvature. In the present invention, however, the grooves 40 cause the streamlines of the material to turn before the material reaches the feed side surface 32, creating an artificial material entry angle. This artificial angle improves the flow of material 20 so that the material can flow more freely into the extrusion die orifice 22, which reduces the material strain rate, smoothes the flow of material, and equalizes the pressure of the material flow. Since the shape (depth and width) of the groove 40 has been designed with a priori consideration of the material flow trajectory and the material entry angle, it provides an improvement in both material flow lines and material flow. In the prior art, the depth of any groove is much deeper, and the material entry angle, or groove angle, is always less than 45 degrees, which results in strong rubbing. The strong friction deteriorates the surface quality and the overall quality of the product. If the material flow lines are directed by the grooves 40 of the present invention, the friction generated between the material 20 and the die 10 is greatly reduced, allowing the extruder 12 to operate at higher speeds and produce high quality products.

In addition to the advantage of increasing the extrusion speed, the grooves 40 also allow the designer to modify the die without adjusting the work belt 46. The working tape 46 is difficult to adjust once formed for reasons of location and size. In contrast, the recess 40 is relatively easy to change after molding. In a trial run of the mold 10, if the designer desires to change the effect of the mold 10 on the flow of material, he may either enlarge the grooves or add material to the grooves, as opposed to modifying the work tape 46. It is feasible to add material to the grooves by welding the material in the desired locations and then grinding.

In general, the size of the groove 40 is determined based on the expected material flow rate along the point on the designed extrusion die orifice 22. For example, at the point of the low flow velocity section, the groove width is wider than at the point of the high flow velocity section. The determination of the groove 40 of the extrusion die orifice 22 begins with the selection of the minimum width 72 at the highest flow velocity section 56 of the extrusion die orifice 22. The minimum width 72 is determined by the skill of the designer and the overall size of the extrusion orifice relative to the diameter of the die 10. The depth 74 of the groove 40 is then determined by multiplying the minimum width 72 by a factor generally ranging between 1.2 and 2.0.

The minimum width is selected to be limited by the shape requirements of groove 40, and groove angle 82 formed by reference line 84 and reference line 86 should be approximately in the range of 25 degrees to 45 degrees. The reference line 84 passes through the edge 88 of the groove 40 and is perpendicular to the feed side surface 32. The reference line 86 extends from the edge 88 of the groove 40 to the edge 90 of the extrusion die orifice 22 directly behind this point. Generally, if the groove angle 82 is small, the grooves slow the flow. If the groove angle 82 is large, the flow encounters less friction faster. Since groove depth 74 is constant, varying groove width results in varying groove angle 82.

The designer then determines the width of groove 40 at point 76 along extrusion orifice 22 closest to edge 58 of die 10. The groove width is the product of the minimum groove width 72 and a factor generally ranging between 1.5 and 2.5 for these points. The groove 40 should be larger at these points because friction between the material flow and the extruder slows the material flow. The designer next increases the groove width again at point 64 along the corner and at point 60 at the end. The increase in the width of the dots is multiplied by a factor roughly ranging from 1.2 to 2.0. In the low flow velocity zone, the groove angle should be between 45 and 70 degrees. After the groove widths at these points are determined, the profile of the entire groove 40 can be determined by linear interpolation or higher order interpolation.

For the low flow rate section of the extrusion die orifice 22, the width of the groove is large. The width of the band 46 of these sections is also minimal so that less friction is generated in the mold 10. The high flow velocity section of the extrusion die orifice 22 has a small groove width. The width of the working band 46 of the high flow velocity section is also long. The designer may design a mold 10 that improves the flow of material using the combination of the working tape 46 and the grooves 40. Once the flow of material is improved, the material can flow smoothly through the die 10, resulting in an improved product with better material properties, satisfactory surface quality. The improved material flow also reduces friction in the die 10, which may increase the extrusion speed through the die 10. The number of trials to produce a mold 10 that produces a satisfactory product according to the method of the present invention can be reduced from about 3 to about 1. Because the die land 46 and the groove 40 are shaped specifically for the extrusion orifice 22 of the die, the number of trials can be reduced.

The foregoing description has been directed to a solid mold 10. The present invention may also be used to increase the speed of the hollow extrusion die 110. A typical hollow extrusion die 110 is shown in fig. 6-8. The hollow mold 110 is used to produce a product with a hollow structure such as a pipe-like product. The hollow mold 110 has a male mold 112 disposed in a female mold 114. A set of support posts 116 support the male die 112 in the female die 114. The space in which the material can flow around the support post 116 supporting the male mold 112 is technically referred to as the mold cavity (pole) and is shown at 118 in the drawings. The gap between the male die 112 and the female die 114 is the extrusion orifice.

The female mold 114 of the hollow mold 110 has a similar structural element to the solid mold 10. For example, the hollow die 110 may be mounted on the same type of extruder that the solid die 10 may be mounted on. The hollow die 110 also has a relief cavity 142 recessed into the discharge side surface 134. The hollow die also utilizes the recesses 140 to control the flow of material into the extrusion die orifice 122. The kickoff blade 144 is located between the working tape 146 and the kickoff blade cavity 142.

Generally, the length of the working tape 146 increases in a direction from the center of the support post 116 toward the center of the mold cavity (pole) 118. The length of the belt is minimized below the support post 116 because the material must pass around the support post 116 to reach the extrusion die orifice, as shown in fig. 7 and 8. The working band 146 is the shortest at the lower portion of the support post 116 so that at these locations the material encounters less friction at the extrusion die orifices than immediately below the die cavity (pole)118, at which locations the material flows directly into the extrusion die orifices 122.

As with the design of a solid model, the designer first determines the shortest operational band that is feasible. The designer determines this shortest operating band as the operating band length of the lowest flow velocity section 162 of the extrusion die orifice located directly below the support column 116. The designer then determines the length of the working band 146 of the highest flow velocity section 156 of the die 110 (these sections are located directly below the die cavity (pole) and have the greatest wall thickness) as the product of the minimum working band length and a factor in the range of 1.11 to 1.67. The length of the operating band at the points between these points is found by interpolation. In addition, the rules for adjusting the work tape 146 based on wall thickness and geometric factors are applied. Thus, if the desired point is at a corner, as shown at 164, the operating band is reduced by 10-30%. If the desired point is located at the end 160 of the extrusion die orifice 122, the operating band length is reduced by 30-50%.

In general, the dimensioning of the grooves 140 of the hollow mold 110 may follow the same rules as the dimensioning of the groove widths of the solid mold 10. For a hollow mold, the groove would have a greater width below the support post 116 and a lesser width below the mold cavity. The designer first determines the minimum groove width based on his experience and the relative sizes of the extrusion die orifice 122 and the die 110. The minimum groove width 172 should be located in the highest flow velocity section 156 of the extrusion die orifice 122, typically directly below the die cavity 118. The depth 174 of the groove can then be calculated to be equal to 1.2 to 2.0 times the minimum width 172. The groove angle of the highest flow velocity zone should also be approximately in the range of 25 degrees to 45 degrees.

The designer then calculates the groove width 178 of the lowest flow velocity section 162 of the extrusion die orifice 122. The lowest flow rate section of the extrusion die orifice 122 is the section of small wall thickness directly below the support column 116. The groove width at these locations is 2.0 to 5.0 times the minimum width. The groove angle of the lowest flow velocity zone should be in the range of approximately 45 to 70 degrees. Likewise, the groove widths at the remaining points may be calculated using line interpolation or high-order interpolation. In addition, the width may also increase or decrease depending on the geometry of the extrusion die orifice. For example, the width may be increased at the corners 164 and decreased at the wider sections of the die hole.

Whether solid or hollow, after the dimensions of the bands 46, 146 and grooves 40, 140 are determined, the dimensions are entered into computer controlled tooling equipment that can machine the molds according to programmed tool paths. For example, these devices may be used to form extrusion orifices 22, 122 with or without the relief blades 44 and 144 in the dies 10 and 110. Generally, the die without the back-offs 44 and 144 is stronger than the die with the back-offs. Even though the mold has much shorter working belts 46 and 146, the mold without the blades 44 and 144 has much better strength than the mold with the blades 44 and 144. Fig. 4 shows the mold 10 with the relief 44 shown in fig. 2 on one half and no relief 44 on the other half. The half indicated at 80 without the relief blades 44 is more resistant to bending forces generated by the material being extruded through the die orifice 22. Grooves 40 and 140 may also be machined by programming tool paths on a suitable machine. The cutter path of the work tapes 46 and 146 may be determined based on the angle of the cutting line of the line cutting apparatus and the depth of the grooves 40, 140.

Although only a preferred embodiment of the present invention has been described, it will be readily appreciated that various modifications thereof may be readily made by those skilled in the art. The scope of the invention is therefore intended to be limited not by the detailed drawings and written description, but should be construed to include all modifications and improvements within the scope of the appended claims.

It is clear that the extrusion die embodying the idea of the invention not only allows to produce acceptable products while increasing the extrusion speed, but also achieves other objects of the invention.

Claims (20)

1. An extrusion die comprising: a body with a feed side surface, a discharge side surface, and a groove machined in the feed side surface; said body also having an extrusion die hole formed in said body extending through said recess to said discharge side surface, said die hole depth defining a working band having a length; the extrusion die orifice having a high flow velocity section defined by a larger work belt length section and a low flow velocity section defined by a smaller work belt length section; the groove has a width; and the groove width at the high flow velocity section of the extrusion die orifice is less than the groove width at the low flow velocity section of the extrusion die orifice.

2. The extrusion die of claim 1 wherein said body has a chamfered relief cavity on said discharge side surface, said extrusion die orifice extending through said body from said recess to said relief cavity; the working tape extends all the way to the relief cavity.

3. The extrusion die of claim 2, further comprising a kickback knife positioned between the working band and the kickback knife cavity.

4. An extrusion die according to claim 1, wherein the working band has a length, said length of the working band being dependent on the shape of the extrusion die orifice at any given point along the extrusion die orifice.

5. The extrusion die of claim 4, wherein said extrusion die orifice has a low flow velocity section and a high flow velocity section; the length of the working tape is longest in the highest flow velocity section of the extrusion die hole, and the length of the working tape is shortest in the lowest flow velocity section of the extrusion die hole.

6. The extrusion die of claim 5, wherein the extrusion die bore has a wall thickness at any given point along the extrusion die bore; if the extrusion die orifice wall thickness in the highest flow velocity section is about the same as the extrusion die orifice wall thickness in the lowest flow velocity section, the land length of the highest flow velocity section of the extrusion die orifice is about 1.4-2.0 times the land length of the lowest flow velocity section of the extrusion die orifice.

7. An extrusion die according to claim 6, wherein said approximate range of 1.4 to 2.0 increases by a first factor when the wall thickness at the region of the extrusion die having the highest flow rate is greater than the wall thickness at the region of the extrusion die having the lowest flow rate.

8. An extrusion die according to claim 6, wherein the approximate range of 1.4 to 2.0 is reduced by a second factor when the wall thickness at the region of the die orifice having the highest flow rate is less than the wall thickness at the region of the die orifice having the lowest flow rate.

9. An extrusion die according to claim 1, wherein the side walls of the recesses are tapered.

10. The extrusion die of claim 1, wherein the extrusion die orifice has a low flow velocity section and a high flow velocity section; the groove has a certain width; the groove width is smallest in the highest extrusion die orifice flow rate section and largest in the lowest extrusion die orifice flow rate section.

11. The extrusion die of claim 10, wherein said groove has a depth equal to the product of the width of the groove at the highest flow velocity section and a factor generally in the range of 1.2 to 2.0.

12. The extrusion die of claim 11, wherein said groove has a groove angle at any given point along the extrusion die orifice; the groove width at the highest flow velocity section forms a groove angle in the approximate range of 25 degrees to 45 degrees.

13. The extrusion die of claim 11, wherein said groove has a groove angle at any given point along the extrusion die orifice; the groove width at the lowest flow rate forms a groove angle in the approximate range of 45 degrees to 70 degrees.

14. A method of designing an extrusion die, comprising the steps of: determining an extrusion die hole required by a die; determining the shape of a groove provided on the feed side surface of the extrusion die and surrounding the extrusion die orifice according to the determined die orifice; determining a groove angle between the groove and the determined die hole; and changing a groove angle of the groove according to the determined die hole.

15. A method of designing an extrusion die according to claim 14, further comprising the steps of: determining a highest flow velocity section and a lowest flow velocity section of an extrusion die hole;

setting the length of the working band of the section with the lowest flow rate of the mold; and

and calculating the length of the working belt of the section with the highest flow velocity of the mold according to the length of the working belt of the section with the lowest flow velocity.

16. The method of designing an extrusion die of claim 15, further comprising the step of adjusting the land length by reducing the land length at the corners and ends in accordance with the extrusion die orifice shape.

17. A method of designing an extrusion die according to claim 16, further comprising the step of interpolating to identify the remainder of the working band.

18. A method of designing an extrusion die, comprising the steps of:

determining an extrusion die hole required by a die;

determining the shape of a recess disposed in the feed side surface of the extrusion die and surrounding the extrusion die orifice in accordance with the determined die orifice such that the material forms an artificial material entry angle as it flows under pressure through the die;

determining a highest flow velocity section and a lowest flow velocity section of an extrusion die hole;

setting the groove width of the highest flow velocity section of the extrusion die hole;

calculating the groove depth according to the groove width of the section with the highest flow velocity;

calculating the groove width of the section with the lowest flow velocity according to the groove width of the section with the highest flow velocity of the extrusion die hole; and

the remainder of the groove is determined by interpolation.

19. The method of designing an extrusion die of claim 18, wherein the step of setting the groove width of the highest flow velocity zone of the extrusion die orifice forms a groove angle in the range of about 25 degrees to about 45 degrees.

20. The method of designing an extrusion die of claim 18, wherein the step of calculating the groove width of the lowest flow velocity zone from the groove width of the highest flow velocity zone of the extrusion die orifice forms a groove angle in the range of about 45 degrees to about 70 degrees.