NL1032519C2 - Device and method for the manufacture of products. - Google Patents

Description

Title: Device and method for manufacturing products.

The invention relates to a device and method for manufacturing products.

Injection molding is a known method that is used for the manufacture of products, in particular but not exclusively from plastic.

A mass in liquid, at least molten form is thereby introduced into a mold cavity under pressure and allowed to solidify therein. A drawback of such a method is that relatively high pressures must be applied to fill the entire mold cavity, whereby the properties of the starting material are adversely affected, in particular when plastic is used. Moreover, the relatively accessible flow path with relatively thin products is relatively short, which means that large, thin-walled products are difficult or even impossible to inject. In particular not from plastics with a high melt.

It has already been proposed to injection mold into a mold cavity with a movable wall part. As a result, the flow path can initially be increased in cross-section, so that the mass can pass more easily. If the mold cavity is completely or partially filled, the movable wall part is then moved forward, in the direction of an opposite wall part, so that the flow path is brought to the desired cross-section.

With this the required pressures for injecting the mass and thus also the required closing pressure for keeping the mold closed can be reduced. Such a method is described, for example, in WO 2004/024416.

The object of the invention is to provide a method for manufacturing products of high quality.

1032519 2

A further object of the invention is to provide a method for manufacturing, in particular, plastic products with low internal voltages.

The invention also has for its object to provide a method for manufacturing products with relatively thin walls, in which relatively low injection pressures have to be used and in which relatively low closing pressures are sufficient, in comparison with conventional injection molding.

At least one of these goals or other goals are achieved with a method according to the invention.

In a first aspect, a device according to the invention is characterized by a mold with at least one mold cavity, which mold cavity has at least one movable wall part. A mass is introduced into the mold cavity under pressure, such that it is moved between said at least one movable wall part and an opposite mold part. Subsequently, the first movable wall part is pressed in the direction of the opposite wall part of the mold cavity, whereby the intermediate mass is somewhat compressed and displaced. As a result, the mold cavity can be filled simply and with little pressure, and emphasis can largely be omitted after the mass has been introduced.

In a second aspect, said first movable wall part extends around said injection point and said injection point is movable together with said at least one first movable wall part. Upon injection of the mass, it can be brought into a relatively large space, so that relatively little injection pressure is required. Moreover, when the first movable wall part is moved to a product-forming second position, little pressure will arise in the mold cavity, as a result of which the pressure at the injection point and in particular an injector is limited, whereby damage is prevented.

3

In a third aspect, at least a second movable wall part is provided that extends at a distance from said injection point, in addition to said at least one first movable wall part, drive means being provided for movement of said at least one second movable wall part relative to said at least one at least one first movable wall part. This means that the mass can be displaced during use, stepped.

In a fourth aspect, the at least one first or second movable wall part is movably received in an opening of a surrounding wall part, wherein a longitudinal edge of said opening facing an opposite wall part of the mold cavity is rounded. The flow path for the mass thereby becomes smoother, while the flow resistance is somewhat reduced. Moreover, this surprisingly prevents sheet formation in an end product at the level thereof.

In or with a device according to the invention, control means are preferably included for controlling the movements of the or each movable wall part, such that the timing, speed and acceleration thereof can be accurately controlled. Preferably, the or each first movable wall part and a second movable wall part extending next to and / or around it can be moved relative to each other and / or from the injection point.

In a fifth aspect, control means are provided for driving the at least one movable wall part along a main direction of movement and for injecting a mass into the mold cavity, which control means are adapted to bring the at least one movable wall part into a first position during at least a first period of injection of said mass, subsequently moving said at least first wall part during or after said injection of said mass, and subsequently moving to at least a second position of said at least first movable wall part wherein the intermediate position and the second position are on opposite sides of the first position, viewed along said main direction of movement.

The invention furthermore relates to a method for the manufacture of products, in particular using a device according to the invention.

To clarify the invention, exemplary embodiments thereof will be further elucidated with reference to the drawing. In the drawing: Fig. 1 schematically shows, in cross-sectional side view, a first embodiment of a device according to the invention; Fig. 2 schematically shows, in cross-sectional side view, a second embodiment of a device according to the invention; Fig. 2A is an enlargement of a detail of a device according to Fig. 2; Fig. 3 schematically shows a product manufactured with a device according to the invention; Fig. 4 schematically shows, in cross-sectional side view, a third embodiment of a device according to the invention; 5A and 5B show two steps in a method according to the invention; and Fig. 6 shows, in side view, another product manufactured with the aid of a device and method according to the invention, on which schematic prints of movable wall parts of a mold with which it is manufactured are indicated.

In this description, the same or corresponding parts have the same or corresponding reference numerals. The embodiments shown are shown for illustrative purposes only and should not be construed as being limitative in any way. Many variations are possible.

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In this description, exemplary embodiments are given of devices, in particular molds, and a method for manufacturing products based on plastic. However, other materials can also be used in such devices, for example masses based on biopolymers, metals and the like. In this description, frontal surface is understood to mean at least a projected surface perpendicular to a relevant direction of movement or view direction. In this context, movable wall part is to be understood to mean at least a part of a wall of a mold cavity that also forms a part of a product to be formed, which movable wall part is at least but not exclusively on an outside, an inside and / or as a core part can be provided with / for the mold cavity. Opposite wall part should at least be understood to mean a wall part of the mold cavity which, viewed in the direction of movement of the relevant movable wall part, lies opposite the relevant wall part. This can have the same size in terms of projected surface area as the movable wall part can be smaller or larger. The wall parts can have flat sides facing each other as well as profiled, curved, angled or otherwise have a shape that deviates from flat. The or an opposite surface or part thereof can also be formed by a movable wall part. In the embodiments shown, hydraulic means such as piston-cylinder assemblies are shown as drive means for movable wall parts. However, other means may also be provided, such as, for example, pneumatic or electric drive means such as a screw spindle motor, a stepper motor, rod mechanisms drivable by, for example, a press which is used for closing the mold or other means immediately clear to the skilled person. The molds shown in the drawing can be used on conventional presses for opening and closing the mold and can be filled with a filling device known per se, for example a screw feeder, hot runner devices or other injection molding devices known per se. In the embodiments shown, a single mold is always shown, but of course multiple (multi cavity) and / or stacked molds (stack molds) can also be made in a comparable manner. In this application, conventional injection molding is understood to mean injection molding as described in the introduction, in a mold of which a mold cavity is in the product-forming state upon injection of the mass and for this purpose has the geometry of the product to be formed.

In this description, left, right, top, bottom, front and rear are used for reference to the plane of the drawing, unless otherwise indicated.

FIG. 1 shows a mold 1 with a first and a second part 2, 3, movable relative to each other with the aid of suitable, known means such as a press (not shown). The mold 1 has a mold cavity 4 formed between the parts 2, 3, for example for forming a product 5 such as a crate or box as shown in Fig. 3, for example from plastic. The mold cavity 4 can of course also be suitable for other types of products. A central opening 6 is provided in the second part 3, in which a first movable wall part 7 is provided. The first movable wall part is coupled to first drive means in the form of piston-cylinder assemblies 8, with which the first movable wall part 7 is movable between a first, retracted position, shown in Fig. 1 on the left-hand side of an imaginary central surface 9, and a second, forward position, as shown in Fig. 1 on the right-hand side of said middle surface 9. It is clear that in the first position the distance between the frontal surface 10 of the first movable wall part 7 and the opposite wall part 11 is greater than in the second position. With the movable wall part 7 in the second position, the mold cavity 4 has a product-forming configuration, while in the first position the mold cavity 4 has a volume that is larger than that of the product 5 to be formed.

The mold 1 and in particular the mold cavity 4 is provided with at least one injection point 12, here formed by an open and optionally closable end 13 of a hot runner injector 14, which is mounted on the movable wall part 7 or at least mounted in such a way that the injection point 12 can move along with the first wall part 7.

A mold 1 according to Fig. 1 can be used as follows.

The mold 1 is closed and the first movable wall part 7, together with the injection point and the injector 14, is brought into the first position, as a result of which the mold cavity 4 has a relatively large volume, in particular seen in injection direction P before the injection point 12. Subsequently a mass 16 is introduced into the mold cavity with the aid of the injector 14. To this end, the injector 14 is connected via a suitable coupling 15, 15, for example, a sliding fit or a flexible coupling, to a feed device (not shown) for plastic or other suitable material, in liquid form, or in a form which is in liquid 14 in the injector 14. can be brought into shape. Liquid in this context should at least be understood as comprising a liquid or a viscous mass, such as, for example, molten plastic. Because the mass 16 (Fig. 5) is introduced into a relatively large space 4A in front of the injection point 12, this can be done with relatively low pressure, as a result of which the injector is loaded little and virtually no shear will occur in the plastic. The properties of the mass such as plastic will therefore only be minimally or preferably not adversely affected. Because the mass can be introduced at relatively low pressure, the part 11A of the wall part 11 situated opposite the injection point can be made substantially flat. That is, it is not necessary to provide a form element on it which, as a result, has to distribute the mass of current and hence the forces which act on the wall part 11. This means that no undesired deformations need to occur in the product 5 on site. This offers, for example, the advantage that the surface in question can easily be labeled, for example by in-mold labeling technique, without having to be injected by that label and underneath that the label will be damaged by a deformation.

After at least the major part of the mass has been introduced into the mold cavity 4, for example more than 90% of the required volume and preferably substantially all plastic, the first movable wall part 7, together with the injection point 12, becomes with the aid of a control device 24 and at least a part of the injector 14 brought to the second forward position by the drive means, whereby the mass 16 confined between the frontal surface 10 and the wall part 11 is at least partially displaced to other parts of the mold cavity 4, parts 19 forming longitudinal edge 18, for example, heat is developed in the mass as a result of a combination of internal friction between molecular chains in the mass, friction between the mass and mold parts and / or compression of the plastic. The displacement of the first movable wall part 7 preferably takes place particularly quickly, for example in tenths to one hundredths of a second. It is clear that the speed, acceleration and displacement distance can be selected depending on the mold and product geometry, the plastic used, and for example the heat capacity of the mold. Without wishing to be bound by any theory, this heat development appears to occur adiabatically, that is to say without the application of external thermal energy, by the abovementioned frictions and / or compression, in particular a combination thereof, as described in WO 2004/024416 . In addition, as shown schematically in FIG. 5, use is made of heat that is present in the mass immediately next to the movable wall part 7, around already partially solidified parts 16A of the mass 16, which lie at a relatively large distance from the injection point 12 and / or near fixed wall parts of the mold cavity , at least partially meltable again, whereby the resistance experienced by the mass 16 in the mold cavity 4 is reduced to a minimum. As a result, the pressure exerted by the mass on the mold parts 2, 3 will be minimal, so that relatively small forces can suffice to keep the mold closed. In this context, it is to be understood relatively to be proportional to the forces that occur in a conventional mold, with conventional injection molding, for the formation of an identical product from the same mass. During the movement of the movable wall part 7, a pressure pulse in the mass 16 may occur. The influence thereof on the occurring forces is, however, minimal, since it will be absorbed in particular by the inertia of the materials used and the mold parts 2, 3.

As a result of the relatively low pressure in the mold cavity 4, a simple shut-off valve of the hot runner or other injector 13 can be used, for example a needle valve, the injector can be of relatively light design and be moved along with the wall part 7. The mass is driven by the movable wall part 7 moved and / or kept moving and the viscosity of at least a part thereof will be reduced by heat development or at least not further increase, whereby the mass can be moved with relatively little pressure to fill the entire cavity 4 . In particular also long and / or narrow and / or complicated flow paths 20, for example with many bends, can be filled completely without the properties of the mass being particularly adversely affected, as will be the case with conventional injection molding of such a product 5. and without the need for a high injection pressure, such as with conventional injection molding. Moreover, emphasis is practically unnecessary.

Fig. 2 shows an alternative embodiment of a mold 1 according to the invention, which differs substantially from that according to Fig. 1 in that the first movable wall part 7 is received in an opening 21 in a second movable wall part 22. The second movable wall part 22 is connected to second drive means 23, similar to the first drive means 8, which can be controlled by the control means 24 for moving from a first position, as shown in Fig. 2 on the left-hand side of the plane 9, to a second position as shown on the right-hand side of surface 9, movement of the second wall part 22 and possibly vice versa. As shown in Fig. 2A, the longitudinal edge 25 of the opening 21 on the side facing the mold cavity is rounded off with a radius R, for example a radius between 0.1 and 5 mm, for example between 0.2 and 3 mm, whereby the mass when forced along it by movement of the wall parts 7 and / or 22 will experience less resistance than if this longitudinal edge were perpendicular, as with known slides. Surprisingly, it has been found that such a rounding has a positive effect on, for example, the prevention of burning of the mass due to excessive local heating, the prevention of skin formation (flash) at the location of the transition in the product to be formed and the necessary tolerances.

With a mold 1 according to Fig. 2, the mass 16 is introduced into the mold cavity 4 with the first 7 and second movable wall part 22 in the first position, so that the volume of the mold cavity is relatively large, in particular for the injection point 12. Subsequently first, the first movable wall part 7 is set in motion, controlled by the control means 24, in the direction of the second position, and thereon according to the second movable wall part 22. This results in a cascade movement 25 and the mass 16 becomes in the direction of the longitudinal edges 18 driven. The wall parts 7, 22 can perform the movements sequentially, but can also move partially together or at least simultaneously. That is, the second movable wall part can move relative to the first movable wall part 7 and / or relative to the injector 14. Thanks to these movable wall parts, an even better controlled displacement of the mass 16 can be obtained.

In a further advantageous embodiment, in the case of a mold according to, for example, Figs. 1 or 2 or an embodiment to be described in more detail below, the first, second and / or further movable wall part can first be slightly withdrawn from the first position during and / or immediately after injection of the mass, from the first position to an intermediate position, wherein the frontal surface of the respective wall part is at a greater distance from the opposite wall part 11 than in the first position, after which the relevant wall part passes beyond the first position the second position described. Surprisingly, it has been found that a particularly good filling of the mold cavity 4 can hereby be obtained, at low pressures for injection and for keeping the mold closed. Without wishing to be bound by any theory, this appears to be due, among other things, to the effect that the frontal surface is slightly moved away from the mass during the movement to the intermediate position, before it is brought back into contact with it at a high speed. while moving part of the still liquid mass during the movement in the direction of the intermediate position, so that movement already occurs in the mass before the wall part is brought to the second position.

Fig. 3 shows a product 5, in the form of a crate, in perspective view, provided with a bottom 26 and an upright wall 27. On the bottom the contours 28, 29 are shown in broken lines of the first one respectively and second wall part 7, 22. In addition, the injection point 12 is schematically shown. In addition, the contours 30 of further movable wall parts 31 are shown on the wall 27 in broken lines, as are applied in an embodiment according to Fig. 4. In the figures, movable wall parts 7, 22, 31 are always shown with a flat frontal surface. However, profiling may, of course, also be provided therein, for example extra fluids, curves, grooves, creases and the like, whereby surfaces of the products to be formed can for instance be profiled.

Fig. 4 schematically shows a mold 1 with a mold cavity 4, comparable to the device according to Fig. 1, wherein, however, the injector 13 is provided on an outer side of the product 5. Only a first movable wall part 7 is shown, but of course the mold can also be provided with second movable wall parts 22, for instance as shown in Fig. 2. In this embodiment, 10 are near the longitudinal edge 18, i.e. at a greater distance from the or each injection point 12 then the first and / or second wall parts 7, further, third movable wall parts 31 provided with drive means 32, controllable by the control means 24. These third movable wall parts 31 have a frontal surface 31A which is relatively small with respect to the surface 15 of the wall part in which it is provided and with respect to the total surface of the product, formed by inside and outside thereof.

The joint frontal surface of these third movable wall parts is, for example, smaller than 10% of the surface of the product 5.

During use, the third movable wall parts 31 are moved from a retracted first position, as shown on the left in Fig. 4, to a moved second position, as shown on the right in Fig. 4, whereby the mass in the region of the longitudinal edge 18 is still somewhat compressed and / or displaced, while shrinkage of the cooling mass can thus be substantially absorbed. As a result, relatively simple deformation of the product can be prevented, while moreover tensions therein can be kept to a minimum.

A method and device with such movable wall parts is described in more detail in the applicant's non-prepublished Dutch patent application NL 1032248, which is here incorporated by reference.

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Figs. 5A and B schematically show a cross-section through a part of a mold 4 and the mass 16 arranged therein, immediately prior to moving a movable mold part 7, 22, 31 respectively from a first to a second position and immediately 5 thereafter. In Fig. 5A, the mold cavity 4 is relatively large and the mass 16 does not completely fill it. A part 16A of the mass is solidified against fixed wall parts 11 of the mold cavity 4 by transferring heat to the material of the mold 1. However, a part of the mass, in particular for the movable wall part 7, 22, 31, still has a temperature above the melting point of the relevant mass, as a result of which this part is still substantially liquid. It is clear that a relatively large part of the mass in a part of the mold cavity 4 is solidified at a distance from the movable wall part and would therefore make passage of more plastic in the direction of a part 18 forming a longitudinal edge difficult or even make it impossible for conventional 15 injection molding. However, in a method according to the present invention, as previously described, use is made of the heat and fluidity of the remaining part of the mass and the movement of the mass under the influence of the movable wall part brought to the second position, as shown in FIG. 5B. As a result, the hot, liquid part is forcefully driven against and into the already solidified part of the mass, while, moreover, friction is generated in the mass itself and between mass and the walls of the mold cavity, whereby heat is generated. As a result, premature cooling of the mass is prevented and even the temperature in the mass can be further increased, because the heat is at least partially passed through into the mass itself than can be completely discharged by the mold. As a result, the mass becomes partially liquid again and at least less viscous, so that it can be forced further into the mold cavity and in particular the longitudinal edge 18 forming part 19, without excessive pressure build-up, for a complete filling of the mold cavity 4. The rounding 33 of the 14 longitudinal edge 25 of the opening 21 with radius R is clearly visible in Figs. 5A and B. The second position (Fig. 5B) of the movable wall part can be such that the frontal surface 10 is positioned such that a small groove 34 arises between the curved surface 36 of the longitudinal edge 25 and 5 and the side 35 of the movable wall part 7, 22, 31, but can also be situated slightly more downwards than shown in Fig. 5B, so that the frontal surface is approximately equal to the beginning of the curved surface 36 of the longitudinal edge 25. The rounding 36 offers the advantage that the friction between the mass and the mold part 3 and / or internally in the mass 16 itself immediately adjacent to said surface. ak 36 is limited so that the temperature there does not become too high, which could cause combustion.

With a method and device according to the invention, the advantage can further be achieved that the mass, in particular plastic, can be introduced into the mold at a lower temperature than with conventional injection molding, for instance just above the melting temperature of the mass.

Due to the heat development in the mold cavity, as described, as a result of friction and / or compression, the mass is kept sufficiently fluid or made to be able to fill the entire mold cavity, without excessive pressure being necessary. Moreover, this achieves the advantage that the cooling time for cooling the mass is shortened because less heat has been added, whereby the cycle time is shortened. Moreover, the material quality of the mass is thereby better preserved than with conventional injection molding of a comparable product.

As can be seen clearly from the figures, the longitudinal edge 37 of each of the movable wall parts 7, 22, 31 is spaced apart from a rib 38 of a product 5 being formed or at least spaced from a place where different flows of the mass come together or where the product will be most heavily taxed during use. For, for example, a crate according to Fig. 3, these are, for example, the ribs 38 of the upright wall, which will be strongly subjected to buckling when stacked. By placing the longitudinal edge 37 at a distance from such a position, the strength thereof is prevented from being adversely affected. A method according to the invention is of particular importance in particular with, for example, long and / or narrow passages, restrictions due to bends and the like.

FIG. 6 shows a somewhat transparent representation of a product 5 in the form of a container 40 with lid 41, interconnected by a hinge construction 42, for example a hinged part in the form of a living hinge, or, as shown, in the form of a clamps 43 rotatable rod 44. A wheel set 45 is connected to the bottom 47, at the rear thereof. A point of contact 12 is shown in a central region of the bottom, but one or more point of contact 12 can also be provided at other positions, for example near an upper longitudinal edge 18. For the formation of the bottom a first and a second moving wall part 7 22 which are arranged asymmetrically with respect to the bottom. In the mold, near the upper longitudinal edge 18, parts 19 forming on the four sides are in each case provided two third moving wall parts 31 with which the mass can be given a final move and moreover any shrinkage of the material during cooling can be absorbed. The third moving wall parts are also preferably moved forward so rapidly from the first to the second position that adiabatic heat development occurs in the mass for the frontal surface thereof. Fig. 6A shows a possible cross-section of the wall of the tray 5, along the line VIA - VIA in Fig. 6, which wall 25 is partially hollow, preferably at a great distance from the bottom, for example over substantially the entire height. As a result, a relatively thin inner wall 48A and relatively thin outer wall 48B are obtained, preferably mutually connected by ribs 49, whereby a particularly light, rigid construction is obtained, while the space between the wall parts 48A, B can be relatively small, for example in the same order 16 of magnitude as the combined thickness of the wall parts 48, B, for example a few millimeters to one and a half centimeters. With a method according to the invention, such a tray 5 can be made light and strong, since the pressure in the mold cavity during the manufacture is relatively low and thus minimizes the chance of deformation of a core part forming the cavity (s) in the wall. Moreover, wall thickness differences can easily occur without this leading to undesired deformations as a result of different cooling trajectories. Fig. 6B shows an alternative embodiment of a cross-section of a wall of a container 5, wherein at least one side 50 of the wall 48 has a corrugated or ribbed pattern or surface, while the opposite side 51 thereof, for example, is substantially flat or has an otherwise corrugated or ribbed surface, whereby the wall thickness D1 varies across the width of the tray 5. The thicker parts will provide rigidity, while the thinner parts will result in a less heavy product. It has been found that such a wall requires less material than a wall with constant thickness and equal strength, in particular with regard to buckling load. Moreover, a light, dimensionally stable container is thereby obtained. The ribs 38 are relatively thick for extra rigidity. Alternatively, ribs can also be formed along the height of the wall, on the inside and / or outside thereof. Inserts, for example electronic and / or programmable tags for recognizing the tray during use, fastening means for for instance the wheels or other types of elements can easily be injected into the production process, wherein the chance of damage by pressure is minimized as a result of low pressure in the mold. Labeling by in-mold labeling is also possible.

The invention is not limited to the embodiments shown in the description and drawings, which are for illustrative purposes only, many variations thereof are possible within the scope of the invention as set forth in the claims. Thus, as indicated, stack molds and 17 multiple molds according to the invention can be used, whereby different products can also be manufactured in one mold in one production cycle, since the injection pressure is of secondary importance and by a suitable method of positioning and controlling the 5 movable wall parts the masses in the different mold cavities can be displaced. Different injection points can be provided, whereby with the help of different of such points different plastics can be injected simultaneously or sequentially. A mold according to the invention can be designed without the first and / or second moving wall parts, for instance only with the third movable wall parts, with which the method according to the patent is then carried out. Several first and / or second positions can also be provided for a first and / or second wall part according to the invention. In that case, for instance, first a first plastic can be injected into the mold cavity, wherein the relevant wall part is brought to a most advanced first position and said plastic is allowed to cure at least partially, after which the moving wall part is retracted to the or a second position, at a distance from the solidified plastic, after which a second amount of plastic can be introduced into the mold cavity, against the solidified plastic. The movable wall part can then be held during curing of the plastic or it can be moved to a new, first position, for the formation of the product. A fully or partially laminated product can hereby be obtained. Furthermore, all the examples shown and / or parts thereof can be combined, for obtaining alternative embodiments of a device or method according to the invention.

These and many comparable and other variations are understood to fall within the scope of the invention as set forth in the claims. 30 1 0 325 1 9

Claims (16)

Device for the manufacture of products, comprising a mold with at least one mold cavity that has at least one first movable wall part, drive means being provided for driving the at least one first movable wall part, which mold cavity comprises at least one injection point and defines at least one flow path between said injection point and a portion of said mold cavity forming a longitudinal edge, spaced from said injection point, said at least one first movable wall part extending around or opposite said injection point, along at least a portion of said flow path. The device of claim 1, wherein said first movable wall part extends around said injection point and said injection point is movable together with said at least one first movable wall part. Device as claimed in claim 1 or 2, wherein at least a second movable wall part is provided that extends at a distance from said injection point, in addition to said at least one first movable wall part, drive means being provided for movement of said at least one second movable wall part with respect to said at least one first movable wall part. Device as claimed in claim 3, wherein first drive means are provided for driving the at least one first movable wall part and second drive means for driving the at least one second movable wall part. Device as claimed in any of the claims 3 or 4, wherein the at least one first movable second wall part is provided with an opening in which the at least one movable wall part is received, preferably together with the at least one injection point. Device as claimed in any of the foregoing claims, wherein the at least one injection point is formed by a hot runner injector. 7. Device as claimed in any of the foregoing claims, wherein the at least one injection point has an injection direction that is approximately parallel to a direction of movement of said at least one first movable wall part, wherein the wall part of the mold cavity opposite the said at least one injection point forms a target 10 that is substantially flat and preferably extends approximately perpendicular to said injection direction. 8. Device as claimed in any of the foregoing claims, wherein said at least one first or second movable wall part is movable in an opening of a surrounding wall part, wherein a longitudinal edge of said opening facing an opposite wall part of the mold cavity is rounded. Device according to claim 8, wherein said longitudinal edge is rounded with a radius between 0.1 and 5 mm, preferably between 0.2 and 3 mm. Device as claimed in any of the foregoing claims, wherein a control device is provided for controlling the drive means, which control device is adapted to drive the at least one movable wall part in the direction of an opposite wall part of the mold cavity after at least 90% of a mass required for the formation of a product has been introduced into the mold cavity. 11. Device as claimed in claims 2 and 10, wherein the control device is arranged for successively moving the at least one first movable wall part and the at least one second movable wall part, for movement thereof in the direction of an opposite wall part of the mold cavity. 12. Device as claimed in any of the foregoing claims, wherein control means are provided for driving the at least one movable wall part along a main direction of movement and for injecting a mass into the mold cavity, which control means are adapted to bring the first into a first position at least one movable wall part during at least a first period of injection of said mass, subsequently moving said at least first wall part, during or after said injection of said mass, and subsequently moving said at least one At least first movable wall part, the intermediate position and the second position being situated on opposite sides of the first position, viewed along said main direction of movement. 13. Method for manufacturing products, in particular from plastic, wherein a device is applied according to any one of the preceding claims, wherein the first movable wall part is moved from a first position to a second position, the first movable wall part being in the the first position is further from an opposite wall part of the mold cavity than in the second position, wherein a mass is introduced into the mold cavity in the liquid state, which mass in the mold cavity is partially allowed to solidify, at least against a part of the walls of the mold cavity, at a distance from said first movable wall part, while a part of the mass resting against said one movable wall part remains liquid, after which said liquid part during moving of the first movable wall part from the first position to the second position of the mass is at least partially displaced into and / or against said solidification part of the mass, wherein said liquid part is displaced so rapidly that friction occurs between molecular chains in the mass such that temperature increase is obtained in the mass, wherein at least a part of the solidified mass is heated to above a melting point and back the liquid takes shape, whereafter the mass is then allowed to solidify completely, after at least said first movable wall part has been brought into the second position. 14. Method as claimed in claim 13, wherein a mold is applied with at least one further movable wall part which is situated in and / or near said longitudinal edge forming part, at a relatively large distance from said injection point, wherein said further movable wall part in a first position has been or will be brought at a relatively large distance from an opposite wall part, wherein a mass is introduced into the mold cavity under pressure, such that the mold cavity is filled with said mass and it moves between the at least one further movable wall part and the opposite wall part and which fills the mold cavity at least in and / or near said longitudinal edge forming part, after which said at least one first movable wall part is moved in the direction of said opposite first wall part, such that said mass between said at least one first movable wall part and the opposite first wall part is pressurized and possibly partially displaced. 15. Method as claimed in claim 13 or 14, wherein said first movable wall part is moved so rapidly in the direction of the opposite first wall part that adiabatic heat development occurs in the mass between them, such that the viscosity thereof is lowered. 16. Method as claimed in any of the claims 13-15, wherein each further movable wall part has a frontal surface which is present in a direction of movement, wherein the frontal surface of said further movable wall part or the joint said further movable wall parts is smaller than about 30% of the total product-forming surface of the mold cavity, preferably less than 20% thereof and in particular less than 10%. 10 3 25 1 9%