Patent Description:
The following advanced injection moulding methods:.

In the co-injection/sandwich injection moulding method two different grades of plastic material form a sandwich structure in the wall cross sections of the injection-moulded part whereby a melt first injected into a cavity forms a comparatively thin surface layer, usually called a "skin", which covers the entire part and at the same time, or shortly after, a second injected melt forms a comparatively thick layer within the skin, called a "core layer", see <FIG> band 1c.

There are two different moulding processes for co-injection:.

The significance of the word "cold" in cold runners is that the walls of the runners may be heated to a surface temperature that is lower than the melting point of semi-crystalline polymers or the softening/melting interval of amorphous polymers and consequently a thin layer of the material will solidify against the surface of the walls in a cold runner when the melt flows through the runner.

Co-injection methods are preferably used either:.

Injection moulding of family parts means that two or more parts with a different shape, size and/or weight are simultaneously moulded in respective mould cavities in the same tool comprising a plurality of cavities. The injection times for filling mould cavities of different sizes, volume and/or shape differ, which means that the holding pressure applied to the melt has to be activated in the cavities at different points of time.

However, the co-injection or sandwich injection moulding and injection moulding of family parts methods are not that well established on the market as other methods such as "Over-Moulding" and "Gas Assisted Injection Moulding" which methods were introduced at the same time as the aforementioned methods. One reason for this, and maybe the main reason, is that an appropriate tool technology not been thoroughly developed ever since these methods were taken into use.

There is a need to eliminate the limitations of current tool and process technology, which limitations have probably prevented co-injection and injection moulding of family parts from increasing their market shares.

The Mono Sandwich process is carried out in a machine with only one injection unit, as shown in <FIG>. A melt volume <NUM> that is intended to form the core layer of the final part is first metered into the injection unit <NUM>. Then, a melt volume <NUM> that is intended to form a thin surface layer of the final part is plasticized in an extruder unit in the machine and metered through the orifice of the injection unit <NUM> to be positioned in front of the melt volume <NUM>. As the screw piston <NUM> of the injection unit <NUM> begins its stroke, as shown in <FIG>, the surface material <NUM> will firstly be injected into the mould cavity <NUM>, whereby a thin layer of the surface material will solidify against the comparatively cold shaping surfaces of the mould cavity. When the surface material <NUM> has been partly injected into the mould cavity <NUM> and the screw piston <NUM> continues making its stroke, the core material <NUM> will penetrate into the surface material <NUM> and press the surface material <NUM> against the shaping surfaces of the mould cavity <NUM>, at the same time as the core material fills the mould cavity inside the surface material layer (as shown in <FIG>). In this manner, a two-layered injection moulded part with a thin surface layer and a continuous and substantially thicker core layer encapsulated therein, is obtained.

When injection moulding of multi-layer parts in accordance with any one of the known co-injection methods, it is usually desired that all cross sections of the part shall have a comparatively thin surface layer of one surface material and a thicker inner layer of a core material. When using co-injection methods the most optimal volume shares of surface material in relation to core material is about <NUM>/<NUM> %. When using current tools in the injection moulding of multi-layer parts according to the co-injection method, these shares of about <NUM>/<NUM> % are achieved only if the parts have a simple and/or symmetrical shape, such as the part/cavity shown in <FIG>.

<FIG> and <FIG> show examples of problems, which may arise when co-injection is used for moulding more complex parts using unsuitable gating into the mould cavity. The melt flow extends in different directions from a sprue gate <NUM> to the outer contour of the mould cavity. If there are different flow distances for the melt and different wall thicknesses of the part between the shaping surfaces of the cavity there will be a different flow resistance for the multi-layer melt in the various flow paths in the mould cavity, which in the co-injection process results in flow fronts for the two plastic melts that are non-uniform with respect to each other and also non-uniform with respect to the outer contour of the mould cavity. In the parts of the mould cavity where the flow paths for the melt are substantially longer than the flow paths in other parts of the mould cavity, reasonable optimal shares of surface and core materials, respectively, are not obtained in the cross section at the end of the flow paths furthest from the sprue gate <NUM> where there is only core material <NUM>, as shown at the right-hand side of the part in <FIG>, which shows the part from above and in a cross section along the line A-A. It can namely be seen in <FIG>, that the core material melt <NUM> has penetrated through the surface material <NUM> at the flow front.

It is possible to partly obtain a multi-layer structure in the parts of the mould cavity which have the longest flow paths by overdosing the surface material melt, but, as can be seen in <FIG>, a too large amount of the surface material <NUM> is obtained at the end of the shorter flow paths, which means that the core material will not reach the outer contour of the mould cavity at these positions. Furthermore the flow front of the multi-layer melt will be split when the flow front passes openings for connections, such as reinforcements <NUM> or attachment means <NUM> etc. This means that optimal volume shares of surface and core materials cannot usually be maintained, due to the breakthrough of core material and the excess of surface material which are obtained at undesired positions in the product as shown in <FIG>, which shows a normal portion of core material in the reinforcements <NUM> and only core material in the snap-action attachment <NUM>. In <FIG>, the reinforcements have a too large portion of surface material, and the snap-action member <NUM> has a more normal share.

For injection moulded parts, such as panels, covers, housings, knobs, handles etc. there are generally specific demands on the properties of the visible surface layer of the parts, such as high finish, special features such as ultra-violet (UV) and heat resistance, high form accuracy, freedom from sinking, etc. This means that in case such parts are injection moulded with current methods using only one comparatively expensive material, the cost of the part will be fairly high. For portions of the parts which are not visible when the parts are in use there are usually no such demands on properties. Features such as connections, reinforcements and attachments, which have to exhibit good mechanical properties, such as toughness and rigidity, may have to be injection moulded using a material which is not suited for portions of the part that are visible in use. These types of parts are often multi-layer injection moulded by using the over-moulding method, often referred to as "double moulding". <FIG> shows the part illustrated in <FIG> and <FIG> injection moulded using the over-moulding method. In this method, a material <NUM> is firstly injected into one mould cavity, which forms the rear part with the connections <NUM> and <NUM>, whereupon the cavity that has formed the upper surface of the rear part is changed automatically in the over-moulding tool to a cavity which is somewhat larger, meaning that over-moulding with a surface layer material <NUM> can take place as shown in <FIG>. However this method results in substantially high investments in machines and tools and a comparatively long cycle time.

By overdosing the surface material melt it is possible to obtain a multi-layer structure also in the parts of the mould cavity, which have the longest flow paths, but as can be seen in <FIG>, a too large amount of the surface material <NUM> is obtained at the end of the shorter flow paths, which means that the core material will not reach the outer contour of the mould cavity at these positions.

<CIT> discloses a method and a tool for multi-layer injection moulding according to the co-injection method which provides a solution to the problems outlined above when using conventional tools for co-injection. According to <CIT> method for co-injection moulding a part incorporating an upper portion of the part and at least one connection integrated therewith is described. The cavity for the at least one connection is positioned in a movable tool core, see <FIG>, which core can be controlled to close and to open the entrance of the cavity for the at least one connection. The upper portion of the part is filled through an appropriate gate, for example a side gate with a plurality of runners upstream of the side gate or through any other suitable type of gate. When the entrance to the at least one connection is in a closed position as shown in <FIG>, the cavity for the upper portion of the part will be properly co-injected as the cavity of the at least one connection will not split the flow front of the co-injection process for the upper portion of the part. When the cavity of the upper portion of the part is completely filled and all metered surface material is used for moulding the surface layer of the upper portion of the part, the tool core for the at least one connection is activated to open the entrance whereby the melt of the core material will break through the surface material layer at the entrance and fill the cavity of the at least one connection, i.e. the at least one connection will consist of only core material. So, the method according to <CIT> will result in a multi-layer moulded part that is similar to the part shown in <FIG>, which is injection moulded by the over-moulding method.

<CIT>aims tp provide a moulding method which is capable of moulding a plurality of products, different in configuration, volume and the like, by one set of dies. <CIT> (<CIT>) shows a tool and a method for injection moulding of a plurality of differently sized and shaped objects in a plurality of mould cavities. The flow of material into the mould cavities and the pressure from the injection moulding machine can be individually regulated by means of control valves.

The object of the invention is to provide an improved method for injection moulding two or more parts with a different size shape and/or volume simultaneously in an injection moulding tool that comprises two or more mould cavities and which tool has a feed system for the melt, which comprises a plurality of runners that is located upstream of at the least one gate. The gate can be a side gate or any other type of gate which lets the melt into the at least two mould cavities. The feed system thus accommodates the melt coming from the injection unit in the injection moulding machine and guides the melt in one or more runners through the injection moulding tool to one or more gates into one or more mould cavities.

The plurality of runners according to the invention comprises at least one movable wall and the method comprises the step of changing at least one cross-sectional dimension of the plurality of runners by moving the movable wall to allow at least one cross-sectional dimension of the plurality of runners, such as height and/or width and/or diameter and/or any other dimension in a cross section with any other shape, to be changed, either manually or automatically before the injection moulding operation starts, or during an ongoing moulding cycle, to thereby apply a holding pressure to the material in the plurality of runners and consequently to the at least two mould cavities, i.e. to allow a mould cavity-specific holding pressure to be applied to each mould cavity, and/or to compress residue in the plurality of runners. The movable wall is arranged to be mechanically, hydraulically or electrically controlled.

The improved method according to the invention is primarily intended to be used to increase versatility and cost-efficiency and to decrease environmental loading and utilization of resources concerning.

A method according to the invention can also be applied to conventional injection moulding in order to reduce or eliminate various process and tool imperfections.

The present invention also concerns an injection moulding tool for performing a method according to any of the embodiments of the invention. The tool comprises at least two mould cavities and a feed system comprising at least one gate and a plurality of runners that is arranged to be located upstream of said at least one gate. The plurality of runners comprises at least one movable wall that is arranged to enable at least one cross-sectional dimension of the plurality of runners to be changed in order achieve at least one of the following:.

whereby said tool comprises means to change said at least one cross-sectional dimension of said plurality of runners.

According to an embodiment of the invention the tool comprises a plurality of adjacently arranged gate inserts that are adapted to change the at least one cross-sectional dimension of the plurality of runners. Each gate insert may be arranged to change the at least one cross-sectional dimension of one runner, whereby the flow front of material entering a mould cavity via the plurality of runners may be accurately controlled.

According to an embodiment of the invention the tool comprises heating means to heat the plurality of runners to a temperature less than a melting point or melting interval of the material in the plurality of runners.

According to an embodiment of the invention the movable wall is arranged to be mechanically, hydraulically or electrically controlled by the means to change the at least one cross-sectional dimension of the plurality of runners.

According to an embodiment of the invention at least part of the means to change said at least one cross-sectional dimension of the plurality of runners constitutes an exchangeable cassette that is arranged to be removably attached to the tool. A "cassette" is a protective case or holder comprising wear-resistant material, such as steel, which will protect its contents from being damaged when the means to change said at least one cross-sectional dimension of the plurality of runners is being operated, under high pressure for example.

The object is achieved by a method and tool having the features recited in the claims, which make it possible to.

It should be noted that the expression "changing at least one dimension in the cross section of the runners" is intended to mean that at least one dimension in at least one part of the plurality of runners may be changed. For example, the height in only one portion of a runner may be changed and not necessarily the height along the entire length of that runner.

The technical term "side gate" means a slot connecting at least one runner to one mould cavity, which slot is not too narrow and has a length that is appropriate for the spread of melt in the mould cavity connected to said gate. A side gate may be located to let in the melt at a lateral edge or close to such an edge of either a single-curved or a double-curved wall or an edge of a straight line of a flat wall of the part to be moulded. A gate should be dimensioned to allow for a sufficient flow of melt to fill the mould cavity without causing a too high shear that could degrade the material.

The melt may be any injection-mouldable material, such as any plastic, glass, elastomer, thermoplastic or thermosetting polymers or edible matter, such as confectionary, or a mixture containing at least one such material.

A method according to the present invention can therefore be used to mould various types of parts that may have a fairly complex design, and especially when used for co-injection moulded parts the share of core layer material is increased and more uniformly spread compared to what is possible with conventional prior art methods of co-injection moulding using tools having a conventional feed system. According to an embodiment of the invention it is possible to reach a share of the core material which is substantially higher compared to the use of conventional tools with a conventional feed system. A share of at least about <NUM> % of the total volume of a part having a fairly complex shape is possible to reach without core material melt breaking through the surface material layer and/or without too much surface material gathering in certain regions of the part. In case the parts have a simple and symmetric form even higher share than <NUM> % will be reached.

Using an electric servomotor as a drive unit provides a versatile and rapid variation of motion and force of the moving core in said runners whereby controlling of holding pressure operations can be performed during an ongoing moulding cycle.

According to an embodiment of the invention, a holding pressure can be applied to the melt in one or more of the plurality of runners whereby the pressure is momentarily transferred into each respective mould cavity via the gate that connects the mould cavity with said runners. A holding pressure is always, in all injection moulding methods, applied in the melt to ensure that the melt in the mould cavity stays densely packed while it solidifies. Said holding pressure operation according to the present invention is individually controlled for each of two or more cavities, which can be expressed "mould cavity-specific", and the holding pressure operation is initiated at the same point of time, or substantially at the same point of time, as filling melt into each of the two or more mould cavities has been completed, also called volumetric filling. The injection moulding machine's holding pressure function is not thereby utilized. Instead, the injection moulding cycle in each mould cavity comprises:.

When injection moulding family parts, the tool comprises mould cavities with unequal size, volume and/or shape that have to be filled using different injection times, which means that the holding pressure operation has to be initiated at different points of time in the various mould cavities.

Applying a holding pressure to the melt in one or more of the plurality of runners may be achieved by mechanical means with a drive unit that is coupled to a moving package/row of gate inserts and/or coupled to moving cores in a plurality of runners in the feed system upstream of the plurality of runners or upstream of any other chosen type of gate into the mould cavity. The mechanics and drive systems that are used for applying a holding pressure to the material in the runners and consequently to the respective mould cavities. The mechanics and drive system have to be adjusted so that enough volume of melt can be accumulated in the runners, constituting a so-called melt cushion, by moving backwards the package/row of gate inserts and/or the cores in one or more runners upstream of said gate inserts, which melt cushion ensures that the drive system pressurizes the melt during the whole holding pressure time.

A device for shutting off the melt flow upstream of runners wherein a holding pressure is intended to be applied, has to be arranged to prevent a portion of the melt in the melt cushion from flowing backwards in said runners thereby avoiding that a desired holding pressure would not be reached. The speed needed to move inserts and/or cores when changing the flow respectively applying a holding pressure are usually different as changing the flow usually is a more rapid movement. Thus, when combining the operations of changing melt flow and applying a holding pressure in the same runner during the same moulding cycle the dimensioning and specifications of the mechanics and the drive system have to be adapted to the force and speed needed for both operations.

This method according to the invention is especially intended to be used for single-material injection moulding family parts in a "multi-cavity mould", i.e. a tool comprising a plurality of mould cavities, where two or more cavities are different regarding shape, size and/or volume and whereby the cavities are only partly simultaneously filled as cavities with a large volume need a longer time to be filled than cavities with a smaller volume.

Accordingly the feed system for injection moulding family parts should comprise means for:.

Hereby the moulding process for the part in each separate mould cavity will turn out practically as if the part has been separately moulded with conventional methods, as whereby each part's weight and quality, such as surface finish, shape accuracy, mechanical properties etc. will remain unchanged.

The present invention is not limited to be used for co-injection moulding and/or injection moulding of family parts, but may also for instance be applied to single-material injection moulding, and to multi-material over-moulding.

The tool and method according to the invention can preferably be used in certain cases of conventional methods of injection moulding, for example in cases where the time for plasticizing and metering is so long that the time for performing the total moulding cycle has to be lengthened. By using the tool and method according to the invention, plasticizing and metering can start as soon as the mould cavity-specific holding pressure operations have been initiated, thus making it possible to shorten the cycle time.

According to an embodiment of the invention, compressing the material residue in the feed system can substantially reduce the amount of to be recycled either by grinding and plasticizing the residue directly in the injection unit of the machine or by separate recycling. Residue in one or more runners upstream of the plurality of side gate runners can be compressed either in case the compressing operation is combined with a holding pressure operation, or by a separate compressing operation in case a holding pressure operation is not used in said one or more runners. In the first case, i.e. combining with a holding pressure operation, a minimum of residue after compressing the residue in said one or more runners is reached by adjusting the melt cushion to contain a volume of melt that is exactly, or slightly larger than the volume that is needed for the holding pressure operation whereby a pressure should be applied to the melt during the whole duration of the holding pressure operation. The moving and pressurizing cores in said one or more runners will then compress the mixture of solidified and molten material residue to a minimum volume.

It should be noted that the degree of reduction of the residue in the feed system by compressing is dependant of factors such as stiffness, melt viscosity, reinforcement etc. of the mixture of molten and solidified material and the temperature of the walls in the runners.

A method for compressing the residue in the plurality of runners is also offered according to the invention by combining the embodiment of two packages/rows of gate inserts assembled opposite each other on both sides of the parting line of the tool and each of them coupled to a drive unit, whereby the compressing and holding pressure operations are performed simultaneously directly after volumetric filling of the cavity. The gate inserts in the package/row of inserts have to be adjusted so that the compressed residue will become as thin as possible without colliding with inserts on the opposite side of the parting line.

According to an embodiment of the invention the method comprises the means of heating the plurality of runners to a temperature less than a melting point or melting interval of the material in the plurality of runners. This can be achieved by heating a tool insert where the runners are positioned, to a temperature that is substantially higher than mould temperatures recommended by plastic material producers. The plastic layer, often called the "skin", of the melt that solidifies against the surface of the plurality of runners will become extraordinarily thin. The higher the temperature on the heated surface, the thinner the thickness of the skin will become. Heating the tool inserts is performed by using a separate heating unit and the inserts must be thermally insulated to prevent heat being conducted or radiated to other parts of the tool, such as mould plates, mould cavity inserts etc. The designation of such runners is still "cold runners" as their wall surface temperature is lower than the melting point or melting interval of the material meaning that a skin will solidify against the surfaces in the runners.

The embodiment of heated runners is primarily provided to ensure that the melt cushions in the runners will contain the highest possible share of molten material so as to achieve an efficient holding pressure operation. Flow resistance and shear in the melt will become lower as well which means that a lower injection pressure is needed for filling the melt through runners and into the mould cavity, which could be favourable when flow paths are long and/or flow resistance in the mould cavity is high.

All thermoplastic injection moulding grades, amorphous as well as semi-crystalline, and also thermoelastic grades, can be used with the embodiments according to the present invention. High viscosity amorphous thermoplastic grades such as PC (polycarbonate), PSU (polysulfone) and PES (polyether sulfone) will flow more easily in runners that are heated to a higher temperature, whereas an increase of injection speed and/or pressure will have less influence. The flowability of thermoelastomers, such as SEBS, is improved by a high shear in the melt. Such polymer-specific processing properties for certain plastic materials indicate that there is a need for runners to be separately heated and for the cross-sectional area of the runners to be adjusted when trying to find a process that provides a robust melt flow in the runners.

Generally, plastic materials with special processing properties/requirements such as high viscosity, high reinforcement, heat sensitive melt, highly shear-dependent flowability etc. could be better performed in injection moulding by utilizing one or more embodiments of the invention compared to the use of current technology for melt feed systems in the tool. Embodiments for runners upstream of the side gate are mainly characterised by.

Costs, environmental loading and utilization of resources in current injection moulding operations can be decreased by implementing a tool and method according to the present invention. The benefits for different injection moulding applications are:.

Any one or more of the features that are described with reference to the method according to the invention also apply to the tool according to the invention, and vice versa.

According to an embodiment of the invention the tool constitutes an exchangeable cassette, comprising one or more features of the tool, which is arranged to be removably attached to the injection moulding tool, using any suitable fastening means. Any part(s) of the tool, such as any or all parts of the pressure-applying means may be housed in such a removable cassette.

The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended schematic figures where;.

It should be noted that the drawings have not necessarily been drawn to scale and that the dimensions of certain features may have been exaggerated for the sake of clarity.

<FIG> and <FIG> show the two halves of an injection moulding tool, one half <NUM> on the stationary side and the other half <NUM> on the moving side of the clamp unit of the injection moulding machine in which the tool is housed, and which tool may be used in a method according to the present invention, such as any co-injection method and the method to mould family parts. The illustrated tool halves <NUM> and <NUM> comprise a three-plate mould in which a stripper plate <NUM> constitutes the third plate. A beam <NUM> mounted on the stripper plate <NUM> comprises side gate inserts <NUM> or <NUM>, and which beam <NUM> and side gate inserts <NUM> or <NUM> are detachable from the stripper plate <NUM>.

The tool halves <NUM> and <NUM> comprise two mould cavities <NUM> in which the parts are to be formed and each mould cavity has a side gate <NUM>. The tool halves <NUM> and <NUM> also comprise tool inserts <NUM> where a plurality of side gate runners <NUM> and a plurality of two branch runners <NUM> and a main runner <NUM> are positioned.

In the illustrated tool halves <NUM> and <NUM> of <FIG> and <FIG>, said runners <NUM> and <NUM> have rectangular cross sections and are completely positioned in tool inserts <NUM> mounted on the moving side tool half <NUM> and the top surface of the moving cores (<NUM> in <FIG>) is located at the bottom of the runners <NUM> and <NUM>, the walls of the through-hole for the moving cores <NUM> are the side surfaces of said runners and the flat or curved surface of the mould plate <NUM>, opposite inserts <NUM>, in the stationary tool half is located at the top surface of said runners.

<FIG> shows that according to an embodiment of the invention, the plurality of branch runners <NUM> and main runners <NUM> may have a substantially circular cross-section, a substantially oval cross-section or any other geometry. By setting the height Sx on the axis of symmetry of the cross-section of the runners <NUM> or <NUM> as shown in <FIG> the cross-section could, if desired, become substantially oval. Features of said runners <NUM> or <NUM> with a substantially circular or an oval cross section are firstly that the plastic residue in the runners <NUM> and/or <NUM> will have a smaller volume at the same flow resistance than corresponding runners with rectangular or square cross sections, secondly that the groove <NUM> together with the radially shaped surface on top of the core <NUM> forms a flange <NUM> that will press against the surface of the through-hole for the cores <NUM>, and, especially when a high pressure is built up in the melt or an extreme low-viscosity plastic melt is used, this design of the top of the core will contribute to an improved tightening in order prevent leakage of melt between the core <NUM> and its through-hole in the tool insert <NUM>.

The tool halves <NUM> and <NUM> in the <FIG> and <FIG> are merely an example of an injection moulding tool which may be used with the method according to the present invention. Generally, a tool does not necessarily have to comprise a stripper plate <NUM> and a beam <NUM>. Side gate inserts <NUM> and <NUM> or cores <NUM> associated with a plurality of runners <NUM>, <NUM> and <NUM>, as shown in <FIG>, <FIG> and <FIG>, no matter if they are coupled to drive mechanics according to the invention or not, can be positioned directly in the stationary half <NUM> as well as in the moving half <NUM> of the tool. A tool according to the present invention may also comprise any number of mould cavities <NUM>, such as two, three, four, five, or more mould cavities, where their shapes, sizes and/or volumes are different.

<FIG> shows features of a feed system according to an embodiment of the invention which is used to feed plastic melt into mould cavities <NUM> (not shown in <FIG>) when the injection moulding tool is in use. When the injection moulding tool is in use, there is namely plastic material in the main runner <NUM>, the two branch runners <NUM> and the plurality of five or two streamlined side gate runners <NUM>. The side gate <NUM> supplies the melt to the cavities <NUM>. <FIG> thus illustrates an exemplary shape and geometry of said side gate <NUM> and said runners <NUM>, <NUM> and <NUM>. The feed system is situated in the parting line of the tool in between the moving half <NUM> and the stationary half <NUM> and the beam <NUM>. The plastic material in the feed system shown in <FIG> has no compressed portions or any other deformations, so the shape/geometry of the plastic material fully corresponds to the surfaces/geometry of the runners and side gate of the feed system in the tool.

The term "gate" means an opening connecting at least one runner to a mould cavity. A side gate is an example of such a gate. A side gate may be located to let in the melt at a lateral edge, or close to such an edge, of either a single-curved or a double-curved wall of the moulded part. A side gate is of course also possible to locate at a straight edge of a flat wall of the part such as the side gate <NUM> into the larger cavity <NUM> shown in <FIG> and <FIG>. A gate is dimensioned to allow for sufficient flow of melt to fill a mould cavity without causing too high shear and degradation of the material. Only one gate <NUM> per mould cavity is preferable to avoid weld lines, when the melt is spreading out in the mould cavity <NUM>, and other defects in the final part. A plurality of runners <NUM> according to the invention can be arranged to feed melt through a side gate <NUM>. A branch runner <NUM> with its extension alongside the inlets to the plurality of side gate runners <NUM>, has to be arranged to feed the melt into this plurality of runners <NUM>, whereby means, such as the wedge-like tip <NUM>, to axially split the melt flow front at the inlet of each runner <NUM>, and then deflect the split portion of the melt into each runner of the plurality of runners <NUM>, which deflection can be facilitated by machining a cross section enlargement <NUM> partly at the inlet of each runner.

The main runner <NUM> and the two branch runners <NUM>, shown in <FIG>, both have a rectangular cross section, with heights Hx and widths Bx. In corresponding runners with substantially circular or oval cross sections, the diameter is Sx for a circular cross section as shown in <FIG> and the width and height for an oval cross section is Sx respective Sx+ΔSx. The plurality of runners <NUM> have a thickness Tx in their cross section across the melt flow direction. The index "x" means that the dimensions Hx, Bx, Sx and Tx belong to more than one of the plurality of runners and thereby may have different, fixed or adjustable sizes. In the illustrated tool, H1, H2 and H3 are the heights of the main runner <NUM> and of each of the two branch runners <NUM> respectively, and these heights may have been set by moving the cores <NUM> either to a fixed position in each runner before the injection moulding operations starts or to be changed gradually or stepless for each cycle during the injection moulding operations. The dimensions Tx for the "thickness" of respective runners in the plurality of runners <NUM> are T1, T2, T3, T4 and T5 for the large cavity <NUM> and T6 and T7 for the small cavity <NUM> and each of the runners <NUM> may be set at different thicknesses by moving the side gate inserts <NUM> with the set screws <NUM>, see <FIG> and <FIG>.

The tool according to an embodiment of the invention is arranged to carry out the one or more of the following functions:.

<FIG> illustrates a holding pressure operation where a substantially circular cross section of a runner <NUM> and/or <NUM> expands from a height Sx to Sx+Sex in order to accumulate a melt cushion that is necessary for the holding pressure operation. At the end of the holding pressure operation, (see the drawing on the right in <FIG>), the melt residue in the runners is compressed to a height Srx = about <NUM>,<NUM> Sx provided that the initial cross section is substantially circular with a diameter Sx.

The embodiment shown in <FIG> can be supplemented with drive mechanics to apply a force on the gate inserts <NUM>, (see <FIG>) to perform a holding pressure operation in the melt in the plurality of gate runners <NUM> upstream of the side gate <NUM> and consequently a holding pressure in the melt that has been fed into the mould cavity <NUM>.

In the embodiment shown in <FIG> there is also a cassette <NUM> with a recess <NUM> where the side gate inserts <NUM> are mounted and which together with the fixed insert <NUM> form a plurality of runners <NUM> upstream of the side gate <NUM>. The set screws <NUM> are connected to the upper wedge <NUM> and the dimension Tx can be adjusted individually by the set screw <NUM> in each gate insert <NUM> in the plurality of runners <NUM>.

<FIG> show an example of holding pressure operational steps, where a plurality of side gate inserts <NUM> are coupled to an upper wedge <NUM> that via a lower wedge <NUM> has a connection <NUM> to a drive unit that may be a double-acting hydraulic cylinder or a hydraulic motor or an electric servo motor. The holding pressure operation is activated to start at the same point of time as the melt filling operation into the mould cavity <NUM> has ceased, or at a point of time shortly before the filling operation has ceased, meaning that the plurality of side gate runners <NUM> that has been set to different dimensions Tx (see <FIG>) in the next step (shown in <FIG>) the package/row of side gate inserts <NUM> is controlled to expand a distance Te which distance is the same for all runners in the plurality of runners <NUM> as the side gate inserts <NUM> are in fixed positions in relation to each other after being set to dimension Tx. The expanding movement Te is carried out by pulling the lower wedge <NUM> a corresponding distance backwards in the cassette <NUM>. Thereby plastic melt is accumulated in the plurality of runners <NUM> to a so-called "melt cushion", which will accomplish a volume, as a result of an appropriately chosen expansion Te, which volume is as large as, or slightly larger than, the volume of plastic melt needed for maintaining a desired holding pressure in the mould cavity <NUM> during the whole holding pressure operation. The compression of the plastic material terminates with different dimensions Trx /See <FIG>) of the plastic residue in the plurality of runners <NUM> and which dimensions Trx usually are slightly larger than Tx.

With this embodiment a holding pressure operation can be performed in the plurality of runners <NUM>, and consequently in the mould cavity <NUM>, provided that there is a device in one of the runners of the plurality of runners <NUM> or <NUM> upstream of the plurality of runners <NUM> for shutting off the melt flow to said mould cavity in order to prevent the melt being pressed backwards whereby a desired holding pressure in the melt that has been supplied to the cavity would not be possible to build up. The shut off device may be positioned in a way that the melt flow can be shut off either in one of the plurality of branch runners <NUM> or in a main runner <NUM>. <FIG> shows two shut off devices <NUM> that each comprise a mini hydraulic cylinder driving a shut off core that closes and opens the two branch runners <NUM>. Such a shut off device may be designed in different ways.

The embodiment according to the invention that is exemplified in <FIG> can be used in tools where there is a need of:.

The embodiment comprising a plurality of side gate runners <NUM> and cassette <NUM> which is shown in <FIG>, comprising the mechanics to apply a holding pressure in the melt, is possible, even without taking down the tool from the injection moulding machine, by mounting and dismounting the tool in the following way:.

The embodiment shown in <FIG> can be combined with a plurality of side gate inserts <NUM> including drive mechanics, (see <FIG>), which replaces the fixed insert <NUM> shown in <FIG>. The purpose of supplementing said embodiment with a plurality of runners <NUM> including driven side gate inserts <NUM> is to compress the plastic material residue in the plurality of runners <NUM> to a minimum volume, corresponding to a dimension Trx, which dimension may be different from side gate runner to side gate runner, in order to get smallest possible amount of residual material when recycling the residue directly into the injection unit of the machine or when recycling the residue separately. The compression operation may be carried out simultaneously from both sides of the plurality of runners <NUM> (see <FIG>). The plurality of side gate inserts <NUM> and its drive mechanics according to <FIG>, is designed just for performing a compression operation on the plastic residue in the plurality of side gate runners <NUM> and thereby has to be combined either with the embodiment for applying a holding pressure to the melt in said runners <NUM> according to <FIG> or combined with a holding pressure operation in the injection unit of the machine. Usually the dimension Tx could be compressed by at least <NUM>%, i.e. the compressed dimension, Trx ≤ <NUM>,<NUM> Tx.

The mechanics of the embodiment for the compression operation of the plastic residue in the plurality of runners <NUM> as shown in <FIG> is identical to the mechanics of the embodiment in <FIG> for carrying out the holding pressure operation, apart from the side gate inserts <NUM>, the set nuts <NUM>, the screws <NUM> and the coil springs <NUM>. As the cross sections of the plurality of runners <NUM> in <FIG> have been set to a dimension Tx and the desired dimension of the compressed plastic residue is Trx the set nuts <NUM> should be turned to move the side gate inserts <NUM> to be set at a dimension Tx - Trx from their initial position where they are fully tightened to the screws <NUM> which screws are permanently fully tightened to the wedge <NUM>. The coil springs <NUM> will ensure that the inserts <NUM>, which are connected to a dowel of the set nuts, are returning together with the set nuts <NUM> when the drive unit is pulling back the wedges <NUM> and <NUM>.

An example of the plurality of branched runners <NUM> and main runners <NUM> according to the invention, all of them being so-called "cold runners" are shown in <FIG> and <FIG> in the form of corresponding plastic residues of the feed system. In the tool consisting of the tool halves <NUM> and <NUM>, <FIG> and <FIG>, said runners have rectangular cross sections and are completely positioned in tool inserts <NUM> mounted on the moving side tool half <NUM> where the top surface of the moving cores <NUM> constitutes the bottom of the runners <NUM> and <NUM>, the walls of the through-hole for the moving cores <NUM> are the side surfaces of said runners and the flat or curved surface of the mould plate <NUM>, opposite inserts <NUM>, in the stationary tool half constitutes the top surface of said runners.

The mechanics according to the invention for the plurality of side gate runners <NUM> is constituted by an upper wedge <NUM> and a lower wedge <NUM> connected to a coupling rod <NUM>, which all are mounted in a cassette <NUM> that is pushed into a recess in between the mould plates <NUM>. The upper wedge <NUM> is, via the set screws <NUM>, connected to the plurality of side gate inserts <NUM> or <NUM>, see <FIG> and <FIG>. The mechanics for the plurality of runners <NUM> and <NUM>, see <FIG>, is also constituted by an upper wedge <NUM> and a lower wedge <NUM> connected to a coupling rod <NUM>, which are all mounted in a cassette <NUM> that is pushed into a recess in between the mould plates <NUM> and the upper wedge <NUM> via inclined hooks <NUM> and notches <NUM> coupled to the moving cores <NUM>.

<FIG> shows the mounting of the moving cores <NUM> in the through-holes in a tool insert <NUM>. Mounting of the mechanics starts by positioning the cassette <NUM>, wherein the upper and lower wedges <NUM> and <NUM> are in a fixed position as shown in <FIG>, a short distance backwards from the very front of the recess whereupon the cores <NUM>, including the bridging pieces <NUM>, are pushed into their through-holes so that the hooks <NUM> will be situated on the upper surface of the wedge <NUM> a short distance to the left of the notches <NUM>. Then the cassette <NUM> is pushed said short distance forward to its very front position whereby the hooks <NUM> will slide down into the notches <NUM> and thus the cores <NUM> are thereby connected to the upper wedge <NUM> as shown in <FIG>. Then, in case the operation of the cores so requires, the coupling <NUM> can connect the lower wedge <NUM> to a drive unit for the purpose of applying a holding pressure in the plurality of runners <NUM> and/or <NUM> or the coupling <NUM> can be connected to a screw device (such a device <NUM> can be seen in <FIG>) for setting the heights Hx or Sx or Sx+ΔSx in fixed but optional positions in said runners with substantially rectangular or circular or oval cross sections. The cores <NUM> have a flat surface on both sides of their lower part which surfaces glide against support pieces <NUM> to ensure that the hooks <NUM> are fully kept down in the notches <NUM> during use of the tool. Demounting is carried out in the opposite order, with the upper and lower wedges <NUM> and <NUM> in a fixed position (as shown in <FIG>), and pulling the cassette <NUM> a short distance backwards etc. The cores <NUM> can, when unfastened, be pulled out from their through-holes.

The functions and operations according to the invention, such as start and stop times and speeds/forces for the drive means coupled to the mechanics for the plurality of runners <NUM>, <NUM> and <NUM>, have to be co-ordinated and controlled in such a manner that this new injection moulding technology can be adapted to specific and different methods that can utilize the invention. Typical operations of the injection moulding machine and the tool according to the invention, are the start of injection and changing injection speed at different positions for the reciprocating motion of the screw piston in the machine, changing the cross section and closing/opening of one or more of the plurality of branch runners <NUM> or main runners <NUM>, switch-over to holding pressure either in the injection unit of the machine or in the plurality of runners <NUM>, <NUM> and <NUM> in the tool and performing the holding pressure and compression operations in one or more of said runners.

The drive means connected via a coupling rod <NUM> to the mechanics connected to side gate inserts <NUM> and/or <NUM> and moving cores <NUM>, which inserts and cores are associated with the plurality of runners <NUM>, <NUM> and <NUM>, may be hydraulic cylinders. Electric servomotors or hydraulic motors may also be used. The drive means in a tool according to the present invention, may be connected to an electronic control system in such a way that the moulding process in each mould cavity in a tool with a plurality of mould cavities and a plurality of runners, can to a great extent be individually and variably controlled regarding operations for holding pressure and/or compression of plastic residue in the gating system. The start and end positions for moving the plurality of side gate inserts <NUM> and <NUM> and the cores <NUM> during the injection and holding pressure operations may be set with the screw device <NUM>. The control system may either be stationary and integrated in the injection moulding machine or located externally to the injection moulding machine, i.e. the control equipment may be transportable between different injection moulding machines.

The tool inserts <NUM>, shown in <FIG> and <FIG>, may be designed in such a way that two functions of the new injection moulding technology according to the present invention will be accomplished, which functions are.

Heating of the tool inserts <NUM> is performed by using a heating unit that is separate from the heating unit that tempers the rest of the tool to achieve and maintain a mould temperature recommended by the plastic producer. The inserts <NUM> must be thermally insulated to prevent heat from being conducted or radiated to other parts of the tool, which is achieved in several ways such as:.

Moving cores <NUM> or side gate inserts <NUM> or <NUM> perform a reciprocating movement under high pressure and high temperature in the plastic melt at each process cycle and mostly during a long period of time. These process conditions will cause a fairly high pressure between cores <NUM> and their through-holes and between side gate inserts <NUM> and/or <NUM> and their recesses. When injection moulding certain types of plastic material, a mixture of air and volatiles from the melt will to some extent force its way out along the moving surfaces of cores/side gate inserts and/or through-holes/recesses. So there might be both mechanical and corrosive wear on these surfaces. Minor wear could be acceptable on the moving cores <NUM> and side gate inserts <NUM> and <NUM> as they are cheaper to manufacture and easy to exchange in the tool, but said process conditions require that the tool inserts <NUM> have to be manufactured from an extremely high hardened and corrosion resistant steel grade such as stainless steel hardened to at least <NUM> HRC. Moving cores <NUM> and side gate inserts <NUM> or <NUM> may be manufactured from a material that is somewhat "softer" but still corrosion resistant. The tool inserts <NUM> can be manufactured conventionally or using a 3D printing additive method using steel powder.

Claim 1:
Method for injection moulding two or more parts with a different size, shape and/or volume using an injection moulding machine and tool (<NUM>, <NUM>) comprising two or more mould cavities (<NUM>), and a feed system comprising at least one gate (<NUM>) a plurality of runners (<NUM>, <NUM>, <NUM>) located upstream of said at least one gate (<NUM>), whereby said plurality of runners (<NUM>, <NUM>, <NUM>) comprises at least one moveable wall and said method comprises the step of changing at least one cross-sectional dimension (Tx, Bx, Hx, Sx) of said plurality of runners (<NUM>, <NUM>, <NUM>) by moving said movable wall, wherein said method is for injection moulding said two or more parts with a different size, shape and/or volume simultaneously, and comprises the step of changing said at least one cross-sectional dimension (Tx, Bx, Hx, Sx) of said plurality of runners (<NUM>, <NUM>, <NUM>) by moving said at least one movable wall in order to achieve at least one of the following:
a) to apply a holding pressure to material in said plurality of runners (<NUM>, <NUM>, <NUM>) and consequently to said two or more mould cavities (<NUM>),
b) to compress residue in said plurality of runners (<NUM>, <NUM>, <NUM>),
characterized in that said at least one cross-sectional dimension (Tx, Bx, Hx, Sx) of said plurality of runners (<NUM>, <NUM>, <NUM>) is individually variable by means of a plurality of side gate inserts (<NUM>, <NUM>) that are adapted to change said at least one cross-sectional dimension (Tx) of said plurality of runners (<NUM>).