Core withdrawal injection molding of plastic components for interior design using a rapid heating and cooling system

Abstract

A core-pull injection mold comprises a positioning device designed to move a first mold half and / or a second mold half, a source of molten plastic, and a source of chemical foaming agent (CFA). A fluid delivery system supplies a first or second fluid at a first or second temperature to a channel defined in the first mold half. A controller supplies the first fluid to the channel of the first mold half; closes the first and second mold halves using the positioning device; supplies a mixture of molten plastic and CFA from the CFA to the cavity; opens at least one of the first and second mold halves by a predetermined distance using the positioning device; supplies the second fluid to the channel of the first mold half; opens the mold using the positioning device; and ejects a molded part.

Description

INTRODUCTION The information contained in this section serves to present the general context of the disclosure. Works of the inventors mentioned herein, insofar as they are described in this section, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, are neither expressly nor implicitly admitted as prior art contrary to the present disclosure. The present disclosure relates to the injection molding of parts, in particular to a core-withdrawal injection molding system. Parts such as interior or exterior trim panels for motor vehicles can be manufactured using an injection molding process. A mold contains a cavity that defines the inverse shape of a part. Molten plastic is injected into the cavity, forming the part. The molded part is then ejected from the mold, and the process is repeated. SUMMARY A core-retract injection mold comprises a mold consisting of a first mold half and a second mold half defining a cavity between them. A positioning device is designed to move at least one of the first mold half and the second mold half. The core-retract injection mold includes a source of molten plastic and a source of a chemical foaming agent (CFA). A fluid delivery system is designed to deliver a first fluid at a first temperature or a second fluid at a second temperature into a channel defined in the first mold half.A control system is designed to supply the first liquid from the liquid delivery system to the channel of the first mold half; to close the first and second mold halves using the positioning device; to supply a mixture of molten plastic from the molten plastic source and CFA from the CFA source to the cavity; to open one of the first and second mold halves by a predetermined distance using the positioning device; to supply the second liquid from the liquid delivery system to the channel of the first mold half; to open the mold using the positioning device; and to eject a molded part. For other characteristics, the first temperature ranges from 90°C to 120°C (200°F to 250°F). The second temperature ranges from 0°C to 30°C (32°F to 90°F). The CFA comprises 0.5% to 5% by weight of the mixture. In other cases, the molded part has a finished side and an opposite side. The first mold half corresponds to the finished side, and the liquid supply system selectively feeds the first liquid and the second liquid into the first mold half. The second mold half is moved relative to the first mold half by a predetermined distance. This predetermined distance is in the range of 0.5 mm to 1.5 mm. Other features include one of the first mold half and one of the second mold half comprising a first channel arranged around the cavity, a flexible sealing material arranged in the first channel, and the flexible sealing material designed for use at a temperature greater than or equal to 120 °C (250 °F). For other features, a section of the cavity of the first mold half includes surface etching with a depth ranging from 70% to 85% of the final etching depth of the molded part. A fluid source is designed to supply a third fluid to the channels of the second mold half. The temperature of the third fluid is lower than the temperature of the first fluid and higher than the temperature of the second fluid. A method for forming a part comprises providing a mold comprising a first mold half and a second mold half defining a mold cavity between them; supplying a first liquid at a first temperature to a channel of the first mold half; closing the first mold half and the second mold half; supplying a mixture comprising molten plastic and a chemical foaming agent (CFA) to the mold cavity; opening the first mold half or the second mold half by a predetermined distance; supplying a second liquid at a second temperature lower than the first temperature to the channel of the first mold half; opening the mold; and ejecting the part. For other characteristics, the first temperature is in the range of 90°C to 120°C (200°F to 250°F). The second temperature is in the range of 0°C to 30°C (32°F to 90°F). The CFA comprises 0.5 wt.% to 5 wt.% of a mixture. The molded part has a finished side and an opposite side; the first mold half corresponds to the finished side, and the first liquid and the second liquid are fed into the first mold half. For other features, the second mold half is moved relative to the first mold half by a specified distance. This specified distance ranges from 0.5 mm to 1.5 mm. A section of the mold cavity of the first mold half includes a surface texture with a depth that is between 70% and 85% of the final texture depth of the molded part. In other features, the process involves introducing a third fluid into a channel defined by the second mold half. The temperature of the third fluid is lower than the temperature of the first fluid and higher than the temperature of the second fluid. Further applications of the present disclosure will become apparent from the detailed description, the claims, and the drawings. The detailed description and the specific examples serve only for illustration and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will be better understood with reference to the detailed description and the accompanying drawings, wherein: Fig. 1 is a functional block diagram of an example of a core-retract injection mold comprising a mold and a fluid supply system that performs rapid heating and cooling of the mold according to the present disclosure; Fig. 2 is a side cross-section of an example of a cavity surface defining a surface scar of the molded part; Fig. 3A is a functional block diagram of an example of a positioning device and a source supplying a mixture comprising molten plastic and a chemical foaming agent (CFA) for the core-retract injection mold according to the present disclosure; Fig.3B is a top view of one of the mold halves, comprising a first channel for receiving a flexible mold material and a second channel selectively connected to a vacuum source according to the present disclosure; Fig. 4 is a functional block diagram of an example of a controller designed to control the core-withdrawal injection molding process according to the present disclosure; and Fig. 5 is a flow diagram of an example of a core-withdrawal injection molding process according to the present disclosure. Reference symbols can be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION Although the present disclosure relates to the core withdrawal injection molding of parts for vehicles, the injection-molded parts can also be used in other applications. Core-withdrawal injection molding can be used to reduce the weight of plastic molded parts, such as those used in automotive interiors and exteriors. The mold consists of a first mold half (e.g., a cavity side) and a second mold half (e.g., a core side). A heated liquid (e.g., water at a temperature of 50 °C (120 °F)) is circulated in the first mold half to heat the cavity side. A liquid (e.g., water at a temperature of approximately 40 °C (100 °F), or about 10 °C (20 °F) lower than in the first mold half) is circulated in the second mold half to control the temperature of the core side. The mold is closed, and a mixture of molten plastic and a chemical foaming agent (CFA) is injected into the cavity. One of the mold halves (e.g. the core side) is withdrawn by a predetermined distance (e.g. 0.5 to 1.5 mm) after the mixture has been added.After a predetermined time period, the mold halves are opened and the part is ejected. The process can be repeated for one or more additional parts. Typically, molded parts for automotive applications can have an exposed surface and a back surface. The exposed surface often needs to be a Class A surface finish. However, the core-pull injection molding process described above results in surface defects on Class A surfaces. Consequently, the molded parts must be painted in a second step to improve surface quality, which increases manufacturing costs. The present disclosure relates to a core-retract injection mold that uses a fluid delivery system to rapidly heat and cool the cavity side of the mold. During molding, the temperature of the first mold half is rapidly increased by a first fluid heated above the temperature of a conventional injection molding process. In some examples, the first fluid is supplied at a temperature in the range of 90°C to 120°C (200°F to 250°F). After one side of the mold has been retracted from the other, the rapid heating and cooling system supplies a second fluid at a temperature in the range of 0°C to 30°C (32°F to 90°F) to rapidly cool the cavity side of the mold. The use of the fluid delivery system in conjunction with a core-retraction injection mold minimizes Class A surface defects. As a result, lighter parts with high quality and improved appearance can be produced without the need for a secondary process such as painting. With reference to Fig. 1, a mold 10 comprises a first mold half 10-A (e.g., a cavity side), corresponding to a finished surface, and a second mold half 10-B (e.g., a core side), corresponding to a back surface. The first mold half 10-A includes channels 12 for receiving a heated or cooled liquid, such as water or oil, from a liquid dispensing system 13. The second mold half 10-A includes channels 14 for receiving fluid from a liquid source. A liquid delivery system 13 provides rapid heating and cooling by supplying a first liquid at a first temperature during the first part of a molding cycle (e.g., during the injection of a mixture of molten plastic and CFA) and a second liquid at a second temperature lower than the first temperature during the second part of the molding cycle (e.g., after retraction). The liquid delivery system 13 comprises a first set of valves 38 and channels 34 and 36 that selectively connect a first liquid source 30 to the first mold half 10-A, a second set of valves 68 and channels 64 and 66 that connect a second liquid source 60 to the first mold half 10-A, and crossing channels 37. The first liquid source 30 can include a heater 44 and a temperature sensor 42 for controlling the temperature of the first liquid in the first liquid source 30. The second liquid source 60 can include a cooler 74 and a temperature sensor 72 for controlling the temperature of the second liquid in the second liquid source 60. In some examples, the liquid dispensing system 13 includes a Variotherm temperature control system available from Single Group in Germany, although other systems can also be used. With reference to Fig. 2, an enlarged section of the surface of a cavity 90 is shown. The cavity 90 defines surface pitting of a finished surface. The surface pitting has a depth d1 that is in the range of 70% to 85% of the depth of a final surface pitting of the molded part. When working at higher temperatures, the depth of the surface pitting of the molded part increases. To compensate for this increase, the pitting depth defined by the cavity is reduced. With reference to Fig. 3A, a positioning device 110 is designed to move one or both mold halves 10A and 10B of the mold 10 in order to close, partially open (retract), and / or fully open the mold 10. A molten plastic source 114 and a chemical foaming agent (CFA) source 118 are designed to supply a mixture of molten plastic and CFA to the mold 10. In some examples, the CFA comprises 0.5 wt% to 5 wt% of the molten plastic and CFA mixture. In some examples, the CFA comprises 2 wt% to 5 wt% of the molten plastic and CFA mixture. In some examples, the CFA comprises 3 wt% to 5 wt% of the molten plastic and CFA mixture, as higher molding temperatures, compared to lower molding temperatures, may require an additional CFA concentration. With reference to Fig. 3B, in some examples a surface 131 of one or both mold halves comprises a channel 132 arranged around a cavity 137. A flexible sealing material 134 is arranged in the channel 132 to form a seal with the facing surface of the other mold half. In some examples, the flexible sealing material 134 is designed for a temperature higher than that of the first fluid. In some examples, the seal 134 is designed for a temperature greater than or equal to 250 °F. In some examples, the seal 134 is made of silicon. A channel 136 is arranged inside the channel 132 and outside the cavity 137 and is connected to a vacuum source 140 via a valve 138. With reference to Fig. 4, a controller 150 is designed to control the injection molding process. The controller 150 is designed to control the valves 38 and 68 of the liquid delivery system 32 to supply the first liquid for heating the cavity side of the mold and the second liquid for cooling the cavity side of the mold during each cycle. In some examples, the controller 150 is designed to receive the temperatures detected by the temperature sensors 42 and 72 to control the heater 44 and the cooler 74, respectively. The controller 150 is designed to control the positioning device 110 for opening and closing the mold. The controller 150 is designed to control the molten plastic source 114 and the CFA source 118 to supply the mixture and deliver it into the cavity. The ejector 152 comprises one or more extending and retracting pins, a lever, or other device.The controller 150 selectively controls the valve 138 to provide a vacuum for the channel 136. In some examples, the vacuum is applied during filling and terminated before the core retraction movement of the mold halves. With reference to Fig. 5, a method for forming a part according to the present disclosure is shown. At 220, the first fluid is supplied to the cavity side of the mold. At 224, the mold halves are closed. In some examples, the heated fluid is supplied before, during, or after the mold is closed. At 228, the molten plastic is injected into the mold cavity with the CFA. At 232, the mold halves are moved apart by a predetermined distance (e.g., 0.5 mm to 1.5 mm). At 236, the second fluid is supplied to the cavity side of the mold. At 238, the mold is opened. At 239, the first fluid is supplied to the cavity side of the mold half. At 240, the formed part is ejected. At 244, the method determines whether another part is to be formed. If so, the method is repeated. Otherwise, the method is terminated. The above description is for illustrative purposes only and is not intended to limit the disclosure, its application, or its use in any way. The comprehensive teachings of the disclosure can be implemented in a wide variety of ways. Although this disclosure includes certain examples, the true scope of the disclosure should therefore not be limited to them, since other modifications will become apparent upon study of the drawings, the patent specification, and the following claims. It is understood that one or more steps within a process may be carried out in a different order (or simultaneously) without altering the principles of the present disclosure.Even though the embodiments described above are each provided with certain features, each or more of these features described in relation to one embodiment of the disclosure can also be implemented with features of any of the other embodiments and / or combined with them, even if this combination is not expressly described. In other words, the described embodiments are not mutually exclusive, and the interchangeability of one or more embodiments remains within the scope of this disclosure. Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "interlocking," "coupled," "adjacent," "next to," "on top of," "above," "below," and "arranged." If a relationship between first and second elements is not explicitly described as "direct" in the above disclosure, this relationship may be a direct relationship, in which no other intervening elements exist between the first and second elements, or an indirect relationship, in which one or more intervening elements (either spatial or functional) exist between the first and second elements.As used herein, the expression “A, B and / or C” should be interpreted using a non-exclusive logical OR operation as logical (A OR-connected with B OR-connected with C) and not as “at least one of A, at least one of B and at least one of C”. In the diagrams, the direction of an arrow, as indicated by its tip, generally illustrates the flow of information (such as data or instructions) that is relevant to the illustration. For example, if Element A and Element B exchange a variety of information, but the information transferred from Element A to Element B is relevant to the illustration, the arrow may point from Element A to Element B. This unidirectional arrow does not mean that no other information is transferred from Element B to Element A. Furthermore, Element B may send requests or acknowledgments of receipt for information sent from Element A to Element B. In this application, which includes the definitions below, the term "module" or "controller" may be replaced by the term "circuit." The term "module" may refer to, be part of, or include: an application-specific integrated circuit (ASIC), a digital, analog, or mixed analog / digital discrete circuit, a digital, analog, or mixed analog / digital integrated circuit, a combinational logic circuit, a field-programmable gate array (FPGA), a processor circuit (common, dedicated, or group) that executes code, a memory circuit (common, dedicated, or group) that stores code executed by the processor circuit, other suitable hardware components that provide the described functionality, or a combination of some or all of the above components, for example, in a Systemon chip. The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces connected to a local area network (LAN), the internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of this disclosure may be distributed among multiple modules connected via interface circuits. For example, multiple modules may enable load balancing. In another example, a server module (also called a remote or cloud module) may perform some functions on behalf of a client module. The term "code," as used above, can include software, firmware, and / or microcode, and can refer to programs, routines, functions, classes, data structures, and / or objects. The term "shared processor circuit" includes a single processor circuit that executes some or all of the code from multiple modules. The term "group processor circuit" includes a processor circuit that, in combination with additional processor circuits, executes some or all of the code from one or more modules. References to multiple processor circuits include multiple processor circuits on discrete chips, multiple processor circuits on a single chip, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination thereof. The term "shared memory circuit" includes a single memory circuit that stores some or all of the code from multiple modules.The term "group memory circuit" encompasses a memory circuit that, in combination with additional memory, stores code from one or more modules, either partially or in its entirety. The term "memory circuit" is a subset of the term "computer-readable medium." The term "computer-readable medium," as used herein, does not include transitory electrical or electromagnetic signals propagating through a medium (e.g., on a carrier wave); the term "computer-readable medium" can therefore be considered tangible and non-transient. Non-restrictive examples of a non-transient, tangible, computer-readable medium include non-volatile memory circuits (e.g., a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (e.g., a static random-access memory circuit or a dynamic random-access memory circuit), magnetic storage media (e.g., an analog or digital magnetic tape or a hard disk drive), and optical storage media (e.g.,a CD, a DVD or a Blu-ray Disc). The devices and methods described in this application can be implemented partially or completely by a specialized computer created by configuring a general-purpose computer to perform one or more specific functions contained in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications that can be translated into computer programs through the routine work of an experienced technician or programmer. Computer programs comprise processor-executable instructions stored on at least one non-transient, tangible, machine-readable medium. Computer programs may also include or rely on stored data. Computer programs may include a basic input / output system (BIOS) that interacts with the hardware of the specialized computer, device drivers that interact with specific devices of the specialized computer, one or more operating systems, user applications, background services, background applications, and so on. The computer programs may include: (i) descriptive text to be parsed, e.g. B. HTML (Hypertext Markup Language), XML (Extensible Markup Language), or JSON (JavaScript Object Notation), (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. For example, source code can be written using the syntax of languages ​​including C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5th Revision), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK, and Python®.

Claims

Core-withdrawal injection mold, comprising: a mold with a first mold half and a second mold half defining a cavity between them; a positioning device designed to move the first mold half and / or the second mold half; a molten plastic source; a chemical foaming agent (CFA) source; a liquid delivery system designed to deliver a first liquid at a first temperature or a second liquid at a second temperature into a channel defined in the first mold half; a control designed to: supply the first liquid from the liquid delivery system to the channel of the first mold half; close the first mold half and the second mold half using the positioning device; supply a mixture of molten plastic from the molten plastic source and CFA from the CFA source to the cavity;Opening one of the first and second mold halves by a predetermined distance using the positioning device; supplying the second liquid from the liquid dispensing system to the channel of the first mold half; opening the mold using the positioning device; and ejecting a formed part. Core retraction injection molding tool according to claim 1, wherein the first temperature is in a range of 90°C to 120°C (200°F to 250°F). Core retraction injection molding tool according to claim 1, wherein the second temperature is in a range of 0 °C to 30°C (32 °F to 90 °F). Core retraction injection molding tool according to claim 1, wherein the CFA comprises 0.5 wt.% to 5 wt.% of the mixture. Core withdrawal injection molding tool according to claim 1, wherein: the mold part has a finished side and an opposite side, the first mold half corresponds to the finished side, and the liquid delivery system selectively supplies the first liquid and the second liquid to the first mold half. Core retraction injection molding tool according to claim 5, wherein the second mold half is moved by the predetermined distance relative to the first mold half. Core retraction injection molding tool according to claim 1, wherein the predetermined distance is in a range of 0.5 mm to 1.5 mm. Core retraction injection molding tool according to claim 2, wherein: the first mold half or the second mold half comprises a first channel arranged around the cavity, a flexible sealing material is arranged in the first channel, the flexible sealing material is designed for use at a temperature greater than or equal to 120 °C (250 °F). Core retraction injection molding tool according to claim 1, wherein a section of the cavity of the first mold half comprises a surface texture with a depth that is in the range of 70% to 85% of a final texture depth of the molded part. Core-withdrawal injection molding tool according to claim 1, further comprising: a fluid source designed to supply a third fluid to channels of the second mold half, wherein a third temperature of the third fluid is lower than the first temperature of the first fluid and higher than the second temperature of the second fluid.

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