METHOD FOR MOLDING A PART USING AN INJECTION MOLDING PROCESS WITH LASER CUTTING IN THE MOLD

Abstract

A process for forming a part comprises providing a mold comprising a first mold half and a second mold half, which define a first cavity and a second cavity. The first cavity defines the shape of a first subsection and a projection section. The second cavity defines the shape of a second subsection that at least partially surrounds the first subsection. The process includes closing the first mold half and the second mold half; injecting a first shot of molten plastic using a shot gate positioned along the projection section to form the first subsection of the formed part; opening the second mold half; trimming the projection section with a laser; rotating the first mold half and / or the second mold half; closing the second mold half; and injecting a second shot into the mold to form the second subsection.

Description

INTRODUCTION

[0001] The present disclosure relates to a method for forming a part using injection molding, in particular a multi-shot injection molding process, in which a shot gate is cut and removed in the mold using a laser.

[0002] A method for back-injection molding of formed components is disclosed in DE 103 25 530 A1. US 5 800 759 A describes a method in which excess sections of a part held in an injection mold are cut in the injection mold. JP H07-9 504 A discloses the use of a laser for cutting injection-molded parts.

[0003] Parts can be manufactured using an injection mold consisting of a first and second mold half, each defining a cavity in the shape of the molded part. The first and second mold halves are closed, and molten plastic is poured into the cavity between them. The first and second mold halves are then opened, and the part is ejected. This process is repeated for another part.

[0004] One object of the invention is to provide an improved method for forming a part, in particular one that is visually appealing. SUMMARY

[0005] The problem is solved by a method having the features of claim 1.

[0006] An inventive method for forming a part comprises providing a mold comprising a first mold half and a second mold half, which define a first cavity and a second cavity. The first cavity defines the shape of a first subsection and a projection section. The second cavity defines the shape of a second subsection that at least partially surrounds the first subsection.The process includes closing the first mold half and the second mold half; injecting a first shot of molten plastic using a shot gate positioned along the protruding section to form the first subsection of the molded part; opening the second mold half; trimming the protruding section with a laser; rotating the first mold half and / or the second mold half; closing the second mold half; and injecting a second shot into the mold to form the second subsection.

[0007] Advantageous further training can be found in the dependent requirements, the following description and the attached drawings.

[0008] In other features, the protruding section is removed by the laser, while the first subsection is located in the first or second mold half. The first and second shots comprise transparent plastic. The first and second shots comprise polymethyl methacrylate (PMMA). The first and second shots comprise polycarbonate. The first and second shots comprise plastic of different colors.

[0009] Other features of the laser include a carbon dioxide (CO2) laser. The laser operates at a wavelength greater than 4 micrometers. A robot is configured to position the laser relative to the first mold half and the protruding section of the first sub-section. The process involves using a vacuum to evacuate any vapor generated during laser trimming of the protruding section.

[0010] A multi-shot injection mold for producing a molded part comprises a mold with a first mold half and a second mold half, the latter defining a first cavity that defines the shape of a first sub-section and a projection section, and a second cavity that defines the shape of a second sub-section that at least partially surrounds the first sub-section. The multi-shot injection mold further comprises a laser, a positioning device, a first injection nozzle, and a second injection nozzle.A control device is configured to cause the positioning device to close the first mold half and the second mold half; to cause the first injection nozzle to inject a first shot of molten plastic using a shot gate located along the protruding section to form the first sub-section; to cause the positioning device to open the second mold half; to cause the positioning device and the laser to trim the protruding section; to cause the positioning device to rotate the first mold half and / or the second mold half; to cause the positioning device to close the second mold half; and to cause the second injection nozzle to inject a second shot into the mold to form the second sub-section.

[0011] In other features, the protruding section is removed by the laser, while the first subsection is arranged in one of the first and second mold halves. The first and second shots comprise transparent plastic. The first and second shots comprise polymethyl methacrylate (PMMA). The first and second shots comprise polycarbonate. The first and second shots comprise plastic of different colors.

[0012] Other features of the laser include a carbon dioxide (CO2) laser. The laser operates at a wavelength greater than 4 micrometers. A vacuum nozzle is configured to evacuate vapor generated during the laser cutting of the protrusion section. The formed part includes a taillight lens for a vehicle.

[0013] 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

[0014] The present disclosure will be better understood with the help of the detailed description and the accompanying drawings, whereby: Fig. 1 is a perspective view of an example of a first subsection of a molded part, which is formed using a first shot in a multi-shot injection molding tool; Fig. 2 a perspective view of an example of the shaped part made of Fig. 1 is after a second shot of the multi-shot injection mold has been formed around the first sub-section; Fig. 3 is a perspective view of an example of a first subsection of a molded part formed using a first shot in a multi-shot injection molding tool according to the present disclosure; Fig. 4 a perspective view of an example of the shaped part made of Fig. 1 is after a second shot of the multi-shot injection molding tool has been formed around the first subsection according to the present disclosure; Fig. 5A is a side cross-section of an example of a multi-shot injection molding tool with a first mold half and a second mold half according to the present disclosure; Fig. 5B is a perspective view of an example of a multi-shot injection molding tool according to the present disclosure; Fig. 5C is a functional block diagram of a control system for the multi-shot injection mold according to the present disclosure; Fig. 6 is a functional block diagram of an example of a coaxial vacuum nozzle according to the present disclosure; and Fig. 7 is a flowchart of an example of a process for forming a part using a multi-shot injection mold according to the present disclosure.

[0015] Reference symbols can be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0016] Although an injection molding process according to the present disclosure is described herein in connection with molded parts for vehicles, the injection molding process can be used to manufacture parts for other mobile and / or stationary applications.

[0017] Multi-shot injection molds are used to manufacture plastic parts. In a two-shot injection mold, the mold comprises a first and a second mold half, which define one or more first cavities corresponding to a first section of a molded part. The first and second mold halves also define one or more second cavities corresponding to a second section of the molded part, which surrounds at least part of the first section.

[0018] The first and second mold halves are closed, and a first shot of molten plastic is injected into the first cavity between the first and second mold halves. One of the first and second mold halves is opened. One of the first and second mold halves is rotated, and the first and second mold halves are closed. A second shot of molten plastic is injected around the first section into the second cavity, after which the part is ejected.

[0019] Some types of molded parts, such as taillight lenses, are made from plastic that is injection-molded into a mold cavity using a direct-shot gate. The direct-shot gate is located within the boundaries of the first section of the injection-molded part. When using direct-shot gates, gate remnants typically form. For some molded parts, gate remnants are acceptable; however, the quality of the injection-molded plastic at the gate remnants differs from that elsewhere. For other types of molded parts, such as taillight lenses, the gate remnants compromise the optical properties of the injection-molded part and are therefore unacceptable.

[0020] A similar problem arises when the injection-molded part is formed in a multi-shot injection molding process. For example, the first section of an injection-molded part is produced by injecting a first shot (e.g., of clear, transparent plastic) into the first cavity using a direct gate. The mold is then opened, rotated, and a second shot (e.g., plastic of a different color) is injected around the first section into the second cavity. However, the first section (and possibly the second section) of the injection-molded part will have a gate remnant.

[0021] With the following reference to Fig. 1 and Fig. 2. A first subsection 110 of an injection-molded part is formed using a multi-shot injection molding process. The first subsection 110 of the injection-molded part is formed using a direct shot gate, which leaves a gate remnant 114. It is understood that the gate remnant 114 impairs the visual quality and / or optical performance of the molded part. Fig. 2 is a second subsection 130 of the injection-molded part formed around the first subsection 110.

[0022] With the following reference to Fig. 3 and Fig. Figure 4 presents an example of a first subsection 120 of an injection-molded part using a multi-shot injection molding process according to the present disclosure. The first subsection 120 of the injection-molded part comprises a shot gate 124 formed in a projection section 122 defined in the first cavity and extending from an edge on one side of the first subsection 120. As further described below, a laser is used to remove the projection section 122 along dotted lines 126. In some examples, the projection section 122 is removed while the first subsection is still in one of the mold halves.

[0023] In Fig. 4 is a second subsection 134 of the injection-molded part formed around the first subsection 120 after the projection section 122 has been removed. In some examples, the second cavity also includes a projection section 160, defined within the second cavity and extending from an edge on one side of the second subsection (as in Fig. 5B can be seen). The protruding section 160 can be removed in the molding tool or after the molded part has been removed from the molding tool.

[0024] With the following reference to Fig. 5A and Fig. 5B shows a multi-shot injection mold. Fig. 5A The multi-shot injection mold comprises a first mold half 203 and a second mold half 205. One or both of the first mold half 203 and the second mold half define one or more first cavities 206 and one or more second cavities 208. A first channel 207 supplies molten plastic to the first shot gate in the projection section 122. A second channel 209 supplies molten plastic to the second shot gate in the projection section 160.

[0025] In Fig. Figure 5B shows that the multi-shot injection mold includes a moving clamping device 210 that moves relative to and is guided by tie rods 216. In some examples, a hydraulic cylinder is used to move the moving clamping device 210 relative to a stationary clamping device (partially shown).

[0026] A first rotating clamping device 212 rotates relative to the moving clamping device 210. A first mold half 203 is mounted around the rotating clamping device 212. In some examples, the tie rods 216 extend through the moving clamping device 210 to the stationary clamping device 218. The second mold half 205 is attached to an inner surface of the stationary clamping device 218, which faces the first mold half 203 (not shown). The first mold half 203 and / or the second mold half 205 define one or more first mold cavities 220 for forming the first sub-section 120. The one or more first mold cavities 220 include a projection section 222 (which extends from a finishing edge of the formed part after trimming) for forming the projection section 122. A butt gate 224 is located in the projection section 222.The first mold half 203 and / or the second mold half 205 define one or more second mold cavities 234 for forming the second subsection 134 around the first subsection 120.

[0027] In operation, the one or more first mold cavities 220 form the first subsection 120 of the molded part with the projection section 122. After the first subsection 120 is formed, the second mold half 205 is opened (as would normally happen before rotation for the second shot). Before or after rotation, the projection section 122 is cut off and removed with a laser 244 while the first subsection 120 is still in the first mold half 203. In some examples, the robot 240 controls the position of the laser 244 to cut the projection section 122 along the edge of the first subsection 120 while the first subsection 120 is still held in the first mold half 203. After the removal of the projection section 122 and the shot gate 124, the first mold half 203 is rotated and the second mold half 205 is closed.The second shot is injected to surround at least part of the first subsection 120 without leaving any cut remnant from the first shot in the first subsection 120.

[0028] In Fig. In 5C, a control unit 280 can be used to automate the molding process. The control unit 280 is configured to control one or more positioning devices 281, which are configured to open and close the second mold half and / or rotate the first mold half relative to the second mold half. In some examples, the positioning devices 281 include a hydraulic cylinder and / or a motor for moving and / or rotating the clamping devices. The control unit 280 is configured to control a first plastic injection nozzle 282 and a second plastic injection nozzle 284 for injecting the first and second shots of molten plastic. The control unit 280 is configured to control the robot 286 for positioning the laser 244 during the cutting of the protrusion section 122 and / or the protrusion section 160.The control unit 280 is configured to control the laser 244. The control unit 280 is configured to supply vacuum from a vacuum source 290 to remove vapor generated by laser trimming of the protrusion section 122 and / or the protrusion section 160.

[0029] With the following reference to Fig. 6. When the projecting section 122 is removed with the gate while the first subsection 120 is located in the first mold half 203, a coaxial vacuum nozzle 310 can be used to remove steam generated by laser cutting of the formed part, thus preventing contamination of a mold surface in the mold half 219. The laser 244 emits a laser beam 245 onto a lens 312, which focuses the laser beam 245. The coaxial vacuum nozzle 310 is connected to a vacuum source 330 and an outlet 332 for evacuating the steam.

[0030] In some examples, the rear light lens is made of plastic. In some examples, the plastic is a polymer that can be vaporized with a laser without discoloring the surface at the cut or producing molten plastic. In some examples, the plastic is polymethyl methacrylate (PMMA) or polycarbonate. PMMA absorbs wavelengths of light longer than 4 micrometers (µm), which is in the far-infrared region of the electromagnetic spectrum. The mold halves are typically made of steel, which has a lower absorption rate in the far-infrared range.

[0031] In some examples, the laser includes a carbon dioxide (CO2) laser with a wavelength of approximately 10.6 µm to ensure absorption by the PMMA and to reduce absorption by the steel of the first mold half 203. In some examples, the laser uses power in the range of 10 watts (W) to 1000 W. In some examples, the laser uses power in the range of 10 watts (W) to 200 W. In some examples, the laser uses power in the range of 10 watts (W) to 80 W. Vaporization cutting provides a narrow cutting kerf and high cut quality, and a low laser power (e.g., 60 W) can be used to avoid laser damage to the mold surface.

[0032] With the following reference to Fig.Figure 7 shows a process for forming a part. At 412, the mold halves are closed. At 414, a first shot is injected into the remote injection gate between the first and second mold halves to form the first subsection with the protruding section. At 418, the second mold half is opened. At 422, a laser is used to cut the protruding section from the first subsection while the first subsection is in the first mold half. At 426, the first mold half is rotated, and the second mold half is closed over the first mold half. At 430, a second shot is injected around at least one section of the first subsection. Reference symbol list 110 first subsection 114 Section Remains 120 first subsection 122 Lead section 124 shot cut 126 lines 130 second subsection 134 second subsection 160 lead section 203 first half of the form 205 second half of the form 206 first cavity 207 first channel 208 second cavity 209 second channel 210 movable clamping device 212 Rotating clamping device 216 tie rods 218 stationary clamping device 220 mold cavity 222 Lead section 224 shot cut 234 Mold cavity 240 robots 244 lasers 245 laser beam 280 Control unit 281 Positioning device 282 Plastic injection nozzle 286 robots 290 vacuum source 310 vacuum nozzle 312 lens 330 Vacuum source 332 Outlet 412-430 Procedural steps

Claims

[1] Method for forming a part, comprising: Providing a mold comprising a first mold half (203) and a second mold half (205) defining a first cavity (206) and a second cavity (208), wherein the first cavity (206) defines a form of a first subsection (120) and a projection section (122), and wherein the second cavity (208) defines a form of a second subsection (134) that at least partially surrounds the first subsection (120); Closing (412) of the first mold half (203) and the second mold half (205); Injecting (414) a first shot of molten plastic using a shot gate (124) arranged along the projection section (122) to form the first subsection (120) of the molded part; Opening (418) of the second mold half (205); Trimming (422) the protruding section (122) using a laser (244), while the first sub-section (120) is arranged in a space between the first mold half (203) and the second mold half (205); Rotating (426) the first mold half (203) and / or the second mold half (205); Closing the second half of the mold (205); and Injecting (430) a second shot into the mold to form the second subsection (134). [2] Method according to claim 1, wherein the first shot and the second shot comprise transparent plastic. [3] Method according to claim 1, wherein the first shot and the second shot comprise polymethyl methacrylate (PMMA). [4] Method according to claim 1, wherein the first shot and the second shot comprise polycarbonate. [5] Method according to claim 1, wherein the first shot and the second shot comprise plastic of different colors. [6] Method according to claim 1, wherein the laser (244) comprises a carbon dioxide (CO2) laser. [7] Method according to claim 6, wherein the laser (244) operates at a wavelength of more than 4 micrometers. [8] Method according to claim 6, further comprising a robot (240, 286) configured to position the laser (244) relative to the first mold half (203) and the projection section (122) of the first subsection (120). [9] Method according to claim 1, further comprising using a vacuum to evacuate steam generated during laser cutting of the protrusion section. [10] Method according to claim 1, wherein the shaped part comprises a rear light lens.

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