Injection molding machine

Abstract

The present invention provides an injection molding machine capable of detecting a gap between the nozzle and the mold. [Solution] The injection molding machine 1 includes an injection device 3 that can move forward and backward relative to the mold, a nozzle 32 provided on the injection device 3 that moves toward and away from the fixed side mold 81 in accordance with the forward and backward movement of the injection device 3, a nozzle heater 35 that heats the nozzle 32, and a control unit 7 that controls the energization rate of the nozzle heater 35 so that the temperature of the nozzle 32 reaches a target value. The control unit 7 advances the injection device 3 toward the fixed side mold 81, and determines whether the nozzle 32 is in proper contact with the fixed side mold 81 based on the energization rate of the nozzle heater 35 when the position of the injection device 3 no longer changes and the position of the injection device 3 is within the nozzle touch determination range.

Description

【Technical Field】 【0001】 The present invention relates to an injection molding machine. 【Background Art】 【0002】 Patent Document 1 discloses an example of a conventional injection molding machine. The injection molding machine advances an injection device having a cylinder toward a mold, brings a nozzle provided at the tip of the cylinder into contact with the mold, and injects and fills the resin in the cylinder into the cavity of the mold through the nozzle. The injection molding machine has a heater for heating the cylinder and the nozzle. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Unexamined Patent Application Publication No. 2020-124821 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 In the nozzle touch operation of bringing the nozzle into contact with the mold, the injection molding machine advances the injection device toward the mold and detects the position of the injection device using a position sensor. Then, when the detected position of the injection device no longer changes and the position of the injection device is within a predetermined nozzle touch determination range, the injection molding machine determines that the nozzle has come into contact with the mold, stops the nozzle touch operation, and injects and fills the resin into the cavity. 【0005】 For example, if foreign matter gets caught between the nozzle and the mold, a gap will form between the nozzle and the mold, preventing the nozzle from making proper contact with the mold. Furthermore, if the foreign matter caught between the nozzle and the mold is small, the position of the injection device may fall within a predetermined nozzle touch detection range when the position of the injection device stops changing. In this case, the injection molding machine may determine that the nozzle has made contact with the mold despite the presence of a gap, and the molding operation of the injection molding machine may continue without noticing that resin is leaking from the gap. 【0006】 Therefore, the present invention aims to provide an injection molding machine that can detect when a gap occurs between the nozzle and the mold. [Means for solving the problem] 【0007】 To achieve the above objective, an injection molding machine according to one aspect of the present invention comprises: an injection device that can move forward and backward relative to a mold; a nozzle provided on the injection device that moves toward and away from the mold in accordance with the forward and backward movement of the injection device; a heater for heating the nozzle; and a control device that controls the energization rate of the heater so that the temperature of the nozzle reaches a target value, wherein the control device advances the injection device toward the mold, determines whether the nozzle is in proper contact with the mold based on the energization rate of the heater when the position of the injection device no longer changes and the position of the injection device is within a predetermined nozzle touch determination range. 【0008】 To achieve the above objective, an injection molding machine according to another aspect of the present invention comprises: an injection device that can move forward and backward relative to a mold; a nozzle provided on the injection device that moves toward and away from the mold in accordance with the forward and backward movement of the injection device; a heater for heating the nozzle; and a control device that controls the energization rate of the heater so that the temperature of the nozzle reaches a target value, wherein the control device advances the injection device toward the mold, and determines whether the nozzle is in proper contact with the mold based on the temperature of the nozzle when the position of the injection device no longer changes and the position of the injection device is within a predetermined nozzle touch determination range. [Effects of the Invention] 【0009】 According to the present invention, the injection device is advanced toward the mold, and when the position of the injection device stops changing and the position of the injection device is within a predetermined nozzle touch determination range, it is determined whether the nozzle is in proper contact with the mold based on the energization rate of the heater or the temperature of the nozzle. 【0010】 Since the mold temperature is lower than the target nozzle temperature, if the nozzle is in proper contact with the mold (no gap), the nozzle temperature decreases and the conductivity increases. If the nozzle is not in proper contact with the mold (a gap exists), the nozzle temperature does not decrease or decreases only slightly, resulting in a low conductivity. Therefore, it is possible to detect the presence of a gap between the nozzle and the mold based on the heater conductivity or the nozzle temperature. [Brief explanation of the drawing] 【0011】 [Figure 1] This is a front view of an injection molding machine relating to one embodiment of the present invention. [Figure 2] This is a magnified cross-sectional view of the main part of an injection molding machine. [Figure 3] This is a functional block diagram of an injection molding machine. [Figure 4] This flowchart shows an example of the molding operation of an injection molding machine. [Modes for carrying out the invention] 【0012】 Hereinafter, an injection molding machine according to one embodiment of the present invention will be described with reference to Figures 1 to 4. The injection molding machine plasticizes the resin that will be used as the material for the molded product and injects it into the cavity of the mold to form the molded product. 【0013】 As shown in Figures 1 to 3, the injection molding machine 1 according to this embodiment has a molding machine body 10 which includes a mold clamping device 2, an injection device 3, and a removal device 4. The molding machine body 10 is placed on a base 5. The injection molding machine 1 also has a control unit 7 which controls the molding machine body 10. 【0014】 The mold clamping device 2 opens, closes, and clamps the fixed mold 81 and the movable mold 82. The fixed mold 81 and the movable mold 82 form a cavity 83. The mold apparatus composed of the fixed mold 81 and the movable mold 82 is simply referred to as a "mold". 【0015】 The mold clamping device 2 includes a fixed die plate 21, a movable die plate 22, and a mold clamping drive mechanism 23. The fixed die plate 21 is fitted with the fixed mold 81. The movable die plate 22 is fitted with the movable mold 82. The mold clamping drive mechanism 23 includes, for example, an electric motor, a ball screw mechanism, and a toggle link mechanism. The mold clamping drive mechanism 23 generates a mold clamping force by clamping the fixed mold 81 and the movable mold 82 in the front-rear direction using the fixed die plate 21 and the movable die plate 22. In Figure 1, the left is the front and the right is the rear. 【0016】 The injection device 3 includes a cylinder 31, a nozzle 32, a resin supply unit 33, a cylinder heater 34, a nozzle heater 35, a cylinder temperature sensor 36, a nozzle temperature sensor 37, a screw 38, a screw drive mechanism 39, and an injection device drive mechanism 40. 【0017】 The cylinder 31 has a cylindrical shape. The cylinder 31 is arranged along the front-rear direction. The nozzle 32 is arranged at the tip of the cylinder 31. The resin supply unit 33 is arranged at the rear end of the cylinder 31. The resin supply unit 33 has a hopper in which powdery or granular resin serving as a material for a molded product is accommodated. The resin supply unit 33 supplies resin to the cylinder 31. 【0018】 The cylinder heater 34 is arranged on the outer peripheral surface of the cylinder 31 and heats the cylinder 31. The nozzle heater 35 is arranged on the outer peripheral surface of the nozzle 32 and heats the nozzle 32. The cylinder heater 34 and the nozzle heater 35 are constituted by, for example, a band heater or an induction heating type heater. Note that the nozzle heater 35 may be omitted, and the nozzle 32 may be heated by the heat transmitted from the cylinder 31 heated by the cylinder heater 34. In this configuration, the cylinder heater 34 heats the nozzle 32. 【0019】 The cylinder temperature sensor 36 has a temperature detection part embedded in the cylinder 31 and outputs a signal according to the temperature of the cylinder 31. The nozzle temperature sensor 37 has a temperature detection part embedded in the nozzle 32 and outputs a signal according to the temperature of the nozzle 32. The cylinder temperature sensor 36 and the nozzle temperature sensor 37 are constituted by, for example, a thermocouple. 【0020】 The screw 38 is rotatably and axially movably accommodated in the cylinder 31. The screw drive mechanism 39 has, for example, an electric motor and a ball screw mechanism. The screw drive mechanism 39 rotates and axially moves the screw 38. 【0021】 The injection device 3 is movably mounted on a rail (not shown) on the base 5. This rail extends in the front-rear direction, and the front end of the rail faces the fixed die plate 21. The injection device drive mechanism 40 has, for example, an electric motor and a ball screw mechanism. The injection device drive mechanism 40 moves the injection device 3 forward and backward. When the injection device 3 moves forward and backward, as shown in Fig. 2(a), the nozzle 32 contacts the mold (fixed-side mold 81), or as shown in Fig. 2(b), the nozzle 32 separates from the mold. Further, the injection device drive mechanism 40 includes, for example, a position sensor (not shown) and outputs a signal according to the position of the injection device 3. 【0022】 The take-out device 4 has an ejector pin (not shown) and a protruding mechanism 41. The protruding mechanism 41 has, for example, an air cylinder that drives the ejector pin. The air cylinder protrudes the ejector pin from the outer surface of the movable-side mold 82 or houses the ejector pin in the movable-side mold 82. The protruding mechanism 41 drives the ejector pin to remove the molded product from the movable-side mold 82. 【0023】 The control unit 7 controls the operation of the entire injection molding machine 1. As shown in Fig. 3, the control unit 7 has a display device 71, an input device 72, a storage device 73, and a control device 78. 【0024】 The display device 71 is, for example, a flat panel display such as a liquid crystal display. 【0025】 The input device 72 is, for example, an operation key or a touch panel. The operation key is, for example, a key of a hardware keyboard. The touch panel is arranged over the display surface of the display device 71 and constitutes a software key in combination with button images, toggle switch images, etc. displayed on the display surface. 【0026】 The storage device 73 is, for example, a magnetic disk device or a non-volatile memory. The storage device 73 may include an external storage device such as a USB memory that is detachable from the control unit 7. 【0027】 The storage device 73 stores the molding conditions used for molding the molded product. The molding conditions include setting values ​​for items related to the driving of the mold clamping device 2, injection device 3, and removal device 4 of the injection molding machine 1 (molding condition items). Examples of molding condition items include speed, pressure, temperature, time, and travel distance. 【0028】 The control device 78 has a computer. The control device 78 is communicatively connected to the display device 71, the input device 72, and the storage device 73. 【0029】 The control device 78 displays various information on the display device 71 and performs operations in response to the input device 72. The display device 71 and the input device 72 may be, for example, a tablet device or a laptop computer connected to the control device 78 via wireless communication. 【0030】 Furthermore, the control device 78 is communicatively connected to the mold clamping drive mechanism 23, cylinder heater 34, nozzle heater 35, cylinder temperature sensor 36, nozzle temperature sensor 37, screw drive mechanism 39, injection device drive mechanism 40, and ejection mechanism 41. Based on the molding conditions stored in the storage device 73, the control device 78 controls each mechanism and performs molding operations to mold a molded product together with the molding machine body 10. 【0031】 Next, an example of the molding operation of injection molding machine 1 will be explained with reference to Figure 4. 【0032】 First, we will explain the parameters used in the molding operation, as well as the heating operation of the cylinder 31 and nozzle 32. 【0033】 The memory device 73 stores the target position Pt. The target position Pt is used when advancing the injection device 3 toward the mold during the molding operation. When the injection device 3 reaches the target position Pt, the nozzle 32 makes contact with the mold (nozzle touch). In reality, there is expansion and contraction due to temperature changes of the mold and the fixed die plate 21, so the control device 78 uses a nozzle touch determination range Pa, which includes the range before and after the target position Pt, to determine whether or not the nozzle 32 has made contact with the mold. The nozzle touch determination range Pa is, for example, in the range of target position Pt ± 0.1 to 3 mm. 【0034】 The storage device 73 stores the target temperature of the cylinder 31, Tct, and the target temperature of the nozzle 32, Tnt. The control device 78 acquires the temperature of the cylinder 31 based on the signal output by the cylinder temperature sensor 36 during the molding operation and controls the energization rate of the cylinder heater 34 so that the temperature of the cylinder 31 becomes the target temperature of the cylinder 31, Tct (a constant value). The control device 78 also acquires the temperature of the nozzle 32 based on the signal output by the nozzle temperature sensor 37 during the molding operation and controls the energization rate of the nozzle heater 35 so that the temperature of the nozzle 32 becomes the target temperature of the nozzle, Tnt (a constant value). The energization rate is the ratio of energization time per unit time. For example, if the unit time is 10 seconds, the energization rate is 50% when energization is performed for 5 seconds and then paused for 5 seconds, and the energization rate is 70% when energization is performed for 7 seconds and then paused for 3 seconds. The control device 78 increases the energization rate of the cylinder heater 34 when the temperature of the cylinder 31 decreases, and decreases the energization rate of the cylinder heater 34 when the temperature of the cylinder 31 approaches the target cylinder temperature Tct. The control device 78 also controls the energization rate of the nozzle heater 35 in the same way as the cylinder heater 34. 【0035】 The mold is not heated during the molding operation, or is heated to a temperature lower than the nozzle target temperature Tnt. Therefore, when the nozzle 32 makes proper contact with the mold, heat from the nozzle 32 is transferred to the mold, and the temperature of the nozzle 32 decreases. On the other hand, if the nozzle 32 does not make proper contact with the mold, a gap is created, and heat from the nozzle 32 does not transfer to the mold or transfers little, so the temperature of the nozzle 32 does not decrease or decreases little. Proper contact of the nozzle 32 with the mold means that there is no gap between the nozzle 32 and the mold (fixed side mold 81), and no resin leakage occurs. The control device 78 increases the energization rate of the nozzle heater 35 when the temperature of the nozzle 32 decreases, and maintains the energization rate of the nozzle heater 35 when the temperature of the nozzle 32 does not decrease or decreases little. 【0036】 The memory device 73 stores the reference energization rate Er. The reference energization rate Er is set based on the energization rate of the nozzle heater 35 when the nozzle 32 is in proper contact with the mold immediately before the resin is injected during the molding operation. 【0037】 The memory device 73 stores a reference temperature Tr. The reference temperature Tr is set based on the temperature of the nozzle 32 when it is in proper contact with the mold immediately before the resin is injected during the molding operation. 【0038】 The control device 78 performs preparatory operations before the molding operation, such as a purging operation and a plasticizing operation for the first injection of resin material. 【0039】 The molding operation includes the following steps S110 to S180. Steps S110 to S180 constitute one molding operation (molding cycle). 【0040】 When the control device 78 confirms that the toggle link mechanism of the mold clamping drive mechanism 23 is bent and that the fixed mold 81 and the movable mold 82 are in the open state, it starts the molding operation. 【0041】 [S110: Mold closed] The control device 78 controls the mold clamping drive mechanism 23 to extend the toggle link mechanism, thereby closing and clamping the fixed mold 81 and the movable mold 82. 【0042】 [S120: Nozzle advance] When the fixed mold 81 and the movable mold 82 are clamped together, the control device 78 controls the injection device drive mechanism 40 to start the injection device 3 moving forward. The control device 78 obtains the position of the injection device 3 based on the signal output by the injection device drive mechanism 40. When the position of the injection device 3 stops changing and the position of the injection device 3 is within the nozzle touch determination range Pa, the control device 78 stops the forward movement of the injection device 3 and obtains the energization rate of the nozzle heater 35. If the obtained energization rate of the nozzle heater 35 is greater than or equal to the reference energization rate Er, the control device 78 determines that the nozzle 32 is in proper contact with the mold and proceeds to step S130. If the obtained energization rate of the nozzle heater 35 is less than the reference energization rate Er, the control device 78 determines that the nozzle 32 is not in proper contact with the mold, stops the molding operation, and displays a warning message on the display device 71, for example, indicating that foreign matter is caught between the nozzle 32 and the mold. 【0043】 In step S120, the control device 78 may obtain the temperature of the nozzle 32 instead of the energization rate of the nozzle heater 35. In this configuration, the control device 78 determines that the nozzle 32 is in proper contact with the mold when the obtained temperature of the nozzle 32 is less than or equal to the reference temperature Tr, and determines that the nozzle 32 is not in proper contact with the mold when the obtained temperature of the nozzle 32 is greater than the reference temperature Tr. 【0044】 [S130: Injection] The control device 78 controls the screw drive mechanism 39 to advance the screw 38, injecting the plasticized resin in the cylinder 31 into the cavity 83 through the resin flow path 84 of the fixed mold 81. 【0045】 [S140: Holding pressure] The control device 78 controls the screw drive mechanism 39 to control the forward and backward position of the screw 38 so that a predetermined pressure (holding pressure) is applied to the resin filled in the cavity 83. 【0046】 [S150:Plasticization] When the resin in the resin channel 84 (gate) solidifies, the control device 78 controls the screw drive mechanism 39 to rotate the screw 38, plasticizing the resin and sending it to the front part of the cylinder 31. This causes the screw 38 to retract. 【0047】 [S160: Nozzle retraction] The control device 78 controls the injection device drive mechanism 40 to retract the injection device 3 to a predetermined retracted position. This causes the nozzle 32 to separate from the mold. 【0048】 [S170: Mold opening] When a predetermined cooling time has elapsed since the completion of step S140 (holding pressure), the control device 78 controls the mold clamping drive mechanism 23 to bend the toggle link mechanism and open the fixed mold 81 and the movable mold 82. 【0049】 [S180: Molded product removal] The control device 78 controls the ejection mechanism 41 to make the ejector pin protrude from the outer surface of the movable mold 82, separating the molded product from the movable mold 82, and then retracts the ejector pin into the movable mold 82. The molded product separated from the movable mold 82 is moved to a predetermined location by an automated machine (not shown). 【0050】 The control device 78 returns to step S110 and thereafter repeats steps S110 to S180. 【0051】 As described above, the injection molding machine 1 includes an injection device 3 that can move forward and backward relative to the mold, a nozzle 32 that moves toward and away from the mold in accordance with the movement of the injection device 3, a nozzle heater 35 that heats the nozzle 32, and a control device 78 that controls the energization rate of the nozzle heater 35 so that the temperature of the nozzle 32 becomes the nozzle target temperature Tnt. The control device 78 advances the injection device 3 toward the mold, and when the position of the injection device 3 stops changing and the position of the injection device 3 is within the nozzle touch determination range Pa, it determines whether the nozzle 32 is in proper contact with the mold based on the energization rate of the nozzle heater 35. The control device 78 may also determine whether the nozzle 32 is in proper contact with the mold based on the temperature of the nozzle 32 instead of the energization rate of the nozzle heater 35. Since the mold temperature is lower than the nozzle target temperature Tnt, if the nozzle 32 is in proper contact with the mold (no gap), the temperature of the nozzle 32 decreases and the conductivity increases. If the nozzle 32 is not in proper contact with the mold (a gap is created), the temperature of the nozzle does not decrease or decreases only slightly and the conductivity decreases. Therefore, it is possible to detect whether a gap has occurred between the nozzle 32 and the mold based on the conductivity of the nozzle heater 35 or the temperature of the nozzle 32. 【0052】 Furthermore, the control device 78 determines whether the nozzle 32 is in proper contact with the mold using a reference energization rate Er, which is set based on the energization rate of the nozzle heater 35 when the nozzle 32 is in proper contact with the mold. Alternatively, the control device 78 may determine whether the nozzle 32 is in proper contact with the mold using a reference temperature Tr, which is set based on the temperature of the nozzle 32 when the nozzle 32 is in proper contact with the mold, instead of the reference energization rate Er. In this way, it is possible to accurately detect when a gap has occurred between the nozzle 32 and the mold with a relatively simple configuration. 【0053】 Although this specification describes an injection molding machine that clamps laterally as one embodiment of the present invention, the present invention is not limited to such an injection molding machine. The present invention is also applicable to injection molding machines that clamp vertically. 【0054】 Although embodiments of the present invention have been described above, the present invention is not limited to these examples. Additions, deletions, design modifications, and combinations of features of the embodiments described above, as appropriate by those skilled in the art, are also included within the scope of the present invention, as long as they retain the essence of the present invention. [Explanation of symbols] 【0055】 1...Injection molding machine, 10...Molding machine body, 2...Cold clamping device, 23...Cold clamping drive mechanism, 3...Injection device, 31...Cylinder, 32...Nozzle, 35...Nozzle heater, 34...Cylinder heater, 36...Cylinder temperature sensor, 37...Nozzle temperature sensor, 39...Screw drive mechanism, 40...Injection device drive mechanism, 4...Removal device, 7...Control unit, 73...Memory device, 78...Control device, 81... Fixed mold, 82... Movable mold, 83... Cavity

Claims

[Claim 1] An injection molding machine comprising: an injection device that can move forward and backward relative to a mold; a nozzle provided on the injection device that moves toward and away from the mold in accordance with the movement of the injection device; a heater for heating the nozzle; and a control device that controls the energization rate of the heater so that the temperature of the nozzle reaches a target value, An injection molding machine characterized in that the control device advances the injection device toward the mold, and determines whether the nozzle is in proper contact with the mold based on the energization rate of the heater when the position of the injection device no longer changes and the position of the injection device is within a predetermined nozzle touch determination range. [Claim 2] The injection molding machine according to claim 1, wherein the control device determines whether the nozzle is in proper contact with the mold using a reference current rate set based on the current rate of the heater when the nozzle is in proper contact with the mold. [Claim 3] An injection molding machine comprising: an injection device that can move forward and backward relative to a mold; a nozzle provided on the injection device that moves toward and away from the mold in accordance with the movement of the injection device; a heater for heating the nozzle; and a control device that controls the energization rate of the heater so that the temperature of the nozzle reaches a target value, An injection molding machine characterized in that the control device advances the injection device toward the mold, and determines whether the nozzle is in proper contact with the mold based on the temperature of the nozzle when the position of the injection device no longer changes and the position of the injection device is within a predetermined nozzle touch determination range. [Claim 4] The injection molding machine according to claim 3, wherein the control device determines whether the nozzle is in proper contact with the mold using a reference temperature set based on the temperature of the nozzle when the nozzle is in proper contact with the mold.

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