Design of Injection Mold for Shower Head Handle
Time：2023-08-25 19:38:14 / Popularity： / Source：
1 Molding process analysis
Shower head handle is shown in Figure 1, and its following characteristics will affect mold structure design: ①External thread feature, due to limitation of upper shower head cover, can only use external thread core to rotate and pull core to remove thread; ②Ring groove, demoulding here can only be demolded by forced core pulling. Depth of groove on one side is 0.15mm, and a ring-shaped undercut is formed in demoulding direction. After calculation,orced demoulding under structural size here will not damage local features of plastic part; ③Handle elbow, centerline of sweeping path of circular hole in inner wall section is a circular arc, and core pulling of elbow is required to realize demoulding of center hole in inner wall of elbow; ④ Plastic parts filling problem, it is difficult to find the best balanced pouring point. Although there is an optimal gate opening area according to mold flow analysis, this area is restricted by mold structure and cannot be selected; ⑤Structure of plastic parts is complex, and wall thickness distribution in local areas is uneven, which is prone to defects such as shrinkage marks; ⑥Surface of plastic parts is required to be smooth and bright, inspection requirements for surface roughness are high. Plastic parts are planned to be injection-molded with fireproof and antistatic modified engineering plastic ABS, shrinkage rate is 0.52%~0.58%, material grade is HFA-451, and output is 1.2 million pieces.
2 Mold structure analysis
2.1 External thread demoulding method and mechanism design
Mold structure is shown in Figure 2. For demoulding of external thread of plastic part, due to limitation of design space, a single plastic part can only be demolded by using threaded core 21 to rotate and pull core. In order to ensure that threaded core 21 can rotate around its axis , its upper end is sleeved on cylindrical central core 18, and lower end cooperates with threaded guide ring 20 thread pairs. When external thread is demolded, gear rack 11 drives gear to drive transmission gear 15 to rotate, and transmission gear 15 drives gear 16 to rotate, so that threaded core 21 is rotated under guidance of thread guide ring 20 to remove thread, and moves downward along its own axis to realize complete separation from external thread of plastic part.
Figure 2 Mold structure
2.2 Ring groove demoulding
Forming and demoulding of ring groove is completed by central core 18, upper end of central core 18 participates in molding of inner wall of center hole of plastic part. When demolding, central core 18 is forced to pull core from center hole of plastic part to realize demoulding of ring groove.2.3 Demolding of inner hole of elbow
Inner hole core-pulling mechanism assembly of elbow includes parts 23 to 31. Front end of elbow slider 27 is provided with an elbow core, which slides in elbow groove seat 24, center line of elbow groove of elbow groove seat 24 is same arc as center line of center hole of elbow center hole of plastic part. When mold is in closed state, elbow slide block 27 was locked by locking block 25. Elbow slider 27 is provided with cylindrical pin 26, when driving plate 31 moves downward and is separated from elbow groove seat 24, cylindrical pin 26 is driven downward through drive slots on both sides, cylindrical pin 26 drives elbow slide block 27 to slide in elbow groove of elbow seat 24, so that elbow core at the front end was extracted from molded part.2.4 Mold parting and molded parts design
As shown in Figure 2, mold is parted with bottom edge of plastic part φ29mm cylindrical shell as main parting line. Outer wall molding parts above parting surface are cavity plate inserts 29, and inner wall molding parts below parting surface include core insert 28, threaded core 21 and central core 18, bottom edge of shell is separately provided with an insert plate 30 for molding, which not only facilitates processing of mold parts, but also requires push of insert plate 30 for final separation of plastic part from core insert 28.2.5 Demolding process of plastic parts
Demoulding of molded plastic part is realized in following steps: ①Piston rod of hydraulic cylinder drives threaded core 21 to rotate through rack 11 to complete demoulding of external thread of plastic part; ②Parting surface P1 of mold is opened, central core 18 is forced to pull core from center hole of plastic part, threaded core 21 is far away from plastic part, movable mold backing plate 5 drives driving plate 31 to move downward and separates from elbow groove seat 24, driving groove on driving plate 31 drives cylindrical pin 26 to drive elbow slider 27 to slide in elbow seat 24, so that elbow core at the front end of elbow slider 27 is pulled out from elbow hole of plastic part, inner wall of elbow hole is rotated and core-pulled for demoulding; ③ Parting surface P2 of mold is opened, and outer surface of plastic part comes out from cavity of fixed mold plate 2, and remains on core insert 28; ④Parting surface P3 of mold is opened, and pull rod 22 pulls upper push plate 3 to drive core insert 28 to separate from plastic part, and plastic part stays on insert plate 30 in upper push plate 3 and falls off automatically.2.6 Formwork selection
Function of mold base is mainly to carry various functional system parts and ensure automatic injection molding production of plastic parts. Therefore, mold base can be simplified as a stacked combination of pieces 1 to 8. Installation of mold base auxiliary mechanism is shown in Figure 3. In order to facilitate installation of mold structural parts, movable mold backing plate 5, gear partition 6, backing plate 7 and moving mold seat plate 8 are combined together with screws and positioning pins; Upper push plate 3 and movable mold plate 4 are movable panels that move relatively, opening and closing motion between templates is slidably guided by guide pillar 43 and guide sleeves 40, 41, 42. When mold parting surface P1 is opened, movable mold plate 4 and movable mold backing plate 5 are stretched apart by spring 34, separation distance is fixed by long pull rod 38, which is 120mm; when mold parting surface P3 is opened, separation distance between upper push plate 3 and movable mold plate 4 is fixed by tie rod 44, which is 50mm; opening distance of mold parting surface P2 is 45 mm, controlled by pull rod 22, and hydraulic cylinder 32 is installed on the side of mold base.
Figure 3 Installation of formwork auxiliary mechanism
2.7 Gating system and cooling system
Mold uses a latent side gate for gating. Gate diameter is φ0.8mm. Runner of gating system is set on insert plate 30. With opening of parting surface P3 of mold, pulling rod 38 pulls out runner condensate and separates it from plastic part, runner condensate stays on insert plate 30 and is ejected by spring pin 36 at last. Fixed mold plate 2 of mold is provided with a φ8mm cooling water channel to cool cavity, and movable mold side is provided with a cooling water channel on insert plate 30 to indirectly cool core.2.8 Mold cavity layout
Mold has a layout of 8 cavities. As shown in Figure 4, 8 cavities are respectively V1~V8, which are directly processed on cavity plate insert 29, and insert plate 30 is set on 8 core inserts 28. Fixed mold and movable mold each have a waterway W1, W2, hydraulic cylinder 32 piston rods drive rack 11 to drive 2 transmission gears 15, 2 transmission gears 15 drive 4 threaded cores 21 to rotate and pull core respectively. Each cavity is independently provided with an elbow groove seat 24 , an elbow slider 27 and a core insert 28 . Mold is provided with 5 pulling rods 38, which are respectively arranged at diversion places of runners. Guide pillars 43, pull rods 22, 44, and long pull rods 33 are each provided with 4 pieces in a balanced arrangement, so as to ensure smooth opening and closing movement of mold base. Sprue sleeve 37 is installed on fixed mold plate 2, which can effectively shorten length of runner, and a positioning ring 39 is additionally installed on the fixed mold plate seat plate 1.
Figure 4 Mold cavity layout
3 Mold working process
(1) Clamping injection. After mold is installed and closed on injection molding machine, nozzle of injection molding machine injects molten ABS plastic into cavity through sprue sleeve 37, mold is opened after filling, pressure maintaining, cooling and other processes.(2) External thread core pulling. Hydraulic cylinder 32 piston rod drives threaded cores 21 with 8 cavities through rack 11 to rotate and pull core.
(3) Parting surface P1 of mold is opened. As moving mold goes down, parting surface P1 of mold is stretched by spring 34, and stops after opening 120mm. Central core 18 is forced to pull core from center hole of plastic part, and threaded core 21 is far away from plastic part. Simultaneously, movable mold backing plate 5 drives drive plate 31 to drive elbow core of elbow slide block 27 front end downwards to extract from plastic part elbow hole, so as to realize rotary core-pulling demoulding of inner wall of elbow hole.
(4) Parting surface P2 of mold is opened. Moving mold continues to move downward. Due to locking of die buckle 35 and pushing of spring pin 36, parting surface P2 of mold is opened, and outer surface of plastic part is released from cavity of fixed mold plate 2, remains on core insert 28, and opening distance of mold parting surface P2 is 134mm.
(5) Parting surface P3 of mold is opened. Movable mold continues to descend, pull rod 22 pulls upper push plate 3, core insert 28 is extracted from plastic part. When mold parting surface P3 surface is opened by 50mm, plastic part stays on insert plate 30 and falls off automatically.
(6) RESET. Before reset, hydraulic cylinder 32 piston rod block drives threaded core 21 to reset first, and then mold resets according to P2 → P3 → P1 in sequence, waiting for next injection cycle.
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