Design of Injection Mold for Sports Mountain Bike Lampshade

Time：2023-10-08 10:07:33 / Popularity： / Source：

1 Sports mountain bike lampshade plastic parts

There are one left and one lampshades for sports mountain bikes, which are symmetrically designed according to left and right mirror images. Structure of left lampshade is shown in Figure 1. Appearance requirements are not high, but structural strength requirements are high, so material is modified plastic alloy PP+30%GF, and shrinkage rate is 1.004~1.005. Plastic part is a semi-enclosed shell structure with an average wall thickness of 2.6 mm, a maximum wall thickness of 3.5 mm, and a minimum wall thickness of 2.2 mm. Three surrounding surfaces of plastic part are all curved surfaces, and a circle of reinforced buckles is set on periphery.

Figure 1 lampshade plastic parts

2 Parting surface design

Layout of plastic parts to be formed in mold should not only consider convenience of demoulding, but also reduce processing difficulty of molded parts and complexity of mold structure. On this basis, parting surface can be set to obtain optimal mold structure. Considering structural features of plastic part, main demoulding direction is determined by surrounding shell of plastic part matrix and demoulding direction of most features. Placement of plastic part to be formed in mold and setting of parting surface are shown in Figure 2. Under this parting surface setting, number of demoulding mechanisms required is the least, and mold structure is also simplified to the greatest extent. Parting surface PL is a curved parting surface, main molding parts of mold are cavity plate inserts and core inserts.

Figure 2 parting surface setting

3 Design of ejector components

Plastic part demoulding needs to be equipped with 5 slider side core-pulling mechanisms to implement side core-pulling demoulding. As shown in Figure 3, slider S1 realizes buckle II and wire hole I forming and core-pulling demoulding, slider S2 realizes forming of wire hole II and core-pulling demoulding; buckle I is an insertion hole, no need for side core-pulling; slider S3 realizes undercut forming and core-pulling demoulding formed by pin I; slider S4 realizes undercut forming and core-pulling demoulding formed by buckle IV, pin II and edge; slider S5 realizes undercut forming and core-pulling demoulding under pin III. All 5 sliders are driven by inclined guide posts.

Figure 3 Design of demoulding mechanism
In order to facilitate processing of sliders, sliders S1, S3, and S4 adopt an insert inlaid structure to form upper part of plastic part. Slider S1 is equipped with slider inserts B1, B2, B3, and slider S3 is equipped with slider inserts B4, slider S4 is equipped with slider inserts B5. Similarly, in order to facilitate processing of core, core must also be composed of 9 molding inserts, which are respectively molding inserts A1~A9. In order to enhance cooling of molded parts, cooling water channels are respectively set up on molding inserts A1 and A7. Mold cooling channel is φ10 mm, and diameter of water well pipe is φ14 mm, so as to ensure cross-sectional area of water flow on cooling channel path is consistent after adding water baffle.
All insert materials are P20HH, and heat treatment hardness is 33~37 HRC. P20HH is suitable for manufacturing upper and lower mold plates, sliders, inclined push rods, inclined top fixing seats, inserts and other parts. Because plastic part is a non-appearance part, corrosion resistance requirements of material are not high, and service life of mold is required to be 500,000 times. Selection of P20HH material is sufficient to meet requirements.

4 Cavity layout

Left and right lampshades are left and right symmetrical parts. In order to ensure consistency of molding quality of plastic parts, two plastic parts are produced by injection in same mold. Cavity layout is 2 cavities. As shown in Figure 4, cavity M1 is used for molding right lampshade, and cavity M2 is used for molding left lampshade. Mechanism in cavity M1 and mechanism in cavity M2 are arranged symmetrically in mirror image.

Figure 4 cavity layout

5 Gating system settings

Gating and venting design is shown in Figure 5. In order to reduce length of runner and ensure gating performance of melt, gating system uses a combination of ordinary runners and hot runners. Due to high plastic parts, thickness of required mold plate is relatively thick. If corresponding main runner is set as a common main runner, its length will be longer, which increases flow distance of material flow. Therefore, front end of runner uses hot nozzles to extend nozzle of injection molding machine, rear end uses a common primary channel and a common branch channel. A single cavity is poured with 2 fan-shaped side gates (gates G1 and G2) to facilitate cutting and separation of runner aggregate and plastic part after injection molding. Considering complexity of cavity structure, exhaust enhancement measures are taken on the edge of parting surface of the entire cavity, and multiple exhaust ports are set for exhaust. Width of exhaust port is 6 mm and depth is 0.02 mm. Exhausted high-pressure air is discharged through multiple channels of air-introduction grooves. Depth of air-induction grooves is 0.5 mm and width is 10 mm. Mold adopts an open hot nozzle, and sealing margin must be more than 3 mm. Bottom surface of hot nozzle and parting surface where it is located should keep a distance of 0.2~0.5 mm to release thermal expansion of hot nozzle.

Figure 5 Gating and exhaust design

6 Mold structure design

Mold structure is shown in Figure 6. Following aspects need to be considered in mold design: ①In order to avoid generation of too deep EDM position and shorten processing time, matching position of insert should be inverted R angle, and insert should be inverted C to facilitate fit. Screws are used to lock inserts from bottom of mold when inserts are fastened. Because mold is large in size and high in height, inserts are assembled using blind holes; ② Considering the overall size of mold is large, movable and fixed mold plates must be equipped with matching positioning structures in multiple places, as shown in Figure 6 (a), four tiger mouths are set at four corners of formwork, two positioning grooves are set at central part, positioning inclined walls and positioning wear-resistant plates are set around periphery; ③During processing of movable and fixed mold plates, processing reference shall be set with reference to same unilateral side and tool setting of machine tool shall be performed to avoid difficulty of mold matching due to large deviation of movable and fixed molds during closing; ④Because there are many inserts in moving mold part, a moving mold backing plate is installed at the bottom of moving mold plate to facilitate assembly; ⑤ Use a push rod to push out plastic parts from mold. Diameter of push rod should be selected above φ10 mm to ensure sufficient rigidity of push rod.

Figure 6 Mold structure

7 Working principle

Three-dimensional structure of mold is shown in Figure 7. After plastic melt is injected, movable mold moves downward under drive of injection molding machine. Mold opens at parting surface PL, and inclined guide post drives slider to complete side core-pulling action. After mold is opened and movable mold moves down to a certain position, ejector pin of injection molding machine bears against push plate. As movable mold continues to descend, plastic part is pushed out from movable platen by push rod to achieve complete demoulding, and mold closing process is opposite to mold opening process.

Figure 7 Die three-dimensional structure

Gud Mould Industry Co., Ltd