Design of Injection Mold for Front Grille of a New Energy Vehicle

Time：2023-08-23 19:18:10 / Popularity： / Source：

1 Product Analysis

Figure 1 shows front grille of a certain new energy. Material is PP-T30 with low linear expansion coefficient. Front grille is a surface painted part, and appearance surface must not have surface defects such as weld marks and shrinkage prints. At the same time, it is required that parting line cannot leak on the surface of product.

Figure 1 Front grille
Because front grille has a large height difference in main demoulding direction of mold, in traditional injection mold design, parting lines at left and right ends of product are located at maximum outer contour R angle, resulting in leakage of parting line, as shown in Figure 2.

Figure 2 Parting line outside front grille
Design of this leakage parting line mainly has following defects: ① Parting line at both ends of product is located at R angle of appearance, and parting line can be seen after loading; ② After front grille is painted, visibility of parting line on the surface of product will be enlarged, and perceived quality will be poor; ③Due to mold manufacturing precision and wear in injection production process, misalignment and flashing will often appear at parting line, which will affect appearance quality of product and reduce qualified rate of product.
In order to avoid mold and product quality problems in parting line design of leakage, it is decided to design parting line at both ends of product to bottom of fillet to form an inner parting line, as shown in Figure 3. Internal parting line can be hidden after product is assembled, which not only avoids risk of parting line leakage, but also improves qualified rate of product and surface quality after painting.

Figure 3 Parting line inside front grille

2 Mold scheme design

2.1 Design of gating system

2.1.1 Determination of gate quantity and gate position

According to shape characteristics of front grille, after optimization and analysis by Moldflow, it was decided to adopt 10-point needle valve pouring scheme, layout of gating points is shown in Figure 4. 10 gates are all located at the bottom of product, with a size of 15 mm*1.2 mm; inner diameter of hot runner is φ18 mm, diameter of valve needle is φ6 mm, and diameter of gate of hot runner is φ4 mm. Hot runner sequence valve opening sequence: point 4→point 1/5/6→point 2/3/7/8→point 9/10.

Figure 4 Layout of gating point of front grille
Deformation analysis results of Moldflow products are shown in Figure 5. Except for large deformation in left and right lower corners of product, the overall deformation in other areas is relatively uniform. Since there are installation structures at the left and right lower corners of product, deformation of these two areas can be corrected through installation structure, comprehensive evaluation of this gating scheme meets requirements of product deformation analysis.

Figure 5 Moldflow deformation analysis

2.1.2 Hot runner sequence valve design

Design of hot runner sequence valve is shown in Figure 6. According to analysis results of Moldflow, mold adopts a 10-point hot runner sequence valve design.

Figure 6 Sequence valve hot runner system

2.2 Design of internal parting mechanism

2.2.1 Working principle of internal parting mechanism

In order to prevent rounded undercut at C from being strained when mold is opened, it is necessary to deform undercut area so that product can be elastically deformed to get out of undercut at C. Working principle of internal parting mechanism is shown in Figure 7. First, large lifter block needs to reserve space for deformation of product, then pulling block drives product to deform inwardly along pull deformation fulcrum under action of pull deformation guide rail and pull rod, pulls undercut at C to inner side of product to ensure that undercut at C is normally demoulded in mold opening direction.

Figure 7 Working principle of internal parting mechanism

2.2.2 Pull deformation mechanism

Parting mechanism in the front grille mold mainly includes large lifter block, large straight top block, small straight top block, pulling deformation guide rail, pull rod, pull block, push rod fixing plate and push plate, etc., as shown in Figure 8. Among them, tension deformation guide rail, pull block and pull rod constitute tension deformation assembly, tension deformation guide rail is fixed on mold core, one end of pull rod is fixed with pull block, and the other end is matched with tension deformation guide rail; pull rod passes through large lifter block, and under guidance of pull deformation guide rail, product is stretched and reset. Large lifter block and large straight top block are fixed on push plate, and small straight top block is fixed on push rod fixing plate. Large lifter block, large straight top block and small straight top block play role of undercutting formed product and pushing out product, wherein large inclined top block also provides driving force for movement of pulling deformation component during movement.

Figure 8 Parting mechanism in mold of front grille

2.2.3 Internal type auxiliary mechanism

In order to assist in realization of internal split forming mechanism, mold is also designed with 4 synchronous hook mechanisms, 4 nitrogen springs, 4 large push-out hydraulic cylinders and 4 small push-out hydraulic cylinders, as shown in Figure 9. Wherein 4 push out large hydraulic cylinders are installed on push plate, and 4 push out small hydraulic cylinders are installed on push rod fixed plate.

Figure 9 Parting auxiliary mechanism in mold of front grille

2.3 Cooling system design

During injection molding process of front grille mold, mold temperature directly affects molding quality (deformation, dimensional accuracy, mechanical properties, and surface quality) and production efficiency of product. It is necessary to design temperature adjustment system according to material properties and molding process. In order to avoid warping and deformation caused by uneven cooling of product, front grille mold cavity plate and core waterway have following design features.
(1) According to shape characteristics of front grille, cooling layout of "conformal waterway + water well" is adopted, and conformal waterway is designed as much as possible along shape of product. For insufficient cooling area, water wells or inclined water wells are designed for auxiliary cooling. Cooling water circuit design of mold cavity plate and core is shown in Figure 10.

Figure 10 Mold cooling water circuit arrangement
(2) Diameter of water channel is φ15 mm, and diameter of water well is φ24 mm to ensure sufficient heat transfer area.
(3) Mold adopts centralized water supply mode, and water collecting block is designed to be connected with injection molding machine.

3 Working principle of mold

Injection mold of front grille is pushed out 120 mm in mold opening stage, which is realized in two steps. Push-out distance is 100 mm, which is jointly driven by nitrogen spring, synchronous hook mechanism and piston rod of large hydraulic cylinder. Push-out process is divided into a synchronous pulling deformation stage and a pulling deformation reset stage. Synchronous pulling deformation stage pushes out 55 mm. Pulling deformation reset stage is pushed out by 45 mm; second pushing distance is 20 mm, which is driven by a small hydraulic cylinder for pushing out. Specific working process is as follows.
(1) After mold injection is completed, mold opening action is performed, and ejection system moves 55 mm synchronously with cavity plate under joint action of nitrogen spring and synchronous hook. During this process, large straight top block pushes product to move synchronously with cavity plate, and large lifter block retreats to reserve space for product deformation. Amount of deformation is 8 mm.
(2) After synchronous drawing and deformation stage of a push-out process is completed, moving and fixed molds continue to open mold, and push-out system does not move at this stage.
(3) After mold opening is completed, push out piston rod of large hydraulic cylinder and start to move, drive push-out system to push up 45 mm, and complete one push-out. During this process, pulling deformation component will pull deformation and reset product.
(4) After first push-out stage is completed, piston rod of large hydraulic cylinder no longer moves. At this time, piston rod of small hydraulic cylinder drives push plate and push rod fixing plate to separate, piston rod of small hydraulic cylinder drives push rod fixing plate and small straight top block to move upwards by 20 mm, pushing product out from large straight top block, and completing second push.
(5) After second push is completed, manipulator picks up parts, mold closes and resets to enter next injection cycle.

Gud Mould Industry Co., Ltd