Figure 1 shows interior trim panel of left front door of a certain model. This door panel adopts an integrated structure. Trim panel and horn grille are integrated on door panel interior panel, and horn grille is honeycomb-shaped. Door panel interior panel material is PP-T20, the overall dimensions are 885mm*718mm*122mm, main body wall thickness is 2.2mm, and weight is 1780g.

1. Design of injection mold for door trim panel of SAIC GM
 1 Product Analysis
Figure 1 shows interior trim panel of left front door of a certain model. This door panel adopts an
integrated structure. Trim panel and horn grille are integrated on door panel interior panel, and
horn grille is honeycomb-shaped. Door panel interior panel material is PP-T20, the overall
dimensions are 885mm*718mm*122mm, main body wall thickness is 2.2mm, and weight is
1780g.
Design points of door trim panel are as follows: ① Door trim panel is an important appearance
skin pattern, defects such as welding lines, flow marks, and shrinkage are not allowed on
appearance surface; ② Door trim panel is high-frequency contact part of customers.
Appearance parting line of product should be invisible and smooth to touch, especially parting
lines in upper decorative panel area and glove box area are exposed. The two parting lines are
not allowed to have step difference and flash; ③ Door trim panel is directly assembled on sheet
metal, there can be no assembly gap with sheet metal parts, and deformation of product after
injection molding is required to be within controllable range of loading.
Figure 2 shows front door water-cut bracket. This product is a non-appearance part. It is welded
and installed in decorative area of front door interior panel.
 2 Mold structure design
 2.1 Mold layout design
In order to improve production efficiency of door panel, combined with structure and size
characteristics of front door panel, left front door trim panel, left front door water-cut bracket,

2. right front door trim panel, and right front door water-cut bracket are designed to be formed on
a pair of molds, mold adopts the layout of "1+1+1+1", as shown in Figure 3.
 2.2 Design of mold gating system
 2.2.1 Determination of gate quantity and gate location
Due to large size of front door trim panel and existence of a horn grille structure, it is not easy to
fill, so it is necessary to design multi-point feeding. After optimization and analysis of Moldflow, it
is decided that a single front door trim panel adopts a 10-point needle valve feeding scheme,
left/right water-cut brackets share a 2-point needle valve hot runner. Layout of feeding point is
shown in Figure 4.
Among them, points 1, 2, 3, 4, 5, 6, 7, 8, and 10 use side gates, and gate size is 15mm*1.2mm;

3. point 9 is located on door opening side of car door, and uses horn lurking gates. Size is
6mm*1mm; point 11 and 12 use side gates, and gate size is 20mm*1.2mm. Inner diameter of hot
runner is φ22mm, diameter of valve needle is φ8mm, and diameter of hot runner gate is φ
6mm.
After repeated optimization and analysis by Moldflow, it was finally determined that opening
sequence of hot runner sequence valve of a single front door trim panel is: point 1→point 2/3/4
→point 5/6→point 7/8/9→point 10, hot runner sequence valve opening sequence of left/right
front door water cut bracket is point 11→point 12. Among them, point 1 and point 11 are turned
on at the same time.
Analysis results of Moldflow weld lines are shown in Figure 5. Weld lines are all located in
non-appearance area because there are many mounting holes in this area. The overall
appearance area is well filled and meets design requirements.
Deformation analysis results of Moldflow products are shown in Figure 6. Deformation in X, Y,
and Z directions of product is small, mainly shrinkage deformation, and the overall deformation is
relatively uniform, which meets product design requirements.

4.  2.2.2 Design of hot runner sequence valve
Design of hot runner sequence valve is shown in Figure 7. According to analysis results of
Moldflow, mold adopts a 22-point hot runner sequence valve design.
 2.3 Main mechanism of mold
Main mechanisms of mold include insert structure in upper decorative plate area, insert structure
in sundries box area, door panel horn mesh cover ejection mechanism, and oblique push
mechanism, as shown in Figure 8.

5.  2.3.1 Large insert structure
Since door trim panel is a product that is frequently contacted by customers, parting line in upper
trim panel area and glove box area is exposed, can be touched by hand, in order to ensure quality
of parting line in these two areas, insert structure is designed on mold respectively. , as shown in
Fig. 9(a).
In order to ensure quality of parting line and improve matching accuracy of inserts, positioning
bosses are designed on both upper decorative plate inserts and sundries box inserts, as shown in
Figure 9(b). Positioning boss has two main functions: ① During mold assembly process, insert is
locked on mold cavity plate through positioning boss, so as to correct parting line segment
difference; ② During injection process, inserts are interlocked in mold cavity through
positioning bosses to avoid dislocation and deformation of mold parts due to excessive injection
pressure, and improve quality of parting line. In addition, two inserts are designed with cooling
water circuits to cool inserts during injection.
 2.3.2 Horn grille pop-up mechanism
In order to ensure smooth demoulding of door panel horn grille mesh, ejector mechanism is
designed, including step push rod, ejector push rod fixing plate, ejector ejector plate, ejector
ejector plate guide column, support column, ejector top bottom plate, ejector top bottom plate
guide column, spring, ejector top support plate, etc., as shown in Figure 10 .

6. Among them, step push rod is installed between ejector push rod fixing plate and ejection ejector
push plate, space between ejection ejector push rod fixing plate and ejection ejector push plate
is fixed by screws; ejector push plate guide column passes through ejector push rod fixing plate
and ejection ejector plate, ejector ejector plate guide column is fixed on mold core; two ends of
support column are respectively fixed on ejection ejector ejector plate and ejection ejector
bottom plate by screws, guide column of ejector bottom plate passes through ejector bracket and
ejector bottom plate, guide column of ejector bottom plate is fixed on ejector bracket by screws;
spring passes through guide post of top bottom plate and is installed between top support plate
and top bottom plate, and initial state of spring is in a preloaded state; ejector support plate is
fixed on movable mold base plate of mold by screws.
Movement principle of ejector mechanism is shown in Figure 11. During product pushing process,
push plate moves upward, and spring in pre-loaded state drives the entire ejection mechanism to
move upward with push plate. When product is pushed out 15mm, fixed plate of ejector push
rod contacts mold core, movement of ejector mechanism ends, and other mechanisms continue
to move under drive of ejector plate. When mold is reset, when push plate moves down to 15mm
from end of reset, push plate contacts with bottom plate of ejection top, and push plate presses
ejection mechanism to move down with it until end of reset of push plate. When ejector
mechanism is reset with push plate, spring of ejector mechanism is compressed to store energy
for driving ejector mechanism to move next time.
 2.3.3 Inclined push mechanism
Inverted structures such as buckle mounting seat on the back of interior trim panel of front door
are formed by an oblique push mechanism, as shown in Figure 12.
 2.4 Design of cooling system
In injection molding process, mold temperature directly affects molding quality (deformation,
dimensional accuracy, mechanical properties and surface quality) and production efficiency of
product. It is necessary to design a temperature adjustment system according to material
properties and requirements of molding process. In order to avoid warpage and deformation
caused by uneven cooling of product, cavity plate and core waterway of door panel mold have
following design features.
(1) According to shape characteristics of door panel, cooling waterway layout of "waterway +
water well" is adopted. Follow shape of product as much as possible to design a conformal
waterway. For areas with insufficient cooling, design water wells or inclined water wells for
auxiliary cooling. Cooling waterway design of mold cavity plate and core is shown in Figure 13.

7. (2) Diameter of waterway is designed to be φ15mm, and diameter of water well is designed to
be φ24mm to ensure sufficient heat transfer area.
(3) Cavity plate and core in horn grill area are designed with independent water channels, and
hot water is passed to ensure filling of horn mesh.
(4) Mold adopts centralized water supply method, and water collecting block is designed to be
connected with injection molding machine.
(5) Temperature of cavity plate and core is independently controlled by mold temperature
machine.