Automotive door panels are crucial interior components, located on either side of door, front, back, left, and right. They are an automotive interior system that integrates decorative design with functionality and safety. Due to their high aesthetic requirements, these products are frequently encountered in automotive injection mold design and are widely used. This section uses three door panel parts as examples to illustrate key design considerations for these molds.
Product Features
Product Shape Analysis:
Left rear door panel, as shown below:
Product Dimensions: 813mm long x 716mm wide x 125mm high. Large wall thickness: 2.5mm. 13 bevels, 6 of which are bayonet-style undercuts and 2 are large bevels. Six core inserts are located in the rear mold, one in the front mold, and one speaker mesh. Wall thickness is 2.5mm. Material: PP + T20. Shrinkage is 1.1%. Pillar thickness is 1.4mm at large end, with minimal shrinkage. Rib thickness is 1mm at large end, with minimal shrinkage. A side of product is finished with a leather grain finish.

 

Right rear door panel, as shown below:
Product Dimensions:
1. 863mm long x 560mm wide x 123mm high. Minimum penetration angle is 3 degrees. Fixed mold is finished with a leather grain finish. Material is pure PP with a shrinkage of 1.5%. Product is available in two colors: beige and black.
2. Average wall thickness of product is 3mm, and appearance requirements are high: large end dimension of small rib must be less than 1.2mm, otherwise customer will not accept surface shrinkage; maximum wall thickness of large end of column must be approximately 1.2mm, otherwise customer will not accept surface shrinkage. Weld marks must be confirmed by customer, and 100% air entrapment must be guaranteed. Injection molding process has a wide adjustment range.
3. Undercut portion of this product is a beveled ejector, with two large bevels for water flow, and the rest are smaller bevels. Sleeve pins are used for 18 welded columns, and column area must be fully cooled to minimize shrinkage.

 

Left and right front door panels of car are shown below. Door Panel Dimensions:
Length 895 x Width 640 x Height 90mm. Product Material, Shrinkage Rate: PP+EPDM+T20 1.3%. Average wall thickness: 2.8mm. Large end dimension of reinforcement ribs must be approximately 1mm to prevent surface shrinkage. Support ribs at lifter bracket are 1mm thick. Since they are not fully filled after initial test, a 2mm expansion section is added at section where they connect to product surface, and remaining thickness is increased.
Pillars also shrink after initial test, so during initial product exchange, it is important to ensure that large end thickness of pillars is 40% of average wall thickness. 7 lifters, 10 core inserts, and 1 mesh structure.

 

Gating System Design:
Gating system for right rear door panel is shown in figure below, using a two-point sequential valve hot runner for injection.

 

Gating system for left rear door panel is shown in figure below, using a three-point sequential valve hot runner for injection.

 

Casting system for left rear door panel is shown in figure below. It uses a three-point sequential valve hot runner for gluing.

 

Molding Part System Design:
After part is determined, detailed design begins: First, determine part's position in mold base and identify key points. Design parting surface, separate front and rear molds, design locking mechanism between front and rear molds. Design core pull and core insert. Design water circuits, adding fixing screws and lifting holes.

 

Cooling System Design:
As shown in figure below, mold for right rear door panel uses five water circuits, with a 12mm diameter direct cooling channel and a 25mm diameter water well. Moving mold has five cooling channels, one of which is a lifter water channel integrated into square iron and connected to equipment with a plastic quick-connect faucet.

 

As shown in figure below, fixed mold of right rear door panel uses four water circuits, with a 12mm diameter direct cooling channel and a 25mm diameter water well. Fixed mold has four cooling channels, integrated into hot runner plate and connected to equipment with a plastic quick-connect faucet.

 

Quality of temperature control system design significantly impacts mold's molding cycle and product quality, especially for automotive door panel injection molds, which require high aesthetics. One principle of cooling water channel design is to maintain approximately equal distance from cavity surface to achieve uniform temperature distribution throughout mold cavity. This mold's temperature control system utilizes a combination of "straight-through water pipes + inclined water pipes + water wells," as shown in figure below. This combination prioritizes straight-through water pipes, supplemented by inclined water pipes, and only uses water wells as a last resort. Its advantages include uniform part cooling, fast molding cycles, and high-quality molding, making it suitable for molds with high demands and aesthetic requirements.

 

This fixed and movable mold temperature control system features seven water channels for both fixed and movable molds, with seven inlets and seven outlets for each. Mold cooling water channels are aligned with material flow direction, and a "vertical water pipe + inclined water pipe + spacer-type water well" design tailored to part's shape is preferred. Inlet and outlet distances are approximately equal, ensuring excellent mold cooling and a high-quality part appearance.
In design of automobile molds, similar to molds for interior and exterior trims such as automobile front and rear bumpers, dashboards, central channels, grilles and automobile decorative strips, layout of cooling water channels is generally designed according to following rules:
(1) Direction of cooling water should be consistent with direction of material flow.
(2) Cooling water channels of fixed and movable molds are preferably designed in a cross grid form, and cooling circuits form a water channel interweaving network that crosses each other to evenly cool plastic parts.
(3) When it is not possible to design a cross-shaped water channel, fixed and movable mold water channels are arranged alternately at gaps between them.
(4) Each group of cooling water should be designed with only four circulating water channels as much as possible to avoid long water channel distances that affect cooling effect of plastic parts.
(5) Cooling water channel should be designed in a way that can be connected to another group of water channels through external water pipes to facilitate subsequent adjustment of plastic parts due to deformation, shrinkage, etc. Solving plastic part defects through water channel adjustment is widely used in automobile interior and exterior trim plastic parts molds.
(6) Distance between each cooling water channel should be controlled within 3.5-5 times diameter of water channel (generally about 50-60 mm). Distance between cavity surface and cooling water channel is generally between 15-25 mm, which is determined by size of mold.
(7) Distance between cooling water channel and push rod, inclined push rod and insert should be guaranteed to be more than 8-10 mm. Because mold is large and water channel is long, it is easy to drill off-center. It is necessary to avoid occurrence of cooling water leakage caused by water channel being too close to cavity or other structures.
(8) In design of automobile injection molds, hot nozzle should be designed with a separate set of cooling water channels as much as possible, and it should not be connected in series with other water channels to facilitate heat dissipation in hot nozzle area.