An automotive glove box, also known as a glove compartment, is used to store gloves or other miscellaneous items and is located in passenger seat. A glove box typically consists of three to four parts, requiring three to four sets of molds. A glove box generally comprises a glove box switch, a glove box cover, a glove box frame, and a glove box compartment. Different car models have different configurations. Glove box cover is an exterior component, and its surface needs to be textured.

 

A fixed glove box has a similar basic structure to a tipper glove box, except that inner panel does not have a compartment; storage space is integrated into glove box body, providing a larger storage space and allowing for placement of accessories such as glove box lights.

 

Outer panel of glove box is generally manufactured using injection molding, commonly using PP or PC+ABS materials. PC+ABS is an engineering plastic with excellent comprehensive performance, possessing high strength, hardness, heat resistance, chemical corrosion resistance. PP material has advantages such as excellent performance, low density, ease of molding, and low price, but its wear resistance is slightly inferior, its molding shrinkage rate is relatively large, and its low-temperature performance is poor. Generally, PP used in automobiles is modified to address its shortcomings, such as by adding materials like EPDM (polypropylene diene), talc (TD), and fiberglass (GF).

 

Glove box compartments and bodies are typically manufactured using injection molding, with materials usually being PP and PC/ABS. In high-end cars, flocking is often used for glove box storage space to enhance comfort. Flocking is a process of attaching fine fibers to surface of parts. Generally, glue is applied to relevant areas of component first, then fibers are sprayed onto corresponding areas (this process can be done manually or electrostatically).

 

Glove box compartments and bodies are generally manufactured using injection molding, with materials usually being PP and PC/ABS. In high-end cars, flocking is often used for glove box storage space to enhance comfort. Flocking is a process of attaching fine fibers to surface of parts. Generally, glue is applied to relevant areas of component first, then fibers are sprayed onto corresponding areas (this process can be done manually or electrostatically).

 

There are three ways to design layout of automotive glove box compartment:
The first is to have rib on inclined slide, with ejector block ejecting and a hot runner inlet at the front.
This design is inconvenient for designing ejector structure and requires customer approval.

 

The second is to have rib on the rear mold, with slide on three sides, ejector pins ejecting, and a hot runner inlet at the side.
This design has a more aesthetically pleasing external molding line and is convenient for designing ejector structure, but it is inconvenient for designing injection point.

 

The third is to have rib on the rear mold, with appearance area on slide, ejector pins ejecting, and a hot runner inlet at the side.
This design needs to consider possibility of slide sticking to mold, and appearance molding line requires customer approval.

 

This case study will use first structure as an example to explain in detail design characteristics of inclined slide mold structure.
This mold adopts an integrated structure because plastic part is large, parting surface is complex, and appearance requirements are high.
(2) Is appearance surface of plastic part formed by moving mold or fixed mold?
In general injection molds, outer surface is formed by fixed mold. Therefore, when dealing with products like automotive glove boxes, our normal thinking is to place side with more reinforcing ribs (not outer surface) on moving mold side. However, this makes gating system design complicated. First, main runner would be very long. Second, and most unacceptably, gate marks would be left on outer surface of plastic part (i.e., textured surface). Therefore, it was finally decided that outer surface of this mold would be formed by moving mold, while side with greater clamping force and more reinforcing ribs would be formed by fixed mold. Disadvantage of this is that demolding system must also be designed on fixed mold side, i.e., an inverted mold structure must be used.
(3) How should cavities be arranged? Or, how should plastic parts be placed in cavities?
Since this mold has three large sliders, and sliders are heavy, it is essential to avoid sliding sliders upwards (commonly known as top side). This is because when guide post completes core pulling and leaves slider, slider is prone to falling under gravity, leading to a serious accident of guide post and slider colliding during mold closing.
If only one side has a slider, it's best to place it on non-operating side or ground side for easy part removal.
In other aspects, since mold has three sliders for core pulling, insertion angle of molded parts must be carefully considered during design. Textured cavity surfaces should be designed to prevent excessive etching. Additionally, process screw holes should be designed on sliders to facilitate polishing of sliders and fixed mold. P20 or 718 stainless steel can be used for both fixed and moving mold plates.

 

Most of product's plastic parts are ejected via slides; front mold core only covers a portion of plastic parts.

 

Illustrated rib depth exceeds 30mm.
One-time ejection of slides can easily cause sticking and damage to product.
A secondary slide structure needs to be designed, with internal ribs opened first, followed by larger slides.

 

Slide stroke is 210mm. To ensure smooth mold opening, a hydraulic cylinder core-pulling structure is used. Challenge in this case is designing a secondary slide structure without adding inclined guide pillars.

 

To achieve secondary slide opening control, a locking mechanism is added to bottom of slide structure. Hydraulic cylinder drives slide insert to move 20mm, locking slider pushes locking block back, large slide is released from its restraint, and then mold opens together. This case utilizes a locking mechanism, which is stable and reliable, allowing internal insert to be pulled out first to prevent sticking, then large slide opens and releases its locking mechanism together.

 

Conclusion
In design of temperature control systems for automotive injection molds, there are mainly two combination forms:
(1) First combination form: vertical water pipe + inclined water pipe + partition water well;
(2) Second combination form: vertical water pipe + partition water well + inclined water pipe.
Difference between these two types lies in use of inclined water pipes versus water wells. Inclined water pipes are preferred in the former, while water wells are preferred in the latter. These two combinations emphasize different aspects, resulting in different effects.
Advantages of first type are uniform cooling throughout cavity, a short molding cycle, and high-quality plastic parts. It is suitable for molds with high requirements for performance and appearance, such as injection molds for automotive front and rear bumpers, upper and lower dashboard bodies, left and right door panels (interior and exterior trim). Disadvantage is higher processing costs, making it primarily suitable for molds for European and American clients.
Advantages of second type are lower processing costs and faster processing. Disadvantage is that excessive water wells in mold can negatively impact mold strength, and cavity cooling effect is somewhat inferior to first type. It is more commonly used in Japanese and Chinese domestic automotive molds.
For automotive plastic parts, naturally contoured cooling channels are beneficial for cooling part and mold life. Strictly demanding European and American mold manufacturers may even prohibit or minimize use of cooling water wells and sealing rings. This is because large diameter and excessive number of water wells can affect mold strength, thus shortening mold life. Sealing rings are prone to aging and failure, therefore their use must be minimized in design.
This mold is a large injection mold. Temperature control system adopts first combination of "straight-through water pipe + inclined water pipe + water well". Although mold manufacturing cost is increased, molded parts achieve satisfactory molding quality and molding cycle for customer.
Temperature control system design of this mold also achieved following:
(1) Spacing between water channels is maintained between 50 and 60 mm, distance between cooling water channel and cavity surface is maintained between 20 and 25 mm. Fixed mold structure of this mold is relatively complex, and heat is relatively concentrated, so focused cooling is implemented.
(2) Considering processing issues, cooling water channels of this mold maintain a distance of at least 8 mm from ejector pins, ejector blocks, and other ejector hole holes.
(3) Length of cooling water channels is approximately equal, ensuring that temperature difference between inlet and outlet of cooling water is approximately equal, thereby ensuring a roughly balanced mold temperature.
(4) Based on shape of plastic part, mold adopts a large-angle inclined hole. Although drill bit is prone to slippage and deviation, this problem can be solved by milling a platform perpendicular to inclined hole before drilling.
A single automobile requires 500 sets of hardware molds and nearly 1500 sets of injection molds. Therefore, rapid development of automotive industry is inseparable from development of automotive mold industry. Abroad, research and technological innovation in automotive injection molds have received high attention, relevant technologies are quite advanced and mature. However, domestic research on automotive molds is still weak, many large, high-precision, and long-life automotive injection molds are imported. This mold is one of our self-designed and manufactured automotive injection molds. Since production began, fixed mold side core pulling and inverted mold demolding systems have operated stably and reliably, molding quality and molding cycle have met design requirements.