For previous reading, please refer to Introduction to car lamp mold (I).
As an important part of car, manufacturing process of car light and effect it produces in practical application are crucial to ensure safety of car driving. Due to its function, production of car light molds is the most demanding among all automobile molds.

 

Quality of mold is affected by many factors, mainly including following points:
Industrial design: Scientific, reasonable and forward-looking industrial design is basis for ensuring that mold can meet requirements of product function, appearance and production process. It determines the overall structure and key parameters of mold, and plays a decisive role in subsequent performance of mold.
Processing accuracy: Precise processing accuracy can ensure dimensional accuracy, surface flatness and mutual matching accuracy of each component of mold. The higher processing accuracy, the closer molded product can be to design expectation, reducing errors and defects.
Steel quality: High-quality steel is the key to mold's good strength, toughness, wear resistance and corrosion resistance. Suitable steel can withstand harsh working conditions such as high pressure, high temperature and friction during production process, extend service life of mold.
Quality of mold accessories: Mold accessories are like "joints" and "components" of mold, and their quality directly affects the overall performance of mold. From ejectors, sliders to springs and other accessories, quality problems in any link may cause mold to run poorly or even malfunction frequently.
Mold maintenance: Regular and professional mold maintenance can timely clean dirt, wear debris, etc. on mold surface, check and repair potential damage, so that mold is always in good working condition, effectively extend its service life, and stabilize product quality.

Thermoplastic molds: When working, plastic is placed in heating barrel of injection machine, and plastic is gradually melted by heat. Under powerful driving force of injection machine screw or plunger, molten plastic is quickly and accurately injected into mold cavity through nozzle and mold pouring system. In cavity, plastic hardens and takes shape due to physical cooling and chemical cross-linking, finally becomes an injection molded product that meets requirements.
Thermosetting mold: During operation, plastic is first placed directly into mold cavity with a certain temperature and open, then mold is closed. Under dual effects of heat and pressure, plastic quickly melts and changes to a flowing state. As physical changes and chemical reactions continue, plastic gradually hardens, forming a plastic part with a specific shape and size that can remain stable at room temperature.

Large sprue mold: Its runner and gate are set on parting line. During mold opening process, runner, gate and product are demolded together. This structure is relatively simple and is widely used in production of some products with low appearance requirements and simpler structures.
Fine sprue mold: Runner and gate of this type of mold are not on parting line, but are directly set on product. Therefore, an additional set of sprue parting lines needs to be designed, which makes mold design more complicated and difficulty of processing and manufacturing is greatly increased, but it can achieve more precise injection control and is suitable for products with high appearance requirements and complex structures.
Hot runner mold: This mold structure is roughly similar to fine-gate mold. The biggest difference is that its runner is in one or more hot runner plates and hot nozzles equipped with a constant temperature device. During production process, there is no cold material demoulding, runner and gate are directly connected to product, there is no need to demould runner, so this system is also called a no-gate system, which can effectively save raw materials and improve production efficiency.

 

Advantages: Simple mold production, short production cycle, and low price.
Disadvantages: Gate needs to be trimmed, which will leave gate marks.

 

Advantages: Gate will fall off automatically, which is convenient for automated production.
Disadvantages: Mold structure is relatively complex, production cycle is long, and cost is relatively high. Due to small gate, choice of injection molding materials is relatively limited, and there are many molding problems.

 

Advantages: Gate position and form can be varied. Material fluidity is enhanced, and injection molding can be optimized. Save injection molding materials.
Disadvantages: Hot runner system is expensive and mold processing is more complicated.

 

Hot runner structure: open and needle valve type detailed explanation
In the field of injection molds, hot runners are playing an increasingly important role as a heating component system that injects melted plastic particles into mold cavity. Hot runner molds are heated so that runners and runners of traditional molds do not need to be removed during each molding, greatly improving production efficiency. Its system is generally composed of hot nozzles, manifolds, temperature control boxes and accessories. Hot nozzles are mainly divided into open hot nozzles and needle valve hot nozzles. Based on this, hot runner systems are often divided into open hot runner systems and needle valve hot runner systems.

Structural features: Open hot runner structure is relatively simple, mainly consisting of injection nozzles, manifolds, hot nozzles, temperature control boxes and accessories. Manifold is used when there are multiple cavities in one mold, multiple feeding points, or single feeding point but material level is offset. Material is mostly P20 or H13. Its structural form depends on cavity distribution, nozzle arrangement and gate position. Hot nozzle is usually heated by a round sleeve heater or copper tube, temperature sensing line and temperature control box are used to control temperature of hot runner. When an open hot runner is used in a micro semi-hot runner, hot nozzle does not directly contact product, but contacts tiny runner, which can avoid some disadvantages of adiabatic runners.
Working principle: During injection molding cycle, injection molding machine injects molten plastic into hot runner system. Relying on pressure of injection molding machine, plastic melt is distributed to each hot nozzle through manifold and then injected into mold cavity. After injection molding cycle, product in mold cavity is shaped under pressure-maintaining cooling of mold core. When mold is opened, hot runner gate is pulled off by mold opening force. Some open hot runner gates have a little cold material handle, while some gates are as small as a needle tip.
Application scenarios and limitations: Open hot runners are suitable for injection molding of some small products with low requirements for appearance quality. Its structure is simple, processing requirements are low, cost is relatively cheap, and equipment maintenance is relatively easy. However, since it directly contacts surface of product, it is easy to cause wire drawing and leakage during molding process, resulting in poor surface quality of product. In addition, for multi-point open hot runners, all gates are opened at the same time, weld lines or clamp lines are easily generated at confluence of rubber materials, affecting appearance and performance of product.

 

Structural features: Needle valve hot runner is based on open hot runner, and a valve needle, a cylinder or an oil cylinder and a corresponding drive control device are added. Movement of valve needle is driven by input air pressure or oil pressure, is controlled by solenoid valve to achieve precise opening and closing of gate. System also includes components such as injection nozzles, manifolds, hot nozzles, and temperature control boxes. Design of manifold and hot nozzle is similar to that of open hot runner, but in order to cooperate with valve needle action, higher requirements are placed on structural accuracy and sealing.
Working Principle: During injection molding, under action of control system, cylinder or oil cylinder drives valve needle to open, and injection molding machine injects molten plastic into mold cavity through hot runner. When cavity is filled, valve needle closes gate under action of control device to prevent plastic from flowing back. Compared with open hot runner, needle valve hot runner can more accurately control opening and closing time of gate and injection amount of plastic.
Application Scenarios and Advantages: Needle valve hot runner is widely used in automotive manufacturing, medical, electronics, office equipment and other fields with extremely high requirements for product appearance and quality. For example, in production of integral automotive lampshades, lampshade is a transparent product and requires a smooth and flat gate. Needle valve hot runner can meet this requirement. In medical field, strict requirements are placed on gate quality of plastic parts, and sharp protrusions are not allowed. Needle valve hot runner can effectively improve gate quality. In addition, for multi-point needle valve hot runners, opening time of each gate can be controlled separately according to needs of product structure, which helps to eliminate weld line of product, improve internal quality of product, make surface of plastic part beautiful, make internal structure tight and strong.

 

Two main types of hot runner systems - open hot runner and needle valve hot runner, each has unique structural characteristics, working principles and applicable scenarios. Open hot runner has a simple structure and low cost, and is suitable for small products with low requirements for appearance; although needle valve hot runner has a complex structure and high cost, it has significant advantages in controlling gate and improving product quality, especially for injection molding production of high-end products. In actual mold design and injection molding production, it is necessary to comprehensively consider and select appropriate hot runner system according to specific requirements of product, production scale, cost budget and other factors to achieve efficient and high-quality production goals.

 

Common mold movement mechanism

Structural composition: It is mainly composed of a slider, a slide, a drive device (such as an inclined guide column, a bent pin, etc.) and a positioning device. Slider is usually installed on one side of mold and can slide in slide. Driving device such as inclined guide column is used to drive slider to move horizontally during mold opening and closing process.
Working principle: When opening mold, mold opening force of injection molding machine acts on slider through driving device (such as inclined guide column), so that slider moves along slide to outside of mold, thereby realizing side core pulling or lateral parting action, so as to smoothly remove plastic part. When closing mold, driving device drives slider back to initial position to complete reset of slider.
Application scenario: It is commonly used in molding of plastic parts with lateral holes, grooves, bosses and other structures, such as plastic shells, automotive parts, etc., which can realize molding of complex shapes without affecting appearance and structure of plastic parts.

 

Structural composition: It is generally composed of a lifter rod, a lifter seat, a guide block, etc. One end of lifter rod contacts plastic part, the other end is installed on lifter seat, and is guided by guide block.
Working Principle: When opening mold, ejector mechanism of injection molding machine pushes lifter seat, so that lifter rod moves obliquely along direction of guide block, and while ejecting plastic part, internal undercut or lateral structure of plastic part is demolded. When closing mold, lifter mechanism returns to initial position under action of reset spring or other reset device.
Application Scenario: It is suitable for some plastic parts that have internal undercuts or lateral demolding requirements and are difficult to achieve with slider mechanism, such as small plastic boxes, toys, etc. It can achieve demolding in a smaller space and has less impact on appearance of plastic part.

 

Structural Composition: It mainly includes ejector pins, ejector pin plates, return pins, etc. One end of ejector pin contacts plastic part, and the other end is fixed on ejector pin plate. Ejector pin plate is driven by ejector device of injection molding machine. Return pin is used to reset ejector pin plate.
Working Principle: After opening mold, ejector device of injection molding machine pushes ejector pin plate, so that ejector pin moves upward and ejects plastic part from mold cavity. When mold is closed, reset rod of mold pushes ejector plate to reset, so that ejector returns to initial position.
Application scenario: It is the most common mold demoulding mechanism, widely used in various types of plastic parts molding, especially for some plastic parts with simple appearance and low surface requirements, such as ordinary plastic containers, cover plates, etc., which can reliably realize ejection and demoulding of plastic parts.

 

Structural composition: It is usually composed of a rotating shaft, a rotating disk, a driving device (such as a motor, a gear rack, etc.) and a positioning device. Rotating shaft is installed in mold, rotating disk is connected to rotating shaft, and driving device is used to drive rotating disk to rotate around rotating shaft.
Working principle: During injection molding process, rotating disk drives relevant parts of mold (such as core, cavity, etc.) to rotate according to needs, so as to realize multi-station molding, thread demolding or special shape molding of plastic parts. For example, when molding plastic parts with threads, core is driven to rotate by rotating mechanism to realize demolding of threads.
Application scenario: It is commonly used for plastic parts with threaded structures, complex plastic parts that require multi-station molding, and plastic parts with special shape requirements, such as plastic threaded bottle caps, toys with spiral structures, etc.

 

Structural composition: Generally, it consists of the first ejection mechanism (such as ejector plate, ejector, etc.), second ejection mechanism (such as push plate, push rod, etc.), and connection device, limit device, etc. The first ejection mechanism and second ejection mechanism are connected by connection device, and ejection action is realized successively under action of limit device.
Working principle: After mold is opened, ejection device of injection molding machine first pushes the first ejection mechanism to make plastic part initially ejected from mold cavity for a certain distance. Then, through action of connection device and limit device, second ejection mechanism is triggered to further eject plastic part to meet complex demolding requirements of plastic part, such as overcoming large clamping force between plastic part and mold or realizing step-by-step demolding.
Application scenario: It is suitable for some plastic parts with complex structures and difficult demolding, such as plastic parts with deep cavities, thin walls or special structures, which can effectively avoid deformation, damage and other problems of plastic parts during demolding.
Classic secondary ejection mechanism: cleverly using return pin + stop pin + spring to achieve secondary ejection

 

Mold processing technology

 

Metal cutting machine tools
CNC milling machine: Through digital program control of tool to cut mold blank in three-dimensional space, it can process mold cavities and cores of various complex shapes, with high processing accuracy and efficiency. Suitable for processing small and medium-sized molds, such as cavities, cores and various complex curved surface structures of plastic molds, die-casting molds, etc.
Machining center: It is based on CNC milling machine and adds an automatic tool changer and tool magazine. It can realize automatic processing of multiple processes, reduce number of clamping times during mold processing, improve processing accuracy and production efficiency. It can be used to process various types of molds, especially large and complex molds, such as automobile cover molds, large injection molds, etc., and can complete milling, boring, drilling, tapping and other processing processes.
Electric spark machining machine: Use high temperature generated by pulse discharge to corrode metal materials and perform molding processing on mold. It is mainly used to process complex shapes and high-precision mold parts that are difficult to complete with traditional cutting, such as molds with fine structures, deep and narrow grooves, hard alloys and other materials.

 

Injection molding machine: After heating and melting thermoplastics or thermosetting plastics, they are injected into mold cavity under high pressure, plastic products are obtained after cooling and molding. It is widely used in molding of plastic molds. According to different plastic materials, product shapes and sizes, different specifications and types of injection molding machines can be selected to produce molds for various plastic products, such as daily necessities, electronic product shells, automotive interior parts and other plastic molds.
Die casting machine: Liquid metal is injected into mold cavity at high speed under high pressure, quickly cooled and molded to produce high-precision and high-strength die castings. It is mainly used for molding of die casting molds, is suitable for manufacturing molds for various metal die castings such as automobile engine cylinder blocks, cylinder heads, and transmission housings.
Special processing equipment
Laser processing machine: Use high-energy-density laser beams to cut, weld, and surface treat mold materials. It can be used for precision machining of molds, such as cutting complex contours of molds, welding local damaged parts of molds, strengthening mold surface, etc. It can achieve high-precision and high-efficiency machining, has little thermal impact on mold materials.
Wire cutting machine: Using a moving thin metal wire (electrode wire) as a tool electrode, mold base is cut by pulse discharge. It is often used to process mold parts of various shapes, especially small mold parts with complex contours and high precision requirements, such as punches and concave molds of punching dies, inserts of plastic molds, etc.

Grinding machine: It is used for precision grinding of mold parts to obtain high-precision size, shape and surface finish. Including surface grinders, external cylindrical grinders, internal cylindrical grinders, etc., it can grind plane, cylindrical surface, inner hole and other surfaces of mold to improve matching accuracy and surface quality of mold.
Drilling machine: It is mainly used to process various holes on mold parts, such as mounting holes, cooling holes, ejector holes, etc. There are ordinary drilling machines, CNC drilling machines and other types. Different drilling methods and precision can be selected according to processing requirements of mold.