In process of car lamp design, it is indeed necessary to consider molds, production, injection molding, processes and other aspects to improve design and ensure quality.

 

Design rationality: Structural design of mold should be reasonable to facilitate smooth demolding and ensure accuracy of product. For example, for complex shape of car lamp shell, it is necessary to design a suitable parting surface and core pulling mechanism to avoid situation where mold cannot be opened or product is difficult to demold.
Processing accuracy: Processing accuracy of mold directly affects dimensional accuracy and appearance quality of car lamp. Processing accuracy of mold cavity and core must reach micron level to ensure assembly accuracy and sealing performance of car lamp.
Material selection: Select appropriate mold material according to use requirements and production batch of car lamp. For high-yield car lamp molds, high-quality alloy steel is usually used to improve wear resistance and life of mold.

Material properties: Select appropriate injection molding material, consider heat resistance, weather resistance, mechanical strength, optical properties, etc. of material according to use environment and performance requirements of car lamp. For example, for headlights, polycarbonate (PC) materials are usually used, which have good optical properties and mechanical strength.
Injection molding process parameters: Optimize injection molding process parameters, such as injection pressure, injection speed, mold temperature, cooling time, etc., to ensure quality and performance of product. For example, by adjusting injection molding process parameters, shrinkage deformation and internal stress of product can be reduced, dimensional accuracy and appearance quality of product can be improved.
Injection molding equipment: Select appropriate injection molding equipment, select appropriate injection molding machine model and specifications according to size, weight and production batch of product. At the same time, regularly maintain and maintain injection molding equipment to ensure normal operation of equipment.

 

Here we will briefly introduce mold.
In industrial production, molds are various molds and tools used to manufacture required products through various methods such as injection molding, blow molding, extrusion, die casting, forging molding, smelting, stamping, etc. In short, mold is a special tool for making molded objects. It is composed of a variety of different parts, and parts composition of different types of molds is also different. Mold mainly changes physical state of molding material to complete processing of shape of object. For this reason, it is known as "mother of industry".

 

In the field of headlight manufacturing, we are most exposed to injection molds. Of course, some small parts such as heat sinks will use stamping molds, but here we will not introduce stamping molds separately, but focus on the overall overview of mold.
So, what are benefits of learning mold knowledge?
First, it can cultivate unique mold thinking ideas. When designing products, we can fully consider how to simplify mold structure, thereby shortening mold opening cycle, reducing mold costs, and reducing probability of mold problems.
Second, it promotes deep integration of product, mold, and injection molding concepts. Product design cannot be unrealistic. It must consider whether mold can achieve corresponding design and whether injection molding process is easy to adjust.
Third, it helps us accurately capture relevant information about mold from sample. For example, accurately determine gate position, parting line position, demolding direction, identify where slider is set and where lifter is used, then understand how product is demolded, etc.
Mold is mainly divided into:

Composition and function: Molding system is core of mold, mainly composed of core and cavity. Core is responsible for forming internal shape of product, and cavity is used to shape external contour of product, which directly determines shape, size and surface quality of product.
Working principle: During molding process, molten material is injected into closed space formed by core and cavity. After cooling and solidification, a product matching shape of cavity and core can be obtained.
Application example: In mold for manufacturing plastic toys, core will form internal structure of toy, such as hollow part or internal protrusion, while cavity will shape appearance of toy, including texture, color and other details of its surface.

Composition and function: Gating system consists of main channel, branch channel, gate and other parts. Its function is to introduce molten material from injection molding machine or other molding equipment into cavity of mold.
Working principle: Molten material enters main channel from injection molding machine nozzle, then is distributed to each cavity through branch channel, and finally enters cavity through gate. A properly designed pouring system can ensure that molten material fills cavity evenly and quickly, while controlling flow rate and pressure of molten material.
Application example: In mold for producing multi-cavity plastic parts, runner of pouring system will evenly distribute molten material to each cavity to ensure quality and dimensional consistency of each part.

 

Composition and function: Guide system usually consists of guide pins and guide sleeves, which are installed on movable mold and fixed mold. Its main function is to ensure that movable mold and fixed mold can be accurately matched during opening and closing of mold, prevent core and cavity from being misaligned, ensure accuracy of product.
Working principle: When opening and closing mold, high-precision cooperation between guide pin and guide sleeve provides accurate guidance for movement of movable mold and fixed mold, so that mold can be opened and closed in predetermined direction.
Application example: In mold of precision electronic parts, precision requirement of guide system is extremely high to ensure that dimensional accuracy of produced parts meets requirements and avoid scrapping of parts due to mold misalignment.

 

Composition and function: Ejector system mainly includes components such as ejector pins, ejector rods, and push plates. Its function is to eject molded product from mold cavity or core of mold smoothly and accurately after molding process is completed, so as to remove product and realize automation of production.
Working principle: Through power transmission of injection molding machine or other molding equipment, components of ejector system work together to generate an upward or outward thrust to eject product from mold.
Application example: In mold for manufacturing plastic shells, after injection molding is completed, ejector pin will extend from bottom or side of mold to eject plastic shell from cavity and make it separate from mold.

 

Composition and function: Cooling system consists of cooling water channels and is distributed inside mold. Its function is to remove heat generated by mold during molding process through circulating cooling water, so that molten material can be quickly cooled and fixed, thereby improving production efficiency and product quality.
Working principle: Cooling water circulates in cooling water channel, absorbs heat of mold, reduces mold temperature, enables product to reach temperature and hardness required for demolding in a shorter time.
Application examples: In injection mold of automotive parts, complex cooling system design can ensure uniform cooling of large and complex parts to avoid quality problems such as deformation and shrinkage.

 

Composition and function: Exhaust system is usually composed of exhaust grooves, exhaust holes or gaps between mold parts. Its function is to timely exhaust air in cavity and gas generated by volatilization of material during molding process to prevent defects such as pores and burning and ensure product quality.
Working principle: During mold closing and injection molding process, gas is discharged out of mold through exhaust grooves, exhaust holes or gaps between parts, so that molten material can fully fill cavity.
Application examples: In mold for manufacturing high-precision plastic optical lenses, a good exhaust system can avoid bubbles or surface defects in lens and ensure optical performance of lens.

Composition and function: Lateral core pulling system is mainly composed of parts such as sliders, inclined guide pillars, and wedge blocks. When product has lateral holes, grooves or protrusions, it is used to realize molding and demolding of these lateral structures.
Working principle: When opening mold, inclined guide column drives slider to move sideways to extract core so that product can be demolded smoothly; when closing mold, wedge block fixes slider in correct position to ensure molding accuracy.
Application example: In manufacture of plastic pipe fittings with side holes, lateral core pulling system can extract core of side hole part after pipe fitting is formed, so that pipe fitting can be taken out smoothly, ensuring integrity and dimensional accuracy of pipe fitting.
There are various mold processing methods, the most common ones are as follows:

 

Turning: On lathe, through rotation and tool feeding, mold revolving body parts, such as circular cores, ejectors, etc., are processed to ensure dimensional accuracy and surface quality.
Milling: With the help of a milling machine, milling cutter rotates and worktable moves, mold plane and curved surface can be processed, which is used for production of complex structures such as cavity contours and parting surfaces.
Grinding: Used to improve dimensional accuracy and surface quality of mold parts, mainly for planes, cylindrical surfaces, etc., to make mold surface smoother and meet matching requirements.
Electrospark machining: It uses pulse discharge to remove conductive materials at high temperature. It is suitable for processing complex and difficult mold structures, such as narrow slits, special-shaped holes, etc., can be accurately processed by controlling electrode and discharge parameters.
Wire cutting machining: Cutting is achieved by pulse discharge between electrode wire and workpiece. It is often used to cut various shapes of through holes and contours. It has high precision, small thermal deformation, and can cut small gaps.

Sand casting: It is suitable for large molds or molds with low precision requirements. Make sand molds and pour molten metal into them. It has low cost but poor precision and surface quality, and requires subsequent machining.
Precision casting: It includes investment casting and pressure casting. Investment casting can obtain high-precision complex-shaped parts, and pressure casting is suitable for large batches and high-precision aluminum alloy or zinc alloy molds.
3D printing processing: Based on additive manufacturing, material is stacked layer by layer to make molds. It can quickly manufacture complex mold prototypes or small batches of molds, such as conformal cooling water channel molds, and can also flexibly adjust structure according to design changes.
Next, we will learn about some structures of mold.
As shown in the figure, lifter structure of mold

 

Inclined slider structure: used for side core pulling and core pulling at an angle to horizontal direction.
Automatic thread removal mechanism

 

Slider structure

 

Internal pulling structure

 

Quick return structure

 

Strong pulling structure

 

Double color structure

 

After understanding these structures, we also need to know basic mold frame of mold.
Basic mold frame of mold is basic structure of mold, carrying key components, is related to performance and working stability of mold.
It is mainly composed of a fixed mold base plate, a fixed mold plate, a movable mold plate, a movable mold base plate, a cushion block, a guide column, and a guide sleeve. Fixed mold base plate is connected to fixed mold plate of injection molding machine, fixed mold plate is equipped with fixed model core and cavity; movable mold plate is equipped with movable model core and ejection mechanism, movable mold base plate is connected to movable mold plate of injection molding machine; cushion block leaves space for ejection mechanism; guide column and guide sleeve are responsible for guiding to ensure that fixed and movable molds are accurately matched.
Standard mold frame is made by professional factories such as LKM according to standard sizes. Because of its advanced equipment and mature technology, it has obvious advantages over ordinary mold frames: higher mold precision, which is conducive to improving product molding quality and dimensional accuracy; longer mold life, using high-quality materials and reasonable design, reducing maintenance and replacement; more beautiful appearance, fine surface treatment, high processing and assembly quality. In practice, reasonable selection of standard mold frames can improve efficiency and performance of mold design and manufacturing, and bring economic benefits.

 

After a general understanding of mold structure, you need to know following aspects when designing products:

Demolding method: Consider shape and structure of product and design a structure that is easy to demold. For example, avoid structures that are difficult to demold, such as undercuts or deep holes. If it cannot be avoided, a reasonable demolding mechanism should be designed, such as sliders, lifters, etc.
Wall thickness uniformity: Try to make product wall thickness uniform to avoid defects such as deformation and shrinkage marks caused by uneven cooling during injection molding process. If wall thickness changes, a gradual transition should be used.
Rib design: Reasonable setting of ribs in parts where product needs to enhance strength or rigidity can improve product performance without increasing wall thickness, but attention should be paid to thickness and height of ribs to avoid shrinkage and other problems.

Matching dimensions: Clarify matching dimensions of product with other components, and determine a reasonable tolerance range according to use requirements. For parts with high-precision matching requirements, influence of mold manufacturing accuracy and molding process should be considered to ensure consistency of product dimensions.
Overall dimensions: Consider shrinkage rate during mold molding. Different materials have different shrinkage rates. Even for same material, changes in molding process parameters will affect shrinkage rate. Therefore, according to material properties and mold experience, appropriate shrinkage margins should be reserved to ensure that final size of product meets design requirements.

Molding performance: Understand molding properties of selected material, such as fluidity, thermal stability, shrinkage, etc. Materials with good fluidity are easy to fill mold cavity, but may cause overflow; materials with large shrinkage rates require corresponding compensation measures in mold design.
Product performance requirements: Select appropriate materials according to product's use environment and functional requirements. For example, products that require high strength can choose engineering plastics or metal materials; products that require good insulation performance should choose insulating materials. At the same time, corrosion resistance, wear resistance, heat resistance and other properties of material should also be considered.

Appearance requirements: Determine surface quality standard according to appearance requirements of product, such as whether high gloss, matte, texture and other surface treatments are required. Different surface treatment methods have different surface processing requirements for molds, and it is necessary to communicate with mold manufacturer during design stage to ensure that mold can achieve required surface effect.
Functional requirements: Surface quality of some products will affect their functions. For example, surface roughness of optical products is extremely high to ensure transmission and refraction of light; some surfaces that need to be closely matched with other parts also require high flatness and finish to ensure matching accuracy.
For example:
1. Smoothness at parting surface to avoid rubbing through structure

 

2. Sockets in demoulding direction

 

3. Structure that prevents movement is prohibited within range of lifter movement

 

In summary, when designing structure of our headlight parts:
Optimal mold demoulding direction:
1. Considering height of mold, making product as flat as possible in mold can save costs and shorten mold production cycle.
2. The simplest mold structure, under condition of permitted negotiation, a demoulding direction with as little internal extraction or lifter as possible is given
Determination of parting line:
Principle of determining parting line: It must be in demoulding direction. When outermost contour line of product affects appearance of product, it is necessary to consider modifying product data or confirm with customer whether impact of parting line is acceptable. In addition, trend of parting line needs to be continuous and smooth to reduce right-angle transfers to increase life of parting surface.
Considerations for early production of molds with uncertain structures and sizes:
1. Make screw column hole or other mounting holes and other types of structures larger first for modification.
2. Reinforcement ribs and product profiles should be left out first before modifying allowance.
3. Headlight mounting leg area that needs to be installed on body should be reserved for inserts.
4. Reserve slider area.
5. Optical pattern areas should be reserved for inserts depending on situation.
These are some of impacts and suggestions of molds on products during product design.