''1. Structural characteristics of automobile cover parts:
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''1. Large size. Automobiles are the largest industrial product among consumer products. Car parts mould is the parts that cover the engine and chassis to form the car body. Therefore, the size of its structure depends on the size of the body block. From the functional point of view of the cover itself, the block should be as large as possible. From the perspective of the overall manufacturing process of the body, the bigger the better. Therefore, the structure size of the cover is generally relatively large.
''2. The plate is thin. To reduce the weight of the car, the plates selected for the cover are relatively thin. Thickness is a relative concept. The ratio of the perimeter (m) of the cover to the thickness of the sheet used (mm) is generally above 1.00. The thickness of the cover material is generally between 0.6 mm and 1.2 mm.
''3. The shape is complex. To meet the needs of function and aesthetics, automobile panels are generally composite surfaces composed of three-dimensional regular surfaces and irregular surfaces.
''4. Express it with a model. It is very difficult to express the shape and size of the car cover using mechanical drawing because the cover is composed of a three-dimensional surface. Usually represented by a model. The model representing the shape and size of the car cover is called the main model (there are physical main models and mathematical main models).
''Second, the quality characteristics of automobile cover parts:
''1. High dimensional accuracy. When connected, it is a curved surface. When turning, it is natural and smooth. After the cover piece is overlapped with the cover piece, the overlapped surfaces of the two pieces are one surface, and they fit each other without a gap. The welded body should become a work of art for people to appreciate.
''2. The surface quality is strict. The car cover directly reflects the appearance quality of the car. In addition to the high surface roughness requirements, the ridges on the cover are also required to be clear and clean, smooth and smooth, left and right symmetrical, uniform in transition, smooth in connection, and smooth in surface transition. The surface is not allowed to have defects such as ripples, wrinkles, dents, pull marks, abrasions, bumps, and other damage to the surface.
''3. Strong structural rigidity. Whether it is the cab of a truck or the body of a passenger car, the coverings that constitute them must be sufficiently rigid. Especially the body parts without beam structure, are strong and rigid. Insufficient rigidity will not only cause the deformation of the entire body but also cause noise when the car is running.
''4. Good processing technology. Good manufacturability mainly refers to the feasibility of one-time stamping. The manufacturing process of automobile panels is relatively complicated. Cover dies are quite expensive. Good stamping manufacturability can not only simplify the stamping process but also greatly reduce the capital investment in die manufacturing.
''3. Process characteristics of automobile cover parts:
''1. The preparation of the stamping process mainly relies on practical experience and data accumulation. Due to the influence of several uncontrollable factors in the stamping process of automobile panels, it is impossible to use the theory of sheet plastic deformation to guide the design of the stamping process. The theoretical application conditions are harsh. Now the plastic deformation demonstration analysis software can only play the role of verifying the process. The stamping process of automobile panels mainly relies on long-term accumulated practical experience and accumulated data.
''2. The stamping process is mostly composite. Due to the large size and complex shape of the cover, it is difficult to locate and move. Therefore, composite molds are often used for cover parts, and progressive molds are rarely used. For narrow and long parts, multi-station die or joint installation is sometimes used and progressive die is not used.
''3. The basic process of punching cover parts is forming process, trimming and punching process, and flanging shaping process. The forming process is the key process. To obtain sufficient plastic deformation of the cover, thereby improving the rigidity of the cover, the forming process generally uses a drawing process instead of a pressing process.
''4. Use a press with a large work surface and a relatively small nominal pressure. The requirements for presses for pressing automobile panels are generally that the work surface is relatively large to adapt to the relatively large structure size. Since the cover is made of a thin plate and the deformation force is small, the effective tonnage of the press does not need to be large. For the accuracy of the press, the requirements are also higher due to the thin plate used for the cover, the small gap between the molds, and the accuracy of the cover itself. The most commonly used are closed four-point mechanical presses.
''4. Design features of auto panel die:
''1. The size of the structure is large. In addition to the relatively large cover itself, the positioning of the die for the cover, the installation structure of the die, the guide of the upper and lower dies, and the lifting, turning, and transportation devices of the die should increase the structural size of the die.
''2. The base part is a frame structure. The structure size of the die for automobile cover parts is large. To reduce the weight of the mold and improve the manufacturing process, it is generally designed as a frame structure composed of two plate-shaped members to form two horizontal layers, and the middle is connected by vertical ribs. The basic parts (die bases) of the general die are mostly standardized solid plates.
''3. The degree of standardization is low. Generally, the standardization degree of die design and the selection of standard parts are much larger than that of the cover die. For example, general punching dies can be assembled from standard parts, but at least the basic parts of automobile panel punching dies are non-standard.
''4. The quality requirements of mold materials are relatively low. For the working parts (punch, die, blank holder) of the cover drawing die with a lifespan of fewer than 400,000 times, cast iron with higher strength is generally sufficient. The working parts of the general die are mostly tool steel.
''5. Manufacturing characteristics of auto panel stamping die:
''1. The preparation of blanks for basic parts and working parts of automobile panel dies is the focus of production preparation. They are mostly castings and are produced in single pieces, and the manufacture of casting models is the key to blank preparation. Generally, real casting (a type of disappearing type) is used.
''2. Due to the large outline size of the die for automobile panels, large-scale machining equipment is required to process it. Commonly used are gantry planer, gantry milling machine, floor boring, and milling machine, gantry CNC milling machine, multi-axis CNC milling machine, etc. In addition, to debug the mold, a large R&D press and a try-out press are also required.
''3. The focus of the die manufacturing process for automobile panels is the processing of the working parts. Because it is a composite surface composed of three-dimensional curved surfaces, it is difficult to process and the accuracy is not easy to guarantee. To improve the precision of CNC machining is to improve the car plastic injection mould.
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''The key to precision and shorter manufacturing cycles.
''4. The assembly, research, and pressure test adjustment of the cover die is an extremely important manufacturing process. In particular, the pressure test adjustment accounts for a large proportion of the entire design and manufacturing man-hours. With the advancement of technology and the improvement of machining accuracy, the cycle of research and development and debugging will be gradually shortened.
''5. A cover generally requires more than two sets of dies, and the manufacturing sequence of each set of dies is restricted by the need for process verification. The conventional manufacturing sequence is to manufacture drawing dies first, followed by various forming dies and repairing dies.
Injection molding has been a big help to countless industries ever since it was introduced in the late 19th-century. It allowed the streamlined production of both big and small parts in large amounts and helped manufacturers become more cost-efficient. Thanks to efforts in mold making by China and other major plastic-producing countries, more and more ways to use injection molding are being discovered and developed.
Plastic is a material widely used for injection molding and it's no surprise as to why that is so. There are so many different types of plastic being used, and all of them have different properties that can be applied to suit the need of different products. Thermoplastics, in particular, are more used in injection molding than their thermosetting counterparts. It also comes in many different types. To help you know the specific types and their key features and characteristics, here are some of the most common thermoplastics used in injection molding.
Considered as the most common plastic, polyethylene is one of, if not the, most used plastic in injection molding. The advantages of using polyethylene are its relatively high levels of tensile strength and ductility. Aside from that, it is resistant to impact, heat, and moisture absorption. It is also recyclable, adding to its cost-efficiency and reusable value.
The primary uses of polyethylene include plastic bags, medicine containers, milk bottles, detergent bottles, and plastic bags just to name a few.
Low-density Polyethylene (LDPE)
A subtype of polyethylene regarded as its most flexible version, low-density polyethylene gets a special mention because it is also widely used for injection molding. This plastic subtype has high ductility but low tensile strength thanks to its low density.
LPDE can be found in many consumer goods and housewares, as well as medical products such as chemical wash bottles. However, LDPE is difficult to bond with and should not be used in harsh weather or high-temperature environments.
Polypropylene comes only second to polyethylene when it comes to how frequently it is used around the world. PP is a flexible, dynamic plastic known for its wide range of properties. Specifically, it has a high melting point, high impact strength, as well as resistance to stress and cracking. It also does not easily react to water, acids, and detergents. PP has been observed not to leak chemicals into food products.
For those reasons, it can be seen being used in food and beverage containers such as lunch boxes and water jugs. Outside of its food uses, it is also commonly found in a wide number of household goods such as athletic apparel, area rugs, and automotive parts like car batteries.
ABS is an opaque, engineering-grade terpolymer thermoplastic that is mainly used for objects and products that have metal coatings. Metal coatings can easily adhere to it, making it ideally suited for piping and electronic parts such as adaptors and desktop phones. It also combines well with products like keyboard keys, shower handles, and showerheads.
This type also has outstanding dimensional stability, mechanical strength, and impact resistance. However, it is important to note that ABS does not have good chemical resistance and should not be used in applications requiring ultraviolet resistance and electrical insulation.
Polycarbonate is a polymer that is known for being naturally transparent and very impact-resistant. It is mainly used to produce a variety of materials that require transparency and good resistance (e.g. bullet-proof glass and safety goggles). Unlike most other thermoplastics, polycarbonate can be subjected to large deformations without cracking or breaking.
Other uses for PC include digital disks like CDs and DVDs, automotive components, and eyewear lenses thanks to its natural ability to filter ultraviolet rays. While it is shatter-resistant, it is not scratch resistant. For this reason, coating and treatments are often used after the injection molding process is completed.
Polystyrene is an affordable polymer that is most recognizable for its unique application as a foam (i.e. styrofoam). However, just like polycarbonate, it is also naturally transparent and can come in the form of solid plastic and the previously mentioned rigid foam material.
The solid plastic form of polystyrene is commonly used in medical devices and apparatuses like test tubes and Petri dishes. It is also used for day-to-day items like your smoke detector's housing, CD cases, and most frequently as yogurt containers. The red 'solo' cup is also an iconic application of polystyrene.
When it comes to the rigid foam version, PS is often used for single-use, disposable products such as take-out food packaging and beverage containers. It is also used in roofing applications thanks to its insulating and noise-reducing properties.
Thermoplastics are amazing materials when used for injection molding. With new polymers being created and existing ones being improved, mold making in China and the United States continually pushes the boundaries of plastic innovation. Despite the hesitation to use plastic, it cannot be denied that its uses in injection molding have made man's life better and easier.
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