Introduction:Injection molding is suitable for the mass production of complex-shaped products and other molding processing fields. Although injection molding is widely used in manufacturing. However, the disadvantages of injection molding are still some, which this article will discuss from the following aspects.

Higher Mold Costs Limit the Accessibility of Small Batch Production.

Why Are the High Start-Up Costs?

There Are Many Manufacturing Processes for Injection Molds:

The cost of purchasing standard parts is high, high initial costs, and the complex processes require relatively more manpower. To ensure quality, plastic mold manufacturers also need to go through a lot of tests when the processes are complex.

The Number of plastic injection molding to Be Manufactured Needs to Be Determined Based on the number of Samples:

Sometimes an injection molded part that seems to have a very simple structure requires two or even three sets of injection molds to be processed.

Injection Mold Manufacturing Takes a Long Time:

To achieve high precision, some injection mold manufacturers are very meticulous and have dedicated personnel to follow up and strive to satisfy customers. Therefore, the more time required, the investment will increase accordingly.

Injection molding can realize the one-time molding of plastic products with complex shapes. It is an efficient and large-scale production method, and the quality of the injection mold directly affects the quality of injection molding.

In the mold industry, to process injection molded parts with high precision, high quality, and complex profiles, it is necessary to use advanced computer-aided design and manufacturing software or CNC machining and formulate reasonable processing procedures.

Injection Mold Manufacturing Is Very Difficult:

the design requirements for injection molds are very high, mainly the accurate design of mold flow channels. If the design work is not done well, it is very difficult to modify the mold if subsequent mold trials are unsuccessful, and most molds need to be remanufactured.

There are many manufacturing processes for injection molds, the cost of purchasing standard parts is high, the process is complex, and it requires relatively much manpower. To ensure the quality of the process, plastic mold manufacturers also need to undergo extensive testing. This is an effective way to ensure processing quality, improve production efficiency, and reduce labor intensity.

All in all, the reasons for the high quotation of injection mold manufacturers are that there are many processes for manufacturing injection molds, the number of plastics injection molding to be manufactured needs to be determined based on the number of samples, injection molds take a long time, and injection mold manufacturing is difficult. With the continuous development of industrialization, it has developed into a major country in the world of injection molded products.

The injection molded products produced every year are sold all over the world, especially the GPS shells are sold at home and abroad. The number of molds to be made depends on the sample, and sometimes it seems that a plastic part with a very simple structure requires two sets of injection molds, or even three sets of injection molds to process.

Injection molding products have also made an indelible contribution to the growth of foreign trade. However, while growing rapidly, the industry also encounters many problems that require more attention.

Why Is Injection Molding Not Suitable for Small Batch Production?

Waste of Material: To manufacture a complete injection molding model, certain raw materials are required to fill the mold cavity. If it is produced in small batches, a large amount of material will be wasted. Injection-molded models are not suitable for small-batch production.

Mold Manufacturing Cost Is High:  the procurement cost of standard parts of injection molds is high and the process is complicated. Small batch production will increase the cost of unit products, so injection molding is not suitable for small batch production.

Long Preparation Time: Before injection molding, a lot of time is needed for testing and adjustment, and for small batch production, it will reduce its production efficiency.

Lack of Flexibility: Injection molding is more suitable for mass production of the same product. Small batch production, lacks flexibility and requires constant adjustment.

High Economic Costs: Due to the small quantity of small batch production, it is difficult to achieve economies of scale in terms of production quantity. In addition, injection molding equipment is very expensive. Therefore, the cost shared by a single product is very high, so the economic costs are high. , not suitable for small-batch production.

In summary, injection molding is a process suitable for mass production, and most plastic products today are manufactured through this process. However, the injection molding process requires the manufacturing of molds first, and molds are not only expensive to manufacture but also have a relatively long manufacturing cycle. Therefore, only when the production volume reaches high volumes, it will be economically beneficial to open the mold.

Injection Moulding Design Limitations

Which Product Designs Are Suitable for Injection Molds?

Electronic Product Casings: The casings of electronic products such as mobile phones, TVs, stereos, etc. are injection molded from high-strength and durable plastic materials to meet product appearance and performance requirements.

Toys: including children’s toys, educational toys, sports toys, etc. These toys can be injection molded from different materials, such as polyethylene, polypropylene, etc.

Household Items: such as plastic hangers, plastic buckets, plastic chairs, etc. These products have excellent durability and portability and are very suitable for home use.

Auto Parts: such as car doors, car dashboards, lights, etc. These products need to have high heat resistance, corrosion resistance, and toughness to adapt to the requirements of the automotive working environment.

Medical Devices: such as medical syringes, medical skim yarn, etc. These products need to have good biocompatibility and durability to meet the strict requirements of the medical industry.

What Are the Rules for Injection Molding Mold Design?

When starting mold design, you should pay more attention to considering several options, weigh the advantages and disadvantages of each option, and choose one among them. You should also take the T-mold seriously.

After handing over the design plan, communicate more with the factory to understand the processing process and manufacturing and usage conditions. Each set of molds should have a fixed analysis experience and a process of summarizing gains and losses so that the level of mold design can be continuously improved;

When designing, refer to similar drawings designed in the past and learn from their experiences and lessons; The mold design department should be a whole, and each design member cannot work independently. Especially in the summary of mold design conclusions, there must be a team style.

Injection Moulding Material Limitations

Which Plastic Materials Are Suitable for Injection Molding Process?

Polystyrene (PS), polystyrene, commonly known as hard glue, is a colorless, transparent, glossy granular material. The characteristics of polystyrene include good optical properties, excellent electrical properties, easy molding and processing, and good coloring properties. The biggest disadvantages of polystyrene are its brittleness, low heat resistance (maximum operating temperature of 60 to 80 degrees Celsius), and poor acid resistance.

Typical applications of polystyrene: product packaging, household items (tableware, trays, etc.), electrical (transparent containers, light diffusers, insulating films, etc.).

Polypropylene (PP): Polypropylene, a colorless, transparent, or glossy granular material, referred to as PP, is commonly known as 100% soft glue. It is a crystalline plastic.

The characteristics of polypropylene include good fluidity, excellent molding performance, excellent heat resistance, can be boiled and sterilized at 100 degrees Celsius, high yield strength, good electrical properties, poor fire safety, poor weather resistance, sensitivity to oxygen, and susceptibility to the influence of ultraviolet rays. Ageing.

Typical applications of polypropylene: automotive industry (mainly using PP with metal additives: fenders, ventilation ducts, fans, etc.), equipment (dishwasher door gaskets, dryer ventilation ducts, washing machine frames and covers, refrigerator doors liners, etc.), consumer products (lawn and garden equipment such as lawnmowers, sprinklers, etc.).

Nylon (PA)Nylon is an engineering plastic made of polyamide resin, referred to as PA. There are PA6, PA66, PA610, PA1010, etc.

The characteristics of nylon are that nylon has high crystallinity, high mechanical strength, good toughness, high tensile strength, compressive strength, outstanding fatigue resistance, wear resistance, corrosion resistance, heat resistance, non-toxicity, and excellent electrical properties. Performance: Poor light resistance, easy to absorb water, and not acid-resistant.

Typical application scope of polypropylene: It is widely used in structural parts due to its good mechanical strength and stiffness. Due to its good wear resistance properties, it is also used in the manufacture of bearings.

Polyoxymethylene (POM)Polyoxymethylene, also known as Saigang material, is an engineering plastic. Polyoxymethylene has a crystal structure with excellent mechanical properties, high elastic modulus, high rigidity, and surface hardness, and is known as a “metal competitor.”

The characteristics of polyformaldehyde include a small friction coefficient, excellent wear resistance, and self-lubrication, second only to nylon, but cheaper than nylon, good solvent resistance, especially organic solvents, but not resistant to strong acids, strong alkalis, and oxidants. Size Good stability and can manufacture precision parts. The molding shrinkage is large, the thermal stability is poor, and it is easy to decompose when heated.

Typical application scope of polyoxymethylene: POM has a very low friction coefficient and good geometric stability, and is especially suitable for making gears and bearings. Because it also has high-temperature resistance and very good physical properties, it is also used in pipeline components (pipeline valves, pump housings), lawn equipment, etc.

ABS Plastic (Acrylonitrile-Butadiene-Styrene)ABS plastic is a kind of high-strength modified polystyrene, which is composed of three compounds: acrylonitrile, butadiene, and styrene in a certain ratio, with light ivory Colorful, opaque, non-toxic and odorless.

Characteristics of ABS plastic: high mechanical strength, strong impact resistance, good creep resistance, hard, tough, rigid, and other characteristics. The surface of ABS plastic parts can be electroplated. ABS can be blended and melted with other plastics and rubber to improve its performance. , such as (ABS + PC) ABS Typical ABS application range: automobiles, TVs, refrigerators, washing machines, air conditioners, and other electrical appliance casings.

Polycarbonate (PC), commonly known as bulletproof glass, is a non-toxic, tasteless, odorless, transparent material that is flammable but can self-extinguish after being removed from fire.

Polycarbonate characteristics: It has special toughness and hardness. It has the best impact strength among all thermoplastic materials. Excellent creep resistance, good dimensional stability, high molding accuracy, and good heat resistance (120 degrees). Disadvantages of polycarbonate It has low fatigue strength, large internal stress, and poor wear resistance of easily cracked plastic parts.

Typical application areas of polycarbonate: electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.) ), transportation industry (vehicle front and rear lights, dashboard, etc.).

PC+ABS (PC+ABS Alloy)combines the advantages of PC (engineering plastic) and ABS (general plastic) and improves the performance of both. It contains ABS and PC chemical components and has good fluidity and molding processing of ABS. Performance, PC impact resistance, and resistance to cold and heat cycle changes.

PC+ABS alloy features can be used for dispensing mouth/large nozzle mold design, and the surface can be oil-sprayed, electroplated, and metal-sprayed.

What Are the Requirements for Mold Materials for common injection molding materials?

Polyvinyl Chloride (PVC)PVC is corrosive (easy to decompose) and has poor fluidity. Stainless steel is generally used as the injection mold material.

Polystyrene (PS): Choose an injection mold cavity material with good polishability. polystyrene (PS) is preferred here for its excellent impact resistance and good electrical insulation.

Polyethylene (PE): low flash value, be careful to prevent burrs (burrs).

Polypropylene (PP): No special requirements for molds. and Polypropylene (PP) has excellent chemical resistance and is suitable for coming in contact with food products

Nylon (PA): Low flash value, preventing burrs (burrs).

Polyoxymethylene (POM): It is corrosive, so choose corrosion-resistant materials.

Polycarbonate (PC): transparent material, choose a cavity material with good polishability; and poor fluidity, the injection mold needs to be heated up, and the mold rigidity and mold locking should be good.ABS plastic: no special requirements for injection molds

Polyphenylene Ether (PPO): poor fluidity, the mold needs to be heated to 100 degrees

Organic Glass (PMMA): transparent, choose polished material.

Injection Moulding Manufacturing Process Limitations

What Equipment Is Required for the Injection Molding Process?

Injection Molding Machines

The working principle of the injection molding machine is similar to that of a syringe for injection. It uses the thrust of the screw (or plunger) to inject the plasticized plastic in the molten state (i.e. viscous flow state) into the closed The process of obtaining the finished product after solidification and shaping in the mold cavity.

Injection molding is a cyclic process, and the typical injection molding cycle mainly includes quantitative feeding – melting and plasticizing – pressure injection – mold filling and cooling – mold opening and removal. After taking out the plastic part, the mold is closed again and the next cycle is carried out.

Mold:

Mold (mú jù), various molds and tools used in industrial production to obtain the required products by injection molding, blow molding, extrusion, die-casting or forging, smelting, stamping and other methods.

In short, a mold is a tool used to make shaped objects. This tool is composed of various parts, and different molds are composed of different parts. It mainly achieves the processing of the shape of the object through changes in the physical state of the molded material. Known as the “Mother of Industry”.

Automation Equipment:

Automation equipment includes handling robots, conveyors, blowers, cooling devices, etc., to help realize the automation of injection molding.

For example, handling robots are mainly used to remove formed products from the injection molding machine table, conveyors are used to automatically transport plastic particles to the injection molding machine, and blowers can be used to help cool plastic products.

Offline Equipment: Offline equipment includes weighing devices, storage equipment, pneumatic tools, grinders, etc., which are mainly used to assist the specific operations of the injection molding process and improve production efficiency.

Why Is the Investment Cost of Injection Molding Process Equipment So High?

The Equipment Itself Is Relatively High Initial Costs:

Injection molding equipment usually consists of injection molding machines, molds, automation equipment, offline equipment, etc.

The injection molding machine is one of the most expensive parts and high initial investment. The working principle of the injection molding machine is similar to that of a syringe for injection. It uses the thrust of the screw (or plunger) to transfer the plasticized molten state (i.e. viscous flow state) A process in which plastic is injected into a closed mold cavity and the product is obtained after solidification and shaping.

Injection molding is a cyclic process, and each cycle mainly includes quantitative feeding – melting and plasticizing – pressure injection – mold filling and cooling – mold opening and removal. After taking out the plastic part, the mold is closed again and the next cycle is carried out.

Equipment Depreciation And Maintenance Costs:

refers to the depreciation costs and maintenance costs required to purchase and use equipment. These include equipment purchase costs equipment maintenance costs and High Initial Cost

Equipment purchase costs: When purchasing equipment, companies should comprehensively consider factors such as equipment performance, price, and subsequent maintenance, and choose equipment with high cost-effectiveness, thereby reducing equipment purchase costs.

Equipment maintenance costs: Regular maintenance of equipment to ensure that the equipment is in good working condition can extend the service life of the equipment and reduce equipment maintenance costs.thereby achieving low cost

Labor Cost:

Labor cost includes direct labor cost and indirect labor cost. Moreover, employees are high degree， Direct labor cost refers to the direct labor cost required to produce products, which mainly includes the wages, benefits, and related human resources management expenses of operating workers.

Indirect labor costs refer to the labor costs used for indirect support in the production process, such as production management personnel, maintenance personnel, etc. The employees are very high degree， Although these personnel are not directly involved in product production, their established manufacturing technology plays an important role in ensuring the normal operation of the production process.

What Are the Difficulties in the Injection Molding Process?

Injection molding is a common plastic processing technology, but there are also some difficulties and problems, including but not limited to the following aspects:

The Gate Position of the Mold And the Correctness of the Mold:

Gate: The gate is a short groove with a small cross-sectional area, used to connect the runner and the mold cavity. Placing the gate at the thickest part of the product and pouring from the thickest part can provide better filling and pressure-holding effects. If the holding pressure is insufficient, thinner areas will solidify faster than thicker areas. Avoid placing the gate where the thickness suddenly changes to avoid hysteresis or short shots.

Control of Mold Temperature:

Different rubber materials require different mold temperatures; molds with different surface qualities and different structures require different mold temperatures, which requires the targeted design of the temperature control system; the temperature of the front mold is higher than The temperature difference of the rear mold is generally about 20~30o; the temperature of the front mold required for sparklines is higher than the temperature of the front mold required for smooth surfaces.

When the front mold needs to pass hot water or hot oil, the general temperature difference is about 40o; when the actual mold temperature cannot reach the required mold temperature, the mold should be heated. Therefore, when designing the mold, it should be fully considered whether the heat brought into the mold by the rubber material can meet the mold temperature requirements;

in addition to being consumed through thermal radiation and heat conduction, most of the heat brought into the mold by the rubber material needs to be consumed by the circulating circuit. The heat transfer medium is brought out of the mold. The heat in easily heat-transfer parts such as beryllium copper is no exception; the mold temperature should be balanced and there should be no local overheating or undercooling.

Purification Environment Requirements for the Transportation of Plastic Raw Materials:

During the transportation of plastic particles, attention should be paid to selecting the appropriate transportation temperature to avoid deformation or decomposition of the particles at high or low temperatures; keep the particles in a dry state to avoid damage to the particles by moisture and water influence; avoid contact with harmful substances, such as acids, alkalis, etc.;

strictly abide by various regulations and laws and regulations, and do not overload, speed, etc. during transportation; regularly check the status of vehicles and packaging materials, and replace damaged parts and materials promptly

Keep the Workshop Environment Clean During the Production Process Control

The injection molding production process will produce various waste gases, wastewater, and unused or waste plastic that pollute the environment. Since the dual carbon emission reduction target is currently being implemented, corresponding environmental protection measures need to be taken for processing.

Conclusion

Injection molding is a widely used molding method, but it also has some shortcomings and limitations in actual production, such as high cost, complex process, long production cycle, and prone to defects. These shortcomings can be improved by optimizing the process, improving equipment performance, improving mold materials, or developing the most cost-competitive technology to meet the demand for higher-quality products.