Die Casting vs. Injection Molding: Comparison and Differences
Engineers and manufacturers often face many considerations when choosing a manufacturing process that suits their product needs. In this complex decision-making process, two manufacturing processes, die casting and injection molding, often emerge as options that receive much attention. This article will explain the comparison between die casting and injection molding, as well as other issues related to injection molding.
The difference between die casting and injection molding
Die casting and injection molding are two common manufacturing processes, the main difference being the materials processed and the process principles. Die casting mainly manufactures metal parts by heating, melting, and injecting metal alloys into metal molds to create high-precision, complex parts(This article provides a detailed analysis of die casting. If you are interested, you can check it out). Injection molding is mainly used to manufacture plastic parts. It achieves efficient mass production by heating, melting, and injecting plastic particles into plastic molds.
The following is a comparison of some specific aspects：
Die-casting material type
Die casting is mainly used to process metal parts. Commonly used metals include:
Aluminum Alloy: Aluminum alloy is one of the most commonly used die-cast metals, popular for its lightweight, good strength, and thermal conductivity. Common aluminum alloys include A380, ADC12, etc.
Zinc alloy: Zinc alloy is often used to make small parts and has good fluidity and corrosion resistance. Common zinc alloys include the Zamak series.
Magnesium alloy: Magnesium alloy is a lightweight metal with good strength and thermal conductivity, making it suitable for manufacturing lightweight parts. Common magnesium alloys include AZ91D, AM60B, etc.
Copper Alloys: Copper alloys, such as electronic parts, are often used in applications that require good electrical and thermal conductivity.
Injection molding material type
Injection molding is mainly used to process various types of plastic materials. Common plastics include:
PP: Polypropylene is a common plastic with good chemical resistance and mechanical properties, making it suitable for many applications such as packaging, automotive parts, etc.
PVC: Polyvinyl chloride is a common plastic that is weather-resistant and chemically stable and is used to make pipes, wire insulation, and more.
PS: Polystyrene has good transparency and mechanical properties and is widely used in injection molded products, such as plastic cups, lids, etc.
PE: Polyethylene is divided into high-density polyethylene (HDPE) and low-density polyethylene (LDPE) and is used in a wide range of applications, including plastic bags, bottles, etc.
PC: Polycarbonate has high strength and transparency and makes high-quality transparent parts, such as eyeglass lenses, mobile phone screens, etc.
During the die-casting process, metal is usually injected into the mold in liquid form. In injection molding, plastic is usually added to the machine as solid particles or powder and then processed into the desired shape through heat and pressure.
Die-casting mold structure
Die-casting molds usually consist of two parts: the upper mold and the lower mold. The two mold parts work together to form the metal part.
Internal cavity shape: The internal cavity shape of a die-casting mold is usually the opposite of the external contour of the desired part. This means that in its liquid state, the metal will flow into the mold and fill the cavity.
High precision: Because metal flows better in a liquid state, die-casting molds can produce high-precision parts, including complex structures and details.
Cooling system: Die-casting molds usually require a powerful cooling system to ensure that the metal solidifies and solidifies quickly for rapid production.
Injection mold structure
The injection mold also consists of an upper and lower mold, but its structure is relatively simple because injection molding processes plastic materials.
Internal cavity shape: An injection mold’s internal cavity shape usually matches the desired part’s actual shape. Plastic pellets or powders are converted into actual parts using heat and pressure in a mold.
Auxiliary components: Injection molds usually include some additional components, such as nozzles, cooling channels, and ejector pins, to ensure that the plastic material can fill the mold cavity.
Mold material: Injection molds are usually made of high-temperature-resistant metal materials to withstand high-temperature and high-pressure environments.
Heating system: The injection mold requires a heating system to heat the plastic particles or powder to its melting temperature and maintain a certain temperature to ensure sufficient fluidity.
Translation of the Chinese words appearing in the picture above:
射嘴防护罩：Nozzle protective cover
液位计：Liquid level gauge
油箱部分：Fuel tank part
Die-casting surface treatment
Surface Quality: Die casting typically enables relatively high surface quality during part manufacturing, often without additional surface preparation.
Polishing: Some die-cast parts may undergo a polishing or grinding process to improve surface finish and appearance.
Painting: Some die-cast parts may need to be painted to change color or provide additional protection against corrosion.
Plating: In some cases, die-cast parts may require electroplating, such as chrome, nickel, or other metal plating, to enhance corrosion resistance and appearance.
Phosphating: Some die-cast parts may require phosphating to improve surface hardness and lubricity.
Sandblasting: Sometimes, sandblasting can change the surface texture or remove undesirable casting imperfections.
Injection molding surface treatment
Higher surface treatment requirements: Since the surface of plastic materials is generally not as smooth as metal, injection molded parts usually require more surface treatment to achieve the required quality standards.
Painting and Printing: Injection molded parts often require painting or printing to change color, add logos, or provide additional decoration.
Sandblasting: Sandblasting can change the texture of plastic surfaces, increase surface roughness, and provide better adhesion.
Sanding and Polishing: Some injection molded parts require sanding or polishing to improve the surface finish.
Ink printing: For some parts that need to be printed with logos or text, ink printing can be used.
Is injection molding cheaper than die casting
Injection molding is cheaper than die casting because the manufacturing costs of injection molding and die casting are mainly reflected in the cost of raw materials and mold opening. For example, the price of aluminum alloy is about US$2,200/ton, while the price of high-density polyethylene is about US$1,200/ton. Die-cast mold costs range from $1,000 to millions of dollars, and injection mold costs typically range from $1,000 to $50,000. The plastic material is also cheaper than metal, making injection molding more cost-effective.
Comparing the advantages and disadvantages of injection molding and die-casting
Advantages of Injection Molding
●Injection molding is suitable for mass production because multiple parts can be manufactured per cycle, and production efficiency is high.
●The injection molding process enables the production of high-precision parts with good dimensional and shape stability.
●Can be used with a variety of plastics: A variety of different types of plastic materials can be used, including thermoplastics and thermosets.
●Since the material is supplied in particle form, there is less waste and high material utilization.
Disadvantages of Injection Molding
●The cost of setting up injection molds is relatively high and is suitable for mass production but not for small batches or customized production.
●It takes a certain amount of time to make injection molds and prepare the production line, so the production cycle is long.
●While various plastics can be used, some specific materials may not be suitable for injection molding.
●Complex part designs may require additional engineering and tooling work.
Advantages of die-casting
●Die casting enables the production of high-precision parts with excellent surface quality.
●Die-cast parts typically offer high strength and rigidity, making them suitable for structural-strength applications.
●Die casting is suitable for high-temperature materials such as aluminum, zinc, and magnesium.
●The production speed is relatively fast and suitable for mass production.
Disadvantages of die-casting
●As with injection molding, the cost of setting up die-casting molds is higher.
●Die casting is available in certain metal alloys, and the material selection is relatively limited.
●Die casting is suitable for relatively small and medium-sized parts and not for manufacturing large ones.
●Die casting generally has a longer production cycle than injection molding.
What is a better process than injection molding
Die casting is more suitable for high-precision, complex geometric metal parts than injection molding, while 3D printing is suitable for complex, personalized, or prototype manufacturing. Precision machining is suitable for high-precision parts, while composite manufacturing is suitable for applications requiring special material properties.
Die Casting: Die casting may be a better choice if you need to manufacture metal parts, especially those with high precision requirements and complex geometries.
3D printing: For complex, personalized, or prototype manufacturing, 3D printing can be a better choice. It creates complex three-dimensional structures without making molds and works with various materials, including plastics, metals and ceramics.
Precision machining: If extremely high precision and surface quality are required, such as high-precision mechanical parts, precision machining processes on CNC machine tools may be required, such as milling, turning, grinding, etc.
Composite manufacturing: For applications that require special material properties, such as composites (such as carbon fiber reinforced plastics), ceramics, or glass products, corresponding manufacturing processes may be required, such as stacked manufacturing, thermoforming, etc.
Forging: A common option for making strong metal parts where the material is heat-resistant, forging works by heating the metal and applying pressure to form it into the desired shape.
Compression molding: Used to produce large plastic parts such as barrels, containers, and sinks. This process involves heating plastic pellets, injecting them into a large mold, and applying pressure to form the part.
Cold stamping: Used to make sheet metal parts such as automotive body parts and electronic device casings. Cold stamping cuts, bends or shapes parts by applying force to a metal sheet.
What are the cheaper alternatives to injection molding
Inexpensive alternatives to injection molding include 3D printing, compression molding, vacuum forming, composite manufacturing, hand machining, injection foam molding, and hot melt welding.
3D Printing (Additive Manufacturing): 3D printing is a layer-by-layer manufacturing technology suitable for making prototypes of low-volume or complex plastic parts. It usually does not require mold manufacturing, so it is suitable for personalized products and short-term production.
Compression Molding: Compression molding is a method of making large plastic parts, often used to make barrels, containers, sinks, etc. It can produce large-size parts at a lower cost.
Vacuum Forming: Vacuum forming is typically used to produce small to medium-sized plastic parts such as packaging, housings, and interior trim parts. It is a relatively low cost to make molds.
Composite Manufacturing: Composite manufacturing processes may be considered for applications requiring special properties, such as carbon fiber-reinforced plastic manufacturing. These materials can provide greater strength and lightweight advantages.
Manual processing: For very small production runs or specially shaped parts, manual processing such as hand cutting, forming, or gluing may be considered.
Injection Foam Molding: Injection foam molding combines plastic with a foaming agent to create lightweight, well-insulated parts. It is suitable for some special applications such as packaging and insulation.
There is a big difference between the two manufacturing processes of die casting and injection molding. I hope you can gain something after reading this article.