Die casting vs. injection molding: What’s the difference?

die casting vs injection molding

Die casting and injection molding are two of the most used manufacturing processes, as the processes and production are similar, so what are some differences between them?
While these processes are pretty similar, there are some differences between them. Following this article, you can know the comparison of die casting vs. injection molding.

Table of Contents

Definition of Die Casting and Injection Molding

Die Casting

Die casting injects metal material into die casting mold through a die casting machine for cooling and molding. The molding requires heating the metal material from solid to liquid state and then cooling and molding by pumping water into the mold like a child with a needle. The hot inlet chamber and cold chamber are more significant than the injection molding inlet. The processing temperature is high. Fast speed.

Injection Molding

Injection molding is the injection of polymer materials into the plastic mold through the injection molding machine for cooling and molding. The molding only heats the plastic material from a solid state to a soft fluid and then pushes the heated and softened plastic into the mold for cooling and molding by rotating the screw. The processing temperature is lower. The speed is slightly slower.

Processes of Die Casting and Injection Molding

The Die Casting Process

  1.  Die-casting machine debugging: test the functions of the die-casting machine to ensure its regular operation.
  2. Die-casting mold installation: the die-casting mold will be installed correctly.
  3. Material configuration: placing the required material in the furnace with a specific mass percentage for configuration.
  4. Mold preheating, material release: preheating and placing the melted material into the mold.
  5. Closing the mold: the mold is closed to form the cavity and sprue, and oxygen is injected into the die casting mold’s injection chamber and cavity through the air injection hole to drive out the air in the chamber and cavity.
  6.  Pouring and pressing: the die-casting machine moving from the press punch to the cavity filling until the end of pressurization.
  7.  Holding pressure: the pressurized injection punch transfers pressure to the cavity through the solidified residual material and the metal in the intersection section, allowing the solidifying metal to crystallize under pressure.
  8.  Mold opening and retrieval: performing mold opening and ejecting the workpiece from the cavity.
  9. Surface quality inspection: observe the removed casting to see the denseness of its surface and check whether it appears to be sticky film or bubbling.
  10. Cleaning: grinding and shot blasting of the casting.
  11.  Secondary inspection: inspection is carried out again.
  12. Storage: place the qualified products in the warehouse
diecast manufacturer

The Injection Molding Process

1、Close the door. A semi-automatic safety door must be opened and closed, and a fully automatic safety door is set to the closed state.
2、Mold locking The moving plate on the moving side is advanced to close the mold, and the mold is locked after the mold is closed.
3、Injection (including pressure-holding)
The screw is pushed forward quickly to inject the molten molding material into the mold cavity to fill the molding.
This action is specially named “pressure-holding.” The pressure the mold is under when it is first filled is generally called the injection pressure or “primary pressure.”
4、Cooling (and the following action of the “plasticization process”)
Waiting for the molded material in the mold cavity to cool and solidify is called “cooling.” The injection device is also ready for the next operation, called the “plasticizing process.”
This process is called the “plasticization process.” The molding material placed in the hopper flows into the heated material tube and is heated based on the screw rotating and shearing the material into a molten state.
Like the principle of dialing the screw, one side of the turn back, the front end of the screw, will store the molten molding material, the screw rotation, and resistance to the backward screw pressure called the screw.
When the screw rotates, the pressure to resist the screw backward is called the screw “back pressure.”
5, open the mold will move the side of the moving plate backward, the mold followed by open.
6、 Open the safety door. The safety door is open, and the molding machine is in standby mode.
7、 Take out the finished product and then check to make sure there is no object left in the mold before closing.

injection molding process

The Advantages of Die Casting and Injection Molding

The Die Casting Advantages

① Good product quality.
1. high dimensional accuracy of castings, generally up to IT11~IT13 level, sometimes even up to IT9 level.
2. good surface finish, surface roughness up to Ra0.8 ~ 3.2µm, sometimes even up to Ra0.4µm.
3. die casting organization is dense, with high strength and hardness: because the liquid metal is cooled and solidified under pressure, coupled with the short filling time, the cooling rate is high-speed, so in the die casting near the surface of a layer of metal grain is fine, dense organization, which not only makes the casting surface has good wear resistance and corrosion resistance, but also improve the hardness of the entire casting – -Die casting tensile strength is generally 25-30% higher than sand casting, but elongation has decreased.
4. stable dimensions, good product interchangeability. 5;
5. can manufacture complex shapes, precise contours, thin-walled deep cavity metal parts: because the molten metal at high pressure and high speed to maintain high mobility, and therefore can obtain other process methods challenging to process metal parts. For example, the current minimum wall thickness of zinc alloy die casting is up to 0.3mm; aluminum alloy casting up to 0.5mm; minimum cast-out hole diameter of 0.7mm; the minimum pitch of 0.75mm.

② High production efficiency.
1. high machine productivity, for example, a domestic J Ⅲ3 type horizontal cold chamber die-casting machine can die-cast 600~700 times in eight hours on average, small hot chamber die-casting machine can die-cast 3000~7000 times in eight hours on average.
2. die-casting die life is long. A pair of die-casting die for die-casting aluminum alloy, life generally up to 6 ~ 80,000 times, sometimes even up to 100,000 times.
3. easy to realize mechanization and automation.

③ Excellent economic effect: 
1. high material utilization rate: because die casting has the advantages of accurate size and low surface roughness value, so they generally do not need to be mechanically processed and can be directly assembled and used, or the processing is minimal, only a tiny amount of mechanical processing can be assembled and used, so it not only improves the utilization rate of the metal but also reduces processing equipment and person-hours. Its material utilization rate is about 60% to 80%, and the utilization rate of the blank is about 90%.
2. The price of die casting is relatively low.
3. die casting can be directly embedded in the casting of other materials parts to save valuable materials and processing hours: this can meet the requirements of use, expand the use of the product, and reduce the assembly workload to simplify the manufacturing process.

The Advantages of Injection Molding

  1. The wall thickness distribution of the billet can be precisely controlled with the injection mold, so that the wall thickness of the resulting container is more uniform, avoiding the thinning phenomenon that tends to occur in the corner part of ordinary blow molded products, and the piece weight of the product can be controlled to +0.1g, and the accuracy of the thread can be controlled within 100µM of the soil, with precise size of the mouth and high precision of the thin-necked product;
  2. The resulting products do not require secondary processing and have no joints, which saves time for product trimming;
  3. All the blanks made by injection can be blown into the blow molding mold, and no waste is produced during processing, thus reducing the waste of molding materials;
  4. Smooth surface products can be obtained with no scratches and clear surface characters and patterns;
  5. Small batch production can be economically carried out;
  6. Wide range of plastic types can be used;
  7. High degree of automation, multi-mold production, and high production efficiency.

Differences between diecasting molds and plastic molds

Differences between die-casting molds and plastic molds
1. The injection pressure of die-casting mold is high, so the template should be relatively thicker to prevent deformation.
2. The gate of die-casting mold is different from that of plastic injection mold, so it needs to make a diversion cone to break down the high pressure of the material flow.
3. die-casting mold die kernel does not need to quench because the temperature inside the mold cavity is more than 700 degrees when die-casting. So every molding is equivalent to quenching once. The mold cavity will become harder and harder. And the general injection mold to quench to HRC52 or more.
4. die-casting mold general cavity to nitriding treatment to prevent the sticky alloy cavity.
5. General die-casting mold corrosion is relatively large, the outer surface of the general blue treatment.
6. Compared with the injection mold, die-casting mold active fit part (such as core slider) with a more significant gap,
Because the high temperature of the die-casting process will cause thermal expansion, if the clearance is too small will cause the mold to get stuck.
7. Die-casting mold parting surface with higher requirements because the alloy fluidity is much better than plastic.
High temperature and high-pressure material flow from the parting surface will fly out very dangerous
8 injection mold generally relies on the ejector, parting surface, etc., and can be the exhaust. The die-casting mold must open the exhaust slot and slag collection package (to collect the cold material head);
9. molding inconsistent, die-casting mold injection speed, a section of injection pressure. Plastic molds are usually divided into several injections, holding pressure.
10. die-casting mold for two plates die (I have not seen 3 plates die-casting die) a mold opening, plastic mold different product structure is not the same
3 plate die is common, the number of times and the order of opening with the mold structure. Our die-casting molds usually do not use square thimbles, syringes,
Slant pin (high temperature and good liquidity of the solution) is easy to jam the mold production instability.
In addition, plastic molds and die-casting molds in the production of steel are different; plastic molds generally use 45# steel, T8, T10, and other steel, while die-casting molds are mainly used 3Cr2W8V such heat-resistant steel.

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