How to calculate the cost of injection molding?

Introduction: Introduction: How much does plastic injection cost?

Usually, the biggest cost in injection molding technology is the mold cost, also known as the tool cost. The cost of mold design and fabrication depends on the production volume requirements, the product complexity, the materials used, and the mold making process.

Simple molds that are 3D printed for small volume production cost only a few thousand dollars, while the cost of designing and manufacturing complex molds for mass production can exceed $200k. In addition to mold cost which is a big investment, other sub-costs such as material cost, production cycle, labor and production scale also play an important role. This means that the larger the number of products produced, the lower the cost per product will be.

Factors in the cost of plastic injection

In order to understand the different types of costs, we need a careful analysis of the manufacturing process.

1. Equipment investment costs

Sumitomo Injection molding Machine

Plastic injection machines are very diverse from desktop machines to industrial-scale equipment. Depends on pressing capacity and pressure.

Industrial plastic injection machines need to invest from $50,000 to more than $200,000 as well as require specialized personnel to operate. So some businesses will choose outsourcing services, and at this time, outsourcing costs will be calculated instead of equipment investment costs.

Producing small quantities of products with desktop injection molding and molds manufactured using SLA 3D printers, is an extremely cost-effective method.

2. Mold cost (Tooling cost)

Mold Making Services

Mold is the main cost in the production of injection molded products. Steel molds used for mass production cost from $1000 to $2500.

With high volume production requires complex metal molds machined by CNC or EDM technology. Technologies such as CNC and EDM require a large investment in equipment and labor to operate. So most of the molds will be contacted for outsourcing.

But if producing a small number of products, an efficient and economical option is to use 3D printing molds and SLA 3D printers. Desktop SLA printers start at under $5,500 and are easily integrated into any injection molding production process. And in addition to mold making, SLA 3D printers can be used to build prototypes for evaluation and testing.

3. Cost of raw materials

molding materials

Some common plastics can be used for injection molding depending on the use conditions such as ABS, PS, PE, PC, PP or TPU.

– The cost of input materials ranges from several tens of thousands of dong/kg depending on the type of material.

The cost of production materials is determined by the product design, the materials used, and the total volume of material filling the mold.

4. Labor cost

Injection molding manufacturers

Injection molding technology and mold processing technologies are largely automated. But the installation and operation both require human involvement.

Labor costs include:

  • Setup and installation costs
  • Repair costs
  • Monitoring costs.

In direct production, these costs are included in the labor cost. But when outsourcing, these costs will be included in the service cost.

Other factors that affect the injection molding process and are directly related to the cost of plastic injection:

  • Product size: With the same design, the larger the product size, the higher the mold production cost will be.
  • Product design: Products with complex structural designs may require sets of molds with multiple combinations, not just two simple A and B molds.
  • Number of products: the mold cost will be distributed into the number of products, and the more production, the more the cost will be reduced.

Reduce the cost of plastic injection

The cost of the mold is determined by the complexity of the mold and the amount of time it takes to manufacture it. We recommend that you follow the manufacturing guidelines to reduce the cost of injection molding.

The cost of the mold manufacturing process can be reduced by following these guidelines:

Remove bottlenecks such as draft angle or steep angle, deep cuts (undercuts) and overly complex geometries.

Remove unnecessary points. This reduces the size of the mold and the material used to develop the sample. Remove the cut lines in the design so that dismantling can be carried out.

Apply the core drilling approach principle to simplify the B-side of the die. The core cavity approach involves sinking the wall cavities into the mold base, thereby reducing the need to mold steep angles while improving surface finish.

Design self-assembled products, to reduce the production of many different molds when a single multi-purpose mold can achieve the same results.

What is plastic injection port?

The plastic injection port, also known as the pump port, the injection mouth… The specialized term called the Gate is the part that connects the plastic channel and the mold cavity. Plastic injection port is responsible for bringing plastic from the channel and filling the mold cavity.

The plastic injection gate is an important component that directly affects the product forming process, so when designing the injection gate, it is necessary to follow a few rules that we will learn together in the series of articles about the plastic injection gate that will published on the website.  

Some principles to keep in mind when designing plastic injection gates:

  1. The nozzle needs to be positioned so that the plastic flows into the place with the largest to the smallest wall thickness so that the material can fill the product.

  2. Based on mold structure, product shape, plastic type and customer requirements, choose the appropriate pump port type.

  3. The optimal nozzle position will create a smooth flow of plastic.

  4. Place the nozzle in an unimportant position of the product because the place where the nozzle is placed tends to have residual stresses during machining.

  5. The nozzle should be positioned so that all the air can be expelled from the vent without creating air bubbles in the product.

  6. The design of the pump port also needs to ensure the optimal cost of mold production and plastic injection processing.

  7. Position the nozzle so that no welds are left, especially when using multiple nozzles.

  8. For round objects, the cylinder needs to place the nozzle at the center to maintain concentricity.

  9. The nozzle is usually kept to the smallest size and enlarged if necessary (except for excess for further machining). However, it is necessary to consider to limit the time to perform additional cutting operations and avoid creating marks on the product.

  10. Use plastic flow simulation software such as moldflow, moldex3D… to determine the optimal pump port placement and predict possible product defects.

Calculation & Design of direct plastic injection port

The actual mold design depends a lot on the designer’s experience and the same goes for the calculation and design of the plastic pump port. For an experienced mold designer, just looking at the product drawing, he can choose the optimal gate type and position.

Common types of plastic injection ports

Depending on product requirements, mold composition, type of raw materials into shape, we will arrange appropriate types of plastic injection ports (gates) when designing – manufacturing molds. There are 3 types of commonly used plastic pump ports:

  • Side gate
  • Submarine gate
  • Point gate

In addition to these three main types, in fact there are several other types of pump ports such as:

  • Sprue gate
  • Fan gate
  • Tab gate
  • Tulner gate
  • Disk (diaphragm) gate
  • Ring gate
  • Spoke (spider) gate
  • Film (flash) gate

Together we will go to learn about these types of plastic injection gates. In the content of this article, we will learn together about the type of direct injection port as well as the calculation and design of the direct injection plastic gate.

Direct injection port

Port, also known as Sprue gate, is one of the types of plastic injection ports commonly found in simple mold structures for 1 product. With this injection, the plastic enters the mold cavity without going through the channel system through the nozzle (Sprue).

Advantages and disadvantages of direct plastic pump port


  • Simple mold structure
  • Less pressure loss
  • Saving raw materials because there is no channel
  • Fast filling speed


  • Large pump port should leave large traces after handling
  • Had to cut the gate
  • The surface of the product near the plastic injection site will be easily deformed due to shrinkage

The calculation of the direct injection port is similar to the calculation of the nozzle. 

Calculate the appropriate number of cavities on the mold

To optimize the cost of mold making as well as the production cost of plastic injection processing. Before making a new mold, we should calculate the number of cavities needed on the mold. In this article, I will list out the relevant factors so that customers and readers have more bases to choose from.

1/ Mold price:

The 1 cavi mold is definitely cheaper than the multi-cavi mold. The higher the number of cavi, the higher the mold size and machining time, the higher the cost of mold components, which means an increase in the cost of the mold.

2/product price:

Multi-cavi mold production cost per unit product will be lower than 1-cavi mold. For example: the same machine, one press cycle, the 8 cavi mold can produce 8 product units per cycle, 8 times more than the 1 cavi mold. Making multi-cavity molds means increasing productivity, reducing labor and reducing the number of machines needed…

How many cavity molds is the best?

Injection Mold design

This is a question asked by many customers when they design and make molds themselves. To get an exact number, I usually use the following formula:

The formula for calculating the number of cavities (cavity)

Cv= Q*N*C*/(24*3600*T)

In there:

CV: Number of cavities needed

Q: Total production quantity per shipment

N: Product coefficient NG (waste), N=1/(1-n). 

C: Time of 1 injection molding cycle.

T: Number of days to complete the total order that the customer wants.


Q: Is injection molding cheap?

A: If you’re looking at the per-unit price, plastic injection is one of the cheapest, most cost-effective forms of production. When injection molding, it’s important to remember that the more units you make with your mold, the cheaper the price per unit. While the startup cost of a large run can be high, the price of the project will get better and better as you continue to produce.


Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.