What determines the cost of an injection mold?

Injection molding is used for the production of various products. The key element is the injection mold, which, when properly designed, is suitable for manufacturing both large products and details in multimillion-piece series. In this article, we take a closer look at what influences its cost.

What is an injection mold? What functions does it serve?

An injection mold is the main component used for producing plastic products through the injection molding technology. It shapes the plastic material, which is softened in the injection molding machine’s cylinder. Another function it serves is to cool the injected material in the forming cavities. This involves effectively and evenly dissipating heat from the hot, molten plastic. The final important function of the injection mold is the ability to eject the finished product from it. This action should occur as quickly as possible, reducing production time and ensuring consistently high-quality finished products.

Components of an injection mold

The injection mold is a highly complex tool composed of numerous components. We distinguish the following functional systems:

• forming cavities,
• gate system,
• cooling system,
• ejection system and sprue,
• securing elements for mold halves,
• drives for plates and segments (if applicable),
• enclosure.

What affects the cost of manufacturing an injection mold?

High-quality steel

Injection molds are made from high-quality steel, which allows them to have a lifespan of even millions of produced parts. The appropriate type of metal is selected individually for each specific component. This depends on factors such as its weight, geometry, and the material from which it will be made. Each type of steel has different shrinkage characteristics, which means the mold is designed based on calculations of material stresses and deformations.

Dedicated mold for a specific production series

Due to the varying geometry of components, it is necessary to invest in dedicated molds tailored to specific design requirements. Unfortunately, it is not possible to produce elements with significantly different geometries, sizes, and weights in a single mold. Only in some cases can two different components be produced in one mold. This cost is one-time, and the produced injection molds belong to the customer.

Availability and the cost of material

Another factor affecting the cost of the mold is the availability and price of the metal required for its production. Prices for both steel and plastics have significantly increased in recent years.

Injection mold design

The time required for mold design is lengthy, and the designers must have appropriate qualifications. The manufactured component may seem simple in construction, but achieving the desired shape and the necessary injection mold for it often involves a high degree of complexity.

Cavity volume

It refers to the size of the mold cavity. The larger the number of cavities or the volume of the cavity required, the longer the press time, which slows down the production process and leads to increased costs.

Methods of manufacturing injection molds

One must not forget the necessity of using various types of machines for the mechanical processing of the designed mold. This also generates costs that later affect the overall cost of the injection mold. The most popular methods of production include:

• CNC machining
  CNC machines are often used for machining stainless steel. CNC machining removes material using a rotating tool and a stationary part. Machining can create molds with highly complex cavity designs. Such tools allow for high precision, which is particularly important for small components. Their operation requires appropriate qualifications and workspace preparation.
• Electro-erosion machining (EDM)
  The EDM method is typically used to create highly complex mold designs that cannot be easily replicated using standard machining methods. It involves the use of a workpiece and a tool electrode to create the desired mold shape. The tool electrode and the workpiece electrode are separated by a dielectric fluid and subjected to voltages that cause repeated electrical discharges. These discharges are responsible for shaping the workpiece electrode into its final mold form. Electro-erosion machining is highly precise and typically does not require any additional finishing processes.

Injection molds – types of systems

One of the main criteria for categorizing injection molds related to plastic processing is the distinction between cold runner and hot runner systems. What are the characteristic features of each?

Cold runner system (CR)

• larger injection volume;
• greater amount of energy required to plasticize a larger quantity of material;
• the creation of a runner, known as a “sprue,” which requires separation from the finished products (if the sprue is not self-removing, an operator may be required for manual removal), grinding of the sprues, and recycling the ground material back into production. All of these activities involve additional labor and additional electrical energy consumption;
• not all materials can be recycled and reused, which can result in generating waste, often costly waste,
• The advantage of molds with a cold runner system is their price, as they are significantly cheaper than molds with a hot runner system.

Hot runner system (HR):

• This system is more sensitive to any type of contamination in the material compared to the cold runner system;
• The use of regrinds in such molds is not recommended;
• A hot runner system requires time from its activation to reach operational readiness – it needs to reach the appropriate temperature;
• A significant drawback of these molds is also their cost because the heaters and other components consume more energy than in the case of cold runner systems;
• ten rodzaj form jest zazwyczaj wybierany przy produkcjach masowych z pełną automatyzacją procesu;
• the cooling system is an extremely important part of the mold because its efficiency depends on it. If the mold operates in short cycles, i.e., below 10 seconds, then the mold cooling system should be highly efficient. This is because the mold acts as a kind of heat exchanger that needs to dissipate heat from the injected material to the sprue. This allows the product to achieve the necessary rigidity, enabling it to be ejected from the mold and obtain the correct shape and dimensions;
• another function of the mold is the ejection of the products, which is accomplished through the ejection system. Ejecting the products from the mold is achieved using standard ejectors (usually round rods or a stripper plate);
• The diameter of the ejector pins is usually as large as possible to avoid damaging the product during ejection. This issue does not occur with plates and stripper plates;
• Sometimes, the ejection of products is assisted by a stream of compressed air, which also aims to prevent deformation of the product and speed up the ejection time from the mold.

Other costs of plastic injection molding

Injection molding is a widely used technology. The production of injection molds often constitutes the largest cost of the entire process. Among other factors influencing the final price, we can mention:

• Part size: the larger the object or part to be molded, the larger the mold will need to be to accommodate it. Larger parts typically require more injected material to complete the production cycle. Therefore, larger mold projects often come with higher costs compared to manufacturing the same design but in smaller dimensions.
• Part design: Complex part designs with advanced geometries require intricate molds for their production. Mold designs typically have two sides: Side A and Side B. Side A, also known as the cosmetic side, is usually the side visible to the user. Side A is expected to be smooth and aesthetically pleasing. Side B contains hidden structures that support the part’s functionality. The structure on Side B may include ribs, bosses, etc. Its finish is usually much rougher than Side A. Complex designs that involve undercuts can also increase the mold cost.
• Production volume: The number of parts to be produced through injection molding determines the production technology and the quality of the material used for making the mold. Projects with low volumes may require machined aluminum molds, whereas high production volumes will require high-quality steel molds.

Examples of the use of injection molds

• RTV and home appliance components
• Inserts
• Nuts
• Cassettes for medical testing
• Spools
• Rosettes
• Furniture components (e.g., legs)
• Rubber components
• Plugs or caps
• Cable connectors
• Children’s building blocks
• Electronic components
• Everyday use items or everyday items
• Components for the medical industry
• Furniture components: boxes
• Door stoppers

Summary

The cost of an injection mold depends on many factors that need to be formulated during the design stage. It is impossible to use the same mold for producing parts with different shapes and geometries. Therefore, during collaboration with the client, we pay close attention to ensuring that the requirements are precisely met during production.

Are you considering how to optimize the cost of injection molds for your products? Consult your project with us and gain the necessary knowledge to save on your production.