Injection molding process is widely used to manufacture plastic parts in large volumes. But to manufacture injection molding parts, an injection molding tool specific to a part is required. Injection mold cost and lead time is very high. But if due consideration is given during injection molding part design injection mold cost can be reduced. In this article we will discuss various factors affecting injection mold cost.
Injection Molding Cost
Plastic injection molding cost consist of following two parts:
- Injection molding tool price.
- Unit Part Cost
Total cost of injection molding is equal to sum of above two costs. For example if you want to manufacture a 10,000 number of plastic parts. If injection mold cost is $4000. Then you need to amortize this $4000 in 10,000 parts. Therefore apart from unit part cost, tool cost (10,000/4000 =$2.4) also needs to be added in part cost.
Therefore while calculating total unit part cost tool cost should be added in that.
Factors Affecting Plastic Injection Mold Cost
Following factors such as Plastic part design, Material, Production volumes and mold construction and mold manufacturer location affect the plastic injection mold cost. By controlling these factors we reduce injection mold price. Let’s discuss these factors affecting injection mold price in detail.
Plastic Part Design
Plastic part design greatly affects overall injection mold cost. By modifying part design, Mold price can be reduced considerably. Following factors in part design affect injection mold price.
1) Part size
Large parts require larger molds. Larger molds require more material and high machining cost. Therefore overall mold cost will increase. For example, 100X100X40 mm housing injection mold cost will be high compared to 70X70X40 mm housing.
2) Part Design Structure / Features Design
To ensure part quality. Plastic part design guidelines should be followed. Following part feature design consideration helps in reducing injection mold price.
2.1) Simplification in Part Design
For complex parts material flow rate, cooling time, injection time and other parameters also need to be optimized. Complex parts are also difficult to machine. That results in increased tool design and manufacturing cost. Therefore by simplifying part design, tool cost can be minimized.
2.2) Reduce number of Sliders and Lifters
Mold price can be reduced considerably by reducing the number of sliders and lifters required to manufacture the parts.
2.3) Avoid Thin Sections
Thin sections inside mold are difficult to machine and require precise machining. It also increases the probability of failure as well. Therefore by avoiding thin sections mold cost can be reduced.
2.4) Part Feature Design
Use of EDM and wire cut during mold manufacturing increases mold cost. Therefore if part design is done in such a way, it requires minimum use of wire cut and EDM, Mold cost can be reduced.
3) Molding Material (Plastic Resin Material)
Abrasive and hard materials damage the injection mold and also shorten tool life. Therefore Harder tool steel is used for abrasive and hard materials. That results in an increase in mold material cost.
For example, “P20 pre-hardened tool steel” tool life for ABS is 5000 shots. Whereas for 20% glass filled PC tool life is approx. 2000 shots.
4) Part Tolerance
To achieve tighter tolerances, very precise injection molds are required. Manufacturing precise mould increases machining cost. Tighter tolerances also increase rejection rate and process control also becomes a challenge. Therefore to reduce mold cost generous tolerances shall be applied to parts. Do not over define part tolerances.
5) Mold cooling
Cooling thicker sections requires special cooling arrangement : Heat Exchanger. Uniform cooling throughout the cavity yields good quality parts and fast cycle time.
Therefore to reduce mold cost, part and mould design shall be done in such a way that heat-exchanger is not required.
6) Part Finish
Injection molded part finish also affects injection mold cost. For example mirror finish requires hard tool material and high labor cost compared to fine matte finish. Refer this article for more details on SPI Mold Finishes.
High production volume parts require more reliable injection molds. Because mold has to run for a long duration, without maintenance and breakdown. Therefore production volumes affect injection tool material.
For example if production volumes are less than 5000 units. Pre-hardened steel (P20) can fulfill the requirement. Whereas to produce millions of units, hardened steel (stavax tool steel) are used.
Injection Mold Design
Injection mold design also affects mold price. By changing mold design we can reduce mold cost considerably. Following factors in mold design affect the injection mold price.
1) Injection Mold Type
Type of mold used depends on part design and production volumes. It greatly affecst the tool price.
Hot runner mold cost more than cold runner molds. Type of mold selected depends on part design, mold cooling channel design and production volumes. Therefore cold runner mold should be preferred to reduce mold cost.
To achieve higher production rate multi cavity tools are used. Multi cavity tool cost is high. But increased cost can be amortized for high production volumes. Therefore based on production volumes, decision for single cavity or multi-cavity tools should be taken.
1.3) Family Mold
Family molds are used to manufacture different parts in a single mold. Therefore using family molds two parts can be manufactured in one injection mold. Family mold also has some limitations. But to reduce mold cost family mold is a good option
2) Injection Tool Steel
Injection mold can be manufactured in various tool steels. Selection of right tool steel can help in reducing injection molding tool price considerably. Read this article for more details on tool steel material. Following factors affect the selection of type of tool steel material.
- Thermoplastic Material
- Production Volumes
- Part finish
Mold Manufacturer Location
Cost and quality of molding tool also depends on tool manufacturing location. In china you can get a low cost tool. Sometimes lower-cost tools gives a bad quality parts. Take a right decision depending on your requirement.
To sum up, It’s very difficult to predict the cost of an injection molding tool without detailed design. Plastic part design, Injection molding tool design and manufacturing location affect the injection mold tool cost.
I will keep adding more information on factors affecting injection mold price. Please add your comments or questions in the comment box.