Plastic injection molding is a method of producing plastic parts. Products usually use rubber injection molding and plastic injection molding. Injection molding machine (abbreviated as injection machine or injection molding machine) is the main molding equipment that uses plastic molding molds to make plastic products of various shapes of thermoplastics or thermosetting materials.
Therefore, the cost calculation of plastic parts produced by injection molding is an important basis for making production plans and decisions. The cost calculation of injection molding involves many aspects, including mold cost, material cost, labor cost, etc. This article will introduce the cost calculation method of injection molding and the core points of its impact to help better understand and apply this technology.
Cost structure of injection molding
The cost of injection molding is mainly composed of raw material costs, processing costs, equipment depreciation, labor costs and period costs. Among them, raw material costs account for about 30%-40%, processing costs account for 25%-35%, equipment depreciation accounts for 10%-15%, labor costs account for 15%-20%, and period costs account for 5%-10%. The specific proportion may vary depending on the actual situation of the enterprise and the type of product. Therefore, the cost of injection molded parts usually includes the following parts:
Material cost
Definition: refers to the cost of raw materials required to produce injection molded parts.
Calculation formula: Material cost = Material unit price × Injection molded part mass (or weight, loss rate needs to be considered). Among them, the material unit price includes the purchase cost, processing cost and transportation cost of raw materials.
Processing cost
Definition: refers to the cost incurred during the injection molding process, mainly including injection molding machine hourly rental, energy consumption, mold wear, etc.
Calculation formula: Processing cost = Injection molding machine hourly rental × Injection molding cycle of each injection molding machine ÷ Production efficiency × Time required for production. Here, the injection molding machine hourly rental usually varies according to the tonnage and regional differences of the injection molding machine.
Auxiliary material cost
Definition: refers to the cost of additional materials such as stickers, packaging boxes, and labels used in the production process.
Calculation: Calculated based on actual usage and unit price.
Labor cost
Definition: refers to the wages, benefits and other expenses of production workers and related technical personnel.
Calculation formula: Personnel cost = Number of production workers × Average salary × Time required for production.
Equipment depreciation
Definition: refers to the cost of fixed assets such as injection molding equipment and molds that gradually depreciate during use.
Calculation formula: Equipment depreciation = original equipment cost × equipment life ÷ expected total output. Equipment life and expected total output need to be estimated based on actual conditions.
Management expenses
Definition: includes financial costs, sales costs, R&D costs, and other daily management costs.
Calculation: usually allocated based on the overall operation of the enterprise.
Taxes
Definition: includes value-added tax, corporate income tax, etc.
Calculation: calculated based on national and local tax policies.
Total cost calculation and analysis
Sum up mold costs, material costs, labor costs and other costs to get the total cost of mold opening and injection molding. By calculating and analyzing the total cost, the cost level and profitability of production can be evaluated, providing a basis for business decisions. At the same time, through cost analysis, the potential for cost reduction and optimization direction can be found to improve production efficiency and reduce costs.
Core Factors Affecting Injection Molding Cost
At Elimold, we want you to have a better understanding of the cost of injection molding. We have summarized our years of experience in this article and broken down the core factors that affect the cost of plastic injection molding. The costs involved in manufacturing injection molded parts are usually divided into two categories. The first category is the one-time cost of the injection mold, and the second category is the cost of producing the part. Therefore, the core factors that affect the cost of injection molding are as follows.
Complexity of the plastic part being produced
The most important factor in the cost of a mold for a plastic molded part is the complexity of the part. Injection molded parts with many sharp corners, thin ribs, or undercuts are generally more expensive to mold. If the location of sharp corners prevents the use of round cutters to machine the mold feature, they will require a secondary machining process called EDM machining. Likewise, rib features that need to be machined in a mold that is deeper than 1/2 inch and thinner than 1/16 inch may also require secondary EDM machining.
Undercut features in a plastic part design always increase the cost of a plastic injection mold. The cost is reduced by the mold design time and machining time. Sometimes they may also require the overall size of the mold to be larger to accommodate the space required for the “sideways action” (moving the part) to form the undercut feature.
Injection Mold Manufacturing Costs
There are many different ways to construct injection molds for a variety of different part shapes. In the basic overall injection mold structure, we like to simplify them into two groups: “Insert Molds” and “Freestanding Molds”. Within each group, there are hundreds of different styles, sizes, and complexities in the industry, but from a general cost perspective, the cost of an insert mold will be significantly lower than a freestanding mold.
Combined with the above, the mold structure types are very rich, and there are many different styles of side actions in the mold construction to release plastic parts with bottom cuts during part ejection. Many of our competitors use the lowest cost side action method, which is generally called “hand loading” in our industry. Hand loading is a loose component of the mold that is ejected from the mold with the part and needs to be manually removed from the part and then reinserted into the mold by hand every molding cycle.
Hand loading is a low-cost tooling option for handling inverted part features in the mold, but they increase part cost and cause inconsistent part quality. At Elimold, we prefer to use more “automatic” side actions in our molds because they allow for a faster, more consistent injection molding process, which results in better parts for our customers at a lower cost.
Injection molds with automatic side actions cost more to make than manually loaded molds, but for any production quantity over a few hundred pieces, the savings in part cost can usually offset the increased mold manufacturing cost.
Number of Cavities in an Injection Mold
The number of cavities in an injection mold will directly impact the price of the mold. A part that only requires a small number of parts per customer order will be constructed as a 1-cavity mold that produces only 1 part per machine cycle, while a part that requires a large number of parts per customer order may be constructed as a 2, 4, or 8-cavity mold that produces multiple parts per machine cycle. The cost of a multi-cavity mold will certainly be higher than that of a single-cavity mold, but remember that part pricing is inversely proportional to the cost of the mold when considering mold cavities and total project cost.
Plastic Part Size
The easiest factor to understand about injection molding cost, or injection mold cost, is the relationship between part size and mold cost, because the size of a plastic part is directly related to the size of the mold required to produce the part. Also, larger molds require more building space and larger, more expensive CNC equipment to machine them. However, in some cases, there may be some crossover between cost and size. For example, a very complex small injection mold design may be more expensive than a very simple large injection mold design.
Material Selection and Part Weight
The plastic material selected for plastic parts is not only critical to the function of the part, but also plays a huge role in its manufacturing cost. The cost of plastic raw materials ranges from $1 to $125 per pound. Therefore, when designing plastic parts, attention should be paid to reducing the weight of the part as much as possible. In addition, choosing the right type of plastic can also help speed up the cycle time or production rate of the part, thereby reducing overall costs. For small parts, material cost has little effect on unit price, but has a great impact on productivity. For larger and bulkier parts, material cost has little effect on unit price, but has a great impact on productivity. The heavier the part, the greater the impact of material cost on unit price and productivity.
Calculation formula: Material Part Cost = Plastic Material Price x Part Weight
Cycle Time and Cavity
“Cycle Time” is a term used in our industry for injection molding and CNC machining. In simple terms, it is the time it takes for the machine to complete one production cycle. Typically a complete injection molding cycle consists of the following steps:
- Close Time
- Injection Fill Time
- Injection Kit/Hold Time
- Cooling Time
- Mold Open Time
- Part Ejection or Pull Out Time
- Recirculation Time (applicable only if the part must be run in semi-automatic mode by the machine operator)
So how does cycle time relate to part cost? Let’s discuss the major sources of non-material related costs for injection molding. Let’s start with machinery and equipment. Today’s high-tech servo-driven injection molding machines are very expensive. The tonnage rating of the machine and the supporting equipment surrounding it will determine the overall capital investment required to run production. Small tonnage machines are used to run small molds and small parts, while large tonnage machines are required to run large molds and large parts.
Even a small injection molding machine and its supporting equipment will cost close to $100,000, while very large machines can cost millions of dollars. This also shows that the effective life cycle of the machine is limited, as it will wear out over time and lose its technological advantage over time, just like everything these days. Knowing that the cost is the capital (dollar) investment of the machine divided by its effective life cycle (time), it is easy to understand that this translates into the hourly operating cost of the equipment.
In addition to the capital equipment costs discussed above, there is a combination of fixed and variable costs, such as manufacturing space rental, electricity usage, etc. These costs can also be easily factored into the hourly operating cost with simple math.
The sum of all non-material related hourly costs plus the profit margin becomes what is known in our industry as the “machine rate.”
Finally, here is a simple formula for how the non-material related costs of an injection molded part are determined by cycle time:
Units per hour = (3600 seconds / cycle time seconds) x number of cavities
Non-material part cost = machine speed per hour / units per hour
Since machine speeds are highly competitive in the injection molding industry, cycle time and the number of cavities in a mold are two important determinants of the total cost of a plastic molded part.
Packaging and Accessories
Two other items that have a significant impact on molded part pricing are packaging and additional handling. The following common requirements can increase the cost of an injection molded part:
- Mounting layers
- Units in packaging
- Polyethylene bags
- Retail packaging
- Plating
- Painting
- Pad printing
- Secondary processing
Summary
According to the experience summarized by Elimold, as long as the raw material procurement channels are optimized, production efficiency is improved, and the product structure is redesigned, the cost of injection molding can be further reduced. Carefully implementing these measures can enable the company to maintain its competitive advantage in the fierce market competition. Understanding how to calculate the cost of injection molding and the factors that affect the cost can also help companies optimize the production process, reduce costs, and improve competitiveness. Through reasonable cost control, companies can achieve better economic benefits and market performance and create greater business value. The right supplier can provide the right service price. If you need injection molding services to produce plastic parts, you can contact Elimold to serve you.