Omar Khalid
Calculating the cost of manufacturing plastic parts is a complex process that involves multiple variables. The cost of producing plastic parts is influenced by factors such as the type of raw material used, labor expenses, overhead costs, and equipment expenses. Raw material costs, such as polyethylene (PE) for packaging films and containers, play a significant role in the overall expenses. Labor costs vary based on direct and indirect labor, with direct labor costs fluctuating according to production volume. Overhead costs can be categorized as fixed, variable, or semi-variable, encompassing expenses like rent, salaries, insurance, utility bills, and maintenance. Equipment costs include the price of molding machines, which may be charged at an hourly rate and then converted to a cost per part. The design complexity and number of cavities in the mold also impact the final cost. Understanding these cost drivers is essential for setting competitive prices, ensuring profitability, and maintaining a strong market position in the plastic product manufacturing industry.
| Characteristics | Values |
|---|---|
| Mold Fabrication Cost | Varies with the number of cavities, the more cavities, the higher the cost |
| Sales Forecast | An accurate estimate of sales forecast over the next 3-5 years is critical |
| Intricate Design | The more intricate the design, the higher the cost |
| Raw Material | Polyethylene (PE) is a commonly used raw material with flexible, durable, and moisture-resistant properties |
| Labor | Direct labor costs vary based on production volume, while indirect labor costs remain fixed |
| Overhead Costs | Rent, salaries, insurance, utility bills, maintenance costs, factory supplies, machinery maintenance, leasing or owning property, and utilities are some examples of overhead costs |
| Equipment Costs | Injection molding machines, blow molding machines, and extrusion equipment are some examples of equipment with associated costs |
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Labour costs
When calculating labour costs, it is essential to account for the time spent on setup and maintenance, as these activities are integral to the plastic parts manufacturing process. Setup time includes activities such as installing the mould, heating the machine, and purging old plastic material. This time is typically billed to the customer, even though the machine is not directly producing parts during this period.
To calculate the labour cost per part, the total labour hours spent on setup, maintenance, and production should be multiplied by the hourly rate. This value can then be divided by the number of parts produced during that period. It is worth noting that labour costs may vary depending on the complexity of the plastic part being manufactured. More intricate designs may require skilled labour, which could command a higher hourly rate.
Additionally, labour costs can be influenced by the volume of production. High-volume manufacturing may allow for economies of scale, where the fixed labour cost can be distributed across a larger number of parts, resulting in a lower cost per part. Conversely, low-volume production may result in a higher cost per part due to the fixed labour expenses.
It is worth noting that labour rates may vary based on geographic location and the expertise of the workers. Labour costs can also be affected by factors such as overtime, shift differentials, and employee benefits. When calculating the overall cost of plastic parts, it is crucial to consider these factors and include them in the labour cost calculations to ensure an accurate estimation.
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Raw material costs
The complexity of the part's design also influences the raw material costs. Intricate designs, complex geometries, and specific shapes can increase the cost of raw materials. For example, certain shapes might require multiple parts to be fabricated together, using more material and increasing expenses. Additionally, the thickness of the part's walls and the presence of a draft angle can impact the material costs. Thin walls, like those in a hollow box, can be challenging to mold and may require additional techniques or steps, increasing the overall cost.
The number of cavities in the mold is another critical factor in determining raw material costs. The number of cavities is based on sales projections, with an 8-cavity mold providing approximately 5 million parts per year, while a 32-cavity mold can produce around 20 million parts annually. While the per-part price decreases with a higher number of cavities, the initial investment in a large mold may not always be financially feasible. Therefore, it is essential to strike a balance between meeting sales forecasts and minimizing raw material expenses.
Finally, the choice between injection molding and CNC machining can impact raw material costs. Injection molding is often associated with higher tooling costs and longer lead times. On the other hand, CNC machining eliminates tooling costs, reduces waste, and allows for faster production and lower material expenses. For intricate designs or complex geometries, CNC milling can be a more cost-effective option.
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Overhead costs
Variable overhead costs, on the other hand, are more dynamic and tend to fluctuate with production levels. These costs include utility bills such as electricity, water, heating, and cooling expenses required to operate the facility. Maintenance costs and factory supplies also fall under variable overhead costs, as they can vary depending on the volume of production.
Semi-variable overhead costs exhibit a hybrid nature, with both fixed and variable components. Machinery maintenance is an example of a semi-variable cost. It may have a base cost that remains constant, but additional expenses may be incurred based on the usage or specific requirements of the machinery.
It is important to note that overhead costs can significantly impact the overall profitability of a plastic parts manufacturing business. By implementing strategies such as energy efficiency, preventive maintenance, lean manufacturing principles, and outsourcing non-core activities, businesses can effectively manage and optimize their overhead costs.
Additionally, it is worth mentioning that the setup fee, which involves installing the mold and purging old material, is typically charged separately by the manufacturer. While this fee may not generate profit, it covers the manufacturer's expenses associated with preparing the molding machine for a new production run.
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Equipment costs
One of the primary equipment costs in plastic part manufacturing is the mould fabrication. The number of cavities in a mould can significantly impact the cost. For instance, an 8-cavity mould may provide approximately 5 million parts per year, while a 32-cavity mould can produce around 20 million parts annually. However, investing in a larger mould may not always be financially feasible, and it is essential to consider the sales forecast when determining the number of cavities required.
The type of equipment used for moulding also affects equipment costs. Injection moulding, for example, can be more costly and may increase the risk of part failure. Additionally, certain geometries and shapes cannot be achieved through injection moulding, requiring multiple parts to be fabricated together, thus increasing costs. CNC machining, on the other hand, offers lower tooling costs and shorter lead times. It is also easier to make design changes with CNC machining as it only requires adjustments to the programming.
The choice of plastic material can also influence equipment costs. For instance, PEEK (polyetheretherketone) is a high-performance plastic known for its strength and temperature resistance. However, due to these properties, PEEK requires special heating equipment and can be tough on injection moulds, limiting the lifespan of the moulding tools. In such cases, CNC milling machines may be preferred for machining PEEK plastic, as they can produce parts with superior mechanical and wear properties.
Another factor that contributes to equipment costs is the machine rate, which is determined by the size and capacity of the machine. Larger machines with higher clamping force capabilities tend to have higher hourly rates, which can impact the overall cost per part. It is important to consider the appropriate machine size and capacity based on the specific requirements of the plastic part to optimise equipment costs.
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Design complexity
One important aspect of design complexity is the number of cavities in a mold. The cost of producing a mold with a higher number of cavities is significantly higher than that of a mold with fewer cavities. For example, an 8-cavity mold may be sufficient to meet the production needs for several years, while a 32-cavity mold, though offering a lower price per part, may not be financially feasible or necessary.
The geometry and shape of the plastic part also contribute to design complexity. Certain shapes and geometries cannot be achieved through injection molding, requiring multiple parts to be fabricated together, thus increasing costs and lead times. Additionally, injection-molded parts often require additional fabrication to achieve tight tolerances, adding to the overall complexity and cost.
Another factor influencing design complexity is the addition of features such as holes, undercuts, or shoulders. These features may require the incorporation of side actions in the design, which adds flexibility but also increases the cost of the mold. Sharp corners without appropriate radii can also increase stress and tension in the part, affecting manufacturability and potentially leading to breakage.
The selection of the right resin or grade of plastic is another critical aspect of design complexity. The resin must be able to meet the functional needs of the part, considering factors such as temperature range, chemical resistance, and mechanical properties. The availability and cost of the resin can also impact the overall production cost.
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Frequently asked questions
The cost of plastic parts is influenced by the type of plastic used, the complexity of the design, the number of parts needed, the manufacturing method, and the labour involved.
Different plastics have different properties, such as strength and temperature resistance, which require specific heating equipment and impact the longevity of moulding tools. For example, PEEK (polyetheretherketone) is a high-performance plastic that requires special equipment and is tough on injection moulds.
Injection moulding can be tricky for complex designs and certain geometries, requiring multiple parts to be fabricated together, increasing costs and lead times. CNC machining, on the other hand, has no tooling costs, shorter lead times, and easily accommodates design changes.
