Understanding the Cost Structure of Plastic Injection Molding Services

What factors affect the price of injection molding services, and how can knowledge of these components steer you toward wiser manufacturing choices? When you ask for an injection molding quote, the answer is usually accompanied by a dizzying array of cost factors: mold design and materials, labor, production time, and, the ever-looming shipping fees. 

What isn’t clear in this procession of dollar signs is how each individual cost element contributes to the total and what you can do to nudge that total down a bit (or a lot) without sacrificing any quality or overrunning your project schedule. This article will clarify things a bit and give you some basic handles to grip as you decide what to do next.

Mold Costs

Mold Design and Development

One of the biggest upfront costs in injection molding is the mold itself. A custom mold design must be carefully planned to assure efficiency, durability, and accuracy. A number of factors influence the cost of design:

• Part complexity. If parts have intricate designs, a lot of machining time is needed to produce them. 
• Cavity count. Multi-cavity molds cost more but reduce per-unit production costs. 
• Mold material. Steel costs more than aluminum, but steel molds last a lot longer.

Factors Influencing Mold Costs

Mold costs are contingent upon a number of factors: 

• High-precision molds command higher prices because they maintain tight tolerances and possess fine details.
•  Large molds necessitate not only more material but also more machining time; thus, they incur greater expense. 
• Mold assemblies for overmolding or insert molding present formidable challenges and require additional manpower and resources to accomplish those tasks; adding to the overall cost of the molds.

Maintenance and Longevity

Over time, injection molds succumb to the relentless forces of wear and require upkeep if they are to remain in the condition necessary for good injection molding. Steel molds can sometimes last well over a million cycles; aluminum molds may wear out after just a few thousand cycles. Though their upfront costs are significantly higher, steel molds may, in the long run, prove to be a more fiscally responsible choice.

Material Costs

Material Selection

Overall expenses are greatly influenced by the kind of plastic selected. The different materials have their own unique, as well as shared, properties. For instance: 

• ABS is inexpensive and used commonly in consumer products. 
• Polycarbonate (PC), while much more costly, is strong, heat-resistant, and used in many safety applications. 
• Nylon (PA) is more durable than either of the above and has much more impact resistance; it is often used in industrial applications. 
• PEEK and Ultem are extremely high-performance plastics used in applications where failure is not an option (the kinds of situations where, say, a space shuttle would need to use plastic components), and they cost much more than all the other materials listed.

Price Range of Materials

The cost of plastic per kg varies: 

• Commonplace plastics: $2 – $5 per kg (e.g., ABS, PP). 
• Quality-engineered plastics: $10 – $50 per kg (e.g., PC, Nylon). 
• Plastics that perform at a high level: $100+ per kg (e.g., PEEK, Ultem).

Material Wastage and Optimization

Costs go up because of waste materials, like sprues, runners, and rejected parts, that must be paid for and eliminated. To get the material cost down, a few strategies can be employed.

• Use hot runner systems, which reduce waste to the absolute minimum. 
• Use part designs optimized to reduce the amount of excess material that must be melted, molded, or otherwise converted. 

Select base materials that are recyclable and that have not just a short-term payback but also long-term gains because of their potential to be reused.

Production Time & Labor Costs

Production efficiency and cycle time have a direct relationship with costs. 

Cycle time—the time required to produce one part—affects costs in two ways. A shorter cycle time means higher efficiency and lower costs per unit. Conversely, longer cycle times mean lower efficiency and higher costs per unit. 

What influences cycle time? Cooling time—How quickly can a part cool? Wall thickness—How thick is the part? Automation—How can we reduce the cycle time through effective part handling?

Factors Affecting Cycle Time

Cycle time is a major factor in part production costs, and when it is reduced, costs go down. Key to cycle time is the material used. Plastics that have rapid cooling capabilities, like Hostaform, make it possible to achieve shorter cycle times. Other key elements are mold temperature and the ejection system used in the press. When these are optimized, faster production is the result.

Labor Costs

The variation in labor costs depends on whether the process is manual or automated. Assembly and inspection that are done by hand add to labor costs. Systems that are fully automated reduce labor costs, but these systems necessitate an initial investment.

Automation and Cost Savings

Efficiency and lowered costs result from the automation of tasks, and these benefits may derive from several sources:

• Mistakes made by human hands are eliminated when we use machines instead.
• Production takes place at a much faster pace and with fewer bottlenecks.
• Reduced labor costs come from both fewer workers and less need for long-term training.

For production in very high volumes, using machines instead of people is often the best and cheapest way to maintain quality.

Tooling, Post-Production & Shipping Costs

Tooling & Setup Costs

Prior to starting mass production, tooling setup must be finished. This involves:

• Calibrating machines for accurate operation.
• Setting up molds (which may require numerous tests and adjustments).
• Running trials to find and cure any defects.

Reducing Tooling Costs

Methods to cut tooling costs consist of the following:  

• Employ standardized mold bases as opposed to ones that are custom.  
• Enhance part design to eliminate avoidable and unnecessary complexity.  
• Collaborate with a seasoned injection molding provider to cut error rates.

Shipping and Post-Production Costs

The factors that affect shipping costs are as follows:

• Location: Is the destination local or international?
• Volume and Weight of Parts: What is being shipped, and how much does it weigh?
• Tariffs and Customs Fees: What charges apply, especially for global manufacturers?
• Post-Production Services: An array of services could inflate costs. What is being done after production to prepare the shipped part?

These factors should all be accounted for in your injection molding quote to avoid surprises.

Conclusion

Plastic injection molding is an affordable way to create parts in large quantities. To keep the process affordable, it’s necessary to budget carefully and optimize production to keep the costs of time and labor down. Mold costs vary greatly depending on both the material used for the mold and how complex the mold is. 

All that said, the main conundrum when using injection molding is that the costs of the mold tend to be inversely related to the costs of the part being cast. If you’re using a custom provider to design the mold, that can drive costs even higher.