Understanding Injection Molding Cost and How to Reduce It
August 20, 2024
Understanding the injection molding cost is crucial for manufacturers and product designers. A comprehensive cost analysis can help in making informed decisions about material selection, mold design, and production strategies. In this post, we will explore what factors determine the plastic injection molding cost and the way to reduce injection molding.
Factors Affecting Injection Molding Costs:
1 Mold Costs
a. Design complexity: More complex designs require more intricate molds, increasing costs. Features like side actions, undercuts, or tight tolerances increase mold complexity and cost. Simple designs with fewer features are generally less expensive to mold.
b. Material of the mold: Steel molds are durable, expensive, suitable for high-volume production. Aluminum molds are less expensive, good for medium production runs. Beryllium-copper moldsare excellent heat conductivity, expensive, and used for specific applications. 3D printed polymer molds are least expensive option, suitable for very low volume runs (100-1000 parts).
c. Number of cavities: Single cavity molds are less expensive but produce one part per cycle. Multi-cavity molds allow producing multiple parts per cycle, increasing initial costs but improving production efficiency.
d. Expected production volume: Higher volumes can justify more expensive, durable molds. Lower volumes might use less expensive molds with shorter lifespans.
2 Material Costs
a. Types of plastics used: Commodity plastics like polypropylene (PP), polyethylene (PE), and ABS are generally less expensive, costing around $0.90-$1.30 per pound. Engineering plastics like polycarbonate, nylon, and PEEK are more expensive, ranging from $2.20-$5+ per pound. The choice of material significantly impacts overall costs.
b. Material quality and properties: Higher quality grades of plastics with enhanced properties (e.g., greater strength, heat resistance, or chemical resistance) typically cost more. Additives to improve specific properties (e.g., UV stabilizers, and flame retardants) increase material costs. Custom color formulations can also add to the cost.
c. Volume of material needed: Larger parts require more material, increasing costs. Efficient design can minimize material usage and reduce costs.
3 Production Costs
a. Cycle time: This is one of the most significant factors, accounting for about 60% of the final part cost. Cycle time includes injection time (a few seconds) and cooling time (about 80% of total cycle time). Longer cycle times increase production costs as fewer parts are produced per hour.
b. Mold complexity: Complex molds with features like side-actions or hot runners may require more sophisticated machines or longer setup times.
4 Labor costs
Operator wages: Skilled machine operators are required to set up and monitor the injection molding process. Labor costs vary significantly between countries (e.g., lower in China compared to the USA).
Setup time: Time required for mold installation, material loading, and initial parameter adjustments. More complex molds or frequent changeovers increase labor costs.
Quality control: Labor costs associated with inspecting parts and monitoring quality.
Maintenance: Regular machine and mold maintenance requires skilled technicians.
5 Additional Factors
a. Part size and complexity: Larger parts require bigger machines and more material. Complex parts may need longer cycle times or additional processing.
b. Tolerance requirements: Tighter tolerances often require more precise (and expensive) molds and machines. This may necessitate additional quality control measures.
c. Surface finish and cosmetic requirements: High-quality finishes may require more expensive molds or additional processing. Texturing or special surface treatments add to costs.
d. Post-processing needs: Secondary operations like painting, assembly, or trimming increase overall costs. Designing parts to minimize post-processing can reduce costs.
How to Reduce the Injection Molding Cost?
Here are several effective ways to reduce injection molding costs:
1 Optimize part design:
Simplify the part design by eliminating unnecessary features and cosmetics. Design for efficient manufacturing, considering part size and material usage. Avoid undercuts and complex geometries that require side-actions or additional mold components.
2 Proper Material selection:
Choose appropriate materials that meet functional requirements without overengineering. Consider lower-cost alternatives when possible, especially for non-critical applications.
3 Optimize Mold Design and Tooling:
Use straight-pull molds instead of those requiring side-actions or complex mechanisms. Design multi-cavity or family molds to produce multiple parts per cycle. Consider 3D-printed molds for smaller production runs to reduce tooling costs.
4 Enhance Production Efficiency:
Reduce cycle times by optimizing part thickness and cooling systems. Implement automation to increase efficiency and reduce labor costs. Use process monitoring and control systems to improve quality and reduce scrap rates.
5 Minimize Finishing and Post-processing:
Minimize or eliminate unnecessary finishing processes like painting or texturing. Design parts to require minimal post-processing.
6 Volume and Scaling production:
Increase production volume when possible to distribute fixed costs over more parts. Consider modifying existing molds instead of creating new ones for product variations.
7 Partner with experienced molders:
Work with molders who can provide design for manufacturability (DFM) analysis.
Leverage their expertise in mold design and process optimization.
Injection Molding Cost Examples
To better understand the relationship between injection molding cost and production volume, we put an example of the custom plastic injection molding cost.
| Cost Item | Low-volume(100 parts) | Mid-volume(5000 parts) | High-volume(10000 parts) |
|---|---|---|---|
| Mold Cost | $100 | $1000 | $10000 |
| Mold Cost per Part | $1.00 | $0.20 | $0.10 |
| Raw Material Cost | $1.00 | $0.20 | $0.10 |
| Labor Cost per Part | $2.50 | $1.00 | $0.50 |
| Cost per Part | $4.00 | $1.70 | $1.10 |
When to Choose Injection Molding?
When deciding whether to choose injection molding over other manufacturing methods, there are several key factors to consider.
Production volume thresholds:
Low volume (100-1,000 parts): Injection molding is generally not cost-effective due to high tooling costs. Other methods like 3D printing or machining are often better for prototypes or small runs.
Medium volume (1,000-10,000 parts): This is where injection molding starts to become competitive. Lower per-part costs offset the initial tooling cost.
High volume (10,000+ parts): Injection molding is typically the most cost-effective option for large production runs.
Part complexity:
Injection molding excels at producing complex geometries consistently. For simple parts, other methods may be more cost-effective at lower volumes.
Material requirements:
Injection molding offers a wide range of material options. If specialized materials are needed, injection molding may be the best or only option.
Surface finish and tolerances:
Injection molding provides excellent surface finish and tight tolerances. If these are critical, injection molding may be preferred even at lower volumes.
Time to market:
While initial tooling takes time, injection molding offers very fast production once the mold is ready. For large volumes needed quickly, injection molding is often the best choice.
Long-term production plans:
If you anticipate scaling up production in the future, starting with injection molding can be advantageous despite higher initial costs.
Comparing costs with other manufacturing methods:
Injection molding: more economical for high production volumes exceed 10000 parts, and long-term, high-volume production is planned.
3D printing: More economical for very low volumes (under 100-200 parts) but becomes expensive for larger quantities.
CNC machining: Can be cost-effective for low to medium volumes of complex parts but is slower and more expensive for high volumes.
Thermoforming: Cheaper for large, simple shapes but limited in design complexity compared to injection molding.
Conclusion
Injection molding is a versatile and cost-effective manufacturing process, particularly for high-volume production. The cost structure of injection molding is complex, influenced by various factors including mold design, material selection, production volume, and part complexity. By carefully considering all cost factors and optimizing each aspect of the process, manufacturers can leverage injection molding to produce high-quality parts efficiently and cost-effectively. The key to success lies in balancing initial investments with long-term production goals, always keeping in mind the specific requirements of each project.
FAQ
Injection molding is generally cheaper than machining for high-volume production due to its lower per-part costs and efficiency in producing large quantities of parts. However, machining is more cost-effective for low-volume production and prototyping due to its lower initial setup costs and flexibility.
Injection molding is generally cheaper than 3D printing for high-volume production (typically over 1,000-10,000 parts), while 3D printing is more cost-effective for low-volume production and prototyping.
