5: Cost Analysis of Traditional Manufacturing vs. Additive Manufacturing Methods
- Page ID
- 115589
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Introduction
Manufacturing costs are a pivotal factor in selecting production processes, balancing efficiency, scalability, and design requirements. Traditional manufacturing methods—such as machining, casting, injection molding, and welding—have been optimized for high-volume production. Additive manufacturing (AM), including techniques like powder bed fusion and material extrusion, offers advantages in low-volume, complex, or customized applications. This chapter analyzes the cost structures of these methods, incorporating material, labor, equipment, tooling, and overhead expenses. By comparing traditional and AM approaches, engineers can optimize decision-making for specific manufacturing scenarios.
Cost Components in Manufacturing
Manufacturing costs are categorized as follows:
- Material Costs: Raw materials consumed in production.
- Labor Costs: Operator time and expertise required.
- Equipment Costs: Initial investment, maintenance, and depreciation of machinery.
- Tooling Costs: Design and fabrication of molds, dies, fixtures, or jigs.
- Overhead Costs: Facility expenses, energy consumption, and post-processing.
These elements vary across methods, influenced by production volume, part complexity, and process characteristics.
Traditional Manufacturing Methods and Costs
Traditional manufacturing encompasses subtractive, formative, and joining processes. Below are cost profiles for key manufacturing methods.
CNC Machining
- Process: Material is removed from a solid block using computer-controlled tools (e.g., milling, turning).
- Cost Breakdown:
- Material: High waste (30–70% removed), e.g., $50/kg for titanium.
- Labor: Skilled operators; $20–$40/hour, 2–5 hours per part for complex shapes.
- Equipment: CNC machines cost $50,000–$500,000; maintenance is 5–10% annually.
- Tooling: Cutting tools ($50–$200 each) require replacement.
- Overhead: Moderate energy (5–15 kW); facility costs vary.
- Cost per Part: $100–$300 for a 1 kg steel bracket in a batch of 50, dropping to $50–$100 at 1,000 units.
Die Casting
- Process: Molten metal is injected into a mold under pressure, cooled, and ejected.
- Cost Breakdown:
- Material: Efficient (5–15% waste); aluminum at $2–$5/kg.
- Labor: Semi-automated; $15–$25/hour, 0.5–1 hour per batch setup.
- Equipment: Machines range from $100,000–$1 million.
- Tooling: High cost ($10,000–$100,000 per die), amortized over large volumes.
- Overhead: High energy (20–50 kW) for melting.
- Cost per Part: $5–$15 for a 0.5 kg part at 10,000 units, $50–$100 at 100 units.
Injection Molding
- Process: Molten plastic is injected into a mold, cooled, and ejected.
- Cost Breakdown:
- Material: Low waste (5–10%); polymers at $1–$5/kg.
- Labor: Minimal; $15–$25/hour for setup.
- Equipment: Machines cost $50,000–$200,000.
- Tooling: Molds range from $5,000–$50,000.
- Overhead: Moderate energy (10–20 kW).
- Cost per Part: $0.50–$2 for a 0.1 kg part at 10,000 units, $20–$50 at 100 units.
Welding
- Process: Metal parts are joined by melting and fusing them, often with a filler material (e.g., MIG, TIG, or arc welding).
- Cost Breakdown:
- Material: Base metals (e.g., steel at $1–$5/kg) plus filler rods/wire ($5–$20/kg); waste is minimal (5–10%) but includes scrap from fit-up.
- Labor: Highly skilled welders; $25–$50/hour, 1–3 hours per assembly depending on complexity (e.g., 2 hours for a 1 kg steel frame).
- Equipment: Welding machines cost $1,000–$50,000 (e.g., MIG welder at $5,000); maintenance is 5–10% annually.
- Tooling: Fixtures or jigs ($500–$5,000) needed for alignment, reusable across batches.
- Overhead: Moderate energy (5–15 kW) plus shielding gas (e.g., argon at $20–$50 per tank).
- Cost per Part: $50–$150 for a 1 kg welded steel assembly in a batch of 50, dropping to $30–$80 at 1,000 units with fixture amortization.
Additive Manufacturing Methods and Costs
AM constructs parts layer by layer, reducing tooling needs but introducing distinct cost factors. Key methods are outlined below.
Powder Bed Fusion (PBF) - Selective Laser Melting (SLM)
- Process: A laser fuses metal powder (e.g., titanium, steel) in a bed.
- Cost Breakdown:
- Material: High cost ($50–$150/kg); low waste (5–10%, recyclable).
- Labor: $20–$40/hour for setup and post-processing (2–3 hours per build).
- Equipment: SLM machines cost $500,000–$1.5 million; maintenance is 5–10% annually.
- Tooling: None required.
- Overhead: High energy (10–20 kW) and inert gas ($50–$100 per build).
- Cost per Part: $150–$300 for a 1 kg titanium bracket in a batch of 50, stable across low volumes.
Material Extrusion (FDM)
- Process: Thermoplastic filament is extruded (e.g., ABS, PLA).
- Cost Breakdown:
- Material: $20–$50/kg; minimal waste (5–10%).
- Labor: $15–$25/hour for setup (1–2 hours per build).
- Equipment: FDM printers range from $2,000–$50,000.
- Tooling: None required.
- Overhead: Low energy (1–5 kW).
- Cost per Part: $5–$20 for a 0.1 kg part in a batch of 50.
Vat Photopolymerization (SLA)
- Process: A UV laser cures liquid resin.
- Cost Breakdown:
- Material: $100–$200/kg; low waste (5–10%).
- Labor: $20–$40/hour for setup and cleaning (1–2 hours).
- Equipment: SLA printers cost $5,000–$100,000.
- Tooling: None required.
- Overhead: Moderate energy (5–10 kW).
- Cost per Part: $20–$50 for a 0.1 kg part in a batch of 50.
Comparative Cost Analysis
Cost-effectiveness depends on volume, complexity, and material:
- Low Volume (1–100 units):
- Traditional: High tooling or labor costs dominate (e.g., $50–$150 for welding, $50–$100 for die casting).
- AM: Lower costs (e.g., $150–$300 for SLM) due to no tooling, ideal for prototypes.
- Medium Volume (100–1,000 units):
- Traditional: Costs decrease with amortization (e.g., $30–$80 for welding, $15–$50 for CNC).
- AM: Stable costs (e.g., $150–$300 for SLM), less competitive unless complexity is high.
- High Volume (1,000+ units):
- Traditional: Highly efficient (e.g., $5–$15 for die casting, $30–$80 for welding).
- AM: Rarely viable due to slow build rates and material costs.
Welding’s labor-intensive nature makes it costly for small batches, while AM eliminates assembly costs for complex parts (e.g., a welded 5-part frame at $200 vs. a single SLM part at $250). Material efficiency favors AM for costly alloys (e.g., 70% waste in CNC vs. 10% in SLM).
A 2 kg aluminum swingarm:
- CNC Machining: $250/part at 50 units (80% waste, 5 hours labor, $10,000 tooling).
- Die Casting: $100/part at 50 units ($50,000 tooling), $10/part at 10,000 units.
- Welding: $120/part at 50 units (5 subparts, 3 hours labor at $40/hour, $2,000 jig), $80/part at 1,000 units.
- SLM: $200/part at 50 units (10% waste, no tooling, 20-hour build).
- Outcome: SLM is cheapest at 50 units ($10,000 total vs. $12,500 for CNC, $52,000 for casting, $6,000 for welding + jig), but casting excels at high volume.
Strategic Considerations
- Break-Even Point: AM suits low volumes or complex designs; traditional methods (e.g., welding, casting) dominate mass production.
- Hidden Costs: AM requires post-processing ($20–$50/part for SLM); welding involves inspection (e.g., $10–$20/part for NDT).
- Future Trends: Decreasing AM equipment costs may shift economics, while welding automation could reduce labor expenses.
Conclusion
Traditional methods like welding, machining, and casting offer cost advantages in high-volume production, while AM excels in low-volume, complex scenarios. Welding’s reliance on skilled labor contrasts with AM’s tooling-free flexibility, highlighting trade-offs designers must evaluate based on volume, complexity, and material costs.