Why Process Selection Matters for Metal Parts
Choosing the right manufacturing process for your metal parts can reduce production costs by 30-50% while improving quality and delivery speed. Whether you are developing a new product or optimizing an existing supply chain, understanding the strengths and limitations of each process is the first step toward smart sourcing decisions.
This guide compares the four most widely used precision metal manufacturing processes — Metal Injection Molding (MIM), die casting, investment casting, and CNC machining — and provides a clear framework for selecting the best fit based on your part geometry, volume, material, and precision requirements.
Overview of Four Key Manufacturing Processes
Metal Injection Molding (MIM)
Metal Injection Molding combines the shape flexibility of plastic injection molding with the material properties of powdered metals. The process involves mixing metal powder with a binder, injecting the feedstock into a mold, removing the binder, and sintering the part to near-full density.
MIM excels at producing small, complex, high-volume metal components with tight tolerances and excellent surface finish, typically in part sizes under 100mm.
Die Casting
Die casting forces molten metal into a steel mold under high pressure. It is best suited for producing medium to large parts in aluminum, zinc, or magnesium alloys at very high production rates.
Die casting delivers fast cycle times and excellent dimensional consistency but is limited to low-melting-point alloys and simpler geometries compared to MIM.
Investment Casting
Investment casting uses a ceramic shell mold created around a wax pattern. When the wax is melted away, molten metal is poured into the cavity. This process handles complex geometries and a wide range of alloys, including steel, titanium, and superalloys.
Investment casting is ideal for medium-complexity parts in small to medium batches, especially when the material requirements exceed what die casting can offer.
CNC Machining
CNC machining removes material from a solid block or bar using computer-controlled cutting tools. It provides the highest precision and works with virtually any metal alloy, but at a higher per-unit cost for complex geometries.
CNC machining is the benchmark for low-volume, high-precision parts and is often used as a secondary operation to refine parts produced by other processes.
Core Comparison: Key Metrics Across All Four Processes
| Metric | MIM | Die Casting | Investment Casting | CNC Machining |
|---|---|---|---|---|
| Tolerance Range | ±0.3% (min ±0.03mm) | ±0.5-1.0% | ±0.5-1.0% | ±0.01-0.05mm |
| Surface Roughness (Ra) | 0.8-1.6 μm | 1.6-3.2 μm | 1.6-6.3 μm | 0.4-3.2 μm |
| Min. Wall Thickness | 0.3mm | 0.8-1.5mm | 0.5-1.5mm | 0.5mm |
| Max. Part Size | ~100mm | ~600mm | ~1000mm+ | No strict limit |
| Geometry Complexity | Very High | Moderate | Very High | High |
| Economic Volume | 5,000-1,000,000+ | 10,000-1,000,000+ | 100-10,000 | 1-1,000 |
| Tooling Cost | $5,000-$30,000 | $10,000-$80,000 | $500-$10,000 | None |
| Lead Time (Tooling) | 4-8 weeks | 8-16 weeks | 2-6 weeks | 1-2 weeks |
| Material Utilization | ~95% (near-net-shape) | ~90% | ~85% | 30-60% (high waste) |
Material Compatibility by Process
Each manufacturing process supports a different range of metal alloys, which directly affects your material selection strategy.
| Material | MIM | Die Casting | Investment Casting | CNC Machining |
|---|---|---|---|---|
| Stainless Steel (316L, 17-4PH) | Excellent | Not Available | Excellent | Excellent |
| Low Carbon Steel | Good | Not Available | Excellent | Excellent |
| Aluminum Alloys | Limited | Excellent | Good | Excellent |
| Zinc Alloys | Not Available | Excellent | Limited | Good |
| Titanium Alloys | Good | Not Available | Excellent | Excellent |
| Copper Alloys | Good | Limited | Excellent | Excellent |
| Superalloys (Inconel) | Limited | Not Available | Excellent | Excellent |
When to Choose Each Process
Choose MIM When Your Project Requires
Small, complex parts with tight tolerances and high volume production. MIM delivers the best value when part weight is under 100 grams, annual volume exceeds 5,000 pieces, and the geometry includes features such as undercuts, internal channels, or fine details that would require expensive secondary machining.
Typical applications include medical instrument components, automotive sensor housings, consumer electronics structural parts, and smart lock mechanisms.
Choose Die Casting When Your Project Requires
Medium to large parts at very high production volumes with moderate complexity. Die casting is the most cost-effective choice for aluminum or zinc parts larger than 50mm, with annual volumes exceeding 10,000 pieces and geometries that do not require extreme precision or complex internal features.
Typical applications include automotive transmission housings, electronics heat sinks, lighting fixtures, and structural brackets.
Choose Investment Casting When Your Project Requires
Complex geometries in high-performance alloys at low to medium volumes. Investment casting handles steel, titanium, and superalloy parts with intricate internal features, especially when volumes are too low to justify MIM tooling investment or when the part size exceeds MIM capabilities.
Typical applications include aerospace turbine blades, medical surgical instruments, industrial valve bodies, and marine hardware components.
Choose CNC Machining When Your Project Requires
The highest precision with maximum material flexibility at low volumes. CNC machining is ideal for prototype development, one-off custom parts, or as a secondary finishing operation for parts produced by MIM, casting, or other primary processes.
Typical applications include precision fittings, custom tooling, aerospace structural components, and medical implant prototypes.
Multi-Process Strategies: Combining Processes for Optimal Results
In many real-world product assemblies, the most cost-effective approach is to combine multiple manufacturing processes rather than relying on a single method.
Strategy 1: MIM Primary + CNC Secondary
Use MIM for the bulk production of complex metal components, then apply CNC machining only to critical features that require tighter tolerances than MIM can achieve in the as-sintered condition. This hybrid approach reduces machining time by 70-90% compared to fully machined parts.
Strategy 2: Die Casting Body + MIM Inserts
For assemblies that combine a large structural body with small precision components, die casting the main housing and MIM the small inserts can achieve the best balance of cost, precision, and assembly efficiency.
Strategy 3: Investment Casting + Surface Treatment
Investment casting produces near-net-shape parts in exotic alloys, while post-casting surface treatments such as shot peening, anodizing, or PVD coating add the required surface properties for demanding applications.
Cost Comparison at Different Volume Levels
| Volume | MIM (per unit) | Die Casting (per unit) | Investment Casting (per unit) | CNC (per unit) |
|---|---|---|---|---|
| 100 pcs | $15-30 | $10-20 | $8-20 | $20-80 |
| 1,000 pcs | $5-12 | $3-8 | $6-15 | $15-50 |
| 10,000 pcs | $2-5 | $1-3 | $5-12 | $12-40 |
| 100,000 pcs | $1-3 | $0.5-1.5 | $4-10 | $10-30 |
Note: Prices are indicative and vary based on material, complexity, and supplier. Tooling costs are excluded from per-unit pricing.
Decision Framework: 5 Steps to Select Your Process
Follow this structured approach to identify the optimal manufacturing process for your metal parts:
Step 1: Define Part Specifications. Document geometry, dimensions, material, tolerances, surface finish, and annual volume requirements. Step 2: Filter by Size and Volume. Use the comparison tables above to eliminate processes that cannot handle your part size or volume range. Step 3: Evaluate Material Compatibility. Cross-reference your required alloy with the material compatibility table to confirm which processes are viable. Step 4: Compare Cost and Lead Time. Request preliminary quotes from qualified suppliers for the remaining process options, including both tooling and per-unit costs. Step 5: Validate with Prototypes. Before committing to production tooling, validate your process selection with prototype parts to confirm dimensional accuracy, material properties, and surface quality.Frequently Asked Questions
Q: Can MIM completely replace CNC machining?A: MIM can replace CNC machining for many high-volume small parts, but CNC remains essential for prototypes, ultra-precision features, and very low-volume production. In practice, MIM and CNC often work together as a hybrid solution.
Q: What is the minimum order quantity for MIM to be cost-effective?A: MIM typically becomes cost-competitive at volumes above 5,000 pieces, depending on part complexity. For simpler parts, the break-even point may be lower. Below 1,000 pieces, investment casting or CNC machining is usually more economical.
Q: How do I decide between MIM and die casting for aluminum parts?A: MIM has limited aluminum capability, so die casting is generally the better choice for aluminum parts. However, if you need stainless steel or titanium with complex geometry, MIM is the superior option.
Q: Can one supplier provide multiple processes?A: Yes, multi-process manufacturers like BRM offer MIM, die casting, investment casting, and CNC machining under one roof. This simplifies supply chain management, reduces lead times, and ensures consistent quality across different processes.
Conclusion
Selecting the right manufacturing process for your metal parts requires a systematic evaluation of geometry, volume, material, precision, and cost. MIM, die casting, investment casting, and CNC machining each have distinct strengths, and the best choice depends on your specific project requirements.
For complex product assemblies, combining multiple processes often delivers the optimal balance of cost, quality, and performance. Working with a multi-process manufacturer can streamline this decision and provide integrated solutions from design through production.
Contact our engineering team to discuss your project requirements and receive a free process recommendation and quotation.