wqManufacturing 100-500 plastic parts requires choosing between three methods: vacuum casting costs $25-45 per part with 5-14 day lead times and works best under 200 pieces; rapid injection molding with aluminum tooling runs $15-35 per part over 14-28 days and becomes economical at 300+ pieces; CNC machining delivers $30-80 per part in 7-15 days for high-precision requirements.
The choice comes down to your exact quantity, tolerance needs, and timeline.
Here’s what actually drives the decision: vacuum casting uses silicone molds that cost $500-2,000 and produce 20-25 parts before replacement. Injection molding requires aluminum tooling at $3,000-15,000 upfront but delivers production-grade materials and tighter tolerances. Most product teams miss the break-even point—around 250-300 pieces—where injection molding becomes cheaper despite higher tooling costs.
Manufacturing Methods Compared: 100-500 Plastic Parts
| Method | Ideal Quantity | Tooling Cost | Per-Part Cost | Lead Time | Tolerance | Best For |
|---|---|---|---|---|---|---|
| Vacuum Casting | 50-200 | $500-2,000 | $25-45 | 5-14 days | ±0.3-0.5mm | Complex geometries, fast iteration |
| Injection Molding | 300-1,000+ | $3,000-15,000 | $15-35 | 14-28 days | ±0.1mm | Production materials, repeat orders |
| CNC Machining | Any (better <300) | $0 | $30-80 | 7-15 days | ±0.01mm | Tight tolerances, engineering plastics |
We’ve manufactured over 10,000 prototypes across these methods in 12 years. The 100-500 range sits in an awkward middle ground where either vacuum casting or injection molding can work—choosing wrong wastes $3,000-8,000.
When Vacuum Casting Makes Sense for Your 100-500 Parts
Vacuum casting shines when you need 50-200 pieces quickly. The process creates a silicone mold from a master pattern (usually CNC machined or 3D printed), then casts polyurethane parts under vacuum to eliminate air bubbles.
The economics work like this: A medical device company needed 150 housing units for beta testing. Vacuum casting delivered them in 8 days at $6,200 total ($1,400 tooling + 150 parts at $32 each). The same order via injection molding would have required $9,500 ($6,000 tooling + 350 minimum order quantity at $10 per part).
Lead times break down to:
- Master model creation: 2-3 days
- Silicone mold fabrication: 1-2 days
- Casting and curing: 2-5 days (depending on quantity)
- Finishing: 1-3 days
Material options include polyurethane resins that mimic ABS, PC, PP, and flexible rubbers. We’ve successfully matched Shore A hardness from 30 to 90D for different applications. The surface finish typically achieves Ra 0.8-1.6μm, which works well for consumer products and housings.
The limitation: each silicone mold lasts 20-25 castings. So at 250 pieces, you’re replacing molds multiple times. That’s where the cost curve intersects with injection molding.
Rapid Injection Molding: The 300+ Piece Sweet Spot
Once you cross 250-300 pieces, aluminum tooling for injection molding starts making financial sense. We use rapid tooling techniques that deliver molds in 7-14 days instead of the traditional 4-8 weeks.
Why aluminum over steel? For quantities under 10,000 pieces, aluminum molds offer several advantages:
- 5-10x faster to machine than steel
- 40% lower tooling costs
- Adequate durability for low-volume runs (10,000-50,000 shots)
- Faster heat transfer = shorter cycle times
A home appliance manufacturer came to us needing 450 control panel housings in PC/ABS. We quoted both methods:
Vacuum Casting: $20,250 total
(3 mold sets at $1,500 each + 450 parts at $38 each)
Injection Molding: $13,500 total
($7,500 aluminum tooling + 450 parts at $13.33 each)
They saved $6,750 by choosing injection molding. Plus, they can reorder future batches at just the per-part cost—no new tooling required for another 9,000+ pieces.
The process timeline:
- Mold design and DFM review: 2-3 days
- Aluminum mold fabrication: 7-14 days
- First article inspection: 1-2 days
- Production run: 3-7 days (depending on quantity)
Materials available include all production-grade thermoplastics: ABS, PC, PC/ABS, PP, PA6, PA66+GF, POM, PMMA. This matters if your 100-500 parts need to match future mass production exactly.
You can learn more about the detailed comparison between vacuum casting and injection molding for small batches if you’re still deciding between methods.
CNC Machining for Ultra-Precise Plastic Parts
CNC machining eliminates tooling entirely. You pay only per part, making it cost-effective for quantities under 200 pieces when tolerances matter most.
We regularly achieve ±0.01mm on critical dimensions—something impossible with casting and difficult with low-volume injection molding. Our 5-axis CNC prototyping capability handles complex geometries in a single setup, reducing tolerance stack-up.
Where CNC wins:
- Engineering plastics requiring extreme precision (PEEK, ULTEM, Delrin)
- Medical devices with regulatory documentation requirements
- Parts with deep pockets or undercuts impossible to injection mold
- Projects where design changes are likely
The cost structure differs completely. A 180-piece order of PEEK surgical instrument handles ran $48 per part via CNC machining—no tooling investment. Total: $8,640 with 10-day delivery.
That same order via injection molding would have cost $18,000+ ($12,000 tooling + $33 per part minimum order of 300 pieces due to mold economics). Vacuum casting couldn’t handle PEEK at all.
Material options focus on engineering-grade plastics: PEEK, PEI (ULTEM), POM (Delrin), PA6, PC, PMMA. These materials machine cleanly and deliver consistent mechanical properties.
If you’re comparing CNC to other rapid methods, this article on CNC machining vs 3D printing for prototypes breaks down when each makes sense.
Cost Breakdown by Quantity: The Real Numbers
Here’s what 100, 200, 300, 400, and 500 pieces actually cost using real project data from our facility:
| Quantity | Vacuum Casting Total | Injection Molding Total | CNC Machining Total | Recommended Method |
|---|---|---|---|---|
| 100 | $3,900 | $8,500 | $4,500 | Vacuum Casting |
| 200 | $7,300 | $9,700 | $9,000 | Vacuum Casting |
| 300 | $13,200 | $11,500 | $13,500 | Injection Molding |
| 400 | $17,600 | $12,800 | $18,000 | Injection Molding |
| 500 | $22,000 | $14,000 | $22,500 | Injection Molding |
Assumptions: Medium complexity part, 50cm³ volume, ABS-equivalent material, standard tolerances (±0.2mm), no complex finishing
The crossover happens between 250-300 pieces. Below that threshold, vacuum casting’s low tooling costs win despite higher per-part prices. Above it, injection molding’s efficiency takes over.
But these numbers shift based on part complexity. Simple parts favor injection molding earlier (around 200 pieces). Complex geometries with undercuts might keep vacuum casting competitive up to 400 pieces.
Lead Time Reality Check: How Long Will It Take?
Timeline expectations need to match reality. Here’s what actually happens from quote acceptance to parts delivery:
Vacuum Casting Timeline:
- Days 1-2: Master model fabrication
- Days 3-4: Silicone mold creation
- Days 5-10: Casting production runs
- Days 11-12: Finishing and QC
- Total: 7-12 days for 100-200 parts
Injection Molding Timeline:
- Days 1-3: Mold design and DFM
- Days 4-17: Aluminum mold manufacturing
- Day 18: First article inspection (T1)
- Days 19-24: Production run
- Days 25-26: Finishing and QC
- Total: 18-26 days for 300-500 parts
CNC Machining Timeline:
- Days 1-2: Programming and setup
- Days 3-12: Machining (depending on quantity)
- Days 13-14: Deburring and finishing
- Day 15: Final QC
- Total: 10-15 days for any quantity
Need parts faster? Our rapid CNC prototyping service can deliver in 5-7 days for quantities under 50 pieces.
Rush fees typically add 30-50% to the base cost but can shave 3-5 days off standard lead times. We’ve delivered emergency orders in 72 hours using existing silicone molds for vacuum casting.
Material Selection: What Works at 100-500 Quantities
Not every material works with every method. Here’s what you can actually specify:
| Material | Vacuum Casting | Injection Molding | CNC Machining | Key Properties |
|---|---|---|---|---|
| ABS | ✓ (ABS-like PU) | ✓ | ✓ | Good impact strength, easy finishing |
| PC | ✓ (PC-like PU) | ✓ | ✓ | High impact, transparent available |
| PC/ABS | ✗ | ✓ | ✓ | Best of both materials |
| PP | ✓ (PP-like PU) | ✓ | ✗ (difficult) | Chemical resistant, living hinges |
| PA6/PA66 | ✗ | ✓ | ✓ | High strength, wear resistant |
| POM (Delrin) | ✗ | ✓ | ✓ | Low friction, dimensional stability |
| PEEK | ✗ | ✗ (requires steel) | ✓ | Medical grade, 260°C heat resistance |
| TPE/TPU | ✓ | ✓ | ✗ | Flexible, rubber-like |
For medical device applications: Biocompatible materials require specific documentation. Injection-molded parts come with material certifications (ISO 10993, USP Class VI) as standard. Vacuum cast parts need third-party testing since polyurethane resins vary by batch.
For automotive applications: PA66+30%GF (glass-filled nylon) requires injection molding—the glass fibers won’t disperse properly in casting resins. We’ve seen teams waste $4,000 on vacuum casting attempts before switching to rapid tooling.
Color matching: Our CMF lab maintains DeltaE <0.5 for both processes. Pantone or RAL color matching adds 2-3 days to lead time but ensures consistency across batches.
Quality Control: What Tolerances Can You Hit?
Tolerance capabilities vary significantly across methods. Here’s what’s realistic for 100-500 piece production:
Vacuum Casting:
- General dimensions: ±0.3-0.5mm
- Critical features: ±0.2mm (with insert molding)
- Surface finish: Ra 0.8-1.6μm as cast
- Dimensional stability: ±0.1-0.2% over 24 hours
Injection Molding:
- General dimensions: ±0.1mm standard
- Critical features: ±0.05mm achievable
- Surface finish: Ra 0.4-0.8μm (mold texture dependent)
- Dimensional stability: ±0.02% after ejection
CNC Machining:
- General dimensions: ±0.01mm standard
- Critical features: ±0.005mm achievable
- Surface finish: Ra 0.2-0.4μm (polished), Ra 0.8-1.6μm (as machined)
- Dimensional stability: Material dependent (±0.01-0.05%)
We measure every production run using CMM (Coordinate Measuring Machine) for critical dimensions. ISO 9001 certification ensures documented quality procedures, and IATF-16949 qualification means automotive-grade process control.
How to Choose: Decision Framework for Your Project
Stop overthinking this. Answer five questions:
1. What’s your exact quantity?
- Under 200 pieces → Start with vacuum casting quote
- 200-300 pieces → Quote both methods
- Over 300 pieces → Injection molding likely wins
2. What tolerances do you need?
- General fit (±0.3mm) → Any method works
- Tight fit (±0.1mm) → Injection molding or CNC
- Precision (±0.01mm) → CNC machining only
3. When do you need parts?
- Under 10 days → Vacuum casting or CNC
- 2-3 weeks acceptable → Any method
- Over 3 weeks → Injection molding for best value
4. Will you reorder?
- One-time production → Favor low/no tooling cost
- Likely reorders → Amortize tooling across future batches
- Guaranteed reorders → Definitely invest in injection tooling
5. What material do you need?
- Production-grade thermoplastic → Injection molding or CNC
- ABS/PC equivalent acceptable → Vacuum casting works
- Engineering plastic (PEEK, ULTEM) → CNC only
Quick decision: If you need 180 pieces of ABS-like material in 10 days with ±0.2mm tolerances, choose vacuum casting. If you need 350 pieces of actual PC/ABS in 3 weeks with ±0.1mm tolerances (and might reorder), choose injection molding.
Still not sure? Upload your CAD file and we’ll quote all applicable methods with lead times and costs.
Industries Using 100-500 Piece Production
Medical Device Prototypes
Surgical instrument housings, diagnostic equipment enclosures, and patient monitoring device components typically need 100-300 units for clinical trials. Biocompatible materials and documentation requirements usually point toward CNC machining or injection molding for validation batches.
Consumer Electronics (3C Products)
Smartwatch cases, wireless earbud charging bases, and IoT device housings commonly run in 200-500 piece batches for design validation. These projects prioritize surface finish quality and exact color matching—both achievable with our CMF capabilities across all three methods.
Home Appliance Components
Control panel bezels, water reservoir housings, and interior mechanism parts often need 300-500 pieces for market testing. These parts typically use injection molding since appliance OEMs require production-grade materials from the prototype phase.
Automotive Interior Trim
Dashboard components, center console parts, and door handle prototypes run 100-300 pieces for fitment testing across vehicle variants. IATF-16949 compliance and PA66+GF material requirements usually mandate injection molding with aluminum tooling.
In our 12 years serving Fortune 500 companies like Midea, Haier, and Xiaomi, we’ve learned that most product teams underestimate lead times by 40%. Building in proper timeline buffers prevents delayed launches.
Common Pitfalls (And How to Avoid Them)
Mistake #1: Not planning for mold life in vacuum casting
Teams order 300 pieces via vacuum casting without realizing they’ll need 12-15 mold sets. By part 150, per-piece costs have skyrocketed 60% over the original quote.
Solution: Get a detailed quote showing mold replacement schedule and true per-piece cost across your full quantity.
Mistake #2: Choosing injection molding for quantities under 200
The tooling investment doesn’t pay back. We’ve seen $8,000 molds produce 120 parts that could have been vacuum cast for $4,500 total.
Solution: Run the break-even calculation. Below 250 pieces, vacuum casting usually wins unless repeat orders are certain.
Mistake #3: Specifying impossible tolerances for the method
Asking for ±0.05mm tolerances on vacuum cast parts guarantees disappointment. The material and process physically cannot achieve it.
Solution: Match tolerance requirements to manufacturing method capabilities. Use CNC for precision features, casting/molding for general dimensions.
Mistake #4: Not considering future production
If these 300 parts succeed and you need 5,000 more in six months, starting with aluminum injection tooling makes that transition seamless. Vacuum casting forces complete process changeover.
Solution: Think two steps ahead. If success means scale-up, invest in production-compatible methods from the start.
Mistake #5: Ignoring material property differences
Polyurethane casting resins have 70-80% the strength of actual thermoplastics. For functional testing under load, this matters.
Solution: Specify true thermoplastics via injection molding or CNC when parts will undergo real-world stress testing.
Design Considerations for Low-Volume Production
Draft angles matter more in injection molding than vacuum casting. Standard practice:
- Injection molding: 1-3° draft on all vertical walls
- Vacuum casting: 0° draft acceptable on many geometries
- CNC machining: No draft limitations (multi-axis capability)
Wall thickness directly impacts cost and quality:
- Optimal range: 2-4mm for most plastics
- Thin walls (<1.5mm): Difficult in all processes, possible with CNC
- Thick sections (>6mm): Risk of sink marks in molding, porosity in casting
- Variable thickness: Plan transitions gradually (avoid sharp changes)
Undercuts and complex features:
- Vacuum casting: Excellent for undercuts (flexible mold removal)
- Injection molding: Requires sliders, lifters, or hand-loaded inserts (adds $800-2,500 to tooling)
- CNC machining: Any geometry accessible to tool paths
Surface finish requirements:
- Polished finishes: All methods capable, adds 2-5 days
- Textured surfaces: Best with injection molding (mold texture), difficult with CNC
- Transparent parts: Injection molding or CNC only (vacuum casting creates haze)
- Painted/coated: All methods work, painting adds $3-8 per part
Get Your 100-500 Piece Quote in 24 Hours
We’ve produced over 10,000 prototypes for companies across 20+ countries in our 12-year history. Our integrated facility handles vacuum casting, rapid injection molding, and 5-axis CNC machining under one roof—cutting your lead time by 40% compared to multiple vendors.
Here’s what happens next:
- Upload your CAD file (STEP, IGES, or STL format)
- Specify quantity, material preference, and target timeline
- Receive detailed quotes for all applicable methods within 24 hours
- Review recommendations from our engineering team
- Approve quote and receive parts within quoted lead time
Our ±0.01mm machining capability, ISO 9001 and IATF-16949 certifications, and proven track record with Fortune 500 clients (Midea, Haier, Panasonic, Xiaomi) ensure your 100-500 pieces meet specifications on schedule.
Contact our engineering team or explore our low-volume production services to start your project.
Frequently Asked Questions
Vacuum casting delivers 200 plastic parts most cost-effectively at approximately $6,500-8,500 total including tooling. The silicone molds cost $1,500-2,000 and produce all 200 pieces from a single mold set, with per-part costs ranging from $25-35 depending on complexity. Lead time averages 8-12 days from quote approval to delivery.
Producing 500 plastic parts via injection molding requires 18-26 days total. This breaks down to 7-14 days for aluminum mold fabrication, 1-2 days for first article inspection, 5-7 days for production runs, and 2-3 days for finishing and quality control. Rush services can reduce this timeline by 4-6 days with premium fees.
For 300 plastic parts, injection molding typically offers better value at $10,500-11,500 total cost compared to vacuum casting at $12,500-14,000. Injection molding also provides production-grade materials, tighter tolerances (±0.1mm vs ±0.3mm), and reusable tooling for future orders. Choose vacuum casting only if you need delivery under 12 days or complex undercuts impossible to mold.
Tolerance capabilities vary by manufacturing method for low-volume production: vacuum casting achieves ±0.3-0.5mm on general dimensions, injection molding delivers ±0.1mm standard (±0.05mm achievable on critical features), and CNC machining maintains ±0.01mm consistently. For precision medical or aerospace applications requiring tighter tolerances, CNC machining is the only viable option among these three methods.
Yes, injection molding and CNC machining use identical production-grade materials (ABS, PC, PC/ABS, PA66, POM) for 100-500 piece runs and mass production. Vacuum casting uses polyurethane resins that mimic production materials but have 70-80% equivalent mechanical strength. For functional testing under load or regulatory validation, specify injection molding or CNC to ensure material consistency with future production.