What Is Small Batch Injection Molding?

Small batch injection molding, also referred to as moulage par injection de faibles volumes¹ (LVIM), is a specialized manufacturing process designed to produce plastic parts in quantities ranging typically from 100 to 10,000 units. Unlike traditional high-volume molding, which prioritizes cycle time optimization over millions of cycles using hardened steel molds, LVIM prioritizes flexibility, low upfront capital expenditure (CapEx), and speed.

For startups, this method offers a critical "startup manufacturing solution²," allowing for market testing and functional validation using real engineering-grade materials—such as Acrylonitrile Butadiene Styrene (ABS) or Polycarbonate (PC)—without the prohibitive cost of P20 or H13 steel tooling.

How Do Tooling Parameters Differ for Low Volume Production Runs?

To achieve cost efficiency, the parameters for low volume production runs differ significantly from mass production standards. The focus shifts from mold longevity to mold fabrication speed and cost.

What Are the Strategic Steps for Short Run Molding?

Mise en œuvre d'un short run molding cost³ strategy requires a shift in the Conception pour la fabrication (DFM)⁴ approach.

1. Material Selection & Verification:
   Choose the final production resin. If the goal is on-demand manufacturing, ensure the material is readily available in smaller quantities (some suppliers have high Minimum Order Quantities or MOQs).

2. Simplified DFM Analysis:
   Modify part geometry to remove complex undercuts or side-actions.

   • Strategy: Use "shut-offs" (where mold faces meet) to create holes rather than sliding cores. Sliding cores increase tooling costs by 15-30%.

3. Tooling Fabrication (CNC vs. EDM):
   Opt for Computer Numerical Control (CNC) machining over Electrical Discharge Machining (EDM) wherever possible. CNC is faster and cheaper for cutting aluminum molds.

4. Master Unit Die (MUD) Implementation:
   Utilize a MUD system. This involves a standard mold base frame that sits in the press, where only the smaller core and cavity inserts are custom-machined. This allows you to pay only for the inserts, not the entire mold base.

5. T0 and T1 Sampling:
   Even in low volume, T0 (first shots) samples are critical. Review for flash, sink marks, or warpage. Since the mold is softer, modifications (removing metal) are easier than with hardened steel.

What Are the Advantages and Disadvantages of Low-Volume Molding?

What Strategies Can Optimize On-Demand Manufacturing Costs?

To maximize the value of fabrication à la demande⁵, technical buyers should leverage specific design and procurement strategies.

• Use Standard Mold Bases: Request standard ISO or MUD bases. Avoiding custom mold bases saves significant steel costs and shipping weight.
• Texturing Hierarchy: Avoid chemical etching for texturing on low-volume molds unless necessary. Bead blasting is a cheaper alternative that provides a matte finish sufficient for non-cosmetic parts.
• Family Molds: If you require multiple small parts (e.g., a housing top and bottom) made of the same material, use a family mold. This places multiple different cavities in one mold base, producing a full set of parts in a single cycle.
• Surface Finish Rationalization: Do not specify an SPI-A2 (high polish) finish if SPI-B3 (paper finish) or SPI-C1 (stone finish) will suffice. Polishing is labor-intensive and costly.

Where Is Low-Volume Injection Molding Applied?

• Medical Device Clinical Trials: Producing ISO 13485 compliant parts⁶ for testing before committing to Class 101 production molds.
• Automotive Aftermarket: Creating replacement clips, housings, or gears for discontinued vehicle models where demand is finite.
• IoT Hardware Startups: Launching a beta version of a consumer electronic device (1,000 units) for Kickstarter backers.
• Bridge Tooling: Running production on soft tooling to supply the assembly line while waiting 8-12 weeks for the high-capacity hardened steel mold to be completed.

Foire aux questions (FAQ)

Q1: What is the typical crossover point between 3D printing and small batch injection molding?
Generally, once you exceed 50–100 units, injection molding becomes more cost-effective than industrial SLA or SLS 3D printing, primarily because the material cost of injection molding pellets is significantly lower than printing resins.

Q2: Can low-volume aluminum molds be used for high-temperature materials⁷ like PEEK?
Yes, but with caution. Polyetheretherketone (PEEK) requires high mold temperatures (160°C+). Aluminum can handle this, but thermal expansion must be calculated carefully to maintain tolerances, and the mold life will be short.

Q3: How long does it take to manufacture a low-volume mold?
Lead times for startup manufacturing solutions involving simple aluminum tooling⁸ are typically 2 to 4 weeks, compared to 8 to 12 weeks for complex steel production molds.

Q4: Does "low volume" mean lower quality?
No. The part quality (dimensions, surface finish, material properties) is identical to mass production. The "low" refers only to the durability of the tool and the quantity produced, not the part fidelity.

Q5: What happens if demand spikes and I need 100,000 parts?
If demand exceeds the life of the soft tool, you must invest in a hard steel mold. However, the aluminum mold served its purpose by validating the design and funding the expensive mold through initial sales.

Résumé

Is low-volume injection molding cost-effective for your startup? Yes, provided your production needs fall within the 100 to 5,000 unit window. By utilizing aluminum tooling, simple cooling strategies, and fabrication à la demande principles, startups can achieve production-grade quality at a fraction of the traditional tooling cost. This approach mitigates risk, allowing for design iteration and market validation before significant capital is tied up in steel tooling.