---
title: "Plastic Injection Molding Services | Prototype to Production | OpenSpindle"
description: "Get injection molding quotes from independent shops. Low-volume and no-MOQ friendly, from prototype tooling to full production. Upload a part, see tooling and per-part pricing, and skip the marketplace markup."
canonical: https://openspindle.com/capabilities/injection-molding
---

# Plastic injection molding from independent shops

Custom injection molded plastic parts, from a prototype aluminum tool and a few hundred pieces to hardened steel tooling running production volumes. Upload your part and hear back from independent molders with tooling and per-part pricing, including low-volume and short-run work the big platforms turn away.

## Injection molding companies on OpenSpindle

Real injection molding manufacturers, from prototype and low-volume molders to full-production plastic parts companies. See their presses, materials, and certifications and get a competitive quote for tooling and parts.

[Browse all injection molding shops](https://openspindle.com/manufacturers?capability=Injection%20molding)

## Resins our molders run

Common thermoplastics for injection molding are below. Filled grades (glass or mineral) and custom colors are available, and detail pages are linked where we have them. If your resin is not here, ask when you request a quote.

- ABS -- Housings, automotive, consumer parts
- Polypropylene (PP) -- Living hinges, containers, chemical-resistant
- Polyethylene (PE) -- Packaging, bottles, industrial parts
- [Nylon (PA)](https://openspindle.com/materials/nylon.md) -- PA6 / PA66; gears, brackets, structural
- [Polycarbonate (PC)](https://openspindle.com/materials/polycarbonate.md) -- Clear, impact-resistant, safety parts
- TPU -- Flexible seals, grips, overmolds
- [Acetal / POM (Delrin)](https://openspindle.com/materials/delrin.md) -- Precision gears, bearings, low friction
- PET / PETG -- Bottles, clear technical parts
- [PEEK](https://openspindle.com/materials/peek.md) -- High-temp, chemical-resistant grade

## Tolerances

| Feature | With drawing | No callout |
| --- | --- | --- |
| General dimensional | ±0.005 in | DIN 16742 general |
| Tight / critical feature | ±0.002 in | Call out on the drawing |
| Wall thickness | 0.040 to 0.140 in typical | Uniform walls preferred |
| Draft angle | 1 to 2 deg per side | More on textured faces |
| Shrinkage | Resin-dependent | Tool cut steel-safe |

Molding tolerances depend on the resin, its shrinkage, and the tool. Uniform wall thickness and adequate draft matter more to a good part than a tight tolerance callout. Flag the few features that are truly critical and the molder cuts the tool to hold them.

## How to design for Plastic Injection Molding

Molded parts live or die by wall design. These rules keep parts from sinking, warping, or sticking in the mold.

| Design rule | Typical spec | Why |
| --- | --- | --- |
| Nominal wall thickness | 0.040 to 0.140 in (material-dependent) | Uniform walls fill evenly and avoid sink and warp. |
| Draft angle | >= 1 to 2 degrees per side | Lets the part release cleanly from the mold; textured surfaces need more. |
| Rib thickness | <= 0.5 to 0.6x wall | Thicker ribs pull a visible sink mark on the opposite face. |
| Internal corner radius | >= 0.5x wall | Sharp corners concentrate stress and restrict material flow. |
| Boss outer diameter | ~2x the hole diameter | Supports the boss for a screw without causing a sink mark. |
| Wall uniformity | avoid thick-to-thin steps | Thick sections cool slower than thin ones and warp the part. |

Exact wall thickness depends on the resin. Send your material and a shop tunes gates, ribs, and draft to it.

## Threads, Inserts & Finishing

Molded-in bosses take threaded inserts (heat-set or ultrasonic) or self-tapping screws; molded threads are possible on straight-pull features. Insert molding places metal inserts in the tool before the shot.

Surface finish is set by the tool per the SPI (SPE) standard, from A-1 mirror polish to D-3 blasted texture, plus MoldTech textures. Secondary ops include pad printing, painting, ultrasonic welding, and assembly.

| Finish | Materials | Adds | Stacks with |
| --- | --- | --- | --- |
| SPI A-1 / A-2 (mirror / high gloss) | Clear and cosmetic resins | Tool cost up | Optical, lenses |
| SPI B / C (semi-gloss to matte) | Most resins | Standard | General parts |
| SPI D / MoldTech (textured) | Most resins | Hides sink and flow | Grip, cosmetic housings |
| As-molded | All | +0 | Internal / non-cosmetic |

Finish is cut into the tool, so decide cosmetic surfaces before the mold is made. A texture can hide sink marks and flow lines; a mirror polish exposes them and raises tooling cost.

## Mold and tooling options

The mold is the biggest driver of your cost, lead time, and per-part price. These are the tooling choices molders weigh, from a fast prototype tool to a hardened multi-cavity production mold.

### Tooling class and lead time

- **Prototype tooling** -- Single-cavity aluminum or 3D-printed tools for first-article (T1) samples and design validation. Lowest cost, parts in weeks.
- **Bridge tooling** -- A tool that bridges the gap to full production, running thousands of parts while a hardened production mold is being cut.
- **Soft tooling** -- Aluminum or soft-steel molds that are faster and cheaper to cut than hardened steel, ideal for low to mid volumes.
- **Aluminum molds** -- Economical, fast-to-cut tools good for roughly 10,000 to 100,000 shots. The default for prototype, bridge, and low-volume work.
- **Steel molds** -- Hardened steel production tools that run hundreds of thousands to millions of parts. Highest upfront cost, lowest piece price at volume.

### Cavity layout

- **Multi-cavity molds** -- Several identical cavities in one tool so each shot makes many parts, raising output and cutting per-part cost at volume.
- **Family molds** -- Different parts of one assembly molded together in a single tool and shot, handy for matched-set components.

### Runner systems

- **Hot runner systems** -- Heated manifolds keep the runner molten so there is no runner scrap, best for high volume and clean gating on cosmetic parts.
- **Cold runner systems** -- Simpler and cheaper to tool; the runner solidifies with the part each shot and is trimmed off and reground.

### Complex and multi-material molds

- **Insert molds** -- Metal inserts such as threaded bosses, pins, or terminals are loaded into the tool and the plastic is molded around them.
- **Unscrewing molds** -- Automated unthreading mechanisms release parts with internal or external threads, such as caps and closures.
- **Two-shot molds** -- Two materials or colors molded in sequence in one tool (2K molding), for example a rigid body with a soft-touch seal.
- **Overmolding** -- One material molded over another, such as a TPU grip over a rigid nylon or ABS substrate, for grip, seal, or feel.
- **Multi-material molding** -- Combining resins or durometers in a single part to blend structure, flexibility, and function without secondary assembly.

## Injection molding vs other processes

Injection molding wins on per-part cost and repeatability at volume, once its tooling is paid off. When your volume, geometry, or material points elsewhere, here is the better-fit process.

| Process | Best for | Typical volume | Choose it over Plastic Injection Molding when |
| --- | --- | --- | --- |
| [CNC Machining](https://openspindle.com/capabilities/cnc-machining.md) | Low-volume precision | 1 to 1,000 | You need a few to a few hundred precise parts with no tooling cost, the tightest tolerances, or metal. Molding takes over once volumes reach the thousands and the tool amortizes. |
| [3D Printing](https://openspindle.com/capabilities/3d-printing.md) | Rapid prototypes | 1 to 100 | You want fast design iterations, complex geometry, or one-offs with zero tooling. Switch to molding for repeatable, low-cost parts at production volume. |
| Vacuum Casting | Small production runs | 10 to 100 | You need tens to a few hundred parts that look and feel molded, cast from a low-cost silicone tool copied off a master. Molding is the step up for higher volume and end-use resins. |
| Compression Molding | Rubber and composites | Low to high | Your material is rubber, silicone, or a thermoset composite that injection molding cannot process. Injection molding is for thermoplastics. |
| Blow Molding | Hollow parts | High | The part is hollow and thin-walled, like a bottle, tank, or container. Injection molding makes solid and structural parts. |
| Thermoforming | Large thin parts | Low to high | The part is large and thin-walled (trays, panels, packaging) and can be formed from sheet at low tooling cost. Molding suits smaller, thicker, higher-detail parts. |
| Rotational Molding | Large hollow products | Low to mid | You need a large, seamless hollow product such as a tank, kayak, or bin. Injection molding handles smaller, higher-precision parts at higher volume. |

## What Makes a Good RFQ

| Instead of | Send |
| --- | --- |
| "Mold this part in black plastic" | "30% glass-filled nylon, black, SPI B-1, 5,000 pcs/yr, new prototype tool" |
| "Need injection molded parts" | "Polycarbonate, natural, SPI A-2 cosmetic front face, 2,000 pcs first run" |
| "Reorder my molded part" | "Existing steel tool at your shop, run 10,000 more, same PP natural" |

Tell the molder the resin (and any fill), color, cosmetic surfaces, expected annual volume, and whether the tool is new or existing. That is what sets the tooling cost, the piece price, and the lead time.

## Industries Served

- Consumer products
- Medical devices
- Automotive
- Electronics enclosures
- Industrial / OEM
- Robotics

Injection molding shops on OpenSpindle run everything from consumer housings and enclosures to medical and automotive components, including shops with ISO 13485 and IATF 16949 systems.

## Frequently Asked Questions

### How much does injection molding cost?

Injection molding has two costs: a one-time tool (mold) and a per-part price. Tooling ranges from roughly $2,000 to $10,000 for a prototype aluminum mold up to $10,000 to $100,000+ for a hardened multi-cavity steel mold. Per-part prices typically run about $0.50 to $5 depending on part size, resin, and volume. Because the tool is fixed, the more parts you run, the lower the effective cost per part. Upload your part to see real tooling and piece pricing from independent shops.

### How much does an injection mold cost?

A simple single-cavity prototype aluminum mold often runs $2,000 to $10,000; a production-grade hardened steel mold runs $10,000 to $100,000+. Cavity count (each cavity adds roughly 30 to 50 percent), part complexity, undercuts, and cosmetic polish all drive the number. For low volumes, a prototype or bridge tool keeps upfront cost down.

### What is the minimum order for injection molding?

Many shops on OpenSpindle take low-volume and short-run work with no hard MOQ, running as few as a few hundred parts off a prototype tool. This is exactly where a marketplace of independent molders beats the large instant-quote platforms, which favor higher volumes.

### How fast is prototype injection molding?

With rapid aluminum tooling, first-article (T1) samples can come in roughly 2 to 4 weeks, with parts shortly after. Production steel tooling takes longer to cut but lasts for millions of shots. Tell the shop your timeline and volume and they recommend the tool.

### Can I use my existing mold?

Yes. If your tool already exists, you only pay the per-part price to run more parts, not the tooling again. Note that the mold lives at a specific shop; moving it to a new shop is a mold transfer. If you saved a molded part to your OpenSpindle parts library, you can reorder from the existing mold directly.

### Which plastics can be injection molded?

Common thermoplastics include ABS, polypropylene (PP), polyethylene (PE), polycarbonate (PC), nylon (PA), acetal/POM, PC-ABS, TPU/TPE, acrylic (PMMA), and engineering grades like PEEK. Glass- and mineral-filled versions add stiffness and heat resistance. Not sure which resin fits? Say what the part must do and the shop advises.

### What is the difference between prototype and production tooling?

Prototype (aluminum or soft steel) tools are cheaper and faster but wear out sooner, ideal for low volumes and bridge production. Production (hardened steel) tools cost more and take longer to cut but run hundreds of thousands to millions of parts. Many programs start with a prototype tool and move to steel once the design is locked.

### Who owns the mold?

In most custom molding arrangements the customer owns the tool once the tooling cost is paid, even though it physically lives at the molder that runs it. Ownership, storage, and maintenance terms should be spelled out in the quote or purchase order. Confirm the tool is yours to transfer before you commit, especially for a long production program.

### Can I transfer an existing mold to another shop?

Yes. Because a mold is a physical asset you own, it can be shipped to a different molder to run more parts, which is called a mold transfer. Expect a short qualification run to re-sample and verify the tool on the new press. If you saved the part to your OpenSpindle parts library, note that the tool currently lives at another shop when you request the quote.

### How many parts can one mold produce?

It depends on the tool material. A prototype aluminum mold typically lasts on the order of 10,000 to 100,000 shots, while a hardened steel production mold runs hundreds of thousands to millions of parts. Abrasive and glass-filled resins wear tools faster, so tell the shop your resin and annual volume and they size the tool steel to match.

### Can a mold be repaired or modified?

Yes. Molds are cut steel-safe so that changes add material where possible: opening up a feature by adding steel is straightforward, while enlarging a part by removing steel may need welding or a new insert. Worn or damaged tools can often be repaired, re-polished, or have inserts replaced rather than recut from scratch.

### Can silicone be injection molded?

Yes, through liquid silicone rubber (LSR) molding, a separate process from thermoplastic injection molding that injects a two-part silicone into a heated tool where it cures. LSR suits seals, gaskets, medical parts, and soft-touch components that need heat resistance and flexibility. Ask for LSR when you request a quote and shops set up for silicone respond.

### Can you mold threaded features or metal inserts?

Yes to both. Internal and external threads can be molded directly, often with an unscrewing mechanism in the tool, or added as a secondary tapping or insert step. Metal inserts such as threaded bosses, pins, and terminals are placed in the tool and molded in place, which is called insert molding. Call out threads and inserts on the drawing so the tool is built for them.

### How much draft angle does my part need?

A common rule of thumb is 1 to 2 degrees of draft per side, with more on textured surfaces (roughly 1 degree for each 0.001 inch of texture depth). Draft lets the part release from the tool cleanly and reduces drag marks and ejector stress. Deep ribs and tall walls need more, so ask the shop to review draft during design-for-manufacturability.

### What causes sink marks?

Sink marks are shallow depressions that form where thick sections, ribs, or bosses cool and shrink more than the surrounding wall. The fix is usually design: keep walls uniform, core out thick areas, and hold rib thickness to roughly 40 to 60 percent of the adjoining wall. A textured finish can also hide minor sink on cosmetic faces.

### What causes warping?

Warping is distortion from uneven cooling and internal stress, and it is worse with non-uniform walls, glass-filled resins, and poor gate placement. Uniform wall thickness, balanced cooling, adequate draft, and the right gate location all reduce it. Flag any flatness-critical features so the shop can design the tool and process around them.

### What is flash, and what causes it?

Flash is thin excess plastic that squeezes out along the parting line or around ejector pins, usually from too much injection pressure, a worn tool, or not enough clamp force. It is trimmed off, but persistent flash points to a process or tooling issue. A well-maintained tool and a dialed-in process keep parts flash-free.

### How are cosmetic defects prevented?

Cosmetic quality comes from the tool and the process together: the SPI surface finish machined into the steel, the gate location and type (gate vestige is the small witness mark left where the part is de-gated), and process control over flash, sink, and flow lines. Decide cosmetic surfaces before the tool is cut, keep gates off show faces where you can, and specify the finish and any critical A-surfaces on the drawing.

### What is mold flow (DFM) analysis?

Mold flow analysis simulates how molten plastic fills the cavity, predicting fill balance, weld lines, air traps, sink, and warpage before any steel is cut. It guides gate placement, wall thickness, and cooling so the first tool runs good parts. Many shops on OpenSpindle offer mold flow or a free design-for-manufacturability review on request.

## Other Capabilities

- [CNC Machining](https://openspindle.com/capabilities/cnc-machining.md)
- [CNC Turning](https://openspindle.com/capabilities/cnc-turning.md)
- [3D Printing](https://openspindle.com/capabilities/3d-printing.md)
- [Sheet Metal Fabrication](https://openspindle.com/capabilities/sheet-metal-fabrication.md)

## Design Notes That Move Your Price

Not a definition of injection molding. The design and sourcing choices that move your tooling cost, piece price, and lead time.

- **Pick the tool to the volume:** A prototype aluminum mold ($2k to $10k) is the right call for a few hundred to a few thousand parts and gets you samples in weeks. Reserve hardened steel ($10k to $100k+) for high volumes where its million-shot life pays back. Over-tooling a low-volume part is the most common way buyers overspend.
- **Keep walls uniform and add draft:** Thick and thin sections in the same part cause sink and warp. Aim for a uniform wall (often 0.040 to 0.140 in) and add 1 to 2 degrees of draft per side so the part ejects cleanly. Good geometry does more for part quality than a tight tolerance.
- **Decide cosmetics before the tool is cut:** Surface finish (SPI A-1 mirror to D-3 texture) is machined into the steel. A texture hides sink and flow lines; a mirror polish exposes them and raises tooling cost. Lock cosmetic faces up front so the tool is cut once.
- **Amortize tooling across the run:** Because the mold is a fixed cost, effective cost per part drops as volume rises. Ask shops to quote piece price at your realistic annual volume and at the next break up, so you can see where a steel tool starts to pay for itself.

## Get injection molding quotes

Upload your part once and compare tooling and per-part pricing from independent injection molding shops.