What is a two-part mold?

A two-part mold consists of a top half (cavity) and bottom half (core) that fit together to form a hollow space in the shape of your part. Material is injected through a sprue channel, fills the cavity, and solidifies into the desired shape. Two-part molds are widely used in plastic injection molding, resin casting, and educational prototyping.

How do I convert an STL file to a mold?

Upload your STL or OBJ file to the Online Two-Part Mold Tool. The tool auto-scales your model to fit mold constraints, analyzes possible parting planes, and generates a two-part mold design with injection and vent channels. You can then export the mold halves in STL, OBJ, 3MF, or STEP format for 3D printing or CNC machining.

What file formats can I export molds to?

The tool supports exporting mold halves in four formats: STL and OBJ for 3D printing, 3MF for advanced 3D printing with color and material data, and STEP (.stp) for professional CAD and CNC machining workflows.

What is parting plane analysis?

Parting plane analysis determines the optimal split line where the two mold halves separate. The tool evaluates multiple planes along the parting direction, scoring each for undercuts and floating sections, then recommends the best plane for clean mold separation and part ejection.

What is demoldability analysis?

Demoldability analysis evaluates the draft angles of your part relative to the parting plane to determine how easily it can be removed from the mold. The tool generates a color-coded heatmap overlay on your 3D model — green for easy, yellow for medium, orange for difficult, and red for impossible draft angles — helping you identify areas that may stick, deform, or break during demolding before you commit to manufacturing.

Can I use this tool for 3D printed molds?

Yes. Export your mold halves as STL, OBJ, or 3MF files and print them on any FDM or SLA 3D printer. 3D printed molds work well for resin casting, silicone mold making, and low-volume injection molding with desktop machines like the INJEKTO 3. The tool automatically generates proper mold geometry including sprue channels and venting.

What 3D file formats can I upload?

You can upload STL and OBJ 3D model files. The tool automatically scales your model to fit within the mold cavity constraints (up to 69×80×48mm) and validates dimensions before analysis. Models are never scaled up — only scaled down if they exceed the maximum mold dimensions.

Can I use this tool to design silicone casting molds?

Yes. Export the two mold halves as STL, OBJ, or 3MF and 3D print them. You can use the printed halves directly as a two-part mold for low-viscosity resin, wax, plaster, or soap casting, or use them as a master to pour RTV silicone around and produce a flexible two-part silicone casting mold. The same parting plane analysis and demoldability heatmap apply to silicone casting workflows.

What is the difference between an injection mold and a silicone casting mold made with this tool?

The geometry is the same two-part core-and-cavity design. For plastic injection molding, the halves are 3D printed, CNC-machined, or ordered as PPA-CF, resin, or aluminum molds and used with a machine like INJEKTO 3. For silicone casting, the printed halves are used either directly as a rigid two-part casting mold or as a master to pour RTV silicone around, then resin, wax, plaster, chocolate, or soap is cast in the resulting silicone mold.

How the Online Two-Part Mold Tool Works

Go from a 3D model to a ready-to-print two-part injection mold in minutes. Choose a fixed Mold Backer Compatible size for the INJEKTO 3, or let the tool build a Custom Size mold that fits any part. No CAD experience required.

Step 1

Upload Your 3D Model

Upload an STL or OBJ file of the part you want to mold. The tool accepts standard mesh formats exported by all major CAD and 3D modeling software.

Step 2

Choose Your Mold Size

Select Mold Backer Compatible for a fixed mold optimized for the INJEKTO 3 desktop injection molder — your model is automatically scaled to fit within the cavity. Or choose Custom Size, where the mold dimensions adapt to your part with no size limit.

Step 3

Parting Plane Analysis

The tool evaluates multiple parting planes along the mold's parting direction, scoring each for undercuts and floating sections. The best plane is automatically recommended, or you can select one manually.

Step 4

Two-Part Mold Generation

A core (bottom) and cavity (top) mold half are generated with sprue channels for material injection, vent channels for air escape, and optional alignment pins for precise mold registration. Preview the result in 3D with exploded and collapsed views.

Step 5

Demoldability Analysis

A color-coded heatmap overlays your 3D model showing draft angles: green for easy demolding, yellow for medium, orange for difficult, and red for areas that may stick or break during part removal.

Step 6

Export Your Mold

Export both mold halves in STL, OBJ, 3MF, or STEP format. STL and OBJ work with any 3D printer. 3MF supports advanced print settings. STEP is the professional standard for CNC machining and CAD. Mold Backer Compatible molds can also be ordered as manufactured physical molds.

Mold Specifications

Mold Backer Compatible

Fixed dimensions optimized for the INJEKTO 3 desktop injection molder. Models are automatically scaled down to fit — never scaled up.

Mold Half Size

75.6 × 86 × 25.88 mm

Max Part Size

69 × 80 × 48 mm

Max Volume

45 mL

Corner Radius

8 mm

Sprue Diameter

4.8 mm

Vent Channel

2 mm

Custom Size

The mold dimensions automatically adapt to your part with no fixed size limit. Wall thickness, sprue, vent channels, and alignment pin dimensions scale proportionally based on the part geometry.

Who Uses This Tool

Makers and hobbyists use the tool to prototype custom parts like keycaps, figurines, and mechanical components — picking Mold Backer Compatible for quick desktop injection or Custom Size for larger projects.

Educators and students teach and learn manufacturing concepts hands-on: parting planes, draft angles, undercuts, alignment pins, and the fundamentals of injection molding.

INJEKTO 3 users prepare molds in Mold Backer Compatible mode, with dimensions and channels precisely matched to the INJEKTO 3's mold cavity.

Engineers evaluate part moldability early in the design process using Custom Size mode — checking demoldability, identifying undercuts, and testing parting plane options before committing to expensive tooling.

Ready to Make a Mold?

Upload your STL or OBJ file and get started. No signup needed.

Open the Tool