Plastic prototypes usually are manufactured through CNC plastic machining, 3D printing or urethane casting. In this blog, we will explain how to make plastic prototype with different methods to help engineers better understand the plastic prototyping.

What is a plastic prototype 

A plastic prototype is a physical model of a designed plastic product before injection tooling kick off. It is a preliminary version of the final product that is usually made through 3D printing, urethane casting and CNC machining process.

The process to make a plastic prototype

CNC machining

CNC machining is a effective method for creating plastic prototypes with high precision and accuracy. WIth computer controlled cutting tools, CNC machine can cut a solid block into a functional prototype.This process involves the removal of material through milling, drilling and turning operations.

CNC machining offers lots of advantages for plastic prototyping, include fast turnaround times, high quality surface finishes and more.

CNC Machining

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3D printing

3D printing is an additive manufacturing process. it create the prototype by depositing melted plastic material layer-by-layer based on a digital design file. in this way , 3D printing can manufature prototypes with remarkable complexity.

3D Printing

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urethane casting

Urethane casting, also known as silicone molding or vacuum casting, is a cost-effective method for producing plastic prototypes low volume manufacturing less than 100 pieces. This process has something similar with traditional inejction molding, it use a silicone mold to cast Liquid polyurethane resin.

How to make a plastic prototype by CNC Machining step by step  

Step 1: Split the part

The first step is Spliting the product in CAD software, this is to optimize for CNC machining, or it will not be feasible for CNC machining due to the stoke of cutters. According to the function of the prototype, Split line need to be carefully considered. For example, in the picture each color means a small part is spiltted.

Step 2: Choose proper material sheet and cut to size

Choose a suitable plastic material sheet for the prototype based on your project requirements, considering factors such as strength, durability, and cost. Common plastic materials used for CNC machining include ABS, acrylic, nylon, and polycarbonate. Cut the plastic sheet to size according to the dimensions of the splitted part after step one. When come to Clear prototpye , you need to understand Acrylic Vs Polycarbonate , choose the best clear material.

Step 3: Prepare the CNC Machine

Set up the CNC machine by securing the plastic material on the worktable and installing the appropriate CNC cutting tools. Ensure the machine is properly calibrated and programmed with the necessary toolpaths and cutting parameters.

Step 4: Program the CNC Machine

Generate the CNC program by translating the CAD design into machine-readable code, aslo called G-code&M-code. This involves specifying the tool paths, cutting depths, feed rates, and any other machining instructions necessary to produce the desired prototype.  

Step 5: Machine each part

Load the CNC program into the machine’s controller and initiate the machining process. The CNC machine will accurately and precisely cut and shape the plastic material based on the programmed instructions to form the splitted parts.

Step 5: Grinding

After CNC machining, sanding the surface of the prototype to remove any rough edges, burrs, or imperfections, ensuring a smooth surface for next polishing step.

Step 7: Bonding

After the splitted parts prepared, use adhesive bonding techniques to securely join them together. this is to get the complete prototype with a good strength.

Step 6: hand Polishing

Apply polishing methods to further enhance the surface finish of the prototype. use specialized tools, compounds and buffing techniques to achieve the desired level of smoothness and glossy of the prototype surface.

Step 7: Finishing and Quality check

Perform final checks and inspections to ensure the prototype meets the required specifications and tolerances according to engineering drawings. Verify its form, fit, and functionality and address any potential issues.

How to make a plastic prototype with urethane-casting step by step

Step 1: Create the Master Pattern

Master Pattern is used for making sillicon mold. So the quality of cast urethane parts relies on the quality of the master pattern, which is most machined using CNC technology when tight tolerances, glossy finishes or optical clarity are required. For parts with complex shapes and structures, we aslo creat the master pattern using SLA (Stereolithography) 3D Printing.

Step 2: Making the Silicone Mold

Making a sillicon mold for casting use liquid silicone, becasue Silicone has excellent chemical stability, self-releasing properties and flexibility. Liquid silicone is poured around the master and removal all air, creating a vacuum chamber. Then liquid material is cured in an oven, at a temperature of 40℃. It generally takes 8-16 hours depending on the size of the mold.

Step 3: Casting Process

  • Prepare the urethane casting resin by mixing the appropriate ratio of resin and hardener. Preheat them to about 40°C before use
  • Carefully pour the mixed urethane resin into the silicone mold. fully stir and degas for 50-60 seconds under vacuum to avoid air pockets or bubbles.
  • Cure the liquid urethane resin in the mold around two hours for small parts and six hours for big parts.
  • After the resin has fully cured, open the mold and take out the part.

How to make a plastic prototype with 3D printing step by step  

Step 1: Choose the 3D Printing Technology:

Select the proper 3D printing technology based on your project requirements and desired material properties. Three Common technologies include FDM, SLA and SLS could be used for 3D prototyping.

Step 2: Select the Printing Material:

Choose the suitable plastic material for your prototype based on your designed material. Choose one which is similar to your production material. Common 3D printing materials have PLA, ABS, PETG and nylon.

Step 3: Prepare the 3D Printer:

Set up the 3D printer, ensuring it is properly calibrated and the printing bed is clean and level. Install the correct printing material and ensure the printer settings match the desired specifications.

Step 4: Slice the 3D Model Start the Printing

Use slicing software to convert the 3D model into instructions whic is called G-code. Adjust settings such as layer height, infill density and speed, Load the G-code file onto the 3D printer and initiate the printing process and then wait the printer running.

Step 5: Post-Processing

Once the printing is completed, remove the printed prototype from the 3D printer. Remove support structures, sand the surface to achieve the desired finish.


CNC machining is an excellent choice when precision and surface finish are prioritied. 3D printing is ideal for complex geometries rapid prototyping. urethane casting provides cost-effective prototypes for replicating production-like parts. KUSLA provide prototyping services with all these processed to ensure the highest quality and accuracy of your plastic prototype.

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