> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ntop.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How to use the demold constraint

## Question:

How do I set up my topology optimization to use the demold constraint?

## Applies to:

* Optimization
* Demold Constraint

## Answer:

The **Demold Constraint** block ensures the manufacturability of the final results for castings or plastic injection molding parts. The block prevents overhangs or undercuts based on a defined Demold direction. You can use this block for a single draw, a split draw with a variable surface, or a split draw with a known surface.

This article covers the three possible setups for using the **Demold Constraint** block. All of the examples below use the same starting body (shown below), but they require different setups depending on the molding style. **The Demold Constraint block can significantly increase the solve time of the optimization so we recommend starting with a coarser mesh.**

![An imported CAD Part that has been converted to an implicit body.](https://files.learn.ntop.com/help-articles/optimization/25590564097683.png)

## Single Draw:

For a single draw mold, the following parameters should be used:

* Define the Demold Direction
* Uncheck the Auto Split Surface
* Do not define a region

![A topology optimization that was run using a Demold Constraint that was setup for a Single Draw mold.](https://files.learn.ntop.com/help-articles/optimization/25590605015315.png)

## Split Draw Variable Surface:

For a variable surface split draw mold, the following parameters should be used:

* Define the Demold Direction
* Check the Auto Split Surface
* If you don't want the constraint to be applied to the entire design space, specify a region

![A topology optimization that was run using a Demold Constraint that was setup for a Split Draw Variable Surface mold.](https://files.learn.ntop.com/help-articles/optimization/25590605018259.png)

## Split Draw Known Surface:

For a known surface split draw mold, the following parameters should be used:

* Use 2 **Demold Constraint** blocks, 1 for each half of the body
* Uncheck the Auto Split Surface
* Separate the design space using a parting surface (**Region by Body** block or similar)

The green semi-transparent body in the image below shows the right side of the body that is selected in the region input.

![A topology optimization that was run using a Demold Constraint that was setup for a Split Draw Known Surface mold.](https://files.learn.ntop.com/help-articles/optimization/25600760724627.png)

And that's it! You've successfully implemented the **Demold Constraint** block.

Are you still having issues? Contact the support team, and we'll be happy to help!

## Download the Example File:

* [Example File](https://files.learn.ntop.com/Support%20Article%20Example%20Files/Knowledge%20Base/Optimization/demold_constraint_example.ntop)

## Keywords:

*surface topopt mold topology optimization constraint split single known draw molding demold*