Designing your first product or a new product is an incredible feat, and heading into the manufacturing process can seem overwhelming.

Suppose you’ve found yourself in the position to send your designs off to a manufacturing facility. In that case, there are steps you need to take before doing so to ensure the process runs as smoothly as possible, and you receive the product you designed.

This article will walk you through the considerations you need to keep in mind before sending off your designs for your cast urethane parts.


What is Cast Molding?

As a brief synopsis, the process of cast molding involves using gravity to make your mold. You will pour your material into a mold. Injection molding uses pressurized machinery to fill the mold cavities and is done at high pressure. The liquid material is left to sit, cool down, and harden with either process, then is taken out from the molding, and you have your product.

Another difference is that with injection molding, the liquid is inserted into a metal or steel holder, whereas a cast molding is made from a silicone or rubber outer shell.

Cast molding is typically more cost-efficiently and timely. Engineers tend to go with this option when the end product needs to be made out of plastic or a quicker production time is required. For example, if you order from an injection molding facility and the prototype won’t be ready in time for when you need it.


What to Consider When Designing Your Cast Urethane


This may seem obvious, but a step that is often overlooked is to check the accessibility of your product. You should have a general idea of how casting works and what potential problems could arise. For instance, some molds need pockets for air bubbles to release, and others may need extra room in the mold in case overflow happens.

You’ll want to focus on the aerodynamics of your product. Most likely, you won’t be able to sort through all of the potential problems—that’s also where a manufacturer can help—but you’ll want to sort through the low-level issues beforehand. 

It’s important to make sure the design is technically possible before sending it off to a urethane manufacturing company. This will save you time, costs, headache, and possibly your relationship with the urethane manufacturer down the line. The last thing you want to do is waste time and resources designing a cast urethane part that is impossible to deliver.

Wall Thickness considerations before cast molding

Make sure your urethane part has consistent wall thickness throughout. This is a crucial part of the overall casting process, specifically in the cooling process. When the liquid material is cooling down and the walls are not even, it can lead to cracking, sinking, warping, or pure failure.

The recommended wall size is 0.5mm for small parts and 1mm for larger parts. This is not a strict guideline to follow but is definitely a good starting point in your casting process.


Simply put, radii is a technique that means rounding out the edges or corners of a product. This is necessary when manufacturing parts because it increases the load-bearing strength and improves the part’s quality.

The industry’s recommended dimensions are a 0.125” fillet on outside corners and a .060” fillet at the inner corners.

Parts May Shrink

Shrinkage is another typical result of casting that should be acknowledged before you begin the manufacturing process. Factors that affect the amount of shrinkage in the urethane molding process are:

  • Casting size and wall thickness
  • Shop temperature
  • Peak exotherm of the polyurethane
  • Mold material and temperature

It depends on your material’s exact composure, but in general, it’s safe to expect at least a 0.15% shrinkage, so keep that in mind during the prototyping process.

Letters and Logos

Letters and logos can be made on your urethane product, either raised or recessed. Implementing this is a great way to brand your product. The main factors you will want to consider here is the height and depth, width, and radii of your casting.

A few insights on the best practices when it comes to adding letters and logos to your mold are:

  • The space between features should land around 0.050” at the minimum.
  • The width should be twice the measurement of the height.
  • The larger the radius of the letters, the more accurately they will read

Having the tactics mentioned above in place before sending your product to a urethane manufacturer will ultimately save time, money, headache, and resources.

If you need help figuring out these requirements, contact a custom urethane manufacturer for some guidance.