Guide to Rapid Prototyping Through Urethane Molding

Urethane molding is a rapid prototyping method we use to produce soft rubber parts. We normally cannot use other methods like CNC machining in producing these parts. This method uses a silicon mold and a 3D printed master pattern. It allows us to produce top-notch products of up to 30 inches in size. Urethane molding slightly varies from in the following way. It uses a soft silicone tool, unlike the other process that uses a hard tool.

At Creatingway, we take several precautions when coming up with the master pattern. This allows us to ensure the product has the needed features. A working plastic part usually arises from urethane molding. We may then present it as a model or a working part. Its dimensions depend on the accuracy of the casting material and master model. Normally, it has a shrinking rate of 0.15%. Luckily, our experts account for this change when rapid prototyping a part.

 

What’s An Outline of Urethane Molding?

There are four basic steps to urethane molding:

• Step 1

We start by coming up with the master pattern and printing it by rapid prototyping. We can achieve this by 3D printing. A master pattern is an original part. We can also use the master pattern to create the molds and using it in urethane casting. We must develop this part deftly as the final product depends on it. Luckily, there is an array of machining methods for rapid prototyping a urethane master pattern.

• Step 2

The second step involves encasing the master pattern in a silicon mold. This allows us to create a top-notch mold.

• Step 3

Upon curing the mold, we proceed to split it into two halves. We can then use the resultant cavity in casting the final product.

• Step 4

In this final yet crucial step, we inject urethane or any other resin to fill up the spaces. Upon curing the material, we proceed to remove it from the tool. We can redo this process until we obtain the desired outcome. We use this final part in the rapid prototyping of different products.

What’re The Components of the Casting System?

The casting system comprises parts that are vital for the completion of the casting operation. Urethane molding comprises of the following casting system:

• A funnel
• Air channel
• Casting channel
• Fixtures to hold the two mold halves in place
• Urethane mold releasing agent

Our experts arrange the above elements deftly to have a smooth casting process. The funnel and casting channel is plastic in nature. We connect to the mold’s hole. Afterward, we pour the material into this hole allowing it to flow from channel to funnel. A higher funnel results in a higher casting pressure. This allows for proper filling of the pattern’s features.

We normally have air vents on the opposite side of the mold. This allows the air to flow out of the material as we pour into the pattern during rapid prototyping. The urethane molding release agent is a film of air that prevents the sticking of the casted part in the mold. We use it to remove the protruding element that arises from friction. The friction is between the mold and the casted part. Also, it covers the minute holes that arise during the urethane mold casting. This makes the final product smoother.

What is the Tolerance in the Casted Part?

Casted parts have a tolerance that varies between 0.010 into 0.003 in. Its shrinkage rate of 0.15% arises from the thermal expansion of the casted part. Flexible molds respond by shrinking when rapid prototyping through urethane molding. If the geometry is too thick or irregular, deviances may arise from shrinking.

Its surface end may outwardly smoothen to a matte surface or material. Grow lines arise in the internal surface or hidden parts. We usually clearly define custom or polishing finishes.

Comparing Urethane Molding to Injection Molding

Despite using both processes in rapid prototyping, they differ in the following ways.

• Tool Manufacturing

Urethane molding uses a soft tool while injection molding uses a hard tool. We thus can make urethane casts by molding a 3D printed model of the final part. Meanwhile, we machine injection molding tools using CNC machining.

• Cost of Material

The type of plastic we use in injection molding is more expensive than the one we use in urethane molding. Hence, we use urethane molding when rapid prototyping a few products. In the case of products that need certain physical traits, we opt for injection molding.

• Quantity and Production Volume

We use urethane molding in low volume production. In the case of high volume runs, then the lifespan of tool steel molds proves to be more effective. Therefore, It is economical to opt for injection molding instead of urethane molding. For any inquiries regarding rapid prototyping through urethane molding, simply contact us.

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