Vacuum Casting Process: Complete Step-by-step Guide

Complete Step-by-Step guide to Vacuum Casting Process

The vacuum casting process is a highly refined method used to create precise prototypes and small production runs. It involves a series of controlled steps to ensure that the final product accurately replicates the original design. In this article, we’ll dive deep into the vacuum casting process, focusing on the detailed steps involved in creating a high-quality silicone mold and casting the final parts.

Vacuum Casting Process_Master Model

Creating the Master Model

The master model is the most important part of the entire process of vacuum casting and is also the most initial and crucial stage of the entire process. This is like the model, or in a much easier term, the “blueprint” of what is to be produced. The master model is considered to be so important because it is what influences the final parts that are to be cast with detailing, accuracy, and also a smooth and surfaced finish of the parts.

Design and Fabrication:

Use CAD software for designing the master model to ensure the perfection of the features, dimensions and tolerances. Formulate the digital design using either techniques of 3D printing like SLA or CNC machining. Make sure that the material chosen for the master model are durable and capable for withstanding the molding. Material like SLA ABS resin is commonly considered.

Surface Preparation:

Ensure that the master model has a smooth and precise surface to achieve a high-quality finish on the final parts. In cases of any imperfections, transfer the master model to a silicone mold and later to the cast part. Prepare master model for the post-processing steps like sanding, polishing, and also applying surface coat to prevent or eliminate any surface flaws.

Vacuum Casting Process_Silicon Mold Preparation

Silicone Mold Preparation

This step is one of the most crucial in the entire process of vacuum casting, as it is that step where the details of the model are captured. There are many steps in this process which we must discuss in detail for a better understanding.

Preparing the Mold Box and Hanging the Master Model:

Hanging the Master Model:

Carefully position the master model in the mold box which will serve as the container for the silicone. Suspend the model using a support structure in the mold box, making sure that the silicone can flow evenly around it. It is important to maintain the proper and correct position to achieve an even distribution of thickness and also preventing the formation of any air pockets.

Providing a Gate and Risers:

Add a gate (channel through which the casting material will is introduced), and a riser (small channel that allows air to escape when the material is filled in the mold) in the master model set-up, before pouring the silicone. Place the gate at the lowest point of the mold cavity to allow casting material to flow upwards, which will in turn help in pushing out the air through the riser. Place the riser at the highest points of the mold where the air is most likely to be trapped. This reason behind this arrangement is to make sure that the mold is distributed evenly and completely, leaving no room for air pockets or voids.

Mixing and Degassing the Two-Parts Silicone:

Silicone Composition:

The silicone for mold making consist of a two-part system, first, a base silicone, and a curing agent. Mix these two components in a precise ratio to make sure that the silicone cures correctly and reaches the desired mechanical properties.

 

Degassing the Silicone:

Once the silicone components are mixed, place the mixture in the vacuum chamber to remove any air bubbles that may have been introduced during the process of mixing. Degassing process is important to carry out because air bubbles which are trapped can possibly lead to defects in the molds, and can create voids and weak spots. Under vacuum, the mixture will expand as the air bubbles rise to the surface and burst, hence leaving a smooth, bubble-free liquid.

Vacuum Casting Process_Silicon Pouring

Pouring the Silicone and Secondary Degassing:

Pouring the Silicone:

Carefully pour the mixed and degassed silicone mixture into the mold box. Make sure that the mixture is poured slowly and steadily to prevent any introduction of new air bubbles. It is crucial to start the pouring process from one corner of the mold box and allow it to flow naturally around the model to minimize any risk of trapping air.

Vacuuming the Filled Model:

Once the silicone has been poured, place the mold box containing the silicone and the master back into the vacuum chamber. This secondary vacuuming step is crucial as it removes any air that may have been trapped during the pouring process. Under vacuum, any air bubbles will be drawn out, making sure that the silicone fully conforms the details of the master model. This step is particularly important for the complex models with intricate features or undercuts

Vacuum Casting Process_Mold Cutting

Curing the Silicone and Removing the Master Model:

Curing the Silicone:

After the vacuum process, leave the mold to cure. Depending on the type of silicone used and the condition of the environment, the curing time can vary. Some silicones cure at room temperatures and some needs an elevated temperature to speed up. This process allows the silicone to set into a flexible but durable mold that can be used repeatedly.

Careful Mold Separation:

Once the silicone is fully cured, carefully open the mold to remove the master model. Cut the mold typically along the predefined parting lines, which have been strategically planned to ensure easy removal of both the master model and future cast parts. Make sure to cut the mold with utmost precision to maintain the integrity of the mold and also avoid damaging the master model.

Mold Inspection:

After the cutting process, remove the silicone mold and inspect for any defects such as incomplete curing, tears, or trapped air bubbles. A well-prepared mold will be free of defects and ready for the casting process.

Vacuum Casting Process_Machine Setup

Vacuum Casting Process:

The final part of the final step is casting. This is the process where the prepared mold is filled with materials that are suitable and then put under vacuum conditions to ensure the precision and quality of the product.

Mixing the Casting Material Using a Vacuum Casting Machine:

Mixing Resin, A and B.

Mix the two-part resin (that are A and B) under vacuum conditions within the vacuum casting machine. This step is crucial to make sure that the mixture is free from air bubbles, which could compromise with the quality of the final cast part.

Vacuum Casting Process_Mixture Pouring

Filling the Mold Using a Vacuum Casting Machine:

Vacuum Setup and Pouring.

After the resin is mixed, pour the casting material carefully into the silicone mold, while the vacuum casting machine maintains the vacuum environment. The machine itself ensures that the material flows into every part of the mold, hence filling even the smallest details and complex geometries without trapping air. This vacuum-assisted process of pouring is critical for achieving high precision in the final cast part.

Applying Atmospheric Pressure.

After the mold is filled under the vacuum, the vacuum then needs to be released. Apply the relative atmospheric pressure to the mold. This step helps compress any more remaining bubbles, reducing them to negligible sizes, making sure the structural truthfulness and surface quality of the final parts.

Curing the Cast Material.

After the material is poured and the pressure applied, place the mold in the oven to cure. The process of curing is done so as for the material to solidify properly, and achieving the desired mechanical properties. The vacuum casting machine handles both mixing and pouring, but the curing environment needs to be controlled separately in the oven. This will provide the adequate amount of heat and time for the material to set fully.

Post-Processing and Finishing:

The final stage of vacuum casting consists the procedure of the removal of the mold after the cast material has been cured. This material then needs to undergo some necessary post-processing steps which we will be discussing below.

Demolding

Open the silicone mold carefully and extract the cast part. The flexibility of the silicone will allow the cast part to be peeled away without any damage even to the smallest detail. Carry out this step with utmost care to avoid any tear or damage that could possibly occur against the delicate features on the part.

Trimming and Cleaning.

Once the part is removed, the parts have excess materials known as “flash” along the edges where the mold was cut. Trim away the flash using precision tools and clean the parts to remove any residue left from the mold or the process of casting.

Surface Finishing.

Some additional step can be essential depending on the requirements of the final products. Some of the steps can be like sanding, painting, polishing or even application of protective coating. This step is particularly important for the parts that will be used in customer-facing products or for the purpose of prototype, which needs close resemblance.

Inspection

The concluding step in this process is the inspection of the parts to make sure it meets the requirement. Check for the dimension, surface finish and the overall quality of the parts. Any kind of defects identified at this stage will require adjustments to the previous process, such as modification of the master model, mold or the casting material.

Vacuum Casting Process_Final Part

Conclusion

These are the critical steps that are followed in the process of vacuum casting. Every single step makes a big difference in the becoming of the final product to turn out to be as expected and perfect as required. One highlight of the process of vacuum casting is that, through this process, manufacturers can produce very precise and close replicas of the original designs, hence making “Vacuum Casting” priceless tool in the world of fast-growing industries.

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