A Complete Guide To Urethane Casting

“Urethane casting, or sometimes vacuum casting, is a low-volume casting process widely favored for its adaptability. Its use is vital in everything from medical devices to automotive and aircraft interior components. “

Urethane molding has become a cost-effective technique that provides high-standard and resilient end-use molded components like colored rubber plastics, movie props, and bespoke models from polyurethane casting. 

Moreover, 3D master patterns and prototype development are relatively easy by urethane casting. Unlike injection molding, which uses expensive hard toolings, urethane molds are soft silicon plastic. Further to production capacity, it is a highly economical, meticulous, and inexpensive process for low-volume batch production. The process success is determined by part geometry and material being cast. 

This article provides information about urethane molding, its process, benefits, limitations, and applications. Moreover, it will highlight critical details on materials used in urethane casting and when to employ polyurethane casting in your intended project. 

Urethane Casting: How Does it Work?

Urethane casting, also known as vacuum casting or urethane molding, is a widely adopted technique for small-volume production. The urethane liquid material is poured into a silicon mold and cured in a heated oven, which slightly demolds or removes the product or part upon solidification. 

Urethane molding

The urethane casting process is limited to low volumes as the silicon molds have a shorter span cycle, and can only mold around 20 parts in one production cycle. After this limit, designers need to dispose of the soft silicon mold. However, the parts produced entail exceptional surface finish, and higher strength, molded from polyurethane casting compared to the injection molding process. Usually, manufacturers rely on urethane casting to create tighter tolerance parts down to +/-.005″. Moreover, the process is presumed to be a bridge between 3D printing and injection molding processes. The product lead time in urethane casting spans from a few days to a week, according to research, it’s typically around 3-4 weeks. 

In general, the master patterns for molds used for the urethane molding process are designed through speedy, and effective CNC machining and 3D printing techniques like Stereolithography, fused deposition modeling, selective laser sintering, and poly jets. This master pattern is embedded in a urethane-filled silicon mold container to make a mold negative. Then, after applying the optimal pressure, vacuum, and temperature of around 40 degrees Celsius, the product gets the desired shape of the mold, which then solidifies, and the part is ejected for post-processing. In some cases, metal inserts are needed for parts requiring tighter tolerances, and thin walls patterns.

Compatible Materials For Urethane Casting

However, urethane casting usually offers limited material options compared to conventional techniques like CNC machining and injection molding, which offer an expanded range of materials to choose from. This process normally utilizes thermosets. Even though they have few benefits over thermoplastics, they offer exceptional strength, durability, resistance to abrasion, and versatility in terms of colors. 

In addition, it eases product manufacturers in adding more pigments for applications where colored urethane cast parts are essential. This distinction makes it an ideal casting process for toy making, colored schemed branded arts, products, and consumer goods. Moreover, it helps replicate design patterns of complicated prototypes without impacting their surface textures. Moreover, urethane-molded parts can be painted after development. This allows designers to apply multiple shades and achieve the required gloss and matte/frosted surfaces. One of the core advantages of polyurethane is that it is available in transparent crystal formulations and has been adopted for applications such as housings, enclosures for electrical devices, and lightening product manufacturing. 

Generally, urethane casting resin is compatible with two thermoset urethane casting resins: elastomeric polyurethane and rigid clear polyurethane. The ultimate choice of material depends upon mechanical functionality, absorption properties, and gripping capability. 

Rigid Clear Polyurethane

These materials are emphasized by their shore hardness characteristics. They offer a premium-quality gloss and matte finish to the urethane-casted products. Moreover, parts cast through these thermosets provide exceptional durability and longevity. 

Table: Technical aspects of rigid polyurethane

Elastomeric Polyurethane

Elastomeric polyurethane thermosets share characteristics with rubbers and are often characterized by shore A urethane casting material’s group. They offer a high elongation percentage to break, flexibility, and impact resistance. Examples include cable connectors, over molds, buttons, skin grips, and high-strength kits for defense sectors. 

Table: Technical aspects of elastomeric polyurethane

By knowing their distinct aspects and use cases, let’s compare the urethane molding technique with conventional alternatives such as 3D printing, CNC machining, and injection molding. 

Urethane Casting Vs. 3D Printing

Urethane molding and 3D printing techniques are widespread across manufacturing industries due to their ability to produce intricate parts. However, 3D printing is a versatile process. It accommodates various manufactured parts from a broader range of material options. In addition to part complexity, it helps create finer, detailed functional prototypes using stereolithography and fused deposition techniques. 

On the other hand, urethane casting also helps to produce 3D printing master patterns. Although the accuracy level is slightly minimal for 3D printing, it can be more beneficial for applications requiring multiple copies of the same products. Moreover, 3D printing is limited to a few color variants, while vacuum casting or urethane molding allows the addition of pigments and color during operation. 

Urethane Casting Vs. Injection Molding 

Urethane casting and injection molding, however, are similar but have few distinctions. The one common difference is the mold material. For example, injection molding usually uses costly steel or carbide molds to inject end-use parts or products. Inversely, urethane molds are inexpensive and made of soft silicon materials. 

Moreover, injection molding notably benefits large-volume production runs for high-strength-requiring parts. Meanwhile, urethane molding is economical for small-scale batches that produce parts. 

Urethane Casting Vs. CNC Machining

CNC machining has multiple benefits over the urethane casting process. It is more versatile and offers various materials, from engineered-grade thermoplastics to high-strength metals, composites, and elastomers. This makes it accurate and precise for fabricating tight-dimension parts and prototypes. Urethane casting, in contrast, is limited to a few materials. 

Additionally, CNC machining parts manufacturing imprints additional costs on budget, while urethane casting is a faster and more affordable technique for shaping prototypes to mass-produced parts. 

Furthermore, urethane molding is a straightforward process as it generally does not require any tooling for product development. CNC machining is more complicated as parts sometimes need to be lathed, drilled, milled, and routed for intended use applications, thus acquiring additional costs on the project. 

Applications of Urethane Casting

Polyurethane casting has various applications across manufacturing industries, such as medical parts, housing and enclosures, sporting equipment, and functional prototypes for the automotive and aerospace sectors. 

Medical Industry

Medical polyurethane Pipe

Urethane casting primarily uses medical-grade plastics to form non-toxic devices for patients’ safety. These products adhere to strict safety standards and comply with food-safe quality control standards using food-grade biocompatible materials. Some examples include disposable syringes and enclosures of implantable catheters. 

Structural Equipments

Polyurethane casting is usually practicable for fabricating lightweight supporting equipment, including vehicle wheels, gym dumbbells, underwater components, and helmet padding. 

Rapid Prototyping Development

Urethane Prototypes

Urethane casting is a rapid prototyping method that’s fairly considered appropriate for creating functional prototypes, proof-of-concept models, testing prototypes, and mechanically engineered designs. Furthermore, urethane molding helps make parts with lengths up to 30 inches. 

Small Scale Production Volumes

Urethane molding is a popular choice for producing parts at small units of up to 20 – 50 shots because the mold silicon needs to be disposed of occasionally after each unit. So, its employment on large volumes of imprints is a higher expense to the overall scale economy. 

Enclosures & Housing Equipment

Polyurethane casting is heavily used to fabricate enclosures for various industries. Its role is widespread, from consumer electronics to medical devices. Moreover, urethane casting can be combined with the overmolding process to create highly sterilized electrical components encased with rubberized shells to protect the surface and enhance longevity. 

Advantages of Urethane Casting

Urethane molding provides several benefits, including cost-effectiveness, high-performing rapid prototypes, and custom parts production. Besides this, designers must consider a few limitations before choosing urethane molding for their product development projects. Let’s take a look;

• The process is the right choice when choosing small batches to bring to markets in short-time leads. Further, it’s ideal for interior and exterior parts manufacturing applications.  
• The silicon mold used can be reused multiple times, thus reducing the overall cost per part, unlike conventional injection molding, where tooling requirements incur higher expenses than the per-part manufacturing costs.
• One of the core advantages of urethane molding is that you can replicate lost master design parts by considering the original object as the standard for fabricating multiple identical parts.
• It is notably effective for customized manufacturing applications. The designers can forge parts with varying dimensions and add pigments and texture in-process. 
• In addition, the process often produces limited materials waste. Therefore, it is considered cost-efficient for complete product development.

Disadvantages of Urethane Casting

Here are some of the disadvantages of the urethane casting process.

• The urethane molding process is linked to risks of warping and bubbling (cavitation) due to poor maintenance issues and mold wear and tear.
• Generally speaking, urethane casting is labor-intensive due to mold changeover after every unit run. That ultimately impacts the lead times of mold creation. 
• The materials facilitated by urethane molding are limited and offer minimum heat-resistive characteristics. Than other techniques like 3D printing, CNC machining, and injection molding
• Polyurethane molders can expedite minimum-size parts or products up to 30 inches. 
• The process often yields products requiring post-processing, thus increasing fabrication cost per part. 
• Urethane casting is limited to fabricating simpler designs. Complex geometrical parts require professional experts, adding extra budget to the overall expense. 

Vacuum Casting Services at Prolean

Prolean offers a one-stop solution to meet all your casting project requirements. We have gained the reputation of the best  Vacuum Casting Services China by providing high-quality and affordable manufacturing solutions. Our technical team is highly dedicated to bringing excellence to your urethane casting product development projects. 

Our facility offers our valued customers a wide material range from thermoplastics to various composites. Whether you need to develop rapid prototypes for small-scale to large runs on-demand, we meet to fit your needs without compromising on high standards and at an affordable budget to your range. Trust prolean for help, and get an instant online quote. 

Summing Up

Urethane casting or vacuum casting has become an efficient and affordable method for commencing small-scale projects. The upfront costs per part are relatively small compared to traditional machining and molding techniques. Urethane casting, furthermore, helps to create parts or products that possess high dimensional stability, matte, gloss, and the ability to resist chemicals and aliphatic-based oils. Moreover, it’s flexible from a low shore durometer (20 hardness/ rigidity) to several 100s durometer hardness materials. 

However, a few disadvantages limit its use in terms of mold changeability and short-run production. Despite these, urethane casting is immensely employed for various rapid typing developments and has gained significance across several industries, from medical to auto car parts fabrication. 

FAQ’s

Q1. What is the shrinkage rate in the urethane molding process?

When progressing from liquid resins to solids, the shrinkage rate of urethane casting during mold creation is usually around 0.15%. 

Q2. What surface finishing options can provide urethane casting resin?

These resins typically offer exceptional moldability and comprehensive surface finishing options, including frosted/matte, crystal transparency, medium to high gloss shades, and colored textured surfaces. 

Q3. Is polyurethane plastic or not?

Generally speaking, thermoset materials are not considered plastics. Instead, long-chain polymers yield thermoset polyurethanes, which are synthetic elastomeric resins rather than plastic resins. A thermoset is an organic compound made of carbamate links. 

Q4. What are the primary considerations for mold making for urethane casting?

Mold preparation is critically considered as production success depends upon the appropriate mold. Usually, molds are not cured during their making, the reason being inadequate or under-mixing caused while mixing silicons, rigid urethanes, etc. In addition, insufficient temperature and environmental conditions also pose risks of deformation of fabricated parts. 

Q5. Is urethane or urethane casting resin expensive?

The costing criteria of urethane casting typically depend upon parts volume, design complexity, etc. It usually costs between a few 100s to 1000s $ from place to place.