Advantages and Disadvantages of Silicones and Urethanes PDF

Advantages and Disadvantages Silicones and Urethanes Mold Cost, Temperature Resistance, and Production https://www.rapiddirect.com/blog/urethane-casting-vs-injection- molding/#:~:text=contraction%20during%20cooling.- ,Wal...

Advantages and Disadvantages Silicones and Urethanes Mold Cost, Temperature Resistance, and Production https://www.rapiddirect.com/blog/urethane-casting-vs-injection- molding/#:~:text=contraction%20during%20cooling.- ,Wall%20Thickness,for%20larger%20or%20complex%20parts.  Cost Silicone molds are generally more expensive than urethane molds. However, urethane molds require a release agent to be used. Tooling Cost: Plastic injection molding requires robust, typically metal molds, which can be expensive, especially for complex designs. However, these molds are long-lasting and suitable for high-volume production. Urethane casting employs silicone molds, which are less costly to produce. These molds are suitable for short runs and prototypes but have a shorter lifespan than metal molds. Material Costs: In injection molding, thermoplastics are often used, with costs varying based on the type of plastic. Economies of scale play a crucial role, with higher volumes typically reducing the cost per unit. However, the price of urethane resins can vary based on the required properties for the final product. Per Part Cost: Examining the per-part cost reveals more about the economic landscape of these manufacturing processes. For high-volume production, injection molding can be cost-effective. For instance, producing 10,000 units of standard plastic gear might cost around $2.00 per unit. In contrast, urethane casting is more suited for low to medium-volume production. Producing the same plastic gear in volumes of 500 might cost about $3.50 per unit. However, this cost can vary depending on the complexity and material used.  Temperature Silicone rubber can withstand higher temperatures than urethane rubber. Urethane Rubber – for wax that has a pouring temperature between 130°F (54°C) and 200°F (93°C), professional candle makers will choose a urethane rubber like PMC®-744. Silicone Rubber – if you are using wax that melts above 200°F (93°C), silicone rubber is your best choice. Urethane Rubber – Advantages: Easy to use and economical. Disadvantages: Urethane rubber is adhesive and will stick to most original models and some casting waxes. Using sealing agents and release agents in conjunction with urethane rubber is unavoidable. Silicone Rubber – Advantages: Silicone rubber resists higher temperatures vs. urethane rubber and will last longer in production. Also, silicone rubber does not stick to many surfaces so sealing agents and release agents are often not required. Disadvantages: Silicone rubbers tend to be more expensive than urethane rubbers. Also, silicone rubbers that offer high tear resistance require special processing equipment in order to successfully use the material. Specifically, an accurate gram scale for weighing components and vacuum degassing equipment to de-air the liquid rubber are required. The exception to this is OOMOO® Series silicone rubbers, which are low cost and do not require special equipment to process. The trade off is that OOMOO rubber does not have tremendous tear strength and is suitable for relatively simple shapes.  Model Configuration Models that have simple shapes and limited undercuts can be reproduced using a soft to medium hardness (Shore 20A - 60A) urethane or silicone rubber. Highly complicated shapes with severe undercuts require a soft, stretchy silicone rubber such as Dragon Skin® Series silicone. Dragon Skin is incredibly strong and stretchy and will last a long time in the production of wax castings. Sealing agents: Silicone rubber doesn't stick to many surfaces, so sealing agents and release agents are often not required. Tear resistance: Silicone rubbers that offer high tear resistance require special processing equipment. Applications: Silicone is ideal for applications that require high-temperature and weather resistance without painting. Urethane is better for applications that require high strength, durability, and resistance to abrasion and chemicals. Mass production: Urethane molds are well adapted to mass production.  Injection Molding Injection molding suits materials like ABS, polypropylene, polyethylene, and TPU. These materials become highly fluid when melted. Their low viscosity is crucial for the material to fill the mold properly. On the other hand, urethane casting typically uses thermoset materials, such as thermoset polyurethanes. These materials permanently harden as they cure Wall thickness: Injection molding can produce parts with wall thicknesses from 0.5 mm (0.02 inches) to 4 mm (0.16 inches). Urethane casting allows for wall thicknesses from 1 mm (0.04 inches) to 5 mm (0.20 inches).  Production Volume The choice between these techniques largely depends on the quantity of parts needed. Injection Molding is best for producing large quantities. Its metal molds last longer, and the quick cycle times allow for the cost- effective manufacturing of numerous parts, from thousands to millions. Urethane casting is optimal for smaller batches. The silicone molds used in this process have a limited lifespan. The slower pace of production also means that the process is not as cost-effective for mass production.  Tolerance Tolerances play a crucial role in manufacturing, directly impacting precision and consistency. In Injection Molding, tight tolerances of around 0.005 inches (0.127 mm) are achievable. This is a great option for parts needing precise specifications and consistent replication. While capable of good tolerances, urethane casting generally falls short of injection molding’s precision, with average urethane tolerances around 0.01 inches (0.25 mm). While this is suitable for many applications, it is not ideal for ultra- high precision parts. Achieving tight tolerances with cast urethane is challenging due to flexible silicone molds that are susceptible to movement. Conversely, metal injection molds offer less dimension variation but still experience minor changes due to plastic contraction during cooling  Undercut Managing undercuts in injection molding presents difficulties. The inflexibility of metal molds necessitates intricate designs to accommodate undercuts. To eject the part undamaged, it might be necessary to introduce movements, cut holes or slots, or incorporate movable parts like slides or lifters into the mold. Such complexity can escalate both the expense and the time needed to produce the mold. Urethane casting can easily handle undercuts because it uses flexible molds. The elasticity of silicone enables the mold to flex, releasing parts with undercuts without the need for complex mold mechanisms. This characteristic renders the process more suitable for parts featuring intricate designs and undercuts.  URETHANE SILICONE allows production of hundred allows approx. 50-75 parts, even thousands of casts depending on the WEAR RESISTANCE casted pieces depending on design and the easyness the density and design of the of the demolding process. piece. STRONG Perfect for pieces with WEAK TO MEDIUM TEAR AND ABRASION RESISTANCE negatives angles. Works for Depending on the resin, concrete or plaster shore (SHORE A) molding from 10 shore A > 95 shore from 6 shore A > 80 SHORE A shore A. ELONGATION From 200% > 1 300% From 50% > 700%. viscosity from 400 cps ~10,000 à 100,000 cps VISCOSITY ( CPS ) > 2500 cps. depending on the system Easy and Requires the use of efficient demolding DEMOLDING OPERATION a releasing agent process for complex pieces casted pieces can have High level of accuracy COMPLEXITY & complex designs with (more or PRECISION in reproduction of less important) negative details angles Indicated for pieces that indicated for artistic and are to be painted ( no risk industrial pieces that are not to PAINTING of eye’s fich be painted phenomenon) COST $$ $$$$ Consequently, as illustrated in the table, there is pros and cons for each family. To put in a nutshell, silicones are usually the best choices for small production of detailed pieces that might need to be painted but they are also more costly. On the other hands, urethane molds offer higher resistance and are well adapted to mass production. However if urethane molds are usually less expensive than silicone mold, using a release agent is also required.