We previously posted a blog about ways urethane/silicone casting is better than injection molding. While that was certainly true for a significant number of circumstances, there is no doubt injection molding is the better choice over casting for a substantial number of cases as well. In this post, we will examine when those scenarios exist and summarize the ways injection molding is better than casting.
Injection Molding Delivers a Lower Part Price
Injection molding can deliver more cost-effective part prices than casting can and this is probably the single most-relevant input in the decision between the two processes. As production volume increases, so does the value of an automated process that injects and ejects material, respectively, to and from a molding tool. In contrast, casting is inherently manual in nature and the scale economies for urethane casting are not as significant. As a result, the per-part cost of an injection-molded item can be quite low—on the order of pennies or dollars when operating at high volumes—in contrast to casting’s per-part cost that can be on the order of 5 to 50 times higher.
Injection Molding Utilizes a Wider Material Set
Another key benefit of injection molding is the wide variety of different materials, as long as they are offered in a pellet form. Even certain resins can be injection molded using the reaction injection molding process. Hence, the breadth of choices for resin and plastic injection molding is far broader than those available to casting, which creates a significant number of potential advantages related to material properties. While advances in polyurethane have enabled flame-retardant material and a wide variety of shore values, the range of casting options still pales in comparison to injection molding.
Injection Molding is Faster at Large Quantities
Similar to its pricing benefits, injection molding can deliver significant speed gains at scale. The process of injection molding a part can take on the order of seconds to minutes. In contrast, the underlying process for each cast part can take on the order of minutes to hours. So while the amount of time required to set up for an injection mold may be significantly higher than it is for a cast part, the speed with which each individual part is created means that there is a crossover point where the production of a volume of goods will be faster in molding versus casting. Since injection molding tools can take a couple of weeks or longer to set up, this crossover point typically occurs after the production of several 100 to several 1000 parts.
Injection Molding Has a Longer Tool Life
Another key benefit of injection molding over casting is the life of the molding tool. These tools are typically built out of aluminum, stainless, or tool steel. These durable metals can sometimes maintain their form over the course of millions of shots. In contrast, casting tools are far less durable. Silicone and resin can degrade after several dozen to several hundred uses. As a result, they are typically disposable items and those seeking to leverage recurring use of casting molds will want to arrange some kind of maintenance or production plan in advance.
As discussed, there are a wide variety of ways in which injection molding is superior to casting—just as there are a number of ways that casting is superior to injection molding. Which camp does your program fall into? At 3Diligent, we are happy to offer both technologies so we would encourage you to sign up and submit an RFQ today.