Product development teams have been relying on the injection molding process to manufacture polymer parts for decades. This time-tested process is robust, highly repeatable, and ideal for high-volume production. However, when product development teams think about the cost of manufacturing using injection molding, they typically think of the costs only in terms of direct materials, machine time, and direct labor costs¹ (Figure 1). This conventional cost model, although intuitive, does not capture the true total costs associated with manufacturing a part using injection molding.
In reality, mechanical engineers, tooling technicians, and product development teams typically find that the actual costs to manufacture using injection molding are significantly higher than what the conventional model captures. More specifically, this approach misses five additional cost elements associated with injection molding: (1) tooling amortization, (2) prototyping/tooling change, (3) design for injection molding, (4) setup fees, and (5) minimum order quantity (MOQ) inventory waste (Figure 2).
After decades of production experience, the injection molding process is well-characterized. However, the true costs associated with producing a part using injection molding are not as well-understood. Typically, the costs associated with tooling amortization and tooling changes during the prototyping stage are not considered in initial production estimates. These tooling-related costs add up quickly, driving up the total cost as each retooling change can add $5,000 to $50,000 (depending on the application).
The time and labor associated with design for injection molding represent important costs that are generally not factored into the total cost. In order to be manufacturable, mold design requires the correct application of critical design elements such as parting line location, shutoffs, drafts, fillets, gates, and ejector pins. Additionally, the complexity of intricate geometries, textures, and variable wall thickness requirements for a given part can become a considerable cost and time multiple. Setup fees reflect the time and labor it takes to mount the mold into a molding machine, pre-cycle, and calibrate the molding operation. This becomes a sizeable cost addition for most short-run injection molding operations.
Lastly, a natural outcome of the high tooling costs associated with injection molding is the tendency for the process to be chosen for high volume production applications to amortize the upfront tooling cost. However, this volume amortization does not work for many product development teams, since contract manufacturers often hide steep tooling costs under a minimum order quantity (MOQ) requirement. This requirement means that product development teams must often order parts in the thousands, even though they might only need a few hundred units. The MOQ also puts pressure on organizational operations and supply chain teams as it can introduce inventory holding costs and associated wastage of parts. National Institute of Standards and Technology² reported the existence of $537 billion locked in inventory by the manufacturing industry in 2011. This number has likely grown over the years. With additive manufacturing and the ability to produce on-demand, the perfect solution to reduce inventory holding costs and associated wastage is now within reach.