Most complex enclosures and housings start life as an assembly. A formed metal frame here, a molded cover there, a handful of brackets, gaskets, and fasteners holding it together. Each interface is a place where tolerances stack up, where labor gets added, and where a part can eventually fail. For programs running between 100 and 5,000 units a year, that assembly burden often costs more than the parts themselves.
Table of Contents
Reaction injection molding gives engineers a different starting point. Instead of designing several components and joining them later, you can design one part that does the work of many.
Part consolidation is the practice of combining functions that used to live in separate components into a single molded piece. In Exothermic's RIM work, that often means taking what was a five or six-piece subassembly and producing it as one part, with mounting features, ribs, bosses, and even encapsulated hardware molded directly in. Two liquid components are mixed and injected at low pressure, then react and cure inside the tool. Because the chemistry fills the mold under modest pressure, the process tolerates geometry that would force a thermoplastic part to be split into multiple pieces.
Three properties of the process do the heavy lifting. The first is wall thickness freedom. A single RIM part can carry thin cosmetic skins and thick structural ribs without the sink and warpage that limit thermoplastic design. That freedom lets you build mounting pads, stiffening webs, and attachment points into the same molding rather than bolting them on later.
The second is size and geometric range. The low viscosity of the reacting mixture and the relatively low molding pressure make it possible to produce parts measured in feet, with undercuts and deep draws that would demand sliding cores or separate pieces in injection molding.
The third is encapsulation. Metal inserts, threaded bosses, brackets, and sealed electronics can be positioned in the tool and surrounded by material as it cures. That removes a downstream assembly step and creates a sealed, single-piece result.
The clearest savings show up in assembly. Every interface you remove takes out fasteners, labor minutes, inspection points, and an opportunity for misalignment. On the tooling side, RIM aluminum tooling typically costs 40 to 60 percent less than a comparable injection mold for runs under 5,000 units, according to Exothermic's RIM cost data, and a single consolidated tool replaces the several molds you would have needed for the separate parts. Lead time follows the same pattern, with RIM tools generally ready in 4 to 6 weeks against 12 to 16 weeks for hardened steel injection tooling.
Fewer parts also means a simpler bill of materials, fewer suppliers to manage, and fewer line items to forecast and stock. For a sourcing manager, that reduction in complexity is often worth as much as the unit-cost difference.
Consolidation is not free of trade-offs. A single large tool concentrates risk, so a design change late in development can mean reworking one expensive tool instead of one small one. Very high production volumes still favor injection molding, because RIM carries more hand finishing per part and the per-piece cost eventually overtakes the tooling advantage. And not every function belongs in one part. A component that needs frequent service access, or one that pairs a soft sealing element with a rigid structure across an awkward boundary, may be better as two pieces. The right call comes from looking at the whole program, not just the part print.
The strongest candidates share a few traits. They are large or geometrically complex, they run at low to medium volume, and they currently exist as assemblies with several joints, fasteners, or sealed interfaces. If a part is small, simple, and made in the hundreds of thousands, consolidation through RIM rarely pays. If it is a large instrument enclosure built in the hundreds or low thousands, the math usually favors collapsing the assembly into one molding.
There is no fixed limit, but consolidating a five or six-piece subassembly into a single molding is common in Exothermic's work. The practical ceiling is set by part size, tool complexity, and whether every function genuinely belongs in one piece.
Usually the opposite. Removing joints removes failure points. RIM lets you mold ribs and bosses where the load actually sits, so a consolidated part can be stiffer and more durable than the assembly it replaces.
Yes. Threaded inserts, metal stiffeners, and sealed electronics can be encapsulated during the molding cycle, which removes assembly steps and improves environmental sealing.
If you are carrying an assembly that fights you on cost, tolerance, or reliability, it may be a candidate for consolidation. Exothermic's engineering team can review your current design and show you what a single-part approach would look like. Reach out for an engineering consultation.