Louise J. Roop Introduction
Metal injection molding and machining are not competing technologies in any absolute sense. They are different answers to different questions, and the error that costs programmes most is applying one where the other is clearly better suited. Machining has served precision metal component production for well over a century. It is mature, flexible, and capable of tolerances that few other processes can match. Metal injection molding is newer, more constrained in its optimal application window, and substantially more capable than machining when geometry, volume, and material performance must be achieved simultaneously within a fixed cost envelope.
What Machining Does Well
Machining removes material from a solid billet or bar stock through cutting, milling, turning, drilling, and grinding operations. Its strengths are well established. Tolerances as tight as a few micrometres are achievable on well-maintained equipment. A wide range of metals can be machined, including alloys difficult to process through metal injection moulding. And machining requires no upfront tooling investment beyond cutting tools, making it economically accessible for prototype quantities and low-volume production runs.
The limitations are equally well understood. Material removal generates significant waste for complex geometries where a large proportion of the original billet becomes chips rather than finished component. Cycle times for complex parts scale with complexity in a way that makes high-volume production of intricate components expensive. Internal features, undercuts, and cross-holes require specialised fixturing, multi-axis machining strategies, or secondary operations that add cost and lead time.
What Metal Injection Molding Does Well
Metal injection moulding produces components to near-net shape through feedstock injection, binder removal, and high-temperature sintering. Its primary advantage over machining is the ability to produce geometric complexity at volume without the per-part cost penalty that machining imposes for complex features.
Cross-holes, undercuts, threads, knurled surfaces, and internal cavities that would require multiple machining setups can be incorporated into a metal injection moulding tool and reproduced identically across thousands of parts at no additional per-part cost. Material utilisation is high, secondary operations are minimised, and sintered components achieve densities of 96 to 99 percent of theoretical, delivering mechanical properties comparable to wrought or cast equivalents.
The constraints are equally important. Upfront tooling investment is substantial. Sintering shrinkage of 15 to 20 percent must be accurately characterised and compensated for in mould design. And the process is most economically rational for components in the one gram to one hundred gram range at production volumes that justify the tooling investment.
The Break-Even Logic
The decision between metal injection moulding and machining is, in many cases, a question of volume and complexity intersecting at a specific cost break-even point. For simple geometries at low volumes, machining is almost always the more economical choice. As volume increases and geometry becomes more complex, the economics shift. The fixed tooling cost of metal injection moulding is amortised across a growing number of parts, while the per-part cost of machining complex features remains largely constant.
That break-even point depends on component complexity, the alloy being processed, the tolerances required, and the secondary operations each process demands. As a general orientation, metal injection moulding becomes economically compelling at annual volumes above several thousand parts for components of moderate complexity, and at lower volumes for highly complex geometries where machining costs are elevated.
Where Each Process Belongs
Several application characteristics reliably point toward metal injection molding over machining:
- Complex three-dimensional geometry with features requiring multiple machining setups
- Production volumes in the tens of thousands or above that amortise tooling investment effectively
- Material utilisation requirements where machining waste represents a significant cost concern
- Applications where near-net-shape capability eliminates secondary operations that machining would require
Several characteristics reliably point toward machining:
- Prototype or low-volume requirements where tooling investment is not justified
- Very tight tolerances on specific features that exceed the dimensional capability of metal injection moulding after sintering shrinkage
- Alloys not compatible with the sintering temperatures and atmospheres that metal injection moulding requires
- Components whose geometry is simple enough that machining cycle times are short and material waste is modest
Singapore’s metal injection moulding sector serves programmes where the complexity and volume arguments favour the process clearly, particularly in medical device and precision electronics applications where biocompatible alloys, complex geometry, and validated production at scale make machining an impractical alternative.
Conclusion
The choice between metal injection molding and machining is not a matter of one process being superior to the other. It is a matter of matching process capability to programme requirements with clarity about what each approach costs, what it delivers, and where its limitations begin. For programmes that fall within the optimal window of Metal injection molding, the case is strong and well-supported by decades of industrial evidence. For those that do not, machining remains the more rational choice, and recognising that boundary early is what separates good manufacturing decisions from expensive ones.
