Choosing how to make a metal part is a decision most engineers make once per programme and live with for years. Get it right and unit cost, lead time and quality all fall into place. Get it wrong and you either pay too much per part forever, or you commit tooling to a process that cannot hold the tolerances the design needs.<\/p>\n\n\n\n
The three processes that dominate this decision for small to medium metal components are die casting, metal injection molding and CNC machining. They overlap enough to create genuine confusion and differ enough that the wrong choice is expensive.<\/p>\n\n\n\n
This guide compares them on the criteria that actually decide the question.<\/p>\n\n\n\n
The Three Processes in Brief<\/strong><\/p>\n\n\n\n \u0627\u0644\u0635\u0628 \u0628\u0627\u0644\u0642\u0627\u0644\u0628<\/strong> forces molten metal under high pressure into a hardened steel die. It suits non-ferrous alloys, principally aluminium, zinc and magnesium, and produces parts rapidly once tooling exists. Best known for housings, brackets, enclosures and structural components at volume.<\/p>\n\n\n\n Metal injection molding<\/strong>, usually shortened to MIM, mixes fine metal powder with a binder, injects the mixture like plastic, then removes the binder and sinters the part to near full density. It handles ferrous and exotic alloys that die casting cannot, and produces small, complex parts at volume.<\/p>\n\n\n\n \u0627\u0644\u062a\u0635\u0646\u064a\u0639 \u0627\u0644\u0622\u0644\u064a \u0628\u0627\u0633\u062a\u062e\u062f\u0627\u0645 \u0627\u0644\u062d\u0627\u0633\u0628 \u0627\u0644\u0622\u0644\u064a<\/strong> cuts the part from solid stock. It requires no tooling, handles almost any metal, holds the tightest tolerances of the three, and costs the same per part at quantity one as at quantity one thousand, less the setup amortisation.<\/p>\n\n\n\n The Deciding Criteria<\/strong><\/p>\n\n\n\n Volume<\/strong><\/p>\n\n\n\n This is usually the first filter and often the last.<\/p>\n\n\n\n Machining carries no tooling cost, so it wins decisively at low volumes. A handful of parts, or a few hundred, almost always favours machining regardless of geometry.<\/p>\n\n\n\n Die casting and MIM both require significant tooling investment that must amortise across production. Below a certain annual volume, the tooling never pays back. Above it, unit costs fall well below machining and the gap widens with quantity.<\/p>\n\n\n\n Where exactly the crossover sits depends on part complexity and how much material machining would remove. A part that machines quickly from simple stock has a high crossover point. A part requiring long cycle times and heavy stock removal crosses over much sooner.<\/p>\n\n\n\n For any programme near the boundary, calculate it properly. Total cost equals tooling plus unit cost times quantity, for each process, across your realistic lifetime volume.<\/p>\n\n\n\n Part Size and Weight<\/strong><\/p>\n\n\n\n MIM has a firm practical ceiling. The debinding and sintering stages constrain part size, and MIM is generally suited to small components, commonly under about 100 grams. Larger parts become difficult and uneconomic.<\/p>\n\n\n\n \u0627\u0644\u0635\u0628 \u0628\u0627\u0644\u0642\u0627\u0644\u0628<\/a> handles a much wider size range, from small brackets up to substantial housings, limited mainly by machine tonnage.<\/p>\n\n\n\n Machining handles the widest range of all, constrained only by the machine envelope and the availability of stock.<\/p>\n\n\n\n If your part is large, MIM is out. If it is very small and complex, MIM becomes attractive.<\/p>\n\n\n\n \u0627\u0644\u0645\u0648\u0627\u062f<\/strong><\/p>\n\n\n\n This is frequently the decisive constraint.<\/p>\n\n\n\n Die casting works with non-ferrous alloys. Aluminium, zinc and magnesium are the mainstream choices. Zinc offers excellent detail reproduction and long die life. Aluminium offers better strength to weight. Steel cannot be die cast in conventional processes.<\/p>\n\n\n\n MIM handles what die casting cannot. Stainless steels, tool steels, nickel alloys, titanium and specialist materials are all available, which is precisely why MIM exists as a category.<\/p>\n\n\n\n Machining handles essentially anything available as stock, including all of the above plus materials neither casting process can reach.<\/p>\n\n\n\n If your part must be stainless steel, die casting is eliminated immediately, and the choice narrows to MIM or machining.<\/p>\n\n\n\n Geometry Complexity<\/strong><\/p>\n\n\n\n MIM excels at complex geometry. Because the feedstock behaves like plastic during molding, it reproduces thin walls, fine detail, internal features and complex external shapes that would be expensive to machine and impossible to cast.<\/p>\n\n\n\n Die casting handles moderate complexity well, producing thin walls and integrated features, though undercuts require slides that add tooling cost and complexity.<\/p>\n\n\n\n Machining handles complexity but pays for it directly, since every feature adds machine time. Deep pockets, small internal radii and features requiring additional setups all raise cost, in the way covered in our guide to CNC machining cost drivers<\/a>.<\/p>\n\n\n\n The general pattern: the more complex the geometry, the more the moldable processes favour themselves at volume, and the more machining costs.<\/p>\n\n\n\n \u0627\u0644\u062a\u0633\u0627\u0645\u062d<\/strong><\/p>\n\n\n\n Machining holds the tightest tolerances of the three, comfortably, and can go tighter with grinding or wire EDM<\/a> where required.<\/p>\n\n\n\n MIM holds respectable tolerances but the sintering stage introduces shrinkage that must be predicted and compensated. Achievable tolerances are looser than machining and vary with geometry.<\/p>\n\n\n\n Die casting holds moderate tolerances, generally looser than MIM on comparable features.<\/p>\n\n\n\n Importantly, both casting and MIM parts are routinely machined afterward on critical features. This hybrid approach is common and often the correct answer: form the bulk geometry economically by casting or MIM, then machine only the features that require precision. It captures most of the volume economics while meeting tolerance requirements where they matter.<\/p>\n\n\n\n