Differences between Metal Powder Injection Molding (MIM) and CNC Machining
There are two commonly used methods for making metal parts: MIM (Metal Injection Molding) and CNC machining. Industries such as medical, automotive, aerospace, and electronics all rely on these two methods. The principles are different, and the applications are also very different. Choosing the right process is really crucial when making products.
Let's start with MIM (Metal Injection Molding). Simply put, it combines plastic injection molding and powder metallurgy, specifically for making small, complex metal parts. The process involves mixing metal powder with a binder to form a material, then injecting it into a mold to shape it. The binder is then removed by heating, and finally, the material is sintered, resulting in a dense metal part. Many materials can be used, including stainless steel, low-alloy steel, tool steel, and titanium alloys. The powder is typically 5 to 20 micrometers in size, and the metal content in the feedstock is about 65% to 72%, mainly to ensure good molding without making it too brittle. MIM is generally used for small, complex parts, and high-volume production.
Then there's CNC machining, which most people are more familiar with. It involves a computer-controlled machine to cut materials, gradually shaping a solid piece of material into the desired form. It can be used with metals, plastics, and wood, offering high precision and repeatability. It's widely used in demanding fields like aerospace, automotive, and medical.
The biggest difference between the two is that MIM is additive manufacturing, where materials are built up little by little; CNC is subtractive manufacturing, where materials are cut away little by little. They are completely opposite approaches.
The costs are also different. MIM molds are expensive in the early stages, but the cost per unit decreases as the volume increases, especially for complex parts, which CNC cannot match. CNC is the opposite: it is cost-effective for small batches of simple parts, but the more complex the part, the more time and money CNC takes, and the cost does not decrease much even with large volumes.
Design modifications are even more complicated. Changing the structure of a MIM (Mechanical Manufacturing) machine basically requires redesigning the mold, which is costly and time-consuming. CNC (Computer Numerical Control) only requires changing the program, and it can be modified however you want, making it much more flexible.
Design modifications are even more complicated. Changing the structure of a MIM (Mechanical Manufacturing) machine basically requires redesigning the mold, which is costly and time-consuming. CNC (Computer Numerical Control) only requires changing the program, and it can be modified however you want, making it much more flexible.
The advantages of MIM include almost no waste, low internal stress, less susceptibility to deformation, and rapid production ramp-up, with a single mold capable of producing a large quantity of parts. However, the disadvantages are also apparent: sintering can affect material properties and may cause deformation; the feedstock has a shelf life; and the material selection is less extensive than with CNC machining, making it suitable only for small to medium batch production of small parts.
The advantages of CNC machining are high precision, flexible material selection, fast small-batch production, and easy modification. The disadvantages are higher waste, higher cost for complex parts, the need for additional machines for large-volume production, and internal stress during cutting, which may lead to deformation over time.
In terms of materials, MIM can use stainless steel, tool steel, titanium, cobalt-chromium, high-temperature alloys, carbon steel, nickel alloys, and tungsten alloys, mainly in powder form. CNC is even more versatile, capable of using almost all materials such as aluminum, titanium, copper, stainless steel, and alloy steel, and solid materials can be used directly.
When should you choose MIM (Mechanical Manufacturing)? When the volume is large, the parts are small (preferably under 40 grams, not exceeding 100 grams), the structure is complex, the tolerance requirements are not at their limit, the design will not be changed, you want to save materials, and minimize secondary processing.
When to choose CNC? Small batches, extremely high precision, large parts, high stress, special materials, frequent design changes, and exceptionally stable performance.
Quality control of MIM is also very important. The raw materials and binders must be inspected when they enter the factory. After molding, the size of the green body must be measured, and the density and performance must also be checked. After sintering, the size, tolerance, surface and performance must also be checked. Statistical process control is used to keep an eye on it so as to reduce scrap.
In general, MIM is suitable for complex, high-volume, and inexpensive applications; CNC is suitable for high precision, flexibility, and a wide range of materials. There's no single best option; the choice depends on the size, structure, volume, precision requirements, and budget of your parts. Choosing the right option is the most cost-effective.
Practical applications of powder injection molding in various fields
|
Serial Number |
Application areas |
Powder Injection Molded Products |
|
1 |
Electronic communications |
SIM card slot, vibrator, disk drive components, cable connectors, electron tube housings, computer printheads, electronic packages, heat sink materials |
|
2 |
Automotive industry |
Ignition control lock components, turbocharger rotor, valve guide components, automotive brake system components, automotive sunshade components |
|
3 |
Medical devices |
Orthodontic brackets, internal suture needles, biopsy forceps, radiation shield |
|
4 |
Mrticles for daily use |
Watch cases, watch straps, watch buckles, golf club heads and tees, sports shoe buckles, sports firearm parts, document binding punches, small eyeglass parts, safety locks, and barber scissors. |
|
5 |
Machinery industry |
Irregular milling cutters, cutting tools, micro gears and small mechanical parts, textile machine shuttles |
|
6 |
Weapons and Equipment |
Mine rotor, gun trigger, armor-piercing projectile core, front sight base, cluster arrow darts |
|
7 |
Aerospace |
Aircraft wing hinges, rocket nozzles, missile tail fins, ceramic turbine blade cores |
Typical applications of MIM (Mechanical Manufacturing) for automotive precision components
Gears (Power/Transmission Systems)
Application scenarios
Engine timing gear, oil pump/water pump gear, transmission synchronizer hub, actuator pinion.
Material
Fe-Ni alloy steel, 420 stainless steel, 17-4PH (high strength/wear resistant).
Key Value
Complex tooth profiles and integrated hub/keyway reduce machining steps.
Density ≥7.6g/cm³, tooth surface hardness HRC 40~50, wear-resistant and fatigue-resistant.
Mass production (annual capacity ≥ 100,000 units) costs 30-50% less than machining.
Automotive MIM Gear
Sensor housing (electronic control system)
Application scenarios
ABS sensor, temperature/pressure sensor, throttle position sensor housing and base.
Material
304/316 stainless steel (corrosion resistant), aluminum alloy (lightweight).
Key Value
Thin-walled (0.5~1.5mm) + integrated sealing groove/mounting hole, protection level IP67+.
It has good electromagnetic shielding properties, making it suitable for the anti-interference requirements of automotive electronics.
High dimensional consistency, suitable for automated assembly lines.
Fuel injector components (fuel system)
Application scenarios
Gasoline/diesel injector valve body, needle valve seat, flow control ring, high-pressure oil chamber assembly.
Material
High-temperature alloys (such as Inconel 718), 440C stainless steel (resistant to high temperature/high pressure/corrosion).
Key Value
Micro-fine flow path (φ0.1~0.5mm) + high-pressure sealing surface are formed in one piece to meet high-pressure conditions of 200~300bar.
It is resistant to high temperatures (-40℃~150℃), fuel corrosion, and has high long-term reliability.
It replaces precision machining, solves the problem of machining small/deep holes, and improves the yield rate to 95%+.
Automotive MIM fuel injector components
Other precision components
Turbocharger
Small impeller, adjusting ring, heat shield (high temperature alloy, lightweight + high temperature resistant).
Gearbox
Shift forks, sliders, and guide blocks (complex structure + wear-resistant, replacing forging/machining).
Braking system
ABS actuator valve core, proportional valve assembly (high precision + reliable sealing).
MIM has evolved from an "optional" to a "preferred" technology in the field of precision automotive parts, especially for small and complex components such as gears, sensor housings, and fuel injector parts. It balances performance, precision, cost, and lightweighting, making it a key manufacturing technology for the high-end development and new energy transformation of automobiles.
