How many steps does it take to transform a piece of raw material into a precision part?

In this article, we will mainly discuss three things: ① What mainstream processes can and cannot do; ② Process selection comparison table; ③ The most common pitfalls in factories.

Underlying logic: Subtractive manufacturing, additive manufacturing, forming

All machining processes, in essence, fall into three categories:

Key points: 90% of parts are not made using a single process, but rather through a combination of initial forming and finishing. For example, engine blocks: cast blank → CNC precision milling of surfaces and holes. Don't be misled by the idea of a single process.

Subtractive manufacturing (machining): precision work

This is the main method of subtractive machining, and also the most precise. It can be categorized into 7 types based on the relative motion between the tool and the workpiece:

1.Turning (CNC Lathe)

Principle: Workpiece rotates, tool feeds linearly. Capabilities: External diameter, internal diameter, end face, thread, tapered surface. Accuracy: IT6~IT7, Ra 0.8 and up. Applicable to: Shafts, discs, rotating bodies (accounting for 40%+ of machining volume).

2.Milling (Machining Center)

Capabilities: Planes, cavities, curved surfaces, complex 3D contours. Advantages: 3/4/5-axis simultaneous machining; 5-axis setup handles multiple surfaces in one operation, eliminating multiple positioning errors. Disadvantages: Thin-walled parts are easily deformed; "less feed, faster feed" and allowance for stress release are necessary.

3.Drilling

Drilling only guarantees position, not perpendicularity and roundness; reaming/boring is required for higher accuracy. Deep hole drilling (L/D>10) is difficult to chip and prone to tool breakage; high-pressure cooling and segmented retraction are necessary.

4.Boring

Enlarges existing holes and corrects their positions, achieving an accuracy within IT7. This is crucial for large box-type parts (gearboxes, cylinder blocks).

5.Grinding

Grinding is a finishing process for hardened hardware, achieving an accuracy of IT5~IT6. A mirror finish is possible with Ra below 0.1. Note: Grinding heat can "burn" the surface; thorough cooling is essential.

6.Planing/shaping

This method is inefficient and is gradually being replaced by milling, but it is still used for narrow, long slots and racks.

7.Gear

Hobbing/shaping is suitable for batch production; milling is suitable for single-piece or small-batch production with low accuracy; grinding is used for high-precision gears in automotive and aerospace applications.

Process combination: Shaft parts = rough turning → finish turning → keyway milling → outer diameter grinding; Plate parts = flat surface milling → drilling and tapping → wire EDM shaping. Memorizing this process chain will provide a clear understanding of pricing and production scheduling.

Special processing: When the knife can't cut.

Note: Both electrical discharge machining (EDM) and wire cutting have a heat-affected layer/modified layer. If the material is to be subjected to fatigue loads, a polishing or shot peening process must be added.

Molding process: A killer weapon for mass production and cost reduction.

For products selling over 100,000 units, the unit cost of subtractive processing is extremely high; molding is the primary method.

Casting: Sand casting is cheap and rough. Die casting (aluminum) has a good surface finish and is highly efficient. Investment casting is used for complex, thin-walled components.

Forging: Plastic deformation and continuous fiber flow lines result in high strength; crankshafts and connecting rods are almost entirely forged.

Stamping: Sheet metal separation/forming; used for mobile phone back covers, automotive body panels, and springs; cycle times are measured in seconds.

Injection Molding: Plastic particles are injected into the mold cavity; the absolute mainstay for consumer electronics casings.

Cost Truth: Injection/stamping unit costs are extremely low, but mold fees are extremely high (tens of thousands to millions). CNC machining is chosen for small batches, while molds are chosen for large batches. The critical point is usually between 5,000 and 20,000 units (depending on material and complexity).

Process selection comparison table

The 5 most common pitfalls in factories

1. Drawings specify IT6, but using a standard lathe – Standard lathes can reliably reach IT8; forcing IT6 will drastically reduce the pass rate. Check equipment capabilities before setting tolerances.

2. Cutting thin-walled parts to the end in one pass – Residual stress release will cause the part to "grow crooked." Leave a 0.2-0.5mm allowance, aging/resting before finishing.

3. Trying to mill after quenching – The tool will break when the hardness increases. For quenched hard surfaces, directly use grinding or EDM.

4. Drilling deep holes without cooling and chip removal – Tool breakage is a minor issue; workpiece damage is the real headache. Deep holes require high-pressure internal cooling and segmented drill retraction.

5. Forcing injection molding for small batches – The product design is changed before the mold costs are fully amortized. Perform CNC prototyping and verification before deciding on mold making.

Key technology trends to watch in 2026

* Composite machining center: Turning and milling composite, drilling and boring composite, multiple processes can be completed in one clamping, directly cutting the source of error in half.

* Additive + Subtractive Hybrid: 3D printing for near-net-shape forming + CNC finishing, reducing the delivery cycle of complex parts by 50%+.

* AI Process Scheduling: The model automatically recommends tools, parameters, and clamping, enabling even beginners to perform the work of experienced professionals.

* Green Machining: Minimal lubrication (MQL) replaces large amounts of cutting fluid, accelerating the penetration of dry cutting in roughing and medium-scale machining.