Briefly Describe Processing Process and CNC Machine Tool Composition

To briefly describe processing process on a CNC machine, start with the drawing. A CAM programmer imports the 3D model, sets the stock size, and chooses a work coordinate system. Toolpaths are generated as G-code: feed rates, spindle speeds, depth of cut, coolant commands and rapid moves. On a simple bracket this may take 30 minutes. On a 5-axis impeller with undercut surfaces it can take a full day of simulation before a single chip is cut.

Next comes setup. The operator mounts the blank on the table or in a vise, or clamps it to a fixture plate. Fixture stiffness matters more than most people expect. A part that sings during roughing will not hold ±0.005 mm later. The tool is loaded into the spindle or the tool magazine, and each tool length is measured with a probe or a presetter so the control knows where the tip actually sits.

Then the machine runs. The control reads the program block by block and drives the axes. Roughing removes the bulk with a larger tool; semi-finishing brings the wall within a few tenths of a millimeter; finishing cuts to the final dimension and surface finish. A typical aluminum housing may need three tools in roughing and four in finishing, with a probing cycle in between on tight bores.

Inspection closes the loop. The operator checks critical dimensions on the machine with a probe or off-line with a CMM. If a bore runs 0.01 mm small, the tool radius offset is adjusted and the feature is recut. This is why process planning and inspection planning should be written together, not one after the other.

• 1
  Program defines geometryCAM output carries tool, feed, speed and stock allowance.
• 2
  Setup defines repeatabilityFixture stiffness and tool offset accuracy drive the first-part result.
• 3
  Cutting defines finishRoughing, semi-finishing and finishing are separate operations for a reason.
• 4
  Inspection defines controlMeasure, compensate, recut. Do not assume the first part is good.

A CNC machine tool has four functional groups. The machine base and frame carry everything and damp vibration. The spindle holds and rotates the tool. The feed axes move the tool or the table along X, Y and Z, and in a 5-axis machine two rotary axes as well. The CNC control reads the program and commands all of it. Take any of the four away and you no longer have a machine tool, just parts on a bench.

The frame is usually cast iron or a welded steel structure filled with polymer concrete. Mass and damping matter. A 3-axis mill with a 4,000 mm bed needs a stiff frame because the tool hangs far from the column. A compact 500 × 500 × 450 mm machine can be lighter but still needs enough mass to avoid chatter at high spindle speed.

The spindle is where finish and tool life are decided. It rotates at 8,000 to 24,000 rpm on typical machining centers, with a taper such as BT30, BT40 or HSK-A63. Higher speed suits small cutters and aluminum; higher torque suits steel and titanium. The tool magazine sits beside the spindle and swaps tools in a few seconds, which is what makes multi-tool setups practical.

The feed drive on each axis uses a servo motor, a ballscrew or linear motor, and a linear guide. Positioning accuracy of ±0.005 mm depends on the whole chain, not just the control. Thermal growth is the quiet enemy: a spindle that runs for two hours may grow 20–30 μm, which is enough to shift a tight bore. Shops manage this with warm-up cycles and in-process probing.

Axis count is a process decision, not a prestige decision. A flat plate with holes on one face is a 3-axis job. Adding a fourth axis lets the part rotate so features on four sides can be cut in one setup, which removes re-fixturing error. Simultaneous 5-axis is for parts with compound angles, contoured surfaces, or deep pockets that a straight tool cannot reach without a long, weak overhang.

The trade-off is real. A 5-axis cycle usually runs slower per cubic centimeter of metal removed because the rotary axes must be coordinated and the tool often has a smaller diameter. It pays back when the alternative is three or four setups with fixtures, or when a feature simply cannot be reached otherwise. For a one-off prototype, we sometimes cut a 5-axis part in two 3-axis setups to save programming time. For a 10,000-part run, the single-setup 5-axis route usually wins on repeatability.

Material also drives the choice. Aluminum 6061 and 7075 cut fast and tolerate high spindle speed with small radial engagement. Stainless 316L and 17-4PH work-harden, so the tool must stay in the cut and feed rates must be conservative. Titanium TC4 and Inconel need low surface speed, rigid setups and plenty of coolant. A flexible setup that works fine in aluminum will chatter in Inconel.

GreatLight runs 127 high-precision CNC machines: 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size is 4,000 mm, with travels of 4,000 × 400 × 150 mm on the large frame and 750 × 1,150 × 550 mm or 600 × 600 × 600 mm on the mid-size machines. A Ø400 mm rotary table covers most 4-axis work.

Tolerance is not a single number for the whole part. A bolt hole at ±0.1 mm costs almost nothing. A bearing bore at ±0.005 mm requires a finishing pass, a probe check, and often a temperature-controlled room. Surface finish follows the same rule: Ra 1.6–3.2 μm is a normal as-machined finish, Ra 0.8–1.6 μm needs a dedicated finishing pass, and Ra 0.2–0.8 μm may need a smaller stepover, a finer tool, or a secondary operation.

Cost also scales with setup count. Every extra fixture adds labor, and every re-clamp adds error. A part that looks cheap on paper can become expensive if it needs six setups because the design has features on five faces and a tight true-position callout between them. When we review a drawing, the first question is whether the datum scheme matches how the part will actually be held.

Lead time follows from the same logic. Quotation and free DFM analysis come back within 12 hours, production can start within 24 hours, and parts ship in 3–5 days for most jobs. Historical late-delivery probability is below 2%. Those numbers hold only if the drawing is clear and the material is in stock; a special alloy or a hard coating can push the schedule out.

Volume matters less than people think. There is no minimum order quantity, from one prototype to 10,000+ part runs. A single prototype is priced on programming and setup, so its unit cost is high. At 500 pieces the same part may cost a fraction of that. The break-even point is usually where a soft tool, a casting or a die becomes worth the tooling spend.

A CNC process is only as good as its evidence. We run raw material checks on incoming stock, monitor dimensions in process, and inspect 100% of parts before shipment. Reports are available on request, including material certificates and dimensional data. For medical and automotive work this is not optional; ISO 13485:2016 and IATF 16949:2016 both require a traceable inspection record.

The inspection plan should be written at the same time as the process plan. If a feature is called out at ±0.01 mm but no one has decided how to measure it, the drawing is incomplete. We prefer to agree on datums, gauges and sampling frequency before the first chip is cut, because moving a gauge mid-run invalidates the data you already collected.

Surface finishing is often a separate step in the route. Anodizing, plating, powder coating and bead blasting all change dimensions slightly. A hardcoat anodize can add 20–50 μm per surface, which matters on a thread or a press fit. The rule is simple: finish after final machining, and specify whether the finish is cosmetic or functional.

Finally, documentation travels with the parts. Certificates, inspection reports and, when needed, an NDA cover the commercial side. Uploads are secure and confidential. For engineers, the practical takeaway is that a well-planned route is short, uses as few setups as the geometry allows, and states clearly which dimensions are critical and how they will be verified.