Machining processes remove material from a workpiece to produce the required geometry, dimensions and surface finish. They are fundamental to mechanical engineering manufacture and are used both to produce complete components and as secondary operations following processes such as casting, forging and fabrication.
Conventional machining generally removes material as chips using a cutting tool and controlled relative motion between the tool and workpiece. Grinding removes much smaller quantities of material using abrasive cutting grains and is commonly used where dimensional accuracy or surface finish is particularly important.
The workpiece rotates while a cutting tool removes material. Turning is principally used to produce cylindrical, tapered, faced and related rotational features.
TurningMilling uses a rotating multi-edge cutter and controlled movement of the workpiece or cutting tool to produce surfaces, slots, pockets and complex features.
MillingDrilling produces holes using a rotating cutting tool. Associated hole-making operations can include reaming, countersinking, counterboring and tapping.
DrillingGrinding removes material using abrasive cutting grains and is widely used for producing accurate dimensions and controlled surface finishes.
GrindingShaping uses a reciprocating cutting tool to remove material progressively, principally for the production of flat surfaces, slots and related features.
ShapingPlaning is related to shaping but normally uses reciprocating motion of the workpiece relative to the cutting tool. It has traditionally been used for machining large flat surfaces.
PlaningSawing separates material using a multi-tooth cutting tool and is commonly used to cut bar, tube, plate and structural sections into blanks for subsequent manufacturing operations.
SawingModern machine tools use numerical control and automation to control tool paths, machine functions and repeatable production operations.
CNC & AutomationCutting-tool material and cutting-fluid selection influence tool life, cutting speed, surface finish, heat generation and machining economics.
Tools & FluidsMachining requires relative motion between the cutting tool and workpiece. Understanding which element provides the cutting motion and which provides the feed motion is useful when comparing machine-tool processes.
| Process | Principal Cutting Motion | Typical Application |
|---|---|---|
| Turning | Workpiece rotation | Cylindrical and rotational components |
| Milling | Cutter rotation | Faces, slots, pockets and profiles |
| Drilling | Drill rotation with axial feed | Hole production |
| Grinding | Abrasive wheel or tool motion | Precision surfaces and finishing |
| Shaping | Reciprocating cutting tool | Flat surfaces, slots and features |
| Planing | Reciprocating workpiece | Large flat surfaces |
| Sawing | Continuous or reciprocating toothed blade | Cutting stock and blanks |
The performance of a machining operation depends on the combination of workpiece material, cutting-tool material, machine-tool capability and the selected cutting conditions.
Important parameters include cutting speed, spindle speed, feed rate, feed per revolution or tooth, and depth of cut. These influence material removal rate, cutting forces, power requirement, tool temperature, tool life, dimensional accuracy and surface finish.
The cutting tool must retain adequate hardness and strength at the temperature and loading generated during machining. Tool material is therefore an important part of process selection.
RoyMech provides separate information covering cutting-tool materials:
Cutting fluids may be used for cooling, lubrication, chip removal and control of the machining environment. The required fluid and method of application depend on the machining process, tool and workpiece material.
Computer numerical control (CNC) allows machine movements and auxiliary functions to be controlled from a programmed sequence. CNC machining is now fundamental to modern manufacturing because it enables repeatable control of complex tool paths and coordinated machine movements.
Automation can extend beyond axis control to include automatic tool changing, workpiece loading, probing, inspection, pallet systems and integration with wider production systems.
CNC and Machine Tool Automation
The appropriate machining process depends on the component and the features which must be produced. Important considerations include:
Machining cost is influenced by much more than the volume of material removed. Component orientation, workholding, number of setups, tool access, tool changes, inspection and the required tolerances can dominate the manufacturing time.
Machining is frequently used after a primary manufacturing process. Castings may require machined bearing seats and mounting faces, forgings may require finished bores and journals, and extrusions may require holes, threads or local precision features.
The initial manufacturing method should therefore be selected with the subsequent machining route in mind. Providing suitable machining allowance, datum surfaces, tool access and reliable workholding features can simplify production considerably.
The following external resources were included on the original RoyMech page and provide additional information relating to machining and machine shop practice.