Precision Manufacturing Glossary

An electrochemical process that grows a controlled aluminium oxide layer on aluminium, increasing corrosion resistance, wear resistance and providing a dyeable surface.

Type II anodising produces 5 to 25 µm coatings; Type III (hard) produces 25 to 50 µm. The coating grows roughly 50% outward and 50% inward, so a 20 µm coating adds about 10 µm per surface — enough to consume the tolerance on a precision bore.

Raised material left at the edge of a cut or drilled hole, formed when the tool plastically deforms rather than shears the material at exit.

Cross-holes intersecting a bore create internal burrs that cannot be reached by hand deburring. Options are abrasive flow machining, thermal deburring, or designing the intersection to be accessible — decided at DFM, not after machining.

A control system that executes machine movements from a coded program of coordinates, feed rates and spindle speeds rather than from manual handles or cams.

A CNC machine does not interpret a drawing. A CAM programmer derives toolpaths from a 3D model, posts them to machine-specific G-code, and the controller executes them. Positioning accuracy on production machining centres is typically ±0.003 mm.

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A statistical measure of how well a stable process fits inside its tolerance band, accounting for both spread and centring. Calculated as the lesser of (USL − mean) or (mean − LSL), divided by 3σ.

Cpk 1.33 corresponds to roughly 63 defects per million opportunities. Automotive customers typically require Cpk ≥ 1.33 on critical characteristics and ≥ 1.67 on safety-critical ones. A valid Cpk requires at least 125 consecutive parts from stable production.

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The practice of reviewing a design against the constraints of a specific manufacturing process before release, to remove features that force extra setups, special tooling or unachievable tolerances.

A DFM review typically returns 3 to 8 actionable changes per part. The highest-value findings are usually tolerance over-specification and internal corner radii smaller than the available tooling.

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A complete dimensional and material verification of the first production part against every requirement on the drawing and specification.

In aerospace, FAI follows the AS9102 format. An FAI report should list every drawing dimension with its measured value, not a pass/fail column — a pass/fail column can be completed without measuring anything.

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A symbolic language defined in ASME Y14.5 and ISO 1101 that controls form, orientation, location and profile relative to defined datums, rather than controlling size alone.

GD&T usually reduces cost because it permits variation where variation does not affect function. Position tolerance at maximum material condition, for example, grants bonus tolerance as a hole departs from its maximum size.

A unique identifier assigned to a single melt of metal at the mill, used to trace chemistry and mechanical properties from the mill certificate to the finished part.

Heat-number traceability is required for medical, aerospace and automotive safety parts. It allows a material problem to be isolated to specific parts rather than an entire production history.

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The ratio of the neutral axis position to material thickness in sheet metal bending, used to calculate the flat pattern length required to produce a formed part.

K-factor typically ranges from 0.33 to 0.50 depending on material, thickness and bend radius. An incorrect K-factor is the largest single cause of sheet metal rework, because the error appears only after forming and cannot be corrected on the flat part.

A driven tool held in the turret of a CNC lathe that rotates independently of the workpiece, enabling cross-drilling, milling and slotting without moving the part to a second machine.

Live tooling removes one setup, which typically saves 2 to 3 days of schedule time and improves accuracy because the milled feature and the turned diameter share a single datum.

The volume of material cut per unit time, usually expressed in cm³/min, calculated as radial depth of cut × axial depth of cut × feed rate.

Typical roughing rates are 5 to 15 cm³/min in aluminium and a third of that in steel on a 3-axis machining centre. MRR is the main determinant of cycle time and therefore of cost at production volume.

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A blank produced by forging, casting or extrusion that is close to final geometry, minimising the material that must be removed by machining.

Machining cost tracks removed volume, so a near-net forging can cut cycle time by 40 to 60% on parts that would otherwise require 70% or more material removal from billet.

An automotive submission package that demonstrates a manufacturing process can consistently produce parts meeting specification, submitted at levels 1 through 4 depending on customer risk classification.

A PPAP package includes process flow, PFMEA, control plan, MSA, dimensional results, material and performance test results, and initial process capability studies. Preparation typically adds 5 to 10 working days before first production shipment.

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A chemical treatment, typically nitric or citric acid, that removes free iron contamination from a stainless steel surface and restores the chromium oxide layer that provides corrosion resistance.

Any machined 300-series or 17-4PH part should be passivated, because machining embeds free iron that becomes the initiation site for pitting. Free-machining grades such as 303 are the most susceptible due to their sulphur content.

The most common surface roughness parameter, expressing the average deviation of the measured profile from its mean line over the evaluation length, in micrometres.

Ra 3.2 µm is a rough machined surface, Ra 1.6 µm is standard finishing, Ra 0.4 µm requires a dedicated finishing pass, and Ra 0.1 µm generally requires grinding or lapping. Ra alone does not capture whether a surface will seal; Rz and Rmax often matter more for sealing faces.

A turning process where the workpiece is fed through a guide bushing and cut immediately adjacent to the bushing support, allowing very slender parts to be machined without deflection.

Swiss-type lathes handle length-to-diameter ratios of 10:1 and above on parts under Ø20 mm. On a conventional lathe, the same part would chatter, deflect and require multiple supporting operations.

The elastic recovery of material after a forming force is removed, causing the bend angle to open slightly beyond the tool position.

Springback increases with yield strength and thickness. CNC press brakes compensate by over-bending and measuring the angle in process; thin high-strength steel may require multiple corrective hits.

The total permissible variation in a dimension or geometric characteristic, expressed either as a bilateral range (±0.005 mm) or as upper and lower limits.

A ±0.005 mm callout permits 0.01 mm total variation, not 0.005 mm. Achievable tolerance depends on feature size, material, setup count and measurement temperature rather than on the machine specification alone.

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The full range of movement of a dial indicator over one revolution of a rotating part, used to specify runout and concentricity limits.

TIR is a double-sided value: 0.02 mm TIR means the indicator moves 0.02 mm total, corresponding to an axis offset of 0.01 mm. Misreading TIR as a radius value is a common source of over-tight specifications.

The system that locates and clamps a workpiece during machining, determining datum position, rigidity and repeatability between parts.

Workholding error, not machine error, is the dominant cause of out-of-tolerance parts on multi-setup work. Soft jaws suit low volume; dedicated fixtures pay back above roughly 500 units by cutting setup time to minutes.