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CNC Machining Inspection Standards


CNC Machining Inspection Standards

1 Purpose

To standardize the processing and inspection criteria for CNC machined products and to provide a reliable basis for adjudicators.

2. Scope
Applicable to the reliability verification and appearance inspection of CNC machined workpieces of our company and outsourcing factories

3 Inspection items and definitions

3.1 Tool pattern: the pattern resulting from tool wear or oscillation, usually tactile and wave-like.

3.2 bruising: collision or drop stroke collapse shape due to improper handling.

3.3 porosity, trachoma: irregular hole-like defects or honeycomb-like black spots formed due to insufficient casting density.

3.4 abrasion: due to improper operation of the product friction formed strip defects, or due to the tool with residual cutting waste formed spiral line defects.

3.5 segmental differences (steps): due to poorly bevelled tool paths, forming step-like defects.

3.6 burrs: due to the radial force of the tool resulting in local cutting waste not detached from the workpiece to form jagged or strip defects.

3.7 missing material: due to excessive cutting force after tool wear resulting in chipping or missing flesh at weak points of the product.

3.8 rotten teeth: due to small or large tapping base diameter, skewed bottom hole, taps wear resulting in local disorder of threads, no threads, tooth shape does not match

3.9 Crushing: impurities are pressed into the product as a result of cutting residues in the machining tool or by external forces, resulting in a sunken defect.

3.10 Cracking: tearing defects at weak points due to insufficient casting density or excessive cutting forces caused by tool wear.

3.11 poor cutting: due to the product in the jig fixed position offset or tool relative coordinates change caused by cutting too much or too little; including overcut or undercut, where undercut is also called more material.

3.12 hole deviation: due to improper positioning or skewed reinforcement column, or even uneven shrinkage of the die-cast product resulting in deviation of the hole position from the centre of the reinforcement column where the hole is located.

3.13 bad chamfering: due to assembly or safety factors on the sharp edge of the product process chamfering, if there are no special requirements in accordance with C0.2 ± 0.1 control, thread chamfering shall ensure that the tapping phi is not higher than the top surface of the screw column (i.e., the height of the phi should be lower than the height of the chamfer), bad chamfering is divided into two conditions: a, chamfering is too large, due to the tool or program control there is too deep eating knife, resulting in chamfering is large or chamfering is small. After chamfering, there are sharp edges or flanged edges; b. Uneven chamfering (chamfering small and large edges), due to product deformation or fixture clamping there is loose, resulting in chamfering width there are irregular shapes, fixture clamping loose often accompanied by vibration knife pattern.

3.14 Flat (shallow) threads: The threads are tapered when viewed visually because the thread bottom hole is too large, resulting in slippage or insufficient torque.

3.15 Structural discrepancies: the product does not match the 3D inventory, often due to over- or under-materialization or a discrepancy in the roundness of the hole (shaft or column).

3.16 Deformation: Due to the influence of the workpiece material, the thickness and toughness of the workpiece change after machining, which changes the original shape of the workpiece, resulting in an uneven or distorted product shape.

4 Judgement method

4.1 A-level surface: the surface of the product directly exposed after assembly, usually speaking of the appearance of the surface

4.2 B-grade surface: the surface of the product that is not directly exposed after assembly but can be directly observed after rotation at a certain angle

4.3 Class C surfaces: surfaces that are not directly exposed after assembly and that can be observed only after the removal of certain parts.

4.4 Linear class defect judgment method
Length * width * depth * number
L *W *H *N

4.5 Hole-like defects
Area * Depth * Number
A *H *N

5 CNC machined workpiece inspection criteria

CNC workpiece acceptance criteria and defect levels

Inspection itemsAcceptance criteria Inspection tools and methodsDefect descriptionDefect level
Appearance No scratches, colour differences or bruises on the surfaceCaliper drawing hand feel plug gauge Fine scratches, colour differences, bruises
No dents, sand holes, knife scratches, impurities on the main view surfaceDents, sand holes, knife scratches, impurities on the main view
Two other (left, right or top and bottom) sides with 0.1mm diameter dents, sand holes, impurities
No fracture, perforation or missing material on all parts of the productFractures, perforations, missing material
All edges must be of uniform thicknessUniform thickness on all edges
If there is a brushed pattern, it must be clear and consistent in directionUnclear and inconsistent drawing pattern
All holes and edges are free of prickly burrsPrickly burrs at each hole and edge
Structural performance reliability Dimensions and tolerances are in accordance with technical requirements and do not affect assemblyNot in accordance with technical requirements
Clear tooth path, good fit and seal (gap) less than 0.1mmDifficult assembly and sealing (gap) greater than 0.1mm
No deviation, penetration or leakage of holesHole position is off, punched through or missed
The flatness of the upper and lower surfaces is less than 0.3mmFlatness of top and bottom surfaces greater than 0.3mm
No air holes are allowed on secondary surfaces after machiningAir holes on secondary surfaces after machining

CNC Machining Standard

Serial number Inspection contentInspection standards
1Finishes1、Split surface and material position surface processing fan height h≤0.001mm; 2、avoidance of empty position surface processing fan height H=0.003mm-0.005mm; 3、flat processing without obvious scratch round knife pattern; 4、finishing surface without obvious bullet knife pattern; 5、no water ripple after surface bare knife; 6、inlet point into the knife mark grade difference ≤0.02mm; 7、R angle bit processing smooth, no No stepped cutter pattern.
2Joint marksThe grade difference of the jointing position is ≤0.02mm when the workpiece is processed
3Corner clearance1、Finishing part without popping tool marks, smooth and excessive; 2、Finishing part with ≤0.02mm grade difference in the joint position; 3、Leaving EDM part according to the tool length-diameter ratio of 1:5 to clear the angle.
4Machining allowances1、Light in place ≤ 0.02mm; 2、Insert through surface in the convex side stay ≤ 0.05mm; 3、To be EMD bit ≤ 0.15mm, horizontal bottom surface ≤ 0.05mm; 4、Deep cavity open rough bit ≤ 0.35mm
5Data inspection1、Processing error ≤0.03mm (single side); 2、Location tolerance ≤0.03mm
6Degree of finish1、Complete all items required by CNC program sheet; 2、Additional items required by drawings

CNC machining workpiece appearance inspection standard

Inspection itemsNoodle categoryQualifying rangeRemarks
Knife patternANGThe chamfer can have a uniform vibration pattern that is not perpendicular to the direction of processing by hand
BNo feel is OK, no significant difference from the substrate, no water ripples
CSlight handfeel allowed, does not affect structure OK
bruising and crushingAA≤0.05;H≤0.05;N≤1Single face rule; no more than 2 defects in total on a single product
BA≤0.1;H≤0.1;N≤1Single face rule; no more than 2 defects accumulated in a single product
CA≤0.5;H≤0.2;N≤3Single face rule; no more than 5 defects accumulated in a single product
ScuffsAL≤1;W≤0.05;H≤0.05;N≤1Single face rule; no more than 2 defects accumulated in a single product
BL≤2;W≤0.1;H≤0.1;N≤1Single face rule; no more than 2 defects accumulated in a single product
CL≤3;W≤0.3;H≤0.2;N≤2Single face rule; no more than 5 defects accumulated in a single product
Pores and trachomaAA≤0.05;H≤0.05;N≤2Single face rule; no more than 3 defects in a single product
BA≤0.1;H≤0.1;N≤3Single face rule; no more than 3 defects in a single product
CA≤0.5;H≤0.2;N≤4Single face rule; no more than 5 defects accumulated in a single product
CH ≤ 0.02 and no influence on the actual assemblywhere H is the height of the segment difference
Missing materialANG

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