CNC Machining: Quality Inspection and Assurance

CNC Machining: Quality Inspection and Assurance

Whether the material is metal or plastic, CNC machining can create it for you. However, how do we evaluate whether the requirements of CNC machined products are met? This article will introduce HTM’s inspection specifications for CNC machined parts.

To achieve 100% qualified products through CNC machining, HTM sets the inspection specifications for CNC machined parts based on ISO9001:2015 and our years of experience. It serves as the machining and inspection standard for CNC machined products, providing reliable criteria for dimension verification and appearance inspection for QC engineers. Every quality inspector at HTM undergoes professional training before starting work. This is why our products have won the trust of customers worldwide.

Inspection Items and Definition of Common Defects in CNC Machining

  1. Cutting Marks: Marks caused by cutter abrasion or swing, usually tactile and with wave shapes.
  2. Crash: Subsidence areas that occur when there is a crash or drop due to improper operation.
  3. Air Hole/Sand Hole: Irregular pore-shaped defects or cellular black spots caused by insufficient casting density.
  4. Scratch: Strip defects caused by product friction during improper operation or spiral linear defects caused by residual cutting scrap around the cutter.
  5. Mismatch (Step): “Step” defects resulting from uneven jointing between cutting paths.
  6. Burr/Flash: Serrated or strip defects caused by partial cutting waste not separating from the part under the radial force of the cutter.
  7. Short Shot: Collapse or lack of material around the wear areas of the part due to excessive cutting stress after the cutter is worn.
  8. Thread Damage: Partial thread disorder, thread missing, or thread mismatching caused by a too small or large bottom hole for tapping, bottom hole skewing, or tap wearing.
  9. Crush: Sunk defects formed when cutting residues are left on machining jigs or external force causes impurities to be pressed into the product.
  10. Crack: Tearing defects caused by insufficient casting density or cutter abrasion resulting in excessive cutting stress.
  11. Defective Cutting: Excessive cutting or insufficient cutting (also known as excessive material) caused by the skewed position of the part being fixed or a change in the relative coordinates of the cutter.
  12. Hole Deviation: Hole position deviating from the center of the strengthening column where the hole is located due to improper positioning, a slant reinforcing column, or uneven shrinkage of die casted parts.
  13. Defective Chamfer: Chamfer the sharp edges of the part for assembly or safety purposes. If there are no special requirements on the drawing, thread chamfering should be controlled according to C0.2±0.1, and the tapping flash should not be higher than the top surface of the screw column (that is, the height of flash should be lower than that of chamfering).
  14. Threaded Flat (Shallow Threaded): Thread sliding or insufficient thread torque caused by a large screw bottom hole, and the thread presents a cone platform when visually inspected.
  15. Structure Mismatch: The product does not match the 3D drawing. Common mismatches include excessive material, missing material, and issues with the roundness of holes (rollers or pillars).
  16. Distortion: Changes in the thickness and toughness of the part after machining due to the influence of the part material, which alters the initial shape of the part and leads to uneven or distorted product shape.

Classification of Part Surfaces

   1.A Surface: The part surface that is directly exposed outside after assembling, generally referred to as the appearance.

   2.B Surface: The part surface that is not directly exposed outside after assembling but can be directly seen when rotated at a certain angle.

   3.C Surface: The part surface that is not directly exposed outside after assembling and can only be seen after splitting some parts.

Acceptance Standards and Defect Grades of CNC Machined Parts

Quality Inspection and Assurance

Standards for CNC machining process.

Quality Inspection and Assurance

Appearance inspection standards for CNC machining.

Quality Inspection and Assurance

FAQ

How to Ensure the Quality of CNC Machined Parts?

We will select appropriate CNC machines according to customers’ detailed requirements. Secondly, our QA team will inspect the raw materials and strictly control every step in the machining process to ensure that the machining is done as required. Then we will check the size and appearance of the product and confirm that it is 100% qualified before packing and finally deliver the parts to you. Therefore, you don’t need to worry about quality when cooperating with HTM.

Factors That Impact CNC Machining Quality

It mainly includes the precision of CNC machines used in processing, the technologies adopted in processing, the method of finishing treatment, and whether the quality control is standardized.

What is the CNC Machining Process?

Main processes: drawing auditing – technology evaluation – programming and verification – raw material purchasing and inspection – production and measurement of CNC clamps – CNC roughing – CNC precision machining – dimension measurement – post finish – appearance and size measurement – packing & storage – shipment arrangement – shipment following up – customer use following up (feedback).

Summary

Good CNC machined products cannot do without strict inspection standards, and especially cannot do without an experienced and professional CNC machining supplier. HTM not only has dozens of imported CNC machines but also has a strict and standard quality management system, which is the fundamental guarantee to ensure the quality of your products. Therefore, if you have any parts that need customized manufacturing services, send them to us. 

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Lily Zhao

Lily Zhao

Hello everyone, I'm Zhao Lili, the webmaster of cnchtm.com. You can call me Lili. I have more than 15 years of rich experience in the field of CNC machining. Our company is a professional company that focuses on precision CNC machining, the design and manufacture of peripheral equipment of CNC machine tools, the system integration and automation of equipment, and the precision machining of mechanical parts.

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