Quality Control of the CNC Machining Process

CNC machining is a widely used manufacturing process to produce precise
and complex custom-machined parts for various industries, like aerospace, automobile, military, medical, commercial electronics, optical, etc.

CNC machining has the advantages of accuracy, high efficiency, and flexibility,
but it is not perfect, strict quality control measures are required, in order to
ensure that the finished parts meet the specifications and are free from defects.

In this article, we will discuss the importance of quality control in the CNC machining process, as well as some of the key factors involved.

Quality control of the CNC machining process.

Importance of Quality Control in the CNC Machining Process.

Quality control is an essential aspect of CNC machining. It ensures that the finished products meet the required specifications and are free from defects. 

CNC machines are capable of producing parts with high accuracy and precision, but even minor errors or defects can compromise the quality of the final parts. 

Quality control measures help to identify and correct the errors or defects in the machining process, ensuring that the finished parts are of high quality and meet the required standards.

Factors Involved in Quality Control of CNC Machining Process.

There are several factors involved in the quality control of CNC machining process, including:

  • Incoming Quality Inspection of the Raw Material: 

Although many people tend to associate quality checks with the final stage of the production process, it is important to implement quality control measures from the beginning as well. 

If the material errors are identified from the finished parts, it is too late to prevent the waste and recover the cost. 

CNC machine is an accurate system, it can produce the custom machined part according to the input program, but it can’t identify the raw material quality, if low-quality or defective materials are chosen, the finished machined part will be out of specification. 

So, it is essential to do the incoming quality inspection of raw material before machining, to catch the material defects, like cracks, and correct them at the beginning of the manufacturing process.  

  • Selecting the Appropriate Machine:

Selecting appropriate machines will help to make a good quality part in the machining process. For example, if it is a CNC turning machining part, but a milling machine is chosen to produce, it may not be able to meet the desired accuracy, as well as inefficient. 

The wrong machines can cause errors or defects in the finished part. Therefore, it is essential to select the suitable machines for the specific machining process. 

  • Machine Calibration: 

It is important to calibrate CNC machines regularly to ensure that they are operating within the required tolerances. 

Calibration involves checking and adjusting the machine’s errors of linear displacement, vertical straightness, horizontal straightness, angular, and squareness, to ensure that it is operating at the desired level of accuracy
and precision.

  • Cutting Tool Maintenance: 

Cutting tools need to be maintained regularly to ensure that they remain sharp and in good condition. Blunt or damaged cutting tools can cause inaccuracies and defects in the finished product.

  • In-process Inspection: 

In-process inspection is a critical component of quality control in CNC machining.

Using the In-process inspection can help to identify the errors as they occur in the producing stage, then the manufacturers can take action to correct the problems to ensure the part quality. 

The In-process inspections are implemented in real-time, which helps to catch and correct the errors in time, avoid last-minute delays, and prevent waste. 

Usually, there are three types of intervals for In-process inspection, which
are time-based intervals, quantity-based intervals, and free intervals, the manufacturer can determine either or a combination of those three intervals to schedule the In-process inspection.

  • Final Inspection:

The final inspection is a very important quality control step in the CNC machining process. 

It helps to find out the non-conformity which hasn’t been found in previous stages of the machining process. 

Therefore, ensuring that the finished parts meet the required specifications and are free from defects before shipping to the customers. 

  • Documentation: 

Documentation is an essential aspect of quality control in CNC machining. It involves keeping accurate records of the machining process, including the dimensions, tolerances, and other specifications of the finished product.


Quality control is a crucial aspect of CNC machining, ensuring that the finished products meet the required specifications and are free from defects. 

To achieve high-quality output, the manufacturer may need to calibrate the
CNC machines regularly, select appropriate CNC machine tools , 
and inspected teh 
cutting tools regularly, and apply the necessary inspections 
in different stages of the production cycle. 

Additionally, documentation of the entire machining process is essential to
ensure that the quality control measures are effective and that the finished
parts meet the required standards.