CNC Machining Quality Control: Strategies for Precision & Quality

21 November 2023
Quality Control in CNC Machining

Computer numerical control (CNC) machines have become standard fare in the machining industry. Their accuracy, speed, and ease of use make them indispensable tools for manufacturers. Yet nothing is perfect. Quality control remains an essential element in catching and preventing defects.

Although errors are much less likely with CNC machining than with traditional manual manufacturing processes, they can still occur. These errors can have significant knock-on effects, including bottlenecks, and waste materials, and can have damaging impacts on client-customer relations if not caught, due to poor quality products. However, these negative consequences can be mitigated by implementing an effective Quality Management System.

Taking this into account, here’s how manufacturers can improve their CNC quality control:

Choosing the Right CNC Machine Type

Not all CNC machines are built with the same capabilities, and manufacturers must bear this in mind when addressing quality control. Selecting the correct machine for a specific task is essential, as the use of the wrong machine for a task can lead to increased errors. Therefore, facilities need to be selective when assigning orders to specific machines. The complexity of a product or part is directly linked to the sophistication of the machine required.

A three-axis CNC machine, the most common choice for mechanical components, suffices for simpler designs. When dealing with more complex components or products, it is better to employ four- or five-axis machines. These additional axes give machines greater precision, enabling them to undertake more complex tasks without error.

Nonetheless, facilities should not exclusively rely on four- or five-axis machines. Striking a balance between different machines can help alleviate bottlenecks and maintain overall operational efficiency. When facilities distribute their workload, they should assign more complex designs to machines with higher axis counts.

Quality Control in CNC Machining: Material
Image: Kasper Gant

Inspecting Raw Materials Before Machining

Unfortunately, many in the manufacturing industry tend to view quality assessments as the concluding phase of the production process. Although final inspections are undeniably crucial, the pursuit of quality should come at an earlier stage. Detecting errors after machining has begun makes cost recovery impossible while initiating early inspections can prevent wastage.

One of the most pivotal measures for ensuring quality right from the outset involves examining the quality of the materials. CNC machines possess the capability to virtually eliminate human errors, but this becomes irrelevant if they operate with subpar or defective materials. Even an impeccably accurate system will yield substandard products when using inferior materials.

Therefore, employees must evaluate the quality of their raw materials before commencing work. Sourcing materials from reputable suppliers can alleviate numerous material-related issues, yet machinists cannot afford to take any risks in this regard. By diligently examining their materials for cracks, vulnerabilities, or other imperfections, workers can ensure that they harness the full potential of their CNC machines.

CNC plasma cutting
Image: Unsplash

Implement On-Machine Inspection

Quality control can also be integrated into the CNC machining process itself. Devices known as machine tool probing systems can be attached to CNC machines to inspect quality in real time as they operate. This on-machine inspection empowers facilities to promptly identify and address issues as they emerge, thus preventing errors in the final product.

Probing routines do not disrupt or interfere with the machining process, so they do not compromise efficiency. Instead, they automatically redirect machines to correct any issues they detect in real-time. By identifying and addressing errors at an early stage, substantial mistakes are averted, thereby reducing the number of defective or subpar parts in subsequent stages of production.

In addition to reducing scrap, on-machine inspection reduces the possibility of quality control bottlenecks. Given that machining time represents the primary cost driver in this field, optimizing efficiency in these operations is imperative. Tool probing systems mitigate the need for rework, shorten total machining time, and bolster consistency in quality by minimizing disruptions stemming from end-of-line quality checks.

Employ Multiple Quality Control Methods

Just as CNC machining itself is not infallible, neither are individual quality-checking methods Each has its distinct strengths and weaknesses and no single process can catch every conceivable error. To address this, facilities should embrace a variety of quality control methods to ensure that errors overlooked by one process do not pass further down the line.

The sequence in which quality control methods are applied is equally crucial. Human inspections should always be the final checkpoint, a principle that should be applied to all automation-reliant processes. Automated checks are highly effective, but technical glitches can impair their accuracy. Positioning manual inspections at the end of the production process can catch potential mistakes that might otherwise slip through.

It is essential to strike a balance, as an excessive number of different methods can potentially create bottlenecks. You can have too much of a good thing after all. Facilities need not implement every conceivable quality control method but should at least use more than one. As a general guideline, one material check before machining, one on-machine inspection procedure, and one human-driven post-machining inspection should suffice.

Quality Control in CNC Machining: Vendors
Image: Cytonn Photography

When Outsourcing, Seek Certified Vendors

Not all facilities undertake CNC machining in-house, but the importance of CNC quality control remains critical. To guarantee high-quality outsourced CNC operations, companies should seek vendors holding the requisite certifications. While specific certifications may vary by industry, all vendors should, at a minimum, adhere to ISO 9001, a comprehensive quality management certification.

For certain industries, manufacturers should also seek additional certifications. ISO 13485, for instance, signifies compliance with medical-grade product standards, rendering it essential for those in the healthcare sector. Similarly, ISO 16949 applies to automotive parts, so manufacturers in the transportation industry should collaborate with vendors who adhere to this standard.

While these certifications do not guarantee the prevention of 100% of potential errors, they significantly mitigate risk. Attaining these certifications demands stringent adherence to standards, making them reliable benchmarks for selecting quality production partners. Consequently, any facility outsourcing machining processes should possess an understanding of the relevant quality standards.

Reliable Quality Control 

An enhanced QMS not only reduces waste but also yields superior products. Consequently, companies can save costs and bolster their reputation among clientele. Neglecting quality management can have precisely the opposite effect, underscoring the critical significance of this facet in any machine shop operation.

By following these steps, machining processes can ensure that their quality control is both precise and efficient. This optimization allows them to fully harness the potential of these exceptional machines and distinguish themselves from competitors. CNC machining can prove a valuable resource, provided that the companies employing it adhere to rigorous quality control standards. (link to instant quoting)



Achieve peak CNC quality control by implementing these essential steps. Maximize the potential of your machining processes and distinguish your brand in a competitive landscape. Embracing CNC machining as a valuable resource hinges on companies upholding rigorous quality control standards.







To find out how AMFG can streamline your CNC Manufacturing processes with award-winning MES software, click here.




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