Customized CNC machining has some of the most advanced equipment and cutting-edge robot technology. It uses G code and M code for programming, which helps in precise and repeatable manufacturing of parts. In addition, specific components require strict specification tolerances, all of which can be achieved through customized CNC machining processes. However, the next question that arises is how to test complex CNC components?
Stress Testing: The Basic Stage of Quality Assurance
The CNC workshop adopts the most advanced testing tools as its quality management system. Some typical tests include micropore testing, CMM inspection, hardness testing, surface finish testing, etc. These tests comply with ISO 9001:2015 and IATF 16949:2016 certification. However, CNC workshops must use different methods to test parts that contain pressurized fluid or gas due to defects such as pores (voids found in castings). Porosity can cause fluid or gas to leak out of components that should have pressure sealing properties. This type of defect can damage the performance of the component and may lead to internal corrosion or surface defects. It is necessary to actively search for such defects, especially in complex CNC machining parts. These components are completely assembled, including different components bound together.
When should you do a stress test?
Pressure testing is usually carried out after assembly, machining, or vacuum impregnation, which is a process of sealing casting pores and leakage paths with sealant under pressure. This approach helps to contain liquids and gases without leakage. The most common stage after conducting testing is assembly. At this stage, testers use poka yoke methods to determine the correctness of the assembly process and verify the quality of CNC machined parts.
This method allows you to validate the entire component through stress testing. According to customer requirements, if the customer requires the final parts to have extremely high accuracy, the testing may remain within the limit or reach 100%. The more tests, the higher the production cost.
Different types of pressure testing for complex CNC machine tool components
You can follow three basic methods for stress testing complex CNC components:
Air decay
Mass flow rate
Underwater air
1. Air attenuation
This method uses a pressure testing control unit to monitor changes in air pressure within the components. After firmly clamping the parts into the fixture, fill them with compressed air. The pressure is usually between 5 psi and 90 psi and varies with the aperture inside the part. The most commonly used air pressure value is 20-25 psi.
Once the air molecules stop moving, after about 30 seconds, measures will be taken to calculate the pressure drop and whether the value meets the customer's expected specifications.
The complexity of machined parts directly affects the time required to perform testing. If the volume of the processed parts is large and the customer's expectations for accuracy are high, the testing may take a few minutes.
Some practical examples of air decay include the intake port of an engine or an engine housing containing oil.
2. Mass flow rate
Similar to air attenuation, mass flow introduces air into the part at a range of approximately 20 psi. This method uses a pressure gauge to monitor the pressure, which indicates when the part is fully filled and the pressure is 20 psi.
When the processed part reaches a point where no more air can enter, you will notice that the reading on the instrument is zero. If air escapes through the air hole, you will obtain a reading from the pressure gauge indicating that the part is allowing air in, confirming the presence of a leak.
If the customer does not need the highest possible performance specifications, then zero on the instrument may not be the ultimate goal. Usually, a small leakage rate of approximately+5 sccm (standard cubic centimeters per minute) is acceptable.
3. Underwater air
Underwater air is a seamless and accurate testing method because it relies on visual observation rather than pressure gauges to perform pressure tests. This approach is simple to implement and has the characteristic of easy leak detection.
Immerse all inflatable components with sealed openings into the water tank. Inspectors search for bubbles, which can be small or large. These bubbles reach the water surface, indicating a leak.
Considering that this test relies on visual inspection, underwater lights need to be installed to ensure optimal visibility.
