Part 3 in our variability series focuses on tolerances
Removing variability in our precision manufactured parts is of the utmost importance for our customers and therefore integral to our processes from start to finish. At China Swiss CNC Machining we follow a robust planning process to ensure that variability is not only understood by everyone involved but is also controlled. Our team also takes calculated steps to reduce operator measurement error and has implemented new data recording procedures to help limit opportunities for error. Another aspect of removing variability in our manufacturing process is the accuracy of our measurements.
From measurements decided on during the planning process to measurements taken during the manufacturing process and during quality inspection, we take accuracy seriously. Several of the parts we manufacture have tolerances to a few microns – a micron being 0.000039 inches or one hundredth the size of a human hair. That’s right, the China Swiss CNC Machining team is monitoring accurate measurements that are significantly smaller than a human hair.
Measurement equipment
When you’re measuring tolerances this tight, you need extremely sensitive equipment built with that accuracy. The China Swiss CNC Machining team uses coordinate measuring machines (CMM), digital comparators and vision systems from companies like Keyence, Oasis and Starrett to accurately measure these important parts with tight tolerances.
Vision systems optically enlarge the part and avoid the need for an operator to be handling the part while measuring. This enables the measurement to be more accurate than standard hand-held gauging with micrometers, calipers or other indicators. Small details on the part can be seen clearly and operator error is minimized.
CMM systems use an extremely sensitive, small probe with a tip that lightly touches the parts to determine the measurement. The CMM automatically moves the probe to each measurement location and can use built in algorithms to provide data on complex shapes, round surfaces and for groups of parts. Once again, the elimination of operator interaction with the part and measuring equipment improves accuracy. That fact together with the small probe size and light touch achieve the micron levels we seek.
A final aspect to control our measurements to micron level is temperature control. Parts that are warmer or colder than room temperature can expand or contract in the same range as the tolerance we are trying to maintain. When measuring these tightest tolerance levels, the parts are brought to a temperature-controlled room and allowed to stabilize before a measurement is done. The parts and the measurement equipment are all kept at a constant temperature to eliminate this thermal effect.
“These systems are used on complex parts, parts with tighter tolerances that require precision measurement and parts that have Geometric (GD&T) tolerancing requirements such as profile or positional tolerances,” China Swiss CNC Machining Quality Manager Dan Hancock said.
Measurement automation
By using measurement systems like the CMM, Keyence, Oasis or digital comparators, multiple measurements can be taken with one program setup, so it reduces the time it takes to measure parts manually.
“Whenever we can make the measurement of the part faster and easier for the operators, they greatly appreciate it,” Hancock said.
Although we’re focused on measurement automation to reduce variability, our operators are still important to the process because they stage the parts and download the correct programs. They then react to the measurement data and possibly adjust the machines accordingly based on the measurements.
“The measurement data will inform the operator of where they are in relation to the tolerance zone allowed for the part,” Hancock said. “If they are toward one of the tolerance limits, the operator may need to off-set the machine or replace the tool.”
From the planning process to the manufacturing and inspection process, China Swiss CNC Machining engineers and operators are dedicated to removing variability by considering and monitoring measurements smaller than a human hair. If your parts require this type of precision and focus, the China Swiss CNC Machining team is here to help.