First, the measurement needs are considered
Each coordinate measuring machine has its own measurement uncertainty, and the higher the accuracy of the measuring machine is impossible to measure the true value of the product being measured, and what the manufacturer can do is to make the measurement indication and the true value of the product as close as possible, the closer it is, the higher the accuracy of the measuring machine. So how close are we going to meet our actual needs?
● For now, the general requirement of the measuring machine accuracy can not be greater than 1/3 of the tolerance requirements of the product under test, which is the current low limit requirements, if the tolerance requirements of the products we want to measure are 0.03mm, then the accuracy of the coordinate measuring machine can not be less than 0.01mm.
● MSA requirements: At present, many factories need to carry out MSA (measurement system analysis), so that the measurement system meets the entire production process, in the MSA, the specification requires that the accuracy of the measuring instrument cannot be greater than 1/10 of the tolerance requirements of the product under test. That is to say, if the tolerance requirement of the product we want to measure is 0.03mm, then the accuracy of the coordinate measuring machine cannot be less than 0.003mm. Of course, this requirement is more stringent for some enterprises, and even can not be achieved. For example, slow wire walking equipment, its processing accuracy is about 0.003mm, if the measurement equipment is selected according to the MSA regulations, then we need a measurement equipment with an accuracy of 0.0003mm, which is very difficult to achieve.
● Comprehensive consideration: then we must choose one of the above two cases when determining the accuracy of the measuring machine, and more often choose a position in the middle of the two to determine the accuracy. That is to say, if we want to choose the accuracy of E, the product requirements tolerance of D, then 0.1D ≤ E ≤ 0.33D can be.
Second, input cost considerations
The price of the coordinate measuring machine is determined by many aspects, under the premise of not considering factors such as service, generally speaking, the higher the accuracy, the more expensive the price, the larger the range, the more expensive the price. Enterprise production is for the purpose of profit, so we must consider the cost performance problem when the capital is invested. When the accuracy changes between 3um and 2um, the price basically changes little; When the accuracy changes between 2um and 1.5um, the price changes a little more dramatically; when the accuracy changes between 1.5um and 1.0um, the price changes more rapidly, and when the accuracy is less than 1um, the price changes have become very fast. This is because the smaller the accuracy, the higher the cost of improving the accuracy. Therefore, when we choose the accuracy, we can choose the equipment we need within the acceptable price range.
Third, the current accuracy of the equipment on the market
At present, the coordinate measuring machine on the market generally has a range of 1000mm and the accuracy of the equipment will be marked at 2um ~ 3um, and the cost of the measuring machine in this range will not change, that is to say, whether it is calibrated to 2um or 3um is generally determined by the manufacturer's ability. Therefore, the accuracy of the more common small and medium-sized coordinate measuring machines in the industry is generally marked as 2um, and this accuracy is also the first choice of the accuracy of the vast majority of users.
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