With the continuous progress of modern technology, the demand for quality and precision is getting higher and higher. CMM is playing an irreplaceable role in many aspects such as precision test, product quality control, new product development, process flow control, mould manufacturing, working efficiency improvement and quality control approaches. The common concern of the broad users is how to select proper CMM and how to generate higher economic benefits and service value. The following notes should draw your attention in selection and purchase of CMM:

The goal of quality control for the manufacturing industry is to keep the part production consistent with the design requirements. However, the consistency of production process requires to control the manufacturing process. The most effective method to set up and maintain the manufacturing flow consistency is to correctly measure the workpiece dimensions to acquire the dimension information, make analysis and then report the data to production process to enable it to be an effective tool to continuously improve the product quality.

CMM is one of the most effective methods to measure and acquire the dimensional data because it can replace various surface measuring tools and precious combined gauges as well as reduce the measuring time from hours to minutes and quickly and correctly assess the dimensional data to provide useful information about productions to operators.

CMM is one of the most effective methods to measure and acquire the dimensional data because it can replace various surface measuring tools and precious combined gauges as well as reduce the measuring time from hours to minutes and quickly and correctly assess the dimensional data to provide useful information about productions to operators：

1．【Proper measuring precision】

The first key point is to meet the requirements of precision. During the selection of machine, you should compare the measuring precision required by the measured workpiece and the measuring uncertainty given by the measuring machine. For the general measuring, the measuring uncertainty should be 1/3-1/5 of the dimensional tolerance range of the workpiece. As for the measurement of the precision parts or the complex shape and position, the measuring uncertainty should be 1/5-1/8 of the dimensional tolerance range. More importantly, the repeatability precision must meet the relevant requirements because system errors can be compensated by a given method while the repeatability precision depends on the machine. A good measuring machine should have high precision and high stability.

During the measurement for the complex parts, any change to the probe angle and measuring staff may cause slight errors. It is recommended that users select the measuring system with higher precision (including repeatability precision) so as to meet the further development needs of enterprises.

2．【Reasonable measuring scope】

Measuring scope is the basic parameter in selecting the measuring machine. The following three aspects should be considered in the selection of measuring scope.

Normally, the part to be measured may not be the whole workpiece. It should be considered that whether the part to be measured is within the measuring space of the measuring machine and whether the whole workpeice is fixed on the granite worktable. Under normal conditions, the measuring scope is selected according to the sizes of the workpieces.

Relations between Z column stroke and Z direction space height: Z column stroke is the measuring scope of the Z column while the Z direction space height is the height that holds the workpiece. Additionally, you should consider the space that Z column can measure after it is equipped with probe system.

Changes of measuring staff: occasionally, the probe is set up with the star-shape styli which may exceed the measured part of the workpiece during the measuring operation. If the size of the workpiece is 1, the measuring scope required should be L=1+2C, C refers to the length of styli or the lengthened staff. So, the measuring scope equals max. measured dimensions of workpiece plus double styli length.

3．【Proper measuring machine type】

The measuring machine can be categorized into manual (motored) and CNC (automatic) types according to the automation degree. In selection of the machines, you should consider the batch size of the measuring object, automation degree, product features, use frequency and efficiency.

4．【Measuring software system】

The advanced measuring system requires the measuring software to be more powerful in measuring functions, and easy to operate and able to meet some special measuring requirements. The following factors should be considered during the selection of measuring software：

●easy to operate and use (for example, Chinese operating interface , more convenient operating mode )

●Able to measure the parts with complex shapes and complex cambered surfaces

●graphics realization and flexible measuring report output functions with various data output formats

●Automatic feature identification functions

●off-line measuring / programming functions

●virtual simulation measuring, route planning and anti-impact functions

●Visualized graphics analysis functions and optimal combined assessment capability

●Visualized graphics analysis functions and optimal combined assessment capability

●Perfect assessment capability for shape and position tolerance

●Scanning functions for unknown geometrics

●3D data scanning and point cloud dynamic management which is visual and understandable

●Capability for reverse engineering

●dynamic configuration and visualized operation for probe system

●Intelligent programming capability

●Support various optional devices

●Special applications and support capability

5．【Measuring head system with complete functions】

Measuring head system is an important measuring part which directly affects the measuring precision, measuring functions and measuring efficiency. Currently, there are manual and automatic measuring head systems available which may be selected according to the actual measuring requirements of products.

6．【Control system】

Usually, the control system does not draw much attention of people. But, it has important central control function in the coordinate measuring system, which directly determines the whole system functions and moving characteristics. The data transmission also affects efficiency and stability of the measuring system. Additionally, whether the control system could support the expansion functions in the future is also very important.

7．【Compliant measuring efficiency】

The running speed of measuring machine is not only the important index of measuring efficiency but also the important reference of machine performance, which are both closely related to the automatic production. The measuring machine used for the production line or flexible processing line should have the measuring efficiency up to the pace of production.

The quantity of collection points determines the working efficiency of measuring machine on the acceptable uncertainty level. Some measuring machines could reach good measuring precision by collecting over 100 data points within one minute.

To sum up, as the measuring machine could replace the plane measuring tools, fixed or customized gauges and some manual precision measuring tools, it is able to provide sufficient guarantee for the modern manufacturing industry. Besides the dimensional data to be provided to the process control, the measuring machine could also provide incoming product test, lathe calibration, customer quality accreditation, gauge test, processing test, and lathe setup optimization etc. Many factors are to be considered in the investment on the fixed assets. In case of consideration for the improvement of production efficiency, cost reduction and putting the production under control, the measuring machine will be the optimal choice for the factory to control quality.