For most measurement workers in the CNC machine shop, the coordinate measuring machine (CMM) is not strange. CNClathing.com uses our CMM machines every day to take the inspection and verification on product from CNC machining and other processes, for making sure each part be produced in the right dimensions and geometries. This is one of the methods we carried out to ensure our products are qualified and meet the customer requirements. Follow us to learn about what is coordinate measuring machine and how does it work, plus the types of CMMs and applications.
A coordinate measuring machine, also known as CMM, is a device uses a sensitive electronic probe to measure the geometry of physical parts through sensing discrete points on the surface of objects. The purpose is to test if the part is conforming to the required specifications. A coordinate measuring machine is usually composed of the main structure (includes X, Y and Z axes), probing system, data collection, and reduction system. A combination of granite and aluminum is the widely used material of CMM due to the stiffness to weight ratio. There are many types of probes that can be used in CMM, like mechanical, optical, laser and white light. The position of probes can be controlled manually or automatically (CNC). CMM can offer accurate inspection results for complex parts in a short time.
Three axes (X, Y and Z) form the coordinate system, the CMM machine typically specifies the position of a probe according to its displacement from a reference position in the three-dimensional Cartesian coordinate system, and move the probe along the three axes. Each point on the part is unique to the coordinate system of the machine. It also allows the probe angle to be controlled to measure some odd surfaces. In the CNC machine shop, the collected points are used to create a point cloud outlining the shape of the part, so as to confirm the measurement of the final product against the CAD design provided by the customer, and tell the part quality of the CNC machining services.
Before choosing a CMM machine, you need to know about the different types of measuring machine. All CMMs have three orthogonal axes, X, Y and Z, but in varying structures.
1. Bridge CMM Machine
The bridge-type coordinate measuring machine is the most popular style. The typical 3D bridge CMM machine allows the probe to move along X, Y and Z, which are orthogonal to each other, each axis has a sensor for monitoring the probe position, usually with micrometer precision. When the probe contacts the object, the machine samples the three sensors, then measuring the location of one point on the surface. And repeat the process until generating an area that describes the surface. Bridge machines offer better accuracy than other types of coordinate measuring machines and have a low cost and ability to maintain accuracy and repeatability.
2. Cantilever CMM Machine
Cantilever machines are usually used for the measurement of relatively small parts, and gauges, master parts as its high accuracy and low measurement uncertainty, providing open access to the operator on three sides. The X-axis measuring beam is attached on the side of a rigid structure housing the Y-axis, which limits the size of the X beam. Large support base combines with low weight enables Cantilever coordinate measuring machine moves fast. The cantilever type machine also has good capability of automatic loading and unloading.
3. Gantry CMM machine
Gantry type coordinate measuring machines have similar structures to bridge machine, but it’s primarily used to measure large and heavy parts. Most gantry machines are directly mounted on the floor, which is safe setup allows the programmer to easily walk up to the part and make the operation more conveniently. The operator can access the machine in unrestricted, make small features that can be measured carefully. In addition, the surface plates for smaller components are easily inserted into the gantry machine, decrease the difficulty of measurement and complexity.
4. Horizontal Arm CMM Machine
Horizontal Arm type machine has a different configuration where a vertical column (X-axis) and a horizontal arm (Z) mounted on a saddle that runs vertically up and down the X-axis. The Y-axis is the length of a surface plate or a long beam. There are two basic types: plate mounted and two runway mounted. Horizontal arm CMM offers a lower accuracy than the three above CMMs, but it is useful for measuring large surfaces or difficult to reach features including large thin-walled/sheet-metal type components mounted in fixtures that represent car body position, like car door.
Modern coordinate measuring machine can not only complete various kinds of complex measurement under the control of the computer, but also can control the machining by exchanging information with CNC machines, and realize reverse engineering according to the measurement data. CMM has been widely used in the measurement of the machined parts and accessories applied in mechanical manufacturing, automobile, electronics, aerospace, military and defense, furniture, and tool prototype; the box, frame, gear, cam, worm wheel, worm, blade, curve, curved surface, and more in molding industry; as well as hardware, plastic and other fields to measure the size, shape and position tolerance of the workpiece, so as to complete the parts inspection, shape measurement, and process control, it’s the indispensable measuring equipment for modern precise inspection and quality control.