As the industry moves away from manual inspection, CMMs have come to the forefront. Manufacturers rely on high-precision measurements with low error probability. These requirements can only be met by Coordinate Measuring Machines.
Use cases vary across different sectors, and so do CMMs. Choosing the right CMM is essential to gain profitable returns from the investment. The choice often comes down to the unique requirements of each manufacturer. Different classes of CMMs offer differing features and specifications.
Choosing the correct CMM can appear challenging, but we are here to simplify it. In this article, we discuss all the crucial details you must remember while selecting a CMM.
Important Criteria for Choosing CMM
Workpiece Size and Weight
CMMs are versatile devices, but they must be selected according to the nature of the workpiece they operate on. CMMs can have varying tolerance ranges, and the workpiece size can directly impact tolerance requirements.
Precision Requirements
Today, CMMs are used in many critical industries. In aerospace, they perform dimensional analysis on airfoils, turbines, and frames. They are crucial for quality inspection in automobiles. They also process delicate medical and electronic equipment. Manufacturers in different industries have specific precision requirements. Critical industries like aerospace and medicine demand micron-level precision. Other industries do not require such precision and may prioritize production capacity and throughput.
Measurement Speed
Before purchasing a CMM, you must comprehensively grasp your production volume and workshop output. Automated bridge-type CMMs can help synergize assembly line production. Portable arm CMMs are versatile and easy to install. Manual CMMs are slower and, therefore, may cost you valuable time and labor.
Measurement Environment
Your factory environment is critical because it determines what kind of CMM can be installed. For example, CMM manufacturers specify the maximum temperature and vibration their device can withstand. Conditions that exceed these criteria may result in higher measurement uncertainty. Many CMM manufacturers provide active or passive damping systems. Investing in them is a good idea if your factory conditions are less favorable.
Understanding the Basic Types of CMMs
Bridge CMM
Bridge CMMs are reliable, versatile, and industry-standard. They consist of a bridge-like structure over a stage area. The probe descends vertically from a cross-beam, attached to two movable pillars. Bridge CMMs are well known for their accuracy, productivity, repeatability, and automation capabilities. It’s one of the most common CMMs used in the automotive and aeronautical sectors.
Cantilever CMM
It is the original CMM design, featuring only one support pillar. The remainder of the body is similar to a bridge CMM. It offers less accuracy compared to the bridge CMM. Due to its open body, the cantilever CMM can accommodate a wider range of workpieces. It is ideal for workshops processing medium-sized and small-sized parts requiring low measurement uncertainty.
Horizontal Arm CMM
Horizontal arm CMMs have a movable support pillar that slides on a guide rail. The horizontal arm attached to this pillar is capable of two-dimensional movement. They can conveniently measure parts like sheet metal with much more length than thickness. They are commonly seen in shipbuilding, railways, and appliance industries.
Portable CMMs
Also known as articulated arms, portable CMMs are the most flexible. They can perform dimensional analysis straightaway on the workshop stage or the production line. Portable CMMs are easy to install and straightforward to set up. They have an extensive calculation range and are often used to measure heavy machinery. While they offer great value to particular workshops, it must be noted that they lack accuracy compared to other CMMs.
Gantry CMM
Gantry CMMs measure high-volume and heavy workpieces, such as those in the aerospace and automotive industries. Like Bridge CMMs, the probe head descends from a cross-beam. However, the cross-beam moves on guide rails attached to two rectangular frames. This apparatus covers the stage area. Gantry CMMs provide accurate measurements for bulky components. The only limitation is that these parts need to be transported to the Gantry CMM for measurement.
Consider the Technical Specification and Functions
Probe Type
The probe is a touch-sensitive stylus. It acts as the point of contact for the CMM. Multi-axis measurement is a common industry practice today. Elegant probe systems enable it. The most widely employed probe that you will find is the touch trigger probe. They trigger the measurement upon contact with the object’s surface. If you measure deformable objects, go for non-contact probes. Several non-contact probes, scanners, lasers, and multi-sensors are available.
Software Compatibility
Computing systems in modern workshops often employ CAD or CAM software. Is your CMM software compatible with the rest of your production environment? It is definitely a vital consideration. Planning the revamping of software infrastructure can prove to be a substantial hidden cost.
Automation Level
Automatic CMMs are witnessing increasing demand. They feature autonomous measurement and quality inspection. Driven by software and machine vision, they reduce the dependence upon human operators. If you want real-time processing on the assembly line, investing in automatic CMMs is an excellent idea.
Calibration and Maintenance
According to the manufacturer’s recommendations, conserving and caring for your CMM is vital. To calibrate a CMM, its measurements are cross-checked against a standard artifact of known dimensions. Just like other measurement devices, CMMs must undergo regular calibration. It is one of the biggest ways to keep errors and uncertainty within acceptable limits.
Budget and Cost Analysis
Initial Purchase Cost
CMMs require a more substantial initial investment than other measurement systems. Bridge CMMs can start from $20,000 onwards. Portable CMMs vary from $10,000. Large capacity Gantry CMMs can cost up to $1 M.
Long-term Operating Cost
The long-term operational cost of a CMM can be divided into energy consumption, maintenance, and training costs. Regular servicing is advisable when dealing with complex machines like CMMs. Software upgrades and licenses can also incur a hidden cost.
Return on Investment (ROI)
When chosen correctly, CMMs provide the greatest return on investment among all measurement devices. They can reduce labor, inspection time, and measurement errors. They have a twofold benefit – accelerating production pipelines while enhancing quality inspection. Therefore, CMMs lead to long-term savings.
Choose a Reliable Supplier
Securing the services of a reliable supplier can go a long way to making your journey smoother. Accredited manufacturers assist their customers in choosing the appropriate machine. They provide detailed instructions and operating procedures to increase productivity and longevity. Availing technical support from the manufacturer is recommended due to warranty reasons. CMMs are highly modifiable machines, and suppliers often provide additional customizations. We recommend using authentic measurement probes, damping components, and machine parts with your CMM.
Testing and Verification
Trial Machine
We recommend availing a trial for the CMM you want to purchase. It will give you a comprehensive idea of whether it suits you. Manufacturers often have trial and demo options on their websites.
Reference User Evaluation
By evaluating past customers’ experiences, you can understand the pros and cons of a CMM. We recommend thoroughly analyzing customer reviews and industry feedback before purchasing a CMM.
Verify Accuracy and Stability
ISO 10360-2 describes the maximum acceptable uncertainty and testing procedures for CMMs. Always ensure your CMM supplier adheres to this standard or provides an alternative like CMMA or JIS. Compare different CMMs by looking at the specification sheet.
Conclusion
Let’s summarize the key takeaways for you when selecting a CMM. The first is to be sure of your requirements. What is the volume and mass of your workpieces? Your CMM must be able to handle them. You must also keep in mind the desired accuracy. If you use additional probe tips or attachments, the accuracy of the CMM may diminish. Therefore, grabbing a CMM with higher accuracy than your minimum error margin is a good idea. Factory environment, supplier reliability, operational cost, and measurement speed are also critical considerations. MXP Production offers CMM machines and we are ready to help you. Contact us today.