Portable CMMs Go to Inspection Source

Quality Magazine cover story, November 2010

 Discover how rapid shop floor inspection makes quick work of Quality. By Ron Branch

 For the machine shop that supplies the aerospace industry, portable coordinate measuring machine (PCMM) and model based definition (MBD) are everyday terms that are integral parts of its daily inspection routines. In the effort to drive quality and control processes, aerospace OEMs have altered the inspection methodology and the tools of their entire supply chain. Many of these suppliers are small- or mid-sized machine shops that have invested in inspection hardware, software and processes to satisfy strict quality standards. With the success of these supply chain efforts, portable CMMs and the model based definition inspection technology are expected to spread to all industrial segments. Now, it would appear that these new inspection tools and processes would place a big burden on the machine shop while benefitting only the aerospace manufacturer.

It is true that this approach to quality control and inspection does demand more than what the usual assortment of hand tools and gages can deliver. It places much more emphasis on CMM-based inspections, which could mean a big investment in quality control. However, the new quality practices actually benefit the machine shop, fabricator or tool maker and it costs a lot less then they might expect. By deploying PCMMs to the shop floor, these small businesses are realizing gains without staffing up in the quality control department. These companies are performing thorough and accurate measurements quicker than previously possible. They have adopted a convenient and efficient measurement process that covers everything from incoming inspection through final part inspection. And they have gained greater control over their processes. So, how do these small shops respond to the demands of aerospace manufacturers and realize all of these advantages? They have adopted a rapid shop floor inspection approach: taking 3-D measurements on the floor at the source for immediate feedback and reporting against the engineering quality specifications.

The Tools

There are three items needed to implement rapid shop floor inspection: hardware, software and engineering data. To conduct inspections on the shop floor, a PCMM is needed. Although there are several options, the common PCMM choice for the small machine shop is typically an articulated arm with a positive contact probe. Temporarily mounted on any rigid surface, these lightweight devices are easily transported anywhere in the shop. Arms have joints that let the machinist extend and rotate the measurement probe into every channel, bore or pocket. With a reach of 2 to 12 feet, the arms do not have physical size limits common with stationary CMMs. These features make them versatile inspection tools. The second component of a rapid shop floor inspection system is the software that receives all of the information from the arm. In the most basic mode, the software will log and report measurements taken with the arm. However, the big gains in time and efficiency happen when the software’s full functionality is leveraged. For example, the software will create prompted inspection plans as datums and features are selected while in teach mode. It also will provide real-time inspection data with visual, on-screen references. To expedite the inspection process, it can import a computer-aided design (CAD) reference model for direct comparison of the manufactured part to its design intent. Since the arm will be used in a variety of applications, the software will allow the operator several modes of operation: