Inspection/Measurement Pages 87 to 92 Three Lessons Learned about On-Machine Inspection By Ronan Ye For quality control of CNC machined workpieces, many shops use a coordinate measuring machine (CMM) that checks a in-ished part’s geometry and ensures dimensions match the origi-nal design. A CMM identiies even the most marginal errors and allows the machinist to rework a faulty part. However, for a shop owner, the CMM is far from a perfect solution. While this kind of inspection provides security for the customer, it does not guarantee a high level of productiv-ity for the machinist. Identifying errors after machining means it’s already too late to recover costs. When a machinist must rework a part because the CMM returns a negative result, the value of that part diminishes by half. Twice the expected time is going into it, as well as twice the material. An alternative solution is on-machine inspection with a machine tool probing system itted to the CNC machine to set up parts and measure dimensions during and immediately after the machining process. 1. Ease CMM Bottleneck Restricting quality control to a CMM has signiicant draw-backs, and problems can escalate beyond simply doubling the labor time and material costs. In a busy shop, any given CNC machine will likely be assigned a new setup as soon as one set of parts are removed from the worktable. If the CMM rejects some parts later on, the machinist will have to wait for a machine to become available—or worse, interrupt another job—then set up the machine all over again. Rejected workpieces can slow down production, producing a domino effect that delays many jobs. Also, dependence on a CMM may result in long queues, as every job in the shop requires inspection from the same machine or group of machines. Incorporating inspection into the CNC machines themselves can ease the CMM bottleneck, because the inspection burden can be spread across multiple systems or, in some cases, handled wholly by the CNC machine. 2. Improve Efficiency Using a CMM is usually necessary for quality control, especially during precision machining, because it checks that workpieces meet geometric and dimensional speciications. On-machine inspection can work alone or in tandem with the CMM to make inspection—and the entire product cycle—more eficient. A machine tool probing system, mounted on the machine spindle or turret, provides numerous beneits to a shop. The sys-Image courtesy of 3ERP. During machining of this mask frame mold cavity, a probe can automatically realign the cutting tool and update offsets in reaction to changes in temperature. tem can be used to identify and set up workpieces and can mea-sure features during the machining cycle and immediately after, when workpieces are still on the worktable. A probing system can also monitor the surface condition of the workpiece and initiate automatic offset correction. Additionally, many probing rou-tines do not disrupt the machining process. Probes are useful because they catch signiicant errors early, which immediately reduces waste and reduces the chances of the CMM rejecting a part. 3. Increase Mold Accuracy On-machine inspection is a particularly valuable asset in the production of molds for injection molding and other mold-ing processes. Probes increase accuracy with machining cores and cavities, leading to better parts and less post-processing. Moldmaking can beneit from an on-machine probe before, dur-ing and after CNC machining mold components. Before machining, a probe can locate the workpiece, in addi-tion to determining part orientation and rotation. During machining, it can automatically realign the cutting tool and update offsets in reaction to changes in temperature. And before the part leaves the CNC machine, the probe can perform mold-speciic tasks, such as checking and verifying electrode condi-tion. Each of these functions increases the accuracy of mold production and consequently part quality. An on-machine inspection system for CNC machines can be highly valuable for all types of shops, as it can capture errors early, provide immediate feedback and automatic offset cor-rection, reduce inspection backlog, ease CMM bottleneck and decrease CMM sampling rate, total inspection time and scrap, while increasing productivity and machining accuracy. FOR MORE INFORMATION 3ERP / 3erp.com Ronan Ye, Managing Director, 3ERP 92 MoldMaking M g Technology y — — JU JULY 2021