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Inspection/Measurement 38 MoldMaking Technology April 2015 variations in the radius and transmit them wirelessly to a com- puter where software records the deviations, compares them to a perfect circle and analyzes the results. Ballbar diagnostics can also determine machine squareness as a prerequisite for analyzing backlash and reversal spikes. Once the level is set, reversal spikes, backlash and scaling mismatch are diagnosed and remedied using data that compares optimal machine set- tings to the ballbar test results. The comparative data that is generated also can be used to qualify metrology and time maintenance decisions, to implement continuous improve- ment techniques such as total productive maintenance (TPM) and statistical process control (SPC), and even to forecast machine life. By implementing a frequent-testing program, experienced ballbar users can monitor everything from linear- guide and ballscrew wear to vibration analysis. Using the data, operators can make adjustments, schedule downtime and maintain part accuracy as machine components wear out, rather than depend on the quality of finished parts to deter- mine machine capability. The benefits of a good process foundation include increased machine availability, better machine accuracy and repeatability, and less part-to-part variation and scrap/rework. A good pro- cess also provides a foundation for automated process setting. Automated Setting Building on the stability introduced by a solid process founda- tion, process setting then prepares for machining by automat- ing manual processes to eliminate time-consuming setup activities and human error. It also reduces setting times by as much as 90 percent by eliminating setup errors. Predictable sources of variation, for example, part location, tool and offset size, or anything that could cause a non-conforming first part, are taken out of play with proper machine, probe, part and tool settings. Machine setting uses on-machine probing to measure and eliminate errors caused by thermal drift between key moving parts, such as the spindle and bed. Uncorrected machine errors can be a dominant factor in process non-conformance and can cause extended setup times if the effects are confused with other sources of process variation. Probe setting involves datuming the probe so that it can measure accurately on the machine. The stylus size and posi- tion are measured using a datum sphere or ring gage. Or, in the case of tool-setting probes, a tool arbor is used to establish the position of the stylus. Regular probe calibration ensures other measurements on the machine remain reliable. Part setting uses a touch probe to establish workpiece loca- tion and orientation, and to align the machining program by identifying datum positions and angles, and automatically updating coordinates. It eliminates the need for human inter- vention, and can also reduce or eliminate the need for com- plex, precision fixturing as the probe finds the part. Operator miscalculations and improper input of workpiece or tool offset data to the control are the top causes of machine crashes, scrap/rework and tool breakage. Automated part setting allows companies to take advantage of the precision and repeatability of their machines with fast, accurate, repeatable measurements. Automatic updates of tools and work offsets also eliminate calculation and keying errors. Automating part setting and automatically updating fixture offsets to the control can reduce setting time by 95 percent, saving 30 hours per batch of parts. Tool setting measures tool length from the spindle gage line. This establishes height offset and confirms that the length is within specified tolerance. It also establishes the tool size offset by measuring tool diameter while the tool is rotating, which eliminates errors caused by runout and variation in insert height. All tool-setting information is stored in the CNC. Tool setting is more repeatable than manual measurement, and a suite of tools can be set in minutes without "cut-and-measure" trial cuts. In addition, probing software updates tool offsets automatically, which prevents human error and reduces tool and/or part damage. Broken-tool detection functions allow in- cycle checks for broken and/or chipped tool edges, as well as tool position to ensure pullout has not occurred and to prevent scrap/rework. Knowing Parts are Correct Once process control and a calibrated machine are established, shops can measure parts directly on the machine. In-process control monitors and documents operations using probes to deliver intelligent feedback to the process, and to address vari- ables such as temperature and tool wear. No operator interven- tion is needed. It can also perform quick in-process measure- ments of critical part features. In-process control can increase Ballbar analysis allows shops to manage CNC machine tools effectively by determining the machine's capabilities before machining and post-process part inspection. Regular ballbar checks enable scheduled, targeted maintenance and minimize machine downtime and scrap.