Even as manufacturers of all types adopt increasing levels of automation for use throughout their operations, one production process in particular still relies heavily on human intervention. That process is quality control. The most common automation device encountered to replace or support the human eye in this process is machine vision. But this might not be the most suitable device for all applications, especially those processes where adherence to specific dimensional measurements is required.
Two manufacturers – Meyer Tool in Cincinnati and Eponsa of Barcelona, Spain – are breaking new ground in their industries by adopting an automated method of ensuring quality compliance of their finished products.
Aerospace Engine Components
Meyer Tool is a manufacturer of hot-section jet engine components for aerospace OEMs, employing more than 1,000 people at 10 locations. The company designs, builds and maintains dozens of hard gauges every year for in-process measurement of its products. For in-process dimensional measurement, Meyer Tool principally relies on work-cell-based, point-to-point contact gauges, using pneumatic digital probes. Using these gauges in the machining cell gives fast feedback. However, they also tend to be very expensive.
“The design and build of the part nest can cost $6,000, plus probes at $500 each, verification studies and maintenance,” says Beau Easton, quality manager at Meyer Tool. In total, these tools can cost the company as much as $20,000 each.
As an example of how these costs can quickly add up for use precision components of the type Meyer Tool manufactures, consider this: If the company is producing a make-complete nozzle (i.e., the company buys the casting and completes the part in-house) for quality testing of parts, it could require six to ten fixtures, each with six to twenty probes. Then, if a feature or tolerance on the part changes, the gauge must then be altered and verified. These design changes can add another $3,000- $10,000 to re-configure and qualify an existing gauge.
To reduce the costs encountered with hard gauge designing and building, Meyer Tool recently began using a new software-driven comparative gauge from Renishaw known as the Equator.
Equator is automated inspection device that has the appearance of a delta robot. In its inspection process, Equator uses the comparison method of mastering and measuring, in which a master component with features of known dimensions is used to “zero” the system. All subsequent measurements are then compared to this part. Though this simple and well-known mastering and measuring process is at the heart of what Equator does, Dave Emmett, Renishaw’s Computerized Maintenance Management Manager, says that Equator’s primary differentiator is its “high repeatability (less than ±2 μm) and radically different metrology mechanism based on a parallel kinematic structure.”
The Equator gauging system is delivered assembled, so it is usable out of the box and can reportedly be up and running in less than 20 minutes. It weighs 25kg (about 55 lbs.), and operates on single-phase power with no compressed air supply needed. Depending on configuration, Equator units range between $25,000 and $30,000.
Thousands of data points are collected by the device during the 3D scanning mastering phase using an industry standard SP25 probe. Every data point can be used for comparative measurement, meaning that one Equator can perform the same function of thousands of dial test indicators (DTIs), linear variable differential transformers (LVDTs) or handheld instruments.
Emmett says that up to five hard gauges in a Meyer Tool work cell can be replaced by one Equator. In addition, the
Equator can be used for multiple parts, switching between the parts in seconds. It can also be reprogrammed for use on many other parts over its lifetime.
The device can be used in a serial production line between turning centers, machining centers, grinders and other machines, or within a manufacturing cell to gauge components for multiple machines. Equator can also be integrated into automated cells, using an I/O interface to connect it to a robot, or by outputting the gauging results to an SPC package. Some SPC packages also offer the ability to connect to certain modern machine tool controls to update offset values for automated process control.
Meyer Tool is currently using the Equator system in a lean machining cell where it is integrated with Meyer’s Orion SPC system. Orion communicates with the Equator’s Modus software, presenting the operator with results in the form of dimensional data and SPC charts which allow the operator to determine computer numeric control (CNC).
“The machinist sees variable data and can compare the current part with recent measurements, so it’s not just a pass/fail determination,” Nolan explains. This aspect is critical for Meyer Tools components, as its parts must meet tolerances of ±0.001 to ±0.003 inches.
Nolan adds that, though inspection time varies with the part, it typically takes between two to six minutes with the Equator system, which is within the takt time (lean measure of maximum time required to produce a product) of the cell to keep pace with machining operations.
“We gauge five part numbers for two different engine programs, so we have multiple fixturing tiles for the Equator setup and qualified,” Nolan said. “We are doing geometric dimensioning and tolerancing true positions, notches, hole diameters, profiles and runout with touch probing, plus we are implementing contact scanning with the SP25M probe. We have the stylus changing rack and use at least four different styli – usually star styli – so it’s convenient not to have to requalify with every change.”
Across the Atlantic, another component manufacturer is putting the Equator to use as well. Eponsa is a manufacturer of automotive components using the Equator to speed up the quality checking process of its stamped parts and assemblies as well as verify the quality of a large number of different parts that it manufactures. Eighty percent of Eponsa’s business is producing automotive components, the other 20 percent is general subcontract stamping, welding and assembly work.
The quality check process at Eponsa has traditionally involved the use of visual checks to ensure holes are present where needed and that there are no cracks in the material. This step is typically followed by dimensional measurements with hand instruments like calipers and plug gauges. Though this process has been very effective for Eponsa, the process of measuring with hand gauges is time consuming, repetitive and its effectiveness all comes down to the skill of the operator on any given day.
Use of Equator is being adopted by Eponsa as an independent and traceable test of part quality. It also opens up the inspection process to more plant workers because all operators can use it rather than just quality staff.
With all shop floor operators potentially having access to the system, access control is a concern. To address this, Equator’s Modus gauging programs are access-controlled. This means that only programmers can create and change programs, but the interface remains straightforward for operators to find the right program – made easier though inclusion of photos of the part. The interface also shows the operators how the part should be placed on the fixture.
Eponsa is looking to Equator to reduce and potentially eliminate quality room waiting times from its production process. The company’s reasoning behind this is that, since Equator can be used on the shop floor alongside the machines producing the parts, and its purchase cost is so low, the company can have several Equators positioned where they are needed, allowing inspection to take place when and where parts are produced.