The Existing Situation
The final-assembly production floor of an aerospace plane manufacturer was facing a number of problems. Low-volume production runs that involved a constantly changing mix of products were severely impeding efficient machine runtime. In addition to high changeover times and inefficient runtimes, this mix of products wasn’t always manufactured according to spec, was sometimes manufactured using the wrong specs, or wasn’t always correctly labeled. The manufacturer needed to be able to react effectively to the stumbling blocks of a demand-driven manufacturing environment.
With the existing manufacturing process, the aerospace plane manufacturer machined each part in one of their three machining centers. In order to manufacture any number of different part families there was a large inventory of pallets with tools developed over many years to support different airplane programs. Each tool was designed to hold a specific family of parts.
These tools were brought from a storage area, loaded with a (nearly finished) part, and then transported to and loaded into a one of three small vertical machining centers. Work orders were individually scanned by the operator to pull the matching part program from the network. The program was then loaded to the machining center. The system, however, had no way to ensure that the correct part was loaded to the correct tool/pallet and that the correct tool was loaded in the machine.
A New Process
To ensure that the parts were machined accurately and economically and that they were correctly identified, the decision was made to replace the three small machining centers with a single, more effective machining system. They chose to implement an RFID pallet/tool tracking system together with Bertsche Engineering’s high-performance, multipurpose Xi-Mill machining center.
Bertsche Engineering Corporation designs and builds high-performance standard and custom machining tools, automatic tool changers, and robotics. The Xi-Mill is designed for high-speed automated production. It incorporates a number of Lean Manufacturing concepts that allow the machine to be quickly reconfigured to perform multiple tasks. A single machine can handle virtually all the requirements of any shop that needs to manufacture a wide variety of products. While the Xi-Mill can be quickly reconfigured for a different family of parts, one of the key features is its dual work zone mode. The Xi-Mill can be divided into two work zones, each with its own automated tool changer. Machining and load/setup can be performed simultaneously to increase production and minimize downtime.
Equipped with a set of pallet receivers in each work zone, the Xi-Mill easily accepts the existing tool fixtures. While the machine is cutting in the first zone, the operator can remove the finished parts out of the fixtures and load unmachined parts for the next work cycle. It then sequences back and forth between work zones. In this way the spindle is always in cycle and machining. This process also requires only one operator.
An RFID Tracking System
To ensure that the pallets with the correct tools are in the right pallet receiver locations and that the correct part programs are downloaded, Bertsche Engineering chose an IDENT Control RFID system from Pepperl+Fuchs. It’s designed to be easy to use. Any type of read head connects directly to the interface, and no matter which head is used, the PLC or PC programming is the same. The system is completely grounded and shielded so that no noise or any interference enters or exits the interface. All connections are quick-disconnect style and the cast aluminum housing provides an IP67, which is ideal for mounting inside a milling machine.
How it Works
Each pallet receiver is equipped with an RFID tag that identifies the pallet identification number and its descriptive part name. The CNC/PLC validates that the part program matches the loaded tool by reading the ID tag and comparing it to the part program and the pallet receiver location for a valid match. The built-in read/write head is fieldbus linked to the machine’s CNC/PLC. The CNC sends and receives tool ID information to a front end PC. Tool data is written off-line, away from the machine, using a compact portable tag programming device. Data tags are rewritten with updated data when the tools are modified or changed in any way from the previous configuration. These RFID tags provide the ability to track and trace the movement and location of each pallet. This allows information to be available sooner.
The incorporation of the RFID system worked so well reducing labor and error costs and the need to manually collect data, that future plans call for the integration of RFID tags that will be embedded in the tool holder. The machine’s CNC can then (under program control) scan the tools in the tool magazine, verify that the tools are all correct, and that they are loaded into the correct pocket before any machining occurs. This will prevent an accidental machine collision should an operator inadvertently load the wrong tool into the tool change magazine. Additionally, tool life, dimensions, and operating hours can be stored and tracked for each tool, and offset numbers are always readily available.