During his visit, Andrew Allcock found that ROEMHELD Stark Zero Point fixturing location system has boosted machine utilization at CAV Aerospace's 5-axis machining centers.

In Llantrisant, South Wales, trucks carrying large volumes of swarf, otherwise known as filings of stone and metal, are a common sight, especially around the industrial estates and specifically at CAV Aerospace’s facility (formerly Prematec). The company specializes in machining spars, ribs, and detailed machined parts, primarily from aluminum, along with sub-assemblies. Remarkably, over 90 percent of each billet of raw material is machined away to create the final product.

CAV Aerospace in Llantrisant serves major clients such as Airbus, Boeing, Bombardier-Shorts, and Ronaldsway. Thanks to ROEMHELD Stark Zero Point Speedy 2000 Tornado fixturing location system, the company has enhanced its efficiency, producing even more swarf with its trio of SNK HPS-120B 5-axis horizontal machining centers. This improvement translates to more components from the same machine and more cutting with less setup time.

For ribs, the process involves holding raw material billets with vacuum fixtures, after the location side has been prepared. The parts are then machined on the opposite side.

The vacuum fixture plates, measuring 120 inches by 48 inches, must be loaded onto a machine table, manually calibrated, secured, and inspected for proper positioning. If the vertical position is incorrect, the fixture plates need to be skimmed. Billets are then loaded, machined, and once completed, removed from the fixture plates, which are then manually unscrewed, repeating the cycle.

These fixture plates can be as large as the table itself, making the setup process lengthy and prone to errors, as senior CNC engineer Andy Green points out, “The tables have got to be spotlessly clean because of the large contact area between the fixture plate and table.” A single piece of debris can tilt a fixture plate, necessitating skimming to correct the error. Removing, cleaning, and reloading them is not an option, so fixtures are effectively sacrificed over time.

Additionally, any changes in the x-y plane require adjustments to the CNC program origin. Errors in this process could lead to scrapped parts, which, as Green acknowledges, has happened.

Switching to improved fixturing systems significantly boosted capacity and quality at CAV Aerospace. ROEMHELD Stark Zero Point fixturing location system has enhanced machine utilization for CAV Aerospace’s 5-axis machining centers, as Andrew Allcock found during his visit.

CAV Aerospace’s three SNK HPS-120B machines are equipped with 11 ROEMHELD units. The decision to upgrade their fixturing was driven by a project from Australian company Hawker De Havilland for Airbus A320 ribs, numbers 10 to 27. There are 30 ribs in a shipset for this work package, and the size of these parts made it feasible to mount multiple parts per fixture compared to the usual one per vacuum plate for larger items. A320 ribs are about 30 percent smaller than those for the A330/340, measuring just over 1.5 meters long to just under 1 meter.

“We have to deliver in shipsets, so we don’t get the opportunity to manufacture 20, 100 or 1,000 off. Instead, we are limited to one or two parts per shipset. So that means you have to change fixtures much more often than you would do if you were making, say, 100 parts,” explains Green.

Realizing Cost Savings and Quality Improvements with Stark Zero Point System

Switching to improved fixturing systems at CAV Aerospace has yielded numerous benefits, including reduced setup times. By grouping parts on a fixture, only four fixtures were needed to accommodate all 30 parts for the A320 project, with each plate holding up to nine different ribs. Initially, the company used this four-pallet system without the Stark system, resulting in a changeover time of about four hours—too long to maximize machine uptime.

“We wanted to maximize machine up-time, limit set-up time, and the best way we could do this was by loading and unloading the machine in the fastest possible time using an arrangement that would allow us to get the fixture in the same place every time,” says operations manager Mike Fleetwood. Senior CNC engineer Andy Green, leading the setup reduction project, identified and selected the Stark Zero Point system from a shortlist of two options.

The ROEMHELD system was installed on all three SNK HPS-120B machines, with the first machine outfitted in December 2004 and the last in March 2005. Each machine has 11 Stark Zero Point base units on its table, arranged to allow plates to locate in a single orientation. Modifying each machine took five to six hours, with an investment of £12,000 per machine. The results showed a three-month payback period and a productivity improvement of over 14 percent, as setup time was reduced to just 10 minutes.

“The life of a fixture is now almost infinite,” offers Mr. Fleetwood.

In addition to time and cost savings, quality has improved. Issues with achieving flatness and tolerance (typically +0.13 mm to -0.08 mm) have been eliminated. “Parts are a bang on the money every time,” according to Green. The Stark system, with its lower contact surface area and self-cleaning location units, contrasts sharply with the original system.

Although the Zero Point location/clamping system delivers micron-level repeatability, machine setters initially calibrated fixtures thoroughly. As confidence grew, a simple zero check followed by a quick first-off now suffices before running the machine. With increased repeatability, meeting delivery schedules has become easier.

Currently, only the three SNK HPS-120B machines at CAV Aerospace’s Llantrisant facility are fitted with the Stark Zero Point system. Larger machines would require a significant investment for low-volume parts, resulting in a longer payback period, and pallet-changing machines negate the benefits of the Stark system. However, the time saved and capacity gained mean the company won’t need to add a fourth machine for a while. The benefits of the Stark system are being extended to other parts that can be made on these three machining centers.

Universal System Expansion with New Fixture Plates

In addition to product-specific plates, the company uses a grid plate for other components, onto which fixtures are located. These grid plates themselves are positioned in some of the Stark base units. Currently, the company is developing another type of fixture plate that will span just two of the base units, allowing a base plate to run from front to back across the table. Using these straddle plates will support a universal system. The goal is to apply this to A330/340 parts, gaining the benefits of the Stark system for these parts as well, and providing greater production planning flexibility.