5-Axis Aerospace Precision

Trunnion type 5-axis machining centers position a workpiece at almost any angle for machining. This reduces setup time while increasing accuracy by machining multi-sided parts in a single setup. But what happens when the workholding restricts tool access to the part because the jaws or some other vise component gets in the way? Stopping the machine and repositioning the part is required.

Not so at Padgett Machine Inc., a family owned contract precision machine shop known for its quality since it started in 1970. Padgett Machine has implemented new workholding that eliminates the problem of obstruction from its workholding, so that all five axes are utilized in a machining program without having to stop the machine and reposition the part.

Always on the lookout for more productive ways to machine parts, Ed Padgett, president and CEO, says that 5-axis machining was really the answer to many of its complex aerospace and military projects.

However, when using conventional workholding devices on its Haas 5-axis trunnion VMCs, the company experienced limitations at using the machine's full 5-axis capabilities.

"There was always something in the way to restrict machining on all sides of the part in just one setup," Padgett reports. "We found that with the new Kurt Low Profile 5-axis vise, the machine can hold and rotate the part a full 360 and machine it on four facets in the same setup. It allows the machine to rotate and manipulate the part a positive 90 or negative 90 to get in and around areas of the part that require machining. Looking at the vise for the first time, you wouldn't think this is true, but the vise holds the part in an elevated position very rigidly so machining deep pockets at many angles is fast and easy in one setup. We save setup time, plus it allows us to run the machine at top speed so we gain three ways - faster throughput, less setup time and reduced machine downtime."

Aggressive Metal Removal Requires Rigid Workholding

Much of Padgett Machine's 5-axis work is for aerospace military applications, including ribbed parts for the MD11's leading edge wing assembly, and a wide variety of precision parts for the current fleet of B52 bomber's under the government's continual maintenance program. These parts are machined from 4130 aircraft steel alloy, 7075 aluminum alloy, and 7050 high fracture resistant aluminum alloy. Most machined parts require substantial metal removal and very close tolerance drilling and boring operations necessitating very rigid workholding.

The usual method using conventional vises would be to position the unmachined material as far down in the vise clamping station to get the tightest "grip" on the broadest surface area of the part in order to make the most aggressive and fastest cuts possible. That method is satisfactory - taking into account the need to stop the machine and reposition the part - except that a trunnion machine spindle has restricted access to the deepest jaw areas of conventional vises and multiple facets of the material to be machined. In contrast, the new 5-axis Kurt vise elevates the part material so there is clear spindle access while part clamping is done with no loss of rigidity. In fact, the actual clamping force with this new vise is 8,992 lb (40kN), at least 20% greater than conventional 6" vises.

"That added rigidity really helps maintain accuracy for both roughing and finishing operations on these wing rib components," Padgett explains. "Accuracy required is between 0.002" and 0.005" tolerances with boring and drilling each side of the part requiring 0.001" tolerance. Those side boring and drilling tolerances can be difficult to maintain with conventional workholding, but it's a breeze with the new Kurt 5-axis vise. Its stability and holding power is really superior in whatever presentation angle the machine spindle makes to the part: top, bottom and sides.

"To achieve the accuracies for plunging and milling a pocket on the 7050 aluminum wing ribs, we're using a Mitsubishi 1"-diameter polished carbide insert. It operates at 6,000rpm with a 160ipm feedrate at 0.25" deep, and with a side step of 70% of the cutter width," Padgett continues.

Run time for this part is about three hours for the upper surface and about two hours for the bottom surface, including roughing and finishing operations.

According to Padgett, more intricate finishing of the part's special features requires carbide endmills with special radii. Even these operations have a smooth travel of 60ipm to 90ipm feedrate without tool chatter. According to Padgett, vise rigidity is there for all operations – no exceptions. For this project, Padgett Machine operates the Haas VF-6/50TR somewhat below the machine's speed and feedrate range of 7,500rpm in 1.2 seconds.

Interestingly, a right and left sided version of these rib sets are required with a total of 60 rib components machined for this particular part run order. Also, there's more than machining to this project, as with many of Padgett's projects.

For this order, Padgett provides the certified raw material, does all of the machining, non-destructive testing, anodizing, priming, installation of bushings, fasteners and other hardware.

"There's considerable 'value added' to this and similar projects and the key to keeping us competitive with customers is adapting quickly to new technology like this 5-axis workholding," Padgett says. "It allows us to get the most out of our new trunnion-style machining centers."

Low Profile for Complex Machining Operations

Padgett Machine utilizes Kurt's latest 5-axis vise model, (VB 5AX100-L), a lower profile version of the vise with clamping height above the machine table of 100mm (3.937"). It provides extra part clearance, but not as much as the original 175mm (6.889"). Also ideal for machining complex pockets, sculptured and contoured surfaces, and intricate 3D features, this new vise is designed for a range of smaller machining centers.

Like the original, this vise also has a patented design that eliminates jaw deflection and part misalignment during machining operations. By locating the tension spindle directly under the workpiece, the jaws do not flare out under tension and the machine table does not distort.

The workholding handles blank work-pieces, machined workpieces and round and irregularly shaped parts, like those at Padgett Machine, with repeatable accuracy.

This lower-profile vise model is adjustable to handle any desired clamping width limited only by the size of the machine table (64" x 32" x 30" / 1,626mm x 813mm x 762mm; X, Y, Z travel).

The vise system's two clamping jaws, one stationary and one moveable, can be positioned at any desired distance from each other within the working envelope of the machining center. Padgett Machine's side-by-side setup of two 5-axis vises provides the capabilities of permanent fixturing but with versatility for all size parts that fit into the clamping envelope.

Specifications of the Kurt VB 5AX100L Schenke 5.1 Clamping System include a clamping width from 0.0787" to 9.291" (20mm to 236mm) that can be extended with optional spindle screws and a clamping depth of 0.315" (8mm). The system is designed to mount easily on standard T-slot tables, location grid machine tables or custom fixtures. Padgett Machine's vise setup is mounted to a T-slot table removed easily and re-centered quickly as needed.

Modular Vise Design Handles Complete Range of Projects

"Using two of these Kurt 5-axis vises mounted side by side on the T-slot table, we can handle many different size parts within the trunnion table's size range," Padgett explains. "The rigidity of this vise exceeded our expectations, and we're machining jobs in much less time than before. Our machine operators really like them because of how fast they set up for repeat jobs."

In addition to this new 5-axis clamping system, Kurt provides integrated custom-engineered workholding systems and custom gaging systems for automated manufacturing. Both workholding and gaging are designed around a customer's requirements with systems available for many industries including automotive, medical and aerospace applications.