|
Kurt's Ductile Iron ClusterTowers® Provide Needed Clamping Rigidity To Hold 0.001
Tolerances For Roberts Automatic Products --- Kurt Setup Replaces Aluminum Towers
Minneapolis, Minnesota: Holding .001 inch tolerances while machining and removing large amounts of material from a brass part is a challenging task when the job is run at 10,000 rpm with surface speeds of 240 in/min.
 |
 |
| PHOTO ONE CAPTION: Bill Roberts, senior process engineer for Roberts Automatic Products shows off his high rigidity Kurt ClusterTower setup in the company's Mazak PFH 4800 Horizontal Machining Center with the 4th axis and pallet changer. The ductile iron towers provided the rigidity needed for high speed metal removal operations and tolerances of .001 inch. |
PHOTO TWO CAPTION: Finish machined brass parts ready for unloading. Kurt ClusterTower workholding setup provides the needed rigidity to machine the parts correctly. The 80,000 PSI ductile iron ClusterTowers are 2.5 times stiffer than comparable aluminum towers and have 20 times the vibration damping capabilities of aluminum. |
If the workholding isn't rigid enough, part quality suffers. Cutter life is reduced. Downtime occurs. And operator frustration sets in. It's a task that requires the rigidity of ductile iron workholding, as reported by Bill Roberts, senior process engineer for Roberts Automatic Products, a leading supplier of quality, precision production machining for over a half century.
Roberts Automatic Products has seen it all and been successful through three generations in the high precision machining business. Founded in 1947 by Glen Roberts, the company specialized early on in complex screw machine parts, CNC turning and machining cell work. It is an ISO 9001-2000 manufacturer with excellent 48,000 square foot facilities and motivated workforce. It takes pride in the diversity of its capabilities and equipment. From large 2-5/8 Acme-Gridleys, to high speed Davenports and Gildemeisters, to precision Mazak and Hitachi Seiki CNC's, the company can handle almost any precision machining job and solve just about any production problem along the way.
"We try different approaches to come up with the most cost effective machining process," reports Roberts. "When tapped holes on opposite sides of the part wouldn't align, we saw that the aluminum towers we first tried for the project were bending. Aluminum towers have the advantage of light weight and ease of setup, but their rigidity for aggressive cuts is limited. Slowing the machine and tightening the clamping stations failed to do the trick. It was apparent that the problem was not with the machine, but rather the workholding we first tried. We checked with our Kurt Workholding sales representative, Mike Neeley, and with his input settled on a pair of Kurt Model CTHDLM644 ClusterTowers made of ductile iron to provide the workholding solution."
Mazak PFH 4800 HMC Provides Stability And High Accuracy –
Requires Workholding That Compliments Its High Performance Design
"We use all types of workholding including standard vises, towers and dedicated fixturing," reports Roberts. "Selecting the right workholding to get the most out of a high performance machining center is key to good process planning. Even though ductile iron workholding is heavy, there's no substitute for it when you need maximum rigidity, strength and part holding power. We've used Kurt vises for years and know the advantages they provide because of their ductile iron design."
Kurt ClusterTowers are made from 80,000 PSI ductile iron, which has 2.5 times the stiffness of aluminum and vibration damping capabilities 20 times higher than aluminum. Since the Mazak PFH 4800 Horizontal Machining Center is designed for stability and high accuracy in heavy material removal jobs, the Kurt ClusterTowers were the ideal workholding choice.
Roberts said the challenging job came about when his customer redesigned the part from an aluminum extrusion into a part machined from brass bar stock. To machine the parts cost effectively, high speeds were required along with minimal setup time. That made the project ideal for Roberts' Mazak 4800, which has pallet changing capabilities allowing the machine to be in the cut continuously on one ClusterTower while the operator performs part load/unload operations on the second ClusterTower.
 |
PHOTO THREE CAPTION: Finish machined brass bodies are milled, drilled, thread milled, reamed and woodruff milled with .001 tolerances and a 64 micro finish.
|
As for fit, with two 400 mm x 400 mm pallets, the Mazak 4800 handles the two Model CTHDLM644 ClusterTowers perfectly which have standard square bases identical in size as the machine pallets. Weighing 460 lbs each, the towers match up nicely with the machine pallets, which are also made of iron castings. As Roberts puts it, "Everything from the tower clamping stations down to the floor is solid iron. That really maximizes rigidity."
Changeable Ductile Iron Jaws Have
Custom Fixture Advantages Without The Limitations
Using changeable ductile iron jaws machined to hold the brass components' outer dimensions, Roberts' ClusterTower setup replicates much more costly custom fixtures. The machined jaws form a "pocket" into which the parts locate and clamp up quickly. With eight clamping stations on four sides, each holding two parts, the setup takes advantage of the Mazak's 4th axis which provides the fast indexing function from one side of the tower to the next.
The two parts on each tower face are positioned within an inch of each other so there is minimal spindle travel part to part. The machined jaws clamp accurately and tightly on all sides of the parts with 3772 lbs of clamping force at 40 foot lbs of input torque. There's no chance of part misalignment or chatter even at highest speeds. (When this particular part project is completed, jaws can be replaced quickly with others for different jobs.) The jaws themselves relocate quickly and precisely without special alignment tools.
"Part loading and unloading is really fast, less than 10 seconds per clamping station," reports Roberts. "The blank parts position quickly within the jaw plate's machined pockets. There's no alignment needed. There's an "A" and a "B" side to each part which is machined sequentially. After parts are machined, less than a half turn of the two screws at each clamping station releases the part and is ready for clamping of the next part. There's no wasted operator motion or heavy labor with this setup."
 |
| PHOTO FOUR CAPTION:Machined jawplates allow for staggered and close positioning of the components on the ClusterTowers four sides for fastest spindle chip to chip cutting time. |
ClusterTower features that add to Roberts' productivity include a clutch design that automatically returns the jaws to correct clamping position with no timing problems. A chip guard system fully covers the center clamping area at all times so chip and coolant buildup is avoided. In addition, the ClusterTowers incorporate the famous Anglock® clamping design which minimizes movable jaw lift.
64 Micro Finish, ±.002 Tolerance On Reamers
Each brass component is milled, drilled, thread milled, reamed and woodruff milled. The setup utilizes premium toolholders and high performance solid carbide end mills for the milling operations. Most operations are done at speeds up to 10,000 rpm, which is well within the range of the Mazak 4800's maximum spindle speed of 15,000 rpm and X, Y, Z traverse rate of 22 inch x 24.8 inch x 23.6 inch.
When complete, each part has a 64 micro finish and ±.002 tolerance on reamers.
"There are a lot of workholding alternatives out there," says Roberts. "But for certain when the utmost in rigidity is required, you can't beat ductile iron ClusterTowers from Kurt."
For more information about Roberts Automatic Products, contact Bill Roberts. Email: broberts@robertsautomatic.com
Phone: 952-949-1000. Fax: 952-949-9240. Write to Roberts Automatic Products, 880 Lake Drive, Chanhassen, Minnesota 55317. Website: www.robertsautomatic.com
For more information about Mazak machining centers, email info@mazakusa.com Phone: 859-342-1700. Fax: 859-342-1865.
Write to Mazak Corporation Headquarters, 8025 Production Drive, P.O. Box 970, Florence, Kentucky 41042. |
