Options for automatic jaw changing.
According to Dr J F Jackson, technical director, Pratt Burnerd International, West Yorkshire, England. "Authomatic chuck jaw changing can be classified two ways: rapid changing of jaws (or gripping diameter) for finishing consecutive first and second operations on both sides of a workpiece, or automatic changeover of jaws after completing a lot run so the next job can commence without manual intervention. We've designed a system for this second requirement."
Their design uses either a gantry workpiece loader or a floor-mounted robot to both handle parts and change chuck jaws. At the heart of the system is a modified version of the firm's quick-change jaw chuck, Figure 1. A typical sequence for jaw changing with this system follows.
Spindle rotation is stopped with the chuck jaws in the work-piece-loading position. The last workpiece of the lot run is gripped by the robot, the chuck jaws open, and the part is removed. The chuck then rotates at maximum spindle speed and is flooded with coolant to flush away chips and dirt. The spindle stops, positioning the first jaw way opposite the jaw-loading station.
Now the jaws close and a chuck-location device actuates to engage a plunger and accurately position the workholder's body relative to the jaw guide. A jaw-release mechanism advances to engage a chuck-release pin. The plunger then rotates 180 degress to release the jaw.
The robot grabs the top jaw and extracts the complete assembly (including master jaw) from the jaw way. A probe checks that the jaw has moved from the chuck into the guide. The entire assembly is transported by the robot to the storage area.
Next, the first jaw of the replacement set is retrieved from the storage rack and moved by the robot to the jaw-loading position. The jaw assembly is engaged with the jaw guide and moved radially into the chuck's jaw way.
The release plunger then rotates to engage the new assembly and retracts. The locator plunger also retracts.
The machine spindle rotates the chuck so the next jaw is in position and the remove/replace sequence repeats. After changing the last jaw, the spindle rotates to the part-loading position and the jaws open to accept the first workpiece of the next lot.
As of this writing, we didn't have access to the time required to complete a changeover. The system will be unveiled in June at the MACH '84 exhibition (Birmingham, England). Option two
This month, SMW Systems Inc, Cincinnati, OH, will introduce a chuck designed for automatically changing all three jaws simultaneously (only top tooling is changed). This significantly speeds up changeover, making it economically feasible to switch jaws after completing a first operation in individual parts so a second operation can be performed immediately. Again, the workpiece handler (a robot) also is the jaw changer.
An aluminum pallet, with three slots spaced at 120-degree intervals, carries the top jaws. The robot grabs the pilot on the back of the pallet. This pilot is the same size as the workpieces, thus the robot's gripper doesn't need to be replaced to begin changing jaws. See Figure 2 for a description of how the system works.
SMW's Dave Poling comments, "A significant problem associated with using a robot to load chuck jaw is detecting if all the tooling is in place before loading a part. A corollary problem is detecting if a part has been properly loaded before cycling the machine. We've designed a pneumatic sensing system into our new chuck that checks back pressure at several points to ensure all hardware is correctly seated. This system does double duty by blowing off the jaw surfaces after each part is unloaded.
"Also," he continues, "the jaw pallet has a built-in compliance mechanism to compensate for inevitable positioning inaccuracies by the machine tool's spindle and the robot." Option three
Last June, at the 5.EMO machine-tool show in Paris, Yamazaki Machinery Corp (Japan) introduced a dedicated, fully automatic jaw-changing (AJC) system on its Mazak slant-turn 400 CNC lathe. The AJC can store up to 15 sets of jaws (45 separate assemblies). See Figure 3 for a description of this system.
Using a dedicated jaw changer makes the system more expensive than either the SMW or Pratt Burnerd schemes. Jaw changing is performed one at a time nsimilar to the Pratt Burnerd system), thus it appears best suited for completing a first operation on an entire lot before changing over to a second operation, or even a completely different part. The company, though, claims that the time required to change a single jaw assembly can be as quick as 45 sec when jaws at the nearest position are selected.
These are just a few of the automated chuck-jaw-changing systems that are fast coming on the metalworking scene. Curiously, not one was shown at the last International Machine Tool Show (September 1982). You can bet that won't be the case at IMTS '84.
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|Author:||Coleman, John R.|
|Publication:||Tooling & Production|
|Date:||Apr 1, 1984|
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