Page 29 - MetalForming April 2013

realize. All of our dies iron the side- walls using a negative clearance, which allowed us to reduce blank sizes by 20 to 25 percent.”
How much blank ironing occurs? On a 12-quart drawn stockpot, for example, the hydroforming blank measured 24.25-in. dia. Now, deep- drawing the part (8.375-in. draw) in the Greenerd press requires only a 20.75-in.-dia. blank. The bottom thick- ness of the part remains the same as the blank, while the sidewalls thin by near- ly 20 percent.
Feeding Blanks to a Hungry Press
As if making an 8.375-in. draw on a 20.25-in.-dia. sheetmetal blank isn’t tricky enough, consider this: All-Clad’s pots and pans are fabricated from clad blanks—either three- or five-ply (see sidebar).
A three- or five-ply pack (master blank) as large as 2 by 4 ft. can be quite heavy and challenging to manipulate.
As such, All-Clad had grown weary and concerned over numerous strains and sprains experienced by operators plagued with indexing the packs along two- to four-out transfer blanking dies. In 2010, the firm automated the blank- ing process by installing a blanking cell starring a six-axis Fanuc S-430i robot (104-in. reach).
“The robot’s end-of-arm tooling (pneumatic grippers from PHD) fea- tures the lowest-profile tools I could find,” DeHosse says, “identified through my previous experience with tooling Trumpf CNC presses. We did have to modify the die rings on a few of the dies to add clearance for the grippers.”
Other cellmates include a five-roll straightener, a 150-ton 30- by 36-in. Aida mechanical press and a 4-ft. Tenn- smith shear.
“To secure the layers of material during the cladding process, we add a series of resistance welds along one edge of the pack,” DeHosse explains.
“After the robot picks up the straight- ened pack and indexes it through the blanking press, it moves the web to the shear to cut away a 3⁄4 in. strip where the welds are. This allows us to separate the layers so we can maximize the scrap value.”
Blanks feed from the press at up to 60 strokes/min. “We change blanking dies as many as three times/day,” adds DeHosse, who notes that changeover time has been reduced to less than 30 min., compared to approximately 90 min., thanks in part to the recent addi- tion of a magnetic upper bolster.
Before the blanks find their way to the hydraulic-press department, they’re processed through an eight-station automated deburring operation.
Meet the Press
At the new Greenerd hydraulic press, we watched DeHosse form 7-qt. stock pots; a 7.75-in. draw reduces a 17.75- in.-dia. blank to an 8.4-in. dia. pot. “We do everything in a single draw,” notes
Making the Clad Master Blanks Deep-Draw Capable
To build up its clad packs of master blanks, All-Clad brings in coils slit to the various widths needed to match the required blank sizes, which run on cut-to-length lines to produce the required strip lengths.
Strips as large as 48 in. long by 22 in. wide are then layered and processed on a two- stage rolling mill into clad master blanks, referred to as “packs” at All-Clad.
For a three-ply
blank, Type 304 stain-
less steel comprises
the inside cooking sur-
face and a magnetic
stainless-steel grade
comprises the outer
layer. Sandwiched in
between is a layer of
aluminum. Five-ply
packs include two
additional layers of aluminum and a second layer of magnetic stainless. Each pack yields two to four deep-draw blanks.
Since the move to deep drawing the clad blanks, DeHosse and his cohorts have spent considerable time and resources optimizing the cladding process to improve bond strength.
“The window of bond strength has narrowed with deep draw- ing in the hydraulic presses,” DeHosse says. “The challenge has
been to improve process repeatability in our cladding furnaces, in part by installing new temperature-monitoring equipment. Overheating the packs causes excessive grain growth in the alu-
minum, which impacts forming characteristics in the press and can cause an orange-peel texture on the inside of the pan.”
Even as overall scrap rate since the move to hydraulic presses is far below that of hydroforming, “and the blank-size reduction makes the move to deep drawing a no-brainer,” DeHosse says, the quality-con- trol efforts made in the cladding operation have yielded marked and measurable
improvements.
“For example,” shares DeHosse, “one of our big scrap items
historically has been the 8-qt. stock pot, 10.5-in. dia. with a 6.5- in. draw. Scrap rate had been as high as 8 to 10 percent, but on the last run, after making the process modifications in the cladding department, scrap rate scored less than 0.5 percent on a 3000-piece run.”
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