Page 40 - MetalForming November 2013

Tooling by Design
By Peter Ulintz
Stamping Consistency
Tooling Technology
Operating-Temperature Ranges of Extreme-Pressure (EP) Additives
oC 1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
50 0
Consistent part quality no longer is achieved by first-piece and periodic inspections. First of all, the process doesn’t work. Secondly, your customers won’t accept it. In fact, some customers may no longer accept “parts to print;” instead, they expect the same quality part, consistently, from container to container, lot to lot, and shipment to shipment.
Manufacturers who also weld or assemble metal stampings produced inhouse also demand that their press shop supply consistent part quality. Why? Because accepting “parts to print,” permitted to vary through the entire tolerance range from coil to coil or run to run, causes time-consuming adjustments to assembly fixtures, weld- ing jigs, positioners and locators. In high-volume applications, this may require adjustments to multiple fix- tures or process lines. Then, addition- al time must be spent fine-tuning so that the same-quality part comes off each fixture or process.
Part-to-part inconsistencies may result from lack of precision in the die when processing one part to the next; a sloppy press or ram slide that fails to repeat exactly with each stroke, in dis- tance and parallelism; an inconsistent feed that causes the pilots to correct
Peter Ulintz has worked in the metal stamping and tool and die indus- tries since 1978. He has been employed with the Anchor Manufacturing Group in Cleveland, OH, since 1989. His back- ground includes tool and die making, tool engi- neering, process engi-
neering, engineering management and product development. Peter speaks regularly at PMA semi- nars and conferences. He is also vice president of the North American Deep Drawing Research Group. Peter Ulintz
pete.ulintz@toolingbydesign.com www.toolingbydesign.com
strip location in both directions; or camber in material that shifts the strip side to side within short distances. These are only a few of the more than 50 process input variables that can affect part quality and dimen- sional stability. These variables can be organized into groups.
Product design: Depth of draw, consistency of draw depth, features formed in opposite direction, stretch- formed features, size of radii, material thickness specified, material type specified, etc.
Press and press-line equip- ment: Flatness and residual- stress state after straightening, press speed, working tonnage, available press energy, load bal- ance, press rigidity and press guidance.
Die variables: Die-set con- struction, die materials, sur-
face roughness, surface treatments, spotting accuracy (draw dies), die rigid- ity, pressure-pad force and balance, thrust, die heeling, guiding system, alignment, die temperature, wear, dirt, draw beads (change with wear), shims on set blocks (load distribution), shims under tool components (die timing), press operator, etc.
Blank/stock strip: Rolling direction, blank shape (optimized), flatness, cleanliness, burr direction, workpiece temperature, etc.
Lubrication: Lube type, viscosity, amount applied, location applied and the operating temperature range all impact part quality. Lubricants are for- mulated to work within specific pro- cessing-temperature ranges (see figure).
The challenge, then, is to identify the process variables that contribute most to current part-to-part variation, and to control those variables. Let’s start with
the obvious—the better the press, stock straightener and feeder, the better the results. The same goes for the material to be processed—better quality and consistency improves stamped-part quality.
Properly designed and built tooling that does not permit deflections and fluctuations helps as well. Designing dies to process critical dimensions simultaneously will result in stamped parts that are as accurate as the tooling.
Sometimes, small changes in press speed-due to insufficient flywheel ener- gy—will contribute to variations in product quality.
Sleuthing the Prog-Die Strip
Progressive-die processes can be challenging, especially when trying to solve quality-related problems. But a comprehensive inspection of the die strip can tell much about what has
38 MetalForming/November 2013
www.metalformingmagazine.com
Soaps and Esters
Synthetic, Polymeric Esters
Chlorinated Paraffins
Organo-Phosphorous cpds
Sulfur cpds