Page 28 - MetalForming Magazine March 2022

Fabrication: Audit Your CNC Punching Operations
To protect tooling investments, shops should safely store their tools in cabinets or on shelves with protectors/dividers—seems like common sense, but few do this well, according to Visser.
them out for sharpening. “All you really need is a good grinder or sharpening machine,” Visser says.
“And,” he adds: “If you’re removing more than 0.003 in. from a tool during sharpening, you waited too long.”
There are three telltale signs that a punch has become dull, Visser says:
• Sound—a dull tool is loud
• Feel and touch—burrs on the parts • Appearance—Look for heat wear
or heat signatures around the cutting edge of the tool, or a shiny appearance or “chroming effect” on the cutting edge.
Because skill level is relatively low for many of these companies, few peo- ple understand how to properly main- tain tools, Visser says, to get the true maximum life from the tools.
“Any given punch tool can have as much as a 1⁄2-in. grind life,” he explains, “meaning that you can sharpen these tools as many as 500 times. Even at 250 working days in a year, the tools should last 2 years. If you sharpen your tools every week, you’ll might get six years out of the tools. Bottom line: sharpen lightly and sharpen often.”
Organized, Protective Tool Storage
To protect tooling investments, shops should safely store their tools in cabinets or on shelves with protec- tors/dividers—seems like common
26 MetalForming/March 2022
sense, but few do this well, according to Visser. “We see this problem everywhere,” he says. “Storage and organiza-
Here’s an example of what can happen when machine opera- tors fail to clean die stations before installing new tools. Any residual dirt and debris, and under tonnage, scores the tool- ing. “The die holder gets beat up,” says Visser, “so that the die doesn’t sit flat in the machine. That in turn causes wear between the punch and die.”
tion are my top con-
cerns; we see uncared-
for tools all the time.
While most machinists
take good care of their
calipers and other tools
that they personally own, they seem- ingly don’t care as much about the punching tools that belong to their employer. Make sure that your opera- tors know how expensive the tools real- ly are, and the potential impact that damaged tools can have on production schedules and customer relationships.
pens. While initially the misalignment may not be too bad, every crash makes it worse. Therefore, shops should check machine alignment periodically. An easy way to do this: Punch a new slug and check to see if the burr is nice and even. Or, punch four holes in the corner of two sheets, then stack the sheets and make sure that the holes align.”
Visser has this piece of advice when it does come time to sharpen the tools: “Remember to replace the chamfer on the edge; a Scotch Brite wheel works well for this. Otherwise, the tool will scratch the underside of the sheets, potentially turning the entire sheet into scrap. I see this a lot. And, when you scratch the sheet, those shavings may wind up under the dies and in the tool- ing. This can cause damage to the die holder so that the die won’t sit flat, another cause of premature tool wear that easily can double consumable costs and increase machine downtime.”
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“If a tool costs $500 and the press has 36 tool stations, do the math,” Viss- er adds. “Over the life of the machine you may spend more on tooling than on the machine itself.”
In addition to creating scrap, dull tools can wreak havoc on the punching machine.
“When a tool becomes dull it may not exit cleanly out of the sheet,” says Visser. “Instead, it may remain in the sheet for a split second while the machine continues moving the sheet in the X-Y directions, essentially tearing the tool from the machine. This causes machine misalignment. A lot of oper- ators just keep running when this hap-