Extending Tool Life

• Fabricating

Click image to enlargeby Lincoln Brunner

Prevention, maintenance keys to extending bend tooling life

In a world of tight budgets and ever-stricter customer demands, extending the life and quality of your bend tooling is more imperative than ever.

How exactly to do that, however, depends on a number of factors, including:

• The type and thickness of the material you’re bending.
• Your customers’ surface quality demands.
• Your dies’ tonnage capacity.
• Your faithfulness to simple maintenance routines.
• Extending your bend tool and die life also depends on if you maintain dedicated sets of tooling for each of your press brakes and how much you’re willing to invest in tool hardening — induction or laser hardening, for example.

Whatever your mix of considerations, with traditional tooling generally running $2,000 to $4,000 per meter, it’s worth your time to keep your tool sets useable as long as possible.

Fighting Abrasion
That starts with simply preventing and mitigating the premature wear that turns too many tools into scrap before their time.

“The number one cause of tooling wear is abrasion — you can’t get away from that,” says Tom Bailey, TruBend product manager for TRUMPF, Farmington, CT. “The single best thing you can do to extend tool life and prevent wear is to keep the tool lubricated.”

Click image to enlargeThe benefit can be twofold: decreased die wear and less demand on the machine’s hydraulics, gears or servos. For some light gauge material, the answer might be as simple as a layer of WD-40. Heavier sheet or plate may require a heavier oil. However, for some applications, such as stainless steel appliances, oil won’t pass inspection. In that case, coating tools with a hard nitride, zinc or nickel-plate finish can increase tool life, but also cost up to 25 per cent more than standard tooling. Other options include specialty coatings like Wilson Tool’s Nitrex, which is applied as part of a heat-treating process that hardens tools to 68-70 NRC. It also increases the lubricity of the tool without adding to the thickness of it (like an anodized or nickel-plate coating might) because it permeates the tool steel itself.

Fighting entropy, not physics
Physics dictates that forcing too much material into too little space destroys die life. Though they may be tempted to exceed tonnage limits by time, budget or other constraints, operators are well-advised to abide by tonnage charts from the brake or tooling manufacturer. Exceeding tonnage limits may damage the entire brake, or worse yet, shatter a punch and send sharp steel flying across the shop.

“If you’re developing a new product line or taking on doing a volume of work and don’t have the right tooling for it, better to invest in the right tooling rather than put undue wear on the tooling you have,” Baily says.

Taking proper tonnages for granted, one way to fight punch and die degradation is to harden them by induction (with a coil) or a laser, perhaps even with an oxyfuel torch. However, simple torch heating can expand tool material haphazardly and knock it out of tolerance.

In general, the goal of any hardening treatment is to harden the surface of the tool while leaving the core intact.

“I recommend that most production tools be surface hardened to about 1/8-in. [3.175 mm] deep, only in the areas where the tools touch the bend parts,” says Frank Arteaga, head of product marketing for Bystronic, Elgin, IL.

With induction hardening, an electric coil is run over the surface of the tool (on the lower dies’ shoulders and punch tips of upper tooling). The metal is heated to between 25° and 1,050°C, then quenched with water. Most induction hardening penetrates about 3 mm into the surface. Some manufacturers claim that induction hardening can increase tool life by a factor of eight.

Click image to enlarge“It provides more endurance to the tool,” says Steve Brown, press brake product manager for Wilson Tool, White Bear Lake, MN. However, “the manufacturing process changes with induction. You have to heat it up and then finish the tool.”

Laser hardening is more targeted and can pinpoint-harden punch tips and die shoulders, typically at a depth of 0.1 to 1.5 mm. Laser hardening heats the tool surface up much more, to about 1,400°C, but requires much less refinishing work.

Fighting Degradation
Hardness is one thing, but many materials also leave residue of one type or another on bend punches and V-dies. Carbon steel, aluminum, specialty materials such as galvanneal — they all leave residue, probably in the major punch contact zones, that builds up in bend die cavities and impedes proper bending. That residue needs to be scrubbed off regularly if the tooling is to remain viable.

Brown recalls one customer calling him with a bend die problem. He asked them to clean the die before he got there. When he arrived, the galvanneal buildup was visible right away. He gave the die 10 quick strokes with a simple Scotch-Brite pad — good as new.

“They were very relieved … and kind of embarrassed,” Brown says. “I asked them to do exactly what I did when I got there.”

Another tooling-preservation measure that many operators neglect is simply using gloves to handle their tool, as anyone who’s seen a rusty thumbprint on a press brake tool can attest. To prevent corrosion from hand oils and other pollutants, shops should store their press brake tools in safe spot — for example, in an enclosed cabinet, facing down, so that the tools are not exposed to open air, moisture and dust.

“The single biggest thing you see all over the place is people using press brake tools without cleaning them,” TRUMPF’s Bailey says. “A tool cabinet is a great thing for any manufacturer — instruct operators every once in a while, with a rag or brush, just really quick to go over the surface of the tools.” SMT