Getting creative with punch tooling

By Andy Spence-Parsons

April 15, 2008

Keeping a lean program running takes time, effort, and teamwork. To make the most of lean—that is, to understand all of their options in eliminating waste—companies that do extensive work in punching should keep up with innovation in punching tooling. Two such innovations are tools that tap holes and tools that make tabs for sturdy locking joints.

Many fabricators are adopting lean manufacturing techniques to gain a competitive advantage in today's global marketplace. A central element of the lean philosophy is the relentless, systematic, and continuing elimination of waste. The key word is continuing. Starting down the lean manufacturing path and staying on it are different things, as many metal fabricators are discovering.

If you do quite a bit of punching, you might find that, through the creative use of tooling, you can sustain the lean journey, one fabricating project after another.

Going Lean

Figure 1
A tapping tool, loaded into a punch press's autoindex station, cuts threads into punched or extruded holes.

In a recent FabCast presentation by the Fabricators & Manufacturers Association, International®, waste was described as "any element in the conversion of raw material to finished product that does not add value, and which the customer is not prepared to pay for." It follows that the elimination of waste reduces costs and improves the bottom line.

Lean practitioners often highlight eight deadly wastes:

1. Excess inventory
2. Overproduction
3. Overprocessing
4. Rework/defects (scrap)
5. Transportation
6. Waiting
7. Motion
8. Underutilized people

Analyze. When seeking to eliminate waste, many companies begin by evaluating each step in a particular process by using a value stream map or a process map. During this evaluation they examine every step to determine if it is:

Figure 2
Click to view image largerA tapping tool in a punch press eliminates five of the 10 steps needed for this hole-punching and hole-threading process.

• Value-added
• Business non-value-added (any essential task that does not add value, but has to be done)
• Non-value-added (any task that does not add value)

Implement. The next step is to "lean out" the process, or to re-engineer the process to eliminate as much of the non-value-added content as possible. In many cases, a simple change in the manufacturing process will result in huge improvements in productivity and performance.

The most creative ideas come from cross-functional teams—groups that are made up of employees from various disciplines, such as machine operators, engineers, and maintenance personnel. These groups also often include external resources, such as tooling suppliers and machine vendors. Cross-functional teams are particularly successful because participants who are not normally involved in the production process are more likely to ask not-so-obvious questions that may lead to a breakthrough solution.

Creative, out-of-the-box thinking by cross-functional teams, combined with innovative technologies, can go a long way in improving throughput, eliminating waste, and increasing profitability.

Figure 3
Click to view image larger Removing several non-value-added steps from a process that turns out electrical enclosures reduces cycle time from 305 minutes to 150 minutes, a 51 percent reduction in the cycle time. The price was some new tooling and a change to more expensive (coated) material.

Practical Tooling Examples. The following two examples demonstrate a typical lean trade-off: investing in additional tooling but removing non-value-added steps from a fabrication process.

The first example is a simple component with threaded holes.

• In the current state, the threaded holes are created by piercing holes in the punch press, then installing self-clinching fasteners in a secondary operation.
• In the future state, the hole is made by one tool and tapped by another on the punch press (see Figure 1). The hole, which can be punched or extruded, is made by a tapping tool installed in the punch press's autoindex station. Both operations—making the hole and threading it—are accomplished with a single setup on a single machine, thus eliminating setup, wasted transport, waiting time, and motion.

A process chart (see Figure 2) demonstrates that the future state reduces the process time from 160 minutes to 105 minutes.

The second example is a simple electrical enclosure.

• In the current state, the component is punched with a punch press, then formed on a press brake, welded, cleaned, and painted.
• In the future state, the material is changed to precoated steel, and the welded corner joints are replaced by fabricated joints which, when snapped together, lock in place.

Again, the process chart demonstrates that the change has eliminated some non-value-added time and drastically reduced lead-time (see Figure 3).

Figure 4
Specialized tooling for a punch press can create spring-loaded tabs. A button in the top tab engages a hole in the bottom tab, creating a sturdy joint that eliminates several other processes.

The joint tooling assembly eliminates expensive and time-consuming secondary operations such as spot welding, riveting, and fastening with threaded hardware. It is suitable for materials of dissimilar type or thickness and ideal for prefinished materials.

A self-locking, spring-loaded tab that snaps securely into a prepunched hole is the ideal method. The small button in the top of the form is semisheared to provide a positive mechanical lock when engaged with a hole in the receiving tab (see Figure 4).

In both examples, re-engineering the process removed several sources of waste—the time associated with material handling, transportation, and waiting, and the damage that occasionally results from material handling and transportation. It had additional benefits, too, in that it improved the part quality and consistency.