The lowdown on lean fastening
Proper equipment, shop layout, and hardware help free the fastening bottleneck
Selecting the proper equipment, locating that equipment in the right spot on the shop floor, and using the right hardware can help to introduce new efficiencies and reduce costs in a fabricator’s joining and assembly operations.
While fabricators may quickly recognize the value in taking positive steps to improve quality, eliminate waste, shorten overall production time, and reduce costs, less obvious may be the means to achieve these goals. For joining and assembly operations, especially those involving fastening, fabricators can pursue various strategies and technologies to uncover efficiencies and lower costs. And all of this is consistent with the principles of lean manufacturing.
Using the proper equipment can make a big improvement in efficiency. Many try to make do with equipment already available, such as arbor presses and press brakes. While this might be a feasible short-term approach, they may be better served by acquiring presses designed for fastener installation. This ensures other machines aren’t tied up installing fasteners. Dedicated hardware-insertion presses also increase the repeatability and accuracy of fastener installation.
Once the proper equipment is in place, shops can make significant strides with the proper setup, tooling, and even the physical location of insertion presses on the floor. Vendor-managed fastener inventory can help with just-in-time parts availability. And some types of fasteners, like self-clinching versions, can reduce the amount of hardware required in an assembly. These strategies enable high-product-mix, low-volume shops to do more with less, minimize production costs, and fine-tune operations.
Location, Location, Location
The physical location of a press (or presses) can influence productivity greatly. Fabricators typically perform all fastener insertions in one location. At times they will “gang up” on a particular workpiece, setting up multiple presses to handle all installation needs. Sometimes one operator will move from press to press, or multiple operators may hand off parts from one press to another.
On jobs with less demanding delivery requirements, one operator may use a single press and change setups as needed. Presses usually will be left in their locations but, on occasion, they may be grouped differently to facilitate a particular assembly job.
While this approach is quite common, it may not necessarily be ideal or the most efficient for an application. As an alternative, when bending will be involved, shops would do well to add an insertion press to a bending cell. In this way, bending operations, hardware installation, and completion of necessary brake work can be performed in one area.
Pressing for Improvement
Operator-friendly touchscreens and graphics, online help screens, job search and recall modes to reference stored jobs and then return quickly to previous jobs, onboard self-diagnostics and troubleshooting, and a capability to accommodate and execute custom programs can help a fastening operation become more lean. All this makes a press easier to set up and operate. And when an operator can set up and run a fastener-insertion press efficiently, savings accrue.
In-die fastening presents another strategy to consolidate operations and promote efficiencies. Portable systems can be configured in tandem with a stamping press (and a properly tooled die) to feed and install self-clinching nuts, studs, and standoffs. This allows two operations—stamping and fastener installation—to be performed simultaneously in a die (see Figure 1).
Press tooling can play a vital role as well. For instance, rotating turret anvil systems enable presses to perform multiple fastener insertions during one setup. Whether for automatic or manual presses, turret anvil systems shorten setups and reduce their number. Installing four different types of fasteners while handling a workpiece only once can save time and reduce the need to gang up on a job, because many insertions can be performed on one machine.
In an automated setup, these systems integrate four anvil tools that can be manually rotated quickly into position—one dedicated to the automated feed tooling for the highest-volume fastener installation, and the others for manually installing up to three different parts. This means that the operator can auto-feed one fastener type and manually install three other different fastener types by alternating between anvil tools—all without tooling changeovers.
Applied to a manual-feed press, a turret tool system allows the operator to install four different fasteners manually. He can alternate between four anvil tools and install four different types and/or sizes of self-clinching fasteners, using only one press and one initial setup (see Figure 2).
Fastener presses with so-called “smart” tooling can be engineered to install several different types of fasteners in the same chassis, while the system’s computer keeps count and monitors installations for accuracy. This reduces the number of times a chassis needs to be handled, limits the potential for errors or damage, and shortens the job duration. This approach especially benefits jobs in which visual assessment of fastener installation either is impossible or potentially inaccurate, because the monitoring system can measure the optimal installation point and notify operators when fastener installation has been properly completed.
Managing Fastener Inventory
Of course, no matter how efficient presses are, they can’t be productive without the right fastener in stock. For many shops, vendor-managed inventory (VMI) helps ensure the right fasteners are available at the right time. The fabricator typically receives alerts from the distributor reporting parts availability, and then decides when to generate a purchase order. This promotes a strong partnership between the shop and the distributor and accomplishes much operational efficiency.
As an example, before implementing a VMI program, one shop created its own inventory plan and then monitored and controlled its own inventory levels. When the shop perceived that it needed more inventory, a purchase order would be issued. But this approach assumed that inventory would be available in a timely manner whenever and wherever needed, which was not always the case. This inevitably led to interruptions in production. Switching to a VMI system, the fabricator was able to track the distributor’s parts sales and current inventory levels continuously, generate a purchase order when inventory was decreasing, and ensure parts were on hand for delivery and use.
Many forward-thinking distributors, especially those serving the fastening industry, have established VMI programs that demonstrate their value to shops on several levels. For the purchasing function, VMI can reduce paper waste, improve order accuracy, and simplify routines. In terms of parts and materials, VMI supports JIT procurement, reduces inventory, and shortens cycle times. On the manufacturing side, improved flexibility and timely parts availability help to advance the goals of “lean fastening.”
Clinching the Case
Self-clinching hardware usually requires only a single mating piece to complete final component attachment, so it reduces the amount of hardware in an assembly (such as loose washers, lock washers, and nuts) and, as a result, reduces the number of secondary fastener-related operations.
As a recent example, a contract manufacturer traditionally had used 56 M1.2 screws to hold a keyboard assembly in place, but made a switch to self-clinching micropins. This substitution eliminated the time-consuming task of tapping 56 holes in each assembly and ultimately streamlined the assembly process. Now the pins are simply pressed into place, do not require any rotation for permanent installation, and displace very little material during the process.
Dozens of types and thousands of variations of self-clinching fasteners (commonly steel, stainless steel, or aluminum) have been engineered over the years and have logged a long history overcoming thin-metal attachment challenges. They provide permanent and reusable load-bearing threads in sheets too thin to be tapped or where extruded or stamped threads would be impractical.
Notable self-clinching fastener product families include nuts, studs, spacers and standoffs, captive screw assemblies, cable tie mounts and hooks, and face-to-face panel mounting hardware. Micro-self-clinching fasteners, such as those cited in the keyboard application, have expanded possibilities, especially in the consumer electronics market, offering small thread sizes and thin-sheet capability.
Shops with fasteners that can perform more than one function in an assembly will see even more gains. A fastener that can perform more than one function can make life easier for the fabricator by keeping hardware costs low and production runs high.
Can a fastener perform more than one function in an assembly? How many fasteners does an assembly need, and can self-clinching or other fastener types reduce that number? Can workers find the right fastener quickly, in nearby containers that are clearly labeled? Are the right fasteners in stock at the right time? Can a fastener press be automated? How quickly can the operators change over from one fastener to the next? Should fastener presses be located in one department, or within workcells or near upstream machinery like press brakes?
Boiled down, all this really centers on the duration and number of changeovers—or, more broadly, the time it takes to move from one job to the next. Are so many changeovers necessary, or would alternative fasteners or presses help? How many steps do operators walk between machines? How long do they spend looking for the right fastener, or setting up a press? Like most processes on the shop floor, the greatest waste in fastening occurs not during operations, but between them.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.