Where joining and assembly operations are concerned, especially those involving fastening, a variety of strategies and technologies can be pursued to help create efficiencies and ultimately reduce operational costs consistent with the principles of lean manufacturing.
Putting the proper equipment in place can make a big improvement in efficiency. Many fabricators 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 specifically designed for fastener installation. The advantage is twofold: equipment used for its intended purpose will not be 'tied up' and the repeatability and accuracy of installation will be optimised.
Once the proper equipment is in place, workshops can make significant strides with the appropriate set-up, tooling, and even the physical location of fastener-insertion presses on the shop floor. Moreover, vendor-managed inventory of fasteners can result in advantageous just-in-time (JIT) parts availability, and some types of fasteners - most notably self-clinching types - are inherently designed to reduce the amount of hardware required in an assembly, delivering streamlined production.
Pressing for improvement
Cost savings derived from fastener-insertion presses will correlate with the time involved in the set-up and running of a press system and employing the most appropriate tooling for the press. Cycle rates for automated press equipment will be critical to realising potential production cost savings, as will ease of set-up and operation.
Operator-friendly touch screens and graphics, on-line help screens, job search and recall modes to reference stored jobs and then return quickly to previous jobs – all these and more can make a big difference to a fastening operation.
The physical location of a press (or presses) can influence productivity, too. Most fabricators typically perform all fastener insertions in one location, setting up multiple presses to handle all installation needs. Presses are usually left in their locations but may be re-grouped to facilitate a particular assembly job. Sometimes one operator will move from press to press or sometimes multiple operators will be used.
On jobs with less demanding delivery requirements, one operator may use a single press and change set-ups as needed. When bending is involved, economies can be achieved by adding an insertion press to a bending cell, allowing bending operations, hardware installation, and completion of necessary brake work to be performed in one designated area.
The introduction of in-die fastening technology presents yet another strategy to consolidate operations and promote efficiencies. Portable systems can be configured in tandem with a stamping press (and properly tooled die) to feed and install self-clinching nuts, studs, and standoffs during the process of stamping components. Thus two operations can be performed simultaneously to save time and money.
Press tooling can certainly play a role in the delivery of ‘lean fastening’. Rotating turret anvil system, for example, enable presses to perform multiple fastener insertions during one set-up. Whether for automatic or manual presses, turret anvil systems can help to increase productivity by enabling quicker set-up times, easy one-handed rotation of the turret, and elimination of time-consuming tooling changeovers when different fasteners must be installed.
With such a system in an automatic press, the operator can auto-feed one fastener type and manually install three other different fastener types by alternating between anvil tools without tooling changeovers. These systems accomplish this by integrating four anvil tools that can be manually rotated 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.
Some applications, such as those with back flanges or recesses that restrict access for self-clinching fastener installation, preclude the use of automated presses and must be performed manually. However, the recent development of bottom-feed clinch-nut tooling for ‘inside-out installation’ has allowed users to forego manual equipment in favour of automatic presses when the volume of fasteners is significant enough to warrant it
‘Smart tooling’, encompassing sophisticated computers and software for fastener installation, is another technology worth considering. Fastener presses equipped with 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 capability will reduce the number of times a chassis needs to be handled, limit the potential for errors or damage, and shorten job duration.
Managing fastener inventory
In addition to innovative press technologies and tooling, a noteworthy trend consistent with lean fastening involves Vendor Managed Inventory (VMI), which simply means that the vendor (for example, a fabricator) manages the inventory of the fastener distributor and takes control over the inventory to keep real-time tabs on needs and parts availability.
The fabricator typically receives alerts from the distributor reporting parts availability and then decides when it will be appropriate to generate a purchase order. This promotes a strong partnership between the workshop and the distributor, and achieves operational efficiencies.
Many forward-thinking distributors, especially those serving the fastening industry, have established VMI-related programmes and can demonstrate their value to workshops on several levels. For the purchasing function, VMI can reduce paper waste, improve order accuracy, and simplify routine; in terms of parts and materials, VMI supports JIT procurement, reduces inventory, and reduces cycle time; and, on the manufacturing side, improved flexibility and the timely availability of parts will advance the goals of lean fastening.
Clinching the case
For assemblies where self-clinching fasteners have been specified, fabricators large and small will already enjoy a built-in advantage when it is time to install the parts. Self-clinching hardware universally 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 – usually requiring only a single mating piece to complete final component attachment.
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 micro pins. This substitution eliminated the time-consuming task of tapping 56 holes in each assembly and ultimately streamlined the assembly process. The pins are simply pressed into place, do not require any rotation for permanent installation, and displace very little material during the process.
Self-clinching fasteners 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, face-to-face panel mounting hardware, and many others.
Newly introduced ‘micro’ self-clinching fasteners, such as those used in the keyboard application above, have broadened the range of possibilities, especially in the consumer electronics marketplace, offering smaller thread sizes and thinner sheet capability than legacy product. Innovative self-clinching fastener designs continue to be introduced to meet new and emerging application needs and it is safe to say that workshops working with pre-specified self-clinching fasteners will reap the associated production rewards.
In summary, workshops using hardware that can perform more than one function in an assembly are well on the way to achieving lean fastening. A fastener with the capability to perform more than one function can make life easier for the fabricator by keeping hardware costs low and production runs high.
Leon Attarian is with PennEngineering in the USA