Fastening two parts together is the root of almost every conceivable production known to manufacturing. Whether it be welding, screwing, riveting, staking, or any other joining technology, fastening is the core process. All other processes, such as pick and place, testing, vision, etc..., are essentially supporting the fastening process. And while other technologies have their particular niches in the industry, there still is no fastening technology that can offer the precision, control, flexibility and ease of use than the screw.

There is a good reason the screw has been the fastener of choice for centuries. The screw can be used in low torque applications, high torque applications, precision applications and general use applications. But one of the most important advantages of the screw, and the reason it will be with us for a long time to come, is the fact it is a non-permanent joining process. We will always need the ability to take assemblies apart for different reasons. The screw is still the most reliable way to join two parts together precisely and maintain the ability to disassembly the joint if needed.

All of that said, how do you go about deciding the best solution to your screw fastening needs? If you follow the evolution of automated screw driving, each step has been an answer to a specific problem. Ergonomics drove the adoption of the self-feeding driver, balancers and torque arms (and to some part, fixed spindles and robots.) Inconsistent torque applied to the screw drove the adoption of transducers for precision torque control. High volume production requirements drove the adoption of fixed or multi-spindle drivers. Cosmetic problems drove adoption of vacuum tipped drivers. And flexible assembly requirements, as well as short-lived product runs, drove the adoption of screw driving robots.

With so many different choices, how do you decide which solution best matches your production needs? The first thing to consider is the screw itself. Can the screw be blow fed? Most screws can be, unless they require an unattached washer, or the diameter of the head (or attached washer) is equal to or greater than the overall length of the screw. If it cannot be blow fed, you can usually use vacuum to pick the screw up from a presenter, or you can use a magnetic tipped driver. Each of these solutions will result in a slower cycle time for the overall process. Once you have figured out what type of feed method you need, you then have to evaluate your application to find out your core need.
If you are looking into automating your screw driving process, there is a reason you are doing so. This reason will drive the proper solution. You may simply need to reduce the stress on your operators, which may be solved by a handheld with a torque arm, or a fixed spindle. Or you may need to speed up production to meet high volume demands, which will be solved by a multi-spindle work cell. You may have multiple products that are only slightly different and want to run them in the same work cell, which is a perfect application for a robotic screw driver. Cosmetics for consumer products are a high priority, or you may have a screw that is recessed in a pocket. In each case, you will need a vacuum tip for your driver. With product life cycles becoming shorter and shorter, you may want to be able to reuse the equipment for your next product, which is easily done with a robotic work cell as well.

There are two different types of decisions you need to make when selecting your solution; quality and production rate. While closely associated, it is best to separate the two when making your decision.

The chart below will help you determine which solution is applicable to your application needs. Place an X in each column (all the way down the column) for each quality issue for your application. If the box for the process is not colored, then that process is not appropriate for your application. For example, if you need to know your screw is at a proper height after fastening, then a handheld driver is not a proper solution. Also, if you only have a simple application with no real quality issues, the N/A portion of the chart represents over-kill for your application.

The example below shows an application that we need to make sure we have a good torque, a good height after torque and can't touch the part.

Chart 1: Process Selection Guide

As you can see, this has eliminated a handheld driver from consideration.

The next chart evaluates your production rate needs. Using the chart below, place an X in the row which best matches the production rate for your product. Normally, there should only be one row chosen in this chart.

The example below continues our application from above. In this case, we have multiple models of similar types that we want to run with the same equipment.

Chart 2: Practical Selection of the Equipment