2005 Articles

Change(over) is inevitable, and assembly efficiency can be aided by intelligent feeders and better software.

A distinct shift in U.S. electronics assembly began during the downturn of 2001. At this time, the focus of placement machines changed from high volume to high flexibility. A quick, unscientific survey of magazine advertisements for major pick-and-place machine suppliers shows four of five mention either “flexibility” or “modularity;” just one touts “high volume.” Furthermore, no chipshooters were displayed at the past two Apex shows or at Productronica in 2003. In general, this trend is showing no signs of abating. Manufacturers continue to introduce models focusing more on flexibility and modularity rather than sheer speed.

What does this say about the U.S. and European markets for placement machines? OEMs and EMS firms are sending high-volume, low-changeover product overseas, but are not completely abandoning the U.S. Rather, they are adjusting to the types of products that can be profitably assembled in North America. There, assembly has shifted to new product introductions and higher profit margin items. These types of production generally go hand-in-hand with smaller lot sizes and frequent changeover. It does not mean that placement speed is unimportant, but the time lost in changing jobs several times per day can easily negate the high speed of chipshooters. It is like the case of the tortoise and hare, though most placement machine vendors would not like their machines compared to the tortoise.

Most high-speed chipshooters – those capable of placement rates of 50,000 cph or more – were not designed with small lot sizes in mind. They were designed to go as fast as possible and to run the same board for an extended time. Changeover was not a consideration, and complete product changeover can often take more than four hours to perform. In recent years, some flexible features have been added, but it may be too late to save the chipshooter market in the U.S.

Modular machines were invented as the flexible alternative to the big, expensive, fast chipshooter. The overriding goals of most modular machines are flexibility and frequent changeover. The machines themselves are usually much smaller and often come in families of similar models with different specialties that complement each other (such as faster, limited component range or ultra-flexible).

Being smaller, it is comparatively easy to rearrange the entire production line to accommodate changing needs. Adding a machine to increase production capacity or to handle a different type of component usually takes a few hours. Moving a chipshooter, on the other hand, can be an all-day job. The modularity of the newer machines is also helpful when component technologies are introduced. For example, when 0201s first started to appear, many existing machines could not place them. With a chipshooter often costing more than $750,000, it would be very expensive to replace the machine just to add 0201 capability. With a modular line, it is fast, easy and relatively inexpensive to add a new machine that has the capabilities needed. Modular machines can often use the same feeders as existing machines and work seamlessly with the line control software.

FIGURE 1: Offline feeder trolleys coupled with setup software can reduce changeover time to seconds.

Until about 1994, feeder banks were fixed on machines, requiring every feeder to be changed individually. One of the first real breakthroughs that modular machines introduced was the concept of feeder trolleys or carts. Since then, trolleys have become a standard option for virtually every equipment manufacturer. Early trolley designs suffered from some positional errors that meant that pick positions might need to be re-taught, diminishing the quick change benefits. But the early problems have long since been overcome. Trolleys now use more accurate locking mechanisms and may even have fiducials to dynamically adjust for any variations. Using trolleys, complete production jobs can be set up offline (Figure 1). When the time comes to change, entire banks of feeders can be changed in just seconds, or minutes for the whole line. This gives U.S. manufacturers the flexibility to build five or even 10 different jobs in a single day.

Even with trolleys widely available, manufacturers continue to look for even faster changeover. Equipment manufactures look at their overall design and invent new options to shave time from changeover.

On the machine side, there is not much to be done during changeover once all the feeders have been replaced. All that is typically required is adjusting the conveyor width and possibly some tooling or support pins. Automatic conveyor width adjustment is already widely available. Smart machine designers are looking for ways to reduce or eliminate the need for tools during changeover. Support or tooling pins can often be adjusted without any special tools. However, adjustments to the conveyor are quite quick because so few adjustments are needed for each machine. So the opportunities to save additional time are fairly limited.

One of the most time-consuming parts of any changeover is the replacement of feeders. A single board can often have more than 100 feeders and sometimes for a complete changeover the two jobs lack even a single common feeder. This means each feeder needs to be removed and replaced. Trolleys permit the preparation of future jobs offline, which means you can multi-task, but they do not help with the overall time needed to set up all the feeders. For a small lot size with many feeders, it is possible that setting up the new feeders takes longer than the total production time of the previous job. To reduce the feeder loading time, companies have introduced software to simplify the process.

Two common options are setup assistance software and intelligent or smart feeders. Setup assistance software is similar in function to intelligent feeders, but without as much automation. Setup software usually extracts a list of the required feeders and leads an operator through the process of loading and placing the feeder on offline feeder trolleys. This saves time and increases accuracy by providing a graphical step-by-step procedure for the operator. They do not have a simple printed “load list” where operators may jump around in any order and possibly forget feeders. In many systems, there is a positive confirmation, usually by barcode, that the correct reel has been placed in the correct location. The “wizard” guides users through the process and provides peace of mind that the right feeder has been set up.

Intelligent feeders take setup assistance software to the next step. Instead of manually scanning a barcode to verify the feeder has been placed correctly, intelligent feeders communicate directly with the machine (or network) as soon as they are connected to the machine, to verify the part number and location. Intelligent feeders eliminate the need to scan feeder slot numbers, as is commonly required in setup assistance software. This reduces setup time and improves accuracy versus manually scanning barcode labels. Intelligent feeders and setup assistance software often offer additional benefits such as component traceability (the ability to track which lot code or lot number has been placed on every board assembled) and inventory control.

Yet intelligent feeders and feeder trolleys reduce changeover time only to a limited extent. Neither addresses the actual time needed to load each feeder used to assemble a particular board. There really is not an option that reduces the time needed to set up a single feeder. It is incumbent on manufacturers to design feeders that make it easy to reload a reel. But there are ways to reduce the need to replace reels. The first is splicing – when a new reel is spliced to one already loaded on the machine. Splicing is limited because feeders and machines need to be specially designed and it does not offer much benefit unless a fairly high volume of production is being run and more than one reel is needed.

Another option to reduce setup time is to simply reduce the need to change feeders at all. Clustering software can group together boards with similar components into families of a single feeder setup. It can even be used on totally dissimilar boards, but the amount of available feeder space will limit the clustering possibilities. With clustering, an operator can set up a line once and run several boards, usually only limited by the total feeder space available on the line. There are also modified forms of clustering, such as leaving feeders that are common to several jobs in place and replacing only the unique feeders. This can work well when there are too many unique parts to have all feeders online at the same time. Clustering does have limitations, however. It requires feeders to be placed in non-optimal locations, which means the production time of a single board will usually be slow. This tradeoff between optimal speed for individual boards and reduced setup time must be weighed on a case-by-case basis. Some software can simulate the available options, however.

Rapid and frequent changeover has become an unavoidable fact of life in the U.S. assembly market, particularly as higher volume jobs go over sees and domestic manufacturers see a relative increase in lower volume jobs. With no sign of the trend subsiding, it seems unlikely we will see the return of large, dedicated chipshooter lines any time soon in the U.S. Modular machines and an increasing variety of options give manufacturers the benefits of being able to rapidly and economically respond to changes and control costs through relatively painless machine changeovers.

Gerry Padnos is director of technology, Juki Automation Systems (juki.com); gpadnos@jas-smt.com.

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