RAST and IDC: Coming to a Washer Near You?
April 1, 2006
It started in Europe as a means of eliminating mistakes in the final assembly of appliances. It ended up bringing together connector manufacturers, machine builders and wire harness makers in a new set of standards and an assembly technique that is helping save jobs in Western Europe. Now it's coming to North America.
Back in the 1980s, European appliance manufacturers found themselves facing a host of problems stemming from the growing complexity of their products. In contrast to most North Americans, European customers have long been willing to pay a premium for appliances that use less water and electricity. Unfortunately, the sensors, electronic controllers and electrical actuators involved in meeting these demands, resulted in growing quality issues in the form of crossed and mismatched wires.
To solve this problem, appliance OEMs, wire harness makers and wire connector manufacturers, decided to create a block-terminal standard, along the lines of what automotive manufacturers had been using for some time. The result was a connector standard called Raster Anschluss Teck Technik, or RAST, which roughly translated means "pitch connection plug technology."
As part of this process, the appliance industry also hit on the idea of implementing insulation displacement connector (IDC) technology in its harnesses as a means of both improving quality and enabling more efficient assembly.
In contrast to a crimped connector, an IDC connector incorporates preloaded internal contacts that cut through a wire's insulation without having to strip the wire first. An IDC connector's contacts also engage a wire using far less force than is required when crimping. As a result, assemblers don't have to worry about damaging or cutting threads during the terminating process. Nor do assemblers have to be as concerned about problems with the connectors working loose as the stressed wire and crimp materials relax over time-a particular problem when working with smaller-gauge wires.
Because IDC terminals simply snap shut over a wire or are terminated in a single step using hard tooling, they naturally lend themselves to high-speed, fully automated assembly and testing. In fact, depending on the model of connector, more than 30 wires can be terminated and then tested simultaneously. Presented with these kinds of efficiencies, Western European appliance titans like Electrolux, Bosch Siemens and Whirlpool suddenly found themselves with a very good reason to not outsource their wire harness work to countries in Eastern Europe, Asia and Latin America.
"IDC has made a huge difference," says John Risch, North American electronic products manager for German-based connector manufacturer Lumberg Inc. (Midlothian, VA). "In at least one instance, appliance manufacturers have gone from being in the red to being in the black."
Making ConnectionsIn codifying their RAST standards, European manufacturers created two basic categories. The first, RAST 2.5, refers to multiple-wire connectors with a 2.5-millimeter pitch, or spacing. This category is used primarily for low-power control circuits. The second, RAST 5, defines the parameters for connectors with a 5-millimeter pitch. In practice, this type is used primarily for higher-amp power circuits.
At its most basic, a RAST connection is comprised of a header receptacle mounted on, say, a motor housing or a controller PCB, and a block connector terminating anywhere from one to a couple of dozen wires. Although the wire termination portion of each connector model varies depending on the manufacturer, the "plug" side, or connector face for all RAST connectors is standardized. Therefore, a header from, say, Tyco Electronics (Harrisburg, PA) can be used with a connector from Molex (Lisle, IL) or Lumberg, and vice versa.
In addition, the connector faces, which incorporate latching features to ensure a solid assembly, are all manufactured with RAST-standardized keying and color features. This means a connector that is supposed to be plugged into a controller board won't be mistakenly attached to a washing machine turbidity sensor. Similarly, the same RAST connector that a manufacturer uses to plug a wire harness into an electric motor won't be used to create a connection to a pressure switch.
It's this kind of inherent error-proofing that has made believers out of European appliance makers, among which the use of RAST is now almost universal. In fact, throughout the process, there are multiple layers of quality assurance, to ensure that each harness performs as intended. First, you have complete, functional test as an integral part of the assembly process. Second, you have a relatively low-force, minimal-deformation terminating technology that is less susceptible to breakage during shipping, handling and installation. Third, you have a system that makes it virtually impossible for an operator to cross any wires, as is all too easy when using wires individually terminated using ring terminals or spades.
"As sensors and controls were added, [the Europeans] faced a jumble of wires... Having specific types of keys for each component makes things manageable," Risch says.
This is not to say that IDC is a piece of cake. In fact, while simple in concept, creating a reliable IDC connector requires some very precise engineering. Manufacturing tolerances must be extremely tight if each connector's contacts are to effectively pierce each wire's insulation and create a good circuit. "IDC is not a simple thing. It takes quite a bit of know-how," says Risch.
Then there is the equipment required for implementing fully automated, in-line test and assembly. Turnkey systems from wire processing companies like Komax (Buffalo Grove, IL), Schleuniger Inc. (Manchester, NH), Lumberg, or Tyco Electronics represent a substantial investment. In most cases an effective system is the result of experience and close cooperation with terminal manufacturers.
Still, given the flexibility and potential cost savings available through the implementation of IDC and RAST, it is worth the effort in the right settings. It is interesting that the RAST standards can also accommodate conventional crimping. However, over the years, IDC has steadily gained momentum, and with European manufacturers targeting Asia and India as prime targets for market growth, RAST standards are fast becoming the norm worldwide.
Coming to a Washer Near You?One part of the world where RAST has yet to carve out a substantial niche is in the North American appliance market. But that may soon change. According to Jeff Hummel, RAST product manager at Tyco Electronics, RAST connectors can already be found in some top-end washers and driers, and they are fast working their way down into midrange laundry products. RAST connectors are also appearing in some refrigerators and dishwashers.
One of the problems with making the transition to RAST-and the primary reason for the delay in its use on this side of the Atlantic-is that it can't really be done piecemeal.
Hummel says he knows of a handful of cases in which a U.S. manufacturer has been forced to add a RAST terminal to an existing harness design. Generally these manufacturers are forced to take the step because they want to incorporate a European-made component that is only available with a RAST header. But this approach-which can be accommodated using a handheld or benchtop IDC terminating machine, or by using RAST connectors in which the wires are attached into the connector only after being terminated with crimped spades-doesn't begin to take advantage of the cost benefits of the technology.
"If a company implements only partial use of IDC there's no huge benefit," Hummel says. "It's the buying into the complete RAST mindset that makes the difference."
Another impediment to RAST implementation is the fact that it can be difficult or even impossible to retrofit an existing wire harness design to accommodate a dramatically different technology. In a traditional appliance application, the harness is one of the first things to go in. An operator, or operators, runs each machine's requisite wires-its "nervous system," so to speak-after which the machine's various electromechanical subassemblies are attached and plugged in.
With RAST, manufacturers have the option of using multiple wire-connection assemblies, as opposed to a single, all-encompassing harness, thereby delaying much of the wiring until later in the assembly process. In fact, some European designs even include dedicated raceways to help assemblers run their grouped, snap-lock RAST cables from point A to point B. Hummel notes that this wiring approach yields additional benefits in that it lessens the chance of an operator damaging the wires during subsequent assembly stages.
Not surprisingly, it takes time to get used to these kinds of changes in thinking. But according to both Risch and Hummel, the latest appliance designs currently on North American drawing boards are taking advantage of RAST as never before. Hummel adds that most manufacturers' experiences with RAST and IDC have been such that they realize it's the way to go.
"In some cases it's been a crawl, walk, run situation. In some cases it's been, ‘yeah, that's the direction we want to go,'" Hummel says. "Part of the problem is that we're talking about something that was developed over 15 to 20 years in Europe.... [The process] has been very compressed here in North America."
Is There Life Beyond White Goods?In terms of RAST applications outside the appliance sector, the future is mixed to positive. However, given the current success RAST terminals are enjoying, both in terms of quality and cost-effectiveness, it's almost certain that RAST or "RAST-like" connectors will find applications beyond the kitchens and laundry rooms of the world.
For example, RAST is already making inroads into the HVAC market, where manufacturers are taking advantage of the system's mistake-proofing benefits to ensure reliable assembly. Similarly, in the automotive sector, where block terminals are already a fact of life, RAST terminals may some day be used in dashboard applications or in wiring increasingly complex onboard entertainment systems.
For example, Lear Corp. (Dearborn, MI) has been studying the use of IDC connectors in airbags, taking advantage of the technology's cost savings and-even more important given the critical nature of any safety application-their iron-clad reliability. In fact, according to Slobodan Pavlovic, engineering director of Lear's T&C Division, in over 30 million IDC terminal applications in the field, he has yet to encounter a single failure. The connectors have exhibited equally impressive performance in laboratory tests as well.
Pavlovic notes that in many ways, carmakers are dealing with a situation that is analogous to that faced by appliance manufacturers-increasingly complicated onboard electronics are resulting in increasingly complex wire harness assemblies. "Automotive content is changing significantly, to low-power applications using small wires," he says. "When you talk about changing wire sizes you are talking about changing technology."
Beyond the automotive sector, RAST will have to prove itself on a case-by-case basis. In the area of consumer electronics, for example, RAST represents a mixed bag. On the one hand, low-cost and reliability are of vital importance to those assembling products like cell phones and video games. However, because of the never-ending drive toward miniaturization, space is at a premium, and because of their bulk, RAST connectors, by default, are at a disadvantage.
In some cases, manufacturers may be able to employ RAST 2.5 edge-card connectors. Using this approach, the connector is clipped directly to the edge of the printed circuit board, where it makes contact with a set of printed pads. This approach also saves the expense of having to install headers on the board.
However, according to Komax product manager Urs Renggli, RAST connectors face an uphill battle, in part because so much electronics assembly is done in Asia where labor costs are low enough that crimp terminals can still be installed cheaply. Renggli also notes that the fine-pitch requirements of many consumer electronics assemblies are such that even those manufacturers interested in implementing RAST will have trouble doing so, given current RAST standards.
RAST terminals are also having trouble penetrating the small appliance market because the wiring in, say, a blender is far less complex than that in a washing machine: Simply put, crossed wires aren't as much of a concern when you're operators aren't being forced to sort through a bunch of spaghetti.
Ultimately, the RAST approach to wire harness assembly represents a very specific solution to a very specific manufacturing challenge: a wire harness that is robust; reliable; inexpensive to manufacture in large volumes; and easy to install without the possibility of crossing wires. For many manufacturers-like those producing in smaller volumes, or those whose products do not require complex assemblies-the costs of changing over will simply outweigh the benefits.
However, for those manufacturers whose assembly processes fit the bill, RAST or RAST-like automated IDC wire terminating may very well offer a world of opportunity.