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issue: June 2005 APPLIANCE Magazine

IATC 2005 Best Paper
Major Appliance Teardowns: A Review of Electrical Interconnection Results


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by Brian J. Stumm, director of Engineering, Engineered Products Division, ETCO, Inc.

IATC 2005 Best Paper: The following is an edited version of the winning paper presented at the International Appliance Technical Conference (IATC), held March 28-30, 2005. The author was awarded the Dana Chase, Sr. Memorial Award for the best paper presented at the conference.


Figure 1 (left), Figure 2 (middle), Figure 3 (right).

As a manufacturer of connectors, product teardowns are useful in reviewing one�s own product as well as the industry into which it fits. This paper will discuss a series of teardowns and what they revealed. It will further discuss the potential of teardowns as a valuable tool in the pursuit of quality.

The major appliances that are found in most homes today have a common design aspect; they utilize, to varying extents, discreet components that are connected together by standard electrical connectors terminated onto wiring. The wiring used ranges from individual connections to complex wire harnesses (including modern RAST-style harness designs). These harnesses are a key and vital component to the reliability and function of the major appliance in which they are installed; they can also be a source for potential problems, as evidenced in the results of past product teardowns.

In a complete product teardown, all aspects of the unit are observed, documented, and analyzed from a quality and engineering perspective. The process used in the implementation of a product teardown is a matter of personal preference, as long as the methods used are well documented and consistent. The data collected must be collected in sufficient detail, and care must be taken to insure the integrity of any remaining items to be studied.

The process that is selected for a given teardown is typically dictated by the objective of that teardown. Different types of manufacturers will focus their efforts differently in order to benefit their own business. They will use the teardown process to observe their product in the end-state, as well as to gain information with regard to the impact that their product/process has (both up and down stream) on that product. A connector manufacturer, for example, would see how their connectors were terminated and where their product was used throughout the appliance. They would also observe how the wire harness was constructed, installed, and mated to the components within the appliance.

Procedure


Figure 4 (left), Figure 5 (middle), Figure 6 (right).

This paper will discuss several examples taken from actual teardowns that were performed on major appliances to investigate their electrical interconnections. First, a brief description of the process used in the teardowns should be given. Each step of the teardown was fully documented in order to preserve the exact condition of the given appliance and its components for future reference and verification. Documentation took the form of digital photography and detailed written notes.

An appliance teardown is started with the removal of the outer sheet metal and door(s). As with each step of a teardown, anything unusual is recorded as it is observed. Once the wiring is exposed, each of the individual electrical connections are identified and marked. Starting in one location, each electrical connector, regardless of whether it is connected to a switch, heating element, or sensor is carefully photographed to capture its mated, undisturbed state. Once photographed, each side of the connection is numbered and recorded. Figures 1 and 2 show how each layer is documented before being disturbed for numbering and identification.

Each recorded electrical connection is identified by its number on the wire and mating component. The recorded information includes the connector type (ring, spade, disconnect, etc.), the size of the connector (0.187 in, 0.250 in, #8, etc.), its material composition and plating, the wire size to which it is terminated, and information on the termination itself (height, width, and general condition, etc.). Once all of the visible electrical connections have been identified and recorded, they are then disconnected and carefully moved to allow for further disassembly of the appliance. Once the teardown is complete, the documented data is organized for further study.

Figure 7 (left), Figure 8 (middle), Figure 9 (right).

Teardown Results

Reviewing all of the results from the various teardowns that have been completed, we can summarize the problems into four general categories�assembly, design, manufacturing, and termination.

Assembly

The assembly problems that were observed during teardown appear to have been created during the final stages of assembly of the appliance. The following are examples of the various problems observed that could be attributed to assembly. During one teardown, an open control panel revealed a disconnect lying against the metal frame. After some investigation, it was determined that the disconnect was supposed to be connected to a tab that was made out of sheet metal. Figure 3 shows the disconnect as it was originally installed. During another teardown, a disconnect was found partially installed onto the tab of a cooking element; Figure 4 is the image of the disconnect as it was originally discovered. The last example for problems attributed to assembly is a motor-wire connection that was crushed during final assembly, as shown in Figure 5.

Design

It is more difficult to definitively determine the cause of problems related to design issues. This is primarily due to the fact that the original design intents and the product prints are typically not available at the time of the teardown. The sheet metal tab, shown in Figure 3, could be assigned to either assembly or design categories. Based on the fact that the sheet metal tab was not made to the disconnect standard, it is most likely a design issue. Two possible options to correct this problem would be to design the sheet metal tab to the disconnect standard or a different terminal could be chosen that would be a more appropriate connector for a sheet metal edge.

Another potential design issue was a connector that had its attached wire length made too short; Figure 4 shows this straight connector with the short length of wire between the terminals, resulting in the red wire being bent at a 90-degree angle to the mating end. Other design related issues aside from connector selection or harness designs are component connections. One example is a component that has non-standard integrated tabs. The tabs are non-standard in that they are required to have a constant width down to their end, or to an optional shoulder, but do not.

Manufacturing

Manufacturing issues can be found in many aspects of the appliance, but the majority found during these teardowns can be attributed to the process of creating the harnesses. One reason for this is that appliances, in addition to individual components, have a large number of harnesses. In Figure 6, a double wire termination for flag-style connectors is shown. This configuration is common to many wire harnesses. In this figure, it can be seen how the wire insulation was stripped back to two different lengths. This is of serious concern because terminals are not typically designed to accommodate unprotected wire strands within the insulation crimp of a double wire termination. The benefits of having an insulation crimp is lost when this phenomena occurs. Figure 4 showed a tight wire situation that was attributed to a design problem, although it could also have been a manufacturing related issue.

Termination

For the purposes of this work, termination issues will be considered as those that are a group of problems associated with the wire and insulation crimping, as well as the tooling used to create the crimps. Terminations must be inspected in order to identify problems and to ensure that they pass the associated manufacturer�s requirements and any UL requirements. Some of the problems can easily be seen with a casual visual inspection; other termination problems require cross sections and more detailed reviews.

Problems with the wire terminations can potentially lead to abnormal heating of the wire crimp and potential failure of the terminal and appliance. Figure 7 depicts a wire termination with the high-temperature glass insulation braid caught in the wire crimp; aesthetic considerations aside, this situation can also be indicative of a wire stripper problem. A more detailed review of this same termination identified more serious problems. A close-up view reveals a tear in the terminal caused during the termination process. Also, an open gap in the cross section of the crimp is not preferred and is indicative of an applicator problem with either the setting or the tooling itself. The variations in the crimp, and what is preferred, will be discussed in the next section.

Another common termination problem is related to the insulation crimp; Figure 8 is an example of insulation crimp problems. Improperly adjusted terminations that are too tight can allow the insulation ear ends to penetrate the insulation and damage the wire strands. In the other extreme, a termination that is adjusted to be loose can allow the wire to move around, which can damage the wire and lead to a failure of the crimp. One possible reason for these tooling problems is the use of tooling other than that specifically designed by the connector manufacturer for the given terminal and wire combination. Not using the connector manufacturer�s specifically designed tooling could lead to problems with the crimp quality as well as the tooling itself.

Figure 10 (left), Figure 11 (middle), Figure 12 (right).

Crimp Quality

As discussed previously, there have been a wide variety of problems associated with the termination process of the electrical connectors onto the harness wires. Problems have been identified in both the wire and insulation crimps. A worn anvil or rolling tool can appear to create a good termination when viewed externally, but inside the crimp the wire strands may not be properly deformed. Additionally, the ear may be fractured or damaged, allowing for potential reliability problems during the life of the product. Figure 9 shows a typical cross section of a crimped wire termination that has a proper anvil and rolling tool; the section shows minimal side extrusions, tight meeting between the edges along the top, and good deformation of the wire strands into a honeycomb pattern. All of these features should be evident in a wire termination using an open barrel design.

Poor quality tooling can lead to chipping or premature wear on the tooling. If the anvil has been damaged, the cross section of the termination can look similar to Figure 10, which shows extra extrusions along the sides. If the roll tool is damaged or worn, the resulting cross sections can appear similar to Figure 11. When both tools are not properly maintained the resulting crimp will probably look visually poor and the cross section would reveal something like what is shown in Figure 12.

Brian J. Stumm has worked in the electrical connector industry for more than 12 years and is currently the director of Engineering for the Engineered Products Division of ETCO, Inc. (Warwick, RI, U.S.). Mr. Stumm holds B.S. and M.S. degrees in Mechanical Engineering from Rochester Institute of Technology and is completing a M.E. degree in Electrical Engineering from Penn State University.

Conclusions

This work has highlighted a number of problems identified in a fairly small group of products. The teardowns performed were detailed and looked at every connection and termination. Given the small number of products involved in the teardowns, the number of issues revealed by them is somewhat disconcerting. Perhaps more disconcerting is the fact that most of these appliances were taken apart right after being uncrated, having had no usage or movement to explain the observations.

Many times the electrical connectors and wire harnesses are the last items to be designed for an appliance. The importance of choosing the proper terminal is often minimized due to the relative cost of terminals when compared to the other components. This is unfortunate since it is these components that contribute to many field problems. One possible way to minimize these problems is for the appliance producer and harness and electrical connector manufacturer to work together to ensure that proper design decisions are made from the beginning.

As shown in this work, the teardown process, while time-consuming, is a valuable tool that can be used to generate feedback on a wide variety of items within an appliance. The feedback can help improve the overall quality and reliability of the appliance and reduce the potential for field failures.

 

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