Quality Magazine

Quality Test & Inspection: How Good Are Your Crimps?

January 1, 2003
If wire harness manufacturers want to offer world-class products, crimp testing is mandatory.

Quality standards are getting tighter, and customers expect their vendors to have quality assurance systems. This is as true for wire harness assemblers as it is for any other manufacturer. Having a good quality system will not only show prospective customers that your company is serious about quality, but it might also help you win an order against competitors with little or no quality systems.

In the crimping world, the two most common tests for crimp quality are crimp height and pull force. Why? Because terminal manufacturers specify crimp height, and specifications from United Laboratories, the Society of Automotive Engineers (SAE) and the military set minimum pull-force requirements. Crimp width is also specified by terminal manufacturers. This specification is important, but it’s usually assumed to be correct because the width of crimp tooling rarely changes unless something goes wrong.

Crimp-force monitoring is the most cost-effective method of ensuring that these specifications stay within tolerance. Crimp-force monitoring can be performed during production. In most cases, crimp-force monitors detect changes in crimp quality, alert the operator, and shut down the machine to prevent repeating defects.

Life would be much easier for wire harness manufacturers if they did not have to do any of these quality tests. But, if they are serious about delivering world-class products, these tests are mandatory. An increasing number of customers want proof that quality tests have been performed. Even when customers do not demand such data, many companies still employ quality-testing procedures for their own peace of mind. After all, shipping bad product can be costly, not only in terms of corrective action, but even more so in customer confidence.

Either way, gathering this data can be challenging and time-consuming. The traditional method of data collection is to take the measurements with independent crimp height or pull test devices and write the results in a log sheet. This data is then manually keyed into a spreadsheet, and crimp height and pull test statistics are compiled for the customer. Manufacturers usually cannot provide any information about crimp-force monitoring, other than a general assurance that it has been done.

Fortunately, today’s quality-testing systems have come a long way. Today’s systems offer more features for the money, provide better consistency and produce fewer errors. Manual data entry is unnecessary, making data collection more accurate, more efficient and more economical.

PC power

As recently as a few years ago, only high-end test equipment had the capabilities that are now offered on more reasonably priced systems. For instance, PC interfaces were once only available on high-end pull test devices priced more than $35,000. Now, PC interfaces are standard on some units as low as $5,000, with data collection and graphics software costing only a few hundred dollars. PC interfaces are also available on crimp height testers and crimp-force monitors. Many devices have onboard memory, so test data can be downloaded after jobs are completed.

A PC interface and onboard memory enable test equipment to be networked. Networking allows engineers to assign testing and job parameters to each device from a central location. As a result, every tester knows the correct parameters for each job. This saves time, because operators do not need to search for new parameters with every job.

Networking also allows test equipment to be monitored from one station. From this station, software can gather data from every tester for statistical process control. Customers can then be given detailed statistical reports, including average values, minimum and maximum values, the number of good and bad crimps, the standard deviation, and Cpk and Cmk values. The report can also include the company’s name, the customer’s name, job number, test device type, test device serial number, terminal number and wire size, applicator number, the correct crimp height and width, and any other relevant parameters, such as pull test rates and hold times. This information can be delivered to the customer for their ISO or QS requirements. It can also be used internally for device maintenance or backup information.

Better consistency

Manual pull testers and crimp height micrometers can be cumbersome and inconsistent. ISO and QS standards require that a process or test be accurate and repeatable from one operator to the next. They require tests, such as gage repeatability and reproducibility tests, to ensure that different operators will achieve similar results.

Pull testers used to be manually or pneumatically operated. Today, they are motorized to ensure consistent pull speeds. A manually activated pull tester can give different readings depending on how fast the operator pulls. Different operators may get different results. Similarly, a pneumatic device can give different pulling rates depending on the air pressure and the valve setting. Motorized equipment pro-vides more consistent pull rates and adjustable pulling speeds. Military, SAE and American National Standards Institute specifications require a pulling speed of 1 inch per minute, but some European customers prefer rates up to 4 inches per minute.

Typically, pull testers cover one range or a maximum pull force. Some pull testers offer multiple ranges, because their accuracy is usually a percentage of the maximum pull force, typically around ±1%. A 50-pound pull test device (±0.5 pound error) will be more accurate than a 200-pound device (±2 pound error). As a result, you would not want to use a 200-pound pull tester on a wire that has a 5-pound minimum pull-force requirement. Multiple-range devices can increase the degree of accuracy over a wider range of wires. These devices can eliminate the need to purchase multiple pull testers to cover your entire range of wires.

The most common tool for measuring crimp height is the handheld micrometer. However, it can be cumbersome to hold and measure a terminal at the same time. Positioning a terminal correctly can be difficult, which may result in inconsistent readings and take up to 25 or 30 seconds. If multiple crimp height checks are taken at scheduled intervals throughout the day on multiple jobs, the total amount of time spent measuring crimps can add up.

Terminal position can be a factor in obtaining accurate crimp height measurements. Many companies are switching to table-mounted units, so that the operator can use both hands for positioning the terminal. Spring-loaded contacts are used in some devices to ensure that the micrometer contacts cannot be over-tightened on the terminal, leading to incorrect readings. To ensure correct terminal positioning, some units employ a foot pedal to record the measurement. This allows operators to hold the terminal with both hands, improving measurement accuracy.

Fewer errors

Most companies manually record and enter test data. However, manual data entry poses two challenges. There is room for error, and there is room for interpretation. Because we are human, we all make errors. Incorrect numbers may be recorded on the log sheet or sloppy handwriting may be misinterpreted and the wrong data entered into the spreadsheet.

Most companies still use manual data entry, because nothing else has been available. However, today’s test equipment automatically records the data into memory with a time and date stamp. Later, the data can be downloaded to a PC. Such devices do not allow the data to be changed, which ensures that the data is accurate and free of interpretation. The time and date stamp associated with each test reading also assures the customer that the values were taken at the right times and that the data correlates with the job that was actually run.

Today’s crimp quality testing systems can be a significant asset, if your company is serious about quality and willing to meet the increasing demands of customers. Crimp force, pull test and crimp height data can be monitored by one PC to make the data collection more efficient and error-free. With the growing demands of ISO and QS, staying up-to-date with quality assurance procedures may differentiate your company from your competition. Q

Tech Tips

  • Crimp-force monitoring is the most cost-effective method of ensuring specifications stay within tolerance.

  • Crimp-force monitoring can be performed during production and if changes are detected an operator can be automatically alerted.

  • PC interfaces and on-board memory are available on crimp height testers and crimp-force monitors. A PC interface and onboard memory enable test equipment to be networked.

  • Typically, pull testers cover one range or a maximum pull force. Some pull testers offer multiple ranges, because their accuracy is usually a percentage of the maximum pull force, typically around ±1%.