Quality Scan: Buying Measurement Systems
At the same time, the chosen system must be capable of executing the required measurements within the appropriate tolerance range. To resolve this dilemma, there are basic considerations that will guide you towards an educated purchasing decision.
Investigating various measurement and inspection systems can be a daunting task. And it can be particularly frustrating if the requirements of a particular project drive the need for the solution. So what would be a good way to proceed? First and foremost, you must have a firm grasp of the "required" measurements—those determined as critical to the manufacturing process, or measurements that exhibit the greatest fluctuation during manufacturing.
You want to separate those "critical" measurements, which are generally fit-and-function types of dimensions. Ask yourself if each measurement is qualified and quantified appropriately. Can major scrap result in this dimension being out-of-tolerance (OOT)? Or would the OOT condition, although workable, create a major or additional expense (either internal or external) to make the part salvageable?
What types of dimensional data must be gathered from your parts? Do you need to measure or inspect points, features, surfaces, roundness, or other important data types? Are there hard-to-reach areas on your parts that need to be inspected? This information will help determine whether you need additional data acquisition capabilities, such as wireless probing or precision scanning.
Through the years, the industry has evolved towards faster data acquisition. While speed is a factor for consideration, it should not be considered more important than proper measurement methods, even if cost is a sizeable factor. Rather than compromising measurement accuracy, further investigation is warranted to locate metrology solutions that come closer to your specifications for speed and precision.
Now that these factors have been identified, it's time to evaluate the logistics of your inspection task. What is the size/weight of your parts or assemblies? Will the size of your parts change in the future? Do you have a separate room available for a controlled QC environment? What environmental conditions exist on your shop floor—vibration, temperature fluctuation, and more? The answers to these questions will help determine whether your company will need a stationary CMM or a portable CMM.
Next, the price of a dedicated vs. a multitasking measurement system must be weighed against the overall benefits provided to your manufacturing process today—and tomorrow. Too many times, companies buy dedicated metrology equipment for the immediate need, and end up having to buy more equipment (at a greater cost) further down the road.
If a company only needs to measure the roundness of a hole on a part, for example, they would search for a dedicated geometry machine to determine the hole's roundness. But if the company later decides they want to measure hole position, the dedicated system generally will not provide that capability. In the end, you must determine whether it's wiser to buy a system capable of measuring various parameters with single or minimal setups, or a system dedicated to the application at hand.
Finally, look at what the measurement marketplace has to offer in terms of both new technology and proven technology. Which provider is developing innovative new products? Who are the veteran players? There are many metrology companies willing to help you spend capital, but you must find a provider who can explain the definable investment difference for your overall operation. Is there research available to prove the "true benefit" of their system? Are there case studies to prove success in the type of application you are looking to measure?
You must take the time to carefully consider the viability of each metrology manufacturer. What factor enables them to sell into the specific market—price, availability, functionality? This answer can narrow the gap between a provider that can provide fundamentally solid investments, and those more focused on their marketing skills. As the metrology industry continues to evolve, the value of your return on investment is directly linked to your long-term partnership with a reliable technology provider.
This article was first published in the June 2007 edition of Manufacturing Engineering magazine.