----------------------------------------------------Business Index & ASAP------ AUTHOR(s): Fruit, Robert TITLE(s): Move SPC to the shop floor] (statistical process control)(includes related article) illustration photograph Summary: Quality control must be moved as close as possible to where production is taking place so that time and material can be saved. This can be easily achieved by any company since technology has brought statistical process control (SPC) within reach. However, companies wishing to use SPC must do so incrementally. Initially, digital gages can replace mechanical gages for easier and more accurate readings. This can be followed with the purchase of SPC hardware and software applicable to the company's needs. However, caution must be taken in selecting a system. Modern Machine Shop p80(6) April 1993 v65 n11 If your shop is not yet doing statistical process control or is doing it mostly in an inspection lab, here are the basic points about implementing it where it is bound to have the greatest impact. Quality inspection belongs on the shop floor. That's the only place where it can eliminate wasted time and wasted material. There's nothing to be gained with faulty parts piling up while you wait for measurement results from a lab. The closer you move quality measurement and inspection to the place where the work is being done, the sooner you'll know when something goes wrong. You'll catch it, you'll correct it, and you'll continue to make workpieces that meet all of the customer's requirements. And let the customer know you've moved your quality control to the work station and how that step benefits them. It's a plus, especially when seeking contracts from global companies. Fact is, some large companies won't even consider you as a supplier if you haven't taken this step. Some shops have a mind set about quality assurance. They still think of it as the last step before parts are shipped. By then, it's too late. You've lost the time, and you've lost the work. Besides, your customer doesn't even want to think about a part that's out of spec getting past your quality assurance procedures and in his door. The good news is if your shop has a personal computer, you are already halfway to moving measurement to the shop floor. Statistical process control (SPC) has reached a stage of sophistication where almost any size shop can apply it right on the shop floor and benefit from it. No longer is it just for large shops and no longer is it just for high-value parts. Operators Get Feedback SPC at the shopfloor level puts a computer graphic readout at each workstation. It displays whether or not the workpiece--and the process--is in control. The object in SPC is to minimize variability of parts. Operators can "see" how close to nominal dimensions their workpieces are being machined. A display screen shows how each workpiece is being produced against tolerance standards. Should measurements approach allowable limits, adjustments can be made immediately. Workpieces are kept within specifications and rejects avoided. At the same time, data may be fed to a main computer giving management a complete record of what's happening at each station. There are dozens of SPC systems on the market today for moving SPC to the shop floor. You should seek out the one that's right for you. There's a suitable SPC system for just about any size shop with five employees or more. However, not all SPC software products exist on the same level, and shops should be aware of this fact when they evaluate systems for their application. Generally speaking, SPC software can be classified as centered at the workstation level, the supervisor/manager level, or overall shop performance level. Each level requires different functionality. The three products from Mitutoyo Corporation (Paramus, New Jersey) described in the box are representative of products on each of these three levels. How To Get Started For a shop that's been doing its SPC data keeping on paper, the best way to move into SPC is a little at a time. When you need a new caliper, micrometer, height gage or dial indicator, invest in the digital type with an SPC socket. They are much easier to read accurately than mechanical gages, and they don't cost that much more. Typical digital gage costs range between five and twenty percent higher than a comparable mechanical gage. New wireless digital gages are available for radio transmission to computers. A variety of multiplexers, designed for real-time data input from gage to computer is now available. These units eliminate the need for cable between gages and computer. Next step? Acquire the SPC hardware and software tailored to your needs. When you are ready for plant-wide SPC on the shop floor, start with one or two gaging stations. Select the most critical--those upon which the accuracy of the other dimensions depend--as a beginning. The digital gage already eliminates the paper work. No more transcribing errors, either. A caution here. Understand that personnel will be swallowing a lot of new things at once. Go patiently. They may be unfamiliar with computers, the SPC system, the network and new tools and gages. Take the time to train your people, keeping attitudes positive. Keep the initial group small. They, in turn, will become the mentors, motivators and trainers for the rest of the staff. Professional training is available on SPC a few times per year in various parts of the country. Don't Be Hasty Another important point is not to rush out and buy a system. You should work closely with the people who are going to be using the system. You want your people to know what's going on and why it's going on. Talk to them about what it is that will make the process better. You need to do a little pre-selling. You need to point out to the inspectors how some of the gritty details of the inspection job can now be taken to the shop floor. For those operating the machines, you've got a different message. Their job can be enhanced by turning out better workpieces, gaining more responsibility over their own workpieces, and adding to job security. Normally, no changes are made as a system goes into place. You want to find out exactly what's being done. You then ask yourself, "How can we improve this process so that we have less variability?" Studying the gathered data can be revealing. You can spot trends--how one shift compares to another, when operator fatigue is a factor, when tools are wearing abnormally, or what inconsistencies in material properties may exist. Are You Ready For SPC? Even if you are not ready for SPC today, inevitably someday soon, you will be. So why not take some preparatory steps now? Start digitizing your hand gages at purchase time. If you are leaning toward, or even open to the idea of hardwiring your plant for central SPC, it makes sense to go digital. If you presently record measurement data on paper, digital gages connected to a data logging device will quickly pay for themselves out of increased QC productivity. If your shop is not yet doing statistical process control or is doing it mostly in an inspection lab, here are the basic points about implementing it where it is bound to have the greatest impact. If you work in English and Metric, digital gages work in both at the touch of a button. If your operation involves frequent, repetitive measurements, digital will pay off. For instance, if more than 12 micrometer measurements or 20 caliper measurements per hour are made, digital will pay off out of labor savings within three months. Digital eliminates a large source of variation due to the way different people interpolate a vernier. So if different people are measuring the same parameters, digital's best. Also, the tighter the tolerances, the more digital can help. Digital displays give readings down to the 50 millionths resolution. Shops moving to SPC can get a realistic handle on their own success rate by keeping track of three vital statistics: scrap rate, reject rate and rework rate. Shops using SPC are reporting big savings in measurement time in two ways. First, measuring and logging one dimension might take up to 30 or 40 seconds by hand. It's done in two or three seconds with the gage and SPC. Second, as SPC takes over, the need for frequent measurements is significantly reduced through less variability and more reliability. Moving SPC to the shop floor is the logical progression. Spotlight On Software Systems The three software systems from Mitutoyo for acquiring and managing SPC data on the shop floor are fairly indicative of how SPC works on several levels. The systems are MSTAT Real Time, Network Manager and Analytical. Real Time collects data directly from digital gages, connected to a personal computer. It is ideal for fixture applications because it can collect data from multiple gages simultaneously. No operator interaction with the computer is necessary. The operator or inspector looks at measurement data immediately as collected. These data are relative to three criteria: nominal value, engineering specifications and control limits. Each data point is entered and contributes to building six different charts: * colored zone chart (pre-control) * box and whisker chart (plots both the sub-group's mean and range relative to a nominal value) * histogram * statistic screen (CP, Cpk, mean, standard deviation) * X-bar-R, X-bar-S * individual moving range. This system automatically attaches a time and date stamp to the collected data. It can attach traceability and assignable causes to raw measurement data. All data can be collected directly from the gages or entered via keyboard. Up to 99 gaging stations on the shop floor can be monitored simultaneously through the system called Network Manager. From his or her office, the plant manager can oversee all activities via this system. A line of supervision can be established because one Real Time gaging station can serve six different Network Manager stations. The manager's screen has 512 available squares. Each square carries a gaging station number and all other information about the part and process. You can zoom into any gaging station and see exactly what the operator sees. The third system, Analytical, is an SPC analysis package designed to look at data in a more rigorous manner. It features its own macro language for automatic report generation. Any given operator or machine capability can be tracked, and the program can sort measurement data in a variety of ways. The system supports a host of chart types including: X-bar-R, X-bar-S, Individual Moving Range, Interrupted Run Chart, X-bar-S with varying n, Moving Average Moving Range, Histogram, Scatter Charts, Cumulative Probability Plot, N Chart, NP Chart U Chart and Pareto Charts. The Mitutoyo system is unique in that it provides attribute data, not only variable data; things like color and other features. Some other systems give you variable data only. These three systems, and many other systems available today, can be integrated through personal computers. Smaller shops can get a good start with a small investment. For example, one Real Time gaging station and one Analytical system can get a shop going. Not counting the gages needed or the personal computer, a shop will be looking at a ball park figure of under $2,000. For comparison, a larger installation of five gaging stations, one analysis program, and one Network Manager will run close to $5,500. A large installation might have 20 gaging stations, five or six Network Managers, and at least one analysis package. This system might cost up to $20,000, excluding multiplexers, computer hardware, digital gages, and so on. It is important, though, to make sure you work with one integrated database. These systems are compatible with several of the most popular ones.