What to Know About Automatic Gages

Although automatic gages have been a part of the production scene for more than half a century, they are generally misunderstood by more people than any other class of dimensional measuring equipment. This is due to the lack of guidelines for the justification of these gages, and the misconception that an automatic gage is some sort of behemoth performing a multitude of inspection functions at a fantastic rate of speed, around the clock, and costing hundreds of thousands of dollars.

To put automatic gaging in better perspective, let’s take a look at the five functions that are normally considered as basic to automatic gaging.

What five functions are normally considered basic to automatic gaging?

1. Feed. Move the part to the gaging station and position it properly.

2. Measure. Check one or more dimensions  by comparison with a nominal size.

3. Feedback. Send back measured signals to exert some form of control over the producing machine.

4. Classify. Determine whether or not the part dimensions are within tolerances and, in many cases, assign the part to one of several in-tolerance size and out-of-tolerance categories.

5. Dispose. Move the part to its proper destination based on its dimensional classification.

In terms of justification, only three of these functions are relevant to the prime purpose of an automatic gage: determine part size; provide information to prevent bad parts from being made; and ensure that good parts are accepted more accurately, rapidly and with significantly greater efficiency on a continuous basis than is possible using operators. Whether or not feeding and disposal—primarily materials-handling functions—are accomplished automatically really doesn’t alter the ground rules for justification. In fact, with the advent of low-cost industrial robots, part handling is greatly simplified as special chutes, gravity feeds, stops and part pushers are eliminated. Consequently, what was once thought of as an automatic gage has also been greatly simplified.

Where to Apply Automatic Gaging
The most obvious place for an automatic gage in the production process is at final inspection. But this application is becoming less and less common. Such gages usually inspect products from many machines and are unable to provide any feedback control. This means things can go wrong before anything can be done about them and results in higher costs.

In contrast is the type of automatic gage that operates at the output of a machine, checking a part immediately after it is produced—or at least before many other parts are finished. (The time interval is usually governed by how easily the part can be moved from the machine to the gage or how important it is to let the part cool before gaging.)

In this type of application, the automatic gage is more likely to exert a control function over the machine. For example, the gage can count inspected pieces that fall into marginal areas of the specified tolerance. If too many out-of-tolerance parts are produced in a given time so that a trend develops, the feedback control can either stop the machine or exercise incremental correction, keeping production within tolerance bands despite changes in operating temperature, tool wear, etc. And since the speed requirement for a post-process gage is no greater than that of the machine it is checking, gage design and cost is somewhat reduced.

How to Justify Automatic Gaging
There are as many different reasons for buying automatic gaging systems as there are applications for them. But keeping in mind the prime functions of an automatic gaging system, consider two things: 1) the probable cost of gaging parts automatically compared to checking them the next best way and 2) the penalty for part failure.

Obviously, there are situations in which the second consideration makes the first academic. Penalty not only involves the cost of scrap and rework, but more importantly the costs that accrue from failure of an assembly. In this era of product liability lawsuits, calls for government performance standards and emphasis on safety, no manufacturer can afford to allow a near-good but out-of-tolerance part to become a functional element in a machine and then fail to perform properly in the field. Even if the failure does not jeopardize the lives or safety of users, it most certainly can have far-reaching and sometimes disastrous effects on the producer’s reputation. The penalty for part failure can be high.

Automatic gaging is considered to be 98- to 99.5-percent efficient, versus 80- to 90-percent for manual inspection. The difference between the two can be vital, depending on how critical the particular part is to the proper functioning of the product. The more critical the tolerance, the greater the difference.

Labor costs for manual inspection can vary among cities and different areas of the country. However, based on a survey of automatic gage users, the average compensation-package cost per inspection worker can easily approach six figures (three times that for a three-shift production facility). Thus, labor saving can be a prime consideration in justifying automatic gaging equipment.

In today’s manufacturing and inspection world, automation is a key to success. With the increased capabilities of modern measuring tools and significantly lowered cost of part handling, a small,  tabletop automatic gage may help you increase productivity and save you thousands of dollars.