Take Measurement to the Tool

A portable CAM measurement system cuts inspection times by 84 percent, improves accuracy and conducts tooling capability studies.


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Hypothetical space points. No, they're not what you win for playing a Star Wars video game, but nonetheless, they're a critical element of the inspection process for manufacturers of large-scale tooling and products. New plastic materials have freed designers to make incredibly complicated shapes, yet the designs' complexities have greatly increased their manufacturing difficulty, particularly when it comes to proving the accuracy of the tooling and each part.

Just consider building the thermoformed plastic deck for an aerodynamically-designed speedboat. Curved windshield mounts, built-in steps and cutouts for dashboard controls create a 3-D landscape of concave and convex regions with hardly a flat surface in sight. Now, imagine that you are in quality assurance, tasked with verifying those critical dimensions with a fixture that is bigger than two parking spaces.

You know that the mathematical approach to defining the curvature of a surface requires determining one or more tangents (because a sphere would have just one). But you have to measure the tangents against reference points and these are floating in space above or below the surface. How do you make sure that the space points you're using are consistent for all parts? Can you do a thorough, repeatable job at a reasonable cost? And, how well do your measurements recreate the nuances of the surface compared to the 3-D CAD drawings?

Manufacturing engineers and quality assurance staff at Thermoform Plastics (St. Paul, MN) tackle these challenges every day. They design and produce both the tooling and parts for oversized plastic components needed in a variety of industries. Established in 1967, Thermoform has a total of 400 employees at four different plant locations, where its multistage rotary thermoformers convert medium- to heavy-gauge plastic alloy sheets (0.090 inch to 0.500 inch) into dozens of large products. From recreational vehicles and burial vault liners to heavy truck interiors and agricultural equipment roofs and interiors, its products can span up to 10 feet by 22 feet - including a fifty-inch draw.

Like other plastic thermoforming vendors, the company had managed to inspect large parts and fixtures using a combination of flat plates, tape measures and steel precision rules all held together with couplings. However, this process could involve moving a bulky part to the quality control department, where it would take 40 to 48 hours for one first-article inspection. In addition, calipers and straight edges did not offer the accuracy needed to verify increasingly complex curves over distances as long as 20 feet.

Adding even more to the challenge, customers also began requiring statistical process information, reverse engineering capabilities, and of course, cost containment - all tied into standard CAD systems. Thermoform already was working with solid and parametric modeling information, but the company knew that it needed an improved measuring and statistical reporting approach to meet new standards and win new customers.

John Zeidlik-Zimney, Thermoform's corporate quality assurance manager, found the solution to all of these issues with a CAM measurement system from FARO Technologies (Lake Mary, FL). The Control Station Pro system includes a multiaxis, portable measuring machine along with CAD-based software for measurement, analysis and reverse engineering. With this system, Thermoform cut inspection times by 84 percent, improved accuracy and conducted tooling capability studies never before possible.

Proving Both the Tooling and the Parts

"Originally we were having problems completing capability studies on our tooling," explains Zeidlik-Zimney. "Such studies are important because we have to be able to tell our customers that our fixtures are capable of meeting their requirements." Fixture tolerances, tighter than those on the parts, must accommodate the plastic's thermal coefficient of expansion and produce accurate parts from the first one to the hundred-thousandth one. Today's customers ask Thermoform to actually certify its processes according to the industry standard Production Part Approval Process (PPAP), which originated within the automotive industry.

Before acquiring the FARO system, the company was very limited in doing capability studies on either the tooling or final parts. For example, to completely measure 20 to 30 parts for 3 or 4 critical dimensions each part would have taken almost 1 week.

As Zeidlik-Zimney describes it, "We have to inspect combine roofs, snowmobile belly-pans or fenders for recreational vehicles - all with large curvature radii for which the drawings specify dimensions from a theoretical point in space." To find that point, the inspection team previously had to extrapolate the intersection of two planes coming together in space, create the reference point and then use this information to verify a single data point.

Repeating the process over and over again was not only extremely slow, but also meant that errors kept building up. Zeidlik-Zimney adds, "Before, we really had no way of measuring accurately, to see that the shape was consistent - actually a true radius. We used to rely on heavy sampling."

Now, with a FARO system, he says, "We can digitize an entire radius. It will show us in 3-D what we have - our actual shape. It also has allowed us to improve our processes greatly. Now we can offer a capability index figure (CPK) of 1.33 or greater on our drill fixtures, CNC fixtures, etc., which we simply couldn't guarantee before."

More Axes, Much Less Time

The FAROArm is an internally counter-balanced, articulated arm with the ability to attach various sensing probes. Made of aircraft-grade aluminum, its precision bearings and optical encoders at each of the 6 joints accurately report the probe's 3-D location. The arm's freedom of movement provides a basic spherical measurement envelope of up to 12 feet, but users can extend this range indefinitely by moving the arm to a new location and realigning it to target datums, thus handling the Thermoform requirements with ease.

Equally as important as its large range is the way that the FAROArm saves time both in the inspection lab and on the floor. Its easy setup means that the quality team can take the FAROArm to the tool or part instead of the part to a QA lab, mounting the measuring unit either on a fixed surface or a portable tripod - anywhere a 6-inch flat spot is available.

Zeidlik-Zimney recalls, "We have some parts that we make for a recreational company and when we were laying these out mechanically on a surface plate with a gauge, an average first article inspection was taking us between forty and forty-eight hours. This was because of the number of holes to check (40 to 50) and the number of times we had to move the part because we could only check in one axis at a time.

"Every time you needed to go in another direction, you had to reset the tooling or part up on a surface plate. Often, it meant that we had to do it multiple times, because going in the length direction we could only get halfway with the height gauge. Then, we had to turn the part around and come from the other direction. We lost accuracy because we were remounting it and we lost an extreme amount of time.

"Now, by using the FAROArm, we reduced that inspection down to eight hours because we could check in three axes at a time. We just clamp the parts down, lock the FAROArm in place and measure." For example, they'll check the location of drill bushings and trim guides on the tooling itself, then follow up by measuring a number of first-run production parts to ensure that the tooling is repeatable.

Zeidlik-Zimney notes, "We can do a twenty- to thirty-piece capability study in about ten hours or, depending on how big the part is, we can get it down to four or five hours."

Just because a part is big, though, the customers don't cut any slack for accuracy. Even for the twenty-two-foot long dimension, Thermoform verifies parts tolerance of q0.030 to q0.060 inch because the FAROArm can certify its tooling tolerance to as low as q0.010 inch - and better fixtures mean less time spent on in-process inspections.

From Data to CAD to Statistical Process Control

Thermoform uses the FAROArm's coordinate measurement data in several ways. Because FARO's CAM2 software draws an image on-screen in real time, the inspection team can immediately compare measured features (of a tool or part) with those on the original 3-D CAD drawing. If they note any discrepancies in dimensions, placement or alignment, they can make immediate tooling changes as necessary.

As Zeidlik-Zimney puts it, "We analyze the data as we're running. That way if we have questions on the fixturing, we do our process improvements right there, with the right people."

For each new fixture, Thermoform produces twenty to thirty parts, measures each one, and loads the data directly into a comprehensive statistical process control (SPC) software package. In that program, the data from those initial parts then indicates quality assurance whether they have a capable fixture or not - the first question their manufacturing engineers will ask. Periodically, the quality assurance team also will recheck tooling to ensure that it hasn't worn down or shifted out of tolerance.

FARO's CAM2 software also helps Thermoform meet frequent customer demands for individual part information. Automotive companies in particular now require validation data as part of the PPAP for OEMs. For creating a library that tracks all of the measured data for each part and coordinates it with the CAD files, Zeidlik-Zimney bserves, "Obviously the FARO system is the way to go, because it does this so quickly."

Other cost-conscious buyers, rather than asking for the specific data, are asking Thermoform to certify that their process meets a 1.33 CPK. As the quality assurance manager notes, "We want to make not only the first part, but the hundred-thousandth part the same, because we know that it is what works the best. We know that if our parts do not have a lot of variation, our customers do not have to spend a lot of money on their assembly fixtures to compensate for tolerances adding up."

For some rush jobs, Thermoform occasionally outsources the creation of cast aluminum molds; CAM2 then helps them audit all critical dimensions to make sure that the molds are up to their own standards. The company also uses measured data for gauge R&Rs (repeatability and reproducibility analyses), reverse engineering on clay models and constructing machine toolpaths as a service business for their tooling and mold vendors.

Making New Prototypes Possible

One groundbreaking, large-scale project for Thermoform has been creating the first plastic fire truck, the Concept 2000 for Emergency One. Working with both a major resin supplier and the nation's leading rigid sheet extruder, the manufacturer was able to replace metal as the material for all of the major interior and exterior cab components. The project required bringing together more than a dozen tools to thermoform the lightweight, glass-filled material and has recently gone into production. Again, because of the part sizes and complexity, Zeidlik-Zimney notes that the job would not have been economically possible before acquiring the FARO equipment.

Another new company venture is producing parts for street-legal electric cars, which are becoming popular in retirement communities in both the Southeast and Southwest. Thermoform is working with 3 manufacturers on such vehicles.

"The nice thing about working with plastic is that it opens up possibilities for the designers (for new shapes). The nice thing about working with the FARO system is, not only can we check shapes that we couldn't before, but we can see results in a 3-D view in real time."

Portable, Affordable Measurements

Zeidlik-Zimney likes the fact that he is no longer tied down to a quality assurance lab, and as far as equipment cost goes, he says there is no comparison. "The cost of doing business is less with a FARO system, and our customers realize that the equipment we are using will consistently make parts to print with no waste."

Zeidlik-Zimney's quality team now uses five of FARO Technologies' Silver Series portable measurement arms, two of the eight-foot and three of the twelve-foot models along with the CAM2 software. By continually reaching for those far-off points, Thermoform has won both new customers and the ability to produce considerably more complex products.