Mitutoyo Contracer: A More Efficient Measuring Method

At Advics Manufacturing Ohio Inc., a CNC setup has dramatically transformed contour measurement of automotive brake components from a 45-minute specialist’s task to a 3 1/2-minute generalist’s job. Founded in 1987 and located about 40 miles northeast of Cincinnati, Advics Manufacturing Ohio employs more than 500 people dedicated solely to production of disc brake calipers and ABS units. These are supplied to automakers around the world for installation in more than 20 different vehicle models by the company, which has a reputation for being a quality-leader for brake products made in North America.

Improve safety, comfort and environmental responsibility
Advics’ mission is to add value to society by creating products to improve safety, comfort and environmental responsibility. Evidence of this pursuit is the implementation of a program of continuous improvement, which impacts every operation. One area targeted for development was caliper bore measurement and inspection. The objective was to increase both the types of calipers that underwent bore inspection as well as the frequency of those inspections with the net result of dramatically increasing caliper bore measurement/ inspection throughput.

A brake caliper straddles a brake rotor and houses pistons to which brake pads are affixed. When hydraulic pressure is applied by the foot pedal via a brake master cylinder (augmented, if so equipped, by power brake-assist), the pistons squeeze the pads against the rotor to generate stopping friction. The caliper includes cylinder bores into which the pistons fit. A seal must be maintained between the cylinder and the bore to maintain integrity of the hydraulic circuit. This sealing is provided by a piston seal which fits into a groove machined into the cylinder bore. The piston seal itself is a gasket with a square profile on both its ID and OD.

The interaction of the seal’s OD against the geometry of the groove in the bore, as well as of its ID against the piston wall is critical—both from the perspective of sealing fluid and also because it is responsible for providing what is called “rollback.” Rollback occurs when the seal deflects as friction with the piston draws the seal in the direction of piston movement (a minute amount); seal edges are designed with chamfers and other details to facilitate this action. The result is that when braking pedal pressure is released, the seal rolls back to its original position, helping to pull the piston with it. This phenomenon is very important to brake function in terms of noise-related issues attributable to pad-to-rotor contact.

Inspecting critical features
The Advics Quality Group determined that there are several critical caliper bore groove features that need to be measured, inspected and monitored. Advics Manufacturing Ohio’s caliper bore measurement frequency was established by their continuous improvement program and requires sampling at every tool change. The frequency requirement also takes into account extra measurements between tool changes to monitor bore changes as predicted by tool wear experience and other factors. And with 15 machining centers producing millions of differing types of brake calipers per year, the total number of caliper bore measurements at Advics Manufacturing Ohio is extremely high.

Advics uses contour measurement machines to inspect caliper bore grooves. In 2004, the company first installed a manual Mitutoyo CV-3000 Contracer to measure bore grooves. These instruments offer fast traverse speeds (X axis [drive unit]; 80 mm/s MAX; Z2 axis [column; 30 mm/s MAX) and included a precision arc-scale built into the Z1 axis (detector) allowing the arc trajectory of the stylus tip to be read directly, thus minimizing error. The machine’s arms are also equipped with collision auto-stop to assure measurement safety during high-speed movement. Depending on the operator, manually measuring all bore parameters with the Contracer averaged about 45 minutes each.

A way had to be found to avoid overwhelming Advics’ capacity for taking these measurements. As a result of the installation of the manual CV-3000, Advics enjoyed a relationship with Mitutoyo’s M3 Solution Center. Advics supplied the M3 Solution Center with sample parts and asked for a recommendation that would achieve the required bore measurement throughput. Within weeks, the center came back with an approach based on use of a CNC Contracer model CV-3000CNC. This machine has a maximum drive speed of 200 mm/s and a linear displacement accuracy of ±(1+4L/200) μm. Control is via an easy-to-operate remote box.

The M3 Solution Center proposed combining the CV-3000CNC together with an innovative parts-handling system that included bar coding, advanced part programming, and a highly capable analysis/reporting and data archiving/networking routine. Advics deemed the solution on-target. Final development was undertaken jointly by Advics and Mitutoyo, and the system was installed.

Advics developed a modular fixturing system with each fixture designed specifically for a type of caliper. Each of the different fixtures, however, fits into the same type of base plate, which fits the CV-3000CNC. Bar codes matching the caliper type are affixed to each fixture. All the operator has to do is load the fixture/part combination into the CV-3000CNC and then, using a scanner gun, scan the bar code. The code automatically tells the CV-3000CNC which part program to run. Finally, the operator confirms proper part loading, and everything that follows is automatic.

Part programming is via Formtracepak, Mitutoyo’s proprietary contour analysis software. Formtracepak offers total support for measurement system control, surface roughness analysis, contour analysis, contour tolerancing, and generation of inspection reports. Both the Contracer and Formtracepak communicate with MeasurLink, Mitutoyo’s proprietary statistical-processing and process-control program, which performs statistical analysis and provides real-time display of measurement results for SPC applications.

Solve Internal Feature Measurement Challenges

Measuring internal features on intricate parts has long posed a challenge for many manufacturers.  It is common for manufacturers to cut parts in half or section them in order to measure certain features, rendering the parts useless. Depending on the sample size needed for measurement, the process can be costly.

Another practice to measure internal features, without scrapping the part, is to create a mold of the part. The mold can then be measured using an optical comparator.  However, the use of molds prohibits the ability to accurately and repeatedly measure intricate features.

A Contracer, complete with optional accessories, offers an ideal solution to solve these measurement challenges by providing accurate and repeatable results without the need to destroy parts. There are various styli and arm combinations that can measure in different sized internal diameters and hard-to-reach areas.

Challenges such as deep holes and channels can be overcome with different tip height styli and arms for the application. Custom styli have also been designed to make the Contracer a versatile system to implement as opposed to expensive destructive testing techniques of the past.

For certain models a newly designed dual-sided styli can easily measure both the upper and lower surface of an internal diameter without the need to stop and physically change the measuring orientation.