Advics Manufacturing – Case Study 2

Alla Advics Manufacturing Ohio Inc., un nuovo sistema di misura CNC, ha trasformato radicalmente la misurazione dei profili dei freni per autoveicoli, da un compito per specialisti da 45 minuti di drata, a un lavoro generalista da 3 minuti e 1/2. Fondata nel 1987 e situata a circa 40 miglia a nord-est di Cincinnati, la Advics Manufacturing Ohio impiega più di 500 persone dedicate esclusivamente alla produzione di freni a disco e unità ABS. Questi, vengono forniti alle case automobilistiche di tutto il mondo, per l'installazione in oltre 20 diversi modelli di veicoli. La società è riconosciuta come leader in teermini di qualità nel mercato del Nord America.

La missione di Advics è quella di aggiungere valore alla società, creando prodotti per migliorare la sicurezza, il comfort e la responsabilità ambientale. La prova di questa ricerca è l'attuazione di un programma di miglioramento continuo, che influisce su ogni operazione. Un'area destinata allo sviluppo era la misura e l'ispezione del diametro dei fori di alloggiamento dei pistoncini delle pinze freno. L'obiettivo era quello di aumentare sia i tipi di pinze da sottoporre ad ispezione, sia la frequenza di tali ispezioni, con il risultato netto di un aumento drastico della verifica diametro /pinza.

La pinza Una pinza del freno si trova a cavallo di un disco del freno e contiene pistoni sui quali sono fissate le pastiglie dei freni. Quando la pressione idraulica viene applicata dal pedale tramite una pompa del freno (aumentata, se così equipaggiata, da servofreno), i pistoni schiacciano le pastiglie contro il rotore per generare attrito di arresto. La pinza include i fori dei cilindri in cui si inseriscono i pistoni. È necessario mantenere una tenuta tra il cilindro e il foro per mantenere l'integrità del circuito idraulico. Questa tenuta è fornita da una guarnizione del pistone che si inserisce in una scanalatura ricavata nel foro del cilindro. La guarnizione del pistone stessa è una guarnizione con un profilo quadrato su ID e OD.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.

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.

 

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