Universal Grinder Takes The Heat Out Of Brake Servo Production

Dunlop Aviation Braking Systems (Coventry, England) was looking to replace outdated machinery and to "gearup" the match grind cell of its brake system manufacturing module.

The brake system module manufactures complete aircraft braking systems including electronic controllers, dualservo units, master cylinders, emergency parking brakes and various supporting assemblies, while its climate controlled match grind cell is responsible for precision grinding of stainless steel brake servo valves and corresponding housing bores, before selectively "matching"the two components.

After initial CNC turning and then precision grinding operations to surface finish tolerances of 24 microinch, and straightness and roundness to 0.00004 inch, selective matching is carried out between servovalves and control housing bores to achieve working clearances of 1015 microinch. This design clearance is vital—allowing controlled, metered leakage of brake fluid past the servo valve when installed. Once "matched," the two components are non-interchangeable.

So Kevin Dunnion, manufacturing team leader, was faced with the decision of whether to replace or refurbish and upgrade a stand-alone internal grinder and a grinding center, both 25 years old. The two grinders were employed on intermediate grinding operations in preparation for final match grinding using a fully automated Jones & Shipman Series 10 CNC production cylindrical grinder.

If the replacement option was to be taken, the new machine needed to have an internal/external grinding facility, a modest price, quick setup time, the ability to increase productivity through simple automated operation and the accuracy to achieve a limited match grind capability.

After lengthy deliberation, Mr. Dunnion decided to reequip rather than refurbish, opting for the microprocessor based Jones & Shipman (Leicester, England) 1300X universal cylindrical grinder, satisfying both the rigorous specification and tight budgetary constraints demanded by Dunlop.

"Although the new acquisition had to meet a wide range of production parameters, we still needed to remain extremely cost--conscious at all times," says Mr. Dunnion. "Another important consideration was service backup. The after sales and service support for our Jones & Shipman Series 10 has been excellent, while the machine itself has been very reliable and performed very well. Downtime has also been minimal over the nine years we have operated it. Therefore, after a long and considered appraisal of all suitable machinery, the 1300X from Jones & Shipman appeared to be the most cost--effective solution by far."

To satisfy Dunlop's extensive requirements, the 1300X, which was delivered in March 2000, features a universal wheelhead for rapid transfer between external and internal grinding formats, diameter calipers to assist its match grind capability and a high speed internal grinding spindle essential for close tolerance grinding of small diameter holes.

The 1300X has impressed Mr. Dunnion and his team both with its accuracy and its range of facilities, for a relatively modest cost.

"I was pleasantly surprised to find that the 1300X consistently achieves surface finish levels of 48 microinch—which compare favorably with final match grind standards—even on the hardest, heat treated stainless steels that hard turning just wouldn't touch, while the setup between internal and external grinding is quick and easy," timeserved operator Steve Richings says.

Mr. Richings has found grinding cycles on the 1300X very easy to program, using step-by-step parameter prompting with default values that can be accepted or amended as required. At the end of a cycle the wheel retracts automatically. For manual operation, precise control of table traverse and wheelfeed is accomplished by hand pulse generators, and the position of each axis is clearly indicated on digital read outs, which also display parameters.

"The 1300X has already brought considerable benefits in reduced cycle times, particularly in automatic dressing modes." Mr. Dunnion says, "and it has had a major impact on the cell's machining ability." MMS