By re-engineering a machined hydraulic valve body, Unicut precision eliminated previous process problems of porosity in the casting and variation in hole and feature positions.

Unicut Precision was able to reengineer a special hydraulic valve aluminium body to overcome machining problems and so won a contract to machine repeat batches of the 2,000 complex multi-featured components In doing so, Unicut reduced machining operations, that required five or six set-ups when the component was a casting, to one mill-turn set-up from bar on a Citizen M32-V CNC sliding head automatic lathe

To machine the valve body, 24 tools are used on the Citizen sliding head auto, of which 14 are driven.

By machining from bar, Welwyn Garden City, UK-based Unicut precision eliminated previous process problems experienced by the customer.

The problems included porosity in the casting, variation in hole and feature positions and possible breakthrough of holes and counterbores in close proximity to each other.

Unicut also reduced risks of damage or marking.

Machining from bar eliminated such risks associated with multiple set-ups used to machine the castings.

Unicut's CNC automatic lathe setters also introduced precise and consistent deburring of critical areas and maintain sharp corners as specified.

* Accurate hole drilling - joint managing director at Unicut perecision, Jason Nicholson, said: "This is a perfect example of how the flexibility of one of our Citizen M32's can be used to create complicated profiles by extensive interpolation of milling cutters.

Also by working from both ends of a component in the main and subspindle we have been able to drill multiple holes with high repeatability to an accuracy of almost true position to the datum".

* Valve body specification - each valve body part is 32mm long and machined from 28mm diameter bar.

There is a complex milled profile on one end and a turned boss and O-ring groove on the other.

A 6mm wide location tenon runs down the outside diameter and is blended into the milled profile.

This tenon has a long hole drilled 2mm diameter by 21.5mm deep and is also counterbored to a 4.00/4.05mm diameter tolerance to a depth of 0.70/0.75mm.

This hole is also positioned on a precise 20.60mm pitch circle diameter (PCD) toleranced to +0.025mm.

There is more to this 2mm hole: it is broken into by a feed hole of 1.85/1.90mm diameter.

The feed hole has to be perfectly burr free at the intersection.

The Citizen M32, simultaneously drills both intersecting holes.

Drilling is immediately followed by two tools alternately that push over and break the burr.

The holes are finally redrilled to final size and blown clear of swarf.

Six other holes of small diameter are also drilled and counterbored on the same 20.60mm PCD with radial tolerances of +/-0.20 deg from the centre line and to unusual angle positions such as 67.5 deg and 112.5 deg.

To drill these holes the Citizen M32 uses precise NC indexing of the spindles.

One hole is also drilled and tapped to M3.

The main 10mm bore into has a tolerance of 15 micron to receive an insert bush and is counterbored 16mm diameter to a tolerance of 0.13mm with 0.6 CLA surface finish.

* Deburring - most edges of the component have to be deburred in-cycle.

Sharp corners have to be maintained on many of the features in order that the sealing and functionality of the component is not jeopardised.

Unicut Precision uses non-contact, video-based measuring, combined with touch probe to measure very quickly and exactly to a repeatable standard with automated detailed reporting.

Unicut told manufacturtingtalk that this facility avoids the use of costly gauges and checking fixtures and eliminates personal manual 'feel', opinion and possible misinterpretation of results.

To finish off, Unicut uses a modern Durr programmable, ultrasonic cleaning system and vacuum drying to provide the customer with an assembly (body plus inserted bush) ready for assembly.

Each batch is certified with a quality report. 


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