Milling insert overcomes ball nose problems


Milling insert overcomes problems associated with ball nose copying style inserts where zero cutting speed at the centre causes error of form and premature failure of the insert

LMT’s Kieniger tooling division has developed milling inserts that overcome problems associated with ball nose copying style inserts, where zero cutting speed at the centre causes error of form and premature failure of the insert. The FlatBall indexable insert combines the advantages of ball and toroidal style indexable inserts for die and mould and aerospace type applications in what LMT (UK) of Coventry, UK, describes as a ‘double-edger’ geometry.
At zero cutting speed – the design of the FlatBall features a 2mm flat on a 10mm diameter insert, which overcomes the absence of cutting speed as the spindle rotates around the centre line of the tool.

Nomally, this causes a normal carbide insert to suffer from the rapid rise in temperature generated by the resulting ‘rubbing’ rather than a cutting action.

The rubbing action also lincreases wear on the insert, which progressively changes its geometry under cutting conditions.

The result is lost machining time as components have to be checked and new offsets inputted at the machine control – or tools have to be changed frequently, said LMT.

LMT’s solution is to flatten the shape of the ball or more technically, reduce the radius of the insert until it becomes a double-edged cutter.
This modification of form, said LMT to, means the insert works at a constant speed in its centre but without loss of any advantages gained by the ball shape.

This design also prevents any accumulation of chips or built-up edge at the tip of the ball when an initial cut is made into a slope or a helix.

In addition, it can also reduce the number of individual cutting paths required, thus shortening cycle times when complex contours have to be machined.

* Impressive unmanned trial results – recent trials at the Polish subsidiary of Comau, the Italian corporation that supplies the automotive industry with large cast iron, cast steel and tool steel alloy moulds, a LMT FlatBall was recorded with an in-cut running time of over 70h.

The material was a GH240 steel casting with hardened inserts and was machined using LMT’s WPB 16FB-70 der CBN faced cutting insert.

The 5-axis milling centre was run at its maximum cutting speed of over 600m/min and due to the improved security of the process, was able to be left to run unmanned.

In a further hard milling trial to produce a trimming tool out of P20 tool steel, the LMT FlatBall was run at 400m/min to produce a cutting distance of 3,60m over an 11h period and after that time displayed no appreciable signs of wear, reported LMT.