All in one solution

The flexibility of the 5-axis Mollart Centeplex to combine deep hole drilling of compound angle holes and thread milling into a single cycle won Mollart Engineering the order to produce 36 oil feed porting holes in a 7.5 tonne marine bearing.

The nickel chrome steel forging, some 2.2m across by 600mm high, was already part machined by the customer with a series of 36 compound angle holes of 20mm diameter to individually specified depths which then had to be precisely deep hole drilled using gundrilling technology at 5mm diameter to break into target areas in an internal oil gallery within the component. In addition, Mollart had to taper thread mill 30 holes to 3/4 NPT.

Says Neil Anderson, subcontract manager responsible for the one-off project: “Normally due to the size of the part and the number and positioning of individual compound angle holes, a part of this type would take a long time to set. The job would also require very careful attention using a normal machining centre and exact positioning a deep hole drill would be extremely difficult. The Centeplex however enabled the machining operation to be completed in under three days.”

He continues: “With each reset for the next hole there would be a risk of error due to the complexity and accuracy of repositioning the part that could lead to such a high value component, almost in the finished machined state, being scrapped.”

To ensure the start position of each hole was correct, Mollart's toolroom prepared a special guide bush that was fitted into each of the pre-drilled 20mm holes in sequence to ensure perfect concentricity for the start position. This also ensured the self-guidance built into the gundrill design would hit the target breakthrough position called for by the customer.

The value of the Centeplex design is the configuration of the two individual gun drilling and conventional milling spindles able to tilt at up to 15° that are positioned under and over each other (shotgun style). The upper deep hole drilling spindle has a 22kW, ISO 50 taper drive spindle enabling a drill penetration of 2,000mm while the lower milling spindle with a 60 tool magazine is able to carry out normal production sequences such as the threadmilling.

The Centeplex cost some £750,000 to develop by Mollart for its own use and is targeted at medium-to- large workpieces. The table is 2,000mm by 2,740mm and will take loads up to 16 tonnes as well as providing a full CNC rotary axis. The table has axis strokes of 1,800mm in X and 1,325mm in Y and the gundrilling spindle can accommodate hole sizes between 4mm and 100mm. It uses Renishaw probing in the milling spindle to precisely datum the part and each feature to be machined.

Mollart
www.mollart.co.uk