Launched in Europe at this years MACH exhibition, the new Core Drill™ from Allied Maxcut (AMEC) has already achieved outstanding results in North America, where it was introduced in mid-2007. With one customer, Wellhead Inc of Bakersfield California, the Core Drill helped them reduce valve body manufacturing time by 85%.
Like many manufacturers within the oil, gas and energy supply industries, Wellhead needed to enlarge pre-drilled or cast holes up to diameters of 200mm, which required multiple incremental boring passes. On one of its valve bodies, the company needed to machine a blind, 203 mm diameter hole almost 550mm deep - an application that took nearly 8 hours to complete.
Machined from forged 4340 alloy steel using an 11kW Toshiba Shibaura manual horizontal boring mill, running with flood coolant, each part required two holes, which were cut from stock with a two-flute insert drill. A small carbide point created a pilot hole and centred the tool, while inserts arranged along the body enlarged the hole to 150mm diameter in a single pass.
However, it was on the subsequent boring operation, where the bulk of the production time was incurred, where the hole was enlarged to the final 203mm diameter and 533mm depth, which took 6 passes by an adjustable boring bar running at 125 rev/min and 0.15mm/rev feed.
Between each pass, operators had to adjust the set screw or install another boring bar when the first reached the limit of its stroke, which resulted in a total cycle time of 7 hours and 20 minutes. Dissatisfied with the current production process, the company turned to AMEC for assistance and a solution that would reduce the cycle time. AMEC's response was to recommend the Core Drill, a tool that could finish the bore in a single pass and cut cycle time to less than 1 hour.
The key to the Core Drill's abilities is a 'phased asymmetric' replaceable insert arrangement that allows high material-removal rates to be achieved even on low-horsepower machines. Off the shelf, the Core Drill is available in a maximum diameter range of 50.80mm to 142.75mm, but AMEC custom built a special 203mm model specifically for Wellhead's application.
The AMEC Core Drill features two diametrically opposed insert cartridges that are phased to create an overlapping cut. The cartridges are identical; the user simply selects one to cut the bore's finished diameter and the other becomes the inboard cartridge, so each insert cartridge removes only a portion of the total material needed to achieve the finished diameter.
This configuration distributes cutting forces between the two insert cartridges, reducing the overall load on the spindle to allow higher metal-removal rates. The tool is especially useful for low-horsepower machines such as Wellhead's 11kW boring mill as, with a high enough rev/min, the tool's multiple inserts can remove a substantial amount of material, even at low feed rates.
Van Currie, a manufacturing and production engineer with Wellhead, explained: "We were able to open up the 150mm hole easily and quickly with the two-flute drill, but going from 150mm to 203mm with a rotating boring bar that could only take a 5 to 7mm depth of cut per pass was extremely time consuming."
He added: "We went from a process of having to continually adjust and change our old boring head to this 'hole-in-one' solution from AMEC, which paid for itself after completing the first couple of valve bodies, due to the massive reduction in production cycle times."
AMEC's Core Drill also solved Wellhead's hole-straightness issues, as the two-flute drill used to cut the hole from the raw material had a slight wander off centre and create an angled hole, which was followed by subsequent tooling. As the Core Drill has no pilot mechanism for finding a centre on the material, this allowed the overlapping inserts to bore straight into the material and bring the pre-drilled hole into alignment.
Running the tool at 125 rev/min and 0.1mm/rev, Wellhead could open the hole to finished diameter in a single pass. Cycle time was reduced to just 46 minutes, saving 6 hours and 40 minutes per part, generating a cost savings of more than £750 after just 10 holes.