May 17, 2023 Micro Drilling Around the Clock

CoroDrill® 862 with GM geometry supports unmanned 24/7 small part machining.

By: Marcos Morine, Round Tools Specialist — Brazil, Sandvik Coromant

According to Frost & Sullivan, manufacturers could gain a 30 percent increase in productivity output by switching to a lights-out operations model. This also applies when intricately micro drilling holes as small as 1 mm in diameter. However, manufacturers are denying themselves these productivity advantages by choosing the wrong drills for their application.

The Transformative Mega Trends Enabling Lights Out Manufacturing report by Frost & Sullivan predicts that supply chain challenges, increasing diversification among manufacturers, competitive intensity and disruptive technologies will drive manufacturers increasingly toward lights-out production.

Gartner agrees that a rise in lights-out manufacturing can be expected, citing “the supply chain’s demand for factory flexibility and speed” and “eliminating dwell time” between manufacturing and supply stages as key factors, while recommending manufacturers “focus on lights-out processes” rather than lights-out factories. So, what does this mean? For a start, lights-out processes require machinery and tooling solutions that can run 24/7 without the need for human intervention.

Lights-out production is a growing requirement among Sandvik Coromant’s customers in Brazil and demands tooling solutions that demonstrate safety and stability in manufacturing processes. That includes micro drilling, which, according to the research paper “Experimental research on micro hole drilling of polycrystalline” published in the journal Ceramics International, holds numerous advantages for manufacturers, including “good dimensional accuracy” and “a high depth/diameter ratio,” along with suitability for “various machining materials.”

Manufacturers in Brazil are using micro drilling in several industry applications, including for manufacturing medical devices, dies and molds and general engineering parts, such as valves. That said, achieving the best advantages from micro drilling and small part machining applications isn’t always straightforward. It is not uncommon for manufacturers to select the wrong drill for their application or machines that do not achieve the necessary rotation to derive the best results from micro drilling.

Withstands the heat

When exploring the challenges of lights-out micro drilling, let’s first focus on the choice of drill, which is extremely important for producing good quality holes. Hole surface integrity is of paramount importance in any application, by helping to prevent component failure, and depends very much on the manufacturing processes used for machining or finishing the holes. Any instances where a machining process is not meeting tolerance ranges or surface quality requirements should be investigated and corrected as soon as possible.

Another major challenge with micro drilling is the heat generated by the drill itself. The drill’s smaller size makes managing heat more difficult, as the machine cannot supply through-coolant, leaving external coolant as the only option. Excess heat leads to quickly worn-out drills and may necessitate multiple tool changes while machining a single component. Heat can also cause hardening of the tool itself, where the 1 mm diameter drill hardens undesirably, causing it to snap. These factors are exacerbated by the higher productivity requirements — or higher number of holes per workpiece — of micro drilling applications.

Any of these problems, particularly multiple tool changes, are ill-afforded in any machine shop due to their negative impact on production efficiency and the bottom line. But they are intolerable in 24/7 lights-out production, where no human workers are on-hand to intervene if required. So, what can be done to resolve these issues? The answer lies in more secure and stable tooling solutions.

In response to these multiple challenges, Sandvik Coromant introduced a new micro drill family to its product range at the end of 2021: the CoroDrill® 862 with GM geometry. The micro drill’s geometries offer a wide range of cutting diameters and lengths, ideal for precision machining in industries dealing with small parts.

Not only does the tool support customers’ tolerance ranges and surface quality requirements, but it’s also designed to do so when micro drilling difficult-to-machine materials such as Inconel, stainless steel and titanium while maintaining optimal component quality and a flawless surface finish. The CoroDrill 862 with GM geometry is designed to deliver outstanding performance with challenging materials, including ISO P, M, K, N, S, O and H. The drill’s superior wear-resistant properties also help manufacturers meet the rising demand to cut manufacturing costs.

Customers have the option of purchasing the CoroDrill 862 micro drill with a polycrystalline diamond (PCD) vein cutting edge. Based on successful tests of PCD drills on micro parts made from platinum, Sandvik Coromant has found that PCD is up to 100 times more wear resistant than solid carbide (although that doesn’t mean the tool life is 100 times greater than solid carbide). It is also more accurate and can produce tighter tolerances than solid carbide tools. Sandvik Coromant’s engineers recommend that customers seeking to drill micro-sized holes in notoriously difficult-to-machine materials — such as titanium, aluminum, glass and ceramics — should consider PCD for extended tool life in these demanding applications.

But what about the aforementioned issues with managing heat? Sandvik Coromant recognizes that it is critical to have quality coolant delivery to effectively evacuate chips when performing deep-hole drilling with micro tools. That’s why the CoroDrill 862 is designed to easily drill hole depths of up to nine times diameter (xD) when using external coolant. A through-coolant option is also available for drilling diameters of 1.00 mm and above and hole depths of up to 16xD. The immediate benefits of coolant include extended tool life and a reduced risk of chip jamming. We can use this machining strategy to improve heat management during machining.

Process security

The advantages of the CoroDrill 862 with GM geometry were tested in a general engineering machine shop run by a customer of Sandvik Coromant, a plastics manufacturer. The tests were performed on a vertical Haas VM Series computer numerical controlled (CNC) lathe with a machine power of 30 hp (22.4 kW) and maximum rotation (RotMAX) of 12,000 revs per minute (rpm).

The workpiece was made from SAE 316 stainless steel, known for greater tensile strength at higher operating temperatures and a relatively high strength-to-weight ratio. A total of 48,816 holes were drilled in the workpiece, each with a diameter of 1 mm and a depth of 3 mm. The CoroDrill 862 with GM geometry was delivered to the customer by Produs, a local Sandvik Coromant distributor, and tested against a competing micro drill. In terms of cutting data, each tool had an identical diameter (D_c) of 1 mm (0.039 inch), a hole depth 3 inches, with a first depth of cut of 0.5xD and further depth of cut of 0.5xD (5x). A pecking strategy was used for each tool.

Aside from these identical performance parameters, there were also differences in the performance data for each micro drill. The competitor tool was run at a cutting speed (v_c) of 20 m/min (66 ft/min) while the CoroDrill 862 ran at a higher 25 m/min (75 ft/min). The feed per tooth (f_z) was also higher for the CoroDrill 862, 0.004 mm/rev (0.0002 in/rev) compared to 0.015 mm/rev (0.0006 in/rev) for the competitor micro drill.

Overall, the performance of the CoroDrill 862 with GM geometry was faster and longer lasting than the competitor tool. The CoroDrill 862 produced a hole approximately every 4.68 seconds (s) compared to approximately 8 seconds for the competitor micro drill. The latter produced 6,800 holes before showing signs of wear — which Sandvik Coromant’s specialists labelled “average tool life” — compared to 10,000 holes produced by the CoroDrill 862. In the end, Sandvik Coromant’s tool gave a 298 percent productivity increase over the competitor drill and delivered a 32 percent cost reduction for the customer.

Through these performance advantages and added process security, the CoroDrill 862 with GM geometry has helped Sandvik Coromant’s customer run machines 24/7 without the need for a human operator. However, successful lights-out production is about more than just tool performance. Another crucial factor is technical support from Sandvik Coromant’s specialists, which includes formulating a specific machining strategy for the customer’s unique application. The key to successful micro drilling is how the tools are applied — and that includes considering crucial factors such as the hole dimensions and depth.

With all these factors in place, machine shops will be better equipped to embrace lights-out machining. Even with more intricate processes such as micro drilling, manufacturers can still unlock the 30 percent increase in productivity output predicted in Frost & Sullivan’s Transformative Mega Trends Enabling Lights Out Manufacturing report.

To learn more about Sandvik Coromant’s tooling solutions for more stable and secure micro drilling, visit www.sandvikcoromant.com.

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