Hole drilling plays a critical role in automotive manufacturing. Hundreds of holes must be drilled for each vehicle that’s manufactured, including those in transmission shafts, engine blocks, air bag propellant chambers, camshafts, and other internal engine parts. In any automotive vehicle part production line, conveyor belts are running nonstop and efficient tools are a key aspect of profitability. Every minute a spindle is not drilling holes or evacuating chips is a minute when money is lost. Manufacturers must take advantage of seemingly small tooling changes because they can make a huge difference in hole making efficiency.
Technology is available that can be integrated into a process seamlessly without shutting down production. Adopting technology to decrease costs can significantly increase margin dollars.
In the past, all large, high volume automotive metal cutting and drilling operations were performed with transfer lines on dedicated machines. These machines had set running speeds and large chains that conveyed parts between machining stations for the operation to be performed. A set number of parts could be drilled in a day, but if one machine broke down, the entire line shut down. There was no advantage in developing cutting or drilling tooling that sped up operations because the line was only able to run at its designated speed.
This approach continued throughout the 1970s and 1980s, but slowly began to change in the 1990s with the rise of computer numerical control (CNC) machines. Modern automobile manufacturers use flexible CNC equipment, so if parts can go faster on one machine, they can be sped along to the next one. With these CNC-operated transfer lines, manufacturers can be more flexible, making changes and taking advantage of new tooling to increase production. The tooling industry seeks to develop new tools that can speed up the slowest part – the one that is holding back other operations – which can yield significant overall cost savings.
One major factor affecting metal cutting in the last 20 to 30 years is the long-term elimination of free machine metals, those that can be cut easily, allowing material removal with a satisfactory finish at low cost and without rapid tool wear. With the removal of lead in metals and the replacement of cast iron with compacted graphite iron (CGI), the metals used in the automotive industry have gone from machine-friendly to extremely difficult to machine. This means tooling must be adjusted to increase chip control to gain tool life and make holes straighter. Other changes that affect hole-drilling tooling include environmental laws limiting the use of chlorine and sulfur in hole-drilling coolant systems.
The scope of this problem is different in Europe, which requires dry-machining, in which no coolant, or very little, is used, because elimination of waste coolant is prohibited by pollution laws. Many automotive OEMs use global work practices, so dry machining processes adopted for use in Europe are also being used in North America and Asia.
The elimination of chlorine and sulfur has increased problems with chip buildup on the cutting tool, chip sticking, and reduced tool life, so tooling manufacturers have to develop ways to deal with these trends. Some companies are moving toward near-net forging to avoid these issues, but the problems will continue since parts will always differ from forger to forger.
In response to these automobile manufacturing, economic, and environmental/regulatory trends, the market is looking for innovations in turning and drilling – both machines and tooling.
For example, new turning and drilling machines are coming on the market with high-speed tool changing and more accurate hollow taper shank (HSK)-style tool spindles. But there are also opportunities to design tooling that makes up for deficiencies on older machines. Placing 21st century tooling on 20th century machines can significantly improve manufacturing efficiency and increase profitability, making older machines perform like new ones. Improving an existing capital asset can be a huge advantage, since capital requests for major new equipment purchases can be difficult to fund. With the flexibility of new CNC machines, tooling improvements can be integrated without shutting down the production line to re-tool.
Allied Machine & Engineering recently worked with a Tier 1 supplier to a major automotive manufacturer on a high-volume transmission shaft made of steel alloy, a poor chip-forming material. The existing tool used a low tool pressure coolant system and small spindle tapers, resulting in very large, abrasive chips that trapped themselves on the outer dimension of the drill’s holder body. The chips collected in the bottom of the hole and didn’t evacuate. With a poor hole surface finish, the tool could drill only 200-to-400 holes per insert and had a high monthly scrap of about $20,000.
Allied Machine engineers investigated the chip formation in its laboratories – off the manufacturer’s production line and not on their spindle. Allied Machine’s research lab has the facilities to simulate the manufacturer’s exact machine conditions and pump pressures, ensuring that chip evacuation could be optimized.
The tool Allied Machine developed was an engineered special holder – nicknamed the T-A Stealth Drill because it runs so quietly. It enables the tool to drill straighter for longer, produce truer holes, and wear more evenly. The T-A Stealth Drill includes an adjustable locating pin that increases tool precision, an increased bearing diameter on the holder, and additional coolant outlets in the brazed carbide bearing area of the triple gundrill holder. This design decreases the clearance between the holder and blade but increases the support of the wear pad.
The supplier uses the T-A Stealth Drill in combination with a newly developed special insert nicknamed the Ultra T-A insert, which reduces the built-up edge. The Ultra T-A provided the automotive manufacturer superior chip formation, improved tool life, a reduced spindle load, and a smoother cutting edge.
The Ultra T-A and Stealth Drill technology enabled the low-pressure machines to perform dramatically better, on par with modern, high-pressure coolant machines. There is now very small and manageable chip formation, chips are evacuated down the holder flutes, and rifling on the inner dimension of the shaft has been eliminated. The tooling produces consistent surface finish, eliminates about $240,000 per year in scrap, and increases tool life by 280%. Each insert can drill about 1,200 holes – 3x to 6x more than the previous tool.
This tooling has since been used in automotive applications globally, including one tool that is designed to manufacture the ends of crankshafts. A new threadmilling tool and a quick-change reaming head are other recent examples of how tooling can be used to gain an advantage.
With flexible modern CNC manufacturing equipment, any tooling improvements brought to market can be easily integrated. Avoiding a major retrofit that requires huge capital expenditures and tearing up facilities to install new equipment can save manufacturers large amounts of money and improve their bottom line.
Allied Machine & Engineering Corp.
About the authors: Paul Best and Todd Cox are product specialists at Allied Machine and Engineering Corp. They can be reached at 330.343.4283.