Careful approach, modern thinking, offline presets and a focus on coolant and chips unlock the potential of the latest interchangeable tip drills for CNC deep hole machining.
Interchangeable tip drills provide flexibility and cost savings when working with large diameters compared to solid drills. Here, a TA pilot machine from Allied Machine & Engineering is machining a P20 cast steel automotive mold. The hole will be clogged and filled with water to ensure proper cooling.
Bird nests can be one of the results of not being aggressive enough in bit feed, as seen with 1018 mild steel.
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If the drill is working correctly, the chips shorten and segment, retaining their original color.
The top stage of the Allied drilling system with TA inserts consists of a self-driving drill with carbide inserts along the body to ensure stability of the tool. This model, called the Stealth Drill, also features additional coolant outlets and an adjustable pin that moves the insert radially to reduce the tolerance overlap common to all interchangeable tip drills.
Installing indicators on machine tools to measure bit length and runout can be wasteful, error-prone, and potentially dangerous. Digital presetters can eliminate these problems.
Digital presets usually provide greater accuracy than indicators, as well as software that guides the user through the measurement procedure.
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To ensure the safety and accuracy of replacement TA drills, Allied recommends drilling a pilot hole at least 2xD deep. This practice provides enough engagement to keep the drill centered and prevent it from becoming a cannonball when it breaks. Longer drills should be fed at no more than 50 rpm and 12 inches per minute (300 mm/min) as shown until the tip is within 1/16 inch (1.5 mm) of the bottom holes. From this point on, the user must maintain 50% of the recommended speed and 25% of the recommended feed until the drill reaches a depth equal to its diameter. The speed must be reduced to a maximum of 50 rpm before exiting the hole.
“While our customers want the drill to be a finishing tool, it is still a roughing tool,“ said Salvatore DeLuca, product manager for Allied Machine and Engineering. “It will always be a little more.”
Still, he says, it’s easy to understand the high demands placed on interchangeable-tip drills, such as those made by Allied, a holemaking tool specialist. When applied correctly, the latest products can make holes straight and smooth enough that special finishing tools are not required.
However, accurate and efficient drilling is more important than the tool itself, especially in holes with depth to diameter ratios of 9:1 and above. In a recent keynote, Mr. DeLuca laid out five recommendations for deep drilling with the company’s TA System, a wide range of general purpose replacement bits designed to drill in most steels, cast iron, high temperature alloys and aluminum alloys.
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The deeper the hole, the longer the drill. The longer the drill (the greater the distance between the tool tip and the spindle nose), the more runout will affect the results. In some deep hole machining applications, the slightest vibration can cause premature tool wear and affect straightness and surface finish.
However, the need for careful tuning is no excuse for spending a lot of time identifying and correcting runout every time you change tools or blades. In particular, in today’s industrial environment there is no place to climb into the work area to set up an indicator, or place a piece of paper to trigger a tool. Assembling tools offline with a pre-setter can save a lot of time in any deep drilling operation.
In today’s manufacturing environment, there is no place to reach into the work area to set up an indicator, or to hold a piece of paper in place to trigger a tool.
In addition to saving time, making it easier to find and measure drilling allowances prevents costly mistakes. “In my opinion, the ease of installation alone is worth the investment,“ said Mr. De Luca. “When you see the reduction in setup costs and equipment downtime due to incorrect setup measurements, it’s hard to imagine you don’t have an air conditioner.”
At one client’s site, three Allied Machine interchangeable-tip homing drills (named for their quiet operation) are installed in the tool room at the start of each shift. This process takes less than 10 minutes. In contrast, setting up three tools on a production line can take up to 30 minutes, equivalent to 90 minutes of wasted time over three shifts. With 24/7 production, this amounts to almost 2,200 hours per year (this figure does not include machine downtime when changing tools). “The pre-conditioning system can account for 5% of that time loss,“ said Mr. DeLuca.
In this case, Stealth Drill itself increases the time savings offered by offline presets. The drill is equipped with adjustable pins that move the blade radially to reduce the tolerance overlap that is common with all interchangeable tip drills. Thus, eliminating runout no longer requires disassembling and cleaning tool components, adjusting offsets, adding shims to turrets, or having experienced mechanics try out custom solutions.
Aside from some form of X-ray vision, chip formation is the only way to tell how a drill is performing while cutting, and still have time to act. Curly shapes (such as “sixes” and “nines”) are ideal, while longer, thinner chips are less effective at removing heat from the cutting zone. Color is also important. Chips gradually turn gray, black and blue as the cutting zone overheats. Discolored chips may indicate the need to reduce heat by lowering the spindle speed, while sticky chips may indicate the need to increase the feed rate to the point where the workpiece material breaks rather than flakes off.
Other issues can be more easily overlooked. “One of the most underestimated factors in any machining process, even outside of drilling, is coolant,“ said Mr. DeLuca. Given the significant effect of coolant on chip formation, adjusting the concentration and flow of coolant can also help with bird’s nest discoloration.
“One of the most underestimated factors affecting any machining process, even outside of drilling, is coolant.“
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Water soluble coolants are most commonly used in general purpose applications because they dissipate heat well. However, in some cases a semi-synthetic or all-oil formulation may be the best choice for improved lubricity and short, segmented chips. While tools may wear faster and settings need to be less aggressive than water-based coolants, heat resistant blade coatings can help offset this. It all depends on the application.
An indisputable factor is the use of drills with coolant. The machine must also provide sufficient coolant pressure. Smaller drills require more chip pressure to keep up with material removal because they must run at higher RPM to achieve the same surface speed as larger tools. “The higher the pressure, the faster the chips come out of the hole and the faster you can turn the bit,“ said Mr. De Luca.
Allied TA drills are available with 187 different standard insert geometries and coating combinations, and this is just one manufacturer’s toolbox. With so many application-specific options available, the insert-drill strategy that was once standard procedure may no longer apply.
An example is pecking. There is no need to periodically change the feed direction of the tool during cutting to ensure the removal of chips from the hole. “Now when you see pecking, it’s usually someone who misused a tool or used a completely wrong tool,” Mr. De Luca said.
“Now when you see pecking, it’s usually someone who’s using a tool incorrectly, or is using the wrong tool.”
When there is no time to buy new tools or make other process changes, pipping may be the only option. However, drilling is always slower as a result. Also, retracting the tool while cutting can leave a partially formed, unseparated chip in the hole. Carbide is wear resistant but relatively brittle, and this property can make inserts prone to premature and even catastrophic failure when subjected to repeated exposure to this jagged, uneven surface. Even if the blade is intact, the workpiece may be damaged. As mentioned above, most drill bits are slightly oversized. “Maybe only a few thousand (1″ u = 0.001 inches), but in some jobs there can still be a risk of leaving scars inside the hole or cutting the hole too big,“ he explains.
Another obsolete practice is to use small diameter 90 degree spot drills as pilot holes. This makes intuitive sense and, as with pecking, remains a useful rule of thumb for tool applications. After all, smaller holes that are slightly off-center are easier to fix than larger holes, and the sharp corners help the drill penetrate and hold the part quickly and easily. However, the positioning accuracy of most CNC machines is sufficient to ensure that the pilot drill has the same diameter as the main drill. They are also powerful enough to drive blunt points into the original workpiece material.
In fact, most indexable drill bits have self-centering bits with a point angle less than 90 degrees. Therefore, the insert affects the large hole diameter in front of the self-centering point. “If you were to use one of our standard spot drilling tools, our bit would move a little, causing premature wear and possible tool drop,“ Mr. DeLuca explained. “Using the same blade diameter and point angle ensures that the longer drill fits perfectly where the spot drilling stops.“
When deep drilling, immediately accelerating to full speed and feed creates a safety hazard and may affect operation. So most of Allied’s standard recommendations for general purpose indexable drills can be summed up in one sentence: approach the pilot hole with care. See the photos in the gallery above for more details.
“Careful approaching a pre-existing hole can help avoid scarring or damage,“ Mr. De Luca said of the recommendations. “This allows the edge of the drill to make contact with the material before you pick up speed. The hole acts like a sleeve, centering the drill and keeping parts and people safe.”
To create threaded holes in titanium alloys, appropriate methods are required based on an understanding of the properties of these materials and the features of the threading process.
To move to hard turning, you need to switch from carbide to CBN inserts, but it’s easier (and more affordable) than you think. It shifts to higher surface speeds, which may put you off. no need. that’s why.
One of the most common threading techniques used on CNC machines today is “rigid threading” or “simultaneous threading”. Rigid tapping cycles synchronize machine spindle rotation and feed according to a specific pitch. Since the feed into the hole is synchronous, it is theoretically possible to use a solid gripper without any tensile compression.
Post time: May-05-2023