How to Solve the Drilling Mark Problem in Deep Hole Machining
How to solve the drilling mark problem in deep hole manufacturing? This common problem can occur if the drill point has not reached the full diameter of the hole before the drilling operation is completed. This can lead to the appearance of a double hole impression. Here are a few ways to avoid this. You can compensate for tool load, use guide pads and adjust the size of the reamer. But if you are not sure how to deal with this problem, read on.
Tool load compensation
The question is: how to solve the drilling mark problem in deep hole drilling? There are several factors that affect this problem. First, drills are designed to create a hole by piercing the metal and leaving a marking. The second factor is chip evacuation. If the drilling process fails to evacuate the chips, they will be impacted into the flutes of the tool. In a deep hole drilling process, this chip evacuating failure can destroy the tool and the part.
Secondly, the drilling process must end before the drill point expands the hole to its full diameter. If the drill point is already at the full hole diameter, it may leave a double hole impression. The third factor is excessive pressure. Too much pressure on the tool can cause the drill to bend and leave a hole that cannot be fully drilled. Ultimately, this leads to broken tools and damaged parts.
Guide pads
During STS drilling, the drill bit produced a pronounced drilling mark that was difficult to remove. However, tribologically optimized guide pads were able to solve this problem. During the finishing process, the press roll oscillated at up to 20 Hz, and the hardness of the coating could be varied to improve surface quality. However, these solutions did not solve the drilling mark problem completely.
To reduce torsional vibrations, a self-damping CFRP-boring bar was developed. This new product improved the dynamic process stability of deep hole drilling processes by reducing chatter vibrations and maintaining constant mechanical tool loads on the cutting edges. This new drilling tool was tested in STS deep hole drilling of AISI 304. The tool's durability could be extended up to two times by using a self-damping borer bar.
Aligning the center punch mark with the drill point
One tool that is a must-have in any workshop is a center punch. Its conical tip makes it easy to mark the center of a work-piece for subsequent milling or sawing operations. When used correctly, the center punch will create a centered indentation, which is the center of the hole. Ideally, the depth of the hole will be equal to two-thirds of the center punch indentation.
A spotting drill is generally better suited for this task, as it relies on rigidity to make it more accurate. However, the center punch mark must be aligned with the drill point. Aligning the center punch mark with the drill point is a fundamental aspect of deep hole machining. To avoid double holes, it is imperative to complete the drilling operation before the drill point reaches the full diameter of the hole.
Adjusting the size of the reamer
Adapting the size of the reamer is a simple, effective way to fix the drilling mark problem in deep hole machining. Reamers work by removing a thin layer of material and enlarging the hole by a factor of ten or fifteen thousandths. They usually feature a chamfer at the end of their nose to maintain a tight tolerance inside the hole.
To compensate for this issue, the reamer is guided by bushings that have a predetermined angle. The jig or fixture should be of a diameter that matches the hole size. It should also be guided at both ends. The problem is resolved with the proper jig or fixture. This article provides you with a few tips and tricks on how to solve the drilling mark problem.
Supporting the long drill
Several new drilling techniques and geometries have been developed to combat this problem. Self-supporting drills are designed with flutes that fit tightly inside the hole, allowing the walls to support the drill while drilling. Self-supporting drills also taper slightly toward the shank, ensuring the point end only contacts the part. While these innovations have improved the quality of the finished product, the problem remains.
In deep hole machining, it is important to ensure that the tool is properly supported by a guide pad. This guide pad keeps the force balance during drilling and ensures that the hole is consistent. Angles of the guide pad and the cutting edge must not match precisely to prevent chatter or axial deviation. To minimize this problem, angle the drill and guide pad. However, if the two are similar, the cutting edge will not be able to fully support the tool, resulting in chatter and a spike in torque.
Chip Control
The process parameters of deep hole machining can lead to increased chip strain. These parameters are related to drilling speed and feed rate. Different drilling feed rates at 1200 r/min can result in different chip strain increments. The optimum combination of feed rate and chip thickness ratio should be used to avoid the mark problem. This article explains the different factors affecting chip deformation and breaking during deep hole machining.
Ensure proper tool-holder setup is vital to improving chip control. A high quality tool-holder will minimize run-out, improve hole quality, and allow a drill to be pushed harder. Another common problem in machining centers is the wads of chips that hang from drills after drilling. For this problem, use a quick spindle reverse. This can help throw away loose chips and prevent them from getting dragged into tool change arms.