Fine boring, rough machining, large diameter boring-no matter the type of application, it is key to get the most from boring tools. Hole finishing applications, whether in a job shop or a high production environment, require precision. Knowing what challenges might be faced and what boring tools are most suitable for the job can aid in achieving success in an application and producing components that meet specific finishing requirements.
When it comes to getting the most out of boring tools, it is important to remember that boring tools should be selected according to the unique requirements of each job. As a boring tool is adjusted to bore a specific diameter, the balance of the tool is affected, which in turn affects hole size, finish and the penetration rate of the boring tool. While low-volume jobs typically deem versatile boring tools more beneficial, high-volume jobs and those with tighter tolerances or fine finish requirements dictate dedicated tools to be used in each application.
Another important tip is to keep the tool as short as possible to reduce deflection, which can cause poor finish. Length-to-diameter ratio is extremely important to boring tools.
Ideally, the length-to-diameter ratio for nondampened boring systems is 5xD or less, while heavy metal, carbide and vibration dampening technologies can allow boring of up to 10xD. Natalie Wise, Product Manager of Allied Machine's boring product lines, said, "Our NOVITECH modules utilize viscoelastic fluid to minimize vibration, allowing bore depths up to 10xD. Not only does this vibration damping technology improve the life of your boring tools, it also extends the life of the spindle while producing an outstanding surface quality." With modular boring systems, it is important to consider the components selected for a job and then attempt to remove any unnecessary length. Because when it comes to boring tool solutions, the shorter and more robust, the better.
In large diameter boring applications, it is important to determine if the machine planned for use has a quill. A quill is a ram system that extends the spindle beyond its standard position. Also called a boring spindle, quills come in various diameters, typically between 5" and 10", and can have several feet of travel. When boring large diameters that have some depth, quills allow the boring tool to be made as short as possible, which can be the difference between the tool working or not. It is important to keep a few other factors in mind as well. Too large of a nose radius and too light of a depth of cut will cause push-off (radial deflection) and chatter, which results in poor finish and tool life.
One should also look at the inserts being used with boring tools because they play an important role too. Proper geometries and grades should be selected based on the material being machined, the amount of stock being removed and the tool life needed. Additionally, coatings and insert nose radius, which should match the depth of cut, impact the tool performance. Chip breakers affect performance as well because chip control is often a function of the insert's chip breaker and, therefore, can determine success or failure.
It is not just the tool itself that can determine success-it is also a machine's capabilities. For example, large diameters can present issues when considering boring tool weight and tool-moment. Weight and tool-moment will affect the ability of the gripper system to hold the tool in the spindle, which can result in various issues, and will affect the toolchanger system to either perform the tool change or store the tool in its magazine. Another issue may be power available battling against the diameter of the tool and the amount of stock being removed. So, it is clearly important to be mindful of machine limitations.
Nevertheless, evaluating boring tool solutions based on the needs of the application is still key. Modular connections, for example, are largely beneficial in boring applications. Not only do these connections reduce the need for special extensions, but they also provide easy adaption to machines. With a modular connection, shanks can be quickly changed out for different spindle types; additionally, it provides maximum flexibility of a system, allowing for multiple set-ups. When using a modular connection, a tool can be made as short and robust as possible. By optimizing the modular components used to give a boring tool its length like extensions, reducers and extended length master shanks, the LxD ratio can be reduced considerably. For instance, for a 75 mm hole that is 300 mm deep, one boring set-up may result in a 7xD ratio while another of the same length may only be 5xD. The 5xD set-up will ultimately perform better than the 7xD, especially when cycle time is considered.
In addition to modular connections, one must also consider whether a single boring tool or a boring kit is the best option for a specific application. While kits provide flexibility, single boring tools offer consistency when it is needed most. For job shops, it is often beneficial to utilize boring kits to allow for multiple diameter ranges based on a shop's individual requirements. Some of the best kit environments include prototype departments, short batch runs, low production one-off components and repair departments. Basically, boring kits are ideal for machinists looking for a boring tool to do a variety of different things. Conversely, individual boring tools are more often used in a high production environment. If a shop runs production day in and day out, single tool set-ups provide lower tool costs and maintain the consistency needed for a narrower diameter range.
Custom boring tools are another option to be considered when selecting tooling. From reducing cycle time and improving a component's quality to providing cost savings by combining multiple bores into one operation, special boring tools provide a variety of benefits. At the same time, while many boring applications can run off-the-shelf tooling, there are always unique applications that require special solutions. Complex hole profiles and machine tool magazine limitations demand one tool with multiple diameters and steps. Another example would be the development of line boring tools, which were created due to the inherent limitations of boring tools when it comes to length and the need to achieve concentricity between separate holes, as well as the roundness and diameter tolerances of each. Ultimately, custom boring tools provide many benefits but are often developed based on the particular needs of an application.
No matter the boring tool, there are often challenges to be dealt with in order to get the most benefit from your tooling. Take surface finish, for example: boring tools can achieve a very fine surface finish, especially when using a wiper geometry insert. However, feedrate, nose radius and depth of cut play a critical role in meeting the necessary finish requirements as well. Although it is not typically an issue, coolant can help achieve desired surface finish and can improve tool life as long as the coolant is maintained.
Nevertheless, careful consideration needs to be taken regarding coolant in several conditions:
- Integrated digital tools-Some digital boring heads have coolant pressure limitations. Exceeding those limitations can result in damage to the internal components of the boring head. Many shops run 1,000 PSI pumps, which unfortunately can cause seals to fail. Particularly in finish boring, this coolant pressure is not necessary. The chips are often so small that it is overkill for chip evacuation, so if the chip control is proper, 300 PSI is very acceptable.
- Heavy roughing applications-If the amount of stock being removed is greater than the difference between the hole size and body diameter, chip evacuation may be impeded, so coolant will play a large part in those situations.
- CBN inserts-CBN does not handle thermal shock well, which can occur when coolant is used. In most cases, CBN is run dry to prevent issues.
Ultimately, soluble coolants tend to be best for internal components in boring tools as synthetics can cause internal damage and reduce accuracy.
Chip evacuation, although more of an issue when roughing rather than finishing, is a key area where insert selection can make a significant difference. Geometries should be carefully selected based on material being bored and amount of stock being removed.
Another aspect that one should pay attention to is the diameter of the boring tool body and additional modular components, such as extensions and reducers versus the amount of stock being removed. If the stock being removed exceeds the difference between the hole size and body diameter, chip evacuation may be impeded and could result in damage to the boring tool and potentially the workpiece. All in all, the shorter the chip, the better the chip evacuation, so being mindful of tool selection and the application itself results in better chip formation.
Just like new insert coatings being introduced, boring tools as a whole will likely see continued improvements and some innovation. As with any other industry, technology that was previously used only in one-off or low-volume special applications will transfer to more common everyday applications, becoming more accessible while being lower in cost. Eventually, most, if not all, adjustable boring tools will be digital. It may also become commonplace for adjustable boring tools to be adjusted by a separate module or even a phone. While it may not be common knowledge, similar technology exists now in the marketplace. However, as the machining industry awaits these advancements, getting the greatest benefit from one's boring tools requires examining what tooling solutions will work best in the job environment and how these tools can overcome potential challenges.
Authored by Allied Machine & Engineering Corp.
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