Turning is generally considered to be an ideal machining method for precision hole machining on workpieces of various different sizes and shapes. In order to meet the needs of increasing productivity, the design of boring tools is also continuously innovating and improving. In recent years, the technical improvements in boring tools have mainly been reflected in the following four aspects.

（1）Precision boring heads with digital display reading screens

Since the advent of CNC（NC）technology, digital display technology has been widely used inCNCmachine tools and coordinate measuring machines. In addition, digital dial indicators, digital calipers and other digital measuring tools have also been widely used. However, the application of digital display technology on precision boring tools has always been slow, and the main constraints are the cooling fluid used in boring machining and the high-speed rotation of the boring head.In the past, it was necessary to be very careful when performing boring machining on a machining center to avoid the cooling fluid splashing and entering the electronic components of the boring head's digital display device. Now, the new type of boring tool with internal cooling design can better solve this problem. Since the cooling fluid can directly reach the cutting position through the channel inside the tool, it has achieved complete isolation between the cooling fluid and the digital display device of the boring head. In addition, the new type of CNC boring tool is well sealed on the outside to effectively prevent the cooling fluid from contacting the electronic components in the digital display device.In high-speed boring machining, the high-speed rotation of the boring head, centrifugal force and the unbalanced itself of the boring head may cause large vibration, thus damaging the sensitive digital display device. The new type of boring head adopts a built-in balance mechanism, which can reduce or eliminate harmful vibration during high-speed boring machining. At present, the precision boring head with a digital display reading screen can be used for high-speed boring machining with a speed of up to16000r/min.The digital display screen of the new type of boring head can directly show the displacement of the boring tool slide, without having to determine the displacement through the rotation amount of the adjusting screw. Since the boring bar is directly installed on the boring tool slide, the digital display value of the boring head can truly reflect the displacement of the boring tool, without being affected by the screw empty stroke error. This feature of the digital boring head makes it possible to adjust the boring diameter more quickly and precisely, and can achieve error compensation for the machining deviation or tool wear.
 
 Most borers require a cut-and-measure operation to determine their set dimensions, i.e. a small section of the machined hole is first machined by trial cutting, and then the diameter of the machined hole is measured. Typically, this means that the borer must be removed from the machine and then re-mounted on a tool setting device to fine-tune the borer dimensions to obtain the correct hole diameter. This pre-set operation is necessary because it is difficult to read and preset the borer’s scale disk directly on the machine, but this method of operation can result in a hole diameter out of tolerance or damage to the workpiece.Since it is difficult to predict the tool’s tip runout when mounting the borer on the machine, a cut-and-measure operation is required to preset the tool. If a new digital borer with an easily readable display is used, it is possible to directly preset the tool’s machined hole diameter on the machine spindle, with an adjustment range of0.0001″ (0.00254mm). Even if the borer must be removed from the machine for diameter presetting due to the machine spindle’s feed limit, the presetting process is faster and more accurate with the new digital borer. 

2auważ that the tool body is made of aluminum, which is a common material for manufacturing tool bodies. With today’s

CNCmachines operating at ever-higher speeds, many machines are also becoming lighter in weight, and reducing the weight of the tool becomes important.Most CNC machine tool’s tool-changer has a weight limit for the tool. An aluminum-bodied borer ensures that the tool weight does not exceed the tool changer’s weight limit, yet it can machine holes larger than4″ (about100 Mm). (Generally, holes are machined with a diameter smaller than4″
The boring tool, whether of aluminum structure or steel structure, does not exceed the weight limit of the tool-changing robot). The reduction in the weight of the boring tool can reduce the error of the machine tool spindle, thereby improving the accuracy of the bored hole. In addition, the lighter the weight of the boring tool, the smaller the wear and damage to the machine tool spindle itself.When loading and unloading large and heavy boring tools on a CNC machine tool, it is necessary to use manual loading and unloading or high-altitude lifting arms for lifting, which is time-consuming and laborious, because the weight of the steel structure boring tool often exceeds the weight limit of the machine tool tool-changing robot. If a lighter aluminum structure boring tool is used, this problem can be easily solved. For example, a factory in Kansas, USA, originally used a steel structure boring tool for processing a hole diameter of14″（355.6mm）, which weighs about40 pounds and needs to be lifted by a lifting arm to be installed on the machine tool. After replacing it with an aluminum structure boring tool of the same specification, its weight is less than25 pounds, and it can be automatically loaded and unloaded by the tool-changing robot, greatly improving productivity.Aluminum structure boring tools also have advantages in terms of balance performance at high-speed cutting. Since the asymmetric mass of the aluminum structure boring tool is much smaller than that of the traditional steel structure boring tool, it can greatly reduce or eliminate the problems caused by tool imbalance when processed by the same manufacturing process.The durability of the aluminum structure boring tool is also a concern. However, this problem can be solved by coating a hard coating of alumina on the tool surface. By using a special acidic electrolyte oxidation (acid-electrolyte oxidation) coating process, the aluminum on the tool surface can be converted into alumina, and the depth of the oxide layer can reach0.008″（about0.02mm）, and its surface hardness can reach56HRC.

 The surface hard coating of the aluminum structure boring tool can effectively prevent damage to the tool caused by chip friction and corrosion. Since the chips produced by fine boring are generally fine, the impact force on the tool body is also small, and the influence of chip friction on the tool is limited. Therefore, the aluminum structure boring tool with surface coating treatment has good wear resistance in fine boring, but it may not be as impact resistant as the steel structure boring tool.The aluminum structure boring tool with the surface coating of alumina hard coating is also advantageous for rough boring of large holes on workpiece materials that are prone to form long chips or abrasive chips(8.07″～40.1533″，205～1020mm)（small hole diameter rough boring tool usually adopts steel structure）， smooth chip removal （can reduce the impact and wear of chips on the tool） combined with the hard coating on the tool surface can prevent the tool body from wearing out too quickly during rough boring of such materials.

（3）The compound boring tool with rough and fine boring functions

Traditional boring hole processing usually requires multiple processes from rough boring to fine boring （sometimes semi-fine boring is also required before fine boring）， although this multi-process processing method can ensure the reliability of the processing， it is quite time-consuming.With the emergence of near-net-sharp castings （near-net-sharp castings） technology， especially aluminum mold casting technology， the quality of the workpiece blank is improved， the machining allowance is reduced， and the necessity of multi-process machining is reduced or even eliminated. In many cases， the rough boring and fine boring of the hole can be completed on the same machine tool， which can greatly reduce the technical requirements for the machining allowance and eccentricity of the hole to be processed. For this reason， the application of compound boring tools has attracted widespread attention. 

 Compound boring cutters integrate both rough and finish boring cutting edges into a single cutter, allowing the entire boring operation to be completed in a single pass. The rough boring cutting edge removes most of the stock, followed by the finish boring cutting edge to machine the hole diameter to the required size. The difference in working life between the rough and finish boring cutter blades can be adjusted by installing different grades of carbide cutter blades in the cutter holder.The finish boring cutting cutter blade is clamped in an adjustable cutter holder, the position of which can be adjusted using a precision screw and a traditional vernier scale. A precise hole diameter with a tolerance of0.001″（0.0254mm）can be machined in a single pass. Although the feed rate must be set according to the machining requirements for compound machining, the productivity can be significantly increased as the rough or semi-fine boring operation is eliminated.

（4）Self-balancing boring cutters suitable for high-speed cutting

It has long been recognized that the balancing performance of a boring cutter is important to the quality of the boring operation. Under today's high-speed cutting conditions, the balancing problem of the boring cutter has become more prominent than ever before, and even a small unbalanced cutting force can have a significant impact on the size, surface finish, roundness, and tool life of the machined hole diameter. In addition, the unbalanced cutting force can also cause cutting vibration. In recent years, many standard boring cutters have been equipped with balancing mechanisms, which usually consist of movable counterweights. Since the unbalanced state of the boring cutter is mainly caused by the change in the diameter of the machined hole, the balance of the cutter can be adjusted according to the diameter of the hole to be machined set by the cutter holder. Although this method is effective in maintaining the balance of the cutter, it is quite time-consuming. In addition, this type of balancing device is located on the outside of the cutter, exposed to coolant, chips, and oil stains, and is prone to damage.A new type of boring cutter with a self-balancing mechanism built into the interior can better solve this problem. When the adjustable cutter holder that clamps the cutter blade moves in a certain direction to adjust the hole diameter, a balance weight mechanically connected to it moves in the opposite direction within the boring head to keep the cutter balanced. The built-in self-balancing mechanism is sealed in the boring head and is completely isolated from the coolant and chips.This self-balancing boring cutter can be applied to modernCNC

 The high-speed cutting of machine tools can achieve a very good tool balance effect for most cutting tasks. If a cutting task has particularly high technical requirements for tool balance, the tool can also be balanced as a component on a high-precision balancer. For bridge boring tools (whether they are aluminum structure or steel structure), it is usually balanced manually by using balance weight blocks.