Boring is a machining technology for further processing the forged, cast, or drilled holes that already exist in the workpiece, boring can enlarge the hole, increase its diameter, improve dimensional accuracy, reduce surface roughness, and correct the deviation of the original hole axis. The accuracy and precision of boring are high, the accuracy of precision boring can reach IT8~IT7 and the diameter can be controlled within 0.01mm, the surface roughness of the general boring process is roughly between Ra 1.6 ~ 0.8 μ M.
A boring machine is used to cut large holes in solid materials, there are several different types of boring machines, but most of them consist of a rotating cutting head, chuck, spindle, etc. During the boring process, the head of the machine will be put into the drilled or cast hole, when the machine starts working, the tool will broaden the hole by removing the materials from the inner wall.
– Horizontal Boring Machine: used to bore holes horizontally through large and heavy workpieces. The workpiece is mounted on a horizontal table that moves along a track, while the boring head moves along a vertical column.
– Vertical Boring Machine: used to bore holes vertically into a workpiece that is mounted on a rotating table. The boring head moves along a vertical column and can be adjusted to create holes of different sizes and shapes.
– Jig Boring Machine: used to create very precise and accurate holes in workpieces that require a high degree of precision. The machine uses a specialized cutting tool that is guided by a jig or fixture to ensure that the hole is created exactly where it is needed.
– Portable Boring Machine: designed to bore holes in situ, meaning it can be brought to the workpiece rather than the workpiece being brought to the machine. Portable boring machines are typically used in construction or repair projects where the workpiece is too large or heavy to move.
– Cylinder Boring Machine: designed to bore holes in engine cylinders for automotive or industrial applications. The machine uses a specialized cutting tool to create precise and accurate bores in the cylinders.
– Tunnel Boring Machine: used to create tunnels in rock or other hard materials. The machine can bore through the material by using a rotating cutting head with specialized cutting tools.
– When you need to create holes with larger diameters than a standard drill bit, boring is a better technique.
– If you need a large and precise hole, boring is the preferred choice.
– For applications require deep holes, boring machines can creat holes that are much longer than standard drill bits can reach.
– For hard materials like some metals or rock, boring machines can cut through more easily than a standard drill bit.
– If you need to produce holes in irregular shapes, boring is a useful manufacturing method.
There are common problems operators may meet in CNC machining services like turning, milling, and boring, paying attention to observe and solve the problem in time, high-quality products can also be obtained.
1) Tool wear
In the CNC boring process, the continuous cutting is easy to cause tool wear and damage, which further results in reduced dimensional accuracy of hole boring and increases the surface roughness. In addition, the calibration of fine-tuning feed unit is abnormal, causing adjustment errors and deviation of machining diameter, and even product quality failure.
2) Machining error
The machining error of the boring process is presented in the altering of dimension, shape and position, and surface quality. The problems that may cause machining errors are as follows:
– The length-diameter ratio of the cutter rod is too large or the overhang is too long;
– The blade material does not suit the workpiece material;
– The parameter of boring is improper;
– The allocation of allowance adjustment is unreasonable;
– The offset of the initial hole position leads to the periodic change of the allowance;
– The workpiece material has high rigidity or low plasticity
3) Surface quality
The machined surface of bored parts shows fish scale or thread-like cutting lines
4) Adjustment error
Improper operation in adjusting the distribution feed allowance is easy to cause low accuracy.
5) Measurement error
Improper use of measuring tools and wrong measurement methods are common quality hazards in CNC boring process.
1) Boring tool
After the boring bar is mounted, observe whether the upper plane of the main tool edge of the boring tool is on the same horizontal plane as the feed direction of the boring tool head, to ensure the cutting edges be at the normal machining cutting angle.
2) Trial boring
The boring tool should reserve with an allowance of 0.3-0.5mm, when expanding the bore, adjust the allowance of rough boring ≤0.5mm, to ensure that the subsequent finishing boring machining can meet the allowance requirements.
3) Tips and precautions for boring
– Check out whether the work holding, workpiece positioning, and clamping are stable and reliable before machining.
– Check out if the spindle repeated positioning accuracy and dynamic balance accuracy meet the requirements of CNC manufacturing
– Measure the diameter of the initial hole with a caliper and calculate the reserved machining allowance.
– Check out the dynamic gravity overhang value of the boring bar during the trial boring process, and reasonably modify the cutting parameters to reduce the impact of centrifugal cutting vibration.
– According to rough boring, semi-finish boring, and finishing boring, reasonably allocate the boring allowance, recommended: rough boring – 0.5mm, semi-finish and finishing boring – 0.15mm.
– Add fine boring steps for difficult-to-machine materials and high-precision boring, the boring allowance is not lower than 0.05mm.
– In the tool set of the boring bar, pay attention to avoid the impact between the working part (blade and base) of the tool and block, prevent tool damage, or affect the machining accuracy due to the guiding groove changing the boring tool adjustment value.
– The boring machining process should keep cool, and increase lubrication to reduce cutting force when necessary.
– Remove the chip appropriately and prevent the chips from engaged in the second cutting.
– Check the tool wear frequently and replace the damaged cutter instantly, to ensure the machining quality and accuracy of hole boring, measure the processed hole carefully.