Guide to Boring Machining Process: Challenges, Tips and Methods of Boring Operation | CNCLATHING

2020.3.10

Boring operations can not only be completed on CNC turning lathe machines but also with milling machines. We can bore holes in various sizes with the boring tool for turning and create highly accurate diameters. Today, we want to discuss the difficulties, challenges, tips, and methods of boring process.

 

What is Boring Process

Boring is machining technology of 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 general boring process is roughly between Ra 1.6 ~ 0.8 μ M.

 

What Difficulty to Perform Boring Operation – Errors, Challenges & Problems in Boring

There are common problems operators may meet in CNC machining services like turning, milling, boring, pay attention to observe and solve the problem in time,  high quality product 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, causes adjustment error and deviation of machining diameter and even product quality failure.

 

2) Machining error

The machining error of boring process is presented in the altering of dimension, shape and position and surface quality. The problems may cause machining error 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.

 

Tips and Methods of Boring Machining

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 in the normal machining cutting angle.

 

2) Trial boring
The boring tool should reserve with an allowance of 0.3-0.5mm, when expanding bore, adjust 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 workholding, 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 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 setting of boring bar, pay attention to avoid the impact between working part (blade and base) of the tool and block, prevent tool damage or affect the machining accuracy due to the guiding groove changes the boring tool adjustment value.
– The boring machining process should keep cool, 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 damaged cutter instantly, to ensure the machining quality and accuracy of hole boring, measure the processed hole carefully.

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