Reaming is a processing method that uses a cutting tool to enlarge a prefabricated hole. Boring work can be done on a boring machine or lathe.
Boring can be divided into rough boring, semi-finished boring and fine boring. The dimensional accuracy of precision boring can reach IT8~IT7, and the surface roughness Ra value is 1.6~0.8μm.
So what’s so difficult about boredom? Let’s find out today.
Annoying Steps and Precautions
Installing a boring tool
It is very important to install the working part of the boring tool, especially for work adjustment based on the eccentric principle. After installing the boring tool, you should pay attention to observe whether the upper plane of the main cutting edge of the boring tool. is on the same horizontal plane as the feed direction of the boring tool head? Installation on the same horizontal plane can ensure that multiple cutting edges are at normal machining cutting angles.
Boring tool test
The boring tool is adjusted to reserve a tolerance of 0.3 to 0.5 mm according to the manufacturing requirements of the process. The rough boring tolerance for expansion and drilling holes is adjusted to ≤0.5mm based on the initial hole tolerance. It must be ensured that the subsequent fine boring. the processing allowance is respected.
After the boring tool is installed and ready, a boring test is required to verify whether the boring tool debug meets the rough boring requirements.
Boring Requirements
Before the boring process, carefully check whether the tooling, workpiece positioning reference and each positioning component are stable and reliable.
Use a caliper to check the diameter of the initial hole to be machined? Calculate what machining allowance is currently reserved?
Before boring processing, check whether the repeated positioning accuracy and dynamic balance accuracy of the equipment (spindle) meet the processing and manufacturing requirements of the process.
During the horizontal drilling test drilling process, the dynamic runout value of the gravitational overhang of the boring bar should be checked, and the cutting parameters should be reasonably corrected to reduce the influence centrifugal shear vibrations during processing.
Reasonably allocate layer boring tolerance according to the stages of rough boring, semi-finished boring and fine boring. The tolerance for rough bore is about 0.5mm, the tolerance for semi-finished bore and fine bore is about 0.15mm to avoid excessive tolerance. for semi-finished boring. The phenomenon of tool deviation affects the precision of fine adjustment of the boring allowance.
For difficult-to-machine materials and high-precision boring (tolerance ≤0.02mm), fine boring processing steps can be added, and the boring allowance should not be less than 0.05mm to avoid elastic deflection of the tool on the processing surface.
During the process of setting the boring tool, care must be taken to avoid any impact between the working part of the boring tool (blade and tool holder) and the tool setting block, which could damage the blade and guide groove of the tool holder, causing the adjustment value. Of the boring tool to change and affect the machining accuracy of the opening.
During the boring process, be sure to maintain adequate cooling and increase the lubrication effect of the processed parts to reduce cutting forces.
Strictly remove chips at each processing step to avoid chips participating in secondary cutting and affecting the machining accuracy of openings and surface quality.
During the reaming process, check the wear degree of the cutting tool (blade) at any time and replace it in time to ensure the quality of aperture processing. It is strictly forbidden to replace the blade during the fine boring stage to avoid errors; the process quality control requirements should be strictly implemented after each processing step, and the actual processed opening should be carefully detected and processed. Good records, easy to analyze, adjust and improve bore processing.
Main problems with boring processing
Tool wear
When reaming processing, the tool cuts continuously, which is prone to wear and damage, reducing the dimensional accuracy of hole processing and increasing the surface roughness value, at the same time, the Calibration of the fine-tuning power unit is abnormal, resulting in adjustment errors, and deviations in the diameter of the processed hole may even cause product quality failure.
Changes in blade edge wear
machining error
The processing error of drilling processing is reflected in the changes in size, shape and surface quality after hole processing. The main influencing factors are:
1. The length/diameter ratio of the tool holder is too large or the overhang is too long;
2. The blade material does not match the workpiece material;
3. The boring amount is unreasonable;
4. Unreasonable balance adjustment and distribution;
5. Deviation from the initial hole position causes periodic changes in tolerance;
6. The workpiece material has high rigidity or low plasticity, and the tool or material tends to yield.
surface quality
Annoying scale or thread-like cuts on the machined surface are a common occurrence in surface quality:
Mainly caused by mismatch between tool feed and speed
Mainly caused by rigid vibration and tool wear during boring processing
Setting error
During drilling processing, the operator needs to adjust the cutting quantity of the distribution layer. Incorrect operation when adjusting the distribution feed margin can easily lead to deviations in the dimensional accuracy of processing.
measurement error
Improper use of measuring tools and incorrect measuring methods during and after the drilling process are common quality risks in the drilling process.
1. Error in measuring tools;
2. The measurement method is incorrect.
Analysis of typical drilling processing quality problems
Influencing factors and processing optimization measures for internal hole turning
Turning internal holes is also called reaming. It uses turning to enlarge the inner hole of the workpiece or process the inner surface of the hollow workpiece. It can be processed by most cylindrical turning techniques. During cylindrical turning, the workpiece length and tool holder size selected have no effect on the tool overhang and can therefore withstand the cutting forces generated during machining. When boring and turning internal holes, the depth of the hole determines the overhang. Therefore, the hole diameter and workpiece length greatly limit the tool selection, so the machining plan must be optimized according to various influencing factors.
General rules for machining internal holes
1. Minimize the tool overhang and select the largest tool size possible to achieve the highest machining accuracy and stability.
2. Due to the limited space of the opening of the processed parts, the choice of tool size will also be limited, and chip removal and radial movement also need to be considered during processing.
3. In order to ensure the stability of inner hole processing, it is necessary to select the correct inner hole turning tool, apply and tighten it correctly to reduce tool deformation and minimize vibration to to guarantee the processing quality of the inner hole.
Cutting force in internal hole turning is also an important factor that cannot be ignored for given internal hole turning conditions (workpiece shape, size, clamping method, etc.), size and direction of cutting force must suppress turning of internal holes. Vibration and improvement Important factors in processing quality, when the tool cuts, the tangential cutting force and the radial cutting force deflect the tool, slowly moving it away from the workpiece, causing the cutting force to deflect . The tangential force will attempt to force the tool down and do so. the tool Move away from the center line and reduce the tool clearance angle. When the turning hole diameter is small, the clearance angle should be kept large enough to avoid interference between the tool and the hole wall.
During machining, radial and tangential cutting forces cause internal turning tools to deflect, often requiring forced edge compensation and tool vibration isolation. In case of radial deviation, the cutting depth should be reduced and the chip thickness should be reduced.
From a tool application perspective
1. Selection of blade geometry
The geometry of the insert has a decisive influence on the cutting process. For machining internal holes, a positive rake angle insert with a sharp cutting edge and high edge strength is generally used.
2. Selection of the main declination angle of the tool
The leading angle of the internal turning tool affects the direction and magnitude of the radial force, axial force and resultant force. A larger entry angle results in greater axial cutting forces, while a smaller entry angle results in greater radial cutting forces. Under normal circumstances, the axial cutting force toward the tool holder generally does not have a great impact on machining, so it is advantageous to choose a larger rake angle. When selecting the main declination angle, it is recommended to choose a main declination angle as close as possible to 90° and at least 75°, otherwise the radial cutting force will increase sharply.
3. Tool tip radius selection
In internal hole turning operations, small tool nose radii should be preferred. Increasing the tool nose radius will increase radial and tangential cutting forces, and will also increase the risk of vibration tendencies. On the other hand, the tool deflection in the radial direction is affected by the relative relationship between the cutting depth and the tool nose radius.
When the cutting depth is less than the tool nose radius, the radial cutting force increases as the cutting depth deepens. When the cutting depth is equal to or greater than the tool nose radius, the radial deviation will be determined by the rake angle. The general rule for selecting a tool nose radius is that the tool nose radius should be slightly less than the depth of cut. In this way, radial cutting forces can be minimized. At the same time, using the maximum nose radius achieves a stronger cutting edge, better surface texture and more uniform pressure distribution on the cutting edge while ensuring minimal radial cutting.
4. Selection of edge processing
The cutting radius (ER) of the insert also affects the cutting forces. Generally speaking, the cutting edge roundness of uncoated inserts is less than that of coated inserts (GC), which must be taken into account, especially when working with long leads. tool overhangs and when machining small holes. Insert flank wear (VB) changes the clearance angle of the tool relative to the hole wall, which can also affect the cutting action of the machining process.
5. Efficient chip discharge
When turning internal holes, chip removal is also very important to the processing effect and safety performance, especially when processing deep holes and blind holes. Shorter spiral chips are ideal chips for internal hole turning. This type of shavings is easier to evacuate and will not put much pressure on the cutting edge when the shavings break.
If the chips are too short during processing and the chip breaking effect is too strong, higher machine tool power will be consumed and there will be a tendency to increase vibration. If the chips are too long, it will be more difficult to remove them. The centrifugal force will push the chips toward the hole wall, and the remaining chips will be pressed onto the surface of the workpiece, resulting in the risk of falling. chip clogging and tool damage. Therefore, when turning internal holes, it is recommended to use tools with internal coolant. This way, the cutting fluid will effectively force the chips out of the hole. When machining through holes, compressed air can also be used instead of cutting fluid to blow chips through the spindle. Additionally, choosing the correct insert geometry and cutting parameters will also help control and evacuate chips.
6. Selection of tool tightening method
Tool clamping stability and workpiece stability are also very important in internal hole machining. They determine the magnitude of vibrations during machining and whether these vibrations will increase. It is very important that the tool holder clamping unit meets the recommended length, roughness and hardness.
Clamping the tool holder is a key stabilizing factor. In actual machining, the tool holder deflection depends on the tool holder material, diameter, overhang, radial and tangential cutting force and tool position. support. Clamping in machine tools.
The slightest movement at the tight end of the toolbar will cause the tool to deflect. High performance tool holders must have high stability when clamped to ensure that there are no weak links during machining. To achieve this, the inner surface of the tool clamp must have high surface finish and sufficient hardness.
For ordinary tool holders, the highest stability is achieved through a clamping system that completely clamps the tool holder around the entire circumference. The overall support is better than the toolbar directly tightened by screws. It is more suitable to tighten the toolbar on the V-shaped block with screws. However, it is not recommended to use screws to directly tighten the cylindrical handle toolbar because. the screw will be damaged if it acts directly on the toolbar.
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