CNC boring/Boring machining/Precision boring/Rough boring
CNC boring and milling machining has the characteristics of strong rigidity, high machining accuracy and efficiency, good stability, long transverse travel, large bearing capacity and powerful cutting. It is especially suitable for the boring and milling of the large planes and the finishing of large box parts and hole series. In addition to drilling, boring, expanding and reaming, various accessories can also be used for turning, milling and screw pattern processing.
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What is boring in machining? And how to apply it?

1. The definition of boring

Boring is a cutting process. It cuts the machined surface of the workpiece through the relative movement between the boring tool on the equipment and the workpiece. The machined surface can obtain a certain degree of machining accuracy and surface roughness.

Compared with other hole machining processes, boring is not limited by the tool size. In addition, boring has a strong error correction ability, which can correct the original coarse hole axis error through multiple passes and maintain a high position accuracy of the boring hole and the positioning datum.


2. The type of boring tool

The type of boring tool(1).jpg

(1)Expand boring tool      (2)Module boring tool      (3)Grooving boring tool

(4)Step Boring Tool       (5)Single edge boring tool    (6)Integral boring tool


3. The application of boring

When encountering problems, we can first consider these aspects.

Equipment usedProcessed productsAperture to be processed
Q: Is the spindle speed possibleQ: Whether the processed material has good chip breaking performanceQ: Boring diameter
Q: Coolant supply and pressureQ: Whether the product is stable or whether there is a thin wall part that causes vibrationQ: Boring depth
Q: Whether the capacity of the machine tool is satisfied.Q: HardnessQ: Boring tolerance/surface quality/position/straightness
Q: Whether the spindle interface selection is correct.

Q: Whether the selection of power/torque is reasonable.

Q: Whether the workpiece clamping is stable


3.1. Rough boring application:

(1) Blind hole processing

When machining blind holes, it is important to ensure proper chip removal.

Correct cutting parameters are necessary for obtaining proper chip shapes.

Make sure/check that the chips do not block or wear the blade.

Coolant pressure and cutting fluid flow should be sufficient to discharge chips

Vertical machine tools have higher requirements for effective chip removal than horizontal machine tools.


(2) Intermittent cutting

When performing intermittent cutting (such as cross holes), high requirements are placed on the cutting conditions of the insert.

Choose a material with higher toughness.

Under stable working conditions, choose a solid square negative rake angle basic shape to insert to improve processing safety.

If there are multiple interruptions, reduce the cutting parameters.


(3) Sand cast iron

Sand inclusion in the casting will increase the wear of the blade.

Choose a material with higher toughness.

Reduce cutting parameters.

To improve processing safety and reduce wear as much as possible, choose a solid square negative rake angle basic shape insert.

PS: Sand inclusion means that the casting is doped with sand.


(4) Gas burning

The local area of the air burn hole may harden, which will increase the wear of the blade.

Choose a material with higher toughness.

Reduce cutting parameters.

To improve processing safety and reduce wear as much as possible, choose a solid square negative rake angle basic shape insert.


3.2 Application of fine boring

(1) Cutting force

The effect of cutting force on the product

When the tool is cutting, the tangential and radial components of the cutting force will try to deviate the tool from the workpiece. The tangential element will force the tool down and away from the centerline. In this way, the tool clearance angle will be reduced.

Any radial deformation means that the depth of cut and chip thickness is reduced, which leads to a tendency to vibrate.


(2) Balance

The influence of balance force on processing

The imbalance caused by asymmetric tools or large strokes produces a force acting on the boring tool.

In most applications, the force generated by the imbalance is negligible compared to the cutting force.

Under high speed, imbalance may cause vibration, which will affect the processing quality of the hole


4. boring case

4.1 Blade wear

Boring blade wear.jpg

In the boring process, continuous cutting of the tool is prone to wear and breakage, which reduces the dimensional accuracy of hole processing and increases the surface roughness value. At the same time, there is an abnormality in the calibration of the fine-tuning feed unit, which leads to adjustment errors, deviations in the processing aperture, and even product quality accidents.


4.2 Surface quality

Boring surface quality.jpg

A relatively common surface quality phenomenon is the machined surface's boring scale-like or thread-like cuts.

Left: Mainly caused by the mismatch of boring feed and drilling speed.

Right: Mainly caused by severe vibration and tool wear in boring processing.



FAQ


1. What is the difference between boring and turning?

(1) Different concepts

Boring is an inner diameter cutting process that uses tools to expand holes or circular contours. Turning is lathe processing. Lathe processing mainly uses a turning tool to turn a rotating workpiece.

(2) Different sizes

Boring uses a rotating single-edged boring tool to enlarge the prefabricated hole on the workpiece to a certain size. Turning is a cutting process in which the turning tool moves in a straight line or a curve in a plane.

(3) Using different

When boring, the workpiece is installed on the machine tool table or the machine fixture, and the boring tool is installed on the boring bar (it can also be integrated with the boring bar), and the spindle is driven to rotate. When using a boring mold, the boring bar is floatingly connected to the spindle, and the machining accuracy depends on the accuracy of the boring mold; When the boring die is not used, the boring bar is rigidly connected to the spindle, and the machining accuracy depends on the accuracy of the machine tool.

Turning uses different turning tools or other tools on the lathe to process a variety of rotating surfaces, such as inner and outer cylindrical surfaces, inner and outer conical surfaces, threads, grooves, end surfaces and forming surfaces, etc. The processing accuracy can reach IT8 to IT7. The surface roughness Ra value is 1.6-0.8. Turning is commonly used to process parts with a single axis, such as straight shafts, available discs, and sleeve parts.


2. What are the characteristics of boring?

(1) The tool structure is simple, and the radial size can be adjusted, and holes with different diameters can be machined with one tool.

(2) It can correct the original hole's axis skew and position error.

(3) Since the boring machine has many forms of motion, the workpiece is placed on the worktable, which can conveniently and accurately adjust the relative position of the processed hole and the tool, thus ensuring the accuracy of the mutual position of the processed hole and other surfaces.

(4) The quality of boring mainly depends on the accuracy of the machine tool and the technical level of the workers, so the technical requirements of the operator are relatively high.

(5) Compared with reaming, single-edge boring tools have poor rigidity and use a smaller cutting amount, so low productivity. It is not easy to ensure stable machining accuracy.

(6) It is not suitable for processing slender holes.


3.What are the main functions of boring?

(1) It can process holes of various large and medium-sized parts, such as drilling, expanding, reaming, boring, etc.

(2) Larger holes can be bored by the radial tool post of the machine tool's flat rotating disk (faceplate).

(3) Turning larger end faces, shorter outer circles, end faces, or grooves with the radial tool post of the machine tool.

(4) Installing a milling cutter head and other milling cutters on the spindle can process some milling.

(5) The thread can be cut after installing the thread processing accessory.

(6) With the help of special accessories and devices on the horizontal caster, the processing application range of the boring machine can be expanded, such as the processing of taper holes.


4. What is the difference between a turning tool and a boring tool?

The boring tool can be used for the enlarged turning of the inner hole of the pipe. Generally, the boring tool can be used on the lathe.

Turning tools with replaceable tool holders can be used instead of boring tools on a boring machine within a certain range.

Turning tool: Workpiece rotates, and the tool does not move

Boring tool: The tool rotates, and the workpiece does not move, but the main motion and feed motion of the two processing methods are different

The two tools can be used to a certain extent


5. How do I try the first cut when boring with a fine boring tool, and how do I look at the size?

After rough boring, move the worktable to the center of the hole. Then move the fine boring tool down (Note: First, adjust the boring tool to a small size so that the tip of the tool cannot touch the wall of the hole), and then adjust the tip of the boring tool to touch the wall of the hole.

Raise the knife and adjust it a few more times. Boring once, use the inner diameter dial indicator to measure, see how much difference is still there, and then boring again. Until boring to the size you need.


6. What are the spindle feed boring method and its characteristics?

Generally, floor boring machines are divided into three boring feed methods:

(1) Rotary table feed

(2) Ram feed

(3) Spindle feed

Among them, the spindle feed has the worst rigidity, and it is easy to overlap when machining the hole to cause the concentricity of the hole to be too poor. Still, the spindle processes the surface roughness of the hole will be better.

Most boring machines on the market now use rotary table feeds.


7. What should I do when I encounter chip removal problems in boring?

Rough boring

(1) For through holes and blind holes:

In the through-hole, the removal of iron chips is relatively smooth, and the rigidity is generally given priority. It is better to choose a tool holder with a larger diameter, which is not prone to tool vibration, effectively improving processing efficiency and quality.

For blind holes, if the gap between the toolbar and the whole wall is too small, it will cause chip removal, which will lead to easy chip jams, blade breakage, tool vibration, and poor finish, which greatly affects processing efficiency, cost, and quality. In this case, rather than sacrificing some rigidity, priority should be given to the problem of iron removal. Choosing a tool holder with a smaller diameter for machining can increase the chip removal space and correspond to the problems caused by chip removal.

(2) Segment cutting and balanced cutting:

Normally, balanced cutting is used, which can be processed at high feed rates with high efficiency.

When the machining allowance is large, the bottom hole is eccentric, the chip breaking is not good, etc., the step cutting can be selected. While increasing the chip capacity and chip removal space effectively solves the problem of two-tool boring, saving tool costs and greatly improving efficiency.


Precision boring

When selecting a fine boring tool, rigidity, and space for removing iron chips should also be considered.

There are three options for the same hole. In the case of unsmooth removal of iron chips, you can also choose a relatively small tool holder with a larger insert seat to ensure sufficient chip removal space during finishing and improve the accuracy and stability of hole processing.

The above is one of the common solutions to the problem of chip removal. Because different brands of boring tools have different product lines, the options for solving the problems are also different for your reference. In practical applications, you need to consider the processing content, workpiece material, product requirements, processing efficiency, total cost, etc., and choose a solution that suits you.


8. How to use the spindle positioning during boring tool processing?

To find the correct positioning by the dial indicator measuring device. This method must first use a dial indicator centering device or positioning mandrel to determine the coordinates of the reference hole on the workpiece. Then determine the coordinate position of the spindle according to the coordinates of the reference hole. It is characterized by high accuracy and convenient operation.

By the test stick. This method is characterized by low positioning accuracy and is time-consuming. But this positioning method can directly find the correct coordinate position of the boring machine spindle and the starting hole.

By the interface of the hole. The characteristic of this method is that it can be used for boring the hole system of the separated box body. The disadvantage is that the auxiliary time is longer.

By template positioning. The characteristic of this method is that the model structure is simple and does not require complicated adjustments. However, the template is easy to deform, and when the workpiece needs to process holes on several different surfaces, several samples are needed, and the positioning accuracy is also low.


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