Cutting knowledge for design and precision machining II

2020-09-05 11:27:34

8、Hope to produce a beautiful inner corner arc R

When machining the small arc R in the corner of the deep cavity, the tool will vibrate. How to process a beautiful inner corner arc R？

The choice of blade diameter size is the key point

When machining the arc R of the inner corner, if a flat-head end mill of the same size is used, the contact length of the cutting edge will be increased, resulting in undesirable phenomena such as chatter, so it is recommended to choose a flat-head end mill with a blade diameter of 70 ~ 80% ×2R.

●(Example) Arc finishing of the inner corner part R1


At the same time, improving the cutting speed, reducing the feed speed, choosing the most suitable clamping tool and shortening the extension length of the tool as far as possible are effective measures.

9、Tool interference occurs during side machining, which is troublesome. If the 5-axis machining center is used for side machining, the tool position can be arbitrarily changed relative to the workpiece, then the extension length of the tool can be controlled to a minimum range. However, in the commonly used 3-axis linkage cutting process, the extension length of the tool may cause a part of the tool to come into contact with the workpiece surface, which requires appropriate preventive measures. In particular, the interference between the tool and the workpiece may lead to failure, please inform the solution.

Adverse effects of tool interference If the side machining of deep cavities is performed with an end mill with the same blade diameter and handle diameter, the non-cutting edge parts such as the tool or tool bar may come into contact with the workpiece, resulting in vibration during machining, causing damage to the tool or workpiece.

The tool that avoids interference with the workpiece is machined with a tool whose blade diameter is larger than the handle diameter, which can effectively avoid the interference of the handle diameter.

Or set the neck avoidance part on the handle diameter to obtain the same effect.

10、How to process a positive tolerance countersink? Is there any other way to process countersunk holes than by using a flat end mill with a positive tolerance?

Contour cutting with a positive tolerance end mill When making the same deep cuts as the drill, a positive tolerance end mill must be used. On the other hand, using an end mill with a tool diameter smaller than the aperture, the tool is moved from the center of the hole in a spiral shape, and the countersink surface is processed by contour cutting, and the countersink diameter of any size can be easily processed. At this time, the diameter of the end milling cutter is measured in advance, and the cutting tool compensation method is used to achieve high-precision machining.

11、When machining various T-slots, it is hoped to improve the machining accuracy and shorten the processing time. T-slot machining When using high-speed steel T-slot milling cutter, the tool is prone to flutter, and the machining accuracy is difficult to ensure. Moreover, the bottom and side of the groove have a specified shape and size, and the processing is very time-consuming and brain-wrenching. What methods can improve the machining accuracy and shorten the processing time?

Cutting with carbide T-slot milling cutter

Compared with cemented carbide, high-speed steel has the advantages of strong toughness and is not easy to break, but it is easy to bend and chatter. In order to improve the machining accuracy, the use of carbide T-slot milling cutter can effectively suppress chatter.

When the bottom and side of the T-groove have a specified shape and size, the processing time can be shortened by using a T-groove cutter that can specify the shape and size. At this time, in order to meet the machining accuracy

It is recommended to use carbide T-slot milling cutter.

12、What is the difference between the sharp Angle type and the sharp Angle protection type of the flat-head end mill? In the product catalog, flat end milling cutter has two types of sharp Angle type and sharp Angle protection type, what is the difference between the two? How to distinguish between use？

The difference between sharp Angle type and sharp Angle protection type

Cutting performance is enhanced by the pointed tip with a blade. The angular protection retains the thickness of the tip tip. Therefore, compared with the sharp Angle type, the edge strength of the sharp Angle protection type is increased. You can choose 1 of 2 tip types to use according to the specific conditions of use.

Angle type · Use when the workpiece is clear. · The cutting sharpness of the corner is good, but the blade is easy to break. Carbon steel and tempered steel can also be used, especially widely used in the processing of non-iron materials such as aluminum. For high-hardness workpieces, it is not suitable because it is easy to break the edge. Zoom in on the tip of the blade

Angle protection type · High rigidity of the corner, the blade is not easy to defect. · The edge sharpness of the corner is slightly lower. Zoom in on the tip of the blade

13、How to distinguish the use of end mills with different spiral angles? The spiral Angle of the end mill can be divided into 30º · 45º · 50°, etc., which is rich and diverse. So how to distinguish the use of good?

The larger the spiral Angle of the end mill, the longer the contact length between the workpiece and the cutting edge. This reduces the load per unit length of the cutting edge and therefore extends the tool life. But at the same time, the cutting resistance will become larger, so it is necessary to consider the use of a tool handle with high clamping rigidity.

Small helical Angle end mill Large helical Angle end mill cutting edge length (blue line length) ⇒ short cutting edge length (red line length) ⇒ length

Helix Angle selection

For stainless steel, which has low thermal conductivity and great influence on the heat of the edge tip, the use of large spiral Angle end milling cutter is helpful to extend the life of the tool. In addition, the characteristics of the finished surface vary depending on the helix Angle. For example, when smooth finishing is required, a large helical Angle end mill is sometimes used.

However, when using a large spiral Angle end mill, the cutting resistance will increase, and the force of the right spiral Angle tool will also increase, so corresponding measures must be taken, such as the use of a tool handle with high clamping rigidity.

Although the rigidity of the tool can be ensured, the small helical Angle end mill is sometimes used in the case of low workpiece rigidity such as sheet processing.

14、How to distinguish the use of end mills with different blade numbers and blade lengths? It is difficult to choose end mills with different blade numbers and different blade lengths listed in the product catalog. So how do you distinguish between choices?

Choice of blade number

Select the number of blades according to the cutting mode of the end mill. For example, when the cutting width is the same as the tool diameter of the groove cutting, the need for a larger chute, at this time generally choose a 2-edge end mill. When the cutting width is small, the tool rigidity should be given priority and the multi-edge end mill should be selected。

Groove cutting

Side cutting

The transverse cutting width is the same as the tool diameter ⇒ large chute is required

Small transverse cutting width ⇒ tool rigidity is preferred

Blade length selection

According to the depth of the groove shape and other machining shapes, choose the best end mill blade length. If you pay attention to the number of re-grinding and choose the end mill with too long a blade, it will produce chatter, resulting in the inability to give full play to the characteristics of the end mill, resulting in difficult to achieve high precision finishing surface and other adverse effects.

15、The small end mill often breaks, causing headaches. The small end mill is needed to process fine shapes, but it is easy to collapse and break, causing headaches. So what is the right measure to take?

Run-out accuracy

Because of the low rigidity, the small end mill is easy to break, the main reason is the beating of the tool itself and the impact of the clamping tool. In order to prevent breaking, the beating accuracy must be strictly controlled. Therefore, the effective method is to use the thermal expansion tool handle with high clamping accuracy to grip the end mill.

Increase cutting speed and improve cutting characteristics

In general, without sufficient cutting speed, the cutting characteristics of the end mill blade cannot be fully utilized. Even if the small end mill increases the speed, it may not achieve enough cutting speed, especially the ball end mill, the actual cutting diameter is very small, so many times can not give full play to the cutting characteristics of the blade. Therefore, when using the small end mill, effective measures must be taken for the actual cutting speed.

Use the best cut depth

Because of the low rigidity of the small end mill, too much cutting depth will cause breaking. Reduce the depth of cut when breaking occurs.

It is also important to control the size of the depth of cut to avoid sudden load on the tool. Especially in the corner part, the cutting depth will be larger, so that the load borne by the end mill will increase, and it is necessary to add a pre-processing procedure and other measures to make the cutting depth of the small end mill uniform.
The tool path with cycloid can balance the cutting depth effectively. However, the cycloidal tool path moving with circular trajectory has a longer tool path and a correspondingly longer processing time compared with the linear feed, so the cutting conditions need to be improved to offset the extended processing time.

16、Side, groove and bottom cutting, hopefully with a tool to complete the processing. If each processing has to change the tool, the tool management is very troublesome. Is there a cutting tool that can process multiple processes with just one?

Tool characteristics with different spiral Angle and blade number

The general 2-edge, 4-edge 30° spiral Angle tool can also be used for side cutting, groove cutting and bottom cutting with one tool. However, when the 2-edge end mill cuts the side, the feed can not be too large, and the processing efficiency is low. However, when the 4-edge end mill is grooving, the width of the peripheral grooves is narrow, and the chips are difficult to discharge. The 3-edge end mill has the advantages of 2-edge and 4-edge, and is suitable for side and groove cutting.

Comparison of tool cross sections

The 3-edge end mill is characterized by both flutter suppression and high rigidity for the following reasons, and its shape is suitable for both side and groove cutting.
First, unlike even edges, there is no blade on the other side of the diagonal of the cutting edge, so its shape is less prone to chatter.
Second, the index to measure rigidity is the core thickness of the blade diameter and the shape to maintain rigidity. The core thickness of the 30° spiral Angle flat head cutter is 65%, and the core thickness of the 45° spiral Angle end mill is roughly 70%, which improves the core thickness rigidity of more than 5° through the shape design.