Milling tools are rotary tools with one or more teeth for milling. During work, each cutter tooth intermittently cuts off the remainder of the work piece. The milling tool is mainly used for milling planes, steps, grooves, forming surfaces, cutting work pieces etc.
And I believe that when selecting a milling tool, you need to pay attention to both the milling tool body and tool holder:
- Whether the milling tools used on a CNC machining center or an ordinary milling machine.
- Milling material and hardness.
- Specifications of milling tools, such as: blade length, full length, blade diameter, shank diameter, etc.
If it is used on CNC machining centers, then you should choose solid carbide. For ordinary milling machines, white steel can be used.
White steel milling tools are softer than hard alloy milling tools. High-speed steel blades are cheap and have good toughness, but the strength is not high and it is easy to cut less, the wear resistance and heat hardness are relatively poor. The high speed steel milling tool has a thermal rigidity of about 600 degrees and a hardness of about 65HRC. Obviously when milling hard materials with white steel, it is easy to burn the knife if the coolant is not enough, which is one of the reasons for the low heat rigidity.
Cemented carbide milling tools have good thermal rigidity and abrasion resistance, but the impact resistance is poor, for the blade will break if they are dropped. Cemented carbide is a material made by powder metallurgy, with a hardness of about 90 HRA and a thermal rigidity of about 900-1000 degrees.
Therefore, white steel milling tools are suitable for ordinary milling machines, and alloy milling tools are suitable for CNC machining centers.
1. Selection of milling tool diameter
The choice of milling tool diameter varies greatly depending on the product and production batch. The choice of cutter diameter depends mainly on the specifications of the equipment and the processing size of the work piece.
Plain milling tool
When selecting the diameter of a face milling tool, it is mainly necessary to consider that the power required by the tool should be within the power range of the machine tool, and the diameter of the machine tool spindle can also be used as a basis for selection.
The diameter of the face milling tool can be selected according to D = 1.5d (d is the spindle diameter).
In mass production, the tool diameter can also be selected according to 1.6 times the cutting width of the work piece.
The choice of end mill diameter should mainly consider the requirements of the work piece processing size, and ensure that the power required by the tool is within the rated power range of the machine tool.
If it is a small-diameter end mill, the main consideration should be whether the maximum number of revolutions of the machine can reach the minimum cutting speed of the tool (60m / min).
The diameter and width of the slot milling tool should be selected according to the size of the work piece to be processed, and its cutting power should be within the power range allowed by the machine tool.
2. Selection of milling tool blade
1). For fine milling, it is a best choice to use a grinding blade. This kind of insert has better dimensional accuracy, so the positioning accuracy of the cutting edge in milling is higher, and better machining accuracy and surface roughness can be obtained.
In addition, the development trend of grinding and milling inserts used for finishing is to grind out the chip flute to form a large positive rake angle cutting edge, allowing the insert to cut at a small feed and a small depth of cut.
For carbide inserts without sharp rake angles, when using small feeds and small cutting depths, the tool tip will rub the work piece and the tool service life will be short.
2). In some processing occasions, it is more appropriate to choose a pressed blade, and sometimes it is necessary to choose a ground blade.
For roughing, it is better to use a pressed blade, which can reduce the processing cost.
The dimensional accuracy and sharpness of the pressed blade are worse than those of the ground blade, but the edge strength of the pressed blade is better, and it is resistant to impact during rough machining and can withstand large cutting depth and feed.
Pressed blades sometimes have chip flutes on the rake face, which can reduce cutting forces, and at the same time reduce friction with the work piece and chips, reducing power requirements.
3). However, the surface of the pressed blade is not as close as the ground blade, the dimensional accuracy is poor, and the heights of the tips on the milling tool body are much different. Since press blades are cheap, they are widely used in production.
4). Sharpened large rake angle inserts can be used to mill viscous materials (such as stainless steel). Through the cutting action of the sharp blade, the friction between the blade and the work piece material is reduced, and the chips can leave the front of the blade faster.
5). As another combination, the pressed blade can be installed in the blade seat of most milling tools, and a grinding scraping blade can be configured.
Using a scraping blade to remove rough machining marks can achieve better surface roughness than using only a pressed blade.
Moreover, the application of the scraping blade can reduce the cycle time and cost.
The scraping technology is an advanced technology, which has been widely used in the fields of turning, grooving and drilling.
3. Selection of milling tool body
The price of a milling tool is relatively expensive. A face milling tool body with a diameter of 100mm may cost more than $ 600, so you should choose it carefully to meet the specific processing needs.
1). First, when choosing a milling tool, the number of teeth must be considered.
For example, a coarse-tooth milling tool with a diameter of 100mm has only 6 teeth, while a dense-tooth milling tool with a diameter of 100mm can have 8 teeth.
The size of the tooth pitch will determine the number of cutter teeth participating in the cutting at the same time during milling, which affects the smoothness of the cutting and the requirements on the cutting rate of the machine tool.
Each milling tool manufacturer has its own series of coarse and dense tooth milling tools.
2). Coarse tooth milling tools are mostly used for rough machining because it has a large chip flute. If the chip flute is not large enough, it will cause difficulty in chip curling or increase friction between the chip and the cutter body and work piece.
At the same feed rate, the cutting load per tooth of a coarse-toothed milling tool is larger than that of a dense-toothed milling tool.
3). The cutting depth is shallow during fine milling, generally 0.25 to 0.64mm, and the cutting load per tooth is small (about 0.05 to 0.15mm).
The required power is not large, so you can choose a close-tooth milling tool, and you can choose a larger feed.
Because the metal removal rate is always limited in fine milling, it is not a problem to have a smaller chip flute in the dense tooth milling tool.
4). For spindles with larger taper hole and better rigidity, rough milling can also be performed with close-tooth milling tools.
Since the dense-tooth milling tool has more teeth to participate in cutting at the same time, when using a large cutting depth (1.27 ~ 5mm), pay attention to whether the machine tool’s power and rigidity are sufficient, and whether the milling tool chip flute is large enough.
Chip removal needs to be verified by tests. If there is a problem with chip removal, the cutting amount should be adjusted in time.
5). During heavy-duty rough milling, excessive cutting forces can cause chattering on less rigid machines.
This chattering can cause chipping of carbide inserts, reducing tool life. The use of coarse-tooth milling tools can reduce the requirements for machine power.
Therefore, when the size of the spindle hole is small (such as R8, 30 #, 40 # taper hole), it can be effectively milled with a coarse-tooth milling tool.
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