Basics of machining (drilling, turning, milling, wedge angle, clearance angle, rake angle, feed, ...
In this video, we cover the basics of machining. Depending on the cutting tool material and the material being machined, a compromise must always be found between the smallest possible wedge angle while still maintaining sufficient cutting edge stability.
During machining, the cutting surface must not touch the cutting surface of the workpiece. This is also referred to as the clearance angle. If the clearance angle and the cutting surface touched, enormous frictional forces would arise. Therefore, a clearance angle must always be present. For soft workpieces, the clearance angle is somewhat larger than for harder materials due to the greater elastic deformation.
The surface over which the chip is removed is called the rake face. The angle between the rake face and the perpendicular to the cutting surface is called the rake angle and influences chip formation. Large rake angles create favorable machining conditions, the chip is not deflected as much, and long chips are usually produced. Such flowing chips are undesirable because they can get caught in the machine and damage the workpiece, endangering work safety.
Flow chips can be avoided by using a smaller rake angle, which deflects the chips more strongly. This causes the chips to break off more quickly and creates ripples. However, due to the strong deflection and the relatively low cutting forces, relatively high cutting forces are required.
The sum of the clearance angle, wedge angle, and rake angle is always 90°. Depending on the size of the wedge angle, the rake face can extend beyond the perpendicular to the cutting surface, and the rake angle becomes negative! This is then referred to as scraping. Negative rake angles and thus large wedge angles are used when machining very hard workpieces. Positive rake angles, on the other hand, produce a cutting effect. This is used when machining softer materials.
The machining process is characterized by three movements: the cutting movement, the feed movement, and the infeed movement. Milling, drilling, and turning are circular cutting movements. While the tool performs a circular motion in milling and drilling, the workpiece performs a circular motion in turning.
The infeed indicates the amount in millimeters by which the tool moves through the workpiece in one revolution (cutting depth). A distinction is made between feed and feed rate. The feed is the amount in millimeters by which the tool moves forward in a single rotation within the workpiece. The feed rate, on the other hand, indicates the speed in millimeters per minute at which the tool advances through the material.
In machining, and especially in milling and turning, a distinction can be made between roughing and finishing. Roughing is about high cutting performance, while finishing is about high surface quality, dimensional accuracy, and shape precision!
00:00 Cutting with a geometrically defined cutting edge
00:35 From cutting to chip removal
00:55 Clearance face and clearance angle
01:44 Rake face and chip angle
02:20 Flowing chip and chip breaker
03:19 From chip removal to shaving
03:55 Cutting motion in turning, milling, and drilling
04:40 Cutting speed, rpm, and diameter
06:39 Calculating rpm
07:36 Tool life
08:01 Infeed and feed rate in turning
09:31 Infeed and feed rate in drilling
10:14 Infeed and feed rate in milling
10:43 Feed rate per tooth
11:16 Roughing and finishing