Milling cutters are generally multi-tooth cutting tools. Due to the involvement of multiple teeth in cutting simultaneously and the longer cutting edges enabled, higher material removal rates can be achieved for higher productivity. Different milling cutters allow the machining of flat surfaces, grooves, slots, steps and complex contours, as well as gear teeth, threads, spline shafts and other shaping applications.
Grooving Tool Structures
For indexable grooving inserts:
（1）The geometry of Indexable Milling Cutters
An indexable milling cutter has one main helix angle and two lead angles, an axial lead angle, and a radial lead angle.
The radial lead angle γf mainly affects the cutting power, while the axial lead angle γp influences chip formation and the direction of axial force, with positive γp producing climbing cuts on the workpiece.
Lead angles (rake faces):
Negative lead angle: used for steel, steel alloys, stainless steel, and cast iron.
Positive lead angle: used for adhesive materials and some high-temperature alloys.
Centered lead angle: used for gear cutting, grooving, profile milling, and form cutters.
A negative lead angle should be used whenever possible.
（2）The geometry of Milling Cutters
1. Positive angle-positive angle
Cutting is light and chip evacuation is smooth, but cutting edge strength is relatively low. Suitable for machining soft materials, stainless steel, heat-resistant steel, plain carbon steel, and cast iron. Should be preferentially selected for small power machine tools, rigidness insufficient process systems, and where built-up edges are likely to form.
Advantages: 1. Smooth cutting 2. Smooth chip evacuation 3. Good surface roughness
Disadvantages: 1. Cutting edge strength 2. Unfavorable for cut-in contact 3. Workpiece detachment from machine table
2. Negative angle-negative angle
High impact resistance, uses negative inserts, suitable for rough milling of cast steel, cast iron, and high hardness, high strength steel. However, cutting power consumption is high and requires excellent process system rigidity.
Advantages: 1. Cutting edge strength 2. Productivity 3. Pushes workpiece towards machine table
Disadvantages: 1. Greater cutting forces 2. Chip clogging
3. Positive angle- negative angle
Cutting edge impact resistance is relatively strong and cutting edge is also sharper. Suitable for machining steel, cast steel, and cast iron. Also good for heavy machining.
Advantages: 1. Smooth chip evacuation 2. Beneficial cutting forces 3. Broader application range
（3）Cutter tooth pitch
1. Fine pitch: high-speed feed, larger milling force, small chip space.
2. Standard pitch: conventional feed speed, milling force, and chip space.
3. Coarse pitch: low-speed feed, smaller milling force, larger chip space.
If the milling cutter is not equipped with dedicated wiper inserts, the surface roughness depends on whether the feed per revolution exceeds the width of the wiper face on the insert.
Types and Uses of Milling Cutters
Milling cutters can be classified based on tooth structure into end mills and face mills. Based on the relative position of teeth and the cutter axis, there are cylindrical cutters, side and face cutters, form cutters, etc.
Categorized by tooth shape, there are straight, spiral, angular and curved tooth types. Classification by tool construction includes solid, clamped, indexed, inserted and brazed types.
But the most common classification is by cutting-edge back geometry
Milling cutters with tangential teeth can be divided into the following types:
(1) Face milling cutters. They include whole face milling cutters, inserted tooth face milling cutters, and machine adjustable position face milling cutters. They are used for coarse, semi-fine and fine machining of various flat surfaces, steps, etc.
(2) Side milling cutters. They are used for machining step surfaces, side surfaces, grooves, cavities, various shaped holes on workpieces, and internal and external curved surfaces. If side milling cutters are simply classified, they can be divided into left-hand and right-hand types. Now many people still don’t understand the concept of left-hand and right-hand.
First of all, to determine whether a cutter is left-handed or right-handed, you can use the following method. Facing the vertically placed milling cutter, if the gullet rises from the left bottom to the right top, it is right-handed; if the gullet rises from the right bottom to the left top, it is left-handed. For right-handed, you can also use the right-hand rule – bend the four fingers to indicate the direction of rotation, with the thumb pointing in the direction of ascent as right-handed. The helical gullet plays a role in chip removal and also constitutes the front angle and front part of the milling cutter.
Left-handed milling cutters are generally chosen only when high-precision machining is required. Left-handed milling cutters are generally used in the processing of mobile phone keys, thin film switches, LCD panels, acrylic mirrors and other high-precision machining. But for some requirements that are highly demanding, especially for the production and machining of some mobile phone keys or electrical device panels, where the accuracy and surface smoothness requirements are very high, a downward milling left-turning cutter should be selected to avoid problems such as tool marks, burrs on cut edges, etc.
(3) Slot milling cutters. They are used for milling slots, etc.
(4) Groove milling cutters and saw blade milling cutters. They are used for milling various grooves, sides, steps and sawing.
(5) Special groove milling cutters. They are used for milling various special groove shapes, including form milling cutters, half-moon keyway milling cutters, swallowtail groove milling cutters, etc.
(6) Angle milling cutters. They are used for milling straight grooves, helical grooves, etc. on tools.
(7) Die milling cutters. They are used for milling various forming surfaces such as protrusions and depressions on dies.
(8) Gang milling cutters. They comprise a set of several milling cutters combined for milling complex forming surfaces, surfaces of different parts of large workpieces and wide flats.
Triangular saw blade milling cutters: For some milling cutters require heavy grinding while maintaining the original shape at the front, their back uses triangular saw blade forms, including disc groove milling cutters, convex semi-circular, concave semi-circular milling cutters, double angle milling cutters, forming milling cutters etc.
There are two methods of milling relative to the workpiece feed direction and spindle rotation direction of the milling machine:
The first is conventional milling, where the rotation direction of the milling cutter and the cutting feed direction are the same. When starting to cut, the milling cutter will immediately engage the workpiece and remove the last chip.
The second is climb milling, where the rotation direction of the milling cutter and the cutting feed direction are opposite. Before starting to cut, the milling cutter must slip on the workpiece for a distance, starting with zero cutting thickness and reaching maximum cutting thickness at the end of the cutting.
During milling with three-flute, some side or face mills, the cutting forces will act in different directions. When face milling, the milling cutter is positioned exactly on the outside of the workpiece, so the direction of cutting forces must be paid particular attention. In conventional milling, the cutting force presses the workpiece against the table, while in climb milling the cutting force moves the workpiece away from the table.
Since conventional milling gives the best cutting effect, it is usually the first choice. Only when there are issues like backlash in the machine tool or problems that cannot be solved by conventional milling, climb milling will be considered. Ideally, the diameter of the milling cutter should be slightly larger than the workpiece width, and the axis of the milling cutter spindle should always be kept at a slight distance from the centerline of the workpiece. When the tool is positioned directly on the cutting center, burrs are very likely to form.
As the cutting edge enters and exits cutting, the direction of radial cutting forces will constantly change, which may cause vibration of the machine spindle and damage to the insert. The cutting edge may also break and the machined surface will be very rough. If the milling cutter is slightly offset from the center, the direction of cutting forces will no longer fluctuate – the milling cutter will gain a kind of preload.
When the milling cutter insert enters cutting each time, it needs to bear the impact load of cutting, and the load size depends on the chip cross-section, workpiece material and cutting type. Whether the cutting edge and workpiece can engage correctly during entry and exit is an important issue.
When the axis of the milling cutter is completely outside the width of the workpiece, the initial impact force during entry is borne by the outermost tip of the insert, which means the initial impact load is borne by the most sensitive part of the tool. The cutter also leaves the workpiece with the tip, which means from the start of cutting to leaving, the cutting force always acts on the outermost tip until the impact is unloaded.
When the centerline of the milling cutter is exactly on the edge line of the workpiece, the impact load reaches the maximum during entry and exit when the chip thickness reaches the maximum and the insert disengages from cutting.
When the axis of the milling cutter is within the width of the workpiece, the initial impact load along the cutting edge during entry is borne by a part farther away from the most sensitive tip, and the insert also exits cutting relatively smoothly during retract.
For each insert, the way the cutting edge leaves the workpiece when exiting cutting is important. The remaining material near the exit may somewhat reduce the gap between inserts. When the chip disengages from the workpiece, an instant tensile force will be generated along the front cutting face of the insert and often produces burrs on the workpiece. This tensile force endangers safety in dangerous situations.
|Project||Climb Milling||Conventional Milling|
|Cutting Depth||From Large To Small||From Small To Large|
|Workpiece Surface Hardening Phenomenon||No||Have|
|Action On Workpiece||Impaction||Put up|
|Eliminate The Gap Between Screw And Nut||No||Yes|
|Lost Energy||Small||5 to 15 Percent Larger|
|Applicable Occasion||Finishing||Rough Finishing|
What is the difference between conventional milling and climb milling?
Conventional milling refers to the milling cutter rotation direction being the same as the workpiece feed direction, while climb milling refers to the two directions being opposite.
Is conventional milling or climb milling better?
Generally, conventional milling works better because the insert can engage directly on the workpiece during entry and chips detach earlier. But climb milling may perform better for some difficult-to-cut materials or complex workpieces.
What factors should be considered when choosing conventional or climb milling?
The main factors include workpiece material, surface quality requirements, cutting parameters set and machine tool performance. Conventional milling is preferred for simple materials and low surface quality demands; climb milling can be chosen for materials with high strength or where high surface quality is required.
What problems is conventional milling prone to?
Conventional milling is prone to producing milling marks, streaks or inconsistent surfaces. This is because the insert engages directly on the workpiece during entry, making it difficult to start cutting with an ideal entry attitude.
What are the advantages of climb milling?
In climb milling, the chip thickness starts from 0 and increases uniformly during entry. Additionally, it is easier to control impact loads and reduces the possibility of machine tool vibration.