Milling is a method of manufacturing objects by removing material from a flat surface using a rotating tool. There are two main types of milling: climb and conventional. Both have their advantages and disadvantages, which can make choosing the right method difficult. In this article, we compare the differences between kinematic and conventional milling and present factors to consider when choosing the appropriate machining method.
What is concurrent milling?
The process of climb milling, also known as down milling, involves machining the material by a rotating cutting tool and the workpiece moving in the same direction. One of the benefits of up milling is that there is no risk of recutting. This is because the teeth of the cutting tool during milling will lift onto the workpiece, releasing the cut chips behind the tool. It is important to note that this process begins with the full thickness of the material, but the thickness decreases as the machining progresses.
What is climb milling?
Conventional CNC milling is a traditional machining method, where the cutting tool rotates in the opposite direction to the workpiece. This is also referred to as up milling, as in the case of climb milling, the cutting is done upwards. Unlike face milling, in conventional end milling, chip formation starts from zero and gradually increases. Moreover, the chips remain in the path of the mill, as they rotate upwards.
Main differences between climb milling and conventional milling
There are certain differences between conventional and climb milling that affect the process and results. However, the main difference between them is the way the tool is deflected during cutting. In conventional milling, the tool's deflection is parallel to the direction of cutting, which provides greater control over the process and a lower risk of errors. On the other hand, during climb milling, the tool is deflected perpendicular to the cut, which can affect the width of the cut and its accuracy. For rough machining, climb milling is recommended as it is faster. Moreover, the impact of tool deflection on accuracy is not as significant, as the finishing process improves the precision of the object.
Metal milling through concurrent and climb milling - advantages
Both milling processes of metal and other machined surfaces have their advantages, depending on the application. We will evaluate their mechanisms, as they can influence the choice of the method that best suits the machined object. Analyzing these advantages is crucial, as it can help in choosing the best machining method for a given item. For example, one method may be faster and more efficient for machining a large number of items, while the other method may provide better machining quality but will require more time and costs. Considering the pros and cons of both methods is key to choosing the best option.
Advantages of Concurrent Milling
- Better tool life
Tools used in this milling process generally have better durability than tools used in traditional milling. This is because the tool is not subjected to high stresses during cutting. Cutting tools used for cantilever milling usually generate less heat and deformation than conventional milling. This reduces tool wear and extends its lifespan by even 50% compared to conventional milling.
- Better surface finish
As the bracket milling process progresses, the thickness of the chips decreases, which results in less deflection during cutting. Moreover, the cutting during this process causes the chips to settle behind the tool, eliminating the need for re-cutting and providing an excellent finish of the machined part.
- Low cutting load and heat generation
Less heat is generated during cantilever milling, as the chip width decreases with the progress of machining. Additionally, with downward-directed cutting forces, the overall cutting loads and clamping requirements are reduced, especially during horizontal milling. The downward force exerted by the tool can also help in removing contaminants during machining, as it firmly holds the workpiece on the surface beneath it.
- Easier to mount
Bracket milling works with a force directed downwards, so during face milling it helps to strengthen the object being machined to the surface beneath it, reducing chipping on thin substrates.
Advantages of climb milling
- Higher stability
Conventional milling tends to draw the workpiece towards the operator during cutting, while conventional milling works in the opposite way. This provides the operator with greater control, which translates into greater stability. Conventional milling does not cause excessive vibrations compared to climb milling. Therefore, it is better than conventional milling in terms of stability.
- Zero play
Lack of play is one of the factors distinguishing conventional milling. This advantage results from the fact that conventional milling does not pull the table, thus ensuring optimal stability.
- Best control
During conventional milling, there is a greater tendency for the tool to deviate from the workpiece. This shift provides the least chance of accidental cutting. Moreover, even if such cuts occur, they have negligible depth.
Disadvantages of climb milling
Both concurrent and conventional milling have their advantages, but it is also worth paying attention to their disadvantages. Here are a few of them.
Disadvantages of face milling:
- Rebounds
This is one of the main disadvantages of traditional milling compared to conventional milling. In the upper spindle, especially where the forces acting on the tool are large enough. Let's explain this better. Upward milling is done with a force directed downwards. This force usually acts not only on the workpiece but also on the table, pulling it into the cutting tool. With sufficient clearance, the table may crack, causing injury to the operator. This is particularly relevant when the cutting tool operates at high efficiency. However, today's milling machines are equipped with backlash eliminators. It helps to reduce it, allowing the machine operator to benefit from fast milling without obstacles.
- Excessive vibrations
During bracket milling, working at high speeds or machining thick parts can cause strong vibrations. The cause of these vibrations is the tool's action on the machined object. These vibrations are harmful as they often cause tool deformation, which affects accuracy. They can also damage the machined objects.
- Not suitable for harder materials
Since the thickness of the chips is greatest at the beginning of milling in cantilever milling, machining harder materials in this process can cause damage to the cutting tool. This can happen with cutting tools made of steel, cast iron, titanium, and other hard materials. So when it comes to milling harder tools, conventional milling will be a better choice.
Disadvantages of conventional milling
- Rough machining
The undercutting used in this process makes it difficult to achieve a smooth finish. This is due to the roughness of the surface caused by the number of deformations of the workpiece and the tool. However, this degree of deformation makes conventional milling ideal for machining harder materials such as steel and cast iron.
- Generating too much heat
Another disadvantage of conventional milling is the heat generated during processing. This heat is generated because chips accumulate here, which often causes the cutting tool to overheat. The consequence of overheating the cutting tool is shortening its lifespan.
- Tool damage
Friction and the force directed upwards, generated during conventional milling, often produce excessive heat. Excessive heat can also damage the tool, reducing its lifespan, precision, and accuracy of the machined object.
Down milling vs Up milling - which one to choose?
The right moment to choose between up milling and down milling depends on the application, requirements, material, and several other factors. Generally speaking, when comparing conventional milling with up milling, people often assume that up milling is better because it has minimal load, offers better surface finish, and ensures tool durability for a long time. However, this is not the appropriate approach in every case, as it also has significant drawbacks. Similarly, conventional milling has some obvious advantages. However, its limitations are equally important. Therefore, a thorough understanding of both cutting processes is crucial to ensure that we make the right choice and achieve consistent results.
Here are some tips to help you choose between conventional and climb milling.
- Prefer climb milling for smaller parts that require a flawless finish.
- Do not use climb milling with manual milling machines.
- Make sure that the traditional machine being used has a backlash eliminator during climb milling
- Use conventional milling for hard and rigid materials or hardened elements.
- Do not use climb milling on the first pass if the material is oxidized or has a rough surface.
- To achieve the best accuracy, use climb milling on the final pass.
- Consider using ceramic inserts to improve milling technique.