Climb Vs Conventional Milling For Custom CNC Machining Parts
CNC machining is the most common process for the manufacturing and design of complex machining parts. It creates intricate designs and patterns. Climb milling and conventional milling are the two techniques used by machinists for the creation and manufacturing of machining parts. However, which technique is better for which material is a difficult trade-off decision.
This blog is a complete guideline for machinists and engineers who want to make an informed decision about whether to choose climb milling or conventional milling for manufacturing purposes. It highlights advantages, disadvantages, and a comparison between both processes. This blog assesses both processes from the aspect of different parameters.
What Is Milling？
Before understanding the concepts of conventional mill, and climb milling it is better to first know about milling. Milling is a subtractive method of manufacturing. When a rotating tool moves on the surface of a flat surface and does cutting the process is known as milling.
Climb milling and conventional milling are two ways to perform the milling process. They are both different than each other. Understanding them thoroughly will help machinist and engineers make the right machining decisions.
How Is Climb Milling?
The cutting process in which both the cutting tool and the flat surface rotate in the same direction is known as climb milling. This cutting process is also known as down milling. During climb milling the teeth of the cutting tool climb onto the surface beneath the workpiece, hence the name. The direction of the cutting edge rotation in climb milling affects the machining process by improving the surface quality and reducing clamping requirements.
The chip formation in climb milling is also very interesting. During the initial stage of the process the chip width is higher and it is thicker. As the process progresses the chip becomes thinner.
Machinists prefer the climb milling process because the chances of recutting are almost near to zero. This is also a major advantage of the climb milling process.
How Is Conventional Milling?
Although the preferred way for most of the machinists and engineers is climb milling yet in some cases the use of conventional milling becomes mandatory. Conventional and climb milling differ in terms of tool deflection affecting cutting accuracy, with conventional milling causing the tool to deflect away from the workpiece and climb milling causing it to deflect into the workpiece. During the cutting process the cutting tool faces backlash. The climb milling backlash occurs when the tool is experiencing backlash beyond its capacity.
The cutting tool should have the ability to counteract the backlash otherwise it may face breakage. It can also cause a potential injury because of a sharpnel. Therefore for manual machines that have the backlash are prohobited.
For such unique circumstances conventional milling process is used. Conventional milling process is almost same in procedure to climb milling. The main difference between the two is that it moves in the upward direction as compared to the downward direction in climb milling.
Advantages of Climb Milling
Tool Life
In case of climb milling the cutting tool does not have to face much stress. The level of heat generated is low. Also the tool deflection is low in this process. This causes a reduction in the tool wear. The tool life is increased by a percentage of fifty percent as compared to that of conventional milling. The longer tool life has better service life.
Surface Finish
We have discussed before that the thickness of the chip in a climb cut and milling decreases with the progress in the process. This is a major advantage of climb milling. This causes less tool deflection. The extracted chip tends to deposit behind the cutter. This eliminates the possibility of recutting. Therefore guranteeing a wonderful surface finish.
Less Heat generated and Simpler Workholding
The gradual reduction in the chip width with the process progress has many benefits. One of the benefits is that it causes a reduction in the heat generated. During horizontal milling process the cutting force is in downward direction. This causes a reduction in the cutting load. It also leads to proper workpiece handling.
The downward exertion of force keeps both the workpiece and the cutting tool intact. This causes a reduction in the machining chatter.
Disadvantages of Climb Milling
Increased Vibrations
In cutter in climb milling exerts a very strong force on the workpiece. The downward force of the cutter cause the table or the object holding the workpiece and the workpice itself to exert a reactive force. This force in reaction is known as “backlash”.
Therefore the force and the backlash can sometimes be so strong that it can result in breakage of the table. This can also result in injuries to the person operating the tool.
The possibility of backlash is especialy high when the cutting tool is operatinh at a very high tendency. However these days the potential of backlash is near to zero. It is because of the use of backlash eliminating tools in the market. These tools reduce backlash and enhamce the positive impacts of the climb milling procedure.
Not recommended for Hard Materials
Climb milling is not a favorable techique for use on hard materials. Chip thickness is the main reason behind it. In the initial stage of the process chip thickness is highest. It becomes thinner with the progress of the process.
During application on hard materials the probability of tool breakage increases. This is especialy true when tools are made up of materials like titanium, steel and cast iron.
Chances of Breakage due to Backlash
The harm of breakage is not only limited to the tool holding the cutter. It also impacts the workpiece on which the cutter is being used. When operating at a high capacity the backlash can cause string exertion of forces even on the workpiece. As a result of these cutter forces the workpiece can break.
Less Accuracy
The baccklash and string vibrations can cause deflections in the cutting tools as well. These affect cutting accuracy too. This also has a negative impact on the cutting tool’s accurace. As the cutting tool rotates the resuklting deflection affects surface finish. Not just the surface finish but it also impacts the result
Advantages Of Conventional Milling
Best Technique for Micromilling
Micromilling is an advanced level milling style or technique. This milling style uses CNC milling machines and other tools with hogh calliberations. The purpose of this milling style is to obtain high level of accuracy and creation of intricate patterns and designs.
When using milling machines in micromilling the tool deflection is at its maximum. Therefore in such cases selecting conventional milling machine is the best option. Among the two milling methods i,e conventional milling and climb milling, conventional milling produces less tool deflections.
No Backlash
This is probably the best advantage of conventional milling. The absence of backlash in case of conventional milling is beacause of force is carried upward. This does not cause backlash in the machine table and therefore no vibrations or deflections.
Optimal Control
A condition of dynamic systebn that satisfy design objectives is known as optimal control tool diameter. This is another great advantage of the conventional milling process. Since the force is in upward direction and conventional milling has zero tool deflection effects the chances of producing unexpected cut is in the workpiece are minimum.
Even if accidentaly the operator does a cut in the workpiece its depth is negligible. It does not produce any visible effect on the appearance of the workpiece.It is all because of the optimal control which conventional milling provides to the operator over the cutting tool.
Stable Operations
During climb milling operation the operator exerts force through the cutting tool in the downward diraction. During these operations the cutting tools exrts a force in the opposite direction towards the operator. However in case of conventional milling the case is opposite.
While using the conventional machining both the operator and the conventional cutting tool operate in the downward direction. Along with optimal control it makes the whole conventional milling process more stable. This reduces the chance of inaccuracy and damages as well.
Disadvantages Of Conventional Milling
Rough Finishing
As you know that in conventional milling the cutter geometry forces operate in the opposite direction i.e upward. This makes the achievement of smoot finish impossible. Both the cutting force of the cutter and the deflection in both the cutter and the workpiece cause rough surface finish.
It is these deflections that make conventional milling a preffered process for hard materials. Hard materials inlcude cast iron and steel.
Excessive Heat Generation
The gradual chip formation in the conventional milling process . This causes overheating of the cutting tool since the tool has to rotate for longer periods of time. Overheating not only damages the tool but also affects tool life. It actually reduces the tool life.
Damage to the Tool
The decrease in the tool life comes with many other disadvantages as well. Not only it damages the tool because of excessive heat generation but it also impacts the accuracy surface quality of the results produced.
The Climb vs Conventional Milling Debate
Now that we have gained in-depth knowledge of both conventional and climb milling, it is important to focus on the differences between the two. For some purposes, climb milling is a better option and for others, conventional milling. But which technique is important for what situations needs better understanding. This part focuses on the suitability of both techniques. Here we shall pay attention to the climb mill vs conventional milling debate.
Rough Materials
For rough and harder materials consider conventional milling. However ven in case of harder objects try making the final cut using climb milling. It is because climb milling produces smooth surface finish as compared to the conventional cut milling that produces a rough surface finish.
Manual machines
When you are using manual machines it is always better to use conventional milling. Conventional milling requires force in the upward direction providing more optimal control to the operator. optimal control is a top priority when using manual machining therefore in that climb milling vs conventional milling debate conventional milling wins this debate.
However in case you are using traditional approach of working with traditional machines than you should use a backlash eliminator. It is because in that case their is a possibility of deflections.
Tool Deflection and Cut Accuracy
Considering the climb milling vs. conventional mill finish pass debate tool deflection and cut accuracy are two very important factors. The direction of the cutting edge rotation affects tool deflection and cut accuracy in both milling methods. The deflection force vector in case of conventional milling is parallel to the cut. This indicates an exertion of high cutting forces.
In case of climb milling the deflection force vector is perpendicular to the cut. In both cases there are chances of error. The vector lengths in case of climb cutting and of conventional milling are also longer. Longer lengths indicate the possibility of deflection as well. It is also because of heavy cutting forces.
Therefore for roughing purposes you should choose climb milling. Because in this case tool deflection does not impact accuracy of the process. Also it helps you to rough faster.
The reason behind fast roughing is that the transition of chip from thick to thin causes less heat generation. Also the cutting forces are lighter.
Cutting Geometry
In the Cutting process tool geometry plays a vital role. However in certain cases clim bill might produce negative cutting geometry.
When cutting if the is equivalent to half the cutter diameter than choose climb milling. In this case we assume that the machine has less or no backlash.
The choice between climb vs conventional milling does not matter when you are cutting till 3/4th of cutter diameter.
You should prefer conventional milling when you pass 3/4 1x to the cutter diameter.
Material Compositions
Material compositions are very important in enable climb milling vs conventional debate. Both techniques have different suitabilities for different materials. Aluminum, acrylic, polycarbonate etc are among the category of soft materials. Therefore they use climb milling.
Hard materials such as cast iron and steel require the implemenetation of conventional milling.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.