Introduction

Milling in mold manufacturing is a cornerstone technique, pivotal in shaping and detailing various materials into precise molds. This process involves the removal of material from a workpiece, thereby creating a desired shape or finish. Two primary milling methods stand out in this context: climb milling and more conventional milling processes. These methods, often employed in CNC (Computer Numerical Control) milling operations, differ fundamentally in their approach and impact on the machining process.

The cutting process of mold processing must be divided into at least three processes: roughing, semi-finishing and finishing, sometimes even super-finishing. The roughing process will be suitable for ball end mills, round blade milling cutters and large tip arcs. The semi-finishing process will be used for radius end mills, round blade milling cutters and ball nose milling cutters. During the finishing process, the round blade milling cutter and ball nose milling cutter will be used, and the residual milling process will be used for the round blade milling cutters. Cutters, ball end mills and straight end mills, in each process, it is very important to try to leave an evenly distributed margin for the next process.

It is very important to optimize the cutting process by selecting the bevel shape, special cutting tool, size and cutting parameters, brand combination and suitable milling strategy. So, should it be down milling or up milling in mold processing? The answer is to use climb milling.

II.Climb Milling in Mold Manufacturing

Climb milling is an operating mode in the milling process, which is characterized by the fact that the rotation direction of the milling cutter is the same same direction as the feed direction of the workpiece. Here are some details about down milling:

Applicable situation:

Climbing milling is suitable for workpieces with small machining allowances or thinner machining, and is usually used in finishing. If there is no hard skin on the surface of the workpiece and the machine tool feed mechanism operates smoothly, it is also recommended to choose down milling to ensure the quality of the plastic part surface and reduce the wear of the cutter teeth.

Influence of cutting force:

During down milling, the cutting force will press the workpiece toward the workbench, which helps maintain the stability of the workpiece and improve machining accuracy.

Comparison with other milling methods:

Compared with up-cut milling, the milling cutter can bite the workpiece and cut off the thickest chips when starting cutting, while up-cut milling requires the milling cutter to slide a certain distance on the workpiece before starting. Cut until the maximum cutting thickness is reached.

Note:

Although down milling is beneficial for most situations, there are some specific situations where up milling may be considered, such as when the machine tool has thread clearance issues or when working with workpieces with hard skin.

In summary, down milling is a recommended milling method, especially suitable for high-quality finishing requirements.

III.Conventional Milling in Mold Manufacturing

Exploring Conventional Milling

Conventional milling, often referred to as up milling, is a fundamental technique in the world of machining. Up-milling refers to the relationship between the direction in which the milling cutter rotates into the workpiece and the conventional cutting or feed direction in circumferential milling, where the rotation direction of the milling cutter is opposite to the feed direction of the workpiece. Specifically:

Changes in cutting thickness:

During up milling, the cutting thickness gradually increases from zero and finally reaches the maximum value. This may cause the cutter teeth to slide on the machined surface, thereby aggravating the hardening of the surface and affecting the surface quality of the workpiece.

Influence of cutting force direction:

During down milling, the vertical cutting force component on the workpiece is downward, which helps to stabilize the clamping of the workpiece. When up-milling, the cutting force is upward, which may cause vibration. Especially when milling workpieces with hard skin, it may cause the workpiece to loosen.

Stability:

During up milling, since the direction of the cutting force component is opposite to the direction of the feed movement, the milling machine table is relatively stable and is not prone to axial movement, thereby reducing the impact on the cutter teeth and helping to extend the use of the cutter life.

Applicability:

While up-milling can provide a smoother operating experience in some situations (such as large cuts), it is generally not suitable for machining workpieces with hard skin because this may bring the workpiece into direct contact with the hard skin. causing processing difficulties.

To sum up, up milling is a milling method, which is characterized by the rotation direction of the milling cutter being opposite to the feed direction of the workpiece. However, in practical applications, its advantages and disadvantages need to be weighed according to the specific situation.

IV.Comparing Climb and Conventional Milling

Decision Factors

When deciding between climb milling and conventional milling in mold manufacturing, several critical factors come into play. These factors guide machinists and engineers in choosing the most suitable milling method for their specific needs.

Material Type: The choice of milling method can depend greatly on the type of material being machined. Softer materials like aluminum often fare better with climb milling, while harder materials like cast iron may require the robustness of conventional milling.

Desired Surface Finish: If the priority is achieving a superior surface finish with less surface roughness, climb milling is usually the preferred choice. In contrast, conventional milling might be chosen for roughing operations where finish is less critical.

Machine Capabilities: Not all milling machines, especially older or manual models, can handle the forces generated in climb milling. The machine’s capability to sustain the directional forces and potential for tool deflection plays a crucial role in this decision.

Tool Diameter: The size of the tool can influence the choice. Larger tools might handle the stress of conventional milling better, while smaller tools, which can be more prone to deflection, might benefit from the method of climb milling.

Climb vs. Conventional Milling

Understanding the scenarios that favor each milling type and their impacts is key to optimal machining.

Scenarios Favoring Climb Milling:

Precision CNC machining where a smooth surface finish is required.

Machining softer materials that are prone to tearing or burring.

Operations on modern, CNC milling machines designed to handle the directional forces of climb milling.

Scenarios Favoring Conventional Milling:

Roughing operations where finish is not the primary concern.

Machining hard materials that might cause excessive wear in climb milling.

Use on older or manual milling machines that might not withstand the forces in climb milling.

Impact on Tool Wear, Heat Generation, and Surface Roughness:

Climb Milling: Generally a climb mill results in reduced tool wear due to the chip thickness starting at maximum and reducing to zero. This also leads to less heat generation, preserving the tool and workpiece, and ensures a smoother surface finish, reducing surface roughness.

Conventional Milling: Can lead to increased tool wear as the cutting action starts from zero chip thickness, creating more friction and heat. This might result in a rougher surface finish but can be beneficial for certain materials and roughing operations.

In summary, the choice between climb and conventional milling depends on a myriad of factors, including the material type, desired finish, machine capabilities, and tool size. Both methods have their unique advantages and ideal applications, and the decision should align with the specific requirements of the mold manufacturing process.

V.Reasons for choosing down milling

When the cutting edge is just cutting, the chip thickness can reach the maximum value in forward milling, and it is the lowest in reverse milling. Generally speaking, the tool life in reverse milling is shorter than that of down, conventional and climb milling because of the The heat is significantly higher than in down milling. When the chip thickness increases from zero to the maximum value in up milling, more heat is generated because the friction on the cutting edge is stronger than in milling. The radial force is also significantly higher in up milling. , which has a negative impact on the spindle bearings.

In down milling, the cutting edge is mainly subjected to compressive stress, which has a more favorable effect on carbide inserts or solid carbide tools than the tensile forces generated in up milling. There are exceptions of course, when using solid carbide end mills for side milling, especially in hardened materials, reverse milling is preferred, making it easier to get straight walls with tighter tolerances and better 90 degree angles. Spend. If there is any misalignment between different axial feeds, the tool connection mark is also very small, this is mainly due to the direction of the cutting force, if a very sharp edge is used in the cut, the cutting force will “pull” the knife towards the material, which can Another example of reverse milling is milling with an old manual milling machine. The old milling machine has a large screw clearance. Reverse milling generates cutting force to eliminate the clearance and make the milling action more stable.

Conclusion

The choice of milling technique is not just a technical decision, but a strategic one. This choice can significantly influence the efficiency, outcome, and cost-effectiveness of the mold manufacturing process.

Climb milling, with its advantages in producing a superior surface finish and reducing tool wear, is often the preferred technique in modern CNC machining environments, especially when working with softer materials or when precision is paramount. Its ability to minimize chip thickness and tool deflection makes it an optimal choice for detailed and finish-sensitive projects.

Conventional milling, on the other hand, maintains its relevance and importance, particularly in situations where climb milling might not be suitable. Its effectiveness in roughing operations, compatibility with harder materials, and suitability for traditional or manual milling machines make it an indispensable technique in certain contexts. Conventional milling remains a reliable approach, especially in pre-finishing phases or when working with equipment not optimized for the rigors of the climb milling process.

The decision between climb and a conventional milling process should, therefore, be made after careful consideration of several factors: the material being machined, the desired surface finish, the capabilities of the milling machine, and the specifics of the tooling used. Each project in mold manufacturing is unique, and understanding these nuances is key to selecting the appropriate milling style.

In conclusion, the art of mold manufacturing is significantly enhanced by the judicious application of the right milling technique. Whether opting for climb milling for its finesse and precision or conventional milling for its robustness and suitability for tougher tasks, the ultimate goal remains the same: to optimize the mold manufacturing process for quality, efficiency, and technical excellence.