How to Develop Efficient CNC Machining Routes: A Pratical Case

In the manufacturing process, formulating the process route is one of the critical steps, significantly impacting part quality, production efficiency, and cost control.

The topic of developing process routes can be broad or narrow. This article takes a “narrow” approach, using a practical case study of CNC machining to compare multiple process routes, analyze their advantages and disadvantages, and hopefully provide some inspiration for you.

Preconditions for Developing Process Route

• A thorough understanding of machining processes and equipment characteristics, including the applicability of various machining processes and equipment performance.
• A deep understanding of material properties, such as machinability and deformation characteristics.
• A reasonable sequence of structural machining, determining which structures to machine first and which to machine later, to ensure machining stability and part quality.

Product and Drawing Analysis

This case study involves a small batch of parts of 2000 pcs, made of AL2024 high-strength aluminum alloy, which requires oxidation treatment after machining. The machining characteristics of the parts are as follows:

• Dimensional tolerance: The dimensional tolerance is relatively loose, but the tolerance for the side ear structure of the part is the most strict, 1.95±0.03mm.
• Assembly requirements: The hole positions must ensure positional accuracy and dimensional precision. To ensure stability, the hole positions and their datum should be machined in the same operation.
• Thread machining: M3/M4 thread hole, with M3 being a blind hole. To ensure thread consistency and fullness, a thread milling cutter is used.

Below are the 3D and 2D views of the part.

Practical Case Study: Analysis and Compare Multiple Process Routes

Process Route 1: 3-axis machining from B-side to A-side

Machining Steps:

• CNC1: Multi-station jaw clamping for machining the external shape and holes of the workpiece.

• CNC2: First, use M6 clamping plates to secure both sides of the blank. Pause the machine after the internal cavity is machined, install two M4 screws, remove the M6 clamping plates, and machine the remaining red structures.

Advantages:

• CNC1 simultaneously machines both the external shape and hole positions of the workpiece, with good dimensional stability.
• The thickness dimension is machined with clamping plates. So the height dimension will be very stable.

Disadvantages:

• CNC2 requires pausing to remove the clamping plates, increasing operational complexity.

Process Route 2: 3-axis machining from A-side to B-side

Machining Steps:

• CNC1: Multi-station jaw clamping for machining the external shape, holes, and internal cavity (opposite to CNC1 in Process Route 1).

• CNC2: Use a bench vice for clamping, flip the workpiece for positioning, and machine the thickness dimension.

Advantages:

• The overall processing stability of parts in CNC1 is good and does not require pausing to change clamping plates in CNC2.

Disadvantages:

• CNC2 uses side-push clamping to secure the workpiece, which may cause warping upwards, resulting in the risk of inconsistent thickness dimensions at the four corners, especially at the 1.95±0.03mm tolerance location.

Process Route 3: 4-axis machining from A-side to B-side

Machining Steps:

• CNC1: Uses 4-axis machining to simultaneously complete the external shape, holes, internal cavity, and the critical dimension feature of 1.95±0.03mm, ensuring stability.

• CNC2: It is basically the same as CNC2 in Process Route 2. After the critical 1.95±0.03 mm dimension is machined, a bench vice is used for clamping. Then the workpiece is flipped for positioning, and the thickness dimension is machined. Even if there is still a risk of warping upwards, the dimensional tolerance can be kept within a reasonable range for the rest structure.

Advantages:

• Process Route 3 is an improved version of Process Route 2. CNC1 completes the machining of the critical dimension on the 4-axis machine, reducing the machining difficulty for CNC2.
• In CNC2, the remaining thickness dimensional tolerances of the workpiece can be machined as closely as possible to the required tolerance, reducing processing risks and increasing feasibility.

Disadvantages:

• CNC2 uses the same clamping method as Process Route 2, so there is still a risk of warping upwards for the parts.

Process Route 4: One-time clamping with 5-axis machining

Machining Steps:

CNC1: 5-axis machining completes all dimensions of the part in one operation, with final saw blade cutting.

Advantages:

• There are no process conversion and positioning errors, resulting in optimal dimensional accuracy.

Disadvantages:

• Due to saw blade cutting, some edges cannot be chamfered on the machine. Manual deburring and chamfering are required after the part is removed from the machine.
• Generally, machining factories have limited five-axis machine resources, which may not meet demand during mass production.
• Since the clamping position is at the extended part of the workpiece, the workpiece is suspended. To reduce tool chatter, the machining efficiency must be reduced to balance this.

Conclusion

As we can see, all four process routes can complete the machining of the product structure, each with its unique characteristics. In practical work, as an engineer, I would visualize each route’s advantages, disadvantages, and risk points as if “playing a movie in my mind.” It also involves comprehensively weighing these factors based on the factory’s current available resources to select the most suitable one.

In this case study, I chose Process Route 1. The main reason is that the factory’s machine resource allocation at that time aligned well with the cost-effectiveness requirements of this batch project. And Process Route 1 focuses on “stability,” effectively meeting the machining needs.