Machining and Production Management in A Precision Part Project

With the advancement of technology, the precision machining capabilities of CNC processes have been enhanced, precisely meeting the demand for high-precision components in aerospace, medical devices, and industrial equipment industry.

This article will share WayKen’s expertise in high-precision component machining through a detailed description of the entire process, including technology, equipment, debugging, and measurement, based on a completed production case.

Product Background

The product in this case is a precision component for industrial equipment, with an order quantity of 1,000 pieces. Its dimensions are approximately 66×38×40mm, and it is made of AL2024 material, requiring a black oxide surface treatment.

This product shows the typical characteristics of precision small components, with complete structural dimensions and clear drawings. There is a clear understanding of the dimensional tolerances between key and general structures.

Datum and Tolerance Requirements 

Datum

The A datum is the axis of the concentric holes with diameters  ∅13 and ∅11, which has a perpendicularity requirement of 0.02 with the B datum (plane). The C datum is the axis of the ∅5 hole, which also has a perpendicularity requirement of 0.02 with the B datum.

Dimensional Tolerances

• ∅13+0.018/0;
• ∅11+0.018/0;
• ∅5+0.012/0;
• ∅5+0.03/0.

Geometric Tolerances

• The concentricity of ∅13 and ∅11 is 0.01;
• The runout of the ∅13 bottom surface (red surface) relatives to the ∅13 cylinder is 0.01;
• The symmetry of the ∅5 through slot relative to the center of the ∅5 circle is 0.02.

Analyze Machining Challenges of Precision Parts

• Datums A, B, and C are distributed across three different normal directions, with mutual geometric tolerance requirements.
• The critical dimensions are distributed across two normal directions, involving both dimensional and geometric tolerances. This increases the processing difficulty compared to precision components with only one set of critical dimensions in a single normal direction.
• The three precision holes (∅5, ∅11, ∅13) all have H7-grade tolerances, with the ∅5 tolerance being +0.012, requiring the tolerance to be controlled within 8 μm during the machining. This causes a big challenge for general milling.
• The tolerances for ∅11 and ∅13 are +0.018, which are not overly difficult individually. The precision can be achieved using a milling cutter for finishing. However, incorporating roundness, runout, and parallelism, which are geometric tolerances, into the control makes finish milling a high challenge.

Compare and Dertermine the Process Route Solutions

1. 3-Axis Milling and Conventional Cutter Process

• Advantages: The structure of the parts can be fully processed, with lower costs and simpler operations.
• Disadvantages: It is a challenge to continuously and stably ensure geometric and hole diameter tolerances.

2. 3-Axis Roughing, 5-Axis Milling, and Special Cutter Process

Advantages of 3-Axis Roughing

• Reduces the processing load and cost for the 5-axis milling, releasing roughing stress early.
• Decreases the clamping thickness in the 5-axis machining, shortens the cutter loading length, and enhances cutter rigidity.

Advantages of 5-Axis Milling

• Milling is performed in the same process, reducing the number of operations.
• Ensure the geometric accuracy between various normal directions.

Advantages of Special Cutter

• A dedicated finishing tool is assigned for each precision dimension;
• A ∅4 finishing cutter is used for the ∅5.0+0.03 through slot, with a tolerance stability of approximately 0.015mm.
• A dedicated reamer is arranged for the ∅5+0.012 hole due to its small diameter, which cannot be bored normally, with a tolerance stability of approximately 4 μm.
• Special boring tools are used for the ∅11 and ∅13 precision holes, with tolerance stabilities reaching 1.5 μm.

After continuous optimization and extensive discussions by the WayKen Engineering department, we finally chose Process Route 2 as the most suitable production solution.

How to Ensure the Best Result for Precision Machined Parts?

Equipment Selection

After determining a reasonable process route, selecting suitable machinery is crucial. WayKen has multiple 5-axis machines, and for this case, the Beijing Jingdiao JDGR300 5-axis linkage machine was chosen, which is highly suitable for processing such small-sized precision components. This machine has the following characteristics:

• Installed in a temperature-controlled workshop and equipped with a high-precision grating ruler. It can stably achieve axial positioning and cutting at the micrometer (μm) level.
• AC-axis cradle-type turntable with a positioning accuracy of 6″ and a repeat positioning accuracy of 4″.
• Equipped with a Renishaw in-machine probe for measurement before removing the product from the machine, ensuring dimensional meet the standards.

Verify the Stability of Surface Treatment

Reasonable processes and advanced equipment lay the foundation for high-precision component machining. However, achieving high precision also requires rigorous workflows and scientific quality control.

In this case, the dimensional tolerances for the three precision holes are +0.012 and +0.018mm (12μm and 18μm). Moreover, these tolerances are for the finished product size after oxidation. To ensure accurate delivery, the following factors need to be considered:

• The impact of oxide film thickness on dimensional tolerances.
• Measurement errors and fluctuations in measurement values before and after oxidation.

Therefore, during the debugging process, WayKen adjusted the various factors to the middle of the corresponding tolerances after careful consideration. Additionally, a comparison of CMM measurement data before and after oxidation was conducted to capture the variables affecting variation.

Measurement Equipment and Results

We employed a Zeiss coordinate measuring machine for strict testing:

• The finished precision part was fixed on the measuring table, and all data measurements were completed in one pass using an automatic rotating probe.
• An extended probe was used to measure the geometric dimensional tolerance of the concentricity of 0.01 between the ∅11 and ∅13 holes in the same normal direction. It improves measurement accuracy compared to the method of measuring with the probe rotated 180°.

Conclusion

The batch production capability of high-precision components requires not only advanced machining and measurement equipment but also a temperature-controlled environment and an experienced technical team for support.

WayKen keeps developing a scientific and complete project development process, a strict process review system, and precise preparation of engineering documents for achieving high-quality delivery. Just contact us to start your project today!