Must read before placing an order: 6 must-know points about CNC precision machining parts

 

Converting drawings into products

Must read before placing an order: 6 must-know points about CNC precision machining parts

With the continuous improvement of part quality requirements in high-end manufacturing and precision equipment, CNC precision machining has become the preferred process for mass production of complex parts. It automatically controls tool movement through computer programs to achieve efficient "subtractive" processing of materials.

When selecting and using CNC precision machining parts, the public is most concerned about six core elements: process definition, machinable materials, machining accuracy, tolerance range, surface finish, cost influencing factors and typical delivery cycle. These factors directly determine part quality, functional matching, budget and project progress. This article will answer these six questions in turn to help you quickly understand and make decisions.

1. What is CNC precision machining?

CNC precision machining (computer numerical control machining) is a process for manufacturing high-precision parts by controlling machine tools through computer programs. It uses a numerical control system to convert design files (such as CAD models) into machining instructions, drive the tool to perform cutting, drilling, milling and other operations on the material, and realize the production of CNC precision machining parts with complex shapes and high precision requirements. Its core advantages are high automation and good repeatability. It is suitable for small-batch to large-volume precision manufacturing needs and is widely used in aerospace, medical equipment, electronic communications, precision instruments and other fields.

Compared with traditional manual or semi-automatic processing, it can achieve complex geometric shapes and multi-faceted processing on three-axis to five-axis machine tools, significantly improving processing efficiency and repeatability.

Precision processing not only focuses on dimensional tolerances, but also includes many indicators such as surface roughness and geometric tolerances of parts. It is usually called "precision" or "ultra-precision" processing.

2. Types of materials that can be processed

CNC precision processing can process a wide range of materials, including metal and non-metal materials:

(1) Metal materials

Aluminum alloys (such as 6061, 7075): light and easy to process, commonly used in aerospace and electronic product housings.

Stainless steel (such as 304, 316): corrosion-resistant and high-strength, suitable for medical equipment and food equipment.

Copper and copper alloys (such as brass and copper): good conductivity, mostly used for electrodes and connectors.

Titanium alloy (such as TC4): high strength, high temperature resistance, used for aerospace structural parts.

Alloy steel (such as 45 steel, mold steel): high hardness, suitable for molds and mechanical parts.

Precious metals (such as gold and silver): used for precision electronic components and jewelry processing.

(2) Non-metallic materials

Engineering plastics (such as ABS, nylon, acrylic, POM, PEEK): good insulation and low cost, used for gears, housings, and models.

Composite materials (such as carbon fiber and glass fiber): high strength and light weight, used for high-end equipment components.

Ceramics (such as alumina and zirconia): high temperature resistance and high hardness, used for precision structural parts or insulation parts.

3. Precision (tolerance) of CNC precision machining parts

The precision of CNC precision machining parts depends on the performance of the machine tool, tool accuracy, processing technology and programming parameters, and is usually divided into the following levels:

(1) Conventional precision

Rough machining: tolerance range ±0.1mm ~ ±0.5mm, suitable for blank forming.

Semi-finishing: Tolerance range ±0.05mm ~ ±0.1mm, meeting general precision requirements.

(2) Precision machining

Finishing: Tolerance range ±0.01mm ~ ±0.05mm, suitable for most precision parts (such as automotive parts, electronic accessories).

Ultra-precision machining: Tolerance can reach ±0.001mm ~ ±0.005mm (such as precision grinding, mirror machining), used for aerospace bearings, optical lenses, etc.

Ultra-precision machining of aerospace parts

Note: High-precision machining requires constant temperature workshops, high-precision machine tools (such as coordinate grinders, ultra-precision lathes) and precision measuring equipment (such as three-coordinate measuring machines).

4. Surface finish (surface roughness) of CNC precision machined parts

Surface roughness is expressed as Ra value (arithmetic mean roughness), and different machining processes correspond to different ranges:

(1) Rough machining

Ra 12.5~25μm: suitable for blank surfaces and non-matching surfaces (such as rough milling and rough turning).

(2) Semi-finishing

Ra 3.2~6.3μm: ordinary mating surface (such as ordinary milling, turning).

(3) Finishing

Ra 0.8~1.6μm: precision mating surface (such as fine milling, fine turning, reaming).

Ra 0.4~0.8μm: high-precision surface (such as grinding, honing).

Finishing parts

(4) Superfinishing

Ra 0.1~0.2μm: mirror surface (such as grinding, polishing, superfine grinding), used for optical components and mold cavities.

Note: The higher the surface finish, the higher the processing cost. It needs to be selected according to actual needs.

5. Main factors affecting CNC processing costs

(1) Material cost:

Rare metals (such as titanium alloys, precious metals) or high-performance plastics (such as PEEK) are much more expensive than ordinary aluminum alloys or ABS.

For the cost of metal CNC precision machining parts, generally: aluminum alloy < carbon steel < stainless steel < titanium alloy. In short, material cost and processing scrap rate will significantly affect the total cost.

(2) Part complexity:

Geometry: Complex surfaces (such as free-form surfaces), deep holes, and thin-walled structures require more programming time and processing steps.

Precision requirements: High-precision tolerances (such as ±0.001mm) require multiple processing and testing, which is time-consuming and labor-intensive.

(3) Processing time:

Number of processes: Multi-process processing (such as milling + turning + grinding) increases machine tool occupancy time.

Cutting parameters: Low-speed high-precision processing takes longer than high-speed rough processing.

(4) Batch size:

Small batch (1~10 pieces): Fixed costs (programming, clamping, debugging) account for a high proportion, and the unit price is expensive.

Large batch: The unit price is reduced after the fixed cost is amortized, but the cost of molds or special fixtures needs to be considered.

(5) Equipment and process:

High-end machine tools (such as five-axis machining centers and ultra-precision grinders) have high depreciation costs and more expensive processing fees.

Special processes (such as heat treatment and surface treatment) add additional costs.

Testing costs: High-precision parts require multiple three-coordinate measurements, spectral analysis, etc., which increase quality inspection costs.

Additional requirements: such as customized packaging, certification (such as ISO, aerospace AS9100), etc.

6. Typical delivery cycle (delivery time)

The delivery cycle depends on the complexity of the parts, batch size, process difficulty and supplier capacity, and is usually divided into:

(1) Sample/small batch (1~50 pieces)

Simple parts: 3~7 working days (including programming, processing, and testing).

Complex parts: 1~2 weeks (requires multiple processing steps and precision testing).

(2) Medium batch (50~500 pieces)

Conventional process: 2~4 weeks (including tooling preparation, batch processing, and surface treatment).

Requires heat treatment or special process: 4~6 weeks (waiting for outsourcing processing time).

Surface treatment of metal parts

(3) Large batches (more than 500 pieces)

Standardized parts: 4~8 weeks (mold development and assembly line optimization are required).

High-precision complex parts: more than 8 weeks (staged processing and strict quality inspection are required).

Note: Expedited orders can be compressed to 1~4 days through overtime and priority scheduling, but the cost may increase by 30%~50%.

7. Summary

When you have a procurement demand for CNC precision machining parts, CNC precision machining is a reliable choice for achieving high-precision and complex structural parts. At this time, you need to make a clear plan based on your own product positioning:

(1) Clear technical requirements:

Determine the material type (metal/non-metal), precision tolerance (ordinary or ultra-precision) and surface roughness standard according to the application scenario (such as aerospace, medical equipment, etc.) to avoid over-design or insufficient performance.

(2) Balance cost and efficiency:

Through communication with the processing party, reasonably select cost-effective materials (such as aluminum alloy replacing titanium alloy for non-critical parts), optimize part structure to reduce processes (such as avoiding difficult-to-process structures such as deep cavities and thin walls), and negotiate process plans based on batch size (sample/small batch/large batch) to reduce fixed cost allocation.

(3) Evaluate supplier capabilities:

Investigate the processing party's equipment configuration (such as five-axis machining center, etc.), testing methods (such as three-coordinate measuring machine, etc.) and industry experience to ensure that it can meet the accuracy requirements and control delivery time - simple parts can give priority to fast proofing service providers, while complex and high-precision parts need to connect with manufacturers with full-process control capabilities.

(4) Control the delivery rhythm:

Confirm the time consumption of each link (programming, processing, heat treatment, surface treatment) with the processing party in advance. Expedited orders can shorten the cycle by prepaying expedited fees and accepting them in stages, but the cost increase needs to be evaluated simultaneously.

(5) Core recommendations:

Clear demand definition and in-depth collaboration with the processing party (such as providing 3D models and tolerance annotations) are the key to ensuring that CNC precision processing meets performance, cost and delivery targets. By scientifically planning technical parameters and supply chain resources, high-quality transformation from drawings to finished products can be efficiently achieved.