Manufacturing process revealed: Additive manufacturing VS subtractive manufacturing, how to choose?

Since the industrial revolution, manufacturing technology has undergone several innovations. According to the processing principle, the mainstream manufacturing processes can be divided into three categories: additive manufacturing, subtractive manufacturing and forming manufacturing. This article focuses on the first two, deeply analyzes the technical principles, performance characteristics and application differences of these two manufacturing processes, and provides you with a detailed selection plan for additive manufacturing VS subtractive manufacturing.

1. Subtractive manufacturing: precision technology of cutting and carving

The core logic of subtractive manufacturing is "subtraction". Through mechanical processing methods such as cutting, grinding, and drilling, excess materials are gradually removed from block raw materials, and finally the target parts are shaped. The typical representative of modern subtractive manufacturing is CNC machining technology, which uses CAD design models to generate machining paths, and then drives CNC machine tools through CAM software to complete high-precision material removal.

(1) Analysis of core processes

CNC machining mainly includes four basic processes: turning (rotating workpiece to remove material), milling (rotating tool to process plane/cavity), drilling, and grinding, which can realize the processing of complex geometric features such as planes, threads, and curved surfaces. In addition, special processing technologies such as laser cutting, water jet processing, and electric spark processing are mainly used for the precision processing of two-dimensional plates.

(2) Technical advantages

Strong material adaptability: can process a variety of materials such as metals, engineering plastics, composite materials and even wood

High geometric freedom: can achieve complex structure processing with ±0.025mm level accuracy

Excellent surface quality: can achieve mirror-level surface roughness through fine grinding

(3) Inherent limitations

Low material utilization: the waste rate generated by cutting is usually more than 30%. Although it can be recycled, there is energy loss

Long processing cycle: complex parts require multiple processes and step-by-step processing, and the production efficiency is lower than additive manufacturing

High equipment dependence: high-precision processing requires expensive multi-axis CNC machine tools

2. Additive manufacturing: digital manufacturing with layered stacking

Additive manufacturing has subverted the traditional processing concept. It adopts the "layered accumulation" method to stack materials layer by layer according to the three-dimensional model data until the entity is completed. Its typical application is the well-known 3D printing technology. At present, this technology has been maturely applied in the field of polymer materials, and metal additive manufacturing has also entered a period of rapid development.

(1) Process implementation flow

Digital modeling: Use CAD software to complete the design of the three-dimensional model of the part

Slicing: Use special software to discretize the model into hundreds to thousands of two-dimensional slices

Layered manufacturing: According to different technical principles (such as fused deposition modeling (FDM), light-curing (SLA), laser sintering (SLS), etc.), the raw materials such as wire/powder/resin are solidified and stacked layer by layer

(2) Technical advantages

Zero waste production: The material utilization rate is close to 100%, which significantly reduces the consumption of raw materials

Rapid prototyping: No complex tooling is required, and the process from design to sample can be completed in a few hours at the shortest

Complex structure manufacturing: Easily realize complex geometric forms such as hollowing and bionics that are difficult to process with traditional processes

(3) Application bottlenecks

Limited material range: Currently, it is mainly applicable to polymer materials such as plastics and resins, and the cost of metal printing materials is high

High production cost: The investment in metal additive manufacturing equipment exceeds 10 million yuan, and the processing cost of a single piece is 2-5 times that of CNC times

Batch production shortcomings: The layer-by-layer stacking characteristics lead to low efficiency in large-scale production

3. Additive manufacturing vs subtractive manufacturing: core performance comparison

4. Additive manufacturing vs subtractive manufacturing: process selection guide

(1) Select by application stage

Prototype production: Additive manufacturing is preferred for plastic prototypes (fast and low-cost), and subtractive processing is recommended for metal prototypes (higher precision)

Finished product production: Subtractive manufacturing is more suitable, and its processed parts usually do not require post-processing, and the mechanical properties are more stable

(2) Select by production scale

Very small batch (1-10 pieces): Additive manufacturing (especially plastic parts) has significant cost advantages

Small and medium batch (10-10000) =Parts): Subtractive manufacturing is more cost-effective, and the cost advantage becomes more prominent as the batch size increases

Massive production: It is recommended to use forming manufacturing processes (such as injection molding, die casting)

(3) Selection according to part features

Dimensional specifications: Subtractive manufacturing is suitable for large parts at the meter level, while additive manufacturing is better at small precision parts at the centimeter level

Structural complexity: Additive manufacturing is irreplaceable in complex structures such as hollowing, multi-curved surfaces, and internal flow channels

Material properties: Additive manufacturing is the first choice for difficult-to-process materials (such as TPU elastomers and high-temperature alloys), while subtractive processes can be given priority for conventional metals/engineering plastics

(4) Comprehensive decision-making considerations

In actual production, it is necessary to comprehensively consider multi-dimensional factors such as part geometric features (complexity/size), material type (metal/plastic/composite material), production scale (single piece/batch), and performance requirements (precision/surface quality). Generally speaking:

Additive manufacturing is suitable for rapid prototyping of small batches of complex structural parts made of plastic

Subtractive manufacturing is more suitable for medium and large batch production of conventional materials, especially for parts with high requirements for precision and surface quality

5. Summary

Data shows that the global additive manufacturing market size will exceed US$50 billion in 2024, while subtractive manufacturing will still account for 78% of the precision machining market. This set of seemingly contradictory figures is the best footnote to the coexistence and prosperity of the two processes: additive manufacturing rewrites the rules of small batch production at an annual growth rate of 25%, while subtractive manufacturing occupies the C position in high-precision machining. In the future manufacturing world, there will be no "replacement", only "adaptation" - just like a hammer and a scalpel each have their own uses, choosing the right tool can make the right product.