When engineers design custom parts, the decision between one-piece machining and a welded structure often involves multiple factors such as cost, machining capability, operating conditions, and batch size.
One-piece machining and welded structures each have their own advantages and disadvantages. Which is better is not absolute but depends on the specific application, performance requirements, and economic considerations.
1. What is a welded structural part?
A welded structural part is made by joining multiple CNC‑machined components together through welding. During fabrication, each component must be precisely machined and processed according to design requirements to ensure perfect fit‑up. In addition, the choice of welding process, welding sequence, and quality control must be considered to guarantee the final product's quality and performance.
As a classic manufacturing process, welded structures are widely produced using automatic or semi‑automatic arc welding methods in industrial production. Their main advantages are high welding speed, relatively simple process, and applicability to a wide range of metallic materials.
What welding methods are used for CNC welded structural parts?
TIG welding
MIG welding
Laser welding
Spot welding
Manual arc welding
In custom parts machining, the most common process is MIG welding. For most welded structural parts, MIG welding offers good overall performance.
What is MIG welding?
MIG welding (Metal Inert Gas welding), also known as Gas Metal Arc Welding (GMAW), uses a continuously fed solid wire electrode. When the trigger on the welding gun is pulled, the welding current and shielding gas are turned on. An arc forms between the electrode wire and the workpiece, heating both metals above their melting points. The molten metals mix together and solidify, joining the workpieces into one integral part. This process is one of the core methods for manufacturing welded structural parts.
What materials are used for welded structural parts?
Common materials for welded structural parts include carbon steel, stainless steel, and aluminum alloys.
| Material | Typical Thickness Range | Welding Speed Reference | Key Notes |
| Mild Steel | 1mm – 25mm | 300 – 600 mm/min (Higher achievable) | CO₂ or mixed gas available, low cost |
| Stainless Steel | 0.8mm – 50mm+ | 200 – 500 mm/min (Faster for thin sheets, slower for thick plates) | Pulsed MIG recommended for thin sheets, control heat input |
| Aluminum Alloy | 1.5mm – 30mm | 300 - 600 mm/min | Oxide film must beremoved, pulsed MIGrecommended |
Main characteristics of MIG welding:
High welding speed and high production efficiency
Relatively simple process, easy to automate
Wide applicability to various metallic materials
Weld distortion and quality control
Main application fields of welded structural parts?
Welded structural parts are widely used in the following fields:
Carbon steel: automotive, building structures, general machinery
Stainless steel: food equipment, medical devices, chemical industry
Aluminum alloy: rail transportation, automotive lightweighting, shipbuilding
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2.What is one‑piece CNC machining of a part?
Using metal or engineering plastic as the raw material, one‑piece CNC machining involves programming a CNC machine to follow a preset 3D model and toolpath. The machine cuts, mills, drills, and engraves a solid block of material, progressively removing excess material until a part with complex geometry, high precision, and an integral structure is formed.
Characteristics of one‑piece CNC machining:
1. Multi‑process integration
On a single CNC machine tool, multiple operations such as milling, turning, drilling, boring, and tapping can be performed automatically without transferring the workpiece between different machines or re‑fixturing.
2. High precision and consistency
By precisely controlling toolpaths and machining parameters, dimensional accuracy of 0.005‑0.01 mm is achieved, regardless of part complexity. Since most operations are performed automatically by the machine, dimensional consistency of batch parts is improved. Position feedback devices on precision‑controlled machines further enhance the accuracy of precision CNC machining.
3. High production efficiency
Reduces fixturing time, machine changeover time, and inter‑operation waiting time, thereby improving overall productivity.
4.High flexibility
By simply modifying the machining program, different parts can be produced quickly, adapting to changes in product design or process requirements.
For example, when machining a mechanical part with multiple holes, slots, and curved surfaces, one‑piece CNC machining can complete roughing, finishing, drilling, chamfering, and other operations in a single fixturing setup, directly outputting a finished part that meets specifications.
3.For custom parts, should one‑piece machining or a welded structure be used?
In the CNC machining industry, one‑piece machining and welded structural parts each have their own characteristics. The choice depends on the specific application and requirements.
1.Performance and reliability
One‑piece machined structure:
The material is continuous with no weld seam and no stress concentration points, resulting in long fatigue life. It is especially suitable for applications subject to alternating or impact loads, or those requiring extremely high airtightness or corrosion resistance, as well as critical parts of high‑end machinery.
Welded structure:
The weld zone is the weak link in terms of performance. Defects such as porosity, lack of fusion, and residual stress can significantly reduce fatigue life. Welded structures are not suitable for high‑load or alternating‑load applications.
2.Accuracy
One‑piece machined structure:
Good accuracy and stability, high dimensional consistency, minimal distortion, and high repeatability. Suitable for parts with high precision requirements.
Welded structure:
Welding distortion may affect dimensional accuracy and may require additional straightening or post‑weld machining. Suitable for general mechanical structures.
3.Manufacturability and size/weight
One‑piece machined structure:
Limited by the machine's working envelope (travel, table size), making it difficult to produce very large parts. Moreover, to machine complex internal features, a large amount of material must be removed from a solid blank, resulting in low material utilization (possibly over 90% becomes chips), which increases weight and drives up cost.
Welded structure:
Allows multiple small, simple‑shaped components to be joined into a very large or highly complex structure. By using plates, tubes, and profiles, lightweight frames and shells can be produced with high material utilization.
4.Cost
One‑piece machined structure:
The main costs are the expensive raw material blank and costly machining time (especially for 5‑axis or deep‑cavity machining). Advantages include low assembly cost, no weld‑related failure issues, high long‑term reliability, and low maintenance frequency.
Welded structure:
The main costs are in material, forming, welding, and post‑weld operations. It allows joining of components with different shapes and sizes to realize complex assemblies. In batch production, fixturing can help reduce per‑part cost. For high‑volume or large‑size parts, welded structures are often more economical.
5.Material
One‑piece machined structure:
Offers a wide range of material choices, such as aluminum alloys, carbon steel, stainless steel, and engineering plastics. It provides a fine surface finish and can be used for parts with high aesthetic requirements.
Welded structure:
Some materials have poor weldability, are difficult to weld, or are prone to cracking. In such cases, one‑piece machining is often the only or better choice.
6.Special requirements
One‑piece machined structure:
In heat‑resistant or corrosion‑resistant environments, one‑piece machining maintains uniform material microstructure throughout the part. For vibration or noise control, the damping characteristics of one‑piece machined structures are generally superior to those of welded structures.
Welded structure:
Welding causes local microstructural changes (e.g., grain coarsening, precipitation phases), which can reduce local heat or corrosion resistance. Weld seams and assembly interfaces introduce additional energy dissipation paths, which can lead to vibration or noise. These factors must be given special attention when designing welded structures.
Summary
If the application demands extremely high strength, precision, and reliability (e.g., alternating or impact loads, stringent requirements for airtightness or corrosion resistance, or critical parts of high‑end machinery), one‑piece machining is the preferred choice.
If lower cost, flexible customization, or lower load requirements are the priorities, welded structural parts are a more economical choice. Welded structures offer clear advantages in large‑size, batch production, and cost‑sensitive applications.
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