Selection strategy for bar turning of industrial parts: how to choose bars/castings/tubes/blocks?
When you walk into a modern lathe workshop, you will see two completely different production scenes:
The CNC lathe on production line A is cutting a steel bar with a diameter of 50mm, producing an automobile bolt every 30 seconds. The iron filings in the scrap box are weighed by kilograms and will be recycled;
The five-axis turning and milling machine on production line B is processing an automobile engine block. The blank is a pre-cast casting of an approximate shape. The tool carefully cuts out a complex inner cavity. Each process is optimized to "reduce material waste" and "improve product precision."
 |
The factory is using a five-axis milling machine to finish machining engine block castings |
1. Bar turning of industrial parts: Definition and Core Concepts
Industrial parts bar turning is a core process for cutting metal bars (such as round bars, square bars, hexagonal bars, etc.) through lathes. The basic principle is to clamp the bar-shaped raw material in the lathe spindle and rotate it at high speed, while using the tool to feed along the predetermined path, removing the material layer by layer, and finally processing shafts, sleeves, threaded parts and other parts that meet the design requirements.
● Core features:
Material form: Bars are used as raw materials, usually in the form of continuous long strips.
Processing goal: Produce rotationally symmetrical or cylindrical parts (such as shafts, flanges, gear blanks).
Efficiency advantage: Suitable for mass production, high material utilization (up to 80%~95%).
2. Bar turning of industrial parts：Industrial parts bar turning: process and technical details
(1) Typical processing flow
Raw material clamping → Rough turning of outer circle → Fine turning of contour → Grooving/threading → Cutting and separation → Post-processing (such as polishing, heat treatment)
(2) Key technologies and equipment
● Lathe type:
CNC lathe: high precision, automation, support for complex programming (such as multi-axis linkage).
Swivel lathe: suitable for processing slender small parts (such as watch screws), with synchronous feeding of main and auxiliary spindles.
Ordinary lathe: manual operation, suitable for simple parts or small batch production.
● Tool selection:
Carbide tool: strong versatility, suitable for materials such as steel and aluminum alloy.
Ceramic or CBN tool: used for high hardness materials (such as hardened steel and titanium alloy).
● Fixture system:
Spring chuck: high clamping accuracy (±0.01mm), suitable for bars with a diameter of ≤80mm.
Hydraulic chuck: large clamping force, suitable for heavy cutting.
(3) Processing parameter examples
3. Does turning have to start with bar stock?
Not all turning starts with bar stock. The choice of raw materials for turning depends on the part design, cost and process requirements. Common material forms include:
(1) Bar stock (long strips)
● Applicable scenarios:
Parts with a large aspect ratio, such as shafts and bolts.
In batch production, bar stock can be fed continuously to reduce clamping time.
● Advantages:
High material utilization and standardized processing flow.
Suitable for automated production (such as CNC lathes equipped with feeders).
(2) Casting/forging blanks
● Applicable scenarios:
Parts with complex shapes or requiring special mechanical properties (such as crankshafts and gears).
● Processing logic:
First obtain a blank of approximate shape through casting/forging, and then fine-tune the key parts through turning.
● Advantages:
Reduce material waste (compared to direct cutting of solid bar stock).
Increase part strength (forgings have a denser grain structure).
(3) Pipes
● Applicable scenarios:
Hollow structural parts (such as hydraulic cylinders, bearing sleeves).
● Processing method:
Turning inner and outer circles, controlling wall thickness and concentricity.
(4) Plates/blocks
● Applicable scenarios:
Non-rotationally symmetrical parts (milling and other processes are required).
● Processing logic:
The plate/block is processed into an approximate shape by sawing or wire cutting, and then local features are turned.
4. Core advantages and limitations of bar turning for industrial parts
(1) Advantages
● High efficiency: Continuous processing reduces downtime for material change, suitable for mass production
Bar turning achieves continuous processing through an automated feeding system (such as a bar feeder or a robotic arm), and a single clamping can complete the processing of dozens or even hundreds of parts.
● High precision: CNC lathes can achieve a dimensional tolerance of ±0.005mm
Modern CNC lathes can stably control key dimensions through closed-loop feedback systems and linear guide technology, combined with high-rigidity turrets.
● Low cost: The price of bar stock is low and waste can be recycled
As a standardized raw material, the procurement cost of bar stock is 20%~30% lower than that of customized blanks. Taking aluminum alloy 6061 bar stock as an example, the price of waste recycling can reach 70% of new material.
(2) Limitations
● Shape limitation: It is difficult to directly process complex three-dimensional asymmetric structures
The core principle of bar turning is symmetrical cutting around the main axis, so the processing capacity of non-rotating bodies or special-shaped structures is limited, and multiple processes are required.
● Material waste: When processing hollow parts with solid bar stock, a large amount of material needs to be removed
When processing hollow parts such as hydraulic cylinders and bearing sleeves, the material removal rate of solid bar stock may be as high as 60%~80%, and the material waste rate is high, thereby increasing the processing cost.
5. Typical application cases of bar turning for industrial parts
(1) Automobile manufacturing: engine piston pin
Material: 20CrMo alloy steel bar
Process:
Rough turning of outer circle → carburizing and quenching → fine grinding to Ra 0.4μm → surface phosphating for rust prevention.
(2) Medical equipment: surgical forceps shaft
Material: 316L stainless steel bar
Process:
CNC turning → electrolytic polishing → ultrasonic cleaning and sterilization.
(3) Aerospace: landing gear bushing
Material: titanium alloy TC4 bar
Process:
Cryogenic turning (control cutting temperature) → shot peening → anodizing.
6. Comprehensive selection strategy for raw materials for bar turning of industrial parts
7. Summary
Bar turning of industrial parts is an efficient and precise processing method, especially suitable for mass production of rotationally symmetrical parts. However, turning does not necessarily start from bar stock. The actual selection needs to comprehensively consider the shape of the part, material properties and cost.
Bar stock is preferred: when the part is a solid cylinder and needs to be produced in large quantities.
Choose castings/forgings: when the parts have complex structures or require special mechanical properties.
Hybrid process: combining turning, milling, additive manufacturing and other technologies to achieve low-cost and efficient processing of complex parts.
In the future, with the development of intelligent and composite processing technology, turning technology will be more flexible to adapt to multi-form raw materials, further expanding its application scenarios in high-end manufacturing.
Comments
Post a Comment