Surface Roughness Control Technology for Castings

1.Basic Concepts and Industrial Value

In the field of metal casting, surface roughness is one of the core indicators for evaluating the quality of castings, directly influencing the mechanical performance, sealing effect, and subsequent processing costs of products. According to the ISO 8062-3:2023 standard, surface roughness specifically refers to the microscopic geometric shape characteristics composed of small intervals and peaks and valleys on the processed surface, and its numerical representation directly affects key parameters such as the friction coefficient and fatigue strength of the casting.
Taking the cylinder block of an automotive engine as an example, when the surface roughness Ra value of the cylinder bore is controlled within the range of 3.2-6.3 μm, it can not only ensure the effective sealing of the piston ring but also maintain the stability of the lubricating oil film. If it exceeds this range, for every 1 μm reduction in roughness, the mechanical loss can be reduced by approximately 3%, but the cost of precision processing will increase by 15%. This economic balance of precision is precisely the core issue of modern casting technology.

2. Analysis of International Standard Systems

2.1 ISO Standard System
ISO 1302:2022 divides casting surface roughness into 12 grades from N1 to N12, among which N6 (Ra 6.3) to N8 (Ra 12.5) are the general standards for industrial castings. This standard innovatively introduces a dual-parameter evaluation system of Rz (ten-point height) and Rmax (maximum peak-to-valley height), which can more comprehensively reflect the peak distribution characteristics of the casting surface.
2.2 ASTM Standard Practices
ASTM A802-2024 formulates differentiated standards for different casting processes: sand casting is recommended to have Ra ≤ 25 μm, die castings require Ra ≤ 6.3 μm, and investment casting needs to reach Ra ≤ 3.2 μm. Particularly in the aerospace field, critical load-bearing components must comply with Class A standards (Ra ≤ 1.6 μm).
2.3 Evolution of Chinese Standards
The new national standard GB/T 15056-2024, in addition to the original Ra value, adds the surface waviness Wt parameter for evaluation, requiring important castings to simultaneously meet Ra ≤ 6.3 μm and Wt ≤ 0.05 mm. This composite index system can effectively distinguish between machining marks and casting defects.

3. Breakthroughs in Modern Detection Technologies

3.1 Innovations in Contact Measurement
The new-generation TR200 roughness meter adopts a diamond probe dynamic compensation technology, maintaining a resolution of 0.01 μm while increasing measurement efficiency by 40%. Its intelligent filtering system can automatically identify and eliminate interference factors such as casting oxide scales.
3.2 Three-Dimensional Optical Inspection
The blue light three-dimensional scanning system enables full-surface digital modeling and constructs a three-dimensional roughness cloud map through ISO 25178 standard parameter groups (Sa, Sq, Sz). After a certain turbine blade manufacturer applied this technology, the defect detection rate increased from 78% to 99.6%.

3.3Online Monitoring Systems

Real-time detection devices based on machine vision can complete a surface quality assessment at the moment of casting demolding. Hexagon’s newly developed InSpec system can process 2000 frames of 4K images per second, with a roughness prediction accuracy of ±0.5 μm.

4. Key Technologies for Process Control

4.1Standard for Core Sand Management
The AFS fineness of furan resin sand should be controlled between 50 and 70, with a moisture content of ≤ 2.8%. Experiments show that for every 10-unit increase in particle size, the Ra value of the casting surface increases by approximately 1.2 μm.
4.2 Parameters for Pressure Casting
In ADC12 aluminum alloy die casting, when the injection speed increases from 3 m/s to 6 m/s, the surface roughness can be improved from Ra 6.4 to Ra 3.2, but it is necessary to use a mold temperature control machine to stabilize the mold temperature at 180 ± 5 °C.
4.3 Post-Processing Techniques Vibration grinding technology parameter optimization:

Using Φ2mm ceramic abrasives, with a frequency of 25Hz, and processing for 60 minutes can reduce the Ra value of cast iron parts from 12.5μm to 3.2μm. Compared with traditional sandblasting processes, surface consistency is improved by 300%.

5. Industry Application Frontiers

5.1 New Energy Vehicle Sector
Tesla’s integrated die-casting chassis requires a Ra value of ≤2.5μm. The application of nano-coated mold technology has extended the mold’s lifespan to over 150,000 cycles and reduced the cycle time to 80 seconds.
5.2 Precision Hydraulic Components
Parker Hannifin’s latest standard for hydraulic valve bodies has lowered the Ra upper limit to 0.8μm. By using a combined process of centrifugal casting and electrolytic polishing, the product leakage rate has been reduced to 0.05ml/min.
5.3 Additive Manufacturing Integration
GE Aviation’s use of 3D-printed sand molds has enabled the surface waviness of turbine casings to be controlled within Wt≤0.02mm, improving dimensional accuracy by 50% compared to traditional mold-making methods.
With the in-depth application of digital twin technology and AI process optimization, the control of casting surface quality is entering an intelligent era. The full digitalization from raw material selection to final inspection and packaging allows the Ra value fluctuation range to be controlled within ±0.3μm. In the next five years, nanoscale surface characterization technology based on quantum measurement is expected to break through existing precision limits, driving the casting industry towards ultra-precision manufacturing.

Supplier

Luoyang Fonyo Heavy Industries Co., Ltd, founded in 1998,is a manufacturer in cast railway parts. Our factory covers an area of 72,600㎡, with more than 300 employees, 32 technicians, including 5 senior engineers, 11 assistant engineers, and 16 technicians. Our production capacity is 30,000 tons per year. Currently, we mainly produce casting, machining, and assembly for locomotive, railcar, high-speed trains, mining equipment, wind power, etc. Our products have been exported to Russia, the United States, Germany, Argentina, Japan, France, South Africa, Italy and other countries.
Contact:Cathy
Email:sales@railwaypart.com
Mobile:008615515321683