To optimize the production process of steel rings for HPHT Hydraulic Cubic Press, aiming to increase their service life and significantly reduce total costs, improvements and innovations can be made in four key areas: forging, machining, heat treatment, and welding.
Here is a detailed explanation of the optimization:
1.Forging Process Optimization
Material Selection and Characteristics:
The material selected for the steel ring is the medium carbon alloy steel 58SiMn. Although this material has poor forgeability, it possesses excellent comprehensive mechanical properties, good high-temperature performance, good hardenability, and the ability to withstand heavy load impacts. These characteristics are crucial for improving the steel ring's durability during press operation.
Forging Method Improvement:
The forging method for steel ring blanks was changed from free forging to hydraulic die forging.
Results:
Significantly reduced raw material usage: Taking a Φ175 mm steel ring as an example, free forging initially required 100 kg of material, while die forging reduced the material usage to 73.5 kg, a reduction of 26.5 kg.
Substantially lowered per-piece cost: With a material cost of approximately 15.5 RMB per kg, the material reduction alone resulted in a cost saving of about 410 RMB per piece, accounting for about 30% of the total cost.
More suitable for mass production.
Quality Control:
Reasonable furnace temperature and holding time (forging starting and finishing temperatures controlled at 1000–1200℃) were adopted to reduce the probability of internal defects such as cracks and impurities.
Strict control over the internal quality of forgings ensures compliance with the GB3077—1999 standard, with the total non-metallic inclusion content not exceeding grade 3.5, a forging ratio greater than 3, and no defects like overheating, delamination, cracks, or forging damage.
Annealing treatment is performed after forging to eliminate internal stresses in the material, improve internal organizational properties, and enhance material machinability.
2Machining Process Optimization
Process and Equipment Improvement:
Clear and accurate product drawings were created, machining processes were refined, and advanced CNC machine tools were employed.
Tooling, Fixtures, and Measuring Devices Innovation:
The original milling fixture for steel rings was improved. Due to increased production, a new set of fixtures and measuring tools with more accurate positioning and higher machining precision was designed and manufactured. This helps improve machining efficiency and shortens the processing time of parts on the milling machine.
Additionally, several sets of drilling jigs for large blocks were designed and manufactured for the drilling process.
Steel Ring Machining Process Optimization Workflow:
1.Rough turning, quenching and tempering, and semi-finishing of the forged blank.
2.Milling of four inclined surfaces using a fixture for positioning.
3.Scribing by a fitter.
4.Drilling.
5.Heat treatment: Quenching to achieve the hardness required by the drawing.
6.Hardness inspection.
7.Welding of the annular water groove.
8.Fine turning of the inner taper hole.
9.Grinding of the 3° inner taper hole.
Inspection and Precision Assurance:
Different specifications of gauges were designed to inspect whether the inner hole dimensions of various steel ring models are qualified. The 3° conical surface is required to have no sharp edges and to have a contact area with the gauge of no less than 85%, with the large end making full contact, ensuring machining precision. The gauges adopt a hollow structure to reduce weight and facilitate use.
Strictly implement the first-piece inspection system for production. Workpieces must be inspected after heat treatment to measure their hardness.
During rough machining, reasonable control of machining allowance is applied to improve the production efficiency of the grinding process, thereby reducing the total processing time. This also ensures the depth of the hardened layer formed by quenching and controls product technical parameters, reducing losses.
3.Heat Treatment Process Optimization
Hardness Uniformity and Hardened Layer Thickness:
The technical focus is to ensure the uniformity of product hardness and the thickness of the surface hardened layer.
Process (Connection):
While ensuring the heat treatment process, close衔接 (connection) between machining and heat treatment processes is also considered.
Furnace Type and Operation Optimization:
Considering the large weight and considerable volume of the products, a sealed box furnace was abandoned, allowing heating and quenching of the workpiece to be completed in the furnace in one go.
Results: This simplified the work process, reduced the thickness of the product's oxide layer, and ensured the quality of the product's heat treatment.
Quality Standards:
When inspecting the hardness of the workpiece, it is required not to exceed the drawing parameters' upper and lower deviation of 1%, thus strictly guaranteeing that every product leaving the factory is a high-quality product.
Specific Treatment Steps: Steel rings are quenched after drilling.
4.Welding Process Optimization
Addressing Core Problems:
To address the issue of corrosion and cracking in the water groove of water-cooled steel rings during use, the sealed water channel is made of 2-3 mm thick stainless steel material.
Overcoming Welding Difficulties:
Due to the poor weldability between stainless steel and the steel ring material (medium carbon alloy steel 58SiMn), and the tendency of medium carbon alloy steel to crack when heated, the project team formulated two welding schemes after consulting literature and experts.
Experimental Comparison and Scheme Selection:
Through experimental comparison of the two schemes (A: quench first then weld; B: weld first then quench), the results showed that scheme A's product quality was significantly superior to scheme B, with hardness inspection indicators within technical requirements, proving that the former process is more scientific and reasonable.
Key Reason: Placing the welding process after the steel ring's quenching process avoids cracking due to different expansion coefficients of the stainless steel tube, weld seam, and steel ring material during quenching.
Specific Welding Measures:
Welding wire selected was 304 stainless steel welding wire.
Welding equipment: CO2 gas shielded welding machine and argon arc welding machine (experiments showed argon arc welding has better results) were used.
Pre-welding preheating: The steel ring was preheated to 220℃ and held for 6 hours to prevent internal stress caused by uneven heating.
Post-welding treatment: After welding, the workpiece was placed in the furnace for holding and tempering to eliminate internal stress.
Quality Inspection:
After the water-cooled steel ring cools down in the furnace and is taken out, a leak test is performed. It is required to hold 1 MPa pressure water for 0.5 hours without leakage to meet the design standard.
Through the comprehensive and systematic process optimization described above, including material selection, improved forging methods, enhanced machining precision, controlled heat treatment quality, and innovative welding processes, Hunan Flydisc New Material Co., Ltd. has effectively increased the service life of HPHT Hydraulic Cubic Press steel rings and other parts, and significantly reduced total costs. These optimized products have entered mass production and are sold to diamond production enterprises both domestically and internationally, receiving positive feedback from customers.