Continuous quality and improvement technology of stainless steel spring wire

1. Raising the problem

After more than two years of continuous improvement, in accordance with the principle of “customer-focused” in IS09001:2002, through visiting users, going to the user site to handle quality objections and collecting feedback information. Price and other non-technical issues are excluded, and user feedback is classified. After sorting out, the proportions of various opinions are as follows.

The back surface of the coil spring is scratched and punctured 14%

The dimensional accuracy of the spring after the coiled spring is not enough 29%

The tempered steel wire after the spring turns yellow and gray 21%

Uneven strength of steel wire cleaning rod 18%

The number of spring fatigue after coiling the spring is not enough 7%

Other 11%

It can be seen from the above that the reasons for customer complaints are mainly concentrated in the spring forming process, that is, the spring surface quality (such as color, scratches, etc.), dimensional accuracy and load fluctuations, etc., according to the severity of the problem, “improve the spring coil spring forming “Process stability” is a priority problem, and other issues such as spring fatigue performance are also given full attention and some inspection items are consciously added to collect more data and prepare for the next step of continuous improvement. Stainless steel spring.

2. Cause analysis

Since the products complained by customers are shipped after strict inspection, their mechanical properties, flatness and surface meet the domestic requirements of YB(T)11-83. Obviously YB(T)11-83 can no longer fully guide production. This decision started by studying advanced foreign standards and physical quality to find out the gaps. Compare YB(T)11-83 with related foreign standards such as ASTM A313/A313M-1993, BS2056-1991, JISG4314-1994, IS06931-1:1994 It shows that the foreign standards are more detailed and specific, and the maneuverability is strong. The performance of the collected foreign stainless steel wire samples for springs is higher than the corresponding foreign standards. For example, the springs of Japan Seiki and Sweden Sandvik use stainless steel.

The wire strength dispersion is controlled within 50MPa. The single-turn steel wire is freely placed on the ground, neither expanding nor shrinking, and the two ends are flat on the ground without any warping. The surface of the steel wire has two kinds of oil surface and powder surface. Through horizontal comparison, the three indicators of strength uniformity, flatness and surface quality of the products of Zhengzhou Sanhe Company lag behind foreign advanced products. The author once brought samples produced by several different processes to spring manufacturers for on-site coil spring tests. The results It is found that the coil spring performance of the steel wire with the above three good quality characteristics indicators is significantly improved. It can be seen that as long as the three quality characteristics of the steel wire rod’s strength uniformity, flatness and surface quality are improved, the stability of the spring forming process can be improved.

3. The surface condition of the steel wire

The surface condition of the steel wire can be divided into two categories: (1) The surface quality of conventional inspections such as dimensional tolerance, roundness and the existence of cracks, scratches and other defects. Domestic and foreign standards are basically consistent with this category, but YB(T)11 The tolerance specified in -83 is too large; (2) The quality of the lubricating layer on the surface of the steel wire, that is, the steel wire is drawn in powder or oil, and a coated and smooth surface can be obtained respectively. The two surfaces can also be coated with extremely thin nickel Or copper bottom layer.

The inner layer of the steel wire is nickel or copper plating, and the outer layer is powder or oil. The thickness of each layer is about 0.1~0.2μm. The nickel or copper bottom layer is helpful to improve a certain fatigue strength and lubricating ability. Coated surface (powder surface) ) The lubricating layer is composed of calcium salt and sodium salt. The lubricating layer is sensitive to moisture. Therefore, it must be protected from moisture during storage and transportation. The lubricating layer can be retained on the formed spring or can be cleaned off. Smooth surface (oil surface) The lubrication layer is a very thin oil film. In contrast, the surface of the oil-surface steel wire forming spring is bright after tempering, but the spring with a complicated winding must be additionally provided with lubricant, and the winding spring has the risk of scratching and fatigue failure. The safety is lower than that of flour noodles. This category stipulates that domestic and foreign standards do not have this requirement.

However, well-known foreign manufacturers can provide the above two surface conditions for delivery. In terms of surface quality of Gangsi, the following measures can be taken: (1 ) Change the tolerance requirements, and produce according to the tolerance requirements of JISG4314-1994; (2) Develop the production of oil surface steel wire, provide users with two surface states for delivery, for their choice; (3) Do a good job of technical service and introduce to users The comparison of the advantages and disadvantages of the springs formed by the powdered surface and the oil surfaced steel wire makes it understand that the spring formed by the powder surfaced steel wire is a little yellow and gray after tempering, and other properties are better than the oil surface steel wire, and the surface is yellow and gray. It can also be washed off.