Quality management is a common topic, but there is no fixed mode of management. A set of process-based management methods have been created: that is, the PDCA process management required by ISO. The quality management of heat treatment is no exception. The following is just some of the experience in the management process to communicate with you:
1. Planning According to customer requirements and organizational policies, our heat treatment quality target is 100% pass rate of heat, 98% pass rate for inspection, and 2% for repair. How to achieve the quality goals, we have done a lot of work in the following production process.
2. Implementation process 1. Process formulation Process formulation is the guiding direction of the implementation process. In addition to theory-based process formulation, experience often plays a decisive role. For example, there is a big difference in the results of precision castings and forgings with the same heat treatment requirements. The difference in the amount of NH3 in the process of CN co-infiltration will cause changes in the metallographic structure.
Intermittent production and continuous operation will cause the furnace The internal atmosphere is affected, the material composition fluctuates up and down, the processing results are very different, the use of various media should be optimally matched, and the use of fixtures should be as reasonable as possible… That is to say, the process of process formulation is a comprehensive The process of reunification later.
2. Operation The process of operation is the process by which the craft is executed. In this process, the parts tie and reasonable placement, the monitoring of the media supply, the equipment spot inspection…especially the normal use of the equipment is the key to ensuring the realization of the process. Our Fuma company currently uses a 400Kg non-oxidation multi-purpose furnace imported from Japan. We have formulated a series of regular inspection items according to the characteristics of this furnace, and we are responsible for the hardware and software.
This requires that our professional and technical personnel engaged in heat treatment must have comprehensive skills in order to be able to do their jobs with ease. At present, the effective hardened layer deviation of our parts has been kept within 0.05mm, and the Rockwell hardness deviation is between HRC1″HRC2. This is inseparable from the effective maintenance of the equipment.
3. Inspection This process is to verify the work of the above two steps. We stipulate in the program document that each batch of parts must be subjected to the first furnace section hardness analysis, and metallographic inspection if necessary, and subsequent production can only be carried out after the technical requirements are met. As we all know, the heat treatment of sewing machine parts is mostly carburizing and quenching.
The shape and mechanical properties of the parts determine the thickness of the carburized layer to be mainly thin. At present, most of them are between 0.1″0.6mm. So how to deal with sewing machine parts with smaller dimensions to ensure the thickness of the infiltration layer, through actual production, we found that in addition to the reasonable and accurate process parameters, the material composition of the parts fluctuates It also has an important impact on the thickness of the part carburized layer, core hardness, and mechanical properties. Please refer to the following data: Material used for a certain part: 15CrMo Dimensions: φ12×200mm (shaped) Heat treatment conditions: Comparison of main components of carburizing and quenching under the same conditions
Domestic material C% Si% Mn% Mo% Cr% P% S% First batch 0.13 0.26 0.51 0.43 0.92 0.012 0.018 Second batch 0.16 0.33 0.52 0.46 0.99 0.015 0.015 Third batch 0.18 0.24 0.48 0.45 0.90 0.016 0.019 Standard range 0.12″ 0.18 0.17″0.37 0.40″0.70 0.40″0.55 0.80″1.10 ≤0.03 ≤0.03
Comparison of heat treatment results Effective hard layer (mm) Core hardness (MHV) Core structure first batch 0.53 312 F+M (slats) second batch 0.65 441 M (slats) third batch 0.70 423 M (slats)
It can be seen from the above data that although the material composition is floating within the qualified range, the floating range between batches is relatively large. The material composition fluctuates up and down and the interaction makes the difference in heat treatment results obvious. The relative instability of the material composition has brought certain difficulties to our process formulation and post-fire processing, as shown in the following table: post-fire deformation (mm) The first batch of average 0.26 The second batch of average 0.58 The third batch of average 0.61
At the same time, we hope that the domestic steel market will have requirements for the addition of trace elements in carburized steel and formulate standards to make the quality of heat treatment more stable. The inspection process includes verification of process parameters, verification of whether the equipment is used rationally, verification of whether the use of fixtures is rationalized, verification of customer satisfaction, verification of whether the quality target is achieved, etc.
So far, we have designed and gradually transformed more than ten kinds of fixtures, and each part has a unique furnace loading method, which increases the furnace loading capacity under the premise of ensuring quality. Now our loading capacity of some parts even exceeds the loading capacity of 600Kg equipment. Reached and exceeded the quality target in terms of part quality.
4. Disposal For unqualified parts, first analyze the reasons for the unqualified parts and correct them accordingly. Once the parts are determined to be scrapped, they must be cleaned up and marked. The process parameters that have been verified to be unreasonable or need to be improved are modified and the change records are retained for traceability. A quality management experience often goes through one or several PDCA processes from inception to maturity. The participation of all staff in the process reflects the characteristics of quality management.