The cost of an automated stamping production line invested by a vehicle manufacturer has basically exceeded 100 million yuan. Together with the investment in plant construction, station equipment, and production operations, it has become an important cost component of the vehicle manufacturing process. How to improve the movability and production speed of the production line, improve the quality of stamping products, and then give full play to the manufacturing capacity of the automatic production line is a topic that the managers of the stamping workshop must face.
This article starts with the introduction of the evaluation indicators of the comprehensive efficiency of large-scale production lines, discusses the factors that affect the production capacity of the automatic stamping production line and the solutions, and further discusses how to maximize the production capacity of the automated stamping production line and maintain a high level of measures and work. method.
Production organization of mass manufacturing units
The most representative production instruction system is Toyota’s “Kanban” (Figure 1), which emphasizes the requirements of the entire vehicle production line. Suppliers must supply the parts required by the assembly line on time and in quantity, reducing the inventory on the assembly line side. , Thereby reducing plant area, reducing capital occupation and avoiding large quantities of defective products. Stamping engineering is sometimes regarded as the supplier of the vehicle assembly line. It needs to organize appropriate lean production according to the required goods kanban issued by the vehicle line in order to achieve the goal of maximizing the utility of human, financial and material.
Figure 1 Production indicator system
According to the required goods kanban issued by the post-engineering, comprehensive consideration of the status of the sheet material in the warehouse, the product warehouse, and the warehouse status and storage area of the post-engineering line side, the number of workstations, the recent maintenance status of the stamping machine and the mold, and the fluctuation of product quality Factors, formulating a reasonable tiered production scheduling plan is the prerequisite for stamping engineering to achieve “lean production”. This requires that the production scheduling planner is very familiar with the production situation, and has a deep understanding of the on-site equipment mold status, logistics operation, quality control status, and even the skill status of the operators. The front-line production personnel should also count the production data in a timely manner, especially for the time periods with downtime, and analyze and analyze the results. The analysis results with reference to the equipment/mold maintenance, logistics and production scheduling personnel are timely and horizontally expanded.
Production downtime caused by mold replacement is unavoidable, but it is a matter of time. With the increase of press automation functions, the improvement of mold manufacturing accuracy and the improvement of operator skills, the current average downtime for mold change can be as short as 3 to 5 minutes, and the time to calculate qualified products can be controlled within 10 minutes . Here are some techniques and methods to shorten the downtime of mold change.
⑴ Depending on the degree of automation of the production line, the number of labor required for mold change varies. Generally, the number of mold changes in a working day ranges from several to ten times, and the time cannot be completely fixed. Therefore, it is necessary to visualize the production progress and let relevant personnel know the time of mold change in advance.
⑵ If the conditions permit, the size of the mold should be a uniform height. In the case of inconsistent mold heights, the height difference between the two production molds should be as small as possible, otherwise the slider adjustment time will be too long, which will inevitably cause downtime growth of.
(3) The sheet size of the stamping parts produced by the two connections should be as close as possible. In this way, no matter whether the feeding system uses a set of fully automated universal sheet end pickers, or several sets of semi-automatic or partially universal sheet end pickers that require automatic/manual conversion, the adjustment amount is relatively small and the adjustment time can be shortened. .
⑷The number of presses in the general stamping production line meets the maximum number of processes set for the products produced, and the empty station appliances are used as temporary pallets for the automated handling system when producing products with fewer processes. When arranging the procedures for these products that require the use of empty station appliances, it is necessary to plan the specific procedures of the empty station appliances as a whole, try to arrange them to the same process, and be as versatile as possible. The workbench of the automated press line is shown in Figure 2.
⑸Dual workbenches have become the standard equipment of the automated stamping production line. The reasonable mold storage layout, hoisting route and conversion sequence design are of great benefit to improving the safety and efficiency of the operation. The formulation of the production plan should take into account the time of off-line mold lifting and conversion, so as to avoid the production waiting to be stopped due to the production batch being too small and the previous batch of production is over, and the next batch of molds are not ready.
Figure 2 Automated press line workbench
⑹The judgment of the first qualified part also takes time, and the time required for different products may be longer or shorter. For stamping parts such as side panels and doors, it usually takes more than 10 minutes to conduct surface quality inspection and crack inspection. In the usual production, the parts that have experienced quality problems and the parts that need to be inspected in the process are marked on the “Operation Instructions” on the site. After the first piece is released, the special inspection personnel will follow the product quality history and the “Operation Instructions”. , Quickly judge whether the production of this batch of products can be started, and it will also shorten the downtime caused by mold change work. What needs to be emphasized here is that, on the premise that the work that should be done is not missing items, a reasonable arrangement of the work sequence and connection process can improve work efficiency.
The formulation of the production plan also needs to consider the maintenance cycle of the equipment and molds. The maintenance and general maintenance of the equipment will be arranged during the shutdown period. The composition of the automated stamping production line is complex, and security personnel are required to inspect and maintain in strict accordance with the “Maintenance Manual”. In particular, it should be noted that inspection and maintenance cannot be abandoned due to heavy production tasks or “looks no abnormalities” during equipment operation, which will cause great potential failures.
The recording and statistics of production data is a tedious task. Generally, it takes a whole month or even a whole year of data accumulation and analysis to show the behavior of the automatic stamping production line in a certain aspect. The release of production kanban, the maintenance of equipment and molds, and the improvement of product quality must find the laws that can reflect the working status of equipment and molds, product quality fluctuations and other aspects from the above data. Focus on the work, so that it may be able to achieve twice the result with half the effort. effect.
Full play of equipment tooling performance
Stamping production is a series of complex and coherent manufacturing processes completed by the cooperation of the production line and the mold. Discussing the SPM of the production line or the mold alone cannot fully and effectively describe the production speed of a stamping product. The SPM of the production line is basically fixed after it is manufactured and installed according to customer requirements and industry level. However, the mold is affected by more factors, such as the complexity of the product shape, the amplitude of the automated handling curve, the iteration cycle of the model, and so on. This article focuses on how to improve the overall SPM level of the automated stamping production line.
Assuming that the SPM of the automated stamping production line Ω is 4-12, it is responsible for the three types of A, B, and C (generally one stamping line is responsible for the production of 10-20 or more stamping parts, here for the convenience of description, we will give an example of three) stamping parts The design SPM is 8, 10, and 12 respectively. Then, according to different production plans, the SPM of Ω should be a value between 8 and 12, assuming it is 10. However, in actual production, it often runs at a value lower than the designed SPM. Here, it is assumed that the actual SPMs of A, B, and C are 6, 8, and 10 respectively. At this time, the performance index of Ω is 80%, which is lower than our expected target.
This phenomenon is very common in stamping workshops. Many reasons for production stagnation are directly or indirectly related to production speed, such as the stability of grabbing engineering products, the smoothness of waste discharge, the continuity of various sensor signals, etc. , It can cope with production after reducing the production speed. Therefore, set up a problem-solving team that includes multiple professionals (including professional personnel in process, mechanical and electrical maintenance, mold maintenance, logistics, production planning, production line operation, and quality inspection) to deal with problems such as downtime or slower product production speed. Regular group discussions are organized to analyze downtime, review all aspects of inducing factors, determine the degree of hidden danger, formulate solutions, coordinate online debugging time, etc.
Through discussion, plans α, β, and γ were formulated for products A, B, and C. The offline rectification work and preparation work were also implemented well, and debugging was carried out during the nearly one-round production cycle. There are three main steps. ⑴In online debugging, α was implemented smoothly, and the production speed of A product was successfully restored from 6 to 8; ⑵In the implementation of β, it was found that the previous investigation was not comprehensive enough, and new situations need to be considered. When the production speed is increased to 10, it is still The machine stopped continuously, and the debuggers recorded the new phenomenon in detail and stopped the debugging, and reduced the production speed to 8 to maintain production; ⑶After the implementation of γ, a certain effect was achieved, and the production speed was increased to 11 to maintain stable production. When the speed was raised to 12, the machine still stopped. The commissioning personnel set the production speed of C product to 11, made a record of the commissioning and ended the commissioning.
At this time, the production speeds of A, B, and C products are 8, 8, and 11 respectively. Assuming that the comprehensive SPM is 9, the Ω performance index has increased by 10% through this round of debugging. At this time the team has the following 4 tasks to do: (1) Update the new product production rate to the production operation file; (2) Track whether product A and product C have new problems in production due to speed changes; (3) Summarize the α plan, Prepare summary reports and other materials to facilitate the inheritance of experience, and at the same time review whether the good experience in the α scheme can be extended to the β and γ schemes; ⑷ Continue to review and improve the β and γ schemes based on the newly acquired information to prepare for the new round of debugging ready.
After several cycles of debugging, the production rate of each product has been stabilized at a relatively high level. At present, the performance index of some equipment can reach 95%. The above is the general process of carrying out SPM promotion work, and there are 5 points that need to be emphasized: (1) The working group contains all the majors, involving all aspects of production line operation. ⑵Logistics personnel must participate. When the operating state of the automated stamping production line equipment is relatively stable, we only need to consider how to send the sheet up in time and transport the finished product down. (3) Don’t hope that the production speed of all products can be raised to the highest one time. This is a long and iterative process. Each round of commissioning must go through full program demonstration and a large amount of offline work. It is necessary to measure the balance between production and commissioning from time to time, and constantly collect clues to formulate a more perfect plan for the next commissioning. ⑷The experience of successful cases should be summarized in time and carried out horizontally. ⑸The experience and data from other units have limited implementation effects in this unit. After all, there are factors such as differences in product shapes, differences in production line specifications, and differences in mold manufacturing styles. The work team needs to work independently to accumulate experience.
Quality is a tool for work
Some of the methods and measures to improve the availability and production speed of the production line introduced above are carried out when the statistical data of the production line has already revealed problems or the production has stalled and cannot continue, then how to maintain the efficiency of the production line at a certain level , How to improve the efficiency of the production line again at a higher level? Product quality fluctuations in the production process (Figure 3) are an effective tool for us to carry out our work. The following will give an example of how to use quality as a tool to improve production efficiency.
After several rounds of efforts, the comprehensive SPM of parts A, B, and C reached 9.6, and the GSPH of the production line Ω was also maintained at around 518, that is, the performance index and availability rate were 96% and 90%, respectively. However, in the production, there will be more or less fluctuations in the quality of the parts, such as the growth of trimming burrs, insufficient flanging, nick marks, pull marks, etc. Some can be repaired by hand repair stations, and some cause product scrap. Product quality fluctuations are often the weather vane of the entire OEE line, and if this change is left unchecked, it is likely to cause greater hidden dangers.
Figure 3 Product example attempts
Assuming that the manual repair rate of product A increased by 0.1% during production, the team members investigated and found that when product A was produced, more iron filings fell on the mold and product surface, causing trace defects. Through online observation and debugging, it was found that the edge of the individual inserts of the trimming die had chipping, which produced excessive iron filings during production. After repairing the cutting edge of the mold insert, the iron filings are significantly reduced in the production, and the mark of product A is basically eliminated, which avoids the hidden danger of long-term shutdown due to the continued deterioration of the mold state.
Similarly, the hand repair rate of part B due to traces also increased. The investigation did not find any traces of damage to the cutting edge of the mold insert. Through a more detailed observation of the production process, it was found that the workpiece could not completely fall to the bottom when it was sent to the trimming process. The cutting edge of the insert and the plate formed a certain angle during trimming. A lot of iron filings; it is found that the forming condition of the drawing process near the trimming is less than that of the sample, but the subsequent bending and shaping process can be improved, so it is not found on the finished product. After investigating and analyzing the reasons for insufficient forming in the drawing process, after excluding factors such as die draw bead wear, sheet size out-of-tolerance, and feeding position deviation, it was finally found that the right side of the press hydraulic cushion was blanked during the forming process The force provided is smaller than the set value. The equipment maintenance personnel found that the hydraulic pump one-way control valve had a leakage problem, which returned to normal after replacement. Although the rectification work was caused by fluctuations in the quality of a certain product, it was finally discovered that it was caused by hidden dangers in the production line equipment.
Assuming that the product C also has the problem of increased hand repair rate due to scars, based on experience, we have checked the state of the trimming die insert, whether there are differences in equipment working parameters and setting values, etc. There is no abnormal phenomenon. Through microscopic analysis, it is found that the foreign matter that causes the product to produce scars is not the burr-like iron filings generated during trimming, but the sheet-like sheet material surface falling off during drawing or forming, which is also on the drawing die body or inserts. An accumulation tumor appeared. The mold maintenance staff found that the accumulated tumor was also polished in time during the inspection, but it will be repeated after a few batches are produced. Combined with the above investigation, the team members analyzed that the problem may appear in the material. Investigation of the size and surface quality of the sheet material found that the size of the incoming material met the technical requirements, and there was no foreign matter such as dust on the surface of the sheet material. Next, the logistics staff in the team analyzed the recent material plan and material income records of the C product, and found no abnormalities. After contacting and investigating the sheet material supply unit, it was found that the amount of sheet material that was supposed to be in the warehouse for 1 to 3 days has reached 1 month, which caused the sheet material supplied to the stamping workshop to volatilize after long-term storage. During the product forming process Increase the friction between the sheet material and the mold, and then cause the partial surface galvanized layer to fall off. Through negotiation with the sheet material supply unit, the inventory time of product C and other product sheets was reduced, and at the same time, abnormal information communication channels were established, and finally the quality defects of C product surface marks were basically eliminated.
The improvement process of the three products of A, B, and C illustrates how to improve the mobility of the whole line by solving quality problems. The same is the surface traces of the parts that cause the hand repair rate to increase, but finally solved from three different perspectives From the problem, we can summarize the following 3 points: (1) We must pay attention to the quality fluctuation of stamping products, which is often the manifestation of hidden dangers and problems in the operation of the entire line; (2) When solving problems, we must fully consider molds, equipment, materials, logistics and operations, etc. There are many factors; (3) When searching for the true cause, you must investigate more deeply and ask more why. Product A. Is it a case of damage to the cutting edge of the mold insert? What is the cause of the damaged insert? If the failure of the hydraulic cushion of the press is also the source of the quality problem of product A, it is possible to avoid the quality problem of product B through group work.