Optimize the processing tempo to achieve efficient

Optimize the processing tempo to achieve efficient processing

optimize the workpiece processing process, use OEE to monitor the ratio of actual capacity to theoretical capacity of production equipment, and master the bottleneck of the production process, which is a useful exploration to achieve efficient and low-cost parts processing

the cylinder block is an important part of the engine, and its basic shape is complex: thin wall, box shape, multiple cavities and hole system. Generally, the machining characteristics of the cylinder block production line are: first face, then hole; First carry out the process that is easy to find the internal defects of parts; Finish the deep hole machining first to avoid the influence of large internal stress on subsequent finishing; Properly and reasonably arrange auxiliary processes such as sealing test, press fitting and cleaning

in the optimization of cylinder block production line of a domestic automobile enterprise, technicians adopted the method of beat optimization and used OEE management means to improve production capacity and reduce production costs

optimize the cylinder block processing beat

take the L4 gasoline engine cylinder block production line as an example. The production line consists of 4 domestic horizontal machining centers and 4 vertical machining centers. The workpiece is manually clamped, and the transmission adopts unpowered roller table; The auxiliary machine (cleaning, leak testing and press fitting) shall be a special machine; The position and size shall be measured by coordinate measuring machine, and the hole diameter, hole depth, threaded hole, etc. shall be measured by special measuring tools; The cutting tools are mainly domestic hard alloy cutting tools, and the key cutting tools are foreign well-known brands; The design capacity is 80 sets/day

first, analyze the line balance rate of the production line, that is, the time balance state of the operators constituting the production line in the operation elements

line body balance rate = (sum of all process beats 100%)/(bottleneck process beat personnel)

assuming that each machining center is equipped with one operator, the line body balance rate can be calculated as 43.4% and the loss is 56.6%

generally, the production beat of the production line is determined by the equipment with the longest production time in the whole line. By analyzing the process flow and beat of the cylinder block (Table 1), it can be seen that the processing beat of op60 is the longest, followed by op30 and op100

the optimization process can be divided into single process optimization and whole line beat balance

1. Single process optimization

(1) optimize workpiece fixture

this production line is a flexible processing line composed of machining centers, so it is very important to select appropriate equipment parameters. At present, the rapid moving speed of the high-speed machining center can reach 80m/min, the acceleration of each moving axis is maintained at 10m/s2, the tool change time (tool tool) is 3S, and the spindle speed is 16000r/mi. Under the condition of fixed power, it is inversely proportional to the speed of the initiator n. For machining centers, the common method to save auxiliary processing time is to use double worktables and double stations for processing. Fig. 1 shows the two station fixture for machining the air inlet surface of a cylinder head, which affects the performance of the equipment itself. The machining center adopts the vertical structure of double exchange worktable. The machining content is rough and fine milling the air inlet surface and the bolt mounting holes on the air inlet surface. There are five kinds of tools in this process. The tool change time of each tool is 9s and the exchange worktable time is 8s. When the conventional single fixture processing is adopted, the whole processing beat is 161s; When the duplex fixture is used for machining, the machining beat is 135s. This method is constrained by the processing range of the equipment, the length of the cutting tool, especially the maximum load-bearing of the workbench. It needs to be carefully checked in the design. In addition, when manual clamping is adopted, the clamping time must be considered. When using the double exchange workbench machining center, the processing time must be greater than the time of manual clamping the workpiece

Figure 1 Schematic diagram of double fixture

(2) optimization of tool use

□ optimization of machining path

use optimization design to select a reasonable tool path for surface machining tools; For hole machining tools, the tool approach distance should be reduced

□ optimize the process method

in milling, change multi tool processing to one tool processing, and use more composite tools, such as composite drill and step drill; Multi edge machining is often used in boring and milling plane

□ adopt high-speed machining tools

adopt high-speed machining tools, which can effectively reduce the pure machining time

for example, when the performance of Ci is between the two kinds of phenolic foam: heated foaming and normal temperature foaming, the cemented carbide boring blade is used for rough boring the cylinder hole of an engine on the cinnati four-axis vertical machining center. When the cutting depth is 1.5mm, v=180 m/min, fz=0.17mm/r, single edge boring and 4-edge boring are used respectively, with a difference of 169s (Table 2)

2. The whole line beat balance

the whole line beat balance is a necessary measure to improve the efficiency of the cylinder flexible processing production line. In the specific process preparation process, due to the principle of process concentration, the process designer can divide the processing content of each process into two categories: one is the content that must be completed in the same process according to the product accuracy requirements and process sequence, for example, precision boring the crankshaft hole of the cylinder block and precision machining the front and rear end faces, because it is necessary to ensure the verticality of the front and rear end faces and the crankshaft hole, Therefore, it is reasonable to complete the content in the same process. In addition, other processing contents belong to category 2. For example, the drilling and tapping of water pump bolt holes and oil pump bolt holes on the front and rear end faces are not necessarily completed in a certain process, but have certain adjustability. Therefore, it is suitable for beat balance in type 2 processing content

the cost of metal processing is divided into tool cost, raw material cost, personnel cost, equipment cost and other costs. Their respective proportions in the total cost are about 3% for tools, 22% for raw materials, and 75% for personnel cost, equipment cost and other costs

(1) the tool cost is reduced by 20%, and the total cost can only be reduced by 0.6%

total cost = 3% (%) ＋ 22% ＋ 75% ＝ 99.4%

(2) the tool life is increased by 2 times, and the total cost can only be reduced by 1.5%

total cost = 3%/2 = 22%+75% = 98.5% (3) production efficiency increased by 20% and total cost decreased by 15%

total cost = 3%+22%+75% (%) = 85%

it is clear from the above three schemes to reduce production costs that improving production efficiency is very effective in reducing processing costs

therefore, taking the Op10 process optimization shown in Table 1 as an example, when the processing tool parameters are changed, the processing beat time changes from 1446s (24.1min) to 750S, as shown in Table 3

the overall idea of this process optimization has two points. The first is to decompose the rough milling bottom surface to the rough machining at the blank supplier. The second is to reasonably improve the tool parameters and optimize the tool approach distance. The drill bit used in this process is made of domestic cemented carbide (v=60 ~ 90m/min, fz=0.18 ~ 0.22mm/r), the milling cutter is made of coated cemented carbide (v=150 ~ 220m/min, fz=0.10 ~ 0.22mm/r), reamer (v=40m/min, f=0.10mm/r), tap (v=6 ~ 12m/min)

after optimizing other processes and balancing the tempo, the production line not only shortened the processing tempo, but also reduced two operators. The line body balance rate reached 82.6% and the production capacity reached 80 cylinders per day

use OEE management tools to improve production capacity

for various reasons, after the production beat of the whole line is optimized, the production capacity usually cannot reach the theoretical value immediately. OEE is an independent measurement tool used to measure the ratio of actual capacity to theoretical capacity, availability, performance index and quality index, which are the three key elements of OEE

oee= availability performance index quality index

for example, the operating time of op100 equipment is 24h, the planned downtime before shift is 20min, the actual downtime is 180min, and the production pace is 14.1min. 83 pieces of equipment were produced on duty without scrap, and the OEE is 82%

availability = operation time/planned working time, which is used to evaluate the loss caused by downtime

availability = (24) (24) = 89%

performance index = production beat/(total operation time/total output), used to evaluate the loss of production speed

performance index =14.1 83 (24) = 93%

quality index = qualified products/total output, used to evaluate the loss of quality

quality index =100%

through the analysis of the production line, from the aspects of production organization, logistics distribution, quality assurance, equipment maintenance and tool management, the rectification and preventive measures have been formulated. After one month of improvement, the production capacity of the production line has been successfully achieved more than 80 sets/day, and the OEE value of the equipment has also stabilized to more than 80%

conclusion

cost reduction and efficiency increase are the goals that enterprises strive to pursue. Improving production efficiency is not just about improving tool parameters. Process parameters and process schemes should be adjusted in time according to changes in processing conditions to make the process schemes more reasonable

by using OEE tools in actual production for a long time, enterprises can easily find bottlenecks that affect production efficiency, and improve and track them to improve production efficiency