How to calculate the rhythm of low-pressure casting production line accurately

How to calculate the rhythm of low-pressure casting production line accurately
The production line rhythm should be calculated based on bottleneck processes, not single mode time; The bottleneck of the low-pressure line of the wheel hub often lies in cooling, parts removal, or machining.
Single mode time is not equal to beat
Single mode time refers to the interval between one machine and the next the first mock examination, which is usually 8-12 minutes for hub parts.
The production line rhythm refers to the interval between the entire line producing one piece. When multiple machines are running in parallel, the beat is equal to the single-mode time divided by the number of machines.
This distinction is often confused. Reporting production capacity based on single-mode time may overestimate or underestimate by more than 30%.
Disassemble the composition of single-mode time
A cycle includes seven actions: mold closing, filling, pressure holding, cooling, mold opening, component removal, and mold cleaning.
The total of filling and pressure holding often accounts for 20% -30%, cooling accounts for 30% -50%, and parts taking and mold cleaning accounts for 10% -15%.
Cooling accounts for the largest proportion, so water-cooled molds have the most direct impact on the rhythm. The cooling time can be shortened by 20%, and the entire mold cycle can be reduced by 8% -10%.
The bottleneck lies in machining, not casting
After the wheel hub castings are produced, they need to undergo machining, painting, and testing. The cycle time of machining centers is usually 3-6 minutes per piece.
A machining center paired with a casting machine often has insufficient machining capacity. The common configuration is one casting machine with 2-3 machining centers.
To calculate production line capacity, it is necessary to calculate it backwards based on the number of machining centers, rather than forward based on the number of casting machines.
Replacement loss should be included in the calculation
Changing the model once a day for 2 hours each time, calculated according to a three shift system, results in a loss of approximately 8% of effective working hours.
Multi variety workshops have more frequent model changes. Change the model 5 times a week for 3 hours each time, resulting in a loss of nearly 20%.
The calculation of the rhythm of a flexible production line must include the changeover time, otherwise the production capacity will be inflated.
The impact of scrap rate and repair
A scrap rate of 5% means a 5% discount on effective output. The repaired parts also require processing time.
When calculating, it is recommended to use the "qualified output cycle", which is the single mode time divided by (1-scrap rate).
The scrap rate has decreased from 5% to 3%, and the effective production capacity has increased by about 2%. This magnitude is not significant, but it corresponds to real gold and silver.
Calculation method for Xinfeng mold
Xinfeng Mold will provide a beat calculation table for the wheel hub mold project, including four items: single-mode time, cooling ratio, changeover loss, and scrap rate.
Customers can infer the required number of machines based on this, rather than estimating based on experience.
Usage of Calculation Table
Fill in the four items of single-mode time, number of machines, changeover loss, and scrap rate in the same table, and change any parameter to see the change in production capacity, which is more reliable than verbal estimation.
Practical tips
The calculation results are reviewed once a month. After the order structure changes, the original rhythm data will be distorted, and continuing to use it will mislead production scheduling.
The rhythm chart should indicate the data source date and be updated promptly after equipment or process changes to avoid using outdated data for production scheduling.
For production lines with frequent changeover, it is recommended to separately list the changeover time as a KPI and calculate it on a monthly basis, which is more effective than discussing efficiency in general.
Frequently Asked Questions
Q: How long is the low-pressure single-mode of the wheel hub?
Answer: It usually takes 8-12 minutes, depending on the size and cooling method.
Q: How to calculate the production line rhythm?
Answer: Divide the single-mode time by the number of machines, and then deduct the replacement type and waste.
Q: Which process is the bottleneck usually in?
Answer: Mostly in machining, not in casting.
Q: How much time does cooling take?
Answer: It often accounts for 30% -50% of the single-mode period.
Q: How to calculate the loss of model replacement?
Answer: Estimated by dividing the replacement time by the available working hours.
Q: How to convert the scrap rate?
Answer: Divide the single-mode time by (1-scrap rate).
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