Planning Your Resources Wisely

Unless you are one of a small number of companies that possesses all the resources you need to complete any job you get, you are faced with a tough manufacturing decision: how to properly allocate your resources.

Columns From: 1/18/2010 Modern Machine Shop,

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Wayne Chaneski

 

If you are “waste conscious,” you already understand that time spent producing parts that will not be shipped out for some time is overproduction, and this wastes resources. Other wastes, such as over-processing parts, also drain resources.
 
So assuming we are not overproducing, over-processing or doing other things that prevent us from using our resources to their fullest, how do we best use our limited resources? Here is where an understanding of TAKT time, and how it can be applied to your operation, can help.
 
Simply put, TAKT is the rate of customer demand and the target to which we must gear our manufacturing processes. TAKT is determined by a simple calculation—work time available divided by the demand for product during that time. For example, say a machine works two 8-hour shifts with two 10-minute breaks per shift, and the machine needs to produce 800 parts per day to meet customer demand. TAKT, in this example, is calculated as follows: (2 × 480 minutes of machining time)-(4 × 10 minutes of break time) ÷ 800 parts = 1.15 minutes, or 69 seconds. This means that each step in the manufacturing process must be capable of completing a part within that 69-second target. When planning which resources to use to produce a part, the cycle time (time to produce one part) for each resource needs to be compared to TAKT time. 
 
Let’s assume we are trying to select the best machine to produce the part described in the previous scenario. One machine can complete the part in 50 seconds, and another can complete the part in 58 seconds. We can see right away that both machines can meet the daily requirement for this part because each cycle time is less than the TAKT time of 69 seconds.
 
However, to make the best resource decision, it would be helpful to see how much of each machine’s daily available time would need to be dedicated to this one part. For the machine with the 50-second cycle time, 72 percent of available time (50 seconds of cycle time ÷ 69 seconds of TAKT time), or a little more than 11 hours each day, must be dedicated to this one part. For the machine with the 58 second cycle time, 84 percent of available time (58 seconds of cycle time ÷ 69 seconds of TAKT time), or almost 13 hours each day, must be dedicated to this one part. 
 
Based on the above result, many would draw the conclusion that it is best to assign the job to the faster machine. This may be sound reasoning, but only if you can put the remaining time (a little more than four hours per day) to effective use, perhaps by changing over and running another job during this time. If not, you are faced with two choices: The first is to overproduce and make more than 800 parts per day on the faster machine, incurring the risk that accompanies a decision to produce beyond the daily committed demand. The second is to let the machine sit idle during this period. 
 
In this case, the alternative choice of running the 800 parts on the slower machine is worth considering for a number of reasons. First, the machine can meet the needs of TAKT. In other words, it can produce all the parts required each day. Second, it actually frees up the faster machine to produce other parts. If change-over times are short, it could possibly produce a number of different parts during the two-shift operation. Third, creative machine programming and fixturing could allow this machine to run many parts during a machine cycle, thereby allowing the machine operator to do other things while the machine continues to cut chips. Finally, with a part cycle time that is less than but still relatively close to the TAKT time (actually, 84 percent of TAKT time), this could be an ideal situation to accommodate any problems or delays that might occur. Not that we want to accept waste in our process, but it is not advisable for cycle time to be too close to the TAKT requirement, as this limits flexibility and provides no cushion if the unexpected occurs.
 
Comparing machine cycle times (what can be done) to TAKT times (what needs to be done) is an effective way to help plan your resources. However, be prepared for some unexpected outcomes, such as “faster is not always
better.”
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