Machine Design Principle 1 – Right Sized

When you hear right sized you are probably thinking of the overall dimensions of the machine. That is one element of Right Sized, but there is another very crucial element – run speed of the machine.

Speed

When considering a machine design, understanding takt rate is extremely important. A machine that needs to complete a process in 30 seconds will look different from a machine that has 180 seconds to complete the same task. Knowing how fast the machine needs to operate comes from the takt rate calculation.

Takt rate has two elements – available time that the machine has for operation and product demand over that time frame. I usually prefer to work in a weekly time format. An example is a two-shift operation using 10-hour shifts, two paid 10-minute breaks per shift, a five-minute huddle at start and a five-minute cleanup at the end of each shift. There is also an unpaid 30-minute lunch break on each shift. We have 20 hours minus 40 minutes of breaks, 10 minutes of huddles and 10 minutes of cleaning. The unpaid lunch is not included as we are only looking at 10 hours, not the 10.5 hours personnel are present per shift. This leaves us 19 available hours per day x four days per week = 76 hours available per week. Demand for the product is 3200 parts per week. You can look at takt many ways and you need to find the one that best fits the situation. Parts per hour is 42 – hours per part is 0.02375 – minutes per part is 1.43 – seconds per part is 86. From a machine design viewpoint, I prefer to use 86 seconds. I can visualize one part being made in 86 seconds easier than I can visualize 42 parts being made in one hour. For a supervisor, 42 parts per hour is preferable. One other note on demand. Make sure to understand the projected growth for your product over the next three-to-five years. You don’t want to design a machine that is at max capacity in one year. Your designs should last three-to-five years at a minimum.

Now that you understand how fast to operate, you need to balance that time against your process time. Can one machine complete the needed processes in takt? When thinking about the process, don’t just consider the value-added time. You need to think in terms of the entire cycle – load, process, unload, check, aside. Will the operator be running more than one piece of equipment that may cause some wait time at this operation? You should be working with manufacturing on a standard work combination sheet if that’s the case. Are there dwell times in the process for cooling, heating, curing? What about fatigue and delay of the operator – especially in 10- and 12-hour environments? By now, you should have determined the number of machines needed and what each machine will be doing. Take your time during the sizing step – get this wrong and you’ll be fighting your design the rest of the way.

Dimensional Size

Ideally, the machine would not have a foot print much larger than the parts being processed. That is the ideal, but a machine designer must deal with reality. For a lean operation, width of the machine should be as narrow as possible. When machines are narrow, we can place multiple machines in an area and minimize the operator’s walk time. Wide machines spread the cell out and cause more walk time. In a Chaku-Chaku line the machines are usually placed in a U shape or two parallel lines. Narrow machines will create the smallest foot print for the operator. If the machine has some larger processing components associated with it, think about the larger components being in the rear of the machine and maintaining the narrow width. Increase depth to save width. Height of the machine is another design element that will be discussed later, but please consider line of sight to and from the work area.

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