Time is the single most important commodity in garment production, thus correct measure of time is very important. There are different measures of time in garment manufacturing: Standard Allowed Time, Utilization of Time, Pitch Time and Throughput Time. These are some of the most commonly used terminologies amongst garment production executives across the world. However, there are many other similar terminologies, often used interchangeably but may have different meanings altogether. As long as we are using macro-measures to evaluate our performance, probably many such measures will not make too much difference. But nowadays–companies are using professional micro-measures to measure time. Properly defining and fine tuning these measures to what we want and using correct terminology is of paramount importance.
SMV and SAM: Both are same
Standard Minute Value (SMV) and Standard Allowed Minute (SAM) is arguably the single most controversial topic today amongst garment production executives across the world. Mostly they are used alternatively as many people, even the experts don’t know if there is any difference. There are three schools of thoughts: first, both are same; second, SAM is an extension of SMV; and third, SAM and SMV are completely different measures.
“In all work study books there is only a reference to Standard Time. SMV and SAM are neither defined nor mentioned. In American published books, SAM is mentioned, while in European published books SMV is mentioned. Similarly, factories in Asia which are under the influence of European consultants use the term SMV, while factories in South America which are under the influence of American consultants use the term SAM”.
SMV or SAM is commonly calculated as:
Observed Time (Time Study) + Rating Allowance + PF&D (Personal Fatigue and Delay) Allowances Or
Synthetic Time (PTMS) + PF&D (Personal Fatigue and Delay) Allowances
When SAM is used as an extension to SMV, i.e. it is the allocated time for a task rather than the measured time. It is SMV plus policy allowances, if any. It is worth mentioning that these calculations are from experienced experts and consultants and not from any text book.
While in earlier schools of thoughts, units for both are in minutes, the third school of thought (but not really used in garment industry) talks about completely different things. Standard Allowed Minutes means time (in minutes) that is assigned to a specific operation after doing time study or using PMTS (Predetermined Motion Time Systems). While Standard Minute Value means the Cost Factor (in cost/minute) that is multiplied with SAM to get the cost of the operation. For example:
Operation name: Bottom hemming
SAM: 1.3 minutes
SMV: 0.50 INR/minute
Cost/bottom hemming operation: 0.65 INR
Utilization, Line Efficiency and Balance Efficiency are always same
All three terminologies are again used interchangeably across organizations. All measure as to how efficiently/effectively time is utilized by operators in the line.
While utilization is percentage of attended time that the operator spends “on standard” line efficiency is the calculation of “standard minutes earned”/”time attended”. Although it can be calculated for individual operators, it is most useful as a measure of sections or lines. In reality factories generally calculate line efficiency but often use the term “utilization”. In micro measure, there is a fine line of difference between utilization and efficiency. In first case, simply how much time is utilized productively is calculated; in second case how efficiently the available time is utilized. Let’s explain with an example:
One operator attends work 480 minutes in a day, spends 440 minutes on standard (40 minutes lost due to machine breakdown and no cut components), completes pocket attaching of 500 pieces, and SMV for pocket attach operation is 0.80 minutes.
Operator utilization is 440/480 expressed in percentage, i.e. 91.67% (how productively the operator’s time is utilized).
SMV earned by operator is 500 pieces X 0.80 minutes/piece = 400 minutes. So, operator efficiency will be 400/480 expressed in percentage, i.e. 83.33% (how efficiently the operator’s time is used).
Balance inefficiency (used commonly in Japanese literature) calculation is similar to efficiency calculation above but generally calculated for a line from a different perspective. Basically how much time is proportionately lost due to imperfect balance, as the primary reason behind time loss is attributed to poor balancing. Suppose in a sewing line of 20 operators, a style of 20 SMV is produced in 8-hour shift. If the average daily production of the style is 400 pcs/shift, then
Minutes produced = SMV X pcs/shift = 20 X 400 = 8000
Minutes attended = Number of operators X Number of minutes per shift
= 20 X 480 = 9600
Out of 9600 minutes available, only 8000 minutes of worth is produced, rest minutes are lost due to line imbalance. Thus, balance efficiency is 8000/9600, i.e. 83.33%.
If 83.33% is balance efficiency, then balance inefficiency is 100-83.33 = 16.67%.
Takt Time and Pitch Time are same
Takt Time comes from a German word ‘takt’ meaning rhythm or beat. Takt Time sets the ‘beat’ of the organization in synch with customer demand. Takt Time is a simple concept, yet counter-intuitive, and often confused with cycle time or machine speed. Takt time is the pace of production needed to meet customer demand or production target. The formula for Takt Time is:
Time available for production (Number of operators X Time contracted)
Target or Required number of pieces
Net available time to work = 1 shift X 8 hrs. X 60 min. X 20 operators = 9600 minutes
Customer demand (production target) = 2400 pieces
Takt Time = (9600 minutes)/2400 = 4 minutes/piece
This means a unit needs to be completed every 4 minutes. Therefore, every step or operation in assembly needs to be done/delivered every 4 minutes (or multiples of it).
Pitch Time is the theoretical operation time; each operator should take for a planned balanced line. It is calculated as:
(SAM value of a garment)
(No. of operators required to meet the target)
Suppose the work content (SAM value) of a garment is 40 minutes and there are 10 operators available to meet the target, which means while working in assembly line each operation should take 4 minutes to have a balanced line. Clubbing and Splitting of operations are done to match each operation timings with Pitch Time. Lesser the deviation of operation timings from Pitch Time, better the balancing efficiency that can be achieved.
Both Takt Time and Pitch Time can never be measured using a stop watch, both are always calculated.
Throughput Time and Flow Time are different
Throughput Time is the time required from one cut component fed till the final garment comes out at the end of sewing line. It is the total elapsed time between the point at which cut component enters the sewing line to the point at which the complete garment exits. Throughput time is the total work content of the style (in critical path) plus the total waiting time.
It is calculated as:
Throughput time = (work content of the style in critical path) X (1 + WIP)
In other literature, Throughput Time is defined as the rate at which the production happens. While the elapsed time between the point at which cut component enters the sewing line to the point at which the complete garment exits, is termed as Material Flow Time or Flow Time. If Throughput Time is represented by T and Flow Time by F, then inventory (I) can be calculated by I = T X F
For example, if the Flow Time (F) for a garment assembly process is 10 hours and rate of production (throughput) is 60 pieces per hour, then inventory in the line is 600 garment equivalent of cut components and partially sewn components.
Time Study and Capacity Study are different
Although Time Study is commonly used in the industry, complete exercise is ‘Motion and Time Study’, where Time Study is to establish Target Time (that is achievable). Motion Study explores possibility of improving it through methods improvement. In many of the cases in organizations, Time Study is conducted but the aim is not to establish the target but to only assess the capacity of existing work force.
While Time Study is cumbersome and time consuming, capacity study can be done quickly and easily where element breakdown of operations are not necessary. Simply cycle time taken for complete sewing operation (from pick-up to dispose of) can be calculated to assess how many pieces can be made by existing work force with existing methods and infrastructure. The time lost and hidden potential for improvement are never identified in capacity study.
Cycle time is more important than standard time as it gives an accurate indication of what can be achieved. For balancing purposes, it is much better to use achieved cycle times than standard times.