Work-Factor Learning and Process Control
Management systems on material costs, man costs and machine costs (calculation) and supply and distribution (logistics) have standard times as important common input. These are necessary to manage and control the businesss processes.
Standard times are indissolubly bound with the pre-supposed working method and the á priori determined working tempo, rate or performance.
Work-Factor is, as known, a system of method study with predetermined standard times at a select tempo/rate at MPL level.
Therefore, the results of a Work-Factor analysis are a detailled description of the method to be followed and the corresponding standard time.
Having to one’s disposal good method descriptions and proper standard times, one is indeed compliant with a very important demand for process control, but yet with no garantee that this will lead autonomously to the desired control and productivity. The workers must be able to meet these standard times in practice, in real terms. To that end it is necessary that the workers acquire the required skill and experience which must be established during a learning-in process. This learning-in process is mainly a process of giving instructions and guidance. The detailled method description of the Work-Factor analysis is an excellent basis for the instruction. After that, it is important to coach the workers in building up the required skills and experiences.
Also a learning-in process can be passed predictable and therefore be controlled. Many researchers have studied the course of the learning-in process. Especially within Philips NV The Netherlands much research was carried out in daily practice. For more information see WS Tip 90-96.
1. One of the first was T.P. Wright (1936 “Factors affecting the cost of airplanes”). He noticed that the necessary time decreased by 20% when ever doubling the number of pieces made. A disadvantage was that for very large series the time needed became very small indeed. That is impossible because the time needed has a lower limit no matter how skillfull or fast operators do work.
Dr. Ir. J.R. De Jong (1957 “Skill, series length and necessary time”) has completed the theory of Wright further. Besides the proposition of the regular percentage decrease of the cycletime, he introduced the factor of non-reducibility. He assumed the proposition that non-reducible elements will exist in every cycle. It was proven that the theory of De Jong is very usefull to describe the course of the learning-in process. For more information see the WS Tips 87-89 and 97-99.
2. During the 50-ies, 60-ies till even in the early 70-ies, staff members of TEO in the factories of Philips NV and staff members of Central TEO, have put a lot of effort and time in finding and setting up learning-in curves based and practical experience. So, hundreds of learning-in curves were determined for a vast variety of different cycle times. At first, mainly for the performance range of T30 till T70 Bdx, later expanded for the total range from T0 till T75 Bdx with extrapolation till T85 Bdx.
Mrs. J. van Daatselaar and M. Hogendijk (1962 “Learning-in programs and cycle influence on labour costs in set assembly”) became well known for their analyses and rubrications of the Philips’ learning-in curves. They noticed that these learning curves showed a constant shape for every given cycle length and work content. They came up with the idea to standardize the learning curve, which was dependent on cycle length and percentage new work, on a time axis from 0 till 100, inwhich 0 indicates the start of the first cycle and 100 indicates the end of the last cycle at an á priori set final performance. Checking and testing this idea against the collected data convinced them that there was just one universal learning curve and one universal forgetting or memory curve. For more information, see WS Tip 100-102.
3. Work-Factor Learning curves (tables) for production lines. Work-Factor Learning standards measure the elapsed time for a group of workers (or an individual worker*)) to reach a normal production pace at 60 Bdx or 100% and the relative efficiency during this period. These curves apply to both powerized conveyor lines and to production on roller lines and on push-along and pull-along lines; the tempo or performance of the task time is 75 Bdx or 125%.
*) From the work of Van Daatselaar c.s. it was concluded that “the shape of the learning curves for individual work and for group work on a line, was almost similar”, resulting into one universal learning curve.
“Learning-in” as used here, relates to the necessary time and effort of experienced operators to learn to carry out a specific task. This specific task however belongs to the overall and general kind of work inwhich the operators were experienced. This does not apply for the education and training of unexperienced operators. In general the latter is called Functional Training.
Work-Factor Learning does not use any formulae, but uses tables. The Work-Factor tables consist of a table set for:
1. The number of operators in a group, ranging from 2 to 50, and
2. Cycle time per station (piece), ranging from 0,1 min till 10,5 min at select time pace (between T75 Bdx (125%) and T80 Bdx (133%))
A Work-Factor Learning Table provides the following information:
1a. Pieces produced or series to be produced (in classes from 1 till Run Out)
1b. Number of pieces per class (from 5 till 200)
2. Average unit time per piece, T60 Bdx
3. Average % efficiency
4. Total accumulated unit time, T60 Bdx
5. Total accumulated excess unit time, T60 Bdx.
Partial Learning applies to situations in which
1. The same assembly was partially or completely learned in the past.
2. A similar assembly was partially or completely learned in the past.
3. New experienced operators were added to the group or line.
The (total) time for partial learning will vary with the following:
1. Time lapse between two series of the same products.
2. The amount of learning curve completed on the previous run with similar or the same operations.
3. The amount of work that is new, in case of a new assembly or new operators.
Time lapse between two series with same products and percentage of learning curve already completed.
The longer the time lapse between runs of the same unit, the less will be retained. If the time lapse is long enough, the job will be completely forgotten and complete learning will be required again.
Likewise, more is retained on jobs which were learned 100% than on those jobs which learning was only partly completed.
Another factor which may influence learning time is model change. Operators that were fully learned-in on the last model or type, will need less time to learn the renewed model, than those operators who were not fully learned-in.
Also in these cases we may use the WF-tables. The application is the same as for time lapse between series. For more information, see WS Tips 104-109.
Based on the theory of Wright and De Jong, the Work-Study Foundation has developped an Excell program with which the course of a learning-in process may be estimated and followed simply from T0 Bdx (0%) till T80 Bdx (133%), see WS Tip 48.
Based on the formulae of Van Daatslaar and Hogendijk, the Work-Study Foundation has developped an Excell program, following B. Potse, with which the course of a learning-in process may be approached and followed simlpy from T0 Bdx (0%) till T80 Bdx (133%), see WS Tip 103.
The Work-Study Foundation / Work-Factor Council possesses a copy of the text of the original edition of "Use of Work-Factor Learning allowances” of the “Work-Factor Company”. With these tables the course of the learning-in process can be estimated and followed from about T10 Bdx (16%) till T60 Bdx (100%), see also WS Tip 104.
These are very handy instruments to coach operators effectively towards the desired routine and performance level. For small series, where the series are too small for operators to get fully learned-in, these tables may be used to calculate the small series effect for calculation and planning purposes. For a brief comparison between the above mentioned learning curves, see WS Tip 110.
1 day = 7 working hours
In about 30 working days, under guiding supervision and planned training, a worker may acquire full factory tempo.