Tài liệu Wts_7_compare_estimate

Comparing and Estimating Work and Time Studies Vietnamese German University Dr.-Ing. Marlene Helfert 2016 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 1 Comparing and estimating Contents Comparing and estimating Methods of comparing and estimating Procedure of comparing and estimating Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 2 Comparing and estimating Comparing and estimating Method of work data determination Can lead to sufficiently accurate results when other, more precise values are not available, e.g. in work situations where the application of the time recording or other data acquisition methods is too costly or impossible due to short notice Procedure The work situations in question are compared with already known ones and their times are estimated with appropriate adjustments REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 3 Comparing and estimating Comparing Juxtaposition of facts to determine differences or similarities The time difference between the same or similar process sections, is taken into account by increasing or reducing the available values. These increases and reductions can be determined with time studies, using target times or by estimating. Estimating Approximate determination of quantitative data The target time for the process sections is determined by memory or experience: An expert estimates how much time is needed for the execution of this work REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 4 Comparing and estimating Before estimating comes comparing Estimating without comparing corresponds to an estimate without any benchmark, which does generally not result in sufficiently accurate values Even in supposedly completely new situations, there are benchmarks, experiences, etc. as a guide when estimating REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 5 Comparing and estimating Human perception of time Estimating is always subjective, because it depends on the person guessing and his or her experience and knowledge. REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 6 Comparing and estimating Human perception of time Man has no inherent “sense of time” Sense of time depends on experience, that is affected by the number and type of events that we experienced within a certain time We can estimate time periods only by comparison Setup times are usually overestimated Set-up provides a relatively high level of experience and content variety and therefore appears often longer Times for scheduled operations with a high proportion of monitoring and workflow-related interruption times are usually understated Such processes have a low content of experience and offer little variety REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 7 Comparing and estimating Comparison of work pieces In practice, work pieces, which are processed by the same or similar work processes, are juxtaposed and compared. By comparison of the shape, the dimensions and the material of the to be produced work piece with already made similar work objects, the same or different process sections can be determined. REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 8 Methods of comparing and estimating Methods of comparing and estimating Summary comparing and estimating Subdivided comparing and estimating Interval estimating REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 9 Methods of comparing and estimating Summary comparing and estimating Deals only with the entire process as a whole: As an overall process, e.g. the production of a cabinet door is understood. It takes 72 seconds to mount a trolley with four wheels. How long will it take to produce a trolley with only three wheels? REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 10 Methods of comparing and estimating Subdivided comparing and estimating Combines the estimation with the analytical approach of the work process breakdown into smaller process sections Procedure Divide the entire process into manageable sections Estimate the times for each of these sections Add the individual times to a total time Advantages More accurate results In short process sections the influence factors are more evident than in longer ones For smaller process sections, comparative data for verification can be more easily found Estimation errors partly balance each other: The estimation error decreases with the number of the estimated values REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 11 Methods of comparing and estimating Subdivided comparing and estimating Lay frame on the table and put 4 wheel frames on frame 8 sec Mount wheel 1 12 sec Mount wheel 2 12 sec Mount wheel 3 12 sec Mount wheel 4 12 sec Bring trolley to storage 16 sec Please use subdivided comparing to assess how many seconds will be needed to produce a threewheel-trolley! Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 12 Methods of comparing and estimating Interval estimate Instead of point estimates (e.g. "It takes 12 minutes.") experts can also carry out estimations in the form of interval estimates (e.g. "It takes between 10 and 15 minutes.") The average value of the time class which has been indicated by the expert is used as an estimate Interval time catalogues Base of interval estimates Consist of time classes whose margins increase by a certain law. Each class has: A time class lower limit A time class upper limit A time class mean DMTM 2016 REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 13 Procedure of comparing and estimating 1 Describe task, define usage of data 2 Search similar work piece in comparison documents 3 Compare execution conditions 4 Examine deviations of work pieces 5 Examine deviations of processes 6 Determine times for additional or omitted process sections 7 Determine and add allowances and recovery supplements 8 Confirm and use target time REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 14 Procedure of comparing and estimating Work system description Accuracy is defined by usage 1 Describe task, define usage of data 2 Search similar work piece in comparison documents 3 Compare execution conditions 4 Examine deviations of work pieces 5 Examine deviations of processes 6 Determine times for additional or omitted process sections 7 Determine and add allowances and recovery supplements 8 Confirm and use target time REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 15 Procedure of comparing and estimating From comparison documents, e.g. drawings, work schedules, time classes catalogue 1 Describe task, define usage of data 2 Search similar work piece in comparison documents 3 Compare execution conditions 4 Examine deviations of work pieces 5 Examine deviations of processes 6 Determine times for additional or omitted process sections 7 Determine and add allowances and recovery supplements 8 Confirm and use target time A sufficiently large number of comparable process elements and times for similar work tasks, workpieces, work procedures and working methods is needed. The workflow needs to be adequately described REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 16 Procedure of comparing and estimating E.g. frequency of occurrence, material resources to use 1 Describe task, define usage of data 2 Search similar work piece in comparison documents 3 Compare execution conditions 4 Examine deviations of work pieces 5 Examine deviations of processes 6 Determine times for additional or omitted process sections 7 Determine and add allowances and recovery supplements 8 Confirm and use target time Important  Production technologies and lot sizes are known for both work items  Equipment used for both work objects is comparable  Material is known and can be REFA 2013 differentiated Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 17 Procedure of comparing and estimating 1 Describe task, define usage of data 2 Search similar work piece in comparison documents 3 Compare execution conditions 4 Examine deviations of work pieces 5 Examine deviations of processes 6 Determine times for additional or omitted process sections 7 Determine and add allowances and recovery supplements 8 Confirm and use target time To be compared processes need to be defined and described. Differences must be clarified, e.g. dimensions or shape of the work object REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 18 Procedure of comparing and estimating Comparison shows similarities and differences:  Are all process sections of the known work still needed?  Will new process elements be added?  Will process sections change? 1 Describe task, define usage of data 2 Search similar work piece in comparison documents 3 Compare execution conditions 4 Examine deviations of work pieces 5 Examine deviations of processes 6 Determine times for additional or omitted process sections 7 Determine and add allowances and recovery supplements 8 Confirm and use target time Time needed for each process section can be estimated or calculated by taking into account the REFA 2013 influence factors Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 19 Procedure of comparing and estimating 1 Describe task, define usage of data 2 Search similar work piece in comparison documents 3 Compare execution conditions 4 Examine deviations of work pieces 5 Examine deviations of processes 6 Determine times for additional or omitted process sections 7 Determine and add allowances and recovery supplements 8 Confirm and use target time Estimate the time required for additional and omitted process sections by comparison with known values, • e.g. standard time elements • experience • time studies for individual process sections and summarize values REFA 2013 Dr.-Ing. Marlene Helfert | Work and Time Studies | 2016 | 20