Industrial Engineering and Ergonomics

Transcription

1 Industrial Engineering and Ergonomics Exercise Unit 4 Analysis of the time structure of working processes Fall Winter 2015/2016 Univ.-Prof. Dr.-Ing. Dipl.-Wirt.-Ing. Christopher M. Schlick Chair and Institute of Industrial Engineering and Ergonomics Instructor: Dipl.-Ing. Tobias Hellig t.hellig@iaw.rwth-aachen.de

2 Task 1 A bearing surface has to be milled on work pieces in a small batch for each case. In order to improve the efficiency of the production processes, Mr. Schulze from Industrial Engineering carries out an analysis of the actual times of the process. To do so he observes the process and notes single activities of the process. Help Mr. Schulze by matching the activities of the production process in table 1 with the corresponding classes of operations (MH, MN, MZ, etc.). (Use figure 1 as help!) 5-2

3 Outline of processes and procedures related to the working person Figure 1 Primary activity MH Activity MT Secondary activity MN Additional activity MZ On duty MI Interruption inherent to the cycle MA Working person M Off duty ML Interruption of activity MK Interruption due to dysfunction Interruption due to recovery MS ME Plant closed MR Interruption due to personal reasons MP Not identifiable MX 5-3

4 Task 1 No. Activities Class of Operation 1. Read work order and graph 2. Take cutter, clamp cutter and set milling machine 3. Take work piece and clamp work piece 4. Supervise milling and first cut 5. Milling without supervision 6. Unclamp work piece 7. Check the surface quality of the work piece (planned visual inspection) 8. Deposit work piece Unscheduled changing of the cutter, because the surface quality of the work piece has degraded due to abrasion of the cutter Foreman introduces a new colleague to the employee at the milling machine 5-4

5 Task 2 Calculate the work order time allowed for the manufacturing of 300 pieces of steel protective caps, thereby using the REFA time classification based on the working person s behavior. 5-5

6 Task 2 - Time classification for the work order time work order time allowed T Set up time t r time allowed t a = m * t e time per unit t e Set up basic time Set up recovery time Set up additional time basic time recovery time additional time t rg t rer t rv t g t er t v further classification possible activity time waiting time object-related additional time worker-related additional time t t t w t s t p influencable activity time t tb non-influencable activity time t tu 5-6

7 Task 2 - Time classification based on the working person s behavior Task: Production of steel protective caps Input: Blank plates, Drawing-Nr. 026/417 Equipment: 800 t - drawing press Batch size m: 300 pieces Additional time rate z v : 7 % Recovery time t er : min/piece (separate evaluation) No set up recovery time and no set up additional time. No. Operations Target time in min REFA time classification 1 Mount stamping tool in press Test and control press Grasp plate and transport it to press Insert plate into die Operate press with both hands, stamp Remove protective cap from the die Set protective cap down Walk from transporting rig to pallet Dismantle tool 5.00 Procedure for one work cycle (number of units 1) incl. set up the machine 5-7

8 Task 3 - Work Sampling Study In a work sampling study for the optimization of setup time which is to be accomplished by Mr. Mueller, 45 injection molding machines should be included. How many tours are necessary, if a probability of error of at most 5% should form the basis of the result. Please act on the assumption that a total deviation f of 1.5% is not to be exceeded. Hint: Within the last measurement, the setup time had a proportion of 15%. The following is imperative: N f p 100 p N = Total number of necessary annotations p = Expectancy value as percentage f = Desired spread / tolerated error 5-8

9 Workplaces 08:00 08:15 08:30 08:45 09:00 09:15 09:30 09:45 10:00 10:15 10:30 10:45 11:00 11:15 11:30 11:45 12:00 12:15 12:30 12:45 13:00 13:15 13:30 13:45 14:00 14:15 14:30 14:45 15:00 15:15 15:30 15:45 16:00 16:15 16:30 16:45 17:00 Task 4 Four workplaces (A D) in a service providing company are very similar during an 8-hour workday, but conduct totally irregular service activities. The individual activities can be organized into according time types like t P (primary time), t S (secondary time) or t A (additional times). The duration of the occurring activities will be determined with the help of a work sampling frequency (MMH). The procedure is performed in such a way that an observer makes a tour past the workplaces in a particular randomly generated cycle, thereby noting which activity is being conducted by which worker at the time of observation. Accurately estimate the relative proportions (θ P, θ S, θ A ) to one decimal place of the three time types at shift time T = 8h for the four workplaces A D. Time A B C Lunchbreak D Start of the tour t P t S t A Notation End of the tour 5-9

10 Task 4 After the first multi sampling study, the management of the service company is particularly interested in activities that are assigned to the time type primary time t P. Calculate the accuracy f P of the first multi sampling study estimation based on the following values: Total number of notations n = 32 Relative proportion of activities of the primary time θ P = 0.80 Error probability α = 1.0% Use the following formula as a calculating aid. f P = zα/2 θ P (1 θ P ) n The company management is now requiring an accuracy of ± 5% for the primary time estimation f P. How many tours are required to comply with that accuracy? z /2 2 f( x) A 2 z /2 z /2 1 z /2 f ( x) dx x z α/2 S [%] 0,68 50,0 1,00 68,3 1,64 90,0 1,96 95,0 2,00 95,4 2,58 99,0 3,00 99,7 3,29 99,9 statistical statistische confidence Sicherheit level S S 5-10

11 Task 4 How do an increased number of tours during a work sampling frequency (MMH) affect the relative proportions (θ P, θ S, θ A ) of the three time types at shift time T for the total department? 5-11

12 Task 5 The supplier of automotive components KaiserTec intends to reduce its delivery times. The manufacturing head of gearbox shafts has been given the instruction to conduct a work sampling procedure in order to analyze the holding time of production facilities and the work order time of the employees of the manufacturing department. So far, the line manager conducted 16 observation tours. The Table below shows part of the annotations that the manufacturing head took during his observations. Complete the table with the process types of production facilities according to REFA. Use the abbreviations known from the lecture. Workingstation Activities 1 Unscheduled maintenance of CNC-hobbing machine Process type (production facilities) 2 Cut steep on CNC-hobbing machine 3 Deposit workpiece from CNC-turning machine 4 Restart of CNC-hobbing machine 5 Changing of cooling liquid of CNC-turning machine 6 Deep-hole drilling CNC-turning machine 5-12

13 Task 5 The first Table lists all annotations of the first observation tour. The results of observation tours 2-16 are already summarized in the second Table. Complete the second Table by the activities of the first Table and calculate the relative frequencies of the activities related to the working person after 16 tours. Working station Activities Process type (working person) 1 Programming forging press MN 2 Employee fixes work piece in forging press MZ 3 Employee deposits workpiece from CNC-turning machine MN 4 Employee refills cooling liquid of CNC-turning machine MZ 5 Employee starts CNC-turning machine MH 6 Employee monitors milling process on CNC-hobbing machine MH 7 Employee monitors milling process on CNC-turning machine MH 8 Employee makes lavatory break MP 9 Employee discusses schedule with supervisor MH 10 Employee cleans working station MZ Processes related to the working person Primary activity (MH) 84 Secondary activity (MN) 30 Observation tour Rel. Frequencies Ө x Total Total Additional activity (MZ) 25 Interruption due to personal reasons (MP)

14 Task 5 After the general manager examined the results of the work sampling method, the accuracy of the estimation of primary activities during the 16 tours shall be determined by using the given formular. For this, the deviation f H of the relative frequency Ө H must be calculated, assuming a level of significance of α = 0,05. Indicate your result in percentage, rounded to two decimal places. 5-14

15 Task 5 In order to increase the accuracy of estimations, the general manager would like to initiate further tours on the 10 work stations in the manufacturing department of gearbox shafts. Use formular (2.1) to calculate the amount of tours needed to achieve a maximal deviation f H of the relative frequency Ө H of 1.5%. Assume the same level of significance. 5-15