Idea Transcript
THE INTERNATIONAL UNIVERSITY (IU) Department of Industrial System Engineering
Course IS017IU: Work Design & Ergonomics
MIDTERM EXAMINATION Duration: 120 minutes
WORK DESIGN AND ERGONOMICS Head of ISE Department
Lecturer:
Student ID:
Date: Mar.19, 2013
Assoc Prof. Ho Thanh Phong
Ho Trung Thao
Name:
INSTRUCTIONS: 1. This is an open book examination. 2. Calculator and dictionary are allowed. Student takes 2 decimal digits in calculation. 3. Laptop, mobile phone, discussion and materials transfer are strictly prohibited. 4. There are two parts in this exam. Students do Part I in the question paper, Part II in the answer paper Total pages:
06
(including this page)
PART I: MULTIPLE CHOICE QUESTIONS (20%): There are 10 multiple-choice problems. Please circle the correct choice at each problem number. Each problem is worth for 2 points with a total of 20 points. 1.
Henry Ford is noted for his contributions to a. standardization of parts b. statistical quality control c. assembly line operations d. scientific management
2.
Gibson Valves produces cast bronze valves on an assembly line. If 1600 valves are produced in an 8-hour shift, the productivity of the line is a. 2 valves/hr b. 40 valves/hr c. 80 valves/hr d. 200 valves/hr
3.
Gibson Valves produces cast bronze valves on an assembly line, currently producing 1600 valves each 8hour shift. If the production is increased to 2400 valves each 8-hour shift, the productivity will increase by a. 10% b. 25% c. 40% d. 50%
4.
The Dulac Box plant produces 500 cypress packing boxes in two 10-hour shifts. What is the productivity of the plant? a. 25 boxes/hr b. 50 boxes/hr c. 5000 boxes/hr d. None of the above
Work Design & Ergonomics – Midterm Exam 1
THE INTERNATIONAL UNIVERSITY (IU) Department of Industrial System Engineering
Course IS017IU: Work Design & Ergonomics
5.
The Dulac Box plant produces 500 cypress packing boxes in two 10-hour shifts. Due to higher demand, they have decided to operate three 8-hour shifts instead. They are now able to produce 600 boxes per day. What has happened to production? a. It has increase by 50 sets/shift b. It has increase by 37.5 sets/shift c. It has increase by 20% d. It has increase by 9.1%
6.
The total of all outputs produced by the transformation process divided by the total of the inputs is a. utilization b. greater in manufacturing than in services c. defined only for manufacturing firms d. productivity
7.
Productivity can be improved by a. Increasing inputs while holding outputs b. Decreasing outputs while holding inputs steady c. Increasing inputs and outputs in the same proportion d. Decreasing inputs while holding outputs steady
8.
Method analysis focus on a. The raw materials that are consumed in performing a task b. Reducing the number of steps required to perform a task c. The design of the machines used to perform a task d. How a task is accomplished.
9.
A flow diagram in work study is a. used to examine the ergonomics of a job. b. a chart depicting right- and left-hand motions. c. used to analyze the movement of people or materials. d. a way of improving utilization of an operator and a machine.
10.
One advantage of work sampling over time study method is a. it divides work elements more completely b. timing devices are used to eliminate bias c. the studies must be done in one uninterrupted block of time, so there is no delay in obtaining results. d. it is less expensive.
PART II: WRITING (80%) Question 1 (20 pts) The marketing research department for the Stitch Clothing Company has determined that 22% of the items stocked account for 70% of the dollar sales. A typical outlet store carries 1000 items. The items accounting for the top 60% of sales are replenished from the company’s distribution center. The rest are shipped directly from the supplier (manufacturer) to the stores. How many items are represented by the top 60%? Solution: (10 pts) A = x(1-y)/(y-x) = 0.22(1-0.70)/(0.70-0.22) = 0.1375 (5 pts) For y = 60% = 0.60, x = yA/(1 + A – y) x = 0. 60 (0. 1375)/(1 + 0. 1375– 0. 60) = 0.1535 = 15.35% (5pts) Out of 1000 items, this represents about 154 of the items.
Work Design & Ergonomics – Midterm Exam 2
THE INTERNATIONAL UNIVERSITY (IU) Department of Industrial System Engineering
Course IS017IU: Work Design & Ergonomics
Question 2 (20 pts) A foundry uses the following steps in its procedure for high production of investment casting process: (1) The first step is to produce wax patterns by injection molding. (2) The wax patterns are transported to an assembly work area where they are manually assembled to a wax sprue forming a pattern tree. The entire tree is made of wax. (3) The pattern tree is moved to a separate room where the tree is coated with a thin layer of refractory material. (4) In the same room, the tree is coated with success layers of refractory material to make it a rigid structure that will become the mold for casting. (5) The tree is moved to a furnace room, where it is held in an inverted position and heated to melt the wax out of the mold cavities. With the wax removed, the rigid structure is now a multiple-cavity mold with runners leading to each cavity from the sprue cavity. (6) In the same furnace room, the mold is now heated to a high temperature to ensure that all contaminants are removed from the mold. (7) With the mold still heated at an elevated temperature and in an upright orientation, molten metal is poured into the sprue and flows through the runners to each cavity. (8) After cooling and solidification of the metal, the assemblage is moved to a finishing room, where the mold is broken away from the cast metal and the parts are separated from the runners and sprue. (a) Develop the flow process chart for this casting process (10 pts). (b) Based on your flow process chart, what are some changes in the investment casting procedure that you would recommend? (10 pts) Solution: (a) (10 pts) Flow process chart. No times or distances are included. The application of the flow process chart analysis for this problem is somewhat unusual because the materials being processed change several times during the sequence. The starting material consists of wax patterns, which are used to fabricate the mold for the casting operation. Finally, the mold is used to produce investment castings of an unspecified metal. Date: XX/xx/2XXX Analyst: MPG Job: Investment casting
Flow Process Chart Approval:
Page ___ of ____ Summary of Activities
Part No:
Material: Several materials involved Description: Multiple steps in investment casting sequence.
Activity (symbols)
Count
Operation (○,O) Inspection (□, I)
8
Moves (, M)
4
Delays (Ⅾ, D)
2
Time
Distances
0
Storages (∇, S) Seq. Activity description 1 Injection molding of wax patterns 2 Allow patterns to cool 3 Move patterns to assembly work area Assemble patterns to sprue for pattern 4 tree 5 Move pattern tree to refractory room Coat pattern tree with refractory 6 material 7 Coat tree with refractory multiple times 8 Move tree to furnace room 9 Invert pattern tree and heat to melt wax
Symbol Time Distance Analysis notes O D M O M O O M O
Work Design & Ergonomics – Midterm Exam 3
THE INTERNATIONAL UNIVERSITY (IU) Department of Industrial System Engineering
10 11 12 13 14
Reheat tree to remove contaminants Position mold upright, pour molten metal Allow time for cooling and solidification Move tree and casting to finishing room Break mold and separate sprue from casting
Course IS017IU: Work Design & Ergonomics
O O D M O
(b) (10 pts) Possible recommendations include the following: 1.
Change the casting process from investment casting to die casting, which is a much simpler process consisting of fewer steps. Functional requirements of the part may argue against this recommendation.
2.
Set up all processing steps in one room to eliminate moves between separate rooms.
3.
In addition to all steps being carried out in one room, could a work cell be designed to provide a more sequential work flow between operations.
4.
Where are the inspections? No inspection operations are listed among the investment casting steps. For a rather complex sequence, inspections should be included to make sure that further processing is not performed using defective patterns or molds.
Question 3 (20 pts) The plumber, kneeling on the floor next to the sink, reached for the monkey wrench in his tool kit, pushing around a few other tools before grasping the wrench and picking it up. He then moved it to the pipe beneath the sink, positioned it onto the pipe fitting, and turned the fitting one-third of a rotation to loosen it. Once loose, he put down the wrench and continued turning by hand. Four rotations were required before the fitting was free of the mating pipe threads, during which he had to grasp and regrasp the fitting ten times due to the limited rotation ability of his own wrist. Write a list of the therbligs that comprise this motion sequence and label each basic motion with a brief description. Solution: (Deduct 1.5 pts for each missed motion element) List of therbligs with descriptions. We assume the plumber is right-handed and the dominant motion elements are performed with the right hand. The sequence begins with the plumber kneeling in front of the sink. Seq. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Therblig symbol TE Sh St G TL PP U TL RL TE G DA
Therblig name
Description
Transport empty Search Select Grasp Transport loaded Pre-position Use Transport loaded Release load Transport empty Grasp Disassemble
Reach for monkey wrench Search for monkey wrench in tool kit Select the monkey wrench Grasp the monkey wrench Move wrench to pipe beneath sink Position wrench onto pipe fitting Rotate wrench to loosen pipe fitting Move wrench away from pipe fitting Put down wrench Move hand back to pipe fitting Grasp pipe fitting Turn pipe fitting by hand to separate
Work Design & Ergonomics – Midterm Exam 4
THE INTERNATIONAL UNIVERSITY (IU) Department of Industrial System Engineering
Course IS017IU: Work Design & Ergonomics
Question 4 (20 pts) The foreman in the welding department wanted to know what value of allowance to use for a particular section of the shop. A work sampling study was authorized. Only two activity categories were considered: (1) welding and other productive work, and (2) personal time, rest breaks, and delays. Over a four-week period (40 hours/week), 125 observations were made at random times. Each observation captured the category of activity of each of eight welders in the shop section of interest. Results indicated that category 2 constituted 33% of the total observations. (a) Define the limits of a 96% confidence interval for activity 2. (10 pts) (b) If a total of 725 work units were produced during the 4 weeks, and all category 1 activity was devoted to producing these units, what was the average time spent on each unit? (10 pts) Solution: (a) ( 2 pts) With 8 welders and 125 observations of each welder, the total number of observations n = 125(8) = 1000 observations. (2 pts) For the 96% confidence level, z α / 2 = 2.05.
0.33(0.67) = 0.01487 1000 (2 pts) ˆp 2 – z α / 2 σˆ p = 0.33 – 2.05(0.01487) = 0.33 – 0.0305 = 0.2995 (2 pts) σˆ p =
(2 pts) ˆp 2 + z α / 2 σˆ p = 0.33 + 2.05(0.01487) = 0.33 + 0.0305 = 0.3605 (b) Given Q = 725 work units (2 pts) ˆp1 = 1 – 0.33 = 0.67 (4 pts) Total time TT = (4 weeks)(40 hr/week)(8 welders) = 1280 hr (4 pts) Tc = 0.67(1280)/725 = 1.183 hr/work unit
GOOD LUCK
Work Design & Ergonomics – Midterm Exam 5