Process Planning and Product Costing Assignment

Haramaya University
Haramaya Institute of Technology (HiT)
Department of Mechanical Engineering

Process Planning and Product Costing (MEng 5223) Assignment

Target Group: 5th year Mechanical Engineering Students (Manufacturing Engineering Stream)

Maximum Mark: 25%

Submission Date: on the course final exam day

1. A component can be produced with equal facility using either a numerically controlled milling
machine, or an operator controlled milling machine (conventional machine).
A. Which process should be chosen for minimum costs if two components only are
required? (Assume no special tooling for the conventional machine and hence no fixed
costs, but that it is a tool room universal milling machine with high overheads.).
B. Which process should be chosen for minimum costs if a batch of 100 components is
required? (Assume special tooling such as fixture and gauges are required for the
conventional machine, which is a plain milling machine on a production line).
The following cost information is known.
NOTE: Show all your steps clearly
Situation A Situation B
Costs NC Machine Conventional NC Machine Conventional
Machine Machine
Fixed Cost (Birr) 70.00 - 88 320
Labor/Component (Birr) 2.00 11.50 2.00 0.50
Material/Component (Birr) 1.50 1.50 1.50 1.50
Overhead/Component (Birr) 4.00 40.00 4.00 3.50

2. A component can be produced with equal ease on either a capstan lathe or on a single spindle
cam operated automatic lathe.
A. Find the break-even quantity QE if the following information is known.
B. If the batch size to be manufactured is equal to 500 components, which machine is
economical to use?

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 Process Planning and Product Costing Assignment

Capstan Lathe Automatic Lathe

Tool Cost 50 50
Cost of Cams - 220
Material cost/Component 3.00 3.00
Operating labor cost Birr 3.50/hour Birr 1.75/hour
Cycle time/Component 7 minutes 1 minute
Setting up labor cost Birr 4/hour Birr 4/hour
Setting up time 1 hour and 15 minutes 8 hours and 10 minutes
Machine overheads 300 % of Operating labor cost 1000 % of Operating labor cost
(setting and operating)

3. A cast iron component is to be manufactured as per Fig. 1. Estimate the selling price per piece from
the following data :
 Density of material = 7.5 gms/cc
 Cost of molten metal at cupola spout = Br. 20 per kg
 Process scrap = 20 percent of net weight
 Scrap return value = Br. 6 per kg
 Administrative overheads = Br. 30 per hour
 Sales overheads = 20 percent of factory cost
 Profit = 20 percent of factory cost
Other expenditure are:
Operation Time (min) Labor cost /hr Shop overheads/hr
(Br.) (Br.)
Molding and pouring 15 28 55
Shot blasting 5 9 35
Fettling 6 9 35

The component shown is obtained after machining the casting. The pattern which costs Br. 1,500 can
produce 1,000 pieces before being scrapped. The machining allowance is to be taken as 2 mm on each
side.

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 Process Planning and Product Costing Assignment

All dimensions are in mm

Figure 1: (a) Component as cast, (b) Finished component

4. Calculate the machining time required to produce one piece of the component shown in Fig. 2.
starting from 25 mm diameter bar. The following data are available:
 Material: Mild Steel
 Cutting Tool to be used: HSS Tool
 Maximum Depth of cut: 2 mm
 For both 25 to 15 mm dia. and 15 to 10 mm dia., finish turning of 1 mm is considered.

All dimensions are in mm

Figure 2

5. Work out the welding cost for a cylindrical boiler drum 2.5 m × 1 m diameter which is to be made
from 15 mm thick mild steel plates. Both the ends are closed by arc welding of circular plates to
the drum. Cylindrical portion is welded along the longitudinal seam and welding is done both in
inner and outer sides. Assume the following data:

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 Process Planning and Product Costing Assignment

Description Amount
Rate of welding 2 meters per hour on inner side and
2.5 meters per hour on outer side
Length of electrodes required 1.5 m/meter of weld length
Cost of electrode Br. 0.60 per meter
Power consumption 4 kWh/meter of weld
Power charges Br. 3/kWh
Labor charges Br. 40 per hour
Other overheads 200% of prime cost
Discarded electrodes 5%
Fatigue and setting up time 6% of welding time

6. Calculate the cost of welding two plates 200 mm × 100 mm × 8 mm thick to obtain a piece 200
mm × 200 mm × 8 mm approximately using rightward welding technique Fig. 3. The following
data is available:
 Cost of filler material = Br. 60 per kg
 Cost of oxygen = Br. 700 per 100 cu meters
 Cost of acetylene = Br. 700 per 100 cu meters
 Consumption of oxygen = 0.70 cu m/hr
 Consumption of acetylene = 0.70 cu m/hr
 Diameter of filler rod = 4 mm
 Density of filler material = 7.2 gms/cc
 Filler rod used per meter of weld = 340 cm
 Speed of welding = 2.4 meter/hr
Labor is paid Br. 20 per hour and overheads may be taken as 100 percent of labor cost.

All dimensions are in mm

Figure 3

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 Process Planning and Product Costing Assignment

7. Calculate the net weight and gross weight for the component shown in Figure 4. Density of
material used is 7.86 gm/cc. Also calculate:
A. Length of 14 mm dia. bar required to forge one component.
B. Cost of forging/piece if :
 Material cost = Br. 80 per kg
 Labor cost = Br. 5 per piece
 Overheads = 150 percent of labor cost

All dimensions are in mm

Figure 4

8. A T-slot is to be cut in a C.I. slab as shown in Figure 5. Estimate the machining time. Take cutting
speed 25 m/min, feed is 0.25 mm/rev. Dia. of cutter for channel milling is 80 mm.

All dimensions are in mm

Figure 5

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 Process Planning and Product Costing Assignment

9. Calculate the total cost of producing the CI (Cast Iron) cap shown in Figure 4, from the following
data :
 Cost of molten iron at cupola spout = Br. 30 per kg
 Process scrap = 17 percent of net wt. of casting
 Process scrap return value = Br. 5 per kg
 Administrative overhead charges = Br. 2 per kg of metal poured.
 Density of material used = 7.2 gms/cc

The other expenditure details are:

All money currencies in Birr

All dimensions are in mm

Figure 6

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 Process Planning and Product Costing Assignment

10. Calculate the cost of forging a crank shaft as shown in Fig. 7. The forging is to be made out of a bar
stock of 50 mm and following data is available :
 Material Price = Br. 75 per kg
 Direct labour charges = Br. 20 per piece
 Overhead charges = 150 percent of material cost
 Density of material = 7.5 gms/cc
 Losses = 28 percent of net weight
All dimensions are in mm

Figure 7: Crank Shaft

11. Estimate the cost of manufacturing high carbon steel spanner (Fig. 8) to be made by die forging.
The following data is available :
 Material Price = Br. 75 per kg
 Direct labour charges = Br. 20 per piece
 Overhead charges = 150 percent of material cost
 Density of material = 7.5 gms/cc
 Losses = 28 percent of net weight

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 Process Planning and Product Costing Assignment

Figure 8: Spanner

TABLES

Table 1: Cutting Speeds and Feed Rates for Lathe Operations

Table 2: Cutting Speeds and Feed Rates for Drilling Operations (Tool Material: HSS)

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 Process Planning and Product Costing Assignment

Table 3: Cutting Speeds and Feed Rates for Shaping, Planning and Slotting Operations

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