Teachers Recruitment Board Tamilnadu Multiple Choice Questions for Mechanical Engineering
No cutting fluid is used in the following operation:
- Planning and shaping
- Thread rolling
Planning and shaping
In planning and shaping operation, cast iron work piece machined. Graphite in the cast iron acts as a lubricant in itself. But machining cast iron will get you fine powders everywhere that tend to sneak into your machines nooks and corners and get lodged there. The stuff later becomes very difficult to remove especially after mixing up with machine lube or oil.
Which one of the following is not a decision taken during the aggregate production planning stage?
- Scheduling of machines
- Amount of labour to be committed
- Rate at which production should happen
- Inventory to be carried forward
Scheduling of machines
The aggregate planning is particularly useful for organizations that experience seasonal or other fluctuations in demand or capacity. Planners must make decisions on output rates, employment levels and changes, inventory levels and changes, back orders, and subcontracting. So Aggregate production planning is a short term decision making process.
- It is usually possible to
- hire or lay off workers
- increase or decrease number of shifts
- increase / decrease number of working days in a week
- decrease or increase working hours (overtime or under time)
- subcontract work to other firms
- build up or deplete inventory levels
Which of the following is incorrect regarding template in layout design?
- Templates are three dimensional representation of machines (or) equipments
- Templates are virtual picture of layout
- Templates are used for storage areas
- Templates shows the area occupied by machine
Templates are three dimensional representation of machines (or) equipment’s
Two dimensional plan – Templates
Three dimensional plan – Miniature Models
Arrival rate of telephone calls to a telephone book is 9 minutes between two consecutive arrivals and length of the telephone call is assumed to be exponentially distributed with mean 3 minutes. The probability that a person will have to wait:
Here, N and Nq are the number of people in the system and in the queue respectively. Also W and Wq are the waiting time in the system and in the queue respectively. ρ is the ratio of arrival rate to service rate. Also the probabilities can be given as :
where, p is the probability of zero people in the system and pk is the probability of k people in the system.
Arrival rate λ = 1/9 minutes
Service rate μ = 1/3 minutes.
Probability that a person will have to wait
= (1/9)/(1/3) = 0.333
A dummy activity is used in PERT network to describe:
- Precedence relationship
- Necessary time delay
- Resource restriction
- Resource idleness
A CPM/PERT network consists of branches and node. The arrows in between the nodes indicated the precedence relationships between activities. A dummy activity inserted into the network to show a precedence relationship, but it does not represent any actual passage of time.
Slow cooling rate in solidification of casting results in:
- Fine dendrite with large arm spacing
- Coarse dendrite with large arm spacing
- Coarse dendrite with smaller arm spacing
- Fine dendrite with smaller arm spacing
Coarse dendrite with large arm spacing
Solidification mechanism is essential for preventing defects due to shrinkage. During solidification, cast forms develops cohesion and acquires structural characteristics. Since heat loss is more rapid near the mold walls than any other place, the first metal crystallizes called ‘nuclei’. Slow cooling makes the dendrites to grow long whereas fast cooling causes short dendrite growth. So slow cooling results in larger grain structure and fast cooling results in small grain structure in the solidified metal.