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Lesson 71 of Industrial Engineering ONLINE Course.
Chapter 10 Halevi
https://books.google.co.in/books?id=tcHxCAAAQBAJ - Preview
How to Select a Machine for the Job
1 Parameters to Consider
Consider the size of the workpiece and its accuracy demands and estimate the required parameters, especially the power.
2 Optimization Strategy Two Phase Method
In the first phase, a theoretical process is generated by considering all technical constraints. For each individual operation, the parameters have been already defined; depth of cut, feed rate and cutting speed.
In the second phase, the theoretical operations are transformed from available facilities point of view. Now the operation is specified to comply with the available machine specification.
2.1 Definition of the combinatorial problem
2.2 Mathematical definition of the process planning problem
2.3 Solving the problem by dynamic programming procedure
3 Machine Constraints - Constructing the Operation Machine Matrix
3.1 Power and force adjustment
Power is a linear function of cutting speed and cutting forces.
Cutting force is a function of feed and depth of cut.
We can calculate the power required to do the job in minimum time subject to technological constraints. If power of the available machine is less, we have to modify cutting parameters.
It is more profitable to reduce cutting speed.
The power adjustment guideline:
If the power has to be reduced by less than 50%.
1. Reduce the cutting speed to its lowest value.
2. Reduce the feed to lower limit.
3. Reduce the depth of cut, take more passes and adjust feed upward as possible.
3.2 Maximum depth of cut constraint
Each machine has d.o.c. constraint. A d.o.c above this value will result in chatter. So d.o.c has to be reduced below this value and more cuts are to be taken.
3.3 Maximum torque constraints
Torque is obtained by multiplication of cutting force by radius of part or tool. Hence adjustment has to be done appropriately.
3.4 Machine accuracy constraint
Old machines may be used for roughing operations and finish cuts are taken better machines to achieve the required accuracy.
3.5 Spindle bore constraint
If spindle bore is less than the part diameter, the type of holding the work piece will be different from chucking. The allowable bending forces are to be calculated and cutting conditions are to be modified.
3. 6 Time and cost conversion
The optimization criterion can be either maximum production or minimum cost.
4 Preliminary Machine Selection
4.1 First step in machine selection
Selection based on type of machine and its physical dimension.
For round symmetrical work a lathe machine is required. In the first step exclude machines which cannot do the job.
4.2 Second step
Exclude machines who do not have even the minimum power to run a cutting pass on the job.
4.3 Third step in machine selection
In the third step calculate the time require to machine the part of cost incurred in doing the job.
5 Matrix Solution
A matrix is developed with operations as rows and machines that can be used as columns. The time taken is put in each cell.
51 Single machine solution
If the total of operations times on a single machine is less than than the total of the minimum for each machine plus transfer time, single machine solution may be selected.
52 General matrix solution
General matrix solution is required when multiple machines are to be used to complete the job. The dynamic programming method is used for it.
5.2.1 Upward phase
5.2.2 Downward phase
5.2.3 Complementary phase
6. Conclusion
We’re constantly evaluating the best equipment meant to provide the best quality product and the safest way possible to get it to our customers.”
SSP Fittings Corp. in Twinsburg, Ohio., APR 06, 2020
Selection of products and markets to be served is part of business strategy. The feasibility of production is considered in strategy making. But after finalizing the product portfolio, an initial process plan for each component of the product has to be prepared. Based on the process plans, equipments that are used in multiple processes are to be selected. After machine buying decisions are finalized and details of machines are known, detailed process plans that use these machines and produce the components are to be prepared.
Updated 21.9.2023, 11 August 2021, 29 Dec 2020
First 20 July 2020
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