What is numerical control (NC) and what components traditionally comprised NC sy
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Question
What is numerical control (NC) and what components traditionally comprised NC system? What are four objectives of numerical control? What advantages does numerical control offer over manual methods? What is a computer numerical control (CNC) machine? What improvements do today's modern CNC machines offer over traditional NC machines? What is meant by the terms direct numerical control and distributive numerical control? Name four devices for storing and inputting CNC programs. What advantages do flash drives offer over other types of storage media? What is binary code? Name three advantages offered by machining centers. Describe the financial rewards of CNC investment. What is estimated by payback period? What is estimated by return on investment (ROI)?Explanation / Answer
Traditionally, NC systems have been composed of the following components:
Tape punch: converts written instructions into a corresponding hole pattern. The hole pattern is punched into tape which is passed through the tape punch. Much older units used a typewriter device called a Flexowriter, and later devices included a microcomputer coupled with a tape punch unit.
Tape reader: reads the hole pattern on the tape and converts the pattern to a corresponding electrical signal code.
Controller: receives the electrical signal code from the tape reader and subsequently causes the NC machine to respond.
NC machine: responds to programmed signals from the controller. Accordingly, the machine executes the required motions to manufacture a part (spindle rotation on/off, table and or spindle movement along programmed axis directions, etc.).
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1.3 NC systems offer some advantages over manual methods:
1. Better control of tool motions under optimum cutting conditions.
2. Improved part quality and repeatability.
3. Reduced tooling costs, tool wear, and job setup time.
4. Reduced time to manufacture parts.
5. Reduced scrap.
6. Better production planning and placement of machining operations in the hands of engineering.
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1.4 CNC refers to a system that has a local computer to store all required numerical data. While CNC was used to enhance tapes for a while, they eventually allowed the use of other storage media, magnetic tapes and hard disks. The advantages of CNC systems include but are not limited to the possibility to store and execute a number of large programs (especially if a three or more dimensional machining of complex shapes is considered), to allow editing of programs, to execute cycles of machining commands.
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1.5 ADVANTAGES OF CNC COMPARED WITH NC
1. CNC opens up new possibilities and advantages not offered by older NC machines. 1. Reduction in the hardware necessary to add a machine function. New functions can be programmed into the MCU as software.
2. The CNC program can be written, stored, and executed directly at the CNC machine. 3. Any portion of an entered CNC program can be played back and edited at will. Tool motions can be electronically displayed upon playback. 4. Many different CNC programs can be stored in the MCU.
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1.6 Direct numerical control:
Several CNC machines can be linked together to a main computer. Programs written via the main computer can be downloaded to any CNC machine in the network. This is known as direct numerical control or DNC.
Distributive numerical control system:
Several DNC systems can also be networked to form a large distributive numerical control system.
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1.7 SPECIAL REQUIREMENTS FOR UTILIZING CNC
CNC machines can dramatically boost productivity. However, can only ensure such gains by first addressing several critical issues, such as the following:
1. Sufficient capital must be allocated for purchasing quality CNC equipment.
2. CNC equipment must be maintained on a regular basis by obtaining a full-service contract or by hiring an in-house technician.
3. Personnel must be thoroughly trained in the operation of CNC machines. In particular, many jobs require setups for machining parts to comply with tolerances of form and function .
4. Careful production planning must be studied because the hourly cost of operation of a CNC machine is usually higher than that for conventional machine.
1.10 Binary code is a coding system that uses the binary digits 0 and 1 to represent a letter,digit or other character in a computer or in other electronic device.
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1.12 FINANCIAL REWARDS OF CNC INVESTMENT
Investors are encouraged to look to the CNC machine tool as a production solution with the following savings benefits:
1. Savings in direct labor. One CNC machine’s output is commonly equivalent to that of several conventional machines.
2. Savings in operator training expenses.
3. Savings in shop supervisory costs.
4. Savings due to tighter, more predictable production scheduling.
5. Savings in real estate, since fewer CNC machines are needed.
6. Savings in power consumption, since CNC machines produce parts with a minimum of motor idle time.
7. Savings from improved cost estimation and pricing.
8. Savings due to the elimination of construction of precision jigs, the reduced need for special fixtures, and reduced maintenance and storage costs of these items.
9. Savings in tool engineering/design and documentation. The CNC’s machining capability eliminates the need for special form tools, special boring bars, special thread cutters, etc.
10. Reduced inspection time due to the CNC machine’s ability to produce parts with superior accuracy and repeatibility. In many cases, only spot-checking of critical areas is necessary without loss of machine time.
1.13 a.
The payback period calculation estimates the number of years required to recover the net cost of the CNC machine tool.
Payback period = Net cost of CNC – Net cost of CNC * Tax credit
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Savings – Savings * Tax Rate + yearly Depreciation of CNC * Tax Rate
b.Using Return on Investment (ROI) to Estimate Investment Efficiency The ROI calculation predicts what percent of the net cost of the CNC will be recovered each year. The ROI calculation accounts for the useful life of the CNC machine tool.
ROI= Average yearly savings – Net cost of CNC / Years of life
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Net cost of CNC
Iam facing some problem to upload a diagram for answer 1.6.
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