Manufacturing Processes

Milling Machines

The milling machine is one of the most versatile machines in the shop. Usually they are used to mill flat surfaces, but they can also be used to machine irregular surfaces. Additionally, the milling machine can be used to drill, bore, cut gears, and produce slots into a workpiece. The milling machine uses a multi-toothed cutter to remove metal from moving stock. There is also a quill feed lever on the mill head to feed the spindle up and down. The bed can also be manually fed in the X, Y, and Z axes. Best practices are to adjust the Z axis first, then Y, then X. When an axis is properly positioned and is no longer to be fed, use the gib locks to lock it in place. It is common for milling machines to have a power feed on one or more axes. Normally, a forward/reverse lever and speed control knob is provided to control the power feed. A power feed can produce a better surface finish than manual feeding because it is smoother. On long cuts, a power feed can reduce operator fatigue.

Safety The following procedures are suggested for the safe operation of a milling machine.

1. Have someone assist you when placing a heavy machine attachment like a rotary table, dividing head, or vise.
2. Always refer to speed and feed tables.
3. Always use cutting tools that are sharp and in good condition.
4. Seat the workpiece against parallel bars or the bottom of the vice using a soft hammer or mallet. Check that the work is firmly held and mounted squarely.
5. Remove the wrench after tightening the vice.
6. Most operations require a FORWARD spindle direction. There may be a few exceptions.
7. Make sure there is enough clearance for all moving parts before starting a cut.
8. Make sure to apply only the amount of feed that is necessary to form a clean chip.
9. Before a drill bit breaks through the backside of the material, ease up on the drilling pressure.
10. Evenly apply and maintain cutting fluids to prevent morphing.
11. Withdraw drill bits frequently when drilling a deep hole. This helps to clear out the chips that may become trapped within the hole.
12. Do not reach near, over, or around a rotating cutter.
13. Do not attempt to clean the machine or part when the spindle is in motion.
14. Stop the machine before attempting to make adjustments or measurements.
15. Use caution when using compressed air to remove chips and shavings. They flying particle may injure you, or those around you.
16. Use a shield or guard for protection against chips.
17. Remove drill bits from the spindle before cleaning to prevent injury.
18. Clean drill bits using a small brush or compressed air.
19. Properly store arbors, milling cutters, collets, adapters, etc., after using them. They can be damaged if not properly stored.
20. Make sure the machine is turned off and clean before leaving the workspace.

Source: LamNgeun Virasak , https://openoregon.pressbooks.pub/manufacturingprocesses45/
This work is licensed under a Creative Commons Attribution 4.0 License.

Lathe Machine

OBJECTIVE

After completing this unit, you should be able to:

• Identify the most important parts of the Lathe and their functions.

• Understand the Lathe safety rules.

• Describe setup a cutting tool for machining.

• Describe mount workpiece in the lathe.

• Explain how to install cutting tool.

• Describe the positioning the tool.

• Describe how to centering the workpiece and tailstock center.

Description

The lathe is a very versatile and important machine to know how to operate. This machine rotates a cylindrical object against a tool that the individual controls. The lathe is the forerunner of all machine tools. The work is held and rotated on its axis while the cutting tool is advanced along the line of a desired cut. The lathe is one of the most versatile machine tools used in industry. With suitable attachments, the lather may be used for turning, tapering, form turning, screw cutting, facing, dulling, boring, spinning, grinding, polishing operation. Cutting operations are performed with a cutting tool fed either parallel or at right angles to the axis of the work. The cutting tool may also be fed at an angle, relative to the axis of the work, for machining taper and angles. On a lathe, the tailstock does not rotate. Instead, the spindle that holds the stock rotates. Collets, centers, three jaw chucks, and other work-holding attachments can all be held in spindle. The tailstock can hold tools for drilling, threading, reaming, or cutting tapers. Additionally, it can support the end of the workpiece using a center and can be adjusted to adapt to different workpiece lengths.

Figure 1. Parts of a lathe

1. Power On/OfF
2. Spindle Forward/Reverse (flip handle up or down)
3. Carriage Handwheel
4. Cross Feed Handwheel
5. Compound Feed Handwheel
6. Carriage/Cross Feed Engage
7. Threading Half Nut
8. Threading Dial
9. Spindle Speed
10. Brake
11. Spindle High/Low Range
12. Thread/Feed Reverse (push in/pull out)
13. Feed Ranges (A, B, C)
14. Feed Ranges (R, S, T)
15. Feed Ranges (V, W, X, Y, Z) - V and Z are settings for threading
16. Gear Box
17. Gear Box Low/High
18. Tailstock
19. Tool Post
20. Toolholder
21. Three - Jaw Chuck
22. DRO (Digital Read Out) Threading/Feed Selector

Drill Press

OBJECTIVE

After completing this unit, you should be able to:

• Identify Drill Press
• Understand the safety rules.
• Describe Tooling to be use.
• Describe Reaming a hole.
• Describe Drilling a hole procedure.
• Describe power feed and hand teed tapping procedure.
• Describe Dressing the Wheel procedures.

Description

Drilling machines, or drill presses, are primarily used to drill or enlarge a cylindrical hole in a workpiece or part. The chief operation performed on the drill press is drilling, but other possible operations include: reaming, countersinking, counterboring, and tapping.

The floor type drill press used in the Student Shop is a very common machine, found in both home and industrial workshops. This style drill press is composed of four major groups of assemblies: the head, table, column, and base.

The head contains the motor and variable speed mechanism used to drive the spindle. The spindle is housed within the quill, which can be moved up or down by either manual or automatic feed. The table is mounted on the column, and is used to support the workpiece. The table may be raised or lowered on the column, depending upon the machining needs. The column is the backbone of the drill press. The head and base are clamped to it, and it serves as a guide for the table.

Safety

1. Be familiar with the location of the start and stop switches.
   
2. The drill press table should be cleared of miscellaneous tools and materials.
   
3. Ensure that all drill bits are sharpened and chucks are in working condition. Any dull drill bits, battered tangs or sockets should not be used.
   
4. Never attempt to remove scraps from the table by hand. Use brushes or other proper tools.
   
5. Never attempt to perform maintenance on the machine without the power cord unplugged.
   
6. Never insert a chuck key into the chuck until the machine has been turned off and stopped completely.
   
7. Belts and pulleys should be guarded at all times. If any are frayed, immediately report to the instructor for replacement.
   
8. All workpieces should be secured by a vise or clamp before starting the machining.
   
9. 9. If the workpiece moves while in the vise or clamp:
   • Do not attempt to hold the workpiece in place by hand.
   • Do not try to tighten the vise or clamp while the machine is turned on.
   • Turn the power off and wait for the machine to stop completely before re-tightening the vise or clamp.
   
10. Use the proper speed settings and drill type for the material to be machined.
    
11. When mounting a drill bit, it should be to the full depth and centered in the chuck.
    
12. Eliminate the possibility of the drill bit hitting the table by using a clearance block and by adjusting the feed stroke.
    
13. Always feed the bit slowly into the workpiece. If the hole to be drilled is deep, draw the bit back often to remove shavings.
    
14. Before leaving the drill press for any amount of time, the power should be turned off and machine should be at a complete stop.
    
15. In any unsafe condition or movement is observed on the drill press, report it to the instructor immediately.
    
16. Leave the drill press cleaned and tidy at all times.

Lean Manufacturing

OBJECTIVE

After completing this unit, you should be able to:

• Apply 5S in any Machine shop.
• Describe Kaizen Concept.
• Describe Implementing Lean Manufacturing.

Lean 5S:

"5S" is a method of workplace organization that consists of five words: Sort, Set in order, Shine, Standardize, and Sustain. All of these words begin with the letter S. These five components describe how to store items and maintain the new order. When making decisions, employees discuss standardization, which will make the work process clear among the workers. By doing this, each employee will feel ownership of the process.

Phase 0: Safety

It is often assumed that a properly executed 5S program will improve workplace safety, but this is false. Safety is not an option; it's a priority.

Phase 1: Sort

Review all items in the workplace, keeping only what is needed.

Phase 2: Straighten

Everything should have a place and be in place. Items should be divided and labeled. Everything should be arranged thoughtfully. Employees should not have to bend over repetitively. Place equipment near where it is used. This step is a part of why lean 5s is not considered "standardized cleanup".

Phase 3: Shine

Make sure that the workplace is clean and neat. By doing this, it will be easier to be aware of where things are and where they should be. After working, clean the workspace and return everything to its former position. Keeping the workplace clean should be integrated into the daily routine.

Phase 4: Standardize

Standardize work procedures and make them consistent. Every worker should be aware of what their responsibilities are when following the first three steps.

Phase 5: Sustain

Assess and maintain the standards. The aforementioned steps should become the new norm in operation. Do not gradually revert to the old ways. When taking part of the new procedure, think of ways to improve. Review the first four steps when new tools or output requirements are presented.

KAIZEN

While the lean 5S process focuses on the removal of waste, Kaizen focuses on the practice of continuous improvement. Like lean 5S, Kaizen identifies three main aspects of the workplace: Muda (wastes), Mura (inconsistencies) and Muri (strain on people & machines). However, the Kaizen step-by-step process is more extensive that the lean 5S process.

The Kaizen process overview:

1. Identify a problem.
2. Form a team.
3. Gather information from internal and external customers, and determine goals for the project.
4. Review the current situation or process.
5. Brainstorm and consider seven possible alternatives.
6. Decide the three best alternatives of the seven.
7. Simulate and evaluate these alternatives before implementation.
8. Present the idea and suggestions to managers.
9. Physically implement the Kaizen results and take account of the effects.

Lean manufacturing improves as time goes one, so it is important to continue education about maintaining standards. It is crucial to change the standards and train workers when presented with new equipment or rules.

LEAN

Think of a maintenance department as serving internal customers: the various departments and workers in the company.

Lean is different from the traditional western, mass production model that relies on economies of scale to create profits. The more you make the cheaper the product will become, the greater the potential profit margin. It is based on predictions of customer needs, or creating customer needs. It has difficulty dealing with unusual changes in demand.

Lean production responds to proven customer demand. Pull processing – the customer pulls production. In a mass system the producer pushes product onto the market, push processing.

Building a long-term culture that focuses on improvement.

Respect for workers better trained and educated, more flexible

Lean is a philosophy that focuses on the following:

1. Meeting customer needs
2. Continuous, gradual improvement
3. Making continuously better products
4. Valuing the input of workers
5. Taking the long term view
6. Eliminating mistakes
7. Eliminating waste

Wastes: using too many resources (materials, time, energy, space, money, human resources, poor instructions)
Wastes:

1. Overproduction
2. Defects
3. Unnecessary processing
4. Waiting (wasting time)
5. Wasting human time and talent
6. Too many steps or moving aroundExcessive transportation
7. Excessive inventory

Lean production includes working with suppliers, sub contractors, and sellers to stream line the whole process.

The goal is that production would flow smoothly avoiding costly starts and stops.

The idea is called just in time "produce only what is needed, when it is needed, and only in the quantity needed." Production process must be flexible and fast.

Inventory = just what you need

In mass production = just in case. Extra supplies and products are stored just in case they are needed.

Terminology:

Process simplification –  a process outside of the flow of production

Defects – the mass production system does inspection at the end of production to catch defects before they are shipped. The problem is that the resources have already been "spent" to make the waste product" Try to prevent problems immediately, as they happen, then prevent them. Inspection during production, at each stage of production.

Safety – hurt time is waste time

Information – need the right information at the right time (too much, too little, too late)

Principles:

Poka-yoke – mistake proof determining the cause of problems and then removing the cause to prevent further errors

Judgment errors – finding problems after the process

Informative inspections – analyzing data from inspections during the process

Source inspections – inspection before the process begins to prevent errors.

MEAN LEAN

One of the terms applied to a simply cost cutting, job cutting interpretation of Lean is Mean Lean. Often modern manager think they are doing lean without understanding the importance of workers and long term relationships.

RELIABILITY CENTERED MAINTENANCE

Reliablity centered maintenance is a system for designing a cost effective maintenance program. It can be a detailed complex, computer, statistically driven, but at its basics it is fairly simple. Its ideas can be applied to designing and operating a PM system, and can also guide your learning as you do maintenance, troubleshooting, repair, and energy work.

These are core principles of RCM. These nine fundamental concepts are:

• Failures happen.
• Not all failures have the same probability
• Not all failures have the same consequences
• Simple components wear out, complex systems break down
• Good maintenance provides required functionality for lowest practicable cost
• Maintenance can only achieve inherent design reliability of the equipment
• Unnecessary maintenance takes resources away from necessary maintenance
• Good maintenance programs undergo continuous improvement.

Maintenance consists of all actions taken to ensure that components, equipment, and systems provide their intended functions when required.

An RCM system is based on answering the following questions:

1. What are the functions and desired standards of performance of the equipment?

2. In what ways can it fail to fulfil its functions? (Which are the most likely failures? How likely is each type of failure? Will the failures be obvious? Can it be a partial failure?)

3. What causes each failure?

4. What happens when each failure occurs? (What is the risk, danger etc.?)

5. In what way does each failure matter? What are the consequences of a full or partial failure?

6. What can be done to predict or prevent each failure? What will it cost to predict or prevent each failure?

7. What should be done if a suitable proactive task cannot be found (default actions) (no task might be available, or it might be too costly for the risk)?

Equipment is studied in the context of where when and how it is being used

All maintenance actions can be classified into one of the following categories:

• Corrective Maintenance – Restore lost or degraded function
• Preventive Maintenance – Minimizes opportunity for function to fail
• Alterative Maintenance – Eliminate unsatisfactory condition by changing system design or use

Within the category of preventive maintenance all tasks accomplished can be described as belonging to one of five (5) major task types:

• Condition Directed – Renew life based on measured condition compared to a standard
• Time Directed – Renew life regardless of condition
• Failure Finding – Determine whether failure has occurred
• Servicing – Add/replenish consumables
• Lubrication – Oil, grease, or otherwise lubricate

We do maintenance because we believe that hardware reliability degrades with age, but that we can do something to restore or maintain the original reliability that pays for itself.

RCM is reliability-centered. Its objective is to maintain the inherent reliability of the system or equipment design, recognizing that changes in inherent reliability may be achieved only through design changes. We must understand that the equipment or system must be studied in the situation in which it is working.

IMPLEMENTING LEAN MANUFACTURING

Analyze each step in the original process before making change

Lean manufacturing main focuses is on cost reduction and increases in turnover and eliminating activities that do not add value to the manufacturing process. Basically what lean manufacturing does is help companies to achieve targeted production, as well as other things, by introducing tools and techniques that are easy to apply and maintain. What these tools and techniques are doing is reducing and eliminating waste, things that are not needed in the manufacturing process.

Manufacturing engineers set out to use the six-sigma DMAIC (Design, Measure, Analyze, Improve, Control) methodology - in conjunction with lean manufacturing - to meet customer requirements related to the production of tubes.

Manufacturing engineers were charged with designing a new process layout of the tube production line. The objectives for project were including:

• Improved quality
• Decreased scrap
• Delivery to the point of use
• Smaller lot sizes
• Implementation of a pull system
• Better feedback
• Increased production
• Individual Responsibility
• Decreased WIP
• Dine flexibility

Before making changes, the team analyze each step in the original layout of the tube production line process.

1. There try to understand the original state process, identify the problem area, unnecessary step and non value added.

2. After mapping the process, the lean team collected data from the Material Review Board (MRB) bench to measure and analyze major types of defects . To better understand the process, the team also did a time study for 20 days period production run.

In the original state, the tube line consisted of one operator and four operations, separated into two stations by a large table using a push system. The table acted as a separator between the second and third operation.

The first problem discovered was the line's unbalanced . The first station was used about 70% of the time. Operators at the second station were spending a lot of their time waiting between cycle times. By combining stations one and two, room for improvement became evident with respect to individual responsibility, control of inventory by the operator, and immediate feedback when a problem occurred. The time study and the department layout reflect these findings.

A second problem was recognized. Because of the process flow, the production rate did not allow the production schedule to be met with two stations. Because operators lost track of machine cycles, machines were waiting for operator attention. Operators also tried to push parts through the first station - the bottleneck operation in the process - and then continued to manufacture the parts at the last two operations. Typically, long runs of WIP built up, and quality problems were not caught until a lot number of defective pieces were produced.

The original state data were taken from the last 20 days before the change. The teams analyze each step in the original and making changes. The findings of the time study on the original process provided the basis for reducing cycle time, balancing the line, designing the using Just In Time kanbans and scheduling, improve quality, decrease lot size and WIP, and improve flow. The new process data were taken starting one month after implementation. This delay gave the machine operators an opportunity to train and get to with the new process layout system.

With the U shaped cell design; The parts meet all the customer requirement. Table in the original process was removed ,almost eliminating WIP. With the reducing WIP and increasing production.

Some of the concepts used to improve the process included total employee involvement (TEI), smaller lot sizes, scheduling, point of use inventory, and improved layout. All employees and supervisors in the department were involved in all phases of the project. Their ideas and suggestions were incorporated in the planning and implementation process to gain wider acceptance of the changes to the process. Smaller lot sizes were introduced to minimize the number of parts produced before defects were detected. Kanbans were introduced (in the form of material handling racks) to control WIP and to implement a pull system. And the cell layout decreased travel between operations.

Operators were authorized to stop the line when problems arose. In the original-state , the operators were still continue running parts when a operation was down. With kanban

control, the layout eliminated the ability to store WIP, requiring the operator to shut down the entire line. The cell layout provides excellent opportunities for improving communication between operators about problems and adjustments, to achieve better quality.

Day-to-day inspection of the original-state process the operators spent a lot of time either waiting for material-handling person, or performing as a material handling. With the U-shaped cell, delivery to the point of use is more better for the operator. The operator places boxes of raw material on six moveable roller carts, where it's easily to get. The six boxes are enough to last a 24-hr period.

To reduce setup times, tools needed for machine repair and adjustments are located in the cell. The screws are not standardized; tools are set up in order of increasing size to quickly identify the proper tool.

For three months the process was monitored to verify that it was in control. Comparison of time studies from the original-state and the implemented layout demonstrated an increase in production from 300 to 514 finished products per shift. The new layout eliminated double handling between the second and third operations, as well as at the packing step. It also reduced throughout time by making it easier to cycle all four operations in a pull-system order. Customer demand was met by two shifts, which reduced the labor cost.

The results of the redesign are as follows:

• WIP decreased by 97%
• Production increased 72%
• Scrap was reduced by 43%
• Machine utilization increased by 50%
• Labor utilization increased by 25%
• Labor costs were reduced by 33%
• Sigma level increased from 2.6 to 2.8

This project yielded reduced labor and scrap costs, and allowed the organization to do a better job of making deliveries on time, while allowing a smaller finished-goods inventory. Daily production numbers and single-part cycle time served as a benchmark for monitoring progress towards the goal. Although the sigma level increase , the 43% reduction in defects, 97% reduction in WIP, and production increase of 72% contributed to the project objective.

Implementing lean is a never ending process; this is what continuous improvement is all

about. When you get one aspect of lean implemented, it can always be improved. Don't get hung up on it, but don't let things slip back to the starting point. There will always be time to go back and refine some of the processes.

Before Lean Manufacturing was implemented at Nypro Oregon Inc., we would operate using traditional manufacturing. Traditional manufacturing consists of producing all of a given product for the marketplace so as to never let the equipment idle. These goods them need to be warehoused or shipped out to a customer who may not be ready for them. If more is produced than can be sold, the products will be sold at a deep discount (often a loss) or simply scrapped. This can add up to an enormous amount waste. After implementing Lean Manufacturing concepts, our company uses just in time. Just in time refers to producing and delivering good in the amount required when the customer requires it and not before. In lean Manufacturing, the manufacture only produces what the customer wants, when they want it. This often a much more cost effective way of manufacturing when compared to high priced, high volume equipment.

Unit Test:

1. What is 5S?
2. Please Explain each "S" of the 5S.
3. Please Explain Kaizen concept.
4. What is the Pull processing?
5. What is the Poka-yoke?
6. What is the six-sigma DMAIC?
7. What is the objectives for a new process layout of the tube production line?
8. Before making changes, The Manufacturing engineers team do what first?
9. Please lists the results of the redesign.
10. 10. The key to implementing lean new idea or concept is to do what? 

CNC

Introduction to CNC

What is CNC? CNC is a Computer Numerical Control. CNC is the automation of machine tools that are operated by precisely programmed commands encoded and played by a computer as opposed to controlled manually via handwheels or levers.

In modern CNC systems, end-to-end component design is highly automated using Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) programs. The series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design.

In the CNC machines the role of the operators is minimized. The operator has to merely feed the program of instructions in the computer, load the required tools in the machine, and rest of the work is done by the computer automatically. The computer directs the machine tool to perform various machining operations as per the program of instructions fed by the operator.

The CNC technology can be applied to wide variety of operations like drafting, assembly, inspection, sheet metal working, etc. But it is more prominently used for various metal machining processes like turning, drilling, milling, shaping, etc. Due to the CNC, all the machining operations can be performed at the fast rate resulting in bulk manufacturing becoming quite cheaper.

How It Works

The CNC machine comprises of the computer in which the program is fed for cutting of the metal of the job as per the requirements. All the cutting processes that are to be carried out and all the final dimensions are fed into the computer via the program. The computer thus knows what exactly is to be done and carries out all the cutting processes. CNC machine works like the Robot, which has to be fed with the program and it follows all your instructions.

You don't have to worry about the accuracy of the job; all the CNC machines are designed to meet very close accuracies. In fact, these days for most of the precision jobs CNC machine is compulsory. When your job is finished, you don't even have to remove it, the machine does that for you and it picks up the next job on its own. This way your machine can keep on doing the fabrication works all the 24 hours of the day without the need of much monitoring, of course you will have to feed it with the program initially and supply the required raw material.

Since the earliest days of production manufacturing, ways have been sought to increase dimensional accuracy as well as speed of production. Simply put, numerical control is a method of automatically operating a manufacturing machine based on a code of letter, numbers, and special characters. As they developed, application of digital computers control of manufacturing equipment was realized. Computers were soon used to provide direct control of machine tools. The integrated circuit led to small computers used to control individual machines, and the computer numerical control (CNC) era was born. This Computer Numerical Control era has become so sophisticated it is the preferred method of almost every phase of precision manufacturing, particularly machining. Precision dimensional requirements, mainstay of the machining processes, are ideal candidates for use of computer control systems. Computer numerical control now appears in many other types of manufacturing processes. A distinct advantage of computer control of machine tools is rapid, high-precision positioning of workpiece and cutting tools.

Today, manual machine tools have been largely replaced by Computer numerical Control(CNC) machine tools. The machine tool are controlled electronically rather than by hand. CNC machine tools can produce the same part over and over again with very little variation. Modern CNC machines can position cutting tools and workpieces at traverse feed rates of several hundred inches per minute, to an accuracy of.0001". Once programming is complete and tooling is set up, they can run day or night, week after week, without getting tried, with only routine service and cutting tool maintenance.

These are obvious advantage over manual machine tools, which need a great deal of human interaction in order to do anything. Cutting feed rates and spindle speeds may be optimized through program instructions. Modern CNC machine tools have turret or belt toolholders and some can hold more than 150 tools. Tool change take less than 15 seconds.

Computer Numerical Control machine are highly productive. They are also expensive to purchase, set up, and maintain.

However, the productivity advantage can easily offset this cost if their use is properly managed. A most important advantage of CNC is ability to program the machine to do different jobs. Tool selection and changing under program control is extremely productive, with little time wasted applying a tool to the job.

A program developed to accomplish a given task may be used for a short production run of one, or a few parts. The machine may then be set up for a new job and used for long production runs of hundreds or thousands of production units. It can be interrupted, used for the original job or another new job, and quickly returned to the long production run. This makes the CNC machine tool extremely versatile and productive. Computer-aided design(CAD), has become the preferred method of product design & development. The connection between CAD & CNC was logical. A computer part design can go directly to program used to develop CNC machine control information. A CNC manufacturing machine can then make the part. The computer is extremely useful for assisting the CNC programmer in developing a program to manufacture a specific part. Computer-aided manufacturing, or CAM, systems are now the industry standard for programming. When CAD, CAM & CNC are blended, the greatest capability emerges, producing parts extremely difficult or impossible to make by manual methods.

CNC motion is based on the Cartesian coordinate system. A CNC machine cannot be successfully operated without an understanding of the how coordinate systems are defined in CNC machine and how the systems work together.

To fully understand numerical control programming you must understand axes and coordinates. Think of a part that you would have make. You could describe it to someone else by its geometry. For example, the part you have make is a 5 inch by 8 inch rectangle. All parts can be described in this fashion. Any point on the machined part, such as a pocket to be cut or a hole to be drilled, can be described in term of its position. The system that allows us to do this, called the Cartesian Coordinate or rectangular coordinate system.