Process Plan - Shop Activities

1. Process Plan - Shop Activities Chapter Objectives Introduction Essential CNC Shop Activities Part Drawing Study Methodizing of Operations for CNC Machining Centers Deciding on a CNC Machine Methods of Holding the Part During Machining Machining Determination Cutting Conditions Writing a Programming Manuscript Inputting Programs to the Machine Control Unit Setup Procedure Debugging and Verifying the Program Part Production Chapter Summary

2. OBJECTIVES At the conclusion of this chapter you will be able to 1. Identify the three major areas of activities in a CNC machine shop. 2. Explain the importance and the order of CNC process planning. 3. Describe what factors influence the programmer’s selection of a CNC machine for a job run. 4. Explain the conditions for proper work holding. 5. State what information is important in setup and machining documentation. 6. Understand the terms machine home, part origin, and tool change position. 7. Explain the significance of tool length offset. 8. Identify the functions of the programmer and setup person in getting a job through setup and prove-out.

3. INTRODUCTION This chapter concentrates on the many actions that a CNC shop must perform in order to cost effectively produce quality parts. It cannot be stressed enough that the programmer must be thoroughly familiar with the part drawing and the manufacturing specifications. The order of machining is decided according to the required accuracy and orientation of the workpiece. To get the most out of the CNC machine, the programmer must also select tools that are the most appropriate for the intended cutting operation.

4. ESSENTIAL CNC SHOP ACTIVITIES

5. PART DRAWING STUDY The first step to be taken before preparing any part program is to thoroughly study the part drawing. The drawing indicates what the part looks like, its material, tolerances, surface finish, material treatments (if any), and any other requirements.

6. METHODIZING OF OPERATIONS FOR CNC MACHINING CENTERS Methodizing involves creating a plan that indicates the sequence and methods of operations to be carried out in order to produce a part. In a small machine shop where no methods engineer is available, the programmer takes the responsibility for breaking down the manufacturing of the part into operations. In a larger shop, specially trained manufacturing engineers handle this important job. The operations sheet contains information the programmer needs concerning the condition of the part material prior to machining.

7. DECIDING ON A CNC MACHINE The programmer selects a CNC machine based on its ability to optimize the cutting operations required to manufacture the part. Availability as well as the capacity of the CNC machine must be known. The machine’s capacity is measured by its travel horsepower, tooling magazine size, accuracy, and number of machine axes movements.

8. METHODS OF HOLDING THE PART DURING MACHINING Clamping Device / Work-holding Device. For milling operations, there are three basic types of work-holding devices used: Precision mill vise, Fixture Chuck. A right-angle plate is used to mount the work 900 with respect to the machine table. A tombstone is used to mount parts on pallet work changing systems that are used on horizontal machining centers.

9. Chuck A three-jaw chuck mounted to the machine table is often used in cases where a cylindrical surface is to be clamped.

10. MACHINING DETERMINATION While the fixture is being completed in the toolroom, the programmer continues to plan the machining sequences and the corresponding tooling required. In general, machining should proceed in the following order:

11. The cutting sequence together with the required cutting tools are documented on the CNC Tool and Operations Sheet. See figure below. MACHINING DETERMINATION 2

12. CUTTING CONDITIONS The spindle speed and feed rate must be determined and entered in the part program. A discussion of how these parameters are calculated for milling and drilling was presented in Slide 3. Once entered, they are optimized (adjusted up or down) after a trial machining. The selection of the proper cutting tools for an operation and optimization of the speed and feed during the cutting process will cut down on machining time and subsequently increase productivity.

13. WRITING A PROGRAMMING MANUSCRIPT The program is ready to be coded after all the planning is complete. The programmer makes certain programming decisions based on the drawing requirements and fixturing configuration. These include: • Establishing the location of programming zero or part origin (X0, Y0) • Establishing the location of part Z0 • Determining the mode of programming (absolute or incremental) • Determining the units of programming (English or metric) The tool change position is determined by the machine specifications. For X-axis tool removal the stroke from the spindle must be taken into consideration. In addition, the spindle must be fully retracted with part Z set to maximum before executing any X or Y movements to the tool change position.

14. INPUTTING PROGRAMS TO THE MACHINE CONTROL UNIT Method 2: A floppy disk, Zip disk, or CD-ROM disk drive unit is attached directly to the CNC machine and connected to its MCU. The operator inserts the floppy disk, Zip disk, or CD-ROM containing the part program into the drive and downloads the part program. Method 1: The program file has been created on a PC or workstation and saved. An RS-232 cable runs from the computer’s serial port to the MCU. For this scenario, the operator can use file transfer programs such as Laplink or PC-talk to download the program file from the computer to the MCU. Method 3: For small machining jobs, the programmer can use the alphanumeric keypad on the control panel. First, the mode switch is set to EDIT. Then the PROG button is pressed to create a new program page. The program number is manually keyed in, then the INSERT button is pressed to register the number into the control’s memory. Each block (one line) of the program is entered.

15. INPUTTING PROGRAMS TO THE MACHINE CONTROL UNIT (2)

16. SETUP PROCEDURE Machine Home and Part Origin Locating the Part Origin with an Edge Finder Programming the Tool Length Offsets into the MCU The setup operation can begin after the fixtures, tooling, program, setup sheets, and part blank arrive at the CNC machine. Usually, the setup person starts by securing the cutting tools in the tool holders. The tooling assemblies are loaded into the tool magazine according to the order outlined in the setup sheets. Next, the work-holding device is put into place on the machine table.

17. Manual Handwheel Method Methods of Programming the Part OriginLocation into the MCU Absolute Zero Shift (092) Entry in the Part Program Fixture or Work Offset Method

18. Coordinate Systems Definition Five coordinate systems defined by CNC are considered: that is, Machine Coordinate System (MCS), Setup Coordinate System (SCS), Workpiece Coordinate System (WCS), Feature Coordinate System (FCS), (Figure 6.17) and Path Coordinate System (PCS) (not shown in the figure).

19. DEBUGGING AND VERIFYING THE PROGRAM Physical checking is very important for prove out of items that many graphical simulation programs may not check, including possible collisions between the tool and fixtures or work-holding devices.

20. PART PRODUCTION A completed and checked program is ready for executing production runs only if it is capable of repeatedly producing the same results. That is, quality parts in the time projected. Programs that meet this criteria are a direct reflection of the programmer’s professionalism. The setup person tries to optimize the speeds and feeds when parts are manufactured in production to speed up the cutting cycle, increase tool life, and improve part quality

21. SUMMARY 1. The programmer must make a thorough study of the part drawing as a first step in preparing the part program. 2. Important factors entering into the decision to utilize CNC operations include the quantity of parts to be manufactured, the part quality, the tooling costs, fixture manufacturing, and the cost of running the CNC machine. 3. Methodizing is the process by which a sequence of operations for producing a part is formulated. 4. The operations sheet contains important information concerning the condition of the part material prior to machining. 5. The CNC setup sheet contains information pertaining to where and how the work is to be held during the machining operations. 6. The CNC tool and operations sheets documents the cutting sequence together with the required cutting tools. 7. The programmer is responsible for writing the part program, selecting the required tooling, and specifying the work-holding and fixturing design. 8. The setup person is responsible for loading the tooling into the tool magazine as well as securing the work-holding device and part blank in the CNC machine. Other setup activities include loading the part program into the MCU, measuring the location of the part origin, entering the tool length offsets, and running the part program. 9. Tool length offset is the distance from the bottom of the tool to the part Z0 reference plane with the spindle fully retracted. 10. A part is ready for production only after the program has been tested and proven to consistently manufacture quality parts in the time proposed.

22. Thank you.