Читать книгу Student Workbook for Programming of CNC Machines - Ken Evans - Страница 9
ОглавлениеUnit 1: CNC Basics
Process Planning
Any time a new part is considered for manufacture, it is necessary to have a logical plan in order to machine it efficiently. The following is an explanation of the exercise requirement: Three Process Planning Sheets are provided on the following pages for operations (Chart 1-1), setup (Chart 1-2), and quality control (Chart 1-3). Copy as many as you need. Later in the workbook, CNC Programming Sheets are included for the units covering Turning Center Programming and Machining Center Programming. For a detailed description of the use of these documents, please refer to Programming of CNC Machines, Fourth Edition, Part 1, CNC Basics. You will also find in the units covering Turning Centers and Machining Centers a list of cutting tools that can be used for preparing the Process Planning Sheets.
Use the Operation Sheet (Chart 1-1) to identify each individual operation and the machines necessary to complete the part in the blueprints that follow.
Use the CNC Setup Sheet (Chart 1-2) to identify work holding, cutting tools, work piece coordinate zero locations, and any other pertinent information needed to complete the part setup for these blueprints. Refer to the tool lists provided in Unit 3 (CNC Turning Center Programming) and Unit 4 (CNC Machining Center Programming) to choose the appropriate tools.
Use the Quality Control Check Sheet (Chart 1-3) to list 100% of the dimensional data needed to verify that the parts are made to specification, starting with the blueprints in Figures 1-1 and 1-2.
Figure 1-1 Turning Center Process Planning
Chart 1-1 Process Planning Operation Sheet
| Date | Prepared By | ||
| Part Name | Part Number | ||
| Quantity | Sheet ___ of ___ | ||
| Material | |||
| Raw Stock Size | |||
| Operation Number | Machine Used | Description of Operation | Time |
In the example in Figure 1-1, the parts are provided as 3.0625 long slugs with one end having already been faced. It will be necessary to clamp the 2.50 diameter in pre-machined soft jaws with enough material extended to allow machining of the part, including removal of 1/16 inch from the face of the part. The material is 4340 alloy steel. Dimensional tolerances are as follows: .X = plus or minus .015 inch, .XX = plus or minus .010 inch, .XXX = plus or minus .005 inch, and angular tolerance is plus or minus .5 degree. Please use copies of the Process Planning sheets and develop a plan to machine the part to dimensional requirements.
Chart 1-2 Process Planning CNC Setup Sheet
| Date | Prepared By |
| Part Name | Part Number |
| Machine | Program Number |
Workpiece Zero: X___________ Y __________ Z _________
Setup Description:
| ToolNumber | OffsetNumber | Tool Description | Comments |
Chart 1-3 Process Planning Quality Control Check Sheet
| Date | Checked By | ||
| Part Name | Part Number | ||
| Sheet ___ of ___ | |||
| Blueprint Dimentsion | Tolerance | Actual Dimension | Comments |
Figure 1-2 Machining Center Process Planning
In the example in Figure 1-2, it will be necessary to machine the part from a solid blank of Aluminum that is pre-machined to 4.25 square and is 1.25 thick. The top surface must have .125 inch of material removed as well. Dimensional tolerances are as follows: .X = plus or minus .015 inch, .XX = plus or minus .010 inch, .XXX = plus or minus .005 inch, and angular tolerance is plus or minus .5 degree. Please use the copies of the Process Planning sheets and develop a plan to machine the part to dimensional requirements. Make your tool selections from the CNC Machining Center Tool List found in Unit 4, CNC Machining Center Programming.
Feeds and Speeds
Charts 1-4 and 1-5 are supplied for use in answering the exercise problems presented here. The Surface Feet per Minute (SFPM) and Feed in inches per revolution (in/rev) values represented here are given in ranges. Note that the values starting at the low end of the range are intended as a minimum starting point for calculations; those at the high end are a maximum recommended SFPM and Feed. Final values used for machining may differ based on many factors. As you answer the problems, use values that are within the ranges given. Refer to Programming of CNC Machines (Part 1, CNC Basics, Metal Cutting Factors) for detailed information regarding Feed and Speed calculations. A more comprehensive source for machining data is the Machinery’s Handbook; other valuable sources for machining data are in the tool and insert catalogs and online applications supplied by cutting tool manufacturers.
Chart 1-4 Feeds and Speeds for Turning
| Tool Material | ||
| Material | High Speed Steel | Carbide |
| Carbon Steel Feed in/rev | 30–60.006–.012 | 200–1300.008–.036 |
| Alloy Steel Feed in/rev | 30–120.006–.012 | 125–1000.008–.036 |
| Stainless Steel Feed in/rev | 25–110.006–.012 | 80–945.007–.036 |
| Aluminum Feed in/rev | 500–800.006–.012 | 2800–4500.017–.036 |
Note: As a general rule, the minimum depth of cut should be 1.5 to 2 times the tool nose radius. The maximum feed rate should be approximately one half the tool nose radius for rough turning using carbide inserts.
For milling, the maximum depth of cut is equal to the flute length or the insert height and the maximum width of cut is the cutter diameter. However, these measures are not practical in most cases. A more widely used practice is to set the maximum depth of cut to 2/3 of the flute length and the maximum width of cut to 2/3 of the diameter, as well. These basic conditions should be followed for the remainder of this workbook. Drilling calculations should be based on High Speed Steel (HSS) values for Turning and HSS End Mill values for Milling.
Chart 1-5 Feeds and Speeds for Milling
| HSS End Mill | Carbide End Mill | Carbide Inserted Face Mill | |
| Carbon Steel Feed in/tooth | 25–140.001–.004 | 210–1000.006–.012 | 90–685.020–.039 |
| Alloy Steel Feed in/tooth | 5–85.001–.004 | 40–450.006–.012 | 39–475.020–.039 |
| Stainless Steel Feed in/tooth | 20–80.001–.003 | 200–700.006–.012 | 210–385.020–.039 |
| Aluminum Feed in/tooth | 165–850.002–.006 | 600–2000.008–.015 | 755–1720.020–.039 |
Refer to the following formula to calculate revolutions per minute (r/min).
where
CS = Cutting Speed from the charts above or the Machinery’s Handbook
π = 3.1417
D = Diameter of the workpiece or the cutter
Refer to the charts above or the Machinery’s Handbook for the feed in inches per tooth (in/tooth) for chip load recommendations. Also review the formula below to calculate the feed aspect of the metal-cutting operation.
F = R × N × f
where
F = Feed rate in inches per minute (in/min)
R = r/min calculated from the preceding formula
N = the number of cutting edges
f = the chip load, per tooth, recommended from the charts above or the Machinery’s Handbook
1. On a CNC lathe, a facing cut is needed to establish the part-zero surface. The alloy steel bar stock is 2.5 inches in diameter and has 1/32 inch of excess material to be removed from each side. A carbide-inserted tool with a 1/32 inch nose radius will be used for this operation. Because the diameter changes as the tool travels toward the centerline, what should the r/min be? What should the SFPM be? What should the depth of cut be?
2. When finish turning an aluminum bar that is 2.3125 inches in diameter with a carbide-inserted turning tool that has a 1/64 inch tool nose radius, what is the r/min and feed rate required if the depth of cut is 1/64 inch per side?
3. An internal threading operation is required on a CNC lathe to make a 1-8 UNC thread in a carbon steel part. The cutting tool material is High Speed Steel. What should the r/min be for this operation?
4. Calculate the appropriate speeds and feeds for each of the required tools in the lathe process planning project above and enter your answers on your CNC Setup sheet in the comments section.
5. Calculate the appropriate speeds and feeds for each of the required tools in the mill process planning project above and enter your answers on your CNC Setup sheet in the comments section.
6. In this example, the material is stainless steel. A .5625 inch diameter hole is to be drilled through a plate that is 1.25 inch thick. Calculate the r/min and feed rate best suited for this operation. Use the HSS end mill values from the chart.
7. A carbon steel plate 4.0 inches square requires a 2.0 inch diameter hole to be machined through the center. A pre-drilling operation uses a 1.25 inch diameter HSS drill and a finishing operation uses a .875 diameter 4-fluted HSS end mill to circle mill out the remainder of material. What is the r/min and feed rate for the drill? What is the r/min and feed rate for the end mill?
8. A 5-tooth 3.0 inch diameter carbide face mill is used to machine an alloy steel bar that is 2.0 inches wide and 6.0 inches long. There are two depth passes of .080 inch each required to bring the part to size. What is the r/min and feed rate for this cut?
9. A 4.0 inch flat aluminum bar requires a profile to be cut on both ends. A 2-fluted HSS end mill 7/16 inch in diameter has been selected for the job. The part thickness is 1/2 inch and the amount of axial metal removal is 1/2 inch. What are the appropriate r/min and feed rate?
10. Use the formula and data given above to calculate the feed and speed required for each tool in the programming exercises that follow. List your results in the comments section of the CNC Setup Sheet.
Coordinate Systems
1. Use Figure 1-3 to identify the absolute coordinates for each axis and for each point of the profile of the turned part, based on diametrical considerations.
2. Use Figure 1-3 to identify the incremental coordinates for each axis and for each point of the profile of the turned part, based on radial considerations.
Figure 1-3 Identify Absolute and Incremental Coordinates
3. Use Figure 1-4 to identify the absolute coordinates for each axis and for each point of the profile of the milled part. Start at part zero and proceed clockwise.
4. Use Figure 1-4 to identify the incremental coordinates for each axis and for each point of the profile of the milled part.
Figure 1-4 Identify Absolute and Incremental Coordinates
5. List the absolute coordinate values for X, Y, and Z for each of the 15 points as indicated in Figure 1-5). The part is 3.0 inches long, 2.0 inches wide and has a height of 2.25 inches. The slot is cut through the centerline of the width and is .50 wide and .375 deep.
Figure 1-5 Identify Absolute Coordinates
6. Identify each axis (vertical milling representation) and its positive or negative value on Figure 1-6.
Figure 1-6 Identify Vertical Milling Axes, Polar Rotation, Quadrants, and Angular Values
Figure 1-7 Identify Polar Coordinate Values
Figure 1-8 Identify Polar Coordinate Values
7. Indicate the negative rotation direction for the polar coordinate system in Figure 1-6.
8. Indicate each of the polar quadrants in Figure 1-6.
9. Identify the angular value locations for 0, 90, 180, and 270 degrees in Figure 1-6.
10. Identify the polar (angular and radial) values for each of the holes in Figure 1-7.
11. Identify the polar (angular and radial) values for each of the holes in Figure 1-8.
Trigonometric Calculations
In many cases, it will be necessary to calculate the coordinate values of points for input into your CNC programs. The exercises that follow are a small sampling of the types of problems you are likely to encounter. Use your calculation skills to answer all of the problems and to prepare yourself for others when you complete the actual programming exercises in Units 3 and 4 of this workbook, the CNC Turning and Machining Center sections.
Chart 1-6 (Right Triangles) and Chart 1-7 (Oblique Triangles) are provided for your benefit. Many of the formulas shown are needed to complete the problems.
Chart 1-6 Right Triangles
| Known Sides and Angles | Unknown Sides and Angles | Area | ||
| a and b | ||||
| a and c | ||||
| b and c | ||||
| a and ∠ A | B = 90° − A | |||
| a and ∠ B | b = a × tanB | A = 90° − B | ||
| b and ∠ A | a = b × tabA | B = 90° − A | ||
| b and ∠ B | A = 90° − B | |||
| c and ∠ A | a = c × sinA | b = c × cosA | B = 90° − A | c2 × sinA × cos |
| c and ∠ B | a = c × cosB | b = c × sinB | A = 90° − B | c2 × sinB × cos |
Chart 1-7 Oblique Triangles
| Known Sides and Angles | Unknown Sides and Angles | Area | ||
| All three sides a, b, c | C = 180° − A − B | |||
| Two sides and the angle between them a, b, ∠ C | B = 180° − A − C | |||
| Two sides and the angle opposite one of the sides a, b, ∠ A (∠B less than 90°) | C = 180° − A − B | |||
| Two sides and the angle opposite one of the sides a, b, ∠ A (∠B greater than 90°) | C = 180° − A − B | |||
| One side and two angles a, ° A, °B | C = 180° − A − B |
