Machining

Question 1

State the function of code:

G00

Answer 1

Point to Point positioning (rapid transverse)
This command moves the tool at the machines maximum travel speed to coordinates specified after the command. This code is primarily used to the position before beginning a new cut instead of cutting.

Question 2

State the function of code:

G01

Answer 2

Linear interpolation (Cutting Feed)
This command moves the tool along a straight line to the coordinates that follow it. Additionally, with the G1 code, you apply a feed rate for the cut.

Question 3

State the function of code:

G02

Answer 3

Clockwise Circular Interpolation/Helical

This command moves the tool along a clockwise curve to coordinated specified after the code

Question 4

State the function of code:

G03

Answer 4

Counter-Clockwise Interpolation/HelThis command moves the tool along a counterclockwise curve to coordinated specified after the codeical

Question 5

State the function of code:

G40-G42

Answer 5

Tool Diameter Compensation

G40 - Cutter compensation cancel - Cancels cutter radius compensation utilised in codes G41 and G42.

G41 - Cutter compensation left - This command is used to activate cutter radius compensation (used to ensure the diameter of the tool is compensated for within the coordinates of the cut) and to set the tool to a geometry left of the stock. This method is used for climb milling.

G42 - Cutter compensation right - This command is used to activate cutter radius compensation (used to ensure the diameter of the tool is compensated for within the coordinates of the cut) and to set the tool to a geometry right of the stock. This method is used for conventional milling.

Question 6

State the function of code:

G70

Answer 6

input units set to inchs

Question 7

State the function of code:

G71

Answer 7

Input units set to metric (mm)

Question 8

State the function of codes:

G80-G89

Answer 8

Canned or Fixed Cycles for Drilling

Question 9

State the function of code:

G90

Answer 9

Absolute Programming Mode

Absolute command

Question 10

State the function of code:

G91

Answer 10

Incremental Programming Mode

Incremental command

Question 11

State the function of the following codes:
G00
G01
G02/G03
G40/G41/G42

Answer 11

G00 - Point to Point positioning (rapid transverse)
G01 - Linear interpolation (Cutting Feed)
G02/G03 - Clockwise Circular Interpolation/Helical and Counter-Clockwise Interpolation/Helical
G40/G41/G42 - Tool Diameter Compensation
G40 - Cutter compensation cancel
G41 - Cutter compensation left
G42 - Cutter compensation right

Question 12

State the function of code:

M00

Answer 12

Program Stop:

Cancels the spindle and Coolant functions; stops part program execution

Question 13

State the function of code:

M01

Answer 13

Optional Stop

Program stop often used when the operator want to re-fixture the part

Question 14

State the function of code:

M02

Answer 14

Program End

Marks the end of the program; stops the spindle, coolant and axes feed

Question 15

State the function of codes:
M03
M04

Answer 15

Spindle on CW
M03 - Starts clockwise rotation of the spindle
M04 - Starts counterclockwise rotation of the spindle

Question 16

State the function of code:

M05

Answer 16

Switches the spindle off

Question 17

State the function of code:

M06

Answer 17

Tool Change

Requests an automatic tool change

Question 18

State the function of codes:

M07-M09

Answer 18

Coolant Toggles
M07 - Switches on the secondary coolant systems
M08 - Switches on primary coolant systems
M09 - Switches off both the primary and secondary coolant

Question 19

State the function of code:

M30

Answer 19

Indicates the end of the main program

Question 20

What are three parts of the CNC program

Answer 20

1. Program Setup
2. Material Removal
3. System Shutdown

Example:
% Program start Flag
: 1001 Four digit program number
N5 G90 G20 Use absolute units and inch programming
N10 M06 T2 Stop for tool change, use tool#2
N15 M03 S1200 Turn the Spindle on CW to 1200 rpm
N20 G00 X1 Y1 Rapid to (X1,Y1) from origin point
N25 Z0.125 Rapid down to z0.125
N30 G01 Z-0.125 F5 Feed down to Z-0.125 at 5 ipm
N35 G01 X2 Y2 Feed diagonally to X2,Y2
N40 G00 Z1 Rapid up to Z1
N45 X0 Y0 Rapid to X0,Y0
N50 M05 Turn the spindle off
N55 M30 End of Program

Question 21

State the equation for calculating spindle speed

Answer 21

Vc = π×D×S
Surface Cutting speed (m/min) =
Pi x Diameter x spindle speed

Rearranged as:
Vc/ (π×D) = S

Question 22

State the equation for calculating feedrate

Answer 22

F = z×fz×S
Cutting Feedrate (mm/min) =
Number of cutting edges x Feedrate per cutting edge x spindle speed

Question 23

Describe the operational instructions and the CNC code to enable the operator to machine the outside profile of the component leaving 0.15mm stock for a final finish pass.

Answer 23

When producing a part using a manufacturing machine, you may wish to leave stock remaining for a finishing pass. In order to do this, we must utilise the cutter radius compensation utilised within commands G40, G41 and G42. When establishing the cutter compensation of the tool, the operator will select the tool being used and the program with compensation for its radius when cutting the part to meet its specification, but if we want to leave additional material on the stock, the operator must simply go into the tools settings and override the current radius and increasing it by 0.15mm. Now when the operator begins the cut, the machine will function as if it is removing an additional 0.15mm, when it is not removing that stock.

Question 24

Describe the major benefits of CNC manufacturing

Answer 24

• Repeatability and Quality of Manufactured Components
• Production of Profiled 2 and 3 Dimensional Components
• The speed of Production: Safe Utilisation of High Cutting Surface Speeds and Feedrates
• Amalgamation of Production Operations :
  Reduction of Number of Set-Up Operations
  Reduction of Tooling and Fixture Inventories
  Increased Quality - Manufacture From Minimum Number of Datum Locations
• The utilisation of Lower Cost Standard Tooling
• Flexibility of Manufacture
• Reduction in number of Machine Tools required and consequently Floor Space
• Dynamic Manufacture - Lower Work In Progress
• Reduced Lead Time Implying the Potential for JIT Manufacturing

Question 25

Identify significant manufacturing management/system task necessary to ensure the effective operation of CNC machines

Answer 25

Manufacturing Systems MUST Ensure : - Quality / Optimised / Verified CNC Programs - Full Potential of the CNC Resource Being Used - Procedures for Updating and Maintenance of ALL Programs - Kiazen Methodology to Continually Improve Programming Techniques - Economic Batch Quantities ( EBQ ) Approaching Unity - Efficient and Effective Implementation of Tooling and Fixture Management Systems - Quality Products

Question 26

Define the following terms: Set-up time Cycle time

Answer 26

Setup time: the entire time a machine is down between production runs Cycle time: the time it takes to complete a production run divided by the number of good workpieces produced

Question 27

State the three ways to reduce set-up time

Answer 27

Eliminate (especially on-line) tasks You save the amount of time it was taking to perform the task Move on-line tasks off line At least the machine is not down during the performance of the task Many tasks can be done while the machine is running production Assumes you have adequate lot sizes, cycle times, and available personnel Often requires duplications (especially tooling) Facilitate tasks Make it as quick & easy as possible to perform the task The easier a task is to perform, the faster it can be done! Task simplification makes it possible for people with the lower skill to perform well Often the easiest alternative to justify

Question 28

Describe the concept of single minute exchange of dies (SMED) and the crucial requirement to incorporate this into the manufacturing process

Answer 28

SMED - Single minute exchange of dies Reducing SET-UP times towards zero implies making a manufacturing facility more flexible. Within the SMED concept flexibility is the organizations capability to react to change, rather than resource flexibility. Two aspects of flexibility most concern manufacturing companies: - Variety of products, processes and activities -Uncertainty of the system to predict demand. Crucial Steps for Set-Up Reduction - Select: Selection criteria for machines with highest set-up times, bottleneck operations and most likely to yield savings. - Record: establish accurate records of current practice. - Analysis e.g.. clamp/unclamp, load/unload, adjustment, cleaning, inspection etc. - Eliminate: attempt to simplify and eliminate wasteful activities. - Simplify :- Attempt to simplify all remaining activities eg. material handling, pre-set tooling etc. - Classify :- internal operations - work that must take place when the machine is stopped External: work that must be done before the machine is stopped. The challenge is to convert as much internal work to external work implying the resource is stopped for the minimum time between operations. Develop a method and equipment. These developments will support the new set-up activities for both internal and external work. Implement revised procedures. New methods will become standard practice. New method studied for training purposes and as further projects for improvements.

Question 29

For the programming of a CNC machine tool discuss: - Interactive graphical programming - Off-line (CAD/CAM) programming

Answer 29

Interactive Programming at the Machine Tool: • Simple and Complex Geometric Programming • Skilled Operator Function • Lack of Data Integration • Difficult to Ensure Executive Control • Repeatable Cost per Machine Tool • May Contribute to non-productive time • The utilisation of 3D CAD solid models has enabled the CNC machine tool programmer to generate toolpaths by attaching appropriate tooling strategies directly to the geometrical feature of the solid model. • In a similar way, software exists to enable the CMM programmer to manipulate the probing system around an imported 3D CAD model thereby developing off-line programming capabilities. This has the potential to substantially reduce the time required to develop and approve programs and enables: – full graphical simulation, – eliminates the possibility of a probe crash, – optimises probe positional movements, – increases the productive utilisation of the CMM resource. Off-Line Programming Systems: - Simple and Complex Multi-Axis Programming Capability - Skilled Operator Function - Graphical Simulation to Verify Programming Data - Executive Control - No Alternative for Complex Geometrical Profiles - Potential for Minimum Non-Productive Time at the CNC, M/c Tool - Overheads - Hardware / Software / Programmers etc - Off-Line Programming Systems Aids the Maintenance of CNC Programs. - Component Parts Filed Within the CAD/ CAM Processing System Database Configuration n When Required by the CNC Machine Tool these Files are Processed Using An Independent Master Tooling File to Generate the CNC Code * Comparison against all mainstream CAD formats * Rapid alignment even for complex freeform shapes * Inspection of user-defined sections * The ability to inspect along the edge of a part * Full Geometric Inspection capabilities. * Automatic creation of inspection features from CAD * A step by step Geometric Dimensioning & Tolerancing (GD&T) Wizard * Point, wireframe and surface export for measured entities. * CAD manipulation - including surface offsetting (e.g. reverse side for sheet metal, spark gap for electrodes)