Program, Set Up, and Operate CNC and EDM Equipment

Programming, Setting Up, and Operating CNC and EDM Equipment

Introduction to Numerical Control and Electrical Discharge Machining

The modern Tool and Die Maker must master two families of computer-controlled machines: CNC (Computer Numerical Control) machining centers and EDM (Electrical Discharge Machining) machines. These machines make it possible to achieve tolerances on the order of ±0.005 mm and surface finishes of 0.2 µm Ra, which are impossible to obtain with conventional machining.

The reference standard for machine tools in Canada is CSA B149.1 (Canadian Electrical Code, Part I) for electrical aspects, and ISO 6983 (G and M codes) for programming. The Red Seal exam requires a thorough understanding of operating principles, cutting parameters, fixed cycles, and setup procedures.

Fundamental Principles of CNC Machines

Coordinate Systems and Axes

A CNC machine uses a Cartesian coordinate system. The main axes are:

The machine reference point (home position) is the absolute origin point of the machine, generally detected by limit switches or encoders. The work zero point is defined by the operator using a probe, dial indicator, or a preset tooling system.

Essential rule: the work offset (G54 to G59) must be verified before every operation. An error of 0.01 mm on the offset can result in scrapping a precision part.

Types of CNC Machines in Tool and Die Making

CNC Programming: G and M Codes

Program Structure

A CNC program follows the ISO 6983 standard (formerly RS-274D). Each block (line) contains addresses followed by numerical values. The typical structure:

O0001 (PROGRAM NUMBER 1)

N10 G90 G21 G17 G40 G49 G80

N20 G54

N30 M06 T01 (TOOL CHANGE)

N40 S1200 M03

N50 G43 H01 Z50.0

N60 G00 X0 Y0

N70 G01 Z-5.0 F100

...

N100 M30

Essential G Codes for the Tool and Die Maker

Essential M Codes

Cutting Calculations for CNC

The cutting speed (Vc) in m/min is calculated:

Vc = (π × D × N) / 1000

Where:

To find the rotational speed:

N = (Vc × 1000) / (π × D)

Example: 10 mm end mill in tool steel (Vc = 25 m/min):

N = (25 × 1000) / (π × 10) = 25000 / 31.42 = 796 rpm

The feed rate (F) in mm/min:

F = N × fz × Z

Where:

Example: 2-flute end mill, fz = 0.05 mm/tooth, N = 796 rpm:

F = 796 × 0.05 × 2 = 79.6 mm/min

Cutter Radius Compensation

Radius compensation (G41/G42) is mandatory for machining precise contours. The compensation radius D is entered in the offset table. The programmed path is that of the theoretical profile; the machine offsets the tool by radius D perpendicular to the path.

Compensation rules:

Classic pitfall: if the compensation radius is too large for the profile's radius of curvature, the machine generates an alarm (compensation interference). The solution is to reduce the D radius or modify the program.

Electrical Discharge Machining (EDM)

Physical Principles

EDM uses controlled electrical discharges to remove material. The principle relies on:

The discharge frequency varies from 1 kHz to 500 kHz depending on the desired finish. The capacitance (capacitor) controls the energy of each discharge.

Critical EDM Parameters

Fundamental relationship: surface roughness (Ra) is proportional to discharge energy:

Ra ≈ K × (I × Ton)^(1/3)

Where K is a constant depending on the material.

Types of EDM

Sinker EDM

The electrode (generally graphite or copper) is machined to the negative shape of the cavity. The electrode descends vertically into the workpiece.

Applications:

Electrodes:

Electrode wear: typical volumetric wear is 0.1 to 1% of the removed volume. For finishing operations, wear can reach 5 to 10%.

Wire EDM

A brass or copper wire (diameter 0.1 to 0.3 mm) passes through the workpiece. The wire is continuously unrolled and serves as the electrode.

Applications:

Wire-specific parameters:

Calculations for EDM

The machining time in sinker EDM:

T = V / (MRR)

Where:

The material removal rate depends on the intensity:

MRR ≈ K × I

Where K ≈ 0.5 to 2 mm³/min/A depending on the material and configuration.

Example: Cavity of 20 × 15 × 10 mm in hardened steel (K = 1.0 mm³/min/A) with I = 10 A:

V = 20 × 15 × 10 = 3000 mm³

MRR = 1.0 × 10 = 10 mm³/min

T = 3000 / 10 = 300 min = 5 hours

Pitfall: this calculation ignores finishing time (which is slower) and flushing time. The actual time is generally 1.5 to 2 times greater.

Setup and Operating Procedures

Machine Preparation

Work Offset Setup

The accuracy of the work offset determines the accuracy of the part. Methods:

Recommended procedure:

Program Verification

Before starting production, the operator must:

Safety and Standards

CNC Safety

EDM Safety

Applicable Canadian Standards

Troubleshooting and Problem Solving

Common CNC Problems

Common EDM Problems

Parameter Optimization

CNC Machining Strategies

For machining hardened tool steel (45-60 HRC):

Golden rule: for finishing operations, the depth of cut must be at least equal to the tool radius to avoid rubbing.

EDM Strategies

Principle: always start with roughing at high intensity, then progressively reduce for finishing. Each finishing pass removes approximately 0.1 to 0.2 mm of material.

Exam Tips and Answer Strategies

Typical Red Seal Questions

Problem-Solving Method

For calculation questions, follow this method:

Frequent Exam Pitfalls

Summary

Pitfalls to Avoid